Recent Advances in Direct Optical Patterning of Inorganic Materials and Devices

Direct patterning technology holds significant promise owing to its ability to streamline complex patterning processes, fostering affordable design and production of various devices. Direct optical lithographic techniques have recently been applied to diverse ranges of functional inorganic nanomaterials, providing a viable alternative to conventional photolithography. These techniques facilitate the fabrication of diverse thin‐film devices and enable 3D printability for inorganic microarchitectures. This review discusses the recent progress in the direct patterning of inorganic materials and associated device fabrication. The chemical design of inorganic building blocks is delved into, which entails the photochemistry of surface ligands or additives that respond to external stimuli and the different patterning methodologies predicated on these external stimuli. Moreover, device fabrication is introduced through direct patterning methods, highlighting examples from optoelectronic, electronic, and energy devices. Last, the prospects of this field are presented, focusing on materials and processes.


Introduction
In materials science and engineering, the ability to precisely pattern and manipulate inorganic materials opens up considerable prospects for advancing cutting-edge technologies and devices. [1]Over the past decades, the field of direct patterning has seen substantial advances, facilitating the construction of complex structures and functional devices composed of inorganic materials. [2]Direct patterning refers to the direct deposition of patterned materials on a substrate, simplifying traditional lithographic techniques that often involve multiple steps processes DOI: 10.1002/apxr.202300069such as photomask production, polymer photoresist deposition, exposure, vacuum deposition, and etching.This approach offers several benefits, such as enhanced design adaptability, expedited processing time, and improved scalability.These characteristics render it a compelling choice for diverse applications spanning electronics, optoelectronics, energy devices, and sensors.Among the various direct patterning methods, including direct laser writing, [3] electron beam lithography, [4] and nanoimprint lithography, [5] direct optical patterning method has recently emerged as an innovative technology to pattern diverse ranges of inorganic materials using nanocrystals (NCs) or inorganic complexes as building blocks.In 2017, Wang et al. first reported the direct patterning of inorganic materials, referred to as direct optical lithography of functional inorganic nanomaterials (DOLFIN), integrating photocurable inorganic nanomaterials with photolithography techniques. [6]Since this pioneering report, numerous direct optical patterning methods have been extensively studied, employing functional inorganic materials such as metals, semiconductors, and oxides.
The typical direct optical patterning for creating micro-and nanoscale-patterned inorganic patterns entails the synthesis of photosensitive inorganic building blocks.These blocks dynamically solidify or agglomerate in response to optical stimuli, including ultraviolet (UV) irradiation, electron beams, X-rays, or pulsed lasers. Another approach involves the use of photosensitive additives like a photoacid generator (PAG), which releases protons (H + ) upon photon irradiation, [8] altering the surrounding environment to acidic or triggering charge neutralization of surface-charged NCs or anionic molecular inorganic precursors.This leads to the solidification of inorganic building blocks.Furthermore, various strategies, such as utilizing photosensitive crosslinkers that bridge the building blocks, [9] photochemical reduction of inorganic precursors, [10] and photoexcitation of electron-hole pairs inducing the solidification of semiconductor NCs, [11] have been proposed for direct patterning (Figure 1).Alongside materials, multiple optical patterning techniques like photolithography using UV, e-beam, two-photon, or pulsed lasers; laser writing as local heating or photoreaction; and optical 3D printing methods such as digital light processing (DLP) and stereolithography apparatus (SLA) have been employed for the patterning of inorganics (Figure 1).
A critical domain where direct patterning has revolutionized material fabrication is optoelectronics and photonics.For example, quantum dots (QDs) and perovskite NCs hold significant potential as fundamental components of high-efficiency luminous devices, light-emitting diodes (LEDs), [12] photovoltaic cells, [13] and photodetectors. [14]Integrating QDs or NCs into these devices necessitates precise patterning at the desired locations without degrading the material's properties.Surface modification of QDs with photodecomposable, crosslinkable ligands, or mixing with crosslinking additives has enabled various optical patterning technologies to be applied to these materials, facilitating the formation of patterned microscale pixels in LEDs over a large area.Additionally, electronics and energy devices represent other pivotal areas where direct patterning has been intensively explored.The quest for smaller, faster, and more energy-efficient electronic devices has driven the development of innovative patterning techniques that can surpass the constraints of traditional lithography. [15]The direct patterning approach applied to functional inorganics, comprising metal, semiconductor, and oxide building blocks, proves beneficial in electronic and energy devices, microscale integrated devices like memory devices, fieldeffect transistors (FETs), and thermoelectric devices (Figure 2).
In this review, we aim to provide a comprehensive overview of the state-of-the-art direct optical patterning techniques for inorganic materials and devices.We discuss the underlying principles, advantages, and challenges of each technique, highlighting the remarkable strides made in recent years.Moreover, the various devices fabricated by the direct patterning methods, e.g., LEDs, FETs, and thermoelectric devices, are described.Finally, we discuss the prospects of direct optical patterning methods.

Direct Photolithographic Patterning
Direct optical patterning technologies based on photolithography and laser writing methods have emerged as prominent methods for fabricating high-resolution micro-and nanoscale patterned inorganics.In these methods, synthesizing photocurable inorganic building blocks is an essential prerequisite for direct patterning.Various chemical designs for inorganic building blocks have been proposed to ensure their photocurability, which have been implemented in subtractive lithographic or laser-based direct writing methods.In this section, we cover the recent advancements in synthesizing photoreactive inorganic building blocks and categorize direct optical patterning methods as photolithography, alternative lithography types, and laser-based writing.

Photolithography-Based Optical Patterning
The pioneering research on direct optical patterning of inorganic materials was reported in 2017 by Wang et al. [6] The overall procedure of the direct optical patterning process is described in Figure 3a.Their study introduced a groundbreaking methodology for the DOLFIN, effectively negating the necessity for photoresists in photolithography processes.13b,16] The electrical and optical properties of the colloidal NCs and QDs can be modulated by altering their core sizes and compositions.Additionally, their surface ligands can impart specific functionalities or regulate their colloidal stability in a particular environment. [17]hese features make colloidal NCs and QDs excellent candidates as building blocks for the fabrication of functional thin films and devices. [18]o synthesize photoreactive inorganic building blocks for facilitating direct optical patterning, Wang et al. chemically engineered surface ligands.These ligands comprised of photochemically active X -and Cat + ion pairs, with X -attached to NC surfaces, including Sn 2 S 6 4-, CdCl 4 2-, AsS 4 3-, or MoO 4 2-, and Cat + acting as a counter-balanced cation, known as a PAG, such as diphenyliodonium (Ph 2 I + ) or triphenylsulfonium (Ph 3 S + ).(Figure 3b). [6]Upon light exposure, the PAGs decompose and release acidic protons (H + ), which interact with the X − part of The photo reaction pathways of photoreactive surface ligands and additives.f) OM image of patterned CdSe/ZnS-TDD NCs.g) InP/ZnS-TDD NCs.h) SEM image of patterned test grids with "bare" CeO 2 NCs.i) OM image of two sequential patterned "bare" CeO 2 NC layers with 5 m wide stripes.c-i) Reproduced under terms of the CC-BY license. [7]Copyright 2019, The Authors, published by American Chemical Society.ligands or the NCs surfaces in multiple ways, triggering the precipitation of NCs due to solubility changes in a polar solvent.(Equations 1 and 2). [6]dSe) m ( The researchers also proposed using ammonium 1,2,3,4thiatriazole-5-thiolate (NH 4 CS 2 N 3 , TTT) as photodecomposable anionic ligands on NC surfaces.These ligands photodecompose from the CS 2 N 3 -group to SCN -ions (Equation 3), [6,19] which possess a comparatively lower electrostatic repulsion force than CS 2 N 3 -anions, losing the colloidal stability of NCs in a polar solvent.
Leveraging the photoreactive inorganic building blocks detailed above, they executed direct optical lithography of inorganic nanomaterials via spin-coating of NC layers followed by photolithography.Using a photomask allowed for creating diverse patterns from pre-coated NC thin films by exposing them to UV light at a wavelength of 254 nm with an intensity of 6.3 mW cm −2 for 20 s, equivalent to an exposure dose of 120 mJ cm −2 .By rinsing the film with polar solvents like N,N-dimethylformamide (DMF) and N-methylformamide (NMF) to remove unexposed regions, the resultant metal, semiconductor, and oxide patterns exhibited excellent shape fidelity with high precision to a resolution of ≈1 m.Additionally, they successfully photo-patterned multiple layers of NCs, with thicknesses of 10-300 nm, through a repetitive process of sequential coating, exposure, and development.This technique considerably simplifies the patterning of inorganic layers compared to the number of steps involved in conventional photopolymer-based lithography. [6]ang et al. further developed a series of photoreactive surface ligands for more versatile photopatternable inorganic NCs that were photocurable under i-line (365 nm) and h-line (405 nm) irradiation.These wavelengths offer a higher penetration depth and induce less damage to inorganic layers than deep UV light. [14]The authors screened and classified photoreactive ligands and additive molecules from the deep UV to visible ranges into three categories.The deep UV (254 nm) category included ammonium dithiocarbamate (ADC), butyldithiocarbamate (DTC), 5-mercapto-1-methyltetrazole (MTT), potassium ethyl xanthate (PEX), ammonium 1,1-dithiooxalate (DTO), 1,3,4thiadiazole-2,5-dithiol (TDD), and N-hydroxynaphthalimide triflate (HNT).The i-line light (365 nm) category comprised DTO, TDD, HNT, and 1,2-naphthoquinonediazide-4-sulfonyl chloride (DNQ).Lastly, the h-line (405 nm) and 450 nm light range included DNQ and 2-phenyl-2-(5-((tosyloxy)imino)thiophen-2ylidene)-acetonitrile (PTA).The specific chemical structures and photoreaction pathways of the photoreactive surface ligands and additives for the photopatternable inorganic NCs are depicted in Figure 3c-e. [7,20]In the case of NCs capped with typical charged inorganic ligands such as metal chalcogenides (MCC) [17c,21] or "bare" NC prepared by removing the organic ligands of surfaces with ligand stripping agents, [22] the photoreactive additive molecules (such as PAGs) can be added to serve as a physical spacer between the NCs or to alter the surrounding environment or reduce the surface charge via the generation of photoacids through photochemical reactions.This further enables pattern formation by changing the solubility of the NCs.Utilizing light source wavelengths from DUV to visible light, in conjunction with adaptable inorganic NCs, high-resolution inorganic patterns of various NCs, including cadmium selenide (CdSe), CdSe/zinc sulfide (ZnS), indium phosphide (InP)/ZnS, cadmium telluride (CdTe), cerium (IV) oxide (CeO 2 ), zirconium dioxide (ZrO 2 ), and gold (Au), were directly fabricated on the substrate (Figure 3f,g).The minimum resolution achieved was ≈700 nm, with exposure doses ranging from 31.5 to 600 mJ cm −2 .Multi-layered patterns were also demonstrated through a repetitive sequential patterning process (Figure 3h,i).
Building upon these strategies, additional approaches have been developed that prioritize the preservation of NCs' primary properties.Specifically, this focus has been on the luminescent properties of QDs for targeted applications in LED devices.Cho et al. developed an advanced direct optical lithography approach for luminescent QDs, utilizing PAGs and triggering in situ ligand exchange reactions. [23]They achieved QD patterns with a minimum resolution of 1.5 m using a blend of CdSe-based QDs and PAGs as inks.The included PAGs, 2-(4-methoxystyryl)−4,6bis(trichloromethyl)−1,3,5-triazine (MBT), released reactive chlorine (Cl) radicals upon UV exposure, [24] while 2-diazo-1naphthol-4-sulfonic acid (DNS) converted into an indene ring with carboxyl and sulfo groups.The subsequent creation of hydrochloric acid through the reaction of Cl radicals could trigger the protonation of the QDs' native oleate ligands, causing the oleic acid to detach and the binding of Cl to the QD surfaces. [23,25]hese reactions led to solubility changes in the UV light-exposed region of the spin-coated QD film.Consequently, durable QD patterns could be produced with high resolution and a photoluminescence quantum yield (PLQY) of ≈75% of the initial PLQY.Pan et al. used the photoreactive DNS additive molecules that decompose into 3-sulfo-3H-indene-1-carboxylic acid (SICA) to fabricate high-resolution thick patterns of several positively charged metal oxide NCs, including ZrO 2 , titanium dioxide or TiO 2 , hafnium(IV) oxide (HfO 2 ), and indium tin oxide (ITO). [26]he decomposed SICA molecules, with a strong affinity for NC surfaces, inhibit the formation of electrical double-layer repulsive forces. [26]Furthermore, the dual binding sites of SICA allowed it to act as a crosslinker between the NCs, facilitating selective area solidification (Figure 4a).Due to the transparent nature of oxide materials, patterns over 1 m thick could be successfully fabricated, as the exposed light could deeply penetrate the film (Figure 4b-g).Moreover, they reported the direct photolithography of colloidal CsPbX 3 lead halide perovskite NCs through a photoinduced ligand cleavage mechanism.(Figure 4h). [27]The typical direct optical patterning methods require polar solvent environments or ligand-exchange processes, which can degrade lead halide perovskite NCs.By mixing photosensitive oxime sulfonate ester (─C = N─OSOO─) PA-480 with perovskite NCs  [26] Copyright 2021, American Chemical Society.h) Overall procedures of direct photolithography of CsPbX 3 NCs with photoreactive PA-480.Fluorescence OM images of patterned i,j) CsPbBr 3 NCs and k,l,m,n) others.h-n) Reproduced with permission. [27]Copyright 2021, American Chemical Society.o) Scheme of direct optical patterning of colloidal QDs via light-triggered ligand stripping agent (TPCl).p,q,r) Fluorescence OM images of patterned Cd-based QDs.s) Height profiles of lie patterns.o-s) Reproduced with permission. [32]Copyright 2023, American Chemical Society.t) Schematic illustration of direct optical patterning of QDs using photoreactive additives (PAmG).u,w) OM images of patterned Cd-based QDs.t-w) Reproduced under terms of the CC-BY license. [34]Copyright 2023, The Authors, published by Springer Nature.
capped with oleic acid and oleylamine, partial ligand exchange with PA-480 could be achieved in a non-polar solvent.Subsequent 405 nm UV exposure led to the decomposition of PA-480 molecules, reducing the NCs' solubility in non-polar solvents, and enabling pattern formation with a minimum resolution of 1 m (Figure 4i-n).Although the PLQY was initially below 5%, it could be improved up to 79% by additional spin-coating of PbBr 2 , octanoic acid, and butylamine. [28]In 2022, Hahm et al. reported the state-of-art direct optical patterning of colloidal QDs.They focused on the design of QD surfaces using a novel combination of photocrosslinkable ligands (PXLs) and dispersing ligands (DLs). [29]This strategy achieved direct photopatternability and preserved the optical properties.PXLs are organic molecules with a thiol anchor group at one end and a benzophenone moiety at the other.The chemical structure of the benzophenone moiety was meticulously engineered to optimize photoreactivity within the i-line wavelength range.These specially designed PXLs exhibited strong binding affinities to QD surfaces, allowing them to effectively displace native ligands. [30]Under UV irradiation, the carbonyl group of the benzophenone moiety transforms into ketyl radicals through hydrogen abstraction, forming covalent ligand bonds between neighboring QDs through photocrosslinking. [31]Consequently, this photocrosslinking reaction decreased the colloidal stability of QDs in solvents, facilitating the fabrication of red, green, and blue (RGB) QD patterns with a minimum resolution of 800 nm through selective UV exposure.In 2023, Fu et al. achieved direct optical patterning of RGB colloidal QDs via a light-triggered ligand-stripping approach for creating efficient and stable patterned QDs. [32]They introduced photoreactive triphenylmethyl chloride (TPCl) and similar additives to QDs capped with native organic ligands.Under 254 nm UV irradiation, TPCl dissociated, forming TP + carbocations and Cl − anions.The TP + carbocations, acting as strong Lewis acids, effectively removed the native organic ligands. [33]onversely, the Cl -anions, acting as Lewis bases, bound to the electrophilic metal sites on QD surfaces, passivating the defects and preserving the photophysical properties (Figure 4o).Through these chemical reactions, the solubility of the QDs in non-polar solvents was significantly reduced, enabling the creation of microscale QD patterns with a lateral resolution of ≈4 m (Figure 4p-s).Recently, Xiao et al. developed all-inorganic NCs with high PLQY, maintaining their optical properties after surface treatment.They mixed these NCs with photoreactive additive molecules known as photoamine generators (PAmGs) and applied them in direct photolithography. [34]Upon deep UV irradiation, the PAmGs decomposed, releasing n-butylamine. [35]The released n-butylamine bound to the exposed surface cations of the NCs, reducing their solubility in polar solvents (Figure 4t).This decrease in solubility allowed for the direct fabrication of high-resolution patterns (Figure 4u,w).Moreover, the primary amine released in this process induces solubility changes for solidification and passivates the surfaces of NCs, leading to higher PLQY and improved electrochemical stability. [36]oreover, the development of optically patternable inorganic building blocks using crosslinkers that bind ligands and their application in direct photolithography has been actively studied.9a] The LiXer comprises two fluorinated perfluorophenyl azide groups situated at the ends of the molecule. [37]These groups are renowned for their photoreactive properties, allowing them to form reactive nitrene intermediates upon exposure to UV light at 254 nm.9a,38] By interconnecting the ligands of neighboring QDs, this approach can create high-resolution RGB QD patterns with a minimum feature size of 3 m.The patterning procedure involved spin-coating a mixture of QDs and LiXer, then applying selective UV exposure using photolithography (254 nm, 0.4 mW cm −2 ) and rinsing off the unreacted QD parts (Figure 5b).Researchers successfully implemented lateral and stacked RGB patterns by iteratively repeating these steps, demonstrating superior direct optical patterning capabilities (Figure 5c-g).9b] They employed bisFPA crosslinkers for direct optical patterning of perovskite NCs, eliminating the need for ligand-exchange procedures.These bisFPA crosslinkers exhibited strong absorption in the deep UV region and efficiently underwent photolysis to form nitrene radicals upon UV irradiation. [39]Reactive nitrene radicals form covalent C-N bonds with alkyl chains in the native ligands of perovskite NCs through a C-H insertion reaction (Figure 5h).These photochemical reactions between ligands on NCs lead to crosslinked NCs that are insoluble in non-polar solvents, reducing the colloidal stability (Figure 5i-l).9c] They studied the impact of these photocrosslinkers on the direct optical patterning capabilities and photophysical properties of the patterned QDs.Upon UV irradiation, all four photocrosslinkers underwent photolysis reactions similar to the previous bisFPA crosslinkers, generating reactive radicals that crosslinked neighboring QD ligands.The photolysis efficiency varied depending on the type of photocrosslinker, determined by its absorption wavelength and molar extinction coefficient.Consequently, they demonstrated various light sources suitable for optical patterning, considering the highly reactive UV region associated with each photocrosslinker.
Pan et al. introduced a method for direct optical patterning that eliminates the need for additional photoreactive ligands or additives.Instead, they leveraged the photooxidation mechanism of surface ions to produce high-quality patterns.Combining bare NCs stabilized electrostatically with non-coordinating anions, such as BF 4 − , with the established phenomenon of lightinduced oxidation of semiconductor NCs, pioneered a ligandfree direct optical lithography (Figure 6a). [40]This technique creates high-quality, high-resolution patterns by instigating solubility changes in the NCs through localized photooxidation and desorption of DMF ligands.The oxidation process, which involves the transformation of surface ions (for example, Se 2− to selenium dioxide or SeO 2 ), was analyzed using UV-absorption  [9a] Copyright 2020, The Authors, published by Springer Nature.h) Description of direct patterning of perovskite NCs using a photoreactive crosslinker (bisFPA).i,j,k) Fluorescence OM images of CsPbBr 3 NC patterns.scale bar 100 m (j, top).l) A photograph of patterned NC film on a flexible substrate under UV light.Copyright 2022, American Chemical Society.j) Schematic illustration of direct optical patterning of NCs without additives (native ligand cleavage reaction).k,l) OM images of dot and line patterns of In 2 O 3 NCs with various resolutions (100 -10 m).m,n) Height profiles of corresponding OM images.j-n) Reproduced with permission. [41]Copyright 2022, American Chemical Society.spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR).They successfully fabricated high-resolution (≈1 m feature size) semiconductor NCs and other metal oxide NCs using ZnSe-BF 4 NCs as photosensitizers (Figure 6b-i).Wang et al. described the direct optical patterning of NCs, circumventing the need for photoreactive additives. [41]They showcased that a native organic ligand cleavage reaction stimulated by UV irradiation can cause a solubility change in the NCs.The alkyl chains of native organic ligands, such as oleic acid and oleylamine, can be cleaved and decomposed when exposed to the high-energy photons released by UV, [42] allowing for high-resolution patterning of NCs by reducing the interparticle spacing between NCs (Figure 6j).Accordingly, they successfully produced NC patterns with dimensions of 10 m, using DUV light at an energy dose of 9000 mJ cm −2 (Figure 6k-n).Wang et al. explored the potential of direct optical patterning of a metal chalcogenide semiconductor layer through direct optical lithography of metal-organic molecular precursors based on butyldithiocarbamic acid (BDCA). [43]Under UV irradiation, specifically the h-line with an intensity of 25 mW cm −2 for 2 h, the BDCA molecules decomposed into a metal complex intermediate. [44]The ample UV energy supply facilitated this decomposition.The intermediate then became insoluble in the solvent, allowing for fabricating the desired patterns.Although this process required a relatively long duration, the study showed the potential to create a copper(I) sulfide (Cu 2 S) pattern with a resolution of ≈10 m.
As described above, photolithography-based direct patterning methods for inorganic materials are summarized in Table 1.

E-Beam and X-Ray Lithography-Based Direct Patterning
Beyond UV-vis light sources, extensive research has been carried out on the direct patterning of inorganic materials utilizing e-beams and X-ray lithography.These techniques afford significantly superior resolution compared to traditional photolithography-based direct patterning processes, attributed to their shorter wavelength (0.2-0.5 Å) and capacity to focus at subnanometer scales.E-beam lithography possesses a direct-writing capability, enabling the formation of minuscule feature patterns with remarkable precision.This makes it an optimal choice for the fabrication of precise inorganic structures.To accomplish direct patterning using these techniques, similar strategies are employed to create e-beam or X-ray responsive inorganic building blocks.This includes inorganic NCs, [45] perovskite NCs, [46] inorganic-organic molecules, [43] and metal-organic frameworks (MOFs). [47]High-energy electrons or X-rays can stimulate the crosslinking of NCs organic ligands, induce reactions in additives, cause decomposition, and trigger changes in phase or solubility.
In 2014, Miszta et al. reported the direct patterning of CdSe, CdSe, Cu 2-x Se, and Cu 2-x S NCs using e-beam and X-ray-beam lithography. [45]This was achieved by locally irradiating NC films with beams, inhibiting partial cation-exchange reactions, and successfully integrating direct patterning technology.After the deposition of native organic ligands capped NCs onto a substrate, subjecting the NC film directly to a high-energy beam resulted in the crosslinking of the passivating organic ligands present on the surfaces of the NCs.This process prevented cation flow in subsequent cation exchange reactions (Figure 7a).By immersing the precoated NC films in a Cu(I) complex solution (Cu(I) tetrakis (acetonitrile) hexafluorophosphate) for 45 min, the Cd → Cu exchange was induced. [48]E-beam or X-ray exposure can trigger high-resolution selective phase changes in Cd-based chalcogenide materials, given acceleration voltages of 10 kV and doses of 0.1-20 mC cm −2 or intensities of 30 kJ cm −2 , yielding a minimum resolution of ≈50-100 nm (Figure 7b).This technique does have limitations; the cation exchange is confined to certain material groups, and selective phase-change patterning of materials can only be done within the precoated NC films.Palazon et al. fabricated patterned colloidal perovskite NCs employing X-ray lithography. [46]The main concept of their work was to induce C = C intermolecular bonding of organic ligands surrounding perovskite NCs in the irradiated area using X-ray, forming an insoluble NC network in organic solvents (Figure 7c).A pattern was created by removing the unexposed region through a lift-off process (Figure 7d).However, this method requires a lengthy X-ray irradiation time ranging from 30 min to 5 h.
In 2019, Wang et al. presented a comprehensive approach for direct electron beam lithography of functional inorganic nanomaterials (DELFIN). [7]Similar to the DOLFIN process, DELFIN utilizes e-beam reactive NCs combined with e-beam reactive PAG molecules.When exposed to an e-beam, the PAG molecules instigate a radical reaction, releasing acid that interacts with the ligands of the NCs or with Lewis basic sites on the NC surface.This interaction disrupts the colloidal stability of the NCs in a polar solvent, leading to the formation of ultrahigh-resolution patterned NC layers.They achieved a resolution of 30-50 nm for the patterned CeO 2 NC layers, using an e-beam current of 17.6 pA and doses ranging from 150 to 200 C cm −2 (Figure 7e,f).Higher exposure doses were necessary to pattern smaller features, effectively reducing blurring during exposure.Furthermore, semiconductor QDs, such as CdSe NCs capped with Sn 2 S 6 4-and CdSe/ZnS core shells could also be patterned using a direct ebeam lithography process (Figure 7g,h).In 2020, Wang et al. introduced a novel method for direct e-beam lithography of metal chalcogenide semiconductors using BDCA-based metal-organic molecule complexes. [43]Thermal decomposition of this molecular precursor solution forms metal complex intermediates that are insoluble in organic solvents.E-beam irradiation induces similar chemical changes in the metal-organic precursors, rendering them insoluble and facilitating the formation of patterned structures.Subsequently, the patterned metal complex undergoes thermal decomposition during high-temperature annealing (300-500 °C), producing metal chalcogenide materials akin to the previously described photolithography approach.Depending on the specific material, they achieved a minimum patterning resolution of less than 50 nm using electron radiation doses ranging from 3600 to 7200 mC cm −2 .The unexposed parts were removed via a development process that involved immersing the sample in isopropanol for approximately 1 h.Additionally, they successfully fabricated multi-material 3D heterostructures comprising antimony trisulfide (Sb 2 S 3 ) and ZnS on a silicon substrate using an additive manufacturing method.In 2021, Tu et al. reported the resist-free direct patterning of MOFs using X-ray and e-beam lithography. [47]They identified X-ray-sensitive zeolitic imidazolate frameworks (ZIFs), [49] a subclass of MOFs composed of tetra-  Reproduced under terms of the CC-BY license. [45]Copyright 2014, The Authors, published by American Chemical Society.c) Schematic illustration of direct patterning the perovskite NCs using X-ray lithography (native ligand linking reaction).d) Scheme of direct X-ray lithography procedures, the stencil mask, SEM, and XPS mapping image of CsPbBr 3 NCs.Scale bar 300 m.c,d) Reproduced under terms of the CC-BY license. [46]Copyright 2016, The Authors, published by American Chemical Society.e,f) SEM images of e-beam lithography patterned "bare" CeO 2 NC lines with 50 and 30 nm resolution.SEM images of 100 nm width of line patterns with g) CdSe-Sn 2 S 6 and h) CdSe/ZnS-Sn 2 S 6 -PAG.The inset image shows PL from patterned CdSe/ZnS stripes, scale bar 10 m.e-h) Reproduced under terms of the CC-BY license. [7]Copyright 2019, The Authors, published by American Chemical Society.
hedrally coordinated transition-metal ions interconnected by imidazolate linkers, by exposing ZIF powders to X-rays.Halogenated materials, including ZIF-71, ZIF-71-Co, ZIF-72, and ZIF-8 with 4,5-dichloroimidazole (dc-im), 2-chloroimidazole (Cl-im), and 2bromoimidazole (Bi-im) linkers, showed solubility changes upon X-ray exposure from a threshold dose.Although pristine ZIFs are insoluble in dimethylsulfoxide (DMSO), X-ray irradiation causes chemical changes that make them soluble in the same solvent.Primary bond breaking arises due to interactions between X-rays and materials via photoelectric, Compton, or Auger effects. [50]able 2. Summary of E-beam & X-ray lithography-based direct patterning methods.Secondary reactions arise from radiolytic products such as free radicals generated by high-energy electrons.In the case of ZIF-71, the C─Cl bond undergoes homolysis to produce Cl radicals, initiating the cleavage of C─C, C─N, and Zn─N bonds, [51] leading to further reactions like the formation of Zn─Cl bonds.This results in creating a DMSO-soluble fraction, enabling dissolution and direct X-ray and e-beam lithography.By using optical exposure doses of 60-100 kJ cm −3 and ≈1000 C cm −2 , highresolution patterns of MOFs with features below 50 nm can be produced, even in thick single-crystal MOFs, all while preserving the original properties of the MOFs, such as porosity.A summary of direct patterning methods for inorganic materials using e-beam and X-ray is presented in Table 2.

Laser Writing-Based Optical Pattering
Direct laser writing has emerged as a promising method for the high-resolution patterning of inorganic materials with largearea coverage, high-throughput, and process flexibility.This method offers submicron precision resolution, comparable to photolithography-based direct patterning.However, it eliminates the need for a photomask by enabling arbitrary pattern formation through writing.Accordingly, researchers have explored various approaches, including photoinduced chemical reactions, optical trapping, ionization, and material melting, to create laser responsive inorganic building blocks that facilitate this process.
In 2020, Chen et al. presented a novel in situ patterning technique for inorganic materials using direct laser writing. [10]This method facilitated the patterning of a wide array of materials, encompassing metals, insulators, and magnets, through semiconductor nanoparticle-assisted photoinduced chemical reactions and optical trapping.The inorganic building blocks comprised two aqueous solutions: a metallate-based solution and a semiconductor nanoparticle solution.The mixed solution was drop-cast onto the substrate, and laser writing was performed using a laser wavelength of 532 nm, with a laser power of 60.4 and 0.485 mW for 30 ms -1 s).After the remaining solvent was extracted using a pipette, the patterned material stayed intact.When a con-tinuous laser focuses on the solution, it energizes free electrons from the valence band of semiconductor nanoparticles.This initiates a chemical reaction that changes metal ions into metal particles on the surfaces of semiconductor nanoparticles.Simultaneously, the focused laser serves as an optical trap, guiding the particles to the focus spot. [52]The chemically reduced metal particles function as a binder, joining the trapped particles and forming metal/semiconductor composites on the substrate (Figure 8a,b).They successfully fabricated patterns with a minimum resolution of ≈500 nm on various substrates using gold, silver, and platinum (Pt).(Figure 8c-e).However, the patterning mechanism of this method restricts its use in metal-semiconductor composites, creating certain limitations.(Figure 8f).In 2022, Liang et al. reported high-resolution patterning of 2D perovskite films employing direct femtosecond laser writing. [53]The precursor solution was prepared by dissolving lead iodide and 2-phenylethylammonium iodide in DMF solvent.The femtosecond laser, set at a wavelength of 1030 nm, was focused on the spin-coated perovskite films.This resulted in ionization and alignment of the 2D perovskite through lattice melting and a Coulomb explosion due to the ultrahigh peak intensity of the laser.They examined optimal laser fluences (4, 12, 24, and 40 mJ cm −2 ) and laser scanning speeds (0.1, 0.2, 0.4, 0.6, 0.8, 1, 1.2, 1.4, and 1.6 mm s −1 ), ultimately determining that 40 mJ cm −2 and 0.8 mm s −1 were the most effective due to their sufficient energy for ionization, melting, and the evaporation of the 2D perovskite.They successfully engineered high-resolution patterns of 2D perovskites with features below 2 m, preserving their optical properties.Given the limited research on the laser writing approach, it is necessary to pursue further investigations into patternable inorganic materials and applications using direct laser writing in the future.

Direct Heat-Induced Patterning
Direct heat-induced patterning employs a laser or probe, which functions as a small spot to stimulate thermal reactions, crafting patterned structures.This method relies on heat to selectively transform inorganic materials into high-resolution patterns, necessitating the synthesis of thermally reactive inorganic building (inset SEM image is the patterned platinum dot, scale bar 500 nm).f) Lists of components for patternable inorganic solutions and substrate, reflection type illumination microscopic images of patterned materials on a substrate.a-f) Reproduced under terms of the CC-BY license. [10]Copyright 2020, The Authors, published by Springer Nature.
blocks.Compared to others, a distinct advantage of this technique is its ability to fabricate patterned layers with thick films, circumventing the penetration-depth constraints associated with photons.In this section, we provide a brief overview of the thermally reactive inorganic building blocks and the recently reported heatinduced direct patterning procedures.
Wang et al. recently presented a method for the direct patterning of metal chalcogenide semiconductors through thermal scanning probe lithography (TSPL). [43]This approach features highly localized heating within the tip and sample contact area.During direct local heating, they observed identical phase transition phenomena to those in metal-organic precursor (BDCA) films, forming an insoluble metal-organic complex.The patterning mechanism of TSPL depends on the cantilever's temperature, which can rise to 700 °C (in the case of Sb 2 S 3 ) when scanning at a velocity of 300 m s −1 .In 2022, Wu et al. reported a method known as heat-induced patterning of inorganic nanomaterials (HIPIN), enabling the direct patterning of diverse NCs, including metals, semiconductors, and dielectrics. [54]hey adopted a high-throughput, scalable thermal patterning approach based on optical techniques using thermally reactive inorganic building blocks.They synthesized basic inorganic NCs and developed three thermally reactive surface ligands: ammonium carbamate (ACM), alkylamines, and N-(tert-butoxycarbonyl)-Lcysteine methyl ester (CME).ACM ligands were selected due to their ability to decompose into carbon dioxide (CO 2 ) and amines with temperature-controlled thermal decomposition, facilitated by the bulkiness of the alkyl groups. [55]CME ligands, having a labile tert-butoxycarbonyl group, thermally decompose into CO 2 and isobutene, leaving secondary amines behind. [56]he n-alkylamine ligands, weakly bound to the surfaces, can also be detached from the NCs surfaces through thermal reactions (Figure 9a).With these thermally reactive ligands, inorganic NCs underwent direct patterning due to solubility changes in various solvents at appropriate temperature ranges from 80 to 200 °C.Several selective heating techniques were introduced for NCs films.These techniques include direct laser heating with a 10 nspulsed 532 nm laser for sub-500 nm resolution, indirect laser heating where a CO 2 laser warms the underlying substrate (leading to subsequent heat transfer to the NCs layer), and direct heat transfer utilizing a hot cantilever or stencil (Figure 9b-f).The researchers successfully patterned Au, CdSe, InP, and HfO 2 NCs with a minimum resolution of roughly 570 nm and achieved multimaterial structures through repetitive sequential patterning (Figure 9g-j).Moreover, this method could pattern a layer with a thickness exceeding 1 m, capitalizing on thermal patterning to surpass the light penetration depth limitation inherent in optical patterning.In 2022, Li et al. introduced another thermally activated ligand and an additive method for direct patterning.This approach utilized thermally decomposable TTT ligands in NCs and an ethylene bis(4-azido-2,3,5,6,-tetrafluorobenzoate) (bisPFPA) crosslinker additive to catalyze a chemical transformation, altering the colloidal stability of the NCs (Figure 9k). [57]hermal stimuli caused the TTT ligands to undergo thermal decomposition to thiocyanate (SCN − ) ions on the NC surface, rendering them insoluble in polar solvents.The bisPFPA crosslinkers released nitrogen and generated reactive nitrene radicals that underwent C─H insertion with the native hydrocarbon ligands of the NCs.This process led to the covalent bonding of neighbor-ing NCs and pattern formation (Figure 9l).FTIR and XPS confirmed this crosslinking mechanism.Particularly, the gradual decrease of the azido group's asymmetric stretching mode (-N 3 at ≈2130 cm −1 ) signified the complete decomposition of bisPFPA (Figure 9m).The emergence of notable N 1s and F 1s peaks with binding energies comparable to those of pure bisPFPAs in CdSe/bisPFPAs was also observed (Figure 9n).Through controlling laser parameters, temperature, and penetration depth, they achieved programmable and optically non-destructive patterning.Using this method, they demonstrated the fabrication of CdSe and other NCs patterns with a minimum resolution of ≈10 m and a thickness varying from tens of nm to over 10 m in a single step (Figure 9o-q).They employed a 1060 nm laser with a pulse width of 250 ns, a repetition rate of 55 kHz, a laser power of 34-670 mW, and writing speeds of 30-50 mm s −1 (for thin layers) and 1-10 mm s −1 (for thick layers).
As described above, heat-induced direct patterning methods for inorganics are summarized in Table 3.

Direct 3D Patterning
Optical 3D printing techniques, such as DLP and SLA, are promising alternatives for cost-effective 2D and 3D patterning via bottom-up manufacturing. [58]Patterned light exposure through a digitally designed mask or a path of light and laser generated by computer-aided design (CAD) can solidify liquid-type photoreactive resin inks and create high-resolution patterned structures.Unlike other methods, this approach can directly form 2.5D and 3D patterned structures layer by layer or by directly writing freestanding structures.However, the primary challenge in optical 3D printing is that printable materials are limited to photopolymers or their composites with inorganic materials.Thus, we present the recently developed optical 3D printable inorganic building blocks and direct 3D patterning of inorganic materials.
In 2022, Baek et al. reported a unique optical patterning method for metal chalcogenide semiconductors utilizing a DLPbased optical 3D printing technique (Figure 10a). [59]Anionic inorganic molecules, such as chalcogenidometallate (ChaM) precursors, were prepared to formulate photocurable inorganic inks.This process involved dissolving Sb, Sn, Cu, Pt, and Mo chalcogenide powders in ethylenediamine/ethanethiol alkahest solvent or using traditional coordination chemistry approaches. [60]he resultant ChaM anions were counterbalanced with ammonium or ethylenediammonium cations.To form the photocurable ChaM-based inorganic inks, they added two types of PAGs to the synthesized ChaM solution: 2-[2-(5-methyl furan-2yl) vinyl]−4,6-bis(trichloromethyl)−1,3,5-triazine (MFVT) and N-(trifluoromethylsulfonyloxy)−1,8-naphthalimide (IM-NIT).Exhibiting a broad absorption spectrum from ≈350 to 400 nm, these PAGs were suitable as h-line (405 nm) and i-line (365 nm) light sources.Upon UV irradiation, the PAGs decomposed, inducing the creation of protons (H + ) and photoacids in the ink medium. [24,61]These protons rapidly interacted with the ChaM anions owing to their high proton affinity of chalcogen anions, causing ChaMs to precipitate due to charge loss and reduced solubility in polar solvents (Figure 10b).This mechanism was validated by noting a decrease in zeta potential and an increase in DLS solute size pre-and post-UV irradiation (Figure 10ce).By utilizing a simple digital mask and patterned UV light  [11] They proposed a strategy that used the photoexcitation of semiconductors to produce electron-hole pairs, altering the surface chemistry of QDs, which initiated interparticle chemical bonding.Specifically, they selected CdSe/ZnS core/shell QDs capped with 3-mercaptopropionic acid (MPA).These were linked to the ZnS shell through Zn─S bonds.When the highest occupied molecular orbital (HOMO) of the MPA molecules is located above the valence band maximum (VBM) of CdSe, laser excitation generates excitons inside CdSe that split into separate electrons and holes.These generated holes then tunnel through the outer potential barrier and are transferred to the QD surfaces, where the MPA ligands capture them, desorb from the surfaces, and form dissolved disulfides in the solution (Equation 4). [62]n Subsequently, the exposed Zn + atoms on the surfaces actively bind to the COO -groups from neighboring QDs, prompting interparticle bonding.This mechanism is also applicable when the VBM of QDs is below the HOMO of MPA molecules and metallic NCs.This is because the generated hot carriers of metallic NCs possess enough energy to transfer to the NC surfaces and drive the ligand desorption reaction.By filling a homemade chamber with QD dispersions and exposing it to a femtosecond laser, they fabricated nanopillar patterns of QDs directly, achieving a resolution of less than 100 nm.They reached a minimum of ≈77 nm under optimal laser power and scanning speed conditions, specifically 0.27 nJ pulsed energy and 20 m s −1 .Additionally, they created free-standing curved 3D architectures and heterogeneous material 3D architectures using different mixed QD solutions.However, the concept has been demonstrated using semiconductor QDs, indicating potential to expand the range of printable materials.As outlined earlier, these types of direct 3D patterning technologies for inorganic materials present significant potential for precisely creating 2D, 2.5D, and 3D architectures in a more straightforward manner compared to other methods.

Applications and Patterned Devices
Our previous discussion on tailored inorganic materials and their direct patterning methods has provided an essential pathway for incorporating functional inorganic materials into practical applications and devices.In this section, we will briefly explore the application of the direct patterning process across diverse fields, including optoelectronics, electronics, and energy devices.For optoelectronic devices, there have been studies on patterned LEDs  , c) direct laser in the deposited materials, d) thermal contact can transfer the heat to materials, e) transparent materials can be heated by conduction from a substrate, f) a heat source like LEDs can transfer to deposited materials.g-j) Images of patterned layers using thermal reactive NC inks.Scale bars in (h-j) are 100 m.The inset images showed the corresponding thermal reactive inks.a-j) Reproduced with permission. [54]Copyright 2022, American Chemical Society.k) Schematic illustration of the direct thermal patterning process.l) Chemical structures of bisPFPA crosslinkers and reaction mechanism for thermal patterning.bisPFPA generated singlet nitrene radicals at both ends group response to the heat.These radicals can react with native hydrocarbon ligands, leading to the crosslinking of neighboring NCs.m,n) FTIR and XPS spectra of NC films with crosslinkers before and after thermal patterning.o,p) Height profiles and cross-sectional SEM image of micronthick QD patterns.Scale bar 10 m.q) Fluorescence OM images of RGB QD patterns.k-q) Reproduced with permission. [57]Copyright 2022, The Authors, published by Springer Nature.and photodetectors using colloidal QDs and perovskite NCs.In the electronics and energy devices sectors, we will describe several examples of devices fabricated via a direct patterning process, which is still in its nascent stages.In this section, we underscore the potential of direct patterning as a versatile technology for fabricating microscale optoelectronic, electronic, and energy devices.

Optoelectronic Devices
The precise patterning of luminescent inorganic building blocks, such as colloidal QDs and perovskite NCs, is a crucial requirement for optoelectronic devices, particularly LED displays. [63]eanwhile, it is essential to conserve the primary optical properties of building blocks after the direct patterning deposition.In this section, we will discuss strategies to maintain the photophysical properties of QDs or NCs within the patterned layers and examine the performance of LED devices.This includes critical indicators such as external quantum efficiency (EQE), full width at half maximum (FWHM) of the EL spectra, and pixel resolution measured in pixels per inch (ppi).Additionally, we will briefly discuss the applications of photodetector devices fabricated using the direct patterning method.
Cho et al. investigated the direct optical patterning of core/shell CdSe-based QDs using PAGs, which enabled in situ ligand exchange on the QD surfaces. [23]The patterned QD layers demonstrated high PLQY retention, maintaining ≈75% of their initial PLQY.This result was attributed to the use of QDs originally capped with organic ligands, the integration of PAGs facilitating in-situ ligand exchange-based direct optical patterning, and the presence of Cl-bound QD surfaces.Capitalizing on these properties, the researchers successfully fabricated EL devices featuring QD emissive layers, utilizing patterned layers of CdSe/Cd 1-x Zn x Se 1-y S y /ZnS QDs created through direct optical patterning.The device assembly encompassed multiple layers, including ITO (145 nm), Zn 0.9 Mg 0.1 O (50 nm), the QD layer (30-40 nm), polyethyleneimine ethoxylated (PEIE) (10 nm), poly(N, N'-bis(4-butylphenyl)-N, N'-bis(phenyl)-benzidine (poly-TPD) (30 nm), MoO x (10 nm), and Al (100 nm).The patterned QLEDs attainted 71% of the maximum current efficiency (CE max ) exhibited by pristine QLEDs, primarily ascribed to the diminished PLQY of the patterned QD layers.Moreover, the maximum luminance (L max ) of the patterned QLEDs remained comparable to that of the pristine devices, specifically 22 500 cd m −2 and 31 800 cd m −2 , respectively.Post-patterning, the EL spectra of the patterned QLEDs exhibited no discernible shifts or broadening after the patterning.Conclusively, successful patterning of multicolor QLEDs RGB pixels was achieved, with feature sizes ranging from 5 to 1.5 m.9a] They optimized the LiXer content in the QD solution for patterning to mitigate PLQY loss in the patterned QD layer.They demonstrated that maintaining a LiXer content between 1 and 2 wt.% retained the desired photophysical properties (Figure 11a,b).The QLED devices were constructed in an inverted structure with layers of ITO (cathode)/ ZnO(electron transport layer (ETL))/patterned QD layers (30 nm, 1 wt.% of LiXer)/ 4,4-bis(N-carbazolyl)−1,1-biphenyl (CBP, hole transport layer(HTL))/MoO 3 /Al.(Figure 11c).Comparative analysis of the pristine and patterned QD layers revealed that the peak EQE remained consistent at 14.6%, and the peak position and FWHM of the EL spectra were closely aligned.(Figure 11d).Furthermore, the L max of the patterned QLEDs exhibited negligible variations compared to that of the pristine QD layers, exceeding 100 000 cd m −2 (Figure 11e).This result affirmed the viability of the proposed patterning approach for practical patterned QD array applications while preserving the original properties of the QDs.Finally, they realized pixelated RG QLEDs with a single pixel size of 10 m × 38 m (Figure 11f).9c] They focused on the effects of different crosslinkers and UV wavelengths on the performance of QLEDs featuring patterned QD layers.The EL spectral peaks of the patterned QLEDs remained stable, exhibiting no significant shifts or broadening compared to the pristine devices.The PLQY of each patterned QLED slightly decreased, ranging from 20 to 51%, relative to the pristine sample with a PLQY of 53%.Both pristine and patterned devices achieved maximum EQEs in the 11-13% range.Moreover, the QLED device that utilized the carbene-based crosslinker under 365 nm wavelength UV exposure displayed almost identical EQEs and L max , 11,330 cd/m 2 , compared to pristine devices.Furthermore, the device operating lifetime, denoted as T 95 (the time required for luminance to drop to 95% of its original value) at 1000 nit (i.e., at an initial brightness of 1000 cd m −2 ), surpassed 4800 h for patterned devices, outpacing the pristine devices exhibiting a T 95 value of 4,100 h.This enhanced durability is ascribed to the mild photochemistry and benign electronic structure of the crosslinkers.Wang et al. manufactured patterned QLEDs utilizing a direct optical patterning method incorporating ligand cleavage of colloidal QDs. [41]After the patterning process, the PLQY decreased from 64.4% in the pristine QD films to 19.0% in the CdSe-based patterned layers.This substantial reduction was linked to surface traps generated by the ligand cleavage reaction.However, introducing ZnCl 2 as a ligand exchange agent post-patterning resulted in an enhanced PLQY of 43.7%.This enhancement was attributed to the improved surface passivation of the QDs.The fabricated patterned QLEDs were comprised of ITO/poly(ethylenedioxythiophene/poly(styrenesulfonate)/ poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-secbutylphenyl)diphenylamine/patterned QD layers/ZnMgO/Al.(Figure 11g).The patterned QLED device, treated with ZnCl 2 , exhibited EL spectra comparable to the pristine QD films.Additionally, it achieved an L max of 177,000 cd/m 2 (Figure 11h).The device also attained a maximum EQE of 5.6%, representing ≈76% of the EQE of the pristine QELDs (Figure 11i).In 2022, Hahm et al. investigated the direct patterning of QLED devices through photolithography of colloidal QDs, using an adaptable dual-ligand system. [29]Even after photocrosslinking with PXLs linkers and the subsequent patterning, the patterned RGB InP-and CdSebased QD layers retained their optical properties, such as PLQY and EL spectra, similar to the pristine QDs.The preservation of these photophysical properties was attributed to the mild ligand displacement and rapid photocrosslinking with a low-energy UV source (365 nm), affirming the suitability of patterned QD layers for efficient LED emissive layers.The patterned QLEDs achieved an approximate maximum EQE and luminance of 20% and over 100 000 cd m −2 , respectively, with minimal deviations from the properties of the pristine QDs.Moreover, the researchers created an RGB sub-pixel size of 0.8 × 0.8 m 2 , leading to an exceptional resolution of 15875 ppi.Additionally, they effectively implemented a 10 × 10 array of RGB QLEDs, demonstrating the practical implications of their approach.Fu et al. demonstrated direct patterning of QLEDs exhibiting impressive RGB color efficiency and prolonged device stability. [32]This was achieved by employing light-triggered ligand stripping and passivation of the QD surfaces with Cl -anions.Even after direct optical patterning, the patterned QDs retained their photophysical properties.Specifically, the red and green QDs maintained ≈90% of their original PLQYs, while the blue QDs retained approximately 70% post-patterning.Accordingly, they created patterned QLED devices using red, green, and blue QDs as active emissive layers.These patterned QLED devices demonstrated EL spectra peak positions identical to those of the pristine devices, devoid of shift or broadening.The patterned devices displayed similar EQEs, L max , and operational lifetimes (T 95 at 1000 nit) across all the RGB cases.For instance, the red-patterned QLED showed an EQE of 19.1%, a luminance of 13,649 cd m −2 (Figure 11j), and an operational lifetime of 7657.Similarly, the green-patterned QLED exhibited an EQE of 17.5%, a luminance of 56 918 cd m −2 (Figure 11k), and an operational lifetime of 8707 h.Lastly, the blue-patterned QLED showcased an EQE of 12.0%, a luminance of 4294 cd m −2 (Figure 11l), and an operational lifetime of 61.3 h.Lastly, they successfully fabricated an array of patterned QLED pixels with a resolution of 4 m × 16 m.
9b] The patterned CsPbBr 3 and FAPbBr 3 NCs showed PLQY of 38 and 48%, respectively, exhibiting a reduction from their pristine states of 61 and 86%.This decrease is likely due to side reactions of the crosslinker, such as the reaction of photogenerated nitrene with the NC surface and the related surface trap states.Nevertheless, after post-patterning treatment, the PLQYs of patterned CsPbBr 3 and FAPbBr 3 were recovered to 76% and 75%, respectively.Accordingly, they could fabricate the patterned perovskite NCs as the emissive layers between the cathode, ETL, HTL, and anode (Figure 12a).The EL emission peak of these patterned devices exhibited considerable stability, with a consistent position and FWHM showing no noticeable broadening or shifting.Moreover, the patterned FAPbBr 3 perovskite NCs LED displayed impressive performance characteristics, including a L max of 20 000 cd m −2 and a maximum EQE of 6.8%.These values represent better device performance than the pristine perovskite NCs LED (Figure 12b,c).Finally, the researchers presented a proof-of-concept for pixelated LEDs with pixel sizes of 10 m × 50 m.As introduced above, the summarized performance data for QDs and perovskite NCs-based patterned LED devices achieved by direct patterning methods are presented in Table 4.
In addition to patterned luminescence devices, fabricating optoelectronic devices, such as photodetectors, through direct patterning of inorganic materials could be a demonstrative application.Pan et al. fabricated photodetector devices by direct optical patterning of CsPbBr 3 NCs through surface ligand cleavage onto prefabricated interdigitated Au electrodes using conventional photolithography techniques (Figure 12d,e). [27]Following the patterning step and treatment with a trifluoracetic/butylamine solution, the photodetector exhibited a distinct photoresponse to violet light illumination at a wavelength of 395 nm and an applied voltage of 20 V (Figure 12f).This result suggests the potential for charge injection or extraction into the patterned NC layers.However, the performance of this photodetector was comparatively lower than those of other reported CsPbBr 3 films, indicating a need for further optimization of various factors, including the patterning process, layer thickness, and ligand chemistry.Wang et al. constructed a single-nanoribbon-based photodetector through direct patterning of a Se-doped Sb 2 S 3 metal chalcogenide layer using e-beam lithography. [43]They created the Sb 2 S 3 nanoribbons with a diameter of 5 m on the pre-fabricated parallel Au electrodes, with a channel length of 2.5 m.In dark conditions, the Sb 2 S 3 devices exhibited strong insulating properties with a resistivity of 2.7 × 10 5 Ω m.However, under 450 nm wavelength light illumination, the current in the I-V curve exhibited a significant increase owing to the enhanced conductivity.This increase resulted from the photogenerated carriers surpassing the bandgap energy of the semiconductor materials.While these photodetector devices represent proof-of-concept examples, direct patterning approaches enable the straightforward fabrication of high-resolution and highly sensitive array devices for detection and switching applications.

Electronic Devices
The direct patterning of inorganic materials like metals, semiconductors, and oxides is a promising candidate method for fabricating patterned electronic devices and integrating them into complex circuits. [64]FETs are among the most prevalent electronic applications requiring high-throughput and high-resolution patterned arrays.In this section, we cover an in-depth analysis of the electrical properties of patterned layers and the performance characteristics of the patterned FET devices, including their mobility.9a] Copyright 2020, The Authors, published by Springer Nature.g) Schematic illustration of QELD devices.h) Current densityvoltage-luminance, and i) EQE-luminance of pristine, patterned, and ZnCl 2 -treated patterned devices.g-i) Reproduced with permission. [41]Copyright 2022, American Chemical Society.EQE-luminance, current density-voltage-luminance of pristine and patterned j) red, k) green, and l) blue QLED devices.k-m) Reproduced with permission. [32]Copyright 2021, American Chemical Society.
Wang et al. showed the fabrication of prototype FETs through direct optical patterning of semiconductor layers to serve as channels.PAGs and photodecomposable TTT ligand capped CdSe and IGZO NCs are effective active layers for FET devices, boasting exceptional performance characteristics. [6]Specifically, FETs patterned with CdSe NCs capped with (Ph 2 I) 2 CdCl 4 ligands demonstrated an electron mobility ( e ) of 20 cm 2 V −1 s −1 .A superior  e exceeding 100 cm 2 V −1 was achieved when Cd 2 Se 3 2− surface ligands were combined with PAGs.Moreover, FETs patterned transparent IGZO NCs using PAGs reached a  e ranging from 4 to 10 cm 2 V −1 s −1 .In 2020, Wang et al. fabricated patterned FETs using PbS precursor molecules through direct e-beam lithography. [43]PbS nanowires, 200 nm wide, were precisely patterned onto a Si substrate, connecting parallel Au electrodes that served as the source and drain.This FET device exhibited typical ohmic I-V characteristics, with conductivity decreasing when applying positive voltages, indicating p-type behavior in the PbS nanowires.The measured hole concentration was 2.8 × 10 18 cm −3 , with a corresponding hole mobility ( h ) of 1.8 cm 2 V −1 s −1 .In 2022, Wang et al. fabricated prototype FETs using In 2 O 3 NC patterns as active channel layers through direct optical patterning and a subsequent ligand exchange process (Figure 13a). [41]The initial unpatterned In 2 O 3 FETs exhibited inactive performance owing to the hindered charge transport caused by the insulating organic ligands of the NCs.However, post-direct optical patterning, the patterned In 2 O 3 FETs exhibited a FET performance, attributed to the decreased interparticle distance between the NCs following the light-induced ligand cleavage reaction.The patterned FETs demonstrated a saturation  e of 0.0005 cm 2 V −1 s −1 and a current on/off ratio of 1.6 × 10 3 , indicating relatively low FET device performance (Figure 13b).How-ever, an additional ligand-exchange process using thiocyanate ions (SCN − ) significantly enhanced the device performance, resulting in a mobility of 0.006 cm 2 V −1 s −1 and a current on/off ratio of 2.4 × 10 4 (Figure 13c).Although these properties fall behind those of other In 2 O 3 FETs fabricated via solution processes, the direct optical patterning approach offers a simpler and more cost-effective method for electronic applications.
Besides FET devices, various other electronic devices have been successfully fabricated by direct patterning of functional inorganic materials.Chen et al. demonstrated the adaptability of direct laser writing-based material deposition in executing electronic applications such as resistive flexible sensors and electronic circuit repair. [10]They constructed a resistive flexible sensor and a touch sensor by fabricating platinum lines and square patterns on a flexible Kapton tape (Figure 13d).This allowed them to study the resistance dependency on the substrate curvature (Figure 13e).The resistances of both patterns exhibited distinct trends contingent on the pressure application site, enabling touch location determination via resistance measurement (Figure 13f).Another instance of direct laser-writing based material deposition offers a solution for repairing electronic circuits.When the ITO pad developed cracks tens of micrometers wide, they effectively restored the electrical connection between the ITO contacts by bridging the Pt patterns onto the damaged areas (Figure 13g,h).To introduce MOFs into devices and applications, it is crucial to preserve the physicochemical properties, especially porosity.Tu et al. demonstrated the porosity of patterned ZIF MOF films using direct X-ray and e-beam lithography techniques. [47]Consequently, they fabricated high-resolution chemical sensors capable of converting guest adsorption signals into optical signals.According to Brunauer-Emmett-Teller (BET) surface area per film area analysis, the ZIF-71 films exhibited microporous characteristics, with an initial BET surface area per film of 247 m 2 m −2 before X-ray irradiation.Even after X-ray direct patterning, the BET surface area of the patterned ZIF-71 films saw a negligible change at 236 m 2 m −2 .These results distinctly showed that the physicochemical properties of the ZIF-71 films remained intact throughout the direct patterning process.The ZIF-71 patterns on transparent substrates can function as diffraction-phase gratings for visible light by applying highresolution periodicity patterning to manipulate the refractive index.Thus, as molecules are adsorbed onto MOF pores, the phase difference proportionally increases to the refractive index of the MOF layer.This allows the adsorption process to be monitored by tracking changes in the intensity of the first-order diffraction spots.For instance, fluctuations in methanol vapor pressureinduced changes in the refractive index and first-order diffraction.
As described above, most electronic devices based on direct patterning typically involve creating selected layers through a patterning process, such as the patterned layer for the active channel.However, future research efforts should focus on realizing fully patterned electronic devices, encompassing multimaterial direct patterning and integration within device structures.Moreover, additional applications of direct patterning, such as randomaccess memory (RAM) devices, should be investigated for potential industrial applications.

Energy Devices
Direct patterning of inorganic materials for energy device applications has been limited.However, fabricating patterned in-organic layers at different scales, from micro to macro, holds considerable potential for energy-related applications, including thermoelectric devices and supercapacitors. [65]Among them, thermoelectric devices, directly converting heat into electricity through simple device structures (such as p-and n-type legs connected with electrode materials), are particularly suited for prototype implementation using direct patterning processes.This is primarily because of their potential for energy harvesting in selfpowered devices and other applications that require microscalepatterned legs arranged in high-density arrays. [66]Consequently, we present the electrical and thermoelectric properties of patterned semiconductor layers fabricated through direct patterning.Additionally, we discuss the performance of thermoelectric generator devices, including the output voltages and powers at varying temperature differences.
Baek et al. investigated the electrical and thermoelectric properties of directly patterned p-and n-type metal chalcogenide layers, specifically Cu 2 S and SnSe 2 , respectively. [59]They fabricated these metal chalcogenides using the DLP method, followed by heat treatment for 5, 7, 10, or 15 min to ensure optimal crystallinity.The hole concentration in the patterned Cu 2 S layers varied from 1.58 × 10 20 to 6.29 × 10 19 cm −3 , with longer annealing times correlating with an increase in hole mobility from 1.29 to 3.89 cm 2 V −1 s −1 .(Figure 14a).The patterned SnSe 2 layers showed an electron concentration of ≈1.0 × 10 19 cm −3 , regardless of the annealing time.With increasing annealing time, the electron mobilities increased from 1.06 to 2.25 cm 2 V −1 s −1 (Figure 14b).The researchers also measured the temperaturedependent electrical conductivity and Seebeck coefficients of the patterned Cu 2 S and SnSe 2 layers.The electrical conductivity reached ≈20-30% of bulk sample values for Cu 2 S and SnSe 2 .However, the Seebeck coefficients were similar to those  and c) after ligand exchange with SCN − ions.The gate voltages were changed from 0 to 20 V. a-c) Reproduced with permission. [41]opyright 2022, American Chemical Society.d) Schematic illustration of flexible resistive flexible sensor (top), and resistance-based touch sensor (bottom).e) Resistance dependency on the curvature measured in the flexible sensor (top of d).f) Resistance dependency on the location where pressure was applied in the touch sensor (bottom of d).g,h) Schematic and OM image of repairing the cracks between ITO using platinum patterning,scale bar 100 m.d-h) Reproduced under terms of the CC-BY license. [10]Copyright 2020, The Authors, published by Springer Nature.
of the bulk references (Figure 14c-f).Under optimal heat treatment conditions, the maximum power factor for patterned Cu 2 S and SnSe 2 , annealed for 15 min, was 0.187 W cm −1 K −2 and 0.37 W cm −1 K −2 at 600 K, respectively, preserving their intrinsic properties after the DLP-based direct patterning process (Figure 14g,h).Leveraging on the properties of patterned layers, they fabricated a microscale thermoelectric generator using DLPbased patterning for multiple tens of 300 m-wide p-type Cu 2 S and n-type SnSe 2 legs (Figure 14i).This thermoelectric generator exhibited reliable power generation.The output voltage and power density increased linearly and quadratically, respectively, according to the temperature differences.At the maximum temperature difference of 65 °C, the maximum output voltages and power density reached 223.5 mV and 0.564 mW cm −2 , respec-tively (Figure 14j,k).Given the growing demand for energy devices for small wearable technologies, IoT devices, and sensors, it is necessary to research the direct patterning process and patternable functional materials for energy devices.

Conclusion and Outlook
This review provides a comprehensive overview of recent advancements in the direct patterning of inorganic materials, with a particular emphasis on notable studies in this field.We elucidate the underlying mechanisms in solidifying inorganic building blocks through subtractive lithographic techniques, employing external sources such as UV-vis light, electron beams, Xrays, and lasers.These methods enable the precise patterning of 2D thin films, as well as optical additive manufacturing for the construction of 2.5D and 3D architectures.Furthermore, we discuss the diverse applications of direct patterning technology in fabricating various devices, including optoelectronics, electronics, and energy conversion devices.Optical direct patterning has made remarkable strides in recent years, owing to the fundamental chemical design of nanoscale building blocks that exhibit active responsiveness to external stimuli.This reactivity allows for the solidification of exposed areas, resulting in intricate patterns.Several strategies have been proposed to design curable building blocks, such as the utilization of photodecomposable and photorestructurable ligands to solidify inorganic NCs, enabling the creation of purely inorganic layer patterns.Additionally, photocrosslinkable additives have been employed to form nanocomposite patterns.These strategies, based on NC building blocks and their curing processes, harness the wide range of functional NCs available, including metals, semiconductors, magnets, dielectrics, and more.These NC-based patterning methods combine multiple benefits of well-established synthesis protocols for NCs, and their unique physicochemical properties and surface chemistry, which have been extensively studied over the past three decades.As this field is still in its nascent stage of development, these strategies can be extended to other functional materials and expand the list of patternable materials to include other functional substances such as 1D nanowires, 2D materials like graphene and transitional metal dichalcogenides, as well as molecular clusters.
The most significant advantage of direct patterning technology lies in its ability to simplify the patterning process, thereby enabling more cost-effective design and fabrication of diverse devices.Traditional photolithographic techniques employ an indirect approach involving multiple steps, including photomask production, polymer photoresist deposition, exposure, vacuum deposition, and etching.In this process, functional inorganic thin films are fabricated through vacuum deposition methods such as chemical vapor deposition, sputtering, and thermal evaporation.These techniques yield high-quality epitaxial thin films with exceptional performance in terms of high carrier mobility, making them well-suited for semiconductor electronic devices that require fast operation and low power consumption.Directly patterned materials, on the other hand, such as QDs or amorphous or polycrystalline thin films, typically exhibit nanostructured characteristics even after post-treatment.Although the electrical properties of directly patterned materials may be inferior to those of vacuum-deposited films, this method has a minimal impact on the inherent properties of nanocrystal building blocks.As a result, it is particularly suitable for optoelectronic devices that rely on the preservation of the quantum-confined optical properties of QDs, as well as energy devices that derive their high performance from nanostructured materials.
Another potential benefit of direct patterning lies in its capability to create 3D architectures of inorganic materials through ad-ditive manufacturing.Traditional subtractive bulk micromachining techniques have been employed to fabricate 3D structures.However, this approach is constrained by limitations in terms of materials, scale, and complexity.Furthermore, it involves high costs and lengthy processing times.On the other hand, conventional 3D microprinting methods, such as two-photon stereolithography, suffer from a limited range of printable materials, as they are currently only applicable to photocurable resins.In order to extend the scope of applicable materials to encompass inorganics, the researchers have attempted post-deposition of inorganic materials on the pre-3D-printed polymer skeleton or the use of mixture of photocurable resins and inorganic fillers.These approaches, while capable of producing organic-inorganic hybrid structures, fall short in attaining the full functionality of pure inorganic materials within these constructs.The post-treatment technique of calcination, employed to remove organics in the printed objects, at times gives rise to undesired structural distortions or leaves behind organic residues, consequently impairing the functionalities of the final products.This restriction poses a significant challenge in the field of 3D printing.Very recently, Liu et al. reported a 3D laser nanoprinting method to create patterns and architectures of purely inorganic semiconductor QDs by the surface photochemical reaction. [11]This pioneering report showed the achievement of ultra-high-resolution 3D printing of purely inorganic materials, but the printable materials were still limited to semiconductor QDs with suitable band gaps.Thus, the quest for a comprehensive and universal approach to 3D print inorganic materials remains an ongoing challenge in this field.Given the considerable progress made in developing a diverse range of directly patternable materials thus far, extending the direct patterning method to 3D printing would address the longstanding issue of limited materials in the field of 3D printing.It would also provide a cost-effective means to achieve microarchitectures of functional inorganic materials.

Figure 1 .
Figure 1.Summary of components and strategies for direct optical patterning.

Figure 2 .
Figure 2. Schematic overview of direct optical patterning of inorganic materials and devices.

Figure 3 .
Figure 3. a) Scheme of the direct optical patterning process.b) Schematic illustration of chemically designed NCs.c) Developed a series of photoreactive surface ligands for NCs.d) Developed photoreactive additives.e)The photo reaction pathways of photoreactive surface ligands and additives.f) OM image of patterned CdSe/ZnS-TDD NCs.g) InP/ZnS-TDD NCs.h) SEM image of patterned test grids with "bare" CeO 2 NCs.i) OM image of two sequential patterned "bare" CeO 2 NC layers with 5 m wide stripes.c-i) Reproduced under terms of the CC-BY license.[7]Copyright 2019, The Authors, published by American Chemical Society.

Figure 4 .
Figure 4. a) Direct optical patterning process of metal oxide NCs using photoreactive additives (DNS).b,c,f) OM image and d,g) height profiles of patterned ZrO 2 NCs.e) Tilted-SEM image of thick patterns.a-g) Reproduced with permission.[26]Copyright 2021, American Chemical Society.h) Overall procedures of direct photolithography of CsPbX 3 NCs with photoreactive PA-480.Fluorescence OM images of patterned i,j) CsPbBr 3 NCs and k,l,m,n) others.h-n) Reproduced with permission.[27]Copyright 2021, American Chemical Society.o) Scheme of direct optical patterning of colloidal QDs via light-triggered ligand stripping agent (TPCl).p,q,r) Fluorescence OM images of patterned Cd-based QDs.s) Height profiles of lie patterns.o-s) Reproduced with permission.[32]Copyright 2023, American Chemical Society.t) Schematic illustration of direct optical patterning of QDs using photoreactive additives (PAmG).u,w) OM images of patterned Cd-based QDs.t-w) Reproduced under terms of the CC-BY license.[34]Copyright 2023, The Authors, published by Springer Nature.

Figure 5 .
Figure 5. a) Schematic illustration of direct QDs patterning using photoreactive crosslinker (LiXer).b-d) Scheme of the direct optical patterning process, lateral, and stacked RGB patterns.e,f) OM, AFM images, and height profiles of directly patterned QDs.g) Fluorescence OM image of 4 m × 16 m sub-pixel patterns, corresponding to a resolution > 1400 ppi.a-g) Reproduced under terms of the CC-BY license.[9a]Copyright 2020, The Authors, published by Springer Nature.h) Description of direct patterning of perovskite NCs using a photoreactive crosslinker (bisFPA).i,j,k) Fluorescence OM images of CsPbBr 3 NC patterns.scale bar 100 m (j, top).l) A photograph of patterned NC film on a flexible substrate under UV light.h-l) Reproduced under terms of the CC-BY license.[9b]Copyright 2022, The Authors, published by American Association for the Advancement of Science.

Figure 6 .
Figure 6.a) Direct optical patterning process of inorganic bare NCs via surface photo-oxidation mechanism.b-i) OM images of various patterned NCs with counterions.a-i) Reproduced with permission.[40]Copyright 2022, American Chemical Society.j) Schematic illustration of direct optical patterning of NCs without additives (native ligand cleavage reaction).k,l) OM images of dot and line patterns of In 2 O 3 NCs with various resolutions (100 -10 m).m,n) Height profiles of corresponding OM images.j-n) Reproduced with permission.[41]Copyright 2022, American Chemical Society.

Figure 7 .
Figure 7. a) Scheme of the direct patterning procedure via selective cation exchanges using e-beam and X-ray lithography b) SEM image of patterned CdSe/CdS and Cu 2-x Se/Cu 2-x S. a,b) Reproduced under terms of the CC-BY license.[45]Copyright 2014, The Authors, published by American Chemical Society.c) Schematic illustration of direct patterning the perovskite NCs using X-ray lithography (native ligand linking reaction).d) Scheme of direct X-ray lithography procedures, the stencil mask, SEM, and XPS mapping image of CsPbBr 3 NCs.Scale bar 300 m.c,d) Reproduced under terms of the CC-BY license.[46]Copyright 2016, The Authors, published by American Chemical Society.e,f) SEM images of e-beam lithography patterned "bare" CeO 2 NC lines with 50 and 30 nm resolution.SEM images of 100 nm width of line patterns with g) CdSe-Sn 2 S 6 and h) CdSe/ZnS-Sn 2 S 6 -PAG.The inset image shows PL from patterned CdSe/ZnS stripes, scale bar 10 m.e-h) Reproduced under terms of the CC-BY license.[7]Copyright 2019, The Authors, published by American Chemical Society.

Figure 8 .
Figure 8. a) Schematic illustration of the mechanism of direct laser-writing based optical patterning.b) experimental procedure of direct laser-writing for inorganic materials.c-e) images of directly patterned platinum and gold.The white scale bars are 50 m, and the blue scale bars are 25 m.(insetSEM image is the patterned platinum dot, scale bar 500 nm).f) Lists of components for patternable inorganic solutions and substrate, reflection type illumination microscopic images of patterned materials on a substrate.a-f) Reproduced under terms of the CC-BY license.[10]Copyright 2020, The Authors, published by Springer Nature.

Figure 9 .
Figure9.a) Chemical structures of thermal reactive surface ligands and reaction pathway for heat-induced patterning.b) Scheme of the direct heatinduced patterning procedure.c-f) Several heating sources for patterning, c) direct laser in the deposited materials, d) thermal contact can transfer the heat to materials, e) transparent materials can be heated by conduction from a substrate, f) a heat source like LEDs can transfer to deposited materials.g-j) Images of patterned layers using thermal reactive NC inks.Scale bars in (h-j) are 100 m.The inset images showed the corresponding thermal reactive inks.a-j) Reproduced with permission.[54]Copyright 2022, American Chemical Society.k) Schematic illustration of the direct thermal patterning process.l) Chemical structures of bisPFPA crosslinkers and reaction mechanism for thermal patterning.bisPFPA generated singlet nitrene radicals at both ends group response to the heat.These radicals can react with native hydrocarbon ligands, leading to the crosslinking of neighboring NCs.m,n) FTIR and XPS spectra of NC films with crosslinkers before and after thermal patterning.o,p) Height profiles and cross-sectional SEM image of micronthick QD patterns.Scale bar 10 m.q) Fluorescence OM images of RGB QD patterns.k-q) Reproduced with permission.[57]Copyright 2022, American Chemical Society.

Figure 10 .
Figure 10.a) Scheme of the digital light processing (DLP)-based direct optical patterning of chalcogenidometallate (ChaM)-based inks.b) Photocuring mechanism of the photocurable ChaM-based inks.c) -potential, d) Dynamic light scattering (DLS) size, and e) photograph of ChaM-based inks before and after UV irradiation.f-i) SEM images of various shapes and resolutions of PtS 2 and MoS 2 -based ink.j,k) SEM, 3D scan analysis (inset), and height profiles of patterned 2.5D architectures.All scale bars in (f-j) are 500 m.a-k) Reproduced under terms of the CC-BY license.[59]Copyright 2022, The Authors, published by Springer Nature.

Figure 11 .
Figure 11.a) PLQYs of CdSe/CdZnS QD films as a function of the added contents of LiXer (wt.%).b) Relative PLQYs (red square) of crosslinked QD films with optimum LiXer contents (grey circle) according to the size of QDs.c) Scheme of QLED devices using patterned QDs as emissive layers.d) External quantum efficiency (EQE)-current density and EL spectrum (inset), e) Current density-voltage-luminance, and f) changes in relative luminance of pristine and patterned QLED devices.The inset EL image in (f) is a pixelated RG QLED with a 10 m × 38 m pattern size.a-f) Reproduced under terms of the CC-BY license.[9a]Copyright 2020, The Authors, published by Springer Nature.g) Schematic illustration of QELD devices.h) Current densityvoltage-luminance, and i) EQE-luminance of pristine, patterned, and ZnCl 2 -treated patterned devices.g-i) Reproduced with permission.[41]Copyright 2022, American Chemical Society.EQE-luminance, current density-voltage-luminance of pristine and patterned j) red, k) green, and l) blue QLED devices.k-m) Reproduced with permission.[32]Copyright 2023, American Chemical Society.

Figure 12 .
Figure 12. a) Device structure of perovskite LEDs.b) Current density-voltage-luminance c) EQE-luminance of pristine and patterned devices.Inset in (c) showed the pixelated LED devices, scale bar 200 m.a-c) Reproduced under terms of the CC-BY license. [9b] Copyright 2022, The Authors, published by American Association for the Advancement of Science.d) Schematic of perovskite NCs-based photodetector device structures.e) OM image of the Au electrodes.f) Photocurrent-time response in the dark and 395 nm violet light conditions with an applied voltage of 20 V. d-f) Reproduced with permission.[27]Copyright 2021, American Chemical Society.

Figure 13 .
Figure 13.a) Scheme of In 2 O 3 -based FET device structures and cross-sectional SEM image.Output characteristics of FET devices with patterned In 2 O 3 NCs b) beforeand c) after ligand exchange with SCN − ions.The gate voltages were changed from 0 to 20 V. a-c) Reproduced with permission.[41]Copyright 2022, American Chemical Society.d) Schematic illustration of flexible resistive flexible sensor (top), and resistance-based touch sensor (bottom).e) Resistance dependency on the curvature measured in the flexible sensor (top of d).f) Resistance dependency on the location where pressure was applied in the touch sensor (bottom of d).g,h) Schematic and OM image of repairing the cracks between ITO using platinum patterning,scale bar 100 m.d-h) Reproduced under terms of the CC-BY license.[10]Copyright 2020, The Authors, published by Springer Nature.

Table 1 .
Summary of photolithography-based direct optical patterning methods.

Table 3 .
Summary of heat-induced direct patterning methods.

Table 4 .
Summarized performance of QDs and perovskite NCs-based patterned LED devices fabricated by direct patterning methods.