Large‐Area Electrode Deposition and Patterning for Monolayer Organic Field‐Effect Transistors by Vacuum‐Filtrated MXene

High‐quality organic field‐effect transistors (1L‐OFETs) based on monolayers have made significant progress and are expected to be key components in the development of next‐generation flexible electronics. However, a flexible, low‐cost, damage‐free, and metallic conductance electrode that can accurately demonstrate the exceptional electrical properties of 1L‐OFETs is still in high demand. In this study, the vacuum‐filtrated MXene (Ti3C2Tx) is demonstrated to serve as electrodes without causing chemical or thermal damage to the delicate active layer via a dry‐lithography method. By integrating monolayer 2,9‐didecyldinaphtho[2,3‐b:2,3′‐f]thieno[3,2‐b]thiophene (C10‐DNTT) with MXene, the 1L‐OFETs exhibit a low subthreshold swing of 60.7 mV per decade and high field‐effect mobility of 9.5 cm2 V−1 s−1 on a high‐κ dielectric hafnium oxide. The use of MXene electrodes enables the production of solution‐processed conductors that can achieve uncompromised performance compared to metal contacts. Furthermore, owing to the well‐matched work functions, the contact resistance can be reduced to 165 Ω cm by this printing technique. The 1L‐OFETs fabricated on an ultra‐thin conformal parylene substrate also exhibit uniform electrical properties. It is believed that this processing approach of vacuum‐filtrated MXene conductors is a crucial step toward the application of non‐metal contacts for high‐performance flexible electronics.


Introduction
[13] Controlling the meniscus-guided coating parameters precisely, a wafer-scale 2D single crystal can be obtained via the solution shearing method. [1,14,15]With a few molecular layer thicknesses, the access resistance could be further minimized. [16,17]Owing to high-quality crystallinity, the solutionprocessed 2D OSC shows high intrinsic mobility and low contact resistance. [18,19]][22][23] Smooth underneath layer offers an ideal platform for organic molecules deposition by solution shearing.Hence, bottom-gate top-contact (BGTC) structure is particularly suitable to examine the intriguing properties of monolayer OSC.However, the electrode deposition for delicate monolayer OSC is a non-trivial challenge.For the top metal contacts, limited by the deposition approaches, such as thermal evaporation and e-beam evaporation, a damaged contact interface with OSC could induce poor charge injection area and large contact resistance, which becomes the major bottleneck to reduce operation voltage and downscaling the dimension of OFETs. [18,24]eanwhile, the high cost of metal also limits mass production of OFETs.[27][28][29][30][31][32][33][34] Previous studies have also pointed out that 2D materials could improve the contact quality between electrode and van der Waals assembled semiconductor due to a clean interface and tunable work function compared to traditional metal materials. [35,36]In addition, solution processing compatibility of some non-metal materials is also an essential merit for large-area deposition.However, compared with traditional metal contacts, electrical conductivity, deposition, patterning, and contact interface quality are nonnegligible challenges for solution-processed low-dimensional conductors.These weaknesses limit the OFETs integrated with nonmetal contacts to have comparable electrical performance with the metal contacts devices.
[39][40][41] Sheet-like 2D structure and surfactant-free water dispersion property provide an excellent platform for MXene to be applied as electrode material.As an emerging electrode candidate for thin-film electronics, patterning, conductivity, and work function are key parameters to improve the electrical performance of OFETs.The literature has reported MXene contacts for transistors and sophisticated circuits, and the deposition methods include spray coating, selective wetting, and inkjet printing.Wang et al. integrated 2D MXene (Ti 3 C 2 T x ) with metal oxide semiconductors for field-effect transistors and complementary metal oxide semiconductor (CMOS) inverters via the spray coating method. [28]After this, Lyu et al. utilized a selective-wetting deposition method to print MXene patterns on a flexible substrate, and further integrated the transistors for logic circuits. [32]ecently, Xu et al. realized a high-yield (≈96%) spray-coated MXene contact, and Tang et al. fabricated a wafer-scale MXene-based transistors array by inkjet printing. [30,31]These advanced studies confirm the potential of Ti 3 C 2 T x for large-area flexible electronics.Despite the tunable work function and water dispersibility it offers unique application potential for MXene; however, the metal contacts comparable electric properties, such as field-effect mobility (μ), subthreshold swing (SS), and contact resistance on OFETs are still yet to be realized.In commonly used bottom-up fabrication, the aggressive chemical process used for MXene deposition and patterning can cause damage to the delicate organic active layer, particularly for the monolayer OSC, which presents significant challenges for materials integration.In addition, the contact resistance between electrodes and semiconductors is also crucial in determining the electrical performance, especially for contact limited OFETs.By fully capturing the intrinsic properties of the tunable terminations of MXene, well-matched work functions could be utilized to minimize the contact barrier.Motivated by these challenges and opportunities, a chemical-free MXene deposition and patterning strategy will be a chance to pursue highperformance electronics.
Herein, we propose a new strategy that utilizes a priorphotolithographed mask to pattern vacuum-filtrated MXene during deposition, which eliminates the chemicals in use.The vacuum filtration has been confirmed as a promising method to deposit well-aligned MXene nanoflakes, [37] which improves the electrical conductivity and oxidation resistivity.In this approach, the whole electrode fabrication procedures are chemical-free, therefore, the qualities of MXene and delicate monolayer OSC are well maintained.Together with water assistance, 2D Ti 3 C 2 T x nanoflakes integrate with monolayer 2,9-didecyldinaphtho[2,3b:2′,3′-f ]thieno [3,2-b]thiophene (C 10 -DNTT) film via van der Waals force and exfoliate from the printing stamp.Our MXene based l-L OFETs exhibit exceptional performance, with a high μ of 9.5 cm 2 V −1 s −1 , a small SS of 60.7 mV per decade, and a low contact resistance of 165 Ω cm.This confirms the promising potential of vacuum-filtrated MXene as an electrode material for monolayer transistors.Although non-metal conductors have demonstrated intriguing application potential, the electrical performance of these devices is compromised by the harsh fabrication processes and the delicate properties of the materials used.Therefore, our dry-lithography approach offers MXene contacts the feasibility to serve as low-cost conductors in the commercialization of high-performance OFETs, potentially paving the way for the mass production of organic electronics.

MXene Deposition and Patterning
The fabrication procedures are shown in Figure 1, which indicate the MXene deposition, patterning, and subsequent transfer process.By combining ultra-thin parylene film with photolithography technology, a conformal filtration mask is obtained.The fabrication details can be found in Section 4 and Figure S1 (Supporting Information).Different from the wet lift-off process, our high-resolution patterns are developed on the filter paper directly with vacuum assistance (Figure 1a,b).Compared to parylene, filter paper has a more hydrophobic surface (Figure S2a,b, Supporting Information), which facilitates the spread of MXene dispersion solution toward the openings of the parylene mask during the filtration.Once the deposition is completed, the mask is peeled off, and then flips the filter paper for subsequent electrode transfer.Deionized (DI) water cannot only strengthen the interaction between C 10 -DNTT and MXene but also weakens the adhesion between MXene and filter paper.In a water environment, the hydrophobic surface of the C 10 -DNTT film has a greater affinity to adhere to Ti 3 C 2 T x nanoflakes as compared to hydrophilic filter paper.A detailed discussion on this topic can be found in Figure S2b-g and Tables S2-S4 (Supporting Information).As shown in Figure 1g, the electrode array is formed on the monolayer OSC through van der Waals interaction.The patterning, deposition of MXene, and transfer of electrodes are all chemical-free processes, which prevent chemical damage to the MXene and the organic active layer.With previously reported MXene patterning methods such as photolithography and inkjet printing, it is challenging to obtain a BGTC structure for OSC as the chemicals used in those methods would damage the semiconductor film.

Materials and Devices Characterization
X-ray diffraction (XRD) was used to characterize the alignment of the Ti 3 C 2 T x nanoflakes.After MXene transfer, the peak of the (002) plane shifts from 6.1 °to 6.9 °(Figure 2a).Calculated by Bragg's law, the lattice parameter in c-LP of as-filtrated MXene is 28.9 Å.After the removal of the remaining water between flakes by pressure and heating during the transfer, c-LP changed to 25.6 Å compared to the as-prepared MXene film, which resulted in better interface stacking of MXene layers.X-ray photoelectron spectroscopy (XPS) was utilized to analysis the surface functionalities, and the wide spectrum is plotted in Figure S3a (Supporting Information).Figure 2b,c and Figure S3b (Supporting Information) plot the detailed XPS spectrums of Ti 2p,  S5 (Supporting Information).To calculate the conductivity, the thickness of these samples was acquired by cross-sectional scanning electron microscope.As shown in Figure 2d, for vacuumfiltrated MXene, the conductivity (7035 S cm −1 ) shows two times higher than spray-coated sample (2900 S cm −1 ) and drop-casted (3117 S cm −1 ) sample.We believe the increase in the electrical conductivity is attributed to the higher nanoflakes pack-age density and coverage quality of the MXene sheet.Furthermore, the similar slopes of these four curves of the van der Pauw measurements on the vacuum-filtrated MXene film in Figure S5a (Supporting Information) imply the film has good uniformity.
The vacuum filtration deposition technique coupled with the dry-lithography patterning method proposed in this study is a versatile approach that can be applied to other solution-processed conductors.To pave the way for Ti  S5, Supporting Information), the hole injection barrier could be potentially reduced (Figure 2f), resulting in a low interface resistance.Ti 3 C 2 T x can modify the work function from 1.85 to 5.97 eV for different terminals, [42] allowing for a large tunable range that makes it possible to identify suitable electrode materials for both p-type and n-type semiconductors with different work functions.

Electrical Performance of MXene-Based 1L-OFETs
By optimizing the coating parameters guided by the meniscus (more information can be found in Section 4 and Figure S7, Supporting Information), we were able to obtain large-area monolayer organic single crystals (≈4 nm thickness, Figure S8, Supporting Information) on a hydrophilic hafnium oxide (HfO 2 )/Si substrate.The structure of BGTC MXene-based monolayer OFETs (1L-OFETs) is depicted in Figure 3a.The scanning transmission electron microscope (STEM) of the MXenebased 1L-OFETs is shown in Figure S9 (Supporting Information), which shows the closely packed MXene nanosheets (Figure S9c, Supporting Information) and a smooth contact interface between MXene and C 10 -DNTT (Figure S9a, Supporting Information).The corresponding STEM energy-dispersive X-ray spectroscopy (EDS) image is exhibited in Figure S9b (Supporting Information).The polarized optical microscope (POM) images of the 7 × 7 OFETs array with a large-area monolayer OSCs are shown in Figure 3b,c.Our dry-lithography patterning method allows for the fabrication of 15 μm channel length, and the channel area is well protected during electrode transfer.The monolayer C 10 -DNTT film represents molecularly flat surfaces (R q = 0.27 ± 0.01 nm), and the corresponding morphologies are indicated in Figure S10 (Supporting Information).Figure 3d displays the representative output curve of the MXene-based 1L-OFETs fabricated on a high- dielectric HfO 2 .The areal capacitance (C i ) of 18 nm HfO 2 is 372 nF cm −2 tested by capacitancefrequency measurement (Figure S11, Supporting Information).The saturation regime transfer curves of 49 devices are displayed in Figure 3e.The average saturation μ is 9.5 ± 2.4 cm 2 V −1 s −1 at V DS = −3 V, and the statistical distribution is plotted in Figure S13a (Supporting Information).As displayed in Figure 3f, the SS and transconductance (g m ) are close to the Boltzmann limit (59.6 mV per decade, 38.7 S A −1 ) for over two decades I DS .The statistical distribution of two-decade SS (60.7 ± 1.0 mV per decade) and I ON /I OFF ratio (≈10 9 ) are plotted in Figure 3g and Figure S13b (Supporting Information), respectively.The SS and μ could be ascribed to clean MXene/C 10 -DNTT interface and high-crystalline monolayer C 10 -DNTT.The high-resolution atom force microscopy (HRAFM, lateral-force mode) of monolayer C 10 -DNTT on HfO 2 is shown in Figure S11 (Supporting Information).Herringbone periodicities can be noticed which demonstrates decent crystallinity, and the lattice parameters are elevated (a = 0.59 nm, b = 0.84 nm, and  = 91.8°).The MXene contacts that are transferred do not necessitate the use of harsh electrode deposition or chemical processes, thereby, preserving the inherent advantages of the delicate C 10 -DNTT monolayer.Compared to other field-effect transistors with non-metal or metal contacts fabricated on different dielectrics, such as ZrO 2 , AlO x , and HfO 2 , etc., our vacuum-filtrated MXene-based 1L-OFETs exhibit competitive performance in terms of SS and I ON /I OFF ratio (Figure 3h).Furthermore, these transistors show excellent stability, as demonstrated by storing a MXene-based 1L-OFET in an air environment and testing it weekly for 4 weeks, during which the electrical performances are well-preserved, as shown in Figure 3i and Figure S14 (Supporting Information).As a new generation of electrode materials, MXene exhibits electrical performance that can be compared to that of conventional metal contacts.We believe that our vacuum-filtrated MXene provides a novel strategy for designing field-effect transistors and sophisticated circuits.

Contact Resistance Measurement
To further characterize the contact interface between MXene and C 10 -DNTT, we used the transmission line method (TLM) to extract the contact resistance.MXene electrodes with different channel ranges (length = 20, 30, 40, 50, 60 μm, width = 300 μm) were transferred to monolayer C 10 -DNTT.Figure 4a shows the linear regime (V DS = −0.1 V) transfer curves.The width normalized total resistance (R total •W) and width normalized contact resistance (R c •W) under different gate overdrive voltages (V GS -V TH ) were calculated by Equation (3) and shown in   4c.It is worth mentioning that since we used longer channels, potential defects in the active layer may induce some potential errors in the measurement of contact resistance.The intrinsic mobility of our monolayer C 10 -DNTT remains ≈17 cm 2 V −1 s −1 with gate bias sweeping.High intrinsic mobility implies the monolayer C 10 -DNTT is highly crystalized, and the active channel is not affected during the electrode integration process.The low R c •W are originated from the low access resistance due to the single alkyl chain of the monolayer C 10 -DNTT and the matched work functions which also can suppress the interface resistance between MXene/ C 10 -DNTT.We compared μ and channel length of vacuum-filtrated MXene OFETs with other transistors with non-metal (MXene, graphite, and PEDOT: PSS) electrodes in Figure 4d, and the MXene-based 1L-OFETs reveal a better performance than most of the compared devices.

Ultra-Conformal MXene-Based 1L-OFETs
Different from inorganic materials, the unique superiorities of organic materials are relying on their flexibility, stretchability, bio-compatibility, etc.To unveil these unique properties, we fabricated MXene-based 1L-OFET with layer-by-layer assembly on an ultra-thin substrate (1.6 μm parylene) as shown in Figure 5a,b.The thin substrate can minimize the mechanical stress due to bending and conformably attached onto different objects.Figure 5c exhibits the flexible devices is attached to a brain model.The morphology of the HfO 2 surface (Figure 5b) on aluminum (Al)/parylene substrate was characterized by atomic force microscope (AFM), and the roughness (R q ) is ≈5.2 nm, higher than HfO 2 /Si.High surface roughness induces low surface energy, so we employed a UV-ozone treatment to enhance the hydrophilicity of the substrate for facilitating meniscus formation during solution shearing.The POM images of C 10 -DNTT under different shearing speeds and temperatures are shown in Figure S15 (Supporting Information).The channel width and length of the transistors are 300 and 15 μm, respectively.Figure 5d

Conclusion
In summary, we reported a new MXene-based large-area electrodes deposition and patterning strategy for monolayer OSC, which realizes high resolution (15 μm) and avoids chemical damage.Different like wet lift-off technology, short channel patterns can be obtained directly during deposition by a conformal mask attached to the printing stamp, which simply the procedures and protects the OSC film.With the assistance of vacuum-filtration, MXene nanoflakes achieve closer interface stacking, and resulting in better electrical conductivity and oxidation resistivity.On high- dielectric HfO 2 , the unique combination of monolayer C 10 -DNTT and 2D MXene has a high μ of 9.5 cm 2 V −1 s −1 , a small SS of 60.7 mV per decade, and a high I ON /I OFF ratio that up to ≈10 9 .Due to tunable surface properties and well-matched work functions, MXene-based 1L-OFETs show low contact resistance of 165 Ω-cm.The flexible OFETs array fabricated on an ultra-conformal substrate shows uniform electrical performance, which further demonstrates the application potential of our printing method.It is believed the findings expand the application range of solution-processed conductors, which is a crucial cornerstone toward the mass production of OFETs and related circuits.

Experimental Section
Materials: Si and Si/SiO 2 wafers were purchased from Namkang Hi-Tech.C 10 -DNTT was bought from Luminescence Technology Corp and was used without further purification.MXene (5 mg mL −1 ) dispersion solution was purchased from beike 2D materials Co., Ltd., and diluted to 0.1 mg mL −1 for subsequent vacuum filtration.The pore size of the filter paper was 0.25 μm.
Fabrication of Substrate and Dielectric: After blowing with nitrogen gas, Si/SiO 2 wafers were treated with oxygen plasma (diener electronics, 100 W) for 10 min to generate ─OH, then immersed into octadecyltrichlorosilane (OTS) (Sigma-Aldrich) solution (5×10 −3 m, m-xylene as solvent) for 16 h to form the self-assembly monolayer (SAM) in the glove box.These wafers were further rinsed with chloroform.Next, 1.6 μm parylene SR was deposited (Specialty Coating Systems, PDS 2010) on an OTS-treated wafer to serve as the flexible substrate.After that, 30 nm lowroughness Al gate was thermal evaporated on parylene with 1 nm s −1 speed when the base pressure reached <5 × 10 −5 Pa.For high- dielectric HfO 2 , it was deposited by atomic layer deposition (Cambridge Nanotech Inc.) by using Tetrakis (dimethylamino) hafnium as source.The deposition temperature was 160 °C, and the base pressure was 0.3 Pa.
Solution Shearing of Monolayer C 10 -DNTT: And 0.8 mg C 10 -DNTT powder was dissolved in 4 mL 1,2,3,4-tetrahydronaphthalene (tetralin) to generate 0.2 mg mL −1 solution, which was heated to 58 °C overnight to help dissolve prior to the solution shearing process.Thirty five microliters solution was injected into the gap (100 μm) between the blade and the substrate and kept at 58 °C during the solution shearing process.The moving stage moved with a speed of 2.8 μm s −1 , and the monolayer C 10 -DNTT was deposited on dielectric with the evaporation of the solvent.The flexible substrate was treated by UV-ozone (Jelight Company Inc) for 5 min to make it more hydrophilic before solution injection.Finally, the single crystal was stored in the vacuum oven (OV-12, Jeio Tech) for 12 h to further remove the remaining tetralin.
Fabrication of Ultra-Conformable Filtration Mask: And 1.6 μm parylene SR was deposited on an OTS-treated wafer and patterned by following liftoff technology to fabricate an ultra-conformal mask.AZ nLOF 2020 negative photoresist was utilized to form patterns on the parylene film, and then the unprotected area was etched by reactive ion etching (RIE) (Tailong electronics, 100 W) for 20 min.The remaining photoresist was removed by dimethyl sulfoxide.Finally, the parylene mask was peeled off by thermal release tape from the OTS SAM-treated Si/SiO 2 wafer.
MXene Electrodes Deposition and Transfer: The parylene mask was put on the filter paper and the edge was pressed to make it attached conformally.Twenty microliters of diluted MXene dispersion solution (0.1 mg mL −1 ) was dropped on the parylene mask, and the patterns were formed by the vacuum filtration when vacuum pressure reached ≈0.08 MPa.The mask was peeled off, then the filter paper was flipped to serve as a printing stamp, and contact was made with the target C 10 -DNTT monolayer carefully.And 20 μL DI water was dropped on the backside of the patterns, then cellulose paper was utilized to absorb the extra water.Next, 8.7 × 10 4 Pa was applied on top for MXene transfer and heated on a hot plate at 35 °C for 1 h to evaporate the remaining water.After that, the weight was removed, and the cellulose paper and filter paper were peeled off, correspondingly.The MXene electrode (15 μm channel length and 300 μm channel width) array could be observed on OSC.The SS equation was given by Equation (1): where SS, I DS , and V GS are the subthreshold swing, drain-source current, and gate voltage.The μ in saturation regime was extracted from Equation (2): where W, L, C i , μ sat , and V TH are the channel width, channel length, areal capacitance, saturation mobility, and threshold voltage.
The R total •W and R c •W under different (V GS -V TH ) were calculated by Equation (3): where μ 0 , and R ch are intrinsic mobility and channel resistance.
Statistical Study: For rigid substrate, the sample size (n) is 49 for the statistical study.For flexible substrate, the sample size (n) is 25 for the statistical study.The experimental results were shown as mean ± standard deviation and calculated by OriginPro 2021.

Figure 1 .
Figure 1.The deposition and patterning of vacuum-filtrated MXene electrodes.a) Illustration of the MXene (Ti 3 C 2 T x ) structure.b) Schematic diagram and optical image of the parylene filtration mask.Inset diagram shows the channel length of 15 μm.c) Schematic diagram of the MXene patterns on filter paper.d-f) The printing process on C 10 -DNTT.g) Optical image of MXene array after transfer.
3 C 2 T x as electrodes for monolayer C 10 -DNTT, high conductivity and package density are not the only important factors, work function alignment and charge injection are also playing a significant role in achieving highperformance OFETs.When the electrode and semiconductor come into contact, a Schottky barrier is formed due to the mismatch of work function, which causes potential drop and nonlinear charge injection at the contact area.The work functions of MXene (W MXene ) and C 10 -DNTT (W OSC ) were characterized by scanning Kelvin probe macroscopy (SKPM).The work function of the probe was normalized against gold (Au) (Figure S6, Supporting Information), and the corresponding SKPM maps of MXene and C 10 -DNTT are shown in Figure 2e.Since the work functions of MXene and C 10 -DNTT are well-matched (Table

Figure 2 .
Figure 2. MXene characterizations.a) XRD of the vacuum-filtrated MXene film before and after transfer.b) Ti 2p XPS spectrum of the transferred MXene.c) C 1s XPS spectrum of the transferred MXene.d) Electrical conductivity of MXene films deposited by different methods: spray coating, drop casting, and vacuum filtration.Inset diagram is the schematic of the van der Pauw sheet resistance measurement system.e) SKPM images of Ti 3 C 2 T x MXene and monolayer C 10 -DNTT.f) The energy diagram of MXene and semiconductor.

Figure 3 .
Figure 3. MXene-based monolayer OFETs (1L-OFETs) on HfO 2 .a) Structure of MXene-based monolayer OFETs (1L-OFETs).b) POM image of the fabricated 7 × 7 OFETs array, and the zoom in picture c) indicates the channel (15 μm channel length, 300 μm channel width).d) Representative output curve recorded by sweeping V DS from 0 to −3 V with −0.5 V step.e) Double-sweep transfer curves of 49 OFETs at saturation regime (V DS =−3 f) SS and g m /I DS curves under different I DS .g) Statistical distribution of SS. h) Comparison of SS and I ON /I OFF ratio among non-metal/metal contacts with different dielectrics.i) Transfer curve of the MXene-based monolayer OFETs (1L-OFETs) after one month storage in air condition.Inset diagram is the change of μ and SS with time.

Figure 4 .
Figure 4. Contact resistance measurement by using TLM.a) Transfer curves of MXene-based 1L-OFETs with different channel ranges at linear regime (V DS = −0.1 V).Inset diagram is the POM image of the devices (scale bar represents 200 μm).b) Total resistance as a function of channel length under different gate biases (shown as indicated) and fitted by TLM.Inset diagram is the schematic of TLM electrodes array.c) Contact resistance and intrinsic mobility under different gate biases extracted from the TLM fitting.d) Comparison of channel length and mobility of field-effect transistors with different active layers.

Figure 4b .
Figure 4b.The R c •W under (V GS -V TH ) = −1.6V is 165 Ω cm extracted from the linear fitting as indicated in Figure4c.It is worth mentioning that since we used longer channels, potential defects in the active layer may induce some potential errors in the measurement of contact resistance.The intrinsic mobility of our monolayer C 10 -DNTT remains ≈17 cm 2 V −1 s −1 with gate bias sweeping.High intrinsic mobility implies the monolayer C 10 -DNTT is highly crystalized, and the active channel is not affected during the electrode integration process.The low R c •W are originated from the low access resistance due to the single alkyl chain of the monolayer C 10 -DNTT and the matched work functions which also can suppress the interface resistance between MXene/ C 10 -DNTT.We compared μ and channel length of vacuum-filtrated MXene OFETs with other transistors with non-metal (MXene, graphite, and PEDOT: PSS) electrodes in Figure4d, and the MXene-based 1L-OFETs reveal a better performance than most of the compared devices.
displays the representative output curve of the flexible MXene-based 1L-OFETs, and the saturation regime double-sweep transfer curves of 25 devices are indicated in Figure 5e.These MXene-based 1L-OFETs show uniform electrical performance with an average SS of 70.4 ± 5.4 mV per decade, and an I ON /I OFF ratio of over 10 8 , and the statistical distribution are displayed in Figure 5f,g, respectively.

Figure 5 .
Figure 5. Ultra-conformal MXene-based 1L-OFETs.a) Schematic image of the flexible OFETs with 1.6 μm parylene substrate.b) Schematic structure of the device and AFM image of the HfO 2 surface on Al/parylene substrate.c) Flexible OFETs array laminated on a brain model.d) Representative output curve recorded by sweeping V DS from 0 to −3 V with −0.5 V step.e) Double-sweep transfer curves of 25 OFETs at saturation regime (V DS = −3 V).Statistical distribution of f) SS and g) I ON /I OFF ratio of flexible MXene-based 1L-OFETs.
Materials and Devices Characterization: The POM images of C 10 -DNTT on different substrates were taken by Nikon Eclipse LV100N.The morphology of C 10 -DNTT was characterized by Bruker MultiMode 8 and analyzed by NanoScope Analysis software.Hall Effect Measurement Systems HMS-5500 (Ecopia) was used to measure the sheet resistance and calculate the electrical conductivity.The phase identification of the MXene film was conducted by using an X-ray diffractometer (XRD, PANalytical) with Cu K radiation at 45 kV and 40 mA.The Raman spectrum was measured by a Raman Microscope (inVia, Renishaw), and a He-Ne laser (632.8 nm) with an incident power of ≈25 mW was used as the excitation source.The composition of the MXene film was characterized by XPS (XPS, PHI 5600 multi-technique system, Physical Electronics).The SKPM potential maps were inquired by Oxford Cypher Asylum Research AFM.The specimen for scanning transmission electron microscope (STEM) was fabricated by FEI Quanta 200 3D Focused Ion Beam.The STEM images and corresponding energy-dispersive X-ray spectroscopy image were captured by Thermo Scientific Talos F200X STEM.The high-resolution AFM image was inquired by Oxford Cypher Asylum Research AFM.The electrical performances of the MXene-based 1L-OFETs were conducted by B1500A Semiconductor Device Analyzer in a glovebox environment at room temperature (≈25 °C).