Wafer‐Scale Synthesis of Mixed‐Dimensional Heterostructures via Manipulating Platinization Conditions

2D van der Waals (vdW) hetero integration, which features exotic interplanar interactions derived from mixed‐dimensional heterostructures, is an emergent platform for implementing high‐performance electronics and broadband/wavelength‐tunable photodetectors. However, the production of large‐area 2D spatially homogeneous transition‐metal dichalcogenides (TMDs) and elucidation of the electrostatic dynamics governing the interlayer interactions are two paramount prerequisites for realizing practical 2D‐TMD‐heterostructure‐based photodetectors. Here, a wafer‐scale synthesis of mixed‐dimensional Pt–MoS2‐based vdW heterostructures is unprecedentedly demonstrated by manipulating the platinization conditions. The rationally designed platinization yields dimensionality‐tailored Pt, including Pt nanofilm, Pt nanoparticles, and Pt atoms, with MoS2 as host platform. From density functional theory calculations, this study insights that Mo vacancy sites on the MoS2 surface are thermo‐dynamically favorable sites for Pt with an adsorption energy of −2.25 eV, then Pt clusters are sequentially formed neighboring the specific Pt‐substituted position with a formation energy of 1.30 eV. Intensive microscopic and spectroscopic analyses reveal the structural, chemical, and electrical features, validating the proposed dynamics‐related mechanism. The dimensionality‐tailored vdW heterostructures exhibit outstanding optoelectrical properties with excellent photoresponsivity (2.04 mA W−1) and highly sensitive detectivity (9.82 × 106 cm Hz1/2 W−1).


Introduction
2D van der Waals (vdW) layered semiconductors have revitalized an upsurge of research interest in the development of atomically thin building blocks for fundamental exploration and alternative nanodevices performing beyond the limits of constituent materials-based devices. [1,2]In particular, 2D transition metal dichalcogenides (TMDs) constitute a valid candidate for myriad highperformance optoelectronics owing to their inherent confined properties induced by their restricted dimensionality, such as high exciton-binding energy and high light absorption coefficient. [3,4]To extract the full potential of 2D TMDs for practical applications in emergent optoelectronics, the development of a wafer-scale synthetic platform for 2D TMDs is a crucial prerequisite.However, this remains a standing challenge because of the trade-off between waferscale synthesis and reproducible production of highly crystalline TMD materials for high-performance optoelectronics. [5]8] Employing vdW integration to activate tunneling-assisted interlayer recombination at heterointerfaces enables unprecedented expandability in terms of the combination of distinct nanomaterials with dissimilar chemical and structural features and dimensionality, offering exotic optoelectronic characteristics that can potentially enable new device functionalities beyond those of established material systems. [9,10]In addition, vdW integration is not confined to interplanar interactions in 2D layered heteromaterials, namely layered materials can be coordinated with other dimensional materials through vdW interactions to form mixeddimensional heterostructures. [11,12]Although progress has been made in this regard, it is well documented that vdW heterostructures have been restricted to highly crystalline TMD microflakes acquired by micromechanical exfoliation and chemical vapor deposition, which entails suitability for fundamental studies and proof-of-concept demonstrations and limited applicability for practical optoelectronic applications. [13,14]Additionally, the construction of 2D vdW heterostructures via interlayer interactions in 2D layered materials has been primarily considered, highlighting the necessity of expanding exploration into mixed-dimensional heterostructures.We previously established a wafer-scale synthetic platform for 2D TMDs using straightforward thermal decomposition of solution-processed single-source precursors [5,[15][16][17][18] ; this pioneering scheme, which entails advantages such as facile synthesis, cost-effectiveness, and applicability for large-scale manufacturing, has considerable potential for industrial optoelectronic applications.In the present study, we indeed attained the wafer-scale synthesis of mixed-dimensional based on Pt-MoS 2 heterostructures via manipulating the platinization conditions of the MoS 2 as the host crystal.The host MoS 2 multilayers with spatial homogeneity were gained from a rational synthetic platform based on the thermal decomposition of solution-processed single-source precursors.The designed platinization allows the dimensionality-tailored Pt involving Pt nanofilm (Pt NF), Pt nanoparticles (Pt NPs), and Pt atoms (Pt Ats) combined with the MoS 2 host crystals.We further explored the photoelectric properties of the mixed-dimensional Pt-MoS 2 heterostructures.

Synthesis of Mixed-Dimensional Pt-MoS 2 Heterostructure
For the synthesis of the 2D MoS 2 host crystals, 1.25 wt.% (NH 4 ) 2 MoS 4 as a single-source precursor was mixed with ethylene glycol under magnetic stirring with 500 rpm at room temperature for 60 min.The resultant solution was spin-coated onto hydrophilically treated SiO 2 (300 nm)/Si(001) and two-inchdiameter quartz substrates at 3000 rpm for 30 s.The coated samples were immediately annealed at 130 °C for 1 min to remove the solvent.The as-coated (NH 4 ) 2 MoS 4 films were heated at 280 °C (1st step) under Ar flow (1000 sccm) at a pressure of 1 Torr for 30 min, and the reaction temperature was subsequently elevated to 600 °C (2nd step) for 30 min to synthesize laterally connected MoS 2 host crystals.The reaction involved NH 4 bond rupture and subsequent desulfurization, in which proper thermally driven decomposition energy was supplied to overcome the chemical reaction barrier.For the formation of the mixed-dimensional heterostructures, the platinization parameters of the MoS 2 host crystals were systematically manipulated (Figure 1a).To achieve effective platinization, the MoS 2 host crystal was initially placed 10-13 cm away from PtCl 2 powder (0.01 g) in the reactor, with the variation in distance enabling efficient manipulation of the dimensionality of Pt in the mixed-dimensional heterostructures.The evaporation temperature of PtCl 2 was prudently set to 400 °C to control the platinization of the MoS 2 host crystals.It is noted that the structural transition of Pt arguably relied on the distance (d) between MoS 2 and PtCl 2 , as a Pt NF, Pt NPs, and Pt ATs were yielded in combination with the MoS 2 host crystals (see the balland-stick atomic models in Figure 1b-e).

Structural Characteristics of Mixed-Dimensional Pt-MoS 2
Figure 1f-j presents representative photographs of the mixeddimensional heterostructures structurally engineered by altering the MoS 2 -PtCl 2 distance, which clearly indicates the structural transition of Pt on MoS 2 .Brownish films were produced at d values of 10 and 11 cm, whereas samples without stark differences in color were obtained at d values >11.5 cm.Additionally, all samples had remarkably uniform surfaces throughout their areas.The proof-of-concept of the presented synthetic strategy for dimensionality-tailored Pt-MoS 2 heterostructures was validated by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), which helped gain insight into the elemental distribution of Pt and MoS 2 (Figure 1k-m).Before proceeding further, two distinctive structural features of the MoS 2 host crystals could be ascertained: i) the nanoscopic fingerprints of the trigonal prismatic lattice of MoS 2 multilayers, and ii) a series of Moiré patterns, which was possibly generated owing to the angular rotation of layers (Figure sS1, Supporting Information). [19]In the Pt-MoS 2 heterostructure produced at an inter-reactant distance of 10 cm, a nanograined Pt NF was explicitly formed on the MoS 2 surface (Figure 1k).The platinization conducted using an inter-reactant distance of 11.5 cm yielded Pt NPs that were arbitrarily formed on the MoS 2 host crystals (Figure 1l).Based on these results, the grains and nanoparticles in Pt NF@MoS 2 and Pt NPs@MoS 2 were estimated to be 56 ± 12 nm and 4.9 ± 2.3 nm in size, respectively (Figure S2, Supporting Information).The number of layers of the MoS 2 host crystals was determined to be five (Figure S3, Supporting Information).The interplanar spacing of the Pt NPs is 0.23 nm, which hints the formation of a (111) crystal plane.We previously well-established that the number of MoS 2 layers can be manipulated by solely altering the concentration of (NH 4 ) 2 MoS 4 . [5]Thus, we anticipate that tuning the number of host MoS 2 layers could permit straightforward manipulation of the structural features of Pt-MoS 2 heterostructures, which can serve to attain goal-directed photoelectrical and chemical properties for diverse applications.The selection of MoS 2 multilayers serves to capture key advantages such as high optical absorption, prolonged carrier lifetime, excellent air stability, and minimal device-to-device performance variation, all of which are absolutely imperative for practical optoelectronic applications.At a d value of 13 cm, we found the formation of Moiré pattern by angular rotation of MoS 2 layers.In addition, the localization of Pt atoms can be readily discriminated at the structurally unstable edge sites or basal plane (i.e., Mo-vacancy sites) of the MoS 2 crystals through discernible bright spots corresponding to localized single Pt atoms, because the intensity of the scattered electrons can be determined to be proportional to the mean square of the atomic number (Figure 1m; Figure S2, Supporting Information).Chemical identification of the Pt-MoS 2 hybrid materials was conducted by energy-dispersive X-ray spectroscopy (EDS)based elemental mapping combined with HAADF-STEM observations, demonstrating that dimensionality manipulation in the heterostructure was distinctly attested (Figure S4, Supporting Information).The presence of Pt atoms can cause lattice distortion in the adjacent MoS 2 host lattice, yielding heterostructures that exhibit completely distinct properties compared with those of MoS 2 ; this is because 2D systems are highly susceptible to external structural and electrical stimulation owing to their surface behavior.However, in the systems reported herein, the Ptstimulated lattice distortion in MoS 2 was indistinguishable in the vicinity of the localized Pt atoms because of the interlayer interference associated with its multilayer structure.Certain groundbreaking studies have proposed that the Pt-stimulated lattice distortion with asymmetric reconstruction of the MoS 2 host structure enables modulation of the electronic structure, which is correlated with the bandgap narrowing induced by charge-based interactions between Mo or S and substituted Pt atoms. [20,21]Moreover, the atomic substitution of Pt into the MoS 2 lattice permits the occurrence of the thermodynamically favorable 1T phase transition with strong interlayer coupling in a localized area (layer distance: 3.06 Å for MoS 2 , 2.54 Å for PtS 2 ), which is corroborated by previous studies on the phase transition of MoS 2 via interfacial doping. [22]Hence, the efficacy of Pt substitution correlated with bandgap narrowing or the formation of a metastable structure dictated by the localized 1T-phase structure can be anticipated.Explicit atomic force microscopy (AFM)-based topographical images of the Pt-MoS 2 heterostructures that were synthesized by altering the MoS 2 -PtCl 2 distance (Figure 1n-p) afford a clear manifestation for dimensionality manipulation of the heterostructures; these results are in agreement with the HAADF-STEM observations.The surface morphology of Pt ATs@MoS 2 was nearly identical to that of MoS 2 (Figure S5, Supporting Information).The thickness of pristine MoS 2 was estimated to be 3.2 nm (Figure S5, Supporting Information).We demonstrated the synthesis of large-scale and homogeneous Pt ATs@MoS 2 on a two-inch-diameter quartz wafer (Figure 1p, inset), unveiling the exceptional homogeneity of the film specimen in terms of its thickness.These results hints that the presented methodology captures a large-area-compatible solution-based synthesis route for mixed-dimensional heterostructures.Moreover, the designed method offers notable advantages as it involves relatively succinct mass-production techniques, making it an ideal candidate for synthesizing practically applicable heteromaterials.

Computational Simulation for MoS 2 Platinization Dynamics
Based on the TEM observation, we carried out the density functional theory (DFT) calculation to further gain atomic-scale insights and to unveil a detailed mechanism underlying the MoS 2 platinization dynamics (Figure 2).As a preliminary study on assessing the direct adsorption of Pt atoms onto the MoS 2 backbone, the formation energy of S, S 2 , Mo, and MoS 3 vacancies (V S , V S2 , V Mo , and V MoS3 , respectively) and that related to the substitution of Mo at a S site (Mo S ) and vice versa (S Mo ) were initially analyzed (Figure 2a).All the calculated vacancy formation energies for Vs, V S2 , V Mo , V MoS3 , Mo S , and S Mo (Figure S6, Supporting Information) had positive values, reflecting that the vacancy formation was an endothermic process with an exceedingly high energy irrespective of the vacancy type.These results suggest that the direct substitution of excess Pt atoms into the Mo sites or S anti-sites is difficult.From a structural perspective, the procurement of 2D ternary semiconductors-which are produced by substituting heteroatoms into host crystals-is limitedly induced within the same transition-metal groups owing to their identical lattice symmetry and small lattice mismatches. [23]n such scenarios, homogeneously combined 2D ternary semiconductors can be obtained without any noticeable phase separation in forms such as Mo 1−x W x S 2 , Mo 1−x WxSe 2 , TaS 2(1−x) Se 2x , ZrS 2(1−x) Se 2x , HfS 2(1−x) Se 2x , and ReS 2(1−x) Se 2x owing to their large entropy. [23]However, the large lattice mismatch (≈4%) between MoS 2 and PtS 2 (lattice parameters: 0.32 and 0.36 nm, respectively) indicates that alloying 2D ternary Pt-MoS 2 materials via direct atomic substitution of Pt into MoS 2 is relatively challenging.Nevertheless, the platinization is able to attain by intentionally enhancing the defect density in the host MoS 2 lattice through surface plasma treatments, atomic-selective etching, and manipulation of the reaction temperature.To derive the Pt-substitution dynamics, we calculated the adsorption energy of Pt for various types of favorable adsorption sites on the MoS 2 surfaces involving V MO , V S , V S2 , V MoS3 , Mo S , and S MO (Figure 2b).The Pt adsorption energy E Pt-ads was defined as E Pt-adatom/Surface − (E Pt-adatom + E Surface ), where E Pt-adatom/Surface is the total energy of the system in which a Pt adatom is adsorbed onto the modeled surface, and E Pt-adatom and E Surface are the total energies of an isolated Pt atom and the modeled surface (pristine and defective MoS 2 surfaces), respectively.The Pt adsorption energy for the hollow, top Mo, and top S sites on the pristine MoS 2 surface was calculated as 3.49, 2.99, and 3.39 eV, respectively, which were higher than those of the sites on the vacancy-containing MoS 2 surfaces (Figure 2b).The thermodynamically favorable sites were unequivocally found to , and e) Pt atoms (Ats) hybridized with the host MoS 2 crystal, which were synthesized using d values of 10, 11.5, and 13 cm, respectively.Photographs of f,g) Pt NF@MoS 2 , h,i) Pt NPs@MoS 2 , and j) Pt ATs@MoS 2 .Representative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images of k) Pt NF@MoS 2 , l) Pt NPs@MoS 2 , and m) Pt ATs@MoS 2 (inset in k), l): energy-dispersive X-ray spectroscopy (EDS)-based elemental map of Pt Ats; inset in m): atomic-resolution STEM image showing substituted Pt Ats at the brightest spots).n-p) The corresponding atomic-force-microscopy (AFM) images (inset in p): photograph of a two-inch-diameter Pt ATs@MoS 2 wafer synthesized on a quartz substrate).be Mo vacancy sites with a Pt adsorption energy of −2.25 eV.Single Pt atoms were considered to be preferably present on the surface of the vacancies in the MoS 2 host lattice, which is consistent with the TEM results.Moreover, the Pt atoms adsorbed onto the MoS 2 surface further accelerated the formation of Pt nanoclusters from an additional Pt source by serving as nucleation sites.We surveyed the adsorption energy of the additionally supplied Pt atoms for the MoS 2 surface with V Mo (Pt@V Mo ), which resulted in the lowest energies among the Pt-loaded sites (1.30 eV for Con-figuration1 and 1.87 eV for Configuration2; Figure 2c).Overall, the DFT calculations suggest that specific positions in the vicinity of the Pt-substituted sites were preferred locations for adsorbing the additionally fed Pt atoms, which further expedited the formation of the initial Pt nanoclusters (Figure 2d).Previous studies on Pt clustering and Pt-diffusion directions have indicated that the top Mo sites are preferred for Pt nanocluster growth, which is consistent with the aforementioned results.In addition, this enables to gain Pt 2 dimers and triangular-shaped Pt 3 clusters at the initial clustering stages. [24]

Chemical Identification for Mixed-Dimensional Pt-MoS 2
Further insights into the chemical bonding states of the mixeddimensional Pt-MoS 2 heterostructures were gained from X-ray photoelectron spectroscopy (XPS; Figure 3; Figure S7, Supporting Information).First, we examined XPS survey spectra for the Pt-MoS 2 synthesized by altering the MoS 2 -PtCl 2 distance (Figure S7, Supporting Information).The XPS survey spectrum of pristine MoS 2 corroborates the presence of Mo-and S-related bonding states from MoS 2 and that of Si, O, and C bonding states from SiO 2 /Si and residual carbon.Regarding the XPS analysis depth of ≈10 nm, pristine MoS 2 was estimated to have multilayers that were <10 nm thick.In fact, it is well-acquainted that MoS 2 monolayers exhibit superior photosensitivity, which is indicative of their direct bandgap, whereas MoS 2 multilayers possess an indirect bandgap.However, multilayered platforms have multifaceted strengths in terms of being applicable for 2D-TMDbased photodetectors, such as i) device compatibility, which is induced by the scalability and uniformity of MoS 2 multilayers, resulting in compliance with conventional lithographic techniques; ii) device reliability, which originates from the minimal variation in performance due to the thickness-dependent photoelectric properties; iii) device universality for implementing broadband photodetectors with wide-range optical adsorption; and iv) device stability under atmospheric conditions.From the survey spectrum of Pt NF@MoS 2 (d = 10 and 11 cm), we can discern the marked enhancement of the Pt-related peak intensity and attenuated intensities for the Mo-and S-related components.Conversely, we found an abrupt increase in the MoS 2 -related peak intensity over the distance of 11.5 cm (Pt NPs@MoS 2 ); subsequently, the peak became dominant for the Pt ATs@MoS 2 system (d = 13 cm), which matches with the results on surface color variations (Figure 1f-j).We verified atomic quantity of Mo, S, and Pt concerning the inter-reactant distance (Figure 3a) Interestingly, the transition zones for the altered structural features are wellconsolidated with the evolution of the morphological properties presented from the TEM (Figure 1k-m).In the analysis of the relative atomic ratio (S/[Pt + Mo]) and Pt atomic content (Figure 3a), the ratio of sulfur to metal-anion atoms (S/[Pt + Mo]) provides a meaningful interpretation of the Pt atom substitutions into specific V Mo sites.Notably, the relative ratio for the formation of Pt ATs in the MoS 2 crystal was estimated to be 2.3, analogous to that of the pristine MoS 2 host materials; the corresponding Pt content was ascertained to be 4%.We accordingly believe that the Pt atoms (4%) were considered to be preferentially loaded onto specific atomic-scale vacant sites in the MoS 2 host crystals, such as domain edges.Representative atomistic views of pristine MoS 2 , Pt ATs@MoS 2 , Pt NPs@MoS 2 , and Pt NF@MoS 2 are illustrated in Figure 3b-e, respectively.To analyze the detailed chemical identifications, we investigated the XPS Pt 4f, Mo 3d, and S 2p core-level spectra of Pt NF@MoS 2 , Pt NPs@MoS 2 , and Pt ATs@MoS 2 (Figure 3f-h).In the Pt 4f core-level spectrum of Pt NF@MoS 2 (Figure 3f ).The Pt 4f core-level spectrum of Pt ATs@MoS 2 indicated that the Pt-S chemical bonds were dominant in the ab-sence of metallic Pt clusters.This suggests that the atomic substitution occurred at the Mo vacancies, and that the substituted Pt atoms were coordinated with the adjacent S atoms, as manifested by the aforementioned DFT calculations that revealed the lowest formation energy.This site-specific Pt atom substitution could be leveraged to achieve exceptional catalytic activity in the hydrogen evolution reaction owing to the reduced H 2 adsorption energy.These observations are corroborated by previous computational results, proving that hydrogen atoms can be considerably stabilized via adsorption at the coordinatively unsaturated S atoms adjacent to Pt rather than through direct adsorption with Pt-based on steric hindrance. [25]To assess the structural evolution of the mixed-dimensional Pt-MoS 2 heterostructures, we carried out Raman spectroscopy analysis for pristine MoS 2 , Pt NF@MoS 2 , Pt NPs@MoS 2 , and Pt ATs@MoS 2 (Figure S8, Supporting Information).It can be readily discerned that two representative inplane E 2g and out-of-plane A 1g phonon modes for MoS 2 (380 and 403 cm −1 , respectively) were clearly identified in the Raman spectra, along with four minor peaks pertaining to defect-induced Raman phonon modes (transverse optical [TO(M), 370 cm −1 ], longitudinal optical [LO(M), 377 cm −1 ], out-of-plane optical [ZO(M), 412 cm −1 ]) at the M-point in the Brillouin zone.The difference in peak positions between A 1g and E 2g corroborated the formation of the MoS 2 multilayers.Moreover, the defect-related Raman modes contributed to the spectral asymmetry of the major peak of MoS 2 .Notably, we also find a couple of salient phenomena pertaining to the Raman signals: i) a decrease in the full width at half maximum (FWHM) of the A 1g and E 2g phonon modes with decreasing intensity of the defect-induced Raman modes, and ii) a blueshift of the A 1g phonon modes.It can be interpreted into the combined implications of defect healing induced by anchoring Pt atoms at the vacancy sites and the internal tensile strain stimulated during the heterostructure formation.The interfacial Pt-S bonds were also attested through Raman spectroscopy (Figure S8, Supporting Information).The Pt-S-correlated Raman-active B g and E g phonon modes were confirmed at 333 and 329 cm −1 for Pt NF@MoS 2 , which is consistent with the XPS results.

Photoelectrical Properties for Mixed-Dimensional Pt-MoS 2
To evaluate the applicability of photodetectors based on the constructed mixed-dimensional Pt-MoS 2 heterostructures, we fabricated 2-terminal photodetectors based on Pt NF@MoS 2 , Pt NPs@MoS 2 , Pt ATs@MoS 2 , and pristine MoS 2 on SiO 2 (300 nm)/Si(001) substrates through the thermal evaporation of Cr/Au electrodes (5/70 nm).Channels with a width and length of 50 and 500 μm, respectively, were patterned using a stencil mask.The measurement system developed to examine the photoelectric properties comprised a near-infrared (NIR) laser source ( = 1064 nm, 698 mW cm −2 ) and an optical chopper for generating regulated on-off signals (Figure 4a,b).Figure 4c reveals time-dependent photocurrent modulations of the twoterminal photodetectors based on Pt NF@MoS 2 , Pt ATs@MoS 2 , and pristine MoS 2 , which show periodic photocurrent-switching behavior irrespective of the Pt-clustering type.Figure 4d,e shows dynamic photocurrent curves for Pt NF@MoS 2 -based photodetectors with varied bias voltage and irradiated-laser power.Detailed photodetector performance, such as responsivity, detectivity, and EQE, were summarized in Figure 4f-h.Photocurrents of 348.7, 98.7, and 11.6 nA were recorded using the Pt NF@MoS 2 -, Pt ATs@MoS 2 -, and MoS 2 -based photodetectors with 20 V bias voltage, respectively.Since MoS 2 host crystalswhich typically have atomic vacancies-can be healed by anchoring Pt atoms, the enhancement of photocurrent values are discernible for Pt-MoS 2 heterostructures with an increase of the containing of Pt clusters.Those dependencies can also be confirmed in visible laser irradiation (Figures S9 and S10, Support-ing Information).These results imply that the interfacial Pt-S bonds are able to enhance the photocurrent generated under NIR laser irradiation, which is compelling for enabling applications related to 2D-TMD-based NIR photodetectors.In this regard, the photodetector performance (responsivity, detectivity, and EQE) were enhanced with forming the interfacial Pt-S bonds (Figure 4f,g).Photo responsivities (detectivities) were recorded to be 0.07 (3.35 × 10 5 ), 0.47 (3.40 × 10 6 ), and 2.04 mA/W (9.82 × 10 6 cm Hz 1/2 W −1 ), for pristine MoS 2 -, Pt ATs@MoS 2 -, and Pt NF@MoS 2 -based photodetector, respectively.In addition, 0.0078%, 0.0548%, and 0.2372% of EQE were estimated for Pt NF@MoS 2 -based photodetector, respectively.To clarify the mechanism underlying the boosting in the photocurrent generated by the Pt NF@MoS 2 -based photodetector, we computed the partial density of states for the upper-S, lower-S, and centered-Mo atoms of pristine MoS 2 , Pt ATs@MoS 2 , Pt NPs@MoS 2 , and Pt NF@MoS 2 (Figure S11, Supporting Information).Based on these results, we ascertained that the interfacial coordination bonding between the upper S and Pt atoms led to the formation of mid-gap states between the conduction band minimum (CBM) and valence band maximum (VBM), resulting in bandgap narrowing (Figure S11, Supporting Information).This phenomenon was amplified by the increase in density of the interfacial coordination bonding between the upper S and Pt atoms.For Pt NF@MoS 2 -based photodetectors, the dependency of photo responsivity, detectivity, and EQE was discerned to have an exponentially increasing relationship with the applied-bias voltages, whereas those have an exponential decrease for the illuminated laser power (Figure 4h).

Conclusion
We have unprecedentedly presented a rationally designed platform based on the manipulation of platinization conditions to synthesis of wafer-scale mixed-dimensional vdW heterostructures for realizing broadband photodetectors via manipulating the platinization process.The demonstrated strategy enables the construction of dimensionality-tailored vdW heterostructures, such as Pt NF-, Pt NPs-, and Pt Ats-incorporated with MoS 2 host crystals.Explicit structural and chemical analyses of the mixeddimensional Pt-MoS 2 vdW integration highlighted the possibility of manipulating the thermodynamic evolution of Pt clusters in various defective sites on the MoS 2 surface by altering the induced thermal gradients and Pt-source flux.DFT calculations indicated that the Mo vacancies on the surface were thermodynamically favorable for Pt-adsorption, and that the substituted Pt accelerated the formation of Pt nanoclusters with the additionally supplied Pt source.For the Pt NF-combined MoS 2 vdW integrations, the unequivocally excellent optoelectronic performance under NIR illumination are proven by the bandgap narrowing, which was related to the formation of the mid-gap states produced by the interfacial coordination bonding between S and Pt.We envisage that the proposed approaches will corroborate the innovative strategy for realizing broadband photodetectors, myriad vdW-integration-based photodetectors, and production of largescale 2D-heterostructured TMDs, which can clarify the crucial prerequisites that dictate the development of devices with emergent optoelectronic properties.
Synthesis of MoS 2 : Large-scale synthesis of MoS 2 layers was performed through a well-designed two-step thermal decomposition of the single-source precursor (NH 4 ) 2 MoS 4 . [5](NH 4 ) 2 MoS 4 (1.25 wt.%) was stirred in ethylene glycol at room temperature for 60 min.The resulting solution was spin-coated onto hydrophilically treated SiO 2 (300 nm)/Si and quartz substrates, which were rotated at 3000 rpm, for 40 s.The coated samples were immediately annealed at 100 °C for 1 min to remove the solvent.The resulting (NH 4 ) 2 MoS 4 films were annealed at 280 °C (first step) by introducing Ar (1000 sccm) at a pressure of 1 Torr for 30 min and subsequently annealed at 600 °C for 30 min to synthesize the MoS 2 host materials.
Synthesis of Dimensionality-Tailored Pt-MoS 2 : The synthesized MoS 2host thin film and PtCl 2 powder (0.01 g; Aldrich, 99.99%) were placed 10-13 cm apart in a tube furnace; the distance was varied to efficiently manipulate the dimensionality of the Pt guest in the heterostructure.To maximize the cross-sectional area available for the reaction with the Pt source, the MoS 2 -host thin films were placed orthogonal to the Pt-source flow.The Pt powder and MoS 2 -host thin film were subsequently annealed at 400 °C by introducing Ar (1000 sccm) at a pressure of 1 Torr for 60 min to synthesize dimensionality-tailored Pt-MoS 2 heterostructures.
Density Functional Theory (DFT) calculations: The atomic geometry and Pt-adatom adsorption energy for various defective and Pt-adsorbed MoS 2 surface structures were calculated using the Vienna ab initio simulation package (VASP). [26,27]The exchange-correlation functional was approximated using the Perdew-Burke-Ernzerhof (PBE) expression. [28]To account for the weak vdW interactions between Pt adatoms and MoS 2 surfaces, the optB86b-vdW functional, implemented in VASP by Klimeš et al., was used for all adsorption energy calculations. [29]Electron-ion interactions were modeled using the projector augmented wave (PAW) method. [30]Electronic wave functions were expanded in a basis set of plane waves with a kinetic energy cutoff of 500 eV.Geometry relaxation was repeated until the ionic forces decreased below 0.01 eV Å −1 .kspace integration was performed with finite sampling of the k-points on a 9 × 9 × 1 mesh in the Brillouin zone to optimize the geometry of each modeled structure.To minimize the interactions between neighboring image cells, vacuum regions that were at least 25 Å in length along the direction (z) perpendicular to the 2D surface were included.
Material Characterization: Structural characterization of the combined-dimensional Pt-MoS 2 heterostructures was performed by TEM (Titan Cube G2 60-300, FEI), AFM (Multimode 8, Bruker), and Raman spectroscopy (inVia Raman microscope, Renishaw; excitation wavelength = 532 nm; laser power incident on samples = 30 mW cm −2 ).Chemical identification of the samples was implemented using an XPS device (K-alpha, Thermo Scientific) equipped with a 180°double-focusing hemispherical analyzer and a 128-element multichannel detection system.XPS profiles were obtained with normal emission geometry using conventional micro-focused monochromatic Al K radiation (h = 1486.6eV) with a spot size of 500 × 500 μm 2 .The pass energy was adjusted to 50.0 eV using a step size of 0.1 eV.
Photoelectric Property Analysis: A two-terminal-based photodetector was fabricated to verify the prospects of realizing infrared photodetectors based on the dimensionality-tailored Pt-MoS 2 heterostructures.To create electrical contacts, 70-nm-thick Au was deposited onto a 3-nm-thick Cr layer by thermal evaporation.The channel length and width were 50 and 300 μm, respectively.The measurement system that was used to examine the photoelectric properties comprised an NIR laser source ( = 1064 nm, 1 mW cm −2 ), an optical chopper for generating regulated on-off signals, and a source-meter unit (Keithley 2612 B) to record the electrical signals.

Figure 1 .
Figure 1.a) Illustration of the large-scale synthesis platform for mixed-dimensional Pt-MoS 2 heterostructures.Atomic structure of the b) host MoS 2 crystal and the c) Pt nanofilm (NF), d) Pt nanoparticles (NPs), and e) Pt atoms (Ats) hybridized with the host MoS 2 crystal, which were synthesized using d values of 10, 11.5, and 13 cm, respectively.Photographs of f,g) Pt NF@MoS 2 , h,i) Pt NPs@MoS 2 , and j) Pt ATs@MoS 2 .Representative high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images of k) Pt NF@MoS 2 , l) Pt NPs@MoS 2 , and m) Pt ATs@MoS 2 (inset in k), l): energy-dispersive X-ray spectroscopy (EDS)-based elemental map of Pt Ats; inset in m): atomic-resolution STEM image showing substituted Pt Ats at the brightest spots).n-p) The corresponding atomic-force-microscopy (AFM) images (inset in p): photograph of a two-inch-diameter Pt ATs@MoS 2 wafer synthesized on a quartz substrate).

Figure 2 .
Figure 2. Pt adsorption energy and optimized atomic geometry of various defective and Pt-adsorbed MoS 2 surfaces.a) Atomic geometry of pristine MoS 2 and defect-containing MoS 2 surfaces (defects: S, S 2 , Mo, MoS 3 vacancies, and substitution of Mo and S).b) Pt adsorption energy and optimized atomic surface for each favorable site on MoS 2 and the six defective MoS 2 surfaces.c) Pt adsorption energy and optimized atomic surface for various Ptadsorption configurations on the defective MoS 2 surfaces.d) Top-view (upper) and side-view (lower) of calculated atomic geometries for the formation of initial Pt nanoclusters on the MoS 2 surface.Yellow, cyan, and blue spheres represent S, Mo, and Pt atoms, respectively.

Figure 4 .
Figure 4. a) Schematic of the photoelectric property measurement system, which comprises a near-infrared (NIR) laser source ( = 1064 nm, P = 698.3mW cm −2 ) and an optical chopper for generating regulated on-off signals.b) A representative microscopy image of a two-terminal-based Pt-MoS 2 photodetector.c) Dynamic photocurrent curves for Pt NF@MoS 2 , Pt ATs@MoS 2 , and pristine MoS 2 under periodic illumination of an NIR laser ( = 1064 nm, 698.3 mW cm −2 ) with 20 V bias voltage.Dynamic photocurrent curves for Pt NF@MoS 2 under periodic illumination of d) varied NIR laser with e) different bias voltage.f), g) Summary of responsivity, detectivity, and EQE values recorded using the different dimensionality-coupled Pt-MoS 2 heterostructures.h) Detailed-photoelectrical properties for Pt NF@MoS 2 heterostructures.