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All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on V(MoS2)2 by Materials Project

VMo2S4 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. V4+ is bonded to six S2- atoms to form VS6 octahedra that share corners with twelve equivalent MoS6 octahedra, edges with two equivalent VS6 octahedra, and faces with two equivalent MoS6 octahedra. The corner-sharing octahedra tilt angles range from 51–55°. There are four shorter (2.43 Å) and two longer (2.44 Å) V–S bond lengths. Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with six equivalent VS6 octahedra, edges with six equivalent MoS6 octahedra, and a faceface with one VS6 octahedra. The corner-sharing octahedra tilt angles range from 51–55°. There are a spread of Mo–S bond distances ranging from 2.38–2.60 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 4-coordinate geometry to one V4+ and three equivalent Mo2+ atoms. In the second S2- site, S2- is bonded in a 5-coordinate geometry to two equivalent V4+ and three equivalent Mo2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on V(MoS2)2 by Materials Project

VMo2S4 crystallizes in the monoclinic Cc space group. The structure is three-dimensional. there are two inequivalent V4+ sites. In the first V4+ site, V4+ is bonded to six S2- atoms to form VS6 octahedra that share corners with twelve MoS6 octahedra, edges with two equivalent VS6 octahedra, and faces with two MoS6 octahedra. The corner-sharing octahedra tilt angles range from 48–57°. There are a spread of V–S bond distances ranging from 2.41–2.46 Å. In the second V4+ site, V4+ is bonded to six S2- atoms to form VS6 octahedra that share corners with twelve MoS6 octahedra, edges with two equivalent VS6 octahedra, and faces with two MoS6 octahedra. The corner-sharing octahedra tilt angles range from 49–57°. There are a spread of V–S bond distances ranging from 2.40–2.47 Å. There are four inequivalent Mo2+ sites. In the first Mo2+ site, Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with six VS6 octahedra, edges with six MoS6 octahedra, and a faceface with one VS6 octahedra. The corner-sharing octahedra tilt angles range from 48–57°. There are a spread of Mo–S bond distances ranging from 2.38–2.60 Å. In the second Mo2+ site, Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with six VS6 octahedra, edges with six MoS6 octahedra, and a faceface with one VS6 octahedra. The corner-sharing octahedra tilt angles range from 49–57°. There are a spread of Mo–S bond distances ranging from 2.38–2.61 Å. In the third Mo2+ site, Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with six VS6 octahedra, edges with six MoS6 octahedra, and a faceface with one VS6 octahedra. The corner-sharing octahedra tilt angles range from 50–57°. There are a spread of Mo–S bond distances ranging from 2.37–2.62 Å. In the fourth Mo2+ site, Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with six VS6 octahedra, edges with six MoS6 octahedra, and a faceface with one VS6 octahedra. The corner-sharing octahedra tilt angles range from 51–57°. There are a spread of Mo–S bond distances ranging from 2.37–2.62 Å. There are eight inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to two V4+ and three Mo2+ atoms. In the second S2- site, S2- is bonded in a 5-coordinate geometry to two V4+ and three Mo2+ atoms. In the third S2- site, S2- is bonded in a 4-coordinate geometry to one V4+ and three Mo2+ atoms. In the fourth S2- site, S2- is bonded in a 4-coordinate geometry to one V4+ and three Mo2+ atoms. In the fifth S2- site, S2- is bonded in a 4-coordinate geometry to one V4+ and three Mo2+ atoms. In the sixth S2- site, S2- is bonded in a 4-coordinate geometry to one V4+ and three Mo2+ atoms. In the seventh S2- site, S2- is bonded in a 5-coordinate geometry to two V4+ and three Mo2+ atoms. In the eighth S2- site, S2- is bonded in a 5-coordinate geometry to two V4+ and three Mo2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on V(MoS2)2 by Materials Project

VMo2S4 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are eight inequivalent V4+ sites. In the first V4+ site, V4+ is bonded to five S2- atoms to form distorted VS5 square pyramids that share a cornercorner with one VS6 octahedra, corners with three MoS6 octahedra, an edgeedge with one VS6 octahedra, an edgeedge with one MoS6 octahedra, an edgeedge with one VS5 trigonal bipyramid, and an edgeedge with one MoS5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 20–88°. There are a spread of V–S bond distances ranging from 2.32–2.44 Å. In the second V4+ site, V4+ is bonded to five S2- atoms to form distorted VS5 trigonal bipyramids that share a cornercorner with one VS6 octahedra, corners with four MoS6 octahedra, a cornercorner with one VS5 trigonal bipyramid, a cornercorner with one MoS5 trigonal bipyramid, an edgeedge with one VS6 octahedra, an edgeedge with one MoS6 octahedra, and edges with two MoS5 square pyramids. The corner-sharing octahedra tilt angles range from 32–67°. There are a spread of V–S bond distances ranging from 2.29–2.49 Å. In the third V4+ site, V4+ is bonded to five S2- atoms to form VS5 trigonal bipyramids that share a cornercorner with one VS6 octahedra, corners with four MoS6 octahedra, a cornercorner with one VS5 trigonal bipyramid, a cornercorner with one MoS5 trigonal bipyramid, edges with two MoS6 octahedra, and an edgeedge with one VS5 square pyramid. The corner-sharing octahedra tilt angles range from 40–61°. There are a spread of V–S bond distances ranging from 2.30–2.38 Å. In the fourth V4+ site, V4+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of V–S bond distances ranging from 2.27–2.77 Å. In the fifth V4+ site, V4+ is bonded to six S2- atoms to form distorted VS6 octahedra that share corners with three MoS6 octahedra, a cornercorner with one VS5 square pyramid, corners with two VS5 trigonal bipyramids, corners with two equivalent MoS5 trigonal bipyramids, an edgeedge with one MoS6 octahedra, edges with two MoS5 square pyramids, an edgeedge with one VS5 trigonal bipyramid, and a faceface with one MoS6 octahedra. The corner-sharing octahedra tilt angles range from 22–33°. There are a spread of V–S bond distances ranging from 2.38–2.68 Å. In the sixth V4+ site, V4+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of V–S bond distances ranging from 2.26–2.80 Å. In the seventh V4+ site, V4+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of V–S bond distances ranging from 2.25–2.84 Å. In the eighth V4+ site, V4+ is bonded to six S2- atoms to form distorted VS6 octahedra that share corners with two equivalent MoS6 octahedra, a cornercorner with one MoS5 square pyramid, a cornercorner with one MoS5 trigonal bipyramid, edges with three MoS6 octahedra, and an edgeedge with one VS5 square pyramid. The corner-sharing octahedra tilt angles range from 13–15°. There are a spread of V–S bond distances ranging from 2.30–2.57 Å. There are sixteen inequivalent Mo2+ sites. In the first Mo2+ site, Mo2+ is bonded to six S2- atoms to form MoS6 octahedra that share a cornercorner with one MoS6 octahedra, corners with two equivalent VS6 octahedra, a cornercorner with one MoS5 square pyramid, a cornercorner with one VS5 trigonal bipyramid, a cornercorner with one MoS5 trigonal bipyramid, an edgeedge with one MoS5 square pyramid, an edgeedge with one VS5 trigonal bipyramid, and a faceface with one MoS6 octahedra. The corner-sharing octahedra tilt angles range from 22–51°. There are a spread of Mo–S bond distances ranging from 2.33–2.60 Å. In the second Mo2+ site, Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share corners with two MoS6 octahedra, a cornercorner with one VS5 square pyramid, corners with two equivalent VS5 trigonal bipyramids, edges with two MoS6 octahedra, and edges with two MoS5 trigonal bipyramids. The corner-sharing octahedra tilt angles range from 19–40°. There are a spread of Mo–S bond distances ranging from 2.29–2.59 Å. In the third Mo2+ site, Mo2+ is bonded to five S2- atoms to form distorted MoS5 trigonal bipyramids that share a cornercorner with one MoS6 octahedra, corners with two equivalent VS6 octahedra, a cornercorner with one VS5 trigonal bipyramid, and edges with three MoS6 octahedra. The corner-sharing octahedra tilt angles range from 10–60°. There are a spread of Mo–S bond distances ranging from 2.31–2.58 Å. In the fourth Mo2+ site, Mo2+ is bonded to five S2- atoms to form distorted MoS5 trigonal bipyramids that share a cornercorner with one VS6 octahedra, a cornercorner with one MoS6 octahedra, a cornercorner with one VS5 trigonal bipyramid, edges with three MoS6 octahedra, and an edgeedge with one VS5 square pyramid. The corner-sharing octahedra tilt angles range from 31–77°. There are a spread of Mo–S bond distances ranging from 2.33–2.52 Å. In the fifth Mo2+ site, Mo2+ is bonded to six S2- atoms to form MoS6 octahedra that share corners with three MoS6 octahedra, a cornercorner with one VS5 square pyramid, corners with two MoS5 square pyramids, corners with two equivalent VS5 trigonal bipyramids, an edgeedge with one VS5 trigonal bipyramid, an edgeedge with one MoS5 trigonal bipyramid, a faceface with one VS6 octahedra, and a faceface with one MoS6 octahedra. The corner-sharing octahedra tilt angles range from 40–58°. There are a spread of Mo–S bond distances ranging from 2.34–2.52 Å. In the sixth Mo2+ site, Mo2+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Mo–S bond distances ranging from 2.34–2.99 Å. In the seventh Mo2+ site, Mo2+ is bonded to five S2- atoms to form distorted MoS5 square pyramids that share a cornercorner with one VS6 octahedra, a cornercorner with one MoS6 octahedra, corners with two equivalent MoS5 square pyramids, an edgeedge with one VS6 octahedra, edges with three MoS6 octahedra, and an edgeedge with one VS5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 10–45°. There are a spread of Mo–S bond distances ranging from 2.34–2.62 Å. In the eighth Mo2+ site, Mo2+ is bonded in a 5-coordinate geometry to five S2- atoms. There are a spread of Mo–S bond distances ranging from 2.36–2.85 Å. In the ninth Mo2+ site, Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share a cornercorner with one MoS6 octahedra, corners with two equivalent VS6 octahedra, edges with three MoS6 octahedra, and an edgeedge with one MoS5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 13–19°. There are a spread of Mo–S bond distances ranging from 2.36–2.64 Å. In the tenth Mo2+ site, Mo2+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Mo–S bond distances ranging from 2.27–2.93 Å. In the eleventh Mo2+ site, Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share a cornercorner with one VS5 square pyramid, a cornercorner with one VS5 trigonal bipyramid, a cornercorner with one MoS5 trigonal bipyramid, an edgeedge with one VS6 octahedra, edges with two MoS6 octahedra, and an edgeedge with one MoS5 trigonal bipyramid. There are a spread of Mo–S bond distances ranging from 2.41–2.67 Å. In the twelfth Mo2+ site, Mo2+ is bonded to six S2- atoms to form MoS6 octahedra that share a cornercorner with one MoS6 octahedra, a cornercorner with one VS5 trigonal bipyramid, an edgeedge with one VS6 octahedra, an edgeedge with one MoS6 octahedra, an edgeedge with one VS5 square pyramid, an edgeedge with one VS5 trigonal bipyramid, and an edgeedge with one MoS5 trigonal bipyramid. The corner-sharing octahedral tilt angles are 58°. There are a spread of Mo–S bond distances ranging from 2.40–2.60 Å. In the thirteenth Mo2+ site, Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share a cornercorner with one VS6 octahedra, an edgeedge with one VS6 octahedra, edges with three MoS6 octahedra, and edges with two MoS5 square pyramids. The corner-sharing octahedral tilt angles are 24°. There are a spread of Mo–S bond distances ranging from 2.37–2.70 Å. In the fourteenth Mo2+ site, Mo2+ is bonded to five S2- atoms to form distorted MoS5 square pyramids that share corners with two MoS6 octahedra, corners with two equivalent MoS5 square pyramids, an edgeedge with one VS6 octahedra, edges with two MoS6 octahedra, and an edgeedge with one VS5 trigonal bipyramid. The corner-sharing octahedra tilt angles range from 56–82°. There are a spread of Mo–S bond distances ranging from 2.38–2.72 Å. In the fifteenth Mo2+ site, Mo2+ is bonded in a 6-coordinate geometry to six S2- atoms. There are a spread of Mo–S bond distances ranging from 2.32–2.93 Å. In the sixteenth Mo2+ site, Mo2+ is bonded to six S2- atoms to form distorted MoS6 octahedra that share a cornercorner with one VS5 trigonal bipyramid, an edgeedge with one VS6 octahedra, edges with three MoS6 octahedra, and edges with two MoS5 square pyramids. There are a spread of Mo–S bond distances ranging from 2.36–2.68 Å. There are thirty-two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 5-coordinate geometry to two V4+ and three Mo2+ atoms. In the second S2- site, S2- is bonded in a 4-coordinate geometry to two V4+ and three Mo2+ atoms. In the third S2- site, S2- is bonded to one V4+ and three Mo2+ atoms to form distorted edge-sharing SVMo3 tetrahedra. In the fourth S2- site, S2- is bonded in a distorted L-shaped geometry to two Mo2+ atoms. In the fifth S2- site, S2- is bonded to four Mo2+ atoms to form distorted edge-sharing SMo4 trigonal pyramids. In the sixth S2- site, S2- is bonded in a 5-coordinate geometry to three V4+ and two Mo2+ atoms. In the seventh S2- site, S2- is bonded in a 5-coordinate geometry to two V4+ and three Mo2+ atoms. In the eighth S2- site, S2- is bonded in a 4-coordinate geometry to two V4+ and two Mo2+ atoms. In the ninth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to four Mo2+ atoms. In the tenth S2- site, S2- is bonded in a 4-coordinate geometry to two V4+ and two Mo2+ atoms. In the eleventh S2- site, S2- is bonded in a 5-coordinate geometry to two V4+ and three Mo2+ atoms. In the twelfth S2- site, S2- is bonded in a 6-coordinate geometry to three V4+ and three Mo2+ atoms. In the thirteenth S2- site, S2- is bonded in a 5-coordinate geometry to two V4+ and three Mo2+ atoms. In the fourteenth S2- site, S2- is bonded in a 5-coordinate geometry to two V4+ and three Mo2+ atoms. In the fifteenth S2- site, S2- is bonded in a 3-coordinate geometry to three Mo2+ atoms. In the sixteenth S2- site, S2- is bonded in a 4-coordinate geometry to one V4+ and three Mo2+ atoms. In the seventeenth S2- site, S2- is bonded in a 3-coordinate geometry to three Mo2+ atoms. In the eighteenth S2- site, S2- is bonded in a 1-coordinate geometry to one V4+ and three Mo2+ atoms. In the nineteenth S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to two V4+ and two Mo2+ atoms. In the twentieth S2- site, S2- is bonded in a 4-coordinate geometry to one V4+ and three Mo2+ atoms. In the twenty-first S2- site, S2- is bonded in a distorted see-saw-like geometry to two V4+ and two Mo2+ atoms. In the twenty-second S2- site, S2- is bonded in a 4-coordinate geometry to one V4+ and three Mo2+ atoms. In the twenty-third S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to four Mo2+ atoms. In the twenty-fourth S2- site, S2- is bonded in a 4-coordinate geometry to two V4+ and two Mo2+ atoms. In the twenty-fifth S2- site, S2- is bonded in a 4-coordinate geometry to one V4+ and three Mo2+ atoms. In the twenty-sixth S2- site, S2- is bonded to two V4+ and three Mo2+ atoms to form distorted edge-sharing SV2Mo3 square pyramids. In the twenty-seventh S2- site, S2- is bonded in a 4-coordinate geometry to two V4+ and three Mo2+ atoms. In the twenty-eighth S2- site

36 MATERIALS SCIENCE↗
DOE OSTI2025

All 2D Material Printed Diodes and Circuits on Paper for Sustainable Electronics

Sustainable electronics aim to reduce environmental impact by using ecofriendly materials, energy-efficient manufacturing, and recyclable components. However, existing approaches rely on complex, resource-intensive methods, rare metals, or nanomaterials with limited stability as well as plastic substrates, raising sustainability issues. Solution-processed two-dimensional (2D) materials offer a promising alternative: water-based and biocompatible conductive, semiconductive, and insulating 2D material inks can be produced with scalable techniques and are suitable for the fabrication of fully printed devices on low-cost and biodegradable paper substrates. However, 2D material only and fully printed diodes on paper have not yet been reported. Here, we demonstrate fully inkjet-printed 2D material-based diodes on paper using metal-insulator-semiconductor and metal-insulator-metal-semiconductor architectures. Water-based graphene and MoS2 inks, prepared by liquid-phase exfoliation, are used for the metallic and insulating films, while electrochemical exfoliation is used to produce the semiconducting MoS2 ink. The highest forward-to-reverse current ratio obtained is 330 (at ±2 V), while the forward current density is 1 mA/cm2 (at 1 V), making the diode performance comparable to the best solution-processed diodes reported so far. However, in contrast to previous works, fabrication occurs entirely at room temperature and ambient pressure, without using high-pressure sputtering, thermal evaporation, and any precious metal ink. The devices maintain stable performance under bending up to strain of 4% over 10,000 cycles. Finally, the diodes are successfully integrated with other 2D-material based electrical components to realize fully printed RC circuits, differentiators, integrators, and AC-to-DC converters onto paper, hence demonstrating the suitability of our approach for sustainable and disposable integrated circuits.

2D materials↗
NASA NTRS1972

Evidence of crystal structure in some sputtered MoS2 films.

Electron diffraction patterns and electron micrographs of molybdenum disulfide films sputtered on single-NaCl-crystal and electropolished-aluminum substrates are presented as evidence that crystalline MoS2 films can be sputtered onto various substrates in thicknesses up to 2 microns. Applied to Falex test pins and V-blocks, some of these films exhibited a wear life as long as 65 minutes at 1000 lb jaw load.

Lavik, M. T.↗
DOE OSTI2023

Nanoscale Ferroelectric Control of Novel Electronic States in Layered Two-Dimensional Materials (Final Report)

In this DOE Early Career project “Nanoscale Ferroelectric Control of Novel Electronic States in Layered Two-Dimensional Materials,” the PI’s group has combined ferroelectric field effect with nanoscale domain imaging and writing to design the electronic and optical properties of two-dimensional (2D) van der Waals materials, including graphene and transition metal dichalcogenides MoS2 and ReS2. The van der Waals materials have been prepared into field effect transistor (FET) devices with ferroelectric gates. Through domain patterning in a ferroelectric polymer PVDF-TrEF top-gate via conductive atomic force microscopy, the team has created programmable Schottky junctions in monolayer MoS 2 , where both barrier height and I-V rectifying polarity can be reconfigured. The transport anisotropy of monolayer to few-layer ReS 2 has been mapped out by defining the entire channel into an insulating state and creating nanoscale conducting paths along different directions through domain writing in the ferroelectric top-gate. The result shows that the conductivity along and perpendicular to the Re-chain can differ by >5.5x10 4 . Theoretical modeling points to the band origin of the transport anomaly and reveals the emergence of a flat band in few-layer ReS 2 . The interfacial epitaxial relation between ReS 2 and PVDF-TrFE further promotes the formation of close-packed, highly ordered PVDF-TrFE nanowires with width of 35 nm and 10 nm. Nonvolatile modulation of quantum Hall effect has been achieved in graphene FETs with a ferroelectric oxide Ba 0.4 Sr 0.6 TiO 3 back-gate. Scattering from the remote surface optical phonon in Ba 0.4 Sr 0.6 TiO 3 limits the room temperature mobility of graphene to be about 3x10 4 cm 2 /Vs. Steep-slope switching has been achieved in MoS 2 FETs back-gated by polycrystalline Pb(Zr,Ti)O 3 , which signals a static-state negative capacitance mode without involving an additional dielectric layer. Piezoresponse force microscopy studies show that the sub-threshold swing can be well correlated with the domain wall density in Pb(Zr,Ti)O 3 . The team also observes an unconventional filtering effect of the second harmonic generation response at the MoS 2 /Pb(Zr,Ti)O 3 heterointerface, which can be accounted for by the alignment between one of the polar axes of MoS 2 and the chiral dipole rotation at the surface of domain wall in Pb(Zr,Ti)O 3 . The research supported by this DOE grant has significantly advanced the fundamental understanding and functional design of ferroelectric/2D van der Waals heterostructures for their implementation towards energy applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Large-field magnetoresistance of nanometer scale nickel films grown on molybdenum disulfide

The magnetoresistance of thin nickel films grown on molybdenum disulfide was measured in perpendicular magnetic fields as high as 90 kOe. Films with thicknesses of 20 nm provided continuous surfaces for measurement. The magnetoresistance was found to be linear with respect to the applied magnetic field with no sign of saturation. There was also no evidence of hysteresis or temperature dependence between 100 to 300 K. STM measurement showed the deposited Ni forms a continuous film of extremely small nanoclusters. However, the field dependence of magnetoresistance was found to be significantly larger than bulk Ni, which is in turn larger than Ni with nanoscale grains. We expect the unusual magnetoresistance behavior to arise from some property of the Ni-MoS 2 interface.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Accumulation-Type Ohmic van der Waals Contacts to Nearly Intrinsic WSe 2 Nanosheet-Based Channels: Implications for Field-Effect Transistors

We report the fabrication of ohmic van der Waals (vdW) contacts to nearly intrinsic WSe 2 nanosheet-based channels in field-effect transistors (FETs) using degenerately p-doped MoS2 (p + -MoS2) as a contact metal. We demonstrate that accumulation-type ohmic contacts and the high device performance are achievable without electrostatically gating the drain/source contact regions despite the nearly intrinsic nature of WSe 2 . Back-gated WSe 2 FETs with p + -MoS 2 bottom contacts (which screen the back-gate electric field in the drain/source regions) exhibit linear output characteristics, a high on/off ratio of 10 8 , and a high two-terminal field-effect mobility up to ~200 cm2 V –1 s –1 at room temperature. Our theoretical modeling reveals that the p + -MoS 2 /WSe 2 vdW junction behaves like a metal/semiconductor ohmic contact signified by a vanishingly thin space-charge region of ~1 nm on the p + -MoS 2 side and a substantial accumulation layer of free holes on the WSe 2 side, which is further verified by additional temperature-dependent and dual-gated measurements of WSe 2 FETs. We attribute the formation of accumulation-type ohmic contacts free of a Schottky barrier to the near absence of Fermi-level pinning at the vdW interface and the work function of p + -MoS 2 being larger than the ionization energy of WSe 2 . This study represents an important step toward achieving low-resistance ohmic contacts to two-dimensional (2D) semiconductors by eliminating the Fermi-level pinning effects, which is expected to have significant implications for next-generation 2D semiconductor-based nanoelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Electron Configuration Modulation Induced Stabilized 1T-MoS 2 for Enhanced Sodium Ion Storage

1T-MoS 2 has become an ideal anode for sodium-ion batteries (SIBs). However, the metastable feature of 1T-MoS 2 makes it difficult to directly synthesize under normal conditions. In addition, it easily transforms into 2H phase via restacking, resulting in inferior electrochemical performance. Here, the electron configuration of Mo 4d orbitals is modulated and the stable 1T-MoS 2 is constructed by nickel (Ni) introduction (1T-Ni-MoS 2 ). The original electron configuration of Mo 4d orbitals is changed via the electron injection by Ni, which triggers the phase transition from 2H to 1T phase, thus improving the electrical conductivity and accelerating the redox kinetics of the material. Consequently, 1T-Ni-MoS 2 exhibits superior rate capability (266.8 mAh g -1 at 10 A g -1 ) and excellent cycle life (358.7 mAh g -1 at 1 A g -1 after 350 cycles). In addition, the assembled Na 3 V 2 (PO 4 ) 3 /C||1T-Ni-MoS 2 full cells deliver excellent electrochemical properties and show great prospects in energy storage devices.

1T-MoS2↗
DOE OSTI2022

Domain wall enabled steep slope switching in MoS2 transistors towards hysteresis-free operation

Abstract The device concept of ferroelectric-based negative capacitance (NC) transistors offers a promising route for achieving energy-efficient logic applications that can outperform the conventional semiconductor technology, while viable operation mechanisms remain a central topic of debate. In this work, we report steep slope switching in MoS 2 transistors back-gated by single-layer polycrystalline PbZr 0.35 Ti 0.65 O 3 . The devices exhibit current switching ratios up to 8 × 10 6 within an ultra-low gate voltage window of $$V_{{{\mathrm{g}}}} = \pm \! 0.5$$ V g = ± 0.5 V and subthreshold swing (SS) as low as 9.7 mV decade −1 at room temperature, transcending the 60 mV decade −1 Boltzmann limit without involving additional dielectric layers. Theoretical modeling reveals the dominant role of the metastable polar states within domain walls in enabling the NC mode, which is corroborated by the relation between SS and domain wall density. Our findings shed light on a hysteresis-free mechanism for NC operation, providing a simple yet effective material strategy for developing low-power 2D nanoelectronics.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Engineering Surface Architectures for Improved Durability in III–V Photocathodes

GaInP2 has shown promise as the wide bandgap top junction in tandem absorber photoelectrochemical (PEC) water splitting devices. Among previously reported dual-junction PEC devices with a GaInP 2 top cell, those with the highest performance incorporate an AlInP 2 window layer (WL) to reduce surface recombination and a thin GaInP2 capping layer (CL) to protect the WL from corrosion in electrolytes. However, the stability of these III-V systems is limited, and durability continues to be a major challenge broadly in the field of PEC water splitting. This work provides a systematic investigation into the durability of GaInP 2 systems, examining the impacts of the window layer and capping layer among single junction pn-GaInP 2 photocathodes coated with an MoS 2 catalytic and protective layer. The photocathode with both a CL and WL demonstrates the highest PEC performance and longest lifetime, producing a significant current for >125 h. In situ optical imaging and post-test characterization illustrate the progression of macroscopic degradation and chemical state. The surface architecture combining an MoS 2 catalyst, CL, and WL can be translated to dual-junction PEC devices with GaInP 2 or other III-V top junctions to enable more efficient and stable PEC systems.

08 HYDROGEN↗
DOE OSTI2023

Fully Inkjet‐Printed, 2D Materials‐Based Field‐Effect Transistor for Water Sensing

Abstract Despite significant progress in solution‐processing of 2D materials, it remains challenging to reliably print high‐performance semiconducting channels that can be efficiently modulated in a field‐effect transistor (FET). Herein, electrochemically exfoliated MoS 2 nanosheets are inkjet‐printed into ultrathin semiconducting channels, resulting in high on/off current ratios up to 10 3 . The reported printing strategy is reliable and general for thin film channel fabrication even in the presence of the ubiquitous coffee‐ring effect. Statistical modeling analysis on the printed pattern profiles suggests that a spaced parallel printing approach can overcome the coffee‐ring effect during inkjet printing, resulting in uniform 2D flake percolation networks. The uniformity of the printed features allows the MoS 2 channel to be hundreds of micrometers long, which easily accommodates the typical inkjet printing resolution of tens of micrometers, thereby enabling fully printed FETs. As a proof of concept, FET water sensors are demonstrated using printed MoS 2 as the FET channel, and printed graphene as the electrodes and the sensing area. After functionalization of the sensing area, the printed water sensor shows a selective response to Pb 2+ in water down to 2 ppb. This work paves the way for additive nanomanufacturing of FET‐based sensors and related devices using 2D nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Aging studies on chemical vapor deposition and mechanically exfoliated molybdenum disulfide flakes heated in ambient air

The structural integrity of atomically thin two-dimensional molybdenum disulfide (MoS 2 ) is crucial for high-temperature applications, including nanoelectronics and optoelectronics. This study explores the structural stability and electrical performance, under extended thermal exposure in air, of MoS 2 flakes synthesized via chemical vapor deposition (CVD) and mechanical exfoliation. The MoS 2 flakes, both CVD-grown and mechanically exfoliated, were subjected to heating at 200 °C with a relative humidity of 60(±5)% for a prolonged period and investigated with atomic force microscopy and Raman spectroscopy. This study shows that CVD-grown flakes developed noticeable cracks after prolonged heating, whereas mechanically exfoliated flakes mostly retained their structural integrity. Also, both types of flakes showed a decrease in layer thickness and lateral size over time, with mechanically exfoliated flakes exhibiting a comparatively smaller reduction in substrate coverage area. In addition, MoS 2 -based two-terminal devices were subjected to heating at 150 °C for approximately 1100 h, and their electrical characterization revealed a steady rise in current during constant voltage (5 V) conditions. This study enhances our understanding of MoS 2 stability and provides guidance for improving the reliability of MoS 2 -based devices in high-temperature electronic applications.

2D materials↗
DOE OSTI2025

Phase transition in two-dimensional monolayer (1L)-molybdenum disulfide induced by atomic S-basal plane gliding via synchrotron X-ray monochromatic beam radiation for superior electronic performance

Here, in this work, we report a novel approach to reduce the channel resistance by inducing a phase transition behavior from 2H to 1T in a monolayer MoS 2 (1L-MoS 2 ) by a synchrotron X-ray monochromatic beam (mono-beam) radiation. The effects of the biphase structure by the mono-beam on the 1L-MoS2 film were investigated using Raman spectra, photoluminescence (PL) spectra, scanning tunneling microscopy, and scanning tunneling spectroscopy, respectively. Through material characterization, we identified that the lateral sliding of S-vacancies along the S-plane in the 1L-MoS 2 is the key reason for the origin of unidirectional phase transition. The precise phase engineering triggered by the mono-beam radiation process allows the realization of field-effect transistors (FET) with 2X improvement in mobility toward a high on/off ratio (~10 8 ) and a near-ideal subthreshold swing of ~88 mV per decade. The validity of the phase engineering could be further extended for its application as a memory device, exhibiting a gate tunable conduction modulation behavior and a high resistance ratio of ~10 2 at a gate bias of 5 V with endurance of ~100 cycles. Furthermore, an artificial neural network using the synaptic weight update with accuracy of ~93 % was achieved.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Towards defect engineering in hexagonal MoS 2 nanosheets for tuning hydrogen evolution and nitrogen reduction reactions

Combined computational and experimental approaches were used to evaluate defective 2H-MoS 2 nanosheets for their activity and selectivity for hydrogen evolution reaction (HER) and nitrogen reduction reaction (NRR). Density functional theory calculations were used to understand the relationship between HER and NRR activity on the ideal basal MoS 2 plane, seven grain-boundaries, ten single-/few-atom vacancies and anti-sites, and zigzag and armchair edge sites. The results confirm that 2H-MoS 2 should contain several defects with high activity for HER: armchair and zigzag edges, VS vacancy, MoS 2 anti-site, and S-S and Mo-Mo grain boundaries. Considering Gibbs free energy change for all the steps in the NRR mechanism and kinetic barriers for a key NRR step, we have found that activation of perspective NRR selective sites in 2H-MoS 2 , namely V MoS6 and clusters of S-vacancies, would require large overpotential, conditions at which HER dominates. The DFT conclusions are supported by the electrochemical studies of NRR activity and selectivity under aqueous conditions, which show an increase in NRR activity but a decrease in Faradaic efficiency as applied cell potential becomes more negative. The results of this work therefore highlight the challenges in activating natural 2H-MoS 2 for NRR, which would require additional material engineering or reaction condition optimization as a way to suppress HER, decrease the NRR overpotential or preferentially both.

2H-MoS2↗
DOE OSTI2020

Addressing the Stability Gap in Photoelectrochemistry: Molybdenum Disulfide Protective Catalysts for Tandem III–V Unassisted Solar Water Splitting

While photoelectrochemical (PEC) solar-to-hydrogen efficiencies have greatly improved over the past few decades, advances in PEC durability have lagged behind. Corrosion of semiconductor photoabsorbers in the aqueous conditions needed for water splitting is a major challenge that limits device stability. In addition, a precious-metal catalyst is often required to efficiently promote water splitting. In this work, we demonstrate unassisted water splitting using a nonprecious metal molybdenum disulfide nanomaterial catalytic protection layer paired with a GaInAsP/GaAs tandem device. This device was able to achieve stable unassisted water splitting for nearly 12 h, while a sibling sample with a PtRu catalyst was only stable for 2 h, highlighting the advantage of the nonprecious metal catalyst. In situ optical imaging illustrates the progression of macroscopic degradation that causes device failure. Furthermore, this work compares unassisted water splitting devices across the field in terms of the efficiency and stability, illustrating the need for improved stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

MoS 2 nanosheet integrated electrodes with engineered 1T-2H phases and defects for efficient hydrogen production in practical PEM electrolysis

Low electrical conductivity and poor accessibility of MoS 2 reaction sites raise great challenges in maximizing the triple-phase-boundary (TPB) sites of MoS 2 -based electrodes and minimizing ohmic losses for efficient hydrogen evolution reaction (HER) in practical proton exchange membrane (PEM) water electrolysis. Herein, we report a scalable hydrothermal approach to fabricate ionomer-free integrated electrodes with engineered 1 T-2 H heterophase and defect-rich MoS 2 nanosheets (MoS 2 NSs) in-situ grown onto the carbon fiber paper (CFP). With an ultralow loading of 0.14 mg/cm 2 , a small voltage of 2.25 V was obtained at 2000 mA/cm 2 in a practical cell with Nafion115 membrane, which outperforms all previously reported high-loading non-precious catalyst-based electrodes. Impressively, it shows 44 times higher mass activity than a high-loading and ionomer-mixed MoS 2 assemblies electrode. Furthermore, this work builds a bridge from catalyst optimization to electrode fabrication and provides a promising direction for improving intrinsic catalytic activity, electrode conductivity and stability for practical PEM water electrolysis.

1T-2H heterophase↗
DOE OSTI2022

Effect of Support on Oxygen Reduction Reaction Activity of Supported Iron Porphyrins

In this work, we report the oxygen reduction reaction (ORR) activity in acid of an Fe porphyrin on different supports. While the activity is high (E 1/2 = 0.34 V vs RHE with n = 3.8) when the Fe porphyrin is adsorbed on XC72 (a graphitic carbon), this activity is much lower when the porphyrin is adsorbed on either MoS 2 (E 1/2 = -0.15 V vs RHE with n = 2.2) or g-C 3 N 4 (E 1/2 = -0.24 V vs RHE with n = 3.1). Electron paramagnetic resonance (EPR), X-ray absorption fine structure (XAFS), and magnetometry measurements show the electronic structure around the Fe center is the same for all three supports. Only the Fe porphyrin supported on XC72 exhibits a pH dependence in its ORR activity. This observation, coupled with the increased hydrophilicity of XC72 relative to the other supports, suggests that the support-electrolyte interaction controls the ORR activity. Modification of MoS 2 to increase its hydrophilicity results in a more active ORR catalyst.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗