Predicting and Accelerating Nanomaterial Synthesis Using Machine Learning Featurization.

Materials synthesis optimization is constrained by serial feedback processes that rely on manual tools and intuition across multiple siloed modes of characterization. We automate and generalize feature extraction of reflection high-energy electron diffraction (RHEED) data with machine learning to establish quantitatively predictive relationships in small sets (∼10) of expert-labeled data, saving significant time on subsequently grown samples. These predictive relationships are evaluated in a representative material system (WVSe on c-plane sapphire (0001)) with two aims: 1) predicting grain alignment of the deposited film using pregrowth substrate data and 2) estimating vanadium dopant concentration using in situ RHEED as a proxy for ex situ methods (e.

Multi-Objective Optimization for Rapid Identification of Novel Compound Metals for Interconnect Applications.

Interconnect materials play the critical role of routing energy and information in integrated circuits. However, established bulk conductors, such as copper, perform poorly when scaled down beyond 10 nm, limiting the scalability of logic devices. Here, a multi-objective search is developed, combined with first-principles calculations, to rapidly screen over 15,000 materials and discover new interconnect candidates.

Reduction of Magnetic Interaction Due to Clustering in Doped Transition-Metal Dichalcogenides: A Case Study of Mn-, V-, and Fe-Doped WSe.

Using Hubbard-U-corrected density functional theory calculations, lattice Monte Carlo simulations, and spin Monte Carlo simulations, we investigate the impact of dopant clustering on the magnetic properties of WSe doped with period four transition metals. We use manganese (Mn) and iron (Fe) as candidate n-type dopants and vanadium (V) as the candidate p-type dopant, substituting the tungsten (W) atom in WSe. Specifically, we determine the strength of the exchange interaction in Fe-, Mn-, and V-doped WSe in the presence of clustering.

Monolithic 3D integration of 2D materials-based electronics towards ultimate edge computing solutions.

Three-dimensional (3D) hetero-integration technology is poised to revolutionize the field of electronics by stacking functional layers vertically, thereby creating novel 3D circuity architectures with high integration density and unparalleled multifunctionality. However, the conventional 3D integration technique involves complex wafer processing and intricate interlayer wiring. Here we demonstrate monolithic 3D integration of two-dimensional, material-based artificial intelligence (AI)-processing hardware with ultimate integrability and multifunctionality.

Achieving near-perfect light absorption in atomically thin transition metal dichalcogenides through band nesting.

Near-perfect light absorbers (NPLAs), with absorbance, [Formula: see text], of at least 99%, have a wide range of applications ranging from energy and sensing devices to stealth technologies and secure communications. Previous work on NPLAs has mainly relied upon plasmonic structures or patterned metasurfaces, which require complex nanolithography, limiting their practical applications, particularly for large-area platforms. Here, we use the exceptional band nesting effect in TMDs, combined with a Salisbury screen geometry, to demonstrate NPLAs using only two or three uniform atomic layers of transition metal dichalcogenides (TMDs).

Superior Quality Low-Temperature Growth of Three-Dimensional Semiconductors Using Intermediate Two-Dimensional Layers.

The low-temperature growth of materials that support high-performance devices is crucial for advanced semiconductor technologies such as integrated circuits built using monolithic three-dimensional (3D) integration and flexible electronics. However, low growth temperature prohibits sufficient atomic diffusion and directly leads to poor material quality, imposing severe challenges that limit device performance. Here, we demonstrate superior quality growth of 3D semiconductors at growth temperatures reduced by >200 °C by using two-dimensional (2D) materials as intermediate layers to optimize the potential energy barrier for adatom diffusion.

Impact of Etch Processes on the Chemistry and Surface States of the Topological Insulator BiSe.

The unique properties of topological insulators such as BiSe are intriguing for their potential implementation in novel device architectures for low power and defect-tolerant logic and memory devices. Recent improvements in the synthesis of BiSe have positioned researchers to fabricate new devices to probe the limits of these materials. The fabrication of such devices, of course, requires etching of the topological insulator, in addition to other materials including gate oxides and contacts which may impact the topologically protected surface states.

Controlled crack propagation for atomic precision handling of wafer-scale two-dimensional materials.

Although flakes of two-dimensional (2D) heterostructures at the micrometer scale can be formed with adhesive-tape exfoliation methods, isolation of 2D flakes into monolayers is extremely time consuming because it is a trial-and-error process. Controlling the number of 2D layers through direct growth also presents difficulty because of the high nucleation barrier on 2D materials. We demonstrate a layer-resolved 2D material splitting technique that permits high-throughput production of multiple monolayers of wafer-scale (5-centimeter diameter) 2D materials by splitting single stacks of thick 2D materials grown on a single wafer.

Dislocation driven spiral and non-spiral growth in layered chalcogenides.

Two-dimensional materials have shown great promise for implementation in next-generation devices. However, controlling the film thickness during epitaxial growth remains elusive and must be fully understood before wide scale industrial application. Currently, uncontrolled multilayer growth is frequently observed, and not only does this growth mode contradict theoretical expectations, but it also breaks the inversion symmetry of the bulk crystal.

High-Mobility Helical Tellurium Field-Effect Transistors Enabled by Transfer-Free, Low-Temperature Direct Growth.

The transfer-free direct growth of high-performance materials and devices can enable transformative new technologies. Here, room-temperature field-effect hole mobilities as high as 707 cm V s are reported, achieved using transfer-free, low-temperature (≤120 °C) direct growth of helical tellurium (Te) nanostructure devices on SiO /Si. The Te nanostructures exhibit significantly higher device performance than other low-temperature grown semiconductors, and it is demonstrated that through careful control of the growth process, high-performance Te can be grown on other technologically relevant substrates including flexible plastics like polyethylene terephthalate and graphene in addition to amorphous oxides like SiO /Si and HfO .

Fermi Level Manipulation through Native Doping in the Topological Insulator BiSe.

The topologically protected surface states of three-dimensional (3D) topological insulators have the potential to be transformative for high-performance logic and memory devices by exploiting their specific properties such as spin-polarized current transport and defect tolerance due to suppressed backscattering. However, topological insulator based devices have been underwhelming to date primarily due to the presence of parasitic issues. An important example is the challenge of suppressing bulk conduction in BiSe and achieving Fermi levels ( E) that reside in between the bulk valence and conduction bands so that the topologically protected surface states dominate the transport.

Schottky Barrier Height of Pd/MoS Contact by Large Area Photoemission Spectroscopy.

MoS, as a model transition metal dichalcogenide, is viewed as a potential channel material in future nanoelectronic and optoelectronic devices. Minimizing the contact resistance of the metal/MoS junction is critical to realizing the potential of MoS-based devices. In this work, the Schottky barrier height (SBH) and the band structure of high work function Pd metal on MoS have been studied by in situ X-ray photoelectron spectroscopy (XPS).

Probing Interface Defects in Top-Gated MoS Transistors with Impedance Spectroscopy.

The electronic properties of the HfO/MoS interface were investigated using multifrequency capacitance-voltage (C-V) and current-voltage characterization of top-gated MoS metal-oxide-semiconductor field effect transistors (MOSFETs). The analysis was performed on few layer (5-10) MoS MOSFETs fabricated using photolithographic patterning with 13 and 8 nm HfO gate oxide layers formed by atomic layer deposition after in-situ UV-O surface functionalization. The impedance response of the HfO/MoS gate stack indicates the existence of specific defects at the interface, which exhibited either a frequency-dependent distortion similar to conventional Si MOSFETs with unpassivated silicon dangling bonds or a frequency dispersion over the entire voltage range corresponding to depletion of the HfO/MoS surface, consistent with interface traps distributed over a range of energy levels.

Covalent Nitrogen Doping and Compressive Strain in MoS2 by Remote N2 Plasma Exposure.

Controllable doping of two-dimensional materials is highly desired for ideal device performance in both hetero- and p-n homojunctions. Herein, we propose an effective strategy for doping of MoS2 with nitrogen through a remote N2 plasma surface treatment. By monitoring the surface chemistry of MoS2 upon N2 plasma exposure using in situ X-ray photoelectron spectroscopy, we identified the presence of covalently bonded nitrogen in MoS2, where substitution of the chalcogen sulfur by nitrogen is determined as the doping mechanism.

Impurities and Electronic Property Variations of Natural MoS2 Crystal Surfaces.

Room temperature X-ray photoelectron spectroscopy (XPS), inductively coupled plasma mass spectrometry (ICPMS), high resolution Rutherford backscattering spectrometry (HR-RBS), Kelvin probe method, and scanning tunneling microscopy (STM) are employed to study the properties of a freshly exfoliated surface of geological MoS2 crystals. Our findings reveal that the semiconductor 2H-MoS2 exhibits both n- and p-type behavior, and the work function as measured by the Kelvin probe is found to vary from 4.4 to 5.

HfSe2 thin films: 2D transition metal dichalcogenides grown by molecular beam epitaxy.

In this work, we demonstrate the growth of HfSe2 thin films using molecular beam epitaxy. The relaxed growth criteria have allowed us to demonstrate layered, crystalline growth without misfit dislocations on other 2D substrates such as highly ordered pyrolytic graphite and MoS2. The HfSe2 thin films exhibit an atomically sharp interface with the substrates used, followed by flat, 2D layers with octahedral (1T) coordination.

Defect-dominated doping and contact resistance in MoS2.

Achieving low resistance contacts is vital for the realization of nanoelectronic devices based on transition metal dichalcogenides. We find that intrinsic defects in MoS2 dominate the metal/MoS2 contact resistance and provide a low Schottky barrier independent of metal contact work function. Furthermore, we show that MoS2 can exhibit both n-type and p-type conduction at different points on a same sample.

HfO(2) on MoS(2) by atomic layer deposition: adsorption mechanisms and thickness scalability.

We report our investigation of the atomic layer deposition (ALD) of HfO2 on the MoS2 surface. In contrast to previous reports of conformal growth on MoS2 flakes, we find that ALD on MoS2 bulk material is not uniform. No covalent bonding between the HfO2 and MoS2 is detected.

Geospatial analysis based on GIS integrated with LADAR.

In this work, we describe multi-layered analyses of a high-resolution broad-area LADAR data set in support of expeditionary activities. High-level features are extracted from the LADAR data, such as the presence and location of buildings and cars, and then these features are used to populate a GIS (geographic information system) tool. We also apply line-of-sight (LOS) analysis to develop a path-planning module.