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Indium selenide is a polymorphous material system that has attracted considerable attention due to the outstanding electronic, optical, ferroelectric, and antiferroelectric properties of its various crystalline phases; however, this polymorphism adds a layer of complexity to the analysis of Raman and x-ray photoelectron (XPS) data of these materials. In this report, a method of quantitative analysis of combined Raman and XPS data is developed to determine the stoichiometry of indium selenide thin films, as well as the phase fraction of β-In2Se3, γ-In2Se3, and κ-In2Se3 within the films. A 13:1 ratio of the indium to selenium sensitivity factors (σIn/σSe = 13) was found to yield the most accurate stoichiometry results. Further structural characterization of the κ-In2Se3 film was performed and points to its existence in these films as a distinct phase, rather than strained γ-In2Se3. [ABSTRACT FROM AUTHOR]

Theoretical models have predicted that pH-responsive surface groups can reduce the sensitivity of field-effect transistor biosensors. However, attempts to prove this experimentally have shown conflicting results. In this work, a graphene field effect transistor (gFET) biosensor is used, which, without modification, is pH insensitive. The surface of the graphene is then functionalized using 1-hydroxypyrene to modulate the pH sensitivity of the gFET. A pH sensitivity ranging from 3.9 to 36.8 mV/pH was demonstrated. The biosensitivity of the gFETs was tested using streptavidin–biotin as a model system. The experimental results showed no correlation between biosensitivity and pH sensitivity. An electrochemical membrane model was used to determine the expected relationship between biosensitivity and pH sensitivity. The model results show that biosensitivity does not decrease until a certain threshold pH sensitivity is reached. This threshold is dependent on factors such as the acid dissociation constants of the surface hydroxyl groups and ion concentration. Furthermore, the differences between the simulation and experiment suggest that the effect of screening is greatly reduced when the analyte binds within a membrane. [ABSTRACT FROM AUTHOR]

A Ti2AlN MAX phase layered thin film electrode and oxygen getter layer for HfO2‐based two‐terminal memristors is presented. The Ti2AlN/HfOx/Ti memristor devices exhibit enhanced resistive switching performance, including an ultra‐low reset current density (< 10−8 MΩ cm2), substantial on‐off ratio (≈ 6000), excellent multi‐level functionality (≈ 9 distinct states), impressive retention (up to 300 °C), and robust endurance (>200 million) as compared to conventional TiN and other alternative materials based memristors. Experimental measurements and modeling suggest that the distinctive combination of low thermal conductivity, high electrical conductivity, and unique ultra‐thin layer‐by‐layer structure of the Ti2AlN MAX phase thin film contribute to this exceptional performance with good reproducibility and stability. The results demonstrate for the first‐time the potential of this innovative sputtered MAX phase material for engineering energy‐efficient, high‐density non‐volatile digital, and analog memory devices aimed toward next‐generation sustainable artificial intelligence. [ABSTRACT FROM AUTHOR]

As the demand for computing applications capable of processing large datasets increases, there is a growing need for new in-memory computing technologies. Oxide-based resistive random-access memory (RRAM) devices are promising candidates for such applications because of their industry readiness, endurance, and switching ratio. These analog devices, however, suffer from poor linearity and asymmetry in their analog resistance change. Various reports have found that the temperature in RRAM devices increases locally by more than 1000 K during operation. Therefore, temperature control is of paramount importance for controlling their resistance. In this study, scanning thermal microscopy is used to map the temperature of Au/Ti/HfOx/Au devices at a steady power state and to measure temperature dynamics of the top electrode above the filament location during both resistive switching loops and voltage pulsing. These measurements are used to verify the thermal parameters of a multiphysics finite elements model. The model is then used to understand the impact of thermal conductivities and boundary conductances of constituent materials on resistance change during the first reset pulse in RRAM devices. It is found that the resistance change can be reduced significantly when the temperature in the titanium capping layer is reduced. We find that the greatest temperature reduction and, therefore, the lowest resistance change in the device are afforded by capping layers with increased thermal conductivities. This work links thermal properties to the resistance change in RRAM devices, providing critical insights into engineering devices with improved switching dynamics. [ABSTRACT FROM AUTHOR]

The effects of substrate choice, substrate temperature, Se/In flux ratio, and cooling rate after deposition on the phase composition, surface morphology, and stoichiometry of indium selenide films synthesized via molecular beam epitaxy are presented. In2Se3 films were synthesized on sapphire, Si(111) and highly oriented, pyrolytic graphite (HOPG) substrates. The phase composition, stoichiometry, and surface morphology of the films were characterized via Raman spectroscopy, x-ray photoelectron spectroscopy, and atomic force microscopy, respectively. Higher substrate temperature combined with higher Se/In ratio promoted formation of β-In2Se3 over γ and/or κ-In2Se3 on all substrates. Higher Se/In ratio also independently promoted β-In2Se3 over γ and/or κ-In2Se3 on all substrates at 673 K. The lateral dimensions of In2Se3 flakes increased as the substrate temperature increased on all substrates, and the largest lateral dimensions were observed for β-In2Se3 flakes on HOPG at 973 K. No evidence of α-In2Se3 was observed in the Raman spectra of any of the films at any of the synthesis conditions in this study. β-In2Se3 films on HOPG were cooled at 1200, 120, and 12 K/h and no evidence of a β to α-In2Se3 phase transition was observed. Some evidence of β to α-In2Se3 phase transition was observed in temperature-dependent XRD of In2Se3 powders, suggesting that another parameter besides cooling rate is locking the In2Se3 films into the β-phase. [ABSTRACT FROM AUTHOR]

Hafnium oxide non-volatile memories have shown promise as an artificial synapse in neuromorphic computing architectures. However, there is still a need to fundamentally understand how to reliably control the analog resistance change induced by oxygen ions that partially rupture or re-form the conductive filament. In this work, the impact of measurement conditions (pulse amplitude and pulse width) and titanium dopants on the analog resistance change of atomic layer deposited hafnium oxide memristor synapses are studied. A lower pulse amplitude improves the linearity of resistance change as a function of the number of pulses but results in a smaller memory window. The addition of titanium dopants does not substantively change the analog resistance modulation of hafnium oxide. Density functional theory calculations show that titanium strongly impacts oxygen ion motion in the HfxTiyOz matrix but does not impact significantly in the HfTi metallic filament. This study demonstrates that the analog characteristic of HfxTiyOz artificial synapses is largely independent of the titanium doped bulk oxide since the resistance change is primarily controlled by the HfTi metallic conducting filament. [ABSTRACT FROM AUTHOR]

Changes in the resistance of Ti/HfOx synapses are known to be governed by a thin-oxide barrier associated with the oxidation/reduction of a Hf-rich conducting filament (CF). However, experimental characterization of the CF is challenging. Critical physical properties and processes, such as the barrier location, time-dependent thickness during analog pulsing, and the temperature-effect on current, need to be better established. In this work, a compact model based on Trap-Assisted-Tunneling and Ohmic transport is utilized to analyze the analog switching of HfOx synapses. The model agrees well with the experimentally observed current–voltage relation and its temperature dependence. The extracted barrier heights during analog pulsing are consistent with a barrier situated near the reset anode; the electrode is opposite to the Ti oxygen-reservoir layer. A Finite Element Analysis simulation, which incorporates oxygen-vacancy migration, independently supports this conclusion. The model further permits extraction of the barrier thickness in relation to the analog pulses. [ABSTRACT FROM AUTHOR]

Self-aligned metal-oxide-semiconductor (MOS) capacitors are studied with several low-temperature, wet chemical silicon dioxide (SiO2) interlayers to understand their impact on electrical performance. Self-aligned MOS capacitors are fabricated with a bottom-up patterning technique that uses a poly(methyl methacrylate) brush and dopant-selective KOH etch combined with area-selective atomic layer deposition of hafnium dioxide (HfO2) and Pt. The wet chemical pretreatments used to form the SiO2 interlayer include hydrofluoric acid (HF) etch, 80 °C H2O, and SC-2. Capacitance-voltage measurements of these area-selective capacitors exhibit a HfO2 dielectric constant of ∼19, irrespective of pretreatment. After a forming gas anneal, the average interface state density decreased between 1.8 and 7.5 times. The minimum observed Dit is 1 × 1011 eV−1 cm−2 for the HF-last treatment. X-ray photoelectron spectroscopy shows an increase in stoichiometric SiO2 in the interfacial layer after the anneal. Additional carbon is also observed; however, comparison with capacitors fabricated in a nonselective process reveals minimal impact on performance. [ABSTRACT FROM AUTHOR]

Resistive random-access memory (RRAM) devices have been widely studied for neuromorphic, in-memory computing. One of the most studied RRAM structures consists of a titanium capping layer and a HfOx adaptive oxide. Although these devices show promise in improving neuromorphic circuits, high variability, non-linearity, and asymmetric resistance changes limit their usefulness. Many studies have improved linearity by changing materials in or around the device, the circuitry, or the analog bias conditions. However, the impact of prior biasing conditions on the observed analog resistance change is not well understood. Experimental results in this study demonstrate that prior higher reset voltages used after forming cause a greater resistance change during subsequent identical analog pulsing. A multiphysics finite element model suggests that this greater analog resistance change is due to a higher concentration of oxygen ions stored in the titanium capping layer with increasing magnitude of the reset voltage. This work suggests that local ion concentration variations in the titanium capping layer of just tens of atoms cause significant resistance variation during analog operation. [ABSTRACT FROM AUTHOR]

Mass transport to the sensor surface is a critical step in biosensing, often being the factor determining the limit of detection. Modeling transport of the analyte to a surface under convection and diffusion is a challenging task often requiring complex simulation. Herein, we provide a general model for mass transport to planar and nanowire biosensors under flow that is applicable over a wide range of variables. The model is then used to examine the importance of radial diffusion compared with planar diffusion under flow. Only under diffusive transport nanowires are found to have greatly reduced settling times compared with planar sensors due to radial diffusion. However, the presence of flow restricts the growth of the depletion region, resulting in comparable settling times between nanowires and planar sensors of the same size. Under flow conditions in typical experiments, radial diffusion associated with nanowire sensors is inessential for fast mass transport. Instead, the sensor length in the flow direction is the critical parameter as it limits the concentration drop that can occur as the analyte flows past the sensor. Decreasing the sensor length along the flow direction is found to greatly reduce settling times for both cases of planar and radial diffusion, even approaching the reaction limited case. Similarly, decreasing the channel height decreases the settling time due to restriction of the depletion region, but not as significantly as decreasing the sensor length. [ABSTRACT FROM AUTHOR]

Moving toward the future computing and non-volatile memory, memristors have gained wide attention for their in-memory computing and neuromorphic computing applications. The resistive switching dynamics in oxide-based memristors rely critically on oxygen ions and their recombination with oxygen vacancies to partially rupture and form the conductive filament (CF) for modulating the device between the low resistance state and high resistance state. In this study, we investigated the effect of oxygen ion concentration at the HfOx/Ti interface on the behavior of HfOx-based filamentary memristors. Devices with higher oxygen ion concentrations at the HfOx surface were fabricated by treating with oxygen plasma at various times on the as grown ~ 5 nm HfOx active layer via atomic layer deposition. Detailed X-ray photoelectron spectroscopy and depth profile analyses verify the excess oxygen ion presence at the HfOx surface, and the formation of a thin TiOx layer between the HfOx and Ti layers, resulting in a HfOx/TiOx/Ti interface structure. This work demonstrates the importance of interface chemistry at the HfOx/Ti interface region and its oxygen ion motion for controlled growth of the CF during memristor set operation, which is favorable for analog logic computation. While the components of improving the memristor performance, offering multilevel resistance states, and enhancing the resistance controllability are all have been achievable, displaying a gradual SET behavior in HfOx-based memristor still remains as a challenge. Overcoming this obstacle in the HfOx-based memristor can lead to a tremendous progress toward controlling the resistance on the SET side, which can be thus programmable and be useful for analog logic computation based on spiking networks. This work demonstrates the importance of oxygen ion concentration at the HfOx/Ti interface and its motion for controlled growth of the CF during memristor set operation for resistance controllability. [ABSTRACT FROM AUTHOR]

HfOx-Based resistive random-access memory (RRAM) devices are being widely considered as both non-volatile memories for digital computation and synaptic memory for neuromorphic computing applications. The resistive switching mechanism in these materials is known to be highly dependent on the presence of oxygen vacancies and other dopants. In this work, HfOx is doped with titanium using sequential atomic layer deposition (ALD) of HfOx and TiOx. An increase in the titanium dopant content results in a decrease of the forming voltage, a decrease of both allowable set and reset stop voltages, and a decrease of the high resistance state (HRS) of the RRAM. The physical mechanisms responsible for these observed behaviors are proposed. [ABSTRACT FROM AUTHOR]

The development and application of an analysis methodology for charge pumping (CP) measurements in order to extract spatial distributions of traps in Hf[O.sub.2]/Si[O.sub.2] gate stacks is discussed. An increase in the trap density in the SiO2 layer closer to the high-k dielectric is observed.

AS silicon complimentary metal-oxide-semiconductor (CMOS) technology approaches its limits, new device structures and computational paradigms will be required to replace and augment standard CMOS devices for ULSI circuits. These possible emerging technologies span the realm from transistors made from silicon nanowires to heteroepitaxial layers for spin transistors to devices made from nanoscale molecules. One theme that pervades these seemingly disparate emerging technologies is that the electronic properties of these nanodevices are extremely susceptible to small perturbations in structural and material properties such as dimension, structure, roughness, and defects. The extreme sensitivity of the electronic properties of these devices to their nanoscale physical properties defines a significant need for precise accurate metrology. This paper will describe some of the most critical metrology required to characterize materials and devices in the research and exploratory stage and how these requirements would potentially change if these research devices were to start into a technology development effort. Index Terms--CMOSFETs, ferroelectric materials, ferromagnetic materials, molecular electronics, nanotechnology measurement, quantum dots, quantum wires, semiconductor device fabrication.

We demonstrate a bottom-up process for programming the deposition of coaxial thin films aligned to the underlying dopant profile of semiconductor nanowires. Our process synergistically combines three distinct methodsâ€"vaporâ€"liquidâ€"solid nanowire growth, selective coaxial lithography via etching of surfaces (SCALES), and area-selective atomic layer deposition (AS-ALD)â€"into a cohesive whole. Here, we study ZrO2 on Si nanowires as a model system. Si nanowires are first grown with an axially modulated n-Si/i-Si dopant profile. SCALES then yields coaxial poly(methyl methacrylate) (PMMA) masks on the n-Si regions. Subsequent AS-ALD of ZrO2 occurs on the exposed i-Si regions and not on those masked by PMMA. We show the spatial relationship between nanowire dopant profile, PMMA masks, and ZrO2 films, confirming the programmability of the process. The nanoscale resolution of our process coupled with the plethora of available AS-ALD chemistries promises a range of future opportunities to generate structurally complex nanoscale materials and electronic devices using entirely bottom-up methods. [ABSTRACT FROM AUTHOR]

Research describing the relationship between degradation and breakdown of ultrathin silicon dioxide is presented. In particular the effects of substrate hot hole injection are investigated.

Leakage currents and off-state power consumption for CMOS technology in the 100-nm regime are examined.

Ultrathin silicon dioxide was examined for reliability under substrate hot-electron and constant voltage tunneling stresses.

Conductance limitations in measurement of the interface state density of MOS capacitors with tunneling gate dielectrics.

A metal–oxide–semiconductor (MOS) gate stack that is self-aligned with the underlying silicon doping profile is demonstrated. We combine a new hybrid bottom-up patterning technique with atomic layer deposition (ALD) to selectively deposit a platinum-hafnium dioxide-silicon MOS gate stack. A poly(methyl methacrylate) (PMMA) brush is blanket grown from a Si(100) surface and selectively removed from the lightly doped (∼1018 cm−3) regions using a doping-selective KOH etch. The PMMA brush that remains on the heavily doped (∼1020 cm−3) regions effectively blocks the ALD of both HfO2 and platinum. MOS capacitors exhibit promising capacitance-voltage characteristics with a HfO2 dielectric constant of ∼25 and an average interface state density of 2.1 × 1011 eV−1 cm−2 following forming gas anneal. [ABSTRACT FROM AUTHOR]

Since the invention of the Esaki diode, resonant tunneling devices have been of interest for applications including multi-valued logic and communication systems. These devices are characterized by the presence of negative differential resistance in the current-voltage characteristic, resulting from lateral momentum conservation during the tunneling process. While a large amount of research has focused on III-V material systems, such as the GaAs/AlGaAs system, for resonant tunneling devices, poor device performance and device-to-device variability have limited widespread adoption. Recently, the symmetric field-effect transistor (symFET) was proposed as a resonant tunneling device incorporating symmetric 2-D materials, such as transition metal dichalcogenides (TMDs), separated by an interlayer barrier, such as hexagonal boron-nitride. The achievable peak-to-valley ratio for TMD symFETs has been predicted to be higher than has been observed for III-V resonant tunneling devices. This work examines the effect that band structure differences between III-V devices and TMDs has on device performance. It is shown that tunneling between the quantized subbands in III-V devices increases the valley current and decreases device performance, while the interlayer barrier height has a negligible impact on performance for barrier heights greater than approximately 0.5 eV. [ABSTRACT FROM AUTHOR]

A research investigating the effects of dielectric constant and barrier height on the WKB modeled tunnel currents of metal oxide semiconductor capacitors with effective oxide thickness of 2.0 mm is presented. Results show that alternative dielectrics with higher dielectric constants demonstrate lower tunneling currents than SiO2 at expected operation voltages. It was also observed that the effect of a thin layer of SiO2 on the current properties of the dielectric stack expands as the dielectric constant of an insulator increases.

The mobility behavior of MOSFET's with oxynitride gate dielectrics results from traps in the films. Gate dielectric fabrication involves the use of low-pressure rapid thermal chemical vapor deposition with SiH4, N2O, and NH3. An increase in nitrogen and hydrogen concentration reduces the peak electron mobility in n- and p-channel MOSFET's. Hole mobility decreases for all electric fields.

The rapid thermal processing, involving pre- and post-oxide deposition, improves the characteristics of composite gate oxides which act as gate dielectrics. The composite structure originating from pre-oxidation before the oxide deposition, and post-deposition oxidation in O2 and N2O, has low defect density and high mobility. N2O annealed oxides have high resistance towards hot carriers, low charge trapping capacity and low interface trap densities. The existence of nitrogen at the interface and the decreased interaction between nitrogen and hydrogen are responsible for the improved properties.

Silicon oxynitride films, formed by a low-pressure rapid thermal chemical vapor deposition (RTCVD) process, are useful as MOS gate dielectrics. The RTCVD uses SiH4, NH3 and N2O as the reactive gases. The deposition is possible at low temperatures and the films are a feasible alternative to a nitrided oxide as a gate dielectric in MOS technology. An analysis of MOS capacitors with n-channel and p-channel MOSFET's indicates an increase in fixed oxide charge with an increase in nitrogen and hydrogen content in the film.

Two-dimensional transition metal carbides are promising materials because of their potential for combining the favorable properties of transition metal carbides with the high aspect ratio of two-dimensional materials. Though commonly produced by top-down wet-chemical synthesis methods, synthesis by chemical vapor deposition is being considered because of its ability to achieve large areas, controlled layer thickness, and reduced defect density. Typically, liquid Cu is used as a synthesis substrate, though the high melting temperature of Cu (1085 °C) requires high synthesis temperatures. Thus, alternative substrates have been studied in order to reduce the necessary melting temperature. This work systematically studies the impact of synthesis parameters and substrate composition on the growth of ultrathin Mo2C (∼4–120 nm thick) by chemical vapor deposition on an In-Cu alloy. Mo2C flake size increases, and graphene/Mo2C heterostructures form with an increase in the methane flow rates. Increasing the In composition slightly decreases surface coverage and coalescence but does not appreciably impact the Mo2C flake size. Increasing In content also decreases the alloy substrate melting temperature so that a lower temperature synthesis (800 °C) can be performed. However, the necessary high temperatures for pyrolysis of methane lead to a lower limit for the synthesis temperature, similar to graphene. [ABSTRACT FROM AUTHOR]

This manuscript describes the development and operation of an apparatus for the measurement of steady-state and transient gas permeation through different types of solid materials with varying geometries. It is capable of operation from 293 K to 673 K and could theoretically be used with any non-corrosive gas or a mix of gases, although only hydrogen isotopes are used in the current study. A quadrupole mass spectrometer is used to measure permeation fluxes as low as 1011 molecules/s. This unique test setup allows for the simultaneous measurement of diffusivity, solubility, and permeability. Furthermore, varying the pressure in the fore-sample volume allows for tests of Sievert's law and can give information on surface effects. [ABSTRACT FROM AUTHOR]

While two-terminal HfOx (x < 2) memristor devices have been studied for ion transport and current evolution, there have been limited reports on the effect of the long-range thermal environment on their performance. In this work, amorphous-HfOx based memristor devices on two different substrates, microscopic glass (∼1 mm) and thin SiO2 (280 nm)/Si, with different thermal conductivities in the range from 1.2 to 138 W m−1 K−1 were fabricated. Devices on glass substrates exhibit lower reset voltage, wider memory window and, in turn, a higher performance window. In addition, the devices on glass show better endurance than the devices on the SiO2/Si substrate. These devices also show non-volatile multi-level resistances at relatively low operating voltages which is critical for neuromorphic computing applications. A multiphysics COMSOL computational model is presented that describes the transport of heat, ions and electrons in these structures. The combined experimental and COMSOL simulation results indicate that the long-range thermal environment can have a significant impact on the operation of HfOx-based memristors and that substrates with low thermal conductivity can enhance switching performance. [ABSTRACT FROM AUTHOR]

Filamentary adaptive oxide devices based on HfOx are a promising technology for neuromorphic computing applications. The resistance of these devices depends on the concentration of oxygen vacancies in the filament region. A local temperature rise from joule heating plays a significant role in the movement of oxygen ions, making thermal management crucial to reliable performance. In this work, the role of the substrate thermal conductivity on the analog performance was investigated at biologically realistic pulse widths. Au/Ti/HfOx/Au adaptive oxide devices were fabricated on substrates with two orders of magnitude difference in thermal conductivity. A lower thermal conductivity substrate dissipates heat more slowly, resulting in a large initial change in resistance from a single operation pulse, which is detrimental to the desired analog behavior. The results were validated by a COMSOL Multiphysics® model that models the flow of heat in both samples. [ABSTRACT FROM AUTHOR]

A detailed analysis of the extracted back gated FET mobility as a function of channel length, channel width, and underlying oxide thickness for both exfoliated and chemical vapor deposited (CVD) graphene is presented. The mobility increases with increasing channel length eventually saturating at a constant value for channel lengths of several micrometers. The length dependence is consistent with the transition from a ballistic to diffusive transport regime. The mobility as a function of channel width first increases and then decreases. The increase in mobility for very small channel widths is consistent with a reduction in edge scattering. The decrease in mobility for larger channel widths is observed to be strongly dependent on the oxide thickness suggesting that electrostatics associated with fringing fields is an important effect. This effect is further confirmed by a comparative analysis of the measured mobility of graphene devices with similar channel dimensions on oxides of different thicknesses. The observed electrical measurements are in excellent agreement with theoretical studies predicting the width dependence of conductivity and mobility. The mobility of CVD grown graphene is slightly lower than that of exfoliated graphene but shows similar trends with length and width. The mobility values reported in the literature are in agreement with the trend reported here. [ABSTRACT FROM AUTHOR]

Metal-graphene contact is a key interface in graphene-based device applications, and it is known that two types of interfaces are formed between metal and graphene. In this paper, we apply first-principles calculations to twelve metal-graphene interfaces and investigate the detailed interface atomic and electronic structures of physisorption and chemisorption interfaces. For physisorption interfaces (Ag, Al, Cu, Cd, Ir, Pt, and Au), Fermi level pinning and Pauli-exclusion-induced energy-level shifts are shown to be two primary factors determining graphene's doping types and densities. For chemisorption interfaces (Ni, Co, Ru, Pd, and Ti), the combination of Pauli-exclusion-induced energy-level shifts and hybridized states' repulsive interactions lead to a band gap opening with metallic gap states. For practical applications, we show that external electric field can be used to modulate graphene's energy-levels and the corresponding control of doping or energy range of hybridization. [ABSTRACT FROM AUTHOR]

Tunneling-dominated charge transport is demonstrated in vertically stacked MoS2/interlayer/MoS2 heterostructures with Al2O3, hexagonal boron nitride (h-BN), and HfO2 dielectrics. All devices are highly resistant to 10-keV X-ray irradiation. Only small transient changes in X-ray-induced photocurrent are observed as a result of trap creation in the thin interlayer dielectric, with rapid passivation. Samples with Al2O3 and h-BN interlayer dielectrics show significant increases in conduction current during proton irradiation, due to displacement-damage-induced defects that lower the effective tunnel-barrier height. Density-functional-theory calculations provide insights into the pertinent defects. Devices with HfO2 interlayer dielectrics show great promise for use in radiation tolerant, ultimately scaled tunnel FETs. [ABSTRACT FROM AUTHOR]

Thin film reaction based synthesis techniques are promising for large area, uniform two-dimensional transition metal dichalcogenide (TMD) layers such as MoS2. In this work, the impact of the initial molybdenum film composition (metallic versus oxidized) is explored. Alternating steps of Mo sputtering and H2S soaks are used in conjunction with plasma assisted synthesis techniques to synthesize films at low temperatures. Raman, photoluminescence, x-ray photoelectron spectroscopy, and atomic force microscopy are used to physically characterize the films' atomic structure, stoichiometry, and topography, while devices were fabricated to characterize their electronic properties. MoS2 synthesized from metallic Mo films were found to exhibit better atomic and electronic structure than MoS2 synthesized from MoOx films. Additionally, slowing the rate of synthesis by segmenting growth into repeating cycles resulted in much higher film quality. To understand the impact of atomic structure and stoichiometry on device performance, films synthesized at low temperature were exposed to various high temperature annealing conditions to induce changes in film structure and composition. Physical and electrical characterization reveal that stoichiometry has a significantly weaker influence on electronic performance than grain size and atomic structure. These results provide valuable information on the optimization of low temperature thin film reactions for TMD syntheses. [ABSTRACT FROM AUTHOR]