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Chou, Stanley Shihyao

Publications and source records attributed to Chou, Stanley Shihyao.

9 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Arbitrary Low-Dimensional Film Transfer Enabled by GeO 2 Release Layer

Low-dimensional materials show great promise for enhanced computing and sensing performance in mission-relevant environments. However, integrating low-dimensional materials into conventional electronics remains a challenge. Here, we demonstrate a novel transfer method by which low-dimensional materials and their heterostructures can be transferred onto any arbitrary substrate. Our method relies on a water soluble GeO 2 substrate from which lowdimensional materials are transferred without significant perturbation. We apply the method to transfer a working electronic device based on a low-dimensional material. Process developments are achieved to enable the fabrication and transfer of a working electronic device, including the growth of high-k dielectric on GeO 2 by atomic layer deposition and inserting an indium diffusion barrier into the device gate stack. This work supports Sandia’s heterogeneous integration strategy to broaden the implementation of low-dimensional films and their devices.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Efficient low-temperature, catalyst-free dehydrogenation of alkanes

Steam cracking of ethane, a non-catalytic thermochemical process, remains the dominant means of ethylene production. The severe reaction conditions and energy expenditure involved in this process incentivize the search for alternative reaction pathways and reactor designs which maximize ethylene yield while minimizing cost and energy input. According to the present invention, ethylene yields as high as 68% were obtained with a quartz open tube reactor without the use of a catalyst or a cofed stream of oxidizing agents. The open tube reactor design promotes simplicity, low cost, and negligible coke formation. Reactor designs can be optimized to improve the conversion of ethane to ethylene via non-oxidative dehydrogenation, an approach which shows promise for decentralized production of ethylene from natural gas deposits.

Riley, Christopher Ryan↗
DOE OSTI2023

Influence of surface adsorption on MoS 2 memtransistor switching kinetics

Sulfur-deficient polycrystalline two-dimensional (2D) molybdenum disulfide (MoS 2 ) memtransistors exhibit gate-tunable memristive switching to implement emerging memory operations and neuromorphic computing paradigms. Grain boundaries and sulfur vacancies are critical for memristive switching; however, the underlying physical mechanisms are not fully understood. Furthermore, the adsorption of water and gaseous species strongly perturbs electronic transport in monolayer MoS 2 , and little work has been done to explore the influence of surface interactions on defect-related kinetics that produces memristive switching. Here, we study the switching kinetics of back-gated MoS 2 memtransistors using current transient measurements in a controlled atmosphere chamber. Here, we observe that adsorbed water molecules lead to suppression of the electronic trap-filling processes concomitant with the resistive switching process, resulting in altered kinetics of the resistive switching. Additionally, using the transient response from “bunched” drain voltage pulse trains performed as a function of temperature, we extract the energy of the affected trap state and find that it places the trap roughly midgap [E T = E C – 0.7 (±0.4) eV]. Our results highlight the importance of controlling for surface interactions that may affect switching kinetics in 2D memtransistors, synaptic transistors, and related memory devices.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Electrocatalyst comprising a crumpled transition metal dichalcogenide support loaded with monodispersed metal nanoparticles

An electrocatalyst comprises a crumpled transition metal dichalcogenide support loaded with catalytic metal nanoparticles through spontaneous reduction reactions. The support can be prepared by hydrothermal conversion of 2D nanosheets to 3D hierarchically crumpled sheets. As an example, using crumpled MoS 2 as a support, highly tunable Ru loadings were obtained using the electrostatic interaction between MoS 2 and RuCl 3 in solution. Control over Ru loading was leveraged to produce Ru—MoS 2 electrocatalysts that demonstrate different nitrogen reduction reaction activities, and which show varying resistance to electrochemical sintering and deactivation. Further, these high surface area materials can be utilized for many applications, including electrocatalysts, supercapacitors, and batteries.

Percival, Stephen↗
DOE OSTI2020

Molecular tail chemistry controls thermal transport in fullerene films

Herein we report on the thermal conductivities of alkyl- and indene-group functionalized fullerene derivative thin films as measured via time domain thermoreflectance and steady state thermoreflectance. The thermal conductivities vary from 0.064 ± 0.007 W m – 1 K – 1 for [6,6]-phenyl C 61 -butyric acid methyl ester (PCBM) to 0.15 ± 0.017 W m – 1 K – 1 for indene- C 60 bisadduct at room temperature and do not exhibit significant temperature dependence from 300 to 375 K. In comparison to the thermal conductivity of PCBM, increasing the length of the alkyl chain, as in the case of [6,6]-phenyl C 61 -butyric acid butyl ester, and [6,6]-phenyl C 61 -butyric acid octyl ester leads to higher thermal conductivities. Likewise, increasing the number of alkyl chains attached to the fullerenes as in the case of bisadduct PCBM leads to a higher thermal conductivity compared to that of PCBM. We present atomistic insights into the role of chemical functionalization on the overall heat transfer in these fullerene derivatives by conducting molecular dynamics simulations and lattice dynamics calculations. The thermal conductivities predicted via our atomistic simulations qualitatively agree with the experimental trends for our fullerene derivatives. Lattice dynamics calculations reveal that one of the main factors dictating the ultralow thermal conductivities in fullerene derivatives is the large reduction in modal diffusivities in the molecular crystals as calculated from the Allen-Feldman model, thus providing an explanation for their largely reduced thermal conductivities as compared to that of C 60 crystals. The low diffusivities result from high degrees of localization of Einstein-like vibrations in fullerene derivatives due to the molecular side chains, providing the ability to dial-in the properties of these low thermal conductivity solids via molecular engineering.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗