John Robertson

Combining two-dimensional materials and high-k gate dielectrics offers a promising way to enhance the device performance of tunneling field-effect transistor (TFET). In this work, the device performance of WSe2/SnSe2 TFET with various gate dielectric materials is investigated based on quantum transport simulation. Results show that TFETs with high-k gate dielectric materials exhibit improved on-off ratio and enhanced transconductance. The optimized WSe2/SnSe2 TFET with TiO2 gate dielectrics achieves an on-state current of 1560 μA/μm and a subthreshold swing (SS) of 48 mV/dec. The utilization of high-k gate dielectric materials results in shorter tunneling length, higher transmission efficiency, and increased electron tunneling probability. The performance of the WSe2/SnSe2 TFET would be affected by the presence of the underlap region. Moreover, WSe2/SnSe2 TFETs with La2O3 dielectric can be scaled …

Mott devices, featuring low hardware cost and high energy efficiency, have been demonstrated as a key oscillatory element in artificial neurons to enable spiking neural networks (SNNs) such as conversion-based SNNs (CSNNs). However, there will be inevitably non-ideal fluctuation in the oscillation behavior, causing the accuracy degradation of networks. In this paper, we investigate the Mott neuronal oscillation fluctuation (NOF) through experiments and modeling. The results show that the NOF phenomenon conforms to Gaussian distribution and originates from thermal fluctuation induced switching voltage variations. We construct a two-layer CSNN for image recognition tasks to study the NOF effect and propose the activation function boundary (AFB) method to strengthen the stability of the network. The results indicate that AFB can improve the accuracy of CSNN by up to 15.5% by tightening output distribution.

In this work we present an in-memory computing platform based on coupled VO2 oscillators fabricated in a crossbar configuration on silicon. Compared to existing platforms, the crossbar configuration promises significant improvements in terms of area density and oscillation frequency. Further, the crossbar devices exhibit low variability and extended reliability, hence, enabling experiments on 4-coupled oscillator. We demonstrate the neuromorphic computing capabilities using the phase relation of the oscillators. As an application, we propose to replace digital filtering operation in a convolutional neural network with oscillating circuits. The concept is tested with a VGG13 architecture on the MNIST dataset, achieving performances of 95% in the recognition task.

The use of semiconductor photocatalysis for hydrogen production is an ideal approach for achieving solar energy and conversion. In this work, we systematically examine the photocatalytic properties of WSe2/MoSi2N4 van der Waals heterojunctions using first-principles calculation and nonadiabatic molecular dynamics. The results demonstrate that the WSe2/MoSi2N4 heterojunction possesses a 1.81 eV indirect band gap and type-II band alignment, which ensures that the photoexcited electron–hole (e–h) pairs are spatially separated. The carrier lifetime of the photoexcited e–h pairs is 278 ps significantly longer than the interlayer hole transfer time of 335 fs, implying that the heterojunction has the high quantum efficiency. In addition, this heterojunction possesses superior optical absorption (105 cm−1), low overpotential for OER (0.60 V), and outstanding light absorption properties. These findings indicate that this …

This article describes the ability to use laser-blown powder deposition to repair high γ' IN-100 superalloy gas turbine components. The influence of various process conditions on the ability to make crack-free IN-100 deposits over surrogate high γ' alloys was investigated to identify cracking mechanisms in the deposit and heat-affected zones (HAZs). The various crack formation mechanisms, such as solidification cracking and liquation cracking, were evaluated using multiscale characterization and numerical simulation. The cracking in the deposit region was predominantly solidification cracking, while those observed in the HAZ were liquation cracking. The results showed that controlling thermally induced residual stresses is the key to eliminating cracking, and the optimum preheat temperature was determined. In conclusion, the results were then contrasted with those in published literature and an approach to effectively repair hot section parts was presented.

A crystallographically heterogeneous moiré interface of hexagonal graphene (Gr) and a tetragonal L10-FePd alloy is bonded via van der Waals (vdW) forces. Robust interfacial perpendicular magnetic anisotropy was discovered at the L10-FePd side of the Gr/L10-FePd heterogeneous interface (H. Naganuma et al. ACS Nano, 2022, 16, 4139). This study focuses on the Gr side of the Gr/L10-FePd interface. X-ray absorption spectroscopy measurements of Gr from two different angles demonstrated that in addition to the π* orbital peak being observed at a glance incident angle (θΑ = 30°), it was also observed at a nominal incident (NI) angle (θΑ = 90°). The appearance of the π* peak at NI is attributed to the wavy Gr and strong bonding of the chemisorption-type vdW force. The densities of states of px, py, and pz from first-principles calculations indicate another reason for the π* peak at NI. The pz orbital of C twists into …

Herein, facet‐engineered Cu2O nanostructures are synthesized by wet chemical methods for electrocatalytic HER, and it is found that the octahedral Cu2O nanostructures with exposed crystal planes of (111) (O‐Cu2O) has the best hydrogen evolution performance. Operando Raman spectroscopy and ex‐situ characterization techniques showed that Cu2O is reduced during HER, in which Cu dendrites are grown on the surface of the Cu2O nanostructures, resulting in the better HER performance of O‐Cu2O after HER (O‐Cu2O‐A) compared with that of the as‐prepared O‐Cu2O. Under illumination, the onset potential of O‐Cu2O‐A is ca. 52 mV positive than that of O‐Cu2O, which is induced by the plasmon‐activated electrochemical system consisting of Cu2O and the in‐situ generated Cu dendrites. Incident photon‐to‐current efficiency (IPCE) measurements and the simulated UV–Vis spectrum demonstrate the hot …

This chapter will consider the origins of Scottish Enlightenment conjectural history in the writings of Henry Home, Lord Kames. I will argue that the rise of what is often referred to as the Scottish ‘conjectural’approach to history was driven by a problem in the relation between the history of positive law and natural law and that Kames’ solution in his writings from the early 1730s to the late 1750s gradually took the form of stadial history.The aspects of the Scottish version of stadial history I will highlight were not due to Kames alone. Kames drew on David Hume’s arguments in his conjectures and the two shared goals up to and beyond Hume’s Natural History of Religion. 1 Furthermore Hume’s discussion of time in A Treatise of Human Nature was crucial for how both thought about history and for the development of stadial history. I will not suggest though that from the writings of Kames and Hume stadial history arose in its final form. There was of course also the influence of Montesquieu, with whom Hume corresponded, and who was central for other Scottish philosophers associated with stadial history–Adam Smith, Adam Ferguson and John Millar. But I will resist seeing Scottish stadial history as just Montesquieueanism in plaid. The influence is clear, in particular on the four stages theory, 2 but I will suggest that the form that