Biselective refocusing pulses and the SERF experiment

The SERF experiment is a variant of the homonuclear J-resolved experiment, in which a single coupling constant is measured. It consists of a single chemical shift selective excitation that is followed by a biselective spin echo. Recent articles mention the existence of artefacts in SERF spectra that are supposedly related to pulse imperfections. This article presents a detailed study of the biselective refocusing pulses. It also reports a method for predicting the position and amplitude of the expected and unexpected 2D spectral peaks in SERF spectra. Artefacts can be partially eliminated by phase cycling or by the introduction of static field gradient pulses in the acquisition sequence. A procedure to obtain of pure absorption peaks in SERF spectra is proposed.     

Triplet pairing states with equal spins in ferromagnet/superconductor heterojunctions for noncollinear magnetizations

Four-component Bogoliubov-de Gennes equations are applied to study tunneling conductance spectra of ferromagnet/ferromagnet/d-wave superconductor (F₁/F₂/d-wave S) tunnel junctions and to find out signs of spin-triplet pairing correlations induced in the proximity structure. The pairing correlations with equal spins arises from the novel Andreev reflection (AR), which requires at least three factors: the usual AR at the F₂/S interface, spin flip in the F₂ layer, and superconducting coherence kept up in the F₂ layer. Effects of angle α between magnetizations of the two F layers, polarizations of the F₁ and F₂ layers, the thickness of the F₂ layer, and the orientation of the d-wave S crystal on the tunneling conductance are investigated. A conversion from a zero-bias conductance dip at α = 0 to a zero-bias conductance peak at a certain value of α can be seen as a sign of generated spin-triplet correlations.     

Gap-behavior in the vicinity of a saturation transverse field

We have studied the behavior of the energy gap of the 1D AF spin- XXZ model in a transverse magnetic field (h) using the exact diagonalization technique. The ground state phase diagram consists of two spin-flop and paramagnetic phases. Using a modified finite-size scaling approach, we have computed the critical exponent of the energy gap in the vicinity of the critical transverse field h_c(Δ). Our numerical results confirm that the continuous phase transition from the spin-flop phase to the paramagnetic one is in the universality class of the Ising model in the transverse field (ITF). By applying conformal estimates of a small perturbation (h≪1), we have also justified our numerical results.     

多元杂环萘二酰亚胺衍生物的合成及其场效应性能研究

杂环修饰的萘二酰亚胺(NDI)类化合物由于其独特的光电性能被研究人员广泛关注,并应用于有机场效应晶体管(OFETs)、有机太阳能电池中(OSCs)、传感器等领域。但是含有给受体单元的多元杂环萘二酰亚胺衍生物的合成并不容易,本文通过简单高效的方法设计合成了含有氮、硫原子的11个杂环类萘二酰亚胺衍生物,并通过紫外可见吸收光谱、循环伏安曲线和X射线衍射对其进行了物性研究。通过溶液旋涂法,制备了该材料的底栅底接触场效应晶体管器件,在空气中表现出p型半导体性能,当退火温度为140 ℃时性能达到最优,其空穴迁移率为0.2 cm_²?V_^-1?s_^-1。     

Effect of gate engineering in JLSRG MOSFET to suppress SCEs: An analytical study

In this work, an analytical model of gate-engineered junctionless surrounding gate MOSFET (JLSRG) has been proposed to uncover its potential benefit to suppress short-channel effects (SCEs). Analytical modelling of centre potential for gate-engineered JLSRG devices has been developed using parabolic approximation method. From the developed centre potential, the parameters like threshold voltage, surface potential, Electric Field, Drain-induced Barrier Lowering (DIBL) and subthershold swing are determined. A nice agreement between the results obtained from the model and TCAD simulation demonstrates the validity and correctness of the model. A comparative study of the efficacy to suppress SCEs for Dual-Material (DM) and Single-Material (SM) junctionless surrounding gate MOSFET of the same dimensions has also been carried out. Result indicates that TM-JLSRG devices offer a noticeable enhancement in the efficacy to suppress SCEs by as compared to SM-JLSRG and DM-JLSRG device structures. The effect of different length ratios of three channel regions related to three different gate materials of TM-JLSRG structure on the SCEs have also been discussed. As a result, we demonstrate that TM-JLSRG device can be considered as a competitive contender to the deep-submicron mainstream MOSFETs for low-power VLSI applications.     

Control of electron spin–orbit anisotropy in pyramidal InAs quantum dots

We investigate the electron spin–orbit interaction anisotropy of pyramidal InAs quantum dots using a fully three-dimensional Hamiltonian. The dependence of the spin–orbit interaction strength on the orientation of externally applied in-plane magnetic fields is consistent with recent experiments, and it can be explained from the interplay between Rashba and Dresselhaus spin–orbit terms in dots with asymmetric confinement. Based on this, we propose manipulating the dot composition and height as efficient means for controlling the spin–orbit anisotropy.     

A scheme for a topological insulator field effect transistor

We propose a scheme for a topological insulator field effect transistor. The idea is based on the gate voltage control of the Dirac fermions in a ferromagnetic topological insulator channel with perpendicular magnetization connecting to two metallic topological insulator leads. Our theoretical analysis shows that the proposed device displays a switching effect with high on/off current ratio and a negative differential conductance with a good peak to valley ratio.     

Electrode metal penetration of amorphous indium gallium zinc oxide semiconductor thin film transistors

Penetration effects of various electrode materials, namely Al, Au, and Cu, on the physical and electrical characteristics of amorphous oxide semiconductor thin film transistors (TFTs) were investigated. Amorphous indium gallium zinc oxide (a-IGZO) TFTs were fabricated with conventional staggered bottom gate structures on a p-type Si substrate. X-ray photoemission spectroscopy (XPS) analysis under the electrode deposition area revealed variations in the oxygen bonding states and material compositions of the a-IGZO layer. Field-emission scanning electron microscopy (FE-SEM) with the line scan of energy dispersive spectroscopy (EDS) showed lateral penetration by the electrode metal. To compare the electrical characteristics of the tested TFTs, the initial current–voltage (I–V) transfer characteristics were examined. In addition, the tested TFTs fabricated using various electrode materials were tested under bias stress to verify the correlations between variations in TFT characteristics and both the metal work function and penetration-induced oxygen vacancies in the channel around the contact area.     

Investigation of laterally single-diffused metal oxide semiconductor (LSMOS) field effect transistor

We propose a distinct approach to implement a laterally single diffused metal-oxide-semiconductor (LSMOS) FET with only one impurity doped p-n junction. In the LSMOS, a single p-n junction is first created using lateral dopant diffusion. The channel is formed in the p region of the p-n junction and the n region acts as the drift region. Two distinct metals of different work function are used to form the “n⁺” source/drain regions and “p⁺” body contact using the charge plasma concept. We demonstrate that the LSMOS is similar in performance to a laterally double diffused metal-oxide-semiconductor (LDMOS) although it has only one impurity doped p-n junction. The LSMOS exhibits a breakdown voltage of ∼50.0 V, an average ON-resistance of 48.7 mΩ-mm² and a peak transconductance of 53.6 μS/μm similar to that of a comparable LDMOS.