Nonprecious NiFe, CoFe oxyhydroxide are among the most active materials for oxygen evolution reaction (OER) in basic media. However, phase separation in these composites during water oxidation rema...

Operando Raman Spectroscopy Reveals Cr-Induced-Phase Reconstruction of NiFe and CoFe Oxyhydroxides for Enhanced Electrocatalytic Water Oxidation

A glucose biosensor has been fabricated by immobilizing glucose oxidase (GOx) on unhybridized titanium dioxide nanotube arrays using an optimized cross-linking technique. The TiO2 nanotube arrays were synthesized directly on a titanium substrate by anodic oxidation. The structure and morphology of electrode material were characterized by X-ray diffraction and scanning electron microscopy. The electrochemical performances of the glucose biosensor were conducted by cyclic voltammetry and chronoamperometry measurements. It gives a linear response to glucose in the 0.05 to 0.65 mM concentration range, with a correlation coefficient of 0.9981, a sensitivity of 199.6 μA mM−1 cm−2, and a detection limit as low as 3.8 µM. This glucose biosensor exhibited high selectivity for glucose determination in the presence of ascorbic acid, sucrose and other common interfering substances. This glucose biosensor also performed good reproducibility and long-time storage stability. This optimized cross-linking technique could open a new avenue for other enzyme biosensors fabrication.

Glucose biosensor based on glucose oxidase immobilized on unhybridized titanium dioxide nanotube arrays

As the major redox couple and nonprotein thiol source in human tissues, the level of glutathione (GSH) has been a concern for its relation with many diseases. However, the similar physical and chemical properties of interference molecules such as cysteine (Cys) and homocysteine (Hcy) make discriminative detection of GSH in complex biological fluids challenging. Here we report a novel surface-enhanced Raman scattering (SERS) platform, based on silver-nanoparticle-embedded porous silicon disks (PSDs/Ag) substrates for highly sensitive and selective detection of GSH in biofluids. Silver nanoparticles (AgNPs) were reductively synthesized and aggregated directly into pores of PSDs, achieving a SERS enhancement factor (EF) up to 2.59 × 107. Ellman’s reagent 5,5′-ditho-bis (2-nitrobenzoic acid) (DTNB) was selected as the Raman reactive reporting agent, and the GSH quantification was determined using enzymatic recycling method, and allowed the detection limit of GSH to be down to 74.9 nM using a portable Raman sp...

Silver-Nanoparticle-Embedded Porous Silicon Disks Enabled SERS Signal Amplification for Selective Glutathione Detection

One of the major bottlenecks towards the development of the Na-ion battery system is that graphitic carbon (the commonly used anode material for the Li-ion system) is not suitable for use in Na-ion system. Accordingly, in the pursuit to identify and develop a suitable anode material for the upcoming Na-ion battery system, we report here the feasibility of reversible electrochemical Na-alloying in core/shell-structured Si nanowires having crystalline (c-Si) core and amorphous (a-Si) shell. Vapor–liquid–solid mechanism during nanowire growth allowed systematic variations of the a-Si shell thickness around the c-Si core of constant diameter (∼25 nm; as per the size of Sn catalyst-cum-‘nano-template’ particles). This allowed the development of four different sets of nanowires having overall diameters varying between ∼40 (SiNW-40) and ∼460 nm (SiNW-460); thus providing platforms also for investigating the influences of the dimensional scale and structure of Si (viz., amorphous vs. crystalline) towards Na-storage. While negligible reversible Na-capacity could be recorded with the thickest nanowire set, significantly greater Na-capacities could be recorded upon reduction in the overall diameter; leading to a reversible Na-capacity of ∼390 mA h g−1 for the thinnest nanowire set (i.e., SiNW-40), which is also the highest reported to-date for ‘stand-alone’ Si-based electrodes. Shortened Na-transport distance through the a-Si shell and increased influence of the more conductive c-Si core towards the lowering of charge transfer resistance, with reduced nanowire thickness, are the causes for such a remarkable dimensional effect. Experimental evidences and analytical computational studies indicate that Na-capacity gets contributed primarily by the ‘bulk’ of the amorphous Si shell, but (interestingly) not by the crystalline Si core.

Crystalline core/amorphous shell structured silicon nanowires offer size and structure dependent reversible Na-storage

Effect of water content on the corrosion behavior of X65 pipeline steel in supercritical CO2-H2O-O2-H2S-SO2 environment as relevant to CCS application

The carrier mobility of Si material can be enhanced under strain, and the stress magnitude can be measured by the Raman spectrum. In this paper, we aim to study the penetration depths into biaxially-strained Si materials at various Raman excitation wavelengths and the stress model corresponding to Raman spectrum in biaxially-strained Si. The experimental results show that it is best to use 325 nm excitation to measure the material stress in the top strained Si layer, and that one must pay attention to the distortion of the buffer layers on measuring results while 514 nm excitation is also measurable. Moreover, we established the stress model for Raman spectrum of biaxially-strained Si based on the Secular equation. One can obtain the stress magnitude in biaxially-strained Si by the model, as long as the results of the Raman spectrum are given. Our quantitative results can provide valuable references for stress analysis on strained materials.

Penetration depth at various Raman excitation wavelengths and stress model for Raman spectrum in biaxially-strained Si

The structure model used for calculation was defined according to Vegard’s rule and Hooke’s law. Calculations were performed on the electronic structures of (101)-biaxially strained Si on relaxed Si1−X GeX alloy with Ge fraction ranging from X = 0 to 0.4 in steps of 0.1 by CASTEP approach. It was found that [±100] and [00±1] valleys (δ4) splitting from the [0±10] valley (Δ2) constitute the conduction band (CB) edge, that valence band (VB) edge degeneracy is partially lifted and that the electron mass is unaltered under strain while the hole mass decreases in the [100] and [010] directions. In addition, the fitted dependences of CB splitting energy, VB splitting energy and indirect bandgap on X are all linear.

Calculation of band structure in (101)-biaxially strained Si

The strained Si techique has been widely adopted in the high-speed and high-performance devices and circuits. Based on the valence band E-k relations of strained Si/(111)Si1− x Ge x , the valence band and hole effective mass along the [111] and [−110] directions were obtained in this work. In comparison with the relaxed Si, the valence band edge degeneracy was partially lifted, and the significant change was observed band structures along the [111] and [−110] directions, as well as in its corresponding hole effective masses with the increasing Ge fraction. The results obtained can provide valuable references to the investigation concerning the Si-based strained devices enhancement and the conduction channel design related to stress and orientation.

Valence band structure of strained Si/(111)Si 1− x Ge x

The tunnel field-effect transistor (TFET) is a potential candidate for the post-CMOS era. As one of the most important electrical parameters of a device, double gate TFET (DG-TFET) gate threshold voltage was studied. First, a numerical simulation study of transfer characteristic and gate threshold voltage in DG-TFET was reported. Then, a simple analytical model for DG-TFET gate threshold voltage V
 TG was built by solving quasi-two-dimensional Poisson equation in Si film. The model as a function of the drain voltage, the Si layer thickness, the gate length and the gate dielectric was discussed. It is shown that the proposed model is consistent with the simulation results. This model should be useful for further investigation of performance of circuits containing TFETs.

Double-gate tunnel field-effect transistor: Gate threshold voltage modeling and extraction

An analytical model for quasi-static C – V characteristics of strained-Si/SiGe pMOS capacitor is presented. By analyzing the model, the dependence of the C – V characteristics on the strained-Si layer thickness, doping concentration and Ge fraction is studied. Also, the reason of the shift of the plateau, observed in the gate C – V characteristics of the strained-Si pMOS capacitor, from the inversion region to the accumulation region as doping concentration increasing, has been explained. The results from the models show excellent agreement with the simulations and experimental data. The proposed models can be used to guide the design and has been implemented in the software for extracting the parameter of strained-Si MOSFET.

HuiYong Hu

Papers

Penetration depth at various Raman excitation wavelengths and stress model for Raman spectrum in biaxially-strained Si

Calculation of band structure in (101)-biaxially strained Si

Valence band structure of strained Si/(111)Si 1− x Ge x

Double-gate tunnel field-effect transistor: Gate threshold voltage modeling and extraction

Analytical model for quasi-static C–V characteristics of strained-Si/SiGe pMOS capacitor