Carbon nanotube based miniaturized electron gun and column assembly

We report on the application of silicon micromachining for the fabrication of miniaturized electron gun (MEG) assembly using vertically aligned carbon nanotubes. The proposed MEG consists of two main parts of electron gun and the accelerating column. While the electron gun consists of carbon nanotubes grown on a silicon substrate acting as an electron emission source, the accelerating column is made of micromachined silicon wafers with 5 μm thick membranes operating as objective lenses. These two wafers are placed together and sealed using a three-dimensional packaging technique. The simulation and experimental results show the evolution of a narrow electron beam by applying a proper voltage to the anodes and objective lens. The diverging and focusing of the beam can be controlled by applying the proper voltage on electrostatic lenses. This structure could be suitable for low energy SEM devices and surface physics applications.     

Mechanism of Martensitic to Equiaxed Microstructure Evolution during Hot Deformation of a Near-Alpha Ti Alloy

Metallurgical and Materials Transactions A - In this study, mechanisms of microstructural evolution during hot deformation of Ti-1100 were investigated by EBSD analysis. Misorientation angle...     

Deep Vertical Etching of Silicon Wafers Using a Hydrogenation-Assisted Reactive Ion Etching

A novel hydrogenation-assisted deep reactive ion etching of silicon is reported. The process uses sequential hydrogen-assisted passivation and plasma etching at low-density plasma powers to stimulate the vertical removal of the exposed Si substrate. The main feature of this technique is the sequential alternation of the electrodes while switching between different gases. Three-dimensional structures with aspect ratios in excess of 40:1 and features as small as 0.7 mum have been realized. The net etch rate is about 0.25 mum/min, although higher rates are expected to be achievable.     

Nanoelectromechanical Chip (NELMEC) Combination of Nanoelectronics and Microfluidics to Diagnose Epithelial and Mesenchymal Circulating Tumor Cells from Leukocytes

An integrated nano‐electromechanical chip (NELMEC) has been developed for the label‐free distinguishing of both epithelial and mesenchymal circulating tumor cells (ECTCs and MCTCs, respectively) from white blood cells (WBCs). This nanoelectronic microfluidic chip fabricated by silicon micromachining can trap large single cells (>12 µm) at the opening of the analysis microchannel arrays. The nature of the captured cells is detected using silicon nanograss (SiNG) electrodes patterned at the entrance of the channels. There is an observable difference between the membrane capacitance of the ECTCs and MCTCs and that of WBCs (measured using SiNG electrodes), which is the key indication for our diagnosis. The NELMEC chip not only solves the problem of the size overlap between CTCs and WBCs but also detects MCTCs without the need for any markers or tagging processes, which has been an important problem in previously reported CTC detection systems. The great conductivity of the gold‐coated SiNG nanocontacts as well as their safe penetration into the membrane of captured cells, facilitate a precise and direct signal extraction to distinguish the type of captured cell. The results achieved from epithelial (MCF‐7) and mesenchymal (MDA‐MB231) breast cancer cells circulated in unprocessed blood suggest the significant applications for these diagnostic abilities of NELMEC.     

Polyphenols attached graphene nanosheets for high efficiency NIR mediated photodestruction of cancer cells

Green tea-reduced graphene oxide (GT-rGO) sheets have been exploited for high efficiency near infrared (NIR) photothermal therapy of HT29 and SW48 colon cancer cells. The biocompatibility of GT-rGO sheets was investigated by means of MTT assays. The polyphenol constituents of GT-rGO act as effective targeting ligands for the attachment of rGO to the surface of cancer cells, as confirmed by the cell granularity test in flow cytometry assays and also by scanning electron microscopy. The photo-thermal destruction of higher metastatic cancer cells (SW48) is found to be more than 20% higher than that of the lower metastatic one (HT29). The photo-destruction efficiency factor of the GT-rGO is found to be at least two orders of magnitude higher than other carbon-based nano-materials. Such excellent cancer cell destruction efficiency provided application of a low concentration of rGO (3 mg/L) and NIR laser power density (0.25 W/cm²) in our photo-thermal therapy of cancer cells.     

Formation of Luminescent Silicon Nanowires and Porous Silicon by Metal-Assisted Electroless Etching

Metal-assisted etching of silicon in HF/H₂O₂ aqueous solutions has been used to fabricate luminescent silicon nanowires (SiNWs) and porous silicon. The impact of the gold catalyst layer thickness and the etching solution on the morphology of the synthesized nanostructures and the diameter of the obtained nanowires were systematically investigated. Scanning electron microscopy (SEM) analyses reveal that the morphology of the fabricated structures strongly depends on the composition of the solution and the thickness of the catalyst layer. It has been observed that SiNWs are formed in solutions with H₂O₂ ratios (ξ) below 10 %; increasing the H₂O₂ concentration above this critical value leads to mesoporous (10 % < ξ < 14 %) and macroporous (14 % < ξ < 17 %) structures. Photoluminescence measurements show that SiNWs emit light at about 430 nm. Fourier transform infrared (FTIR) spectroscopy and transmission electron microscopy (TEM) analyses were utilized to determine the origin of the emission in the silicon nanostructures. TEM imaging demonstrates that SiNWs are covered by a thin layer of porous silicon, which is assumed to be responsible for their light emission.     

Accurate analysis of carbon nanotube interconnects using transmission line model

A new technique for analysing the time-domain response of carbon nanotube (CNT) interconnects, based on transmission line modelling, that takes the effects of both contact and fundamental (quantum) resistances into account is introduced. A new sixth-order linear parametric expression for the transfer function of these lines has been presented for the first time. For verification purposes, the step response of a driver-CNT bundle-load configuration for a 32 nm technology node, using the new technique and HSPICE simulation have been compared, with which the obtained results show an excellent match. Also the effect of contact resistance on the step response, especially the propagation delay, has been studied. The obtained results show that for the length of a CNT bundle equal to 50 mum with the diameter of each individual CNT 1 nm, the propagation delay changes from 0.138 to 5.58 ns for the contact resistance values from 1 to 50 k Omega, i.e. a variation range of 39.43 times the minimum value. The related delay variations for the length values 200 mum, 500 mum and 1000 mum, are 31.37, 22.61 and 15.42 times the minimum value, respectively.     

Symmetry reduction for maximization of higher-order stop-bands in two-dimensional photonic crystals

A large absolute higher-order stop-band is achieved in two-dimensional (2D) photonic crystals of square lattice. A genetic algorithm is used to search through a large number of possible structures. In this algorithm, the unit cell is divided into a grid of square pixels and a 2D binary chromosome is assigned to each filling pattern of the pixels. An initial structure with a small higher-order stop-band is included in the initial population to accelerate the search procedure. This initial structure is formed by breaking the symmetry of the supercell of a photonic crystal having a square lattice of square dielectric rods in air. In the optimization process, the effect of reducing the symmetry of the unit cell on the photonic band-gap is investigated. A structure showing an absolute higher-order band-gap as large as 0.1522(2πc/a) is obtained, which is larger than the values reported so far for photonic stop-bands.