Ion‐Current Rectification in Nanopores and Nanotubes with Broken Symmetry

This article focuses on ion transport through nanoporous systems with special emphasis on rectification phenomena. The effect of ion‐current rectification is observed as asymmetric current–voltage (I–V) curves, with the current recorded for one voltage polarity higher than the current recorded for the same absolute value of voltage of opposite polarity. This diode‐like I–V curve indicates that there is a preferential direction for ion flow. Experimental evidence that ion‐current rectification is inherent to asymmetric, e.g., tapered, nanoporous systems with excess surface charge is provided and discussed. The fabrication and operation of asymmetric polymer nanopores, gold nanotubes, glass nanocapillaries, and silicon nanopores are presented. The possibility of tuning the direction and extent of rectification is discussed in detail. Theoretical models that have been developed to explain the ion‐current rectification effect are also presented.     

Morphology of alkali halide thin films studied by AFM

Thin layers of alkali halides were investigated by atomic force microscope (AFM). The studied systems were: LiBr/KBr(0 0 1) with −16.7% misfit, LiF/Si(0 0 1) with +4.4% misfit, LiBr/LiF(0 0 1) with +36.8% misfit and NaCl/Si(0 0 1) with +46.5% misfit. The results show that the surface morphology strongly depends on the temperature of layer formation. The alkali halides deposited on the foreign substrate at elevated temperatures or at room temperature and subsequently annealed form preferentially 3D islands leaving uncovered substrate areas between them. It is suggested that Ostwald ripening takes place at elevated temperatures.     

Profile calculation of gold nanostructures by dispersed-nanosphere lithography through oblique etching for LSPR applications

Nanosphere lithography is an inexpensive method used to fabricate gold nanostructures on a substrate. Using dispersed-nanosphere lithography, in which the nanospheres are dispersed on a substrate, 2D or 3D nanostructures can be fabricated by obliquely depositing a gold film on the nanospheres and etching the gold film afterward. These nanostructures are tunable and acute, and are thus good emitting elements for the localized surface plasmon resonance applications. So far, for the fabrication of nanostructures on a substrate with dispersed nanospheres, only 2D nanostructures have been reported through perpendicular etching. We report in this paper that the 3D nanostructures fabricated by dispersed-nanosphere lithography are rigid non-conformal structures, and perpendicular gold etching can be expanded to oblique etching, which provides more possibilities for fabricating the gold nanostructures in various shapes. The profiles of gold nanostructures after several varying angle depositions, and their final profiles after perpendicular or oblique etching, are calculated in this paper. Our profile simulations are applicable for nanospheres (or microspheres) within the range of tens of nanometers to tens of micrometers, and are consistent with our fabricated nanostructures observed using scanning electron and atomic force microscopy. Electronic Supplementary Material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

基于扫描探针显微镜的纳米加工技术研究进展

扫描探针显微镜(SPM)纳米加工技术是当前非常活跃的纳米加工研究领域，其研究成果有可能成为微纳米器件制作的主要方法。文章主要介绍了单原子操纵、阳极氧化法，以及机械刻蚀加工等SPM纳米加工方法的机理、特点及研究进展，提出了今后需要重视的研究方向。     

Nanofabrication of a quantum dot array: Atomic force microscopy of electropolished aluminum

One step required for the fabrication of a quantum dot array on an aluminum substrate is the preparation of a flat aluminum surface. To enable the optimization of the electropolishing procedure, atomic force microscopy was used to examine the morphology of electropolished polycrystalline aluminum surfaces that were prepared under different electropolishing conditions. The electropolishing voltage, time, and temperature were varied. Two distinctly different surface morphologies were observed for different electropolishing conditions and transitional structures were observed for intermediate conditions. It was found that the type of surface morphology and the surface roughness could be controlled primarily with the electropolishing voltage while temperature and time had relatively little effect over the range examined in this study.     

Template synthesis of nanostructured silica with hollow core and mesoporous shell structures

Silica capsules with hollow macroporous core–mesoporous shell (HCMS) were synthesized through template-assisted replication of submicrometer-size polystyrene spheres as templates. The silica mesoporous shell exhibited highly ordered hexagonal structure as confirmed by X-ray diffraction pattern and TEM image. The pore diameter and BET surface area of this sample were found to be 2.1 nm and 1387 m²/g, respectively.     

Precise nanofabrication with multiple ion beams for advanced circuit edit

Gallium focused ion beam (Ga-FIB) systems have been used historically in the semiconductor industry for circuit edit. Significant efforts have been invested to improve the performance of Ga-FIB. However, as the dimensions of integrated circuits continue to shrink, Ga-FIB induced processes are being driven to their physical limits. A helium ion beam offers high spatial resolution imaging as well as precise ion machining and sub-10 nm nanofabrication capabilities because the probe size can be brought to as small as 0.25 nm. However, it is limited by its relatively low material removal rate. Recently, the new Zeiss Orion-NanoFab microscope provides multiple ion beams (He, Ne and Ga as an option) into one platform and promotes the further studies of He and Ne induced deposition and etching processes to compare with a Ga ion beam. Because of the mass difference between He, Ne and Ga ions, the interactions of ions with sample surface and precursor molecules result in different sputtering rates, implantation and deposition yields. This presentation gives an overview of our current studies using this new platform to deposit or mill nanostructures for circuit edit.     

Recent developments in nanofabrication using scanning near-field optical microscope lithography

In addition to its well-known capabilities in imaging and spectroscopy, scanning near-field optical microscopy (SNOM) has recently shown its great potentials for fabricating various structures at the nanoscale. A variety of SNOM-based fabrication techniques have been developed for different applications. In this paper, the SNOM-based techniques involving three major functions: material modification, addition, and removal, are examined with emphasis on their abilities and reliability to make structures with resolutions at the nanometer level. The principles and procedures underlying each technique are presented, and the differences and uniqueness among them are subsequently discussed. Finally, concluding remarks are provided to summarize the major techniques studied and to recommend the scopes for technology improvement and future research.     

利用STM进行纳米加工的研究

本文对空气中应用扫描隧道显微镜（STM）进行的纳米级加工进行了研究。采用石墨（HOPG）和金薄膜作为样品．通过在STM探针和样品之间施加一定的电压脉冲制造出了具有纳米级尺度的结构。本文对形成的特征结构进行了分析．总结出部分实验规律．认为电场静电力作用使STM针尖或样品产生的机械变形是特征结构形成的主要原因。     

Development of metal etch mask by single layer lift-off for silicon nitride photonic crystals

We present a method for fabrication of nanoscale patterns in silicon nitride (SiN) using a hard chrome mask formed by metal liftoff with a negative ebeam resists (maN-2401). This approach enables fabrication of a robust etch mask without the need for exposing large areas of the sample by electron beam lithography. We demonstrate the ability to pattern structures in SiN with feature sizes as small as 50 nm. The fabricated structures exhibit straight sidewalls, excellent etch uniformity, and enable patterning of nanostructures with very high aspect ratios. We use this technique to fabricate two-dimensional photonic crystals in a SiN membrane. The photonic crystals are characterized and shown to have quality factors as high as 1460.