Pinning Effects in Nb Thin Films with Artificial Pinning Arrays

We summarize some results on the behavior of vortex dynamics and pinning effects in superconducting films with artificial pinning centers. Superconducting thin films with regular arrays of holes were fabricated using electron-beam lithography and reactive dry etching techniques. Vortex dynamics in the mixed state in type II superconductors is strongly influenced by the presence of defects, which act as pinning centers. Periodic critical current matching peaks were observed in magnetotransport measurements. The matching effect is caused by the interplay between the pinning centers and vortex lattice. Therefore, vortex lattice behaviors are changed for different temperatures and the geometry of the pinning centers. Molecular dynamic simulations are made to study this phenomenon. The ground state distribution of vortices obtained from simulations can give a reasonable explanation of the prominent matching peaks we found in the experiments.     

Fabrication of 3D gold nanoelectrode ensembles by chemical etching

A simple chemical etching procedure based on the solubility of polycarbonate membranes in solvent mixtures is reported for fabricating 3D gold nanoelectrode ensembles. A solvent ratio of 50:50 dichloromethane/ethanol was found to be optimum for selective controlled etching of the surface layers of the polycarbonate membranes to expose up to 200-nm lengths of gold nanowires. The absence of double layer charging current in cyclic voltammograms of the resulting 3D nanoelectrode ensemble verified that the seal between the gold nanowires and the polycarbonate membrane was not compromised as a result of the chemical etching.     

Guided three-dimensional catalyst folding during metal-assisted chemical etching of silicon

In recent years metal-assisted chemical etching (MaCE) of silicon, in which etching is confined to a small region surrounding metal catalyst templates, has emerged as a promising low cost alternative to commonly used three-dimensional (3D) fabrication techniques. We report a new methodology for controllable folding of 2D metal catalyst films into 3D structures using MaCE. This method takes advantage of selective patterning of the catalyst layer into regions with mismatched characteristic dimensions, resulting in uneven etching rates along the notched boundary lines that produce hinged 2D templates for 3D folding. We explore the dynamics of the folding process of the hinged templates, demonstrating that the folding action combines rotational and translational motion of the catalyst template, which yields topologically complex 3D nanostructures with intimately integrated metal and silicon features.     

Fabrication of Artificial Washboard Pinning Structures in Thin Niobium Films

We demonstrate a possibility to realize various types of the anisotropic washboard periodic pinning potentials in thin niobium films sputtered onto ??-alumina (11 $\bar{2}$ 0) substrates. Arrays of highly periodic channels as well as ferromagnetic cobalt lines were fabricated using focused ion-beam etching and gas-assisted focused electron beam deposition techniques, respectively. Three different nanostructure profiles which could provoke guided vortex motion were fabricated. By this way either uniaxial or bianisotropic, or asymmetric (ratchet) pinning structures have been realized. The results of scanning electron and atomic force microscopy investigations of the fabricated nanopatterns are discussed.     

3D nanofluidic channels shaped by electron-beam-induced etching

In-plane nanofluidic channels with 3D topography are fabricated. Nanochannel masters are written by electron beam lithography in SU-8 resist and shaped by electron-beam-induced etching (EBIE) with water as the precursor gas. Nanofunnel replicas cast from unmodified and EBIE-modified masters show that the funnel tip dimensions decrease from a 150-nm depth and 80-nm width to a 70-nm depth and 40-nm width.     

Highly-ordered, 3D petal-like array for surface-enhanced Raman scattering

Despite the great potential of the application of surface-enhanced Raman scattering (SERS), the difficulty in fabricating suitable SERS substrates is still a problem. Based on the self-assembly of silica nanoparticles, a simple method is here proposed to fabricate a highly-ordered, 3D, petal-like arrayed structure (3D PLAS) that serves as a promising SERS substrate for both its high reproducibility and enormous SERS enhancement. Such a novel structure is easily achieved by anisotropically etching a self-assembly bilayer of silica nanoparticles, followed by metal deposition. The SERS performance of the 3D PLAS and its relationship with the main parameters, including the etching time, the diameter of silica nanoparticles, and the deposited metal film, are characterized using 632.8 nm incident light. With Rhodamine 6G as a probe molecule, the spatially averaged SERS enhancement factor is on the order of 5 × 10(7) and the local enhancement factor is much higher, both of which can be improved further by optimizing the parameters.     

Enhanced Flux Pinning Properties of BaZrO3-doped YBCO Films Grown by Pulsed Laser Deposition on LaAlO3(100) Substrates Decorated with Y2O3 Nanoislands

In this work, we intend to investigate the interaction between two types of nanoscaled artificial pinning centers and their pinning properties in YBCO thin films grown by pulsed laser deposition technique. The two types of artificial pinning centers were prepared in different processes, (1) Y₂O₃ nanoislands decorated on substrates prior to the deposition of YBCO thin film, and (2) BaZrO₃ nanoparticles self-assembled within YBCO matrix during the deposition of YBCO thin film. We compared the transport characteristics of the YBCO thin films containing these two types of artificial pinning centers with those of pure YBCO thin films grown on decorated substrates and BZO-doped YBCO thin films grown on undecorated substrates. It was found that these two types of artificial pinning centers, which are simultaneously present, acted constructively to enhance the pinning properties of YBCO thin films.     

Growth of CNTs on Fe-Si catalyst prepared on Si and Al coated Si substrates

In this paper we report the effect of Al interlayers on the growth characteristics of carbon nanotubes (CNTs) using as-deposited and plasma etched Fe-Si catalyst films as the catalysts. Al interlayers having various thicknesses ranging from 2 to 42?nm were deposited on Si substrates prior to the deposition of Fe-Si catalysts. It was found that the Al interlayer diffuses into the Fe-Si catalyst during the plasma etching prior to the CNT growth, leading to the swelling and amorphization of the catalyst. This allows enhanced carbon diffusion in the catalyst and therefore a faster growth rate of the resulting CNTs. It was also found that use of an Al interlayer having a thickness of ～3 ± 1?nm is most effective. Due to the effectiveness of this, the normally required catalyst etching is no longer needed for the growth of CNTs.     

Integrated freestanding single-crystal silicon nanowires: conductivity and surface treatment

Integrated freestanding single-crystal silicon nanowires with typical dimension of 100 nm × 100 nm × 5 μm are fabricated by conventional 1:1 optical lithography and wet chemical silicon etching. The fabrication procedure can lead to wafer-scale integration of silicon nanowires in arrays. The measured electrical transport characteristics of the silicon nanowires covered with/without SiO(2) support a model of Fermi level pinning near the conduction band. The I-V curves of the nanowires reveal a current carrier polarity reversal depending on Si-SiO(2) and Si-H bonds on the nanowire surfaces.     

Formation of high aspect ratio GaAs nanostructures with metal-assisted chemical etching

Periodic high aspect ratio GaAs nanopillars with widths in the range of 500-1000 nm are produced by metal-assisted chemical etching (MacEtch) using n-type (100) GaAs substrates and Au catalyst films patterned with soft lithography. Depending on the etchant concentration and etching temperature, GaAs nanowires with either vertical or undulating sidewalls are formed with an etch rate of 1-2 μm/min. The realization of high aspect ratio III-V nanostructure arrays by wet etching can potentially transform the fabrication of a variety of optoelectronic device structures including distributed Bragg reflector (DBR) and distributed feedback (DFB) semiconductor lasers, where the surface grating is currently fabricated by dry etching.     

Intrinsic Pinning in the Layered Superconductor YBa2Cu3O7 Studied by the Conversion of Ultrasonic to Electromagnetic Waves

Intrinsic pinning in a single-crystal YBa₂Cu₃O₇ superconductor has been investigated through the conversion of ultrasonic to electromagnetic waves. The interaction with a longitudinal ultrasonic wave was dramatically enhanced as a result of the intrinsic pinning of the vortex so as to form a sharp peak when a dc magnetic field was applied nearly parallel to the superconducting plane. Not only the height but also the angle width of the peak decreased with the temperature increase because of the weakening two-dimensionality. The crossover between the intrinsic pinning and the point-defect pinning is discussed by taking into account the pinning strength.     

Facile synthesis of fully ordered L10-FePt nanoparticles with controlled Pt-shell thicknesses for electrocatalysis

We report a simple one-step approach for the synthesis of ～4 nm uniform and fully L10-ordered face-centered tetragonal (fct) FePt nanopartides (NPs) embedded in ～60 nm MCM-41 (fct-FePt NPs@MCM-41).We controlled the Pt-shell thickness of the fct-FePt NPs by treating the fct-FePt NPs@MCM-41 with acetic acid (HOAc) or hydrochloric acid (HC1) under sonication,thereby etching the surface Fe atoms of the NPs.The fct-FePt NPs deposited onto the carbon support (fct-FePt NP/C) were prepared by mixing the fct-FePt NPs@MCM-41 with carbon and subsequently removing the MCM-41 using NaOH.We also developed a facile method to synthesize acid-treated fct-FePt NP/C by using a HF solution for simultaneous surface-Fe etching and MCM-41 removal.We studied the effects of both surface-Fe etching and Pt-shell thickness on the electrocatalytic properties of fct-FePt NPs for the methanol oxidation reaction (MOR).Compared with the non-treated fct-FePt NP/C catalyst,the HOAc-treated and HCl-treated catalysts exhibit up to 34％ larger electrochemically active surface areas (ECASAs);in addition,the HCl-treated fct-FePt NP (with ～1.0 nm Pt shell)/C catalyst exhibits the highest specific activity.The HF-treated fct-FePt NP/C exhibits an ECASA almost 2 times larger than those of the other acid-treated fct-FePt NP/C catalysts and shows the highest mass activity (1,435 mA.mg~,2.3 times higher than that of the commercial Pt/C catalyst) and stability among the catalysts tested.Our findings demonstrate that the surface-Fe etching for the generation of the Pt shell on fct-FePt NPs and the Pt-shell thickness can be factors for optimizing the electrocatalysis of the MOR.     

Ion irradiation effects in EuBa2Cu3O y thin film

The effect of He ion irradiation on the pinning potential in EuBa₂Cu₃O _y , thin film was investigated by measuring the temperature dependence of resistivity in magnetic fields. The pinning potential decreased as the ion fluence increased. A slower decrease of pinning potential was observed in higher magnetic field in the fluence region <3.5×10¹⁵ cm^?2.     

Strongly enhanced current densities in superconducting coated conductors of YBa2Cu3O7-x + BaZrO3

There are numerous potential applications for superconducting tapes based on YBa(2)Cu(3)O(7-x) (YBCO) films coated onto metallic substrates. A long-established goal of more than 15 years has been to understand the magnetic-flux pinning mechanisms that allow films to maintain high current densities out to high magnetic fields. In fact, films carry one to two orders of magnitude higher current densities than any other form of the material. For this reason, the idea of further improving pinning has received little attention. Now that commercialization of YBCO-tape conductors is much closer, an important goal for both better performance and lower fabrication costs is to achieve enhanced pinning in a practical way. In this work, we demonstrate a simple and industrially scaleable route that yields a 1.5-5-fold improvement in the in-magnetic-field current densities of conductors that are already of high quality.     

Hybrid Anodic and Metal‐Assisted Chemical Etching Method Enabling Fabrication of Silicon Carbide Nanowires

Silicon carbide (SiC) is one of the most important third‐generation semiconductor materials. However, the chemical robustness of SiC makes it very difficult to process, and only very limited methods are available to fabricate nanostructures on SiC. In this work, a hybrid anodic and metal‐assisted chemical etching (MACE) method is proposed to fabricate SiC nanowires based on wet etching approaches at room temperature and under atmospheric pressure. Through investigations of the etching mechanism and optimal etching conditions, it is found that the metal component plays at least two key roles in the process, i.e., acting as a catalyst to produce hole carriers and introducing band bending in SiC to accumulate sufficient holes for etching. Through the combined anodic and MACE process the required electrical bias is greatly lowered (3.5 V for etching SiC and 7.5 V for creating SiC nanowires) while enhancing the etching efficiency. Furthermore, it is demonstrated that by tuning the etching electrical bias and time, various nanostructures can be obtained and the diameters of the obtained pores and nanowires can range from tens to hundreds of nanometers. This facile method may provide a feasible and economical way to fabricate SiC nanowires and nanostructures for broad applications.     

交替刻蚀制备有序锯齿形硅纳米线阵列及其光学性能研究

采用金属催化化学刻蚀法(MCCE),以金属Ag为催化剂,在HF与H2O2体系中通过交替刻蚀在P(111)硅衬底上制备出锯齿形硅纳米线阵列.利用扫描电子显微镜对硅纳米线的形貌进行了表征,研究了HF浓度与H2O2浓度对纳米线刹蚀方向的调控作用.选取不同的HF与H2O2浓度配比,分别对硅基底各向同性刻蚀与各向异性刻蚀进行调控,使得刻蚀方向对溶液浓度的变化能够快速响应.在溶液Ⅰ([HF]=2.3 mol/L,[H2O2]=0.4 mol/L)与溶液Ⅱ([HF]=9.2 mol/L,[H2O2]=0.04 mol/L)中交替刻蚀,制备出刻蚀方向高度可控的大规模锯齿形硅纳米线.利用紫外-可见分光光度计对锯齿形硅纳米线的减反射性能进行研究,结果表明,其表现出优异的减反特性,最低反射率为5.9％.纳米线形貌的高度可控性使其在微电子器件领域也具有巨大的应用前景.     

Vortex behavior in Nb3Ge microbridges

We have fabricated Nb₃Ge microbridges, including those with variablethickness geometry, with submicrometer lengths, by means of plasma etching combined with lithographic techniques. The measuredI-V characteristic and the temperature variation of the critical current are consistent with that expected from the vortex concept. However, a deviation is observed in the microwave steps: the magnitude of the critical current oscillates with microwave power in a manner which agrees with an analog simulation based on the RSJ model. We have found a strong correlation between the bridge behavior and the film parametersT _c and ρ _n (normal resistivity). The critical current is reduced rapidly with a decrease inT _c and an increase in ρ _n , while in high-T _c and low-ρ _n bridges a linearI-V characteristic appears at low voltages. Taking into account the influence of pinning, we discuss the results in terms of vortex motion.     

化学蚀刻法制备纳米硅线作为高能锂离子电池的负极

采用金属催化剂诱导化学蚀刻法首先在单晶硅片上制备出具有高长径比的纳米硅线阵列, 然后通过超声振荡法将硅线阵列破碎为纳米硅线粉体, 最后将其作为锂离子电池的负极材料, 系统研究了金属银催化剂制备过程和各向异性化学蚀刻过程对硅片表面形貌特征的影响, 发现银催化剂在蚀刻过程出现溶解/再沉积现象。通过优化AgNO₃、HF、H₂O₂等试剂的浓度, 在大面积范围内得到了高长径比的纳米硅线阵列。借助超声波的作用将硅线从硅片上切割下来, 制备成纳米硅线负极进行了充放电循环测试, 观察到标准的硅锂合金/去合金化反应平台, 前五次循环的比容量均超过1800 mAh/g。     

Optimal 3D phase-shifting masks in partially coherent illumination

Gradient-based phase-shifting mask (PSM) optimization methods have emerged as an important tool in computational lithography to solve for the inverse lithography problem under the thin-mask assumption, where the mask is considered a thin two-dimensional object. As the critical dimension printed on the wafer shrinks into the subwavelength regime, thick-mask effects become prevalent and thus these effects must be taken into account in PSM optimization methods. Thick-mask effects are particularly aggravated and pronounced in etching profiles with abrupt discontinuities and trench depths. PSM methods derived under the thin-mask assumption have inherent limitations and perform poorly in the subwavelength scenario. This paper focuses on developing three-dimensional PSM optimization methods that can overcome the thick-mask effects in lithography systems with partially coherent illumination. The boundary layer model is exploited to simplify and characterize the thick-mask effects, leading to a gradient-based PSM optimization method. Several illustrative simulations are presented.     

3D Nanofabrication of Fluidic Components by Corner Lithography

A reproducible wafer‐scale method to obtain 3D nanostructures is investigated. This method, called corner lithography, explores the conformal deposition and the subsequent timed isotropic etching of a thin film in a 3D shaped silicon template. The technique leaves a residue of the thin film in sharp concave corners which can be used as structural material or as an inversion mask in subsequent steps. The potential of corner lithography is studied by fabrication of functional 3D microfluidic components, in particular i) novel tips containing nano‐apertures at or near the apex for AFM‐based liquid deposition devices, and ii) a novel particle or cell trapping device using an array of nanowire frames. The use of these arrays of nanowire cages for capturing single primary bovine chondrocytes by a droplet seeding method is successfully demonstrated, and changes in phenotype are observed over time, while retaining them in a well‐defined pattern and 3D microenvironment in a flat array.