Fabrication and characterization of polycrystalline silicon nanowires with silver-assistance by electroless deposition

Single crystal silicon wafers are widely used as the precursors to prepare silicon nanowires by employing a silver-assisted chemical etching process. In this work, we prepared polycrystalline silicon nanowire arrays by using solar-grade multicrystalline silicon wafers. The chemical composition and bonding on the surface of silicon nanowire arrays were characterized by Fourier Transform Infrared spectroscope, and X-ray photoelectron spectroscope. The photoluminescence spectra of silicon nanowires show red light emissions centered around 700 nm. Due to the passivation effect of Si dangling bonds by concentrated HNO₃ aqueous solution, the photoluminescence intensities are improved by 2 times. The influences of surface chemical states on the wettability of silicon nanowire arrays were also studied. We obtained a superhydrophobic surface on the as-etched silicon nanowire arrays without surface modification with any organic low-surface-energy materials, and realized the evolution from superhydrophobicity to superhydrophilicity via surface modifications with HNO₃ solutions.     

Facile fabrication of superhydrophobic surface with micro/nanoscale binary structures on aluminum substrate

The present work reports a simple method to produce the aluminum superhydrophobic surface based on an interface reaction between an aluminum foil and zinc aqueous solution. The products were characterized by field-emission scanning electron microscopy, X-ray powder diffraction and X-ray photoelectron spectrum. The field-emission scanning electron microscopy images show that the coating surface is composed of micro/nanoscale binary structure, which is similar to the structure of lotus leaf. The wettability of the coating surface was also investigated. It was found that after treatment with stearic acid, the wettability of the aluminum foil changed from superhydrophilic to water-repellent superhydrophobic. The complex micro/nanoscale binary structures along with the low surface energy lead to the high surface superhydrophobicity.     

An oxide/silicon core/shell nanowire metal-oxide semiconductor field-effect transistor

This paper studies an oxide/silicon core/shell nanowire MOSFET(OS-CSNM).Through three-dimensional device simulations,we have demonstrated that the OS-CSNM has a lower leakage current and higher I on /I off ratio after introducing the oxide core into a traditional nanowire MOSFET(TNM).The oxide/silicon OS-CSNM structure suppresses threshold voltage roll-off,drain induced barrier lowering and subthreshold swing degradation.Smaller intrinsic device delay is also observed in OS-CSNM in comparison with that of TNM.     

Raman spectroscopy and field electron emission properties of aligned silicon nanowire arrays

Arrays of aligned silicon nanowire (SiNW) were synthesized on a silicon (1 0 0) substrate by self-assembling electroless nanoelectrochemistry. Compared with that of bulk crystal silicon, the first-order Raman peak of the silver cap-removed SiNW arrays shows a downshift and asymmetric broadening due to the phonon quantum confinement effects, and intensity enhancement. Field electron emission from the SiNWs was also investigated. The turn-on field was found to be about 12 V/μm at a current density of 0.01 mA/cm². These highly densified and ordered SiNW arrays can be expected to have favorable applications in vacuum electronic or optoelectronic devices.     

一种新方法制备硅/聚(3, 4-乙撑二氧噻吩)核/壳纳米线阵列杂化太阳能电池

采用气相聚合法制备了有机/无机杂化的硅/聚3, 4-乙撑二氧噻吩核/壳纳米线阵列(SiNWs/PEDOT)太阳能电池. 相对平面结构Si/PEDOT太阳能电池, SiNWs/PEDOT太阳能电池的能量转换效率提升了7倍, 达到3.23%.对比分析反射光谱、I-V曲线及外量子效率的实验结果, 发现SiNWs/PEDOT太阳能电池性能改进的主要原因可归结为: 气相聚合法能够有效地制备出SiNWs/PEDOT电池的核/壳纳米线阵列结构, 使得器件具有高光捕获、高比结面积和高电荷收集效率. 关键词： Si/PEDOT核/壳纳米线结构 太阳能电池 气相聚合     

Tailoring the wettability of patterned silicon surfaces with dual-scale pillars: From hydrophilicity to superhydrophobicity

Wettability tailoring of patterned silicon surface has great potential in fields producing integrated circuits, solar cells, sensors, detectors, and micro/nano electromechanical systems. The present paper presents a convenient yet effective method of combining reactive ion etching and catalyzed etching to prepare silicon surface with micro-nano dual-scale pillars. The experimental results indicate that the hydrophilic surface transformed to a superhydrophobic surface when micro-nano dual-scale pillars were formed. The surface preserved superhydrophobicity even when the geometric parameters of the micropillars were changed. Overhangs of water drops on steep micro-nano dual-scale pillars result in superhydrophobicity. This method offers a new way for tailoring the wettability of patterned silicon surfaces.     

Synthesis and analysis of silicon nanowire below Si-Au eutectic temperatures using very high frequency plasma enhanced chemical vapor deposition

Silicon nanowires (SiNWs) were synthesized from pure silane precursor gas and Au nanoparticles catalyst at below Au-Si eutectic temperature. The SiNWs were grown onto Si (1 1 1) substrates using very high frequency plasma enhanced chemical vapor deposition via a vapor-solid-solid mechanism at temperatures ranging from 363 to 230 °C. The morphology of the synthesized SiNWs was characterized by means of field emission scanning electron microscope equipped with energy dispersive X-ray, high resolution transmission electron microscopy, X-ray diffraction technique and Raman spectroscope. Results demonstrated that the SiNWs can be grown at the temperature as low as 250 °C. In addition, it was revealed that the grown wires were silicon-crystallized.     

Design optimization of tunneling field-effect transistor based on silicon nanowire PNPN structure and its radio frequency characteristics

Recently, a number of semiconductor devices have been widely researched in order to make breakthroughs from the short-channel effects (SCEs) and high standby power dissipation of the conventional metal-oxide-semiconductor field-effect transistors (MOSFETs). In this paper, a design optimization for the silicon nanowire tunneling field-effect transistor (SNW TFET) based on PNPN multi-junction structure and its radio frequency (RF) performances are presented by using technology computer-aided design (TCAD) simulations. The design optimization was carried out in terms of primary direct-current (DC) parameters such as on-current (I_on), off-current (I_off), current ratio (I_on/I_off), and subthreshold swing (SS). Based on the parameters from optimized DC characteristics, basic radio frequency (RF) performances such as cut-off frequency (f_T) and maximum oscillation frequency (f_max) were analyzed. The simulated device had a channel length of 60 nm and a SNW radius of 10 nm. The design variable was width of the n-doped layer. For an optimally designed PNPN SNW TFET, SS of 34 mV/dec and I_on of 35 μA/μm were obtained. For this device, f_T and f_max were 80 GHz and 800 GHz, respectively.     

Wetting characteristics of ZnO smooth film and nanowire structure with and without OTS coating

ZnO is an important material that is used in a variety of technologies including optical devices, sensors, and other microsystems. In many of these technologies, wettability is of great concern because of its implications in numerous surface related interactions. In this work, the effects of surface morphology and surface energy on the wetting characteristics of ZnO were investigated. ZnO specimens were prepared in both smooth film and nanowire structure in order to investigate the effects of surface morphology. Also, a hydrophobic octadecyltrichlorosilane (OTS) coating was used to chemically modify the surface energy of the ZnO surface. Wettability of the surfaces was assessed by measuring the water contact angle. The results showed that the water contact angle varied significantly with surface morphology as well as surface energy. OTS coated ZnO nanowire specimen had the highest contact angle of 150°, which corresponded to a superhydrophobic surface. This was a drastic difference from the contact angle of 87° obtained for the smooth ZnO film specimen. In addition to the initial contact angle, the evolution of the water droplet with respect to time was investigated. The wetting state of water droplet was analyzed with both Wenzel and Cassie-Baxter models. Spontaneous and gradual spreading, together with evaporation phenomenon contributed to the changing shape, and hence the varying contact angle, of the water droplet over time.     

Fabrication of coaxial p-Cu2O/n-ZnO nanowire photodiodes

The authors report the deposition of Cu₂O onto vertically well aligned ZnO nanowires by DC sputtering. The average length, average diameter and density of these VLS-synthesized ZnO nanowires were 1 μm, 100 nm and 23 wires/μm², respectively. With proper sputtering parameters, the deposited Cu₂O could fill the gaps between the ZnO nanowires with good step coverage to form coaxial p-Cu₂O/n-ZnO nanowires with a rectifying current–voltage characteristic. Furthermore, the fabricated coaxial p-Cu₂O/n-ZnO nanowire photodiodes exhibit reasonably large photocurrent-to-dark-current contrast ratio and the fast responses.     

CoxCu1-x复相纳米线阵列的制备及其磁性的研究

利用电化学沉积方法在同一种富Co²⁺溶液Co²⁺/Cu²⁺=10∶1中,利用不同的沉积电位成功地制备了一系列不同成分(x=0.38—0.87)和复合相结构的Co_xCu_1-x纳米线阵列.发现随着纳米线中Cu含量的变化,Co_xCu_1-x纳米线的复相结构随之发生规律的变化,最终导致纳米线的磁性也随之规律的变化.随着纳米线中Cu含量的不断增加,一部分Cu与Co形成面心立方结构(fcc)的CoCu固溶体,减弱了磁晶各向异性与形状各向异性的竞争,从而提高样品的方形度;一部分Cu以fcc结构的Cu单质的形式存在于纳米线中,并随着Cu颗粒大小的不同分别起到破坏磁晶各向异性和钉扎畴壁的作用,从而增加纳米线的方形度和矫顽力.对比不同成分的样品,发现Co_xCu_1-x纳米线的方形度和矫顽力的最大值分别出现在Co₇₅Cu₂₅和Co₆₀Cu₄₀中,并且由于其特殊的复相结构致使它们的值要好于相同直径的单相结构的结果. 关键词： 纳米线 电化学沉积 磁性     

碳纳米管-硅纳米线复合结构的形成和热稳定性

通过分子动力学方法模拟了在碳纳米管内填充一定数目的半导体元素硅形成碳纳米管-硅纳米线复合结构的过程,并采用Lindemann指数研究了这种复合结构的热稳定性．计算结果表明,当考虑碳纳米管和硅纳米线轴向方向的周期性边界条件之后,在C（13,0）和C （14,0）碳纳米管内能够形成亚稳结构的硅纳米线Si₁₆NW和Si₂₀NW,从而获得一种碳纳米管-硅纳米线的新型复合结构．通过计算这种复合结构的Lindemann指数,可以看到由于碳纳米管的保护作用,碳纳米管包裹的硅纳 关键词： 复合结构 纳米线 碳纳米管 分子动力学     

Composition,temperature and geometric dependent hysteresis behaviours in Ising-type segmented nanowire with magnetic and diluted magnetic,and its soft/hard magnetic characteristics

Abstract

In this paper, a theoretical approach to evaluate the hysteresis behaviours of Ising-type segmented nanowire (ISN) comprising magnetic and diluted magnetic segments is defined. The dependency to the system parameters are calculated for optimising their performance in applications like magnetic sensors or recording media. The effects of the composition (p) and temperature (T) as well as crystal field on the hysteresis behaviours are investigated in detail. We studied the effect of the segment dimensions obtained from the exchange interactions. The coercivity (H_C) and remanence (M_r) of the ISN are derived from hysteresis loops. The phase diagrams are presented in the different planes as function of H_C and M_r to investigate the magnetic characteristics of the ISN. Under certain conditions, namely p = 0 and J_D = 0, we also examined the effect of temperature on the nanowire with magnetic and non-magnetic segments. The distinct hysteresis properties and soft/hard the magnetic characteristics depending upon these factors are observed. We found that the magnetic hardness decreases case as the temperatures increase as well as p and crystal field (Δ) decrease. Moreover, when the p increase and Δ decrease the triple hysteresis loop behaviour occurs in the system. Comparisons between the observed theoretical results and some experimental works of nanowire with hysteresis behaviours are made and a very good agreement is obtained.     

NiFe2O4纳米线阵列的制备与磁性

在氧化铝模板的纳米孔洞中, 用电化学的方法沉积铁镍合金纳米线，经过550℃30h氧化处理 , 成功制备出 NiFe2O4纳米线阵列. 分别用扫描电子显微镜 (SEM) 、透射电 子显微镜 (TEM) 、x射线衍射仪 (XRD) 和振动样品磁场计 (VSM) 对样品的形貌、晶体结构 和磁学性质进行了表征测试. SEM和TEM观察结果显示氧化铝模板的孔洞分布均匀，孔心距约 为110nm; 纳米线的直径约为70nm. XRD显示纳米线阵列的物相结构为NiFe2O4; VSM测试结果表明，NiFe2O4纳米线阵列膜的易磁化方向垂直于膜面. 当垂直 磁化时磁滞回线的矩形比约为05，矫顽力为41×103A/m，比氧化处理前的铁镍合金 纳米线阵列都有显著提高. 关键词： 纳米线 Ni Fe2O4 矫顽力     

Wetting mode transition of nanoliter scale water droplets during evaporation on superhydrophobic surfaces with random roughness structure

During evaporation, shape changes of nanoliter-scale (80-100 nL) water droplets were evaluated on two superhydrophobic surfaces with different random roughness (nm-coating, μm-coating). The square of the contact radius and the square of the droplet height decreased linearly with evaporation time. However, trend changes were observed at around 170 s (nm-coating) and around 150 s (μm-coating) suggesting a wetting mode transition. The calculated droplet radii for the wetting mode transition from the average roughness distance and the average roughness height of these surface structures were approximately equal to the experimental values at these trend changes. A certain level of correlation between the roughness size and droplet radius at the wetting mode transition was confirmed on surfaces with random roughness.     

高矫顽力的Co70Cu30合金纳米线阵列的制备及磁性研究

利用直流电化学沉积法, 在多孔阳极氧化铝模板中首次制备出了具有[220]取向的单晶 面心立方结构的CoCu固溶体合金纳米线阵列, 其Co含量高达70%.透射电子显微镜显示纳米线均匀连续, 具有较高的长径比, 约为300. 磁性测量表明所制备的Co₇₀Cu₃₀ 合金纳米线具有超高的矫顽力H_c//=2438 Oe(1 Oe=79.5775 A/m)和较高的矩形比S//=0.76, 远高于以往报道的CoCu合金纳米线的磁性, 分析表明磁性好的主要原因是由于较高Co含量和高形状各向异性. 通过磁性测量和模型计算, 得到Co₇₀Cu₃₀ 合金纳米线阵列在反磁化过程中遵从对称扇型转动的球链模型, 并从结构的角度分析了Co₇₀Cu₃₀合金纳米线阵列的反磁化行为.     

悬空氧化铟纳米线晶体管制备与光电性能表征

一维(1D)半导体纳米线在纳米电子学和纳米光子学中表现出色.然而,纳米线晶体管的电特性对纳米线与衬底之间的相互作用非常敏感,而优化器件结构可以改善纳米线晶体管的电学和光电检测性能.本文报道了通过一步式光刻.     

The effect of substrate on magnetic properties of Co/Cu multilayer nanowire arrays

Ordered Co/Cu multilayer nanowire arrays have been fabricated into anodic aluminium oxide templates with Ag and Cu substrate by direct current electrodeposition. This paper studies the morphology, structure and magnetic properties by transmission electron microscopy, selective area electron diffraction, x-ray diffraction, and vibrating sample magnetometer. X-ray diffraction patterns reveal that both as-deposited nanowire arrays films exhibit face-centred cubic structure. Magnetic measurements indicate that the easy magnetization direction of Co/Cu multilayer nanowire arrays films on Ag substrate is perpendicular to the long axis of nanowire, whereas the easy magnetization direction of the sample with Cu substrate is parallel to the long axis of nanowire. The change of easy magnetization direction attributed to different substrates, and the magnetic properties of the nanowire arrays are discussed.     

第一性原理研究[111]晶向硅纳米线电子结构，光学性质与压阻特性的应变效应

基于密度泛函理论体系下的广义梯度近似（GGA）,利用第一性原理方法计算研究了单轴应变对[111]晶向硅纳米线的电子结构、光学性质以及压阻性质的影响．能带结构和光学性质的结果表明：压应变导致硅纳米线的带隙明显线性减小,且使其由直隙半导体转变为间隙半导体,而施加拉应变后硅纳米线仍为直隙半导体材料,但是带隙略有减小,且价带顶附近的能带线产生了较为复杂的变化．由于能带的应变效应导致其光学性质也相应发生了较大改变：拉应变使硅纳米线的介电峰出现宽化现象,低能区内的光吸收增强,静态折射率和反射率峰值增大,而压应变的效果则相反．结合能带结构与压阻系数计算模型得到的压阻特性结果表明：随着压应变的增加压阻系数单调减小,这主要归因于空穴浓度随压应变显著变化引起的;而拉应变作用时,压阻系数呈现波动趋势,这主要是由于空穴有效传输质量的增加程度和载流子浓度的增加程度不同而相互竞争导致的．上述计算结果表明,设计基于硅纳米线的光电和力电器件时,需考虑其应变效应．     

Hybrid solar cells with conducting polymers and vertically aligned silicon nanowire arrays: The effect of silicon conductivity

Organic/inorganic hybrid solar cells, based on vertically aligned n-type silicon nanowires (n-Si NWs) and p-type conducting polymers (PEDOT:PSS), were investigated as a function of Si conductivity. The n-Si NWs were easily prepared from the n-Si wafer by employing a silver nanodot-mediated micro-electrochemical redox reaction. This investigation shows that the photocurrent-to-voltage characteristics of the n-Si NW/PEDOT:PSS cells clearly exhibit a stable rectifying diode behavior. The increase in current density and fill factor using high conductive silicon is attributed to an improved charge transport towards the electrodes achieved by lowering the device's series resistance. Our results also show that the surface area of the nanowire that can form heterojunction domains significantly influences the device performance.