电化学阳极氧化条件对阵列多孔硅的影响

采用电化学阳极氧化法,将预光刻图案的p型硅片制备成阵列多孔硅.讨论电化学阳极氧化条件对阵列多孔硅形貌的影响.结果表明:随着HF浓度、电流密度、阳极氧化时间的增大,阵列多孔硅的孔深逐渐加大;当HF:C2H5OH:H2O(体积比)为1:1:1～1:2:5,电流密度为1.56mA/cm2,阳极氧化时间为3h时,制备出的阵列多孔硅具有比较规整的阵列孔,并且孔深能够达到50pm;表面活性剂对阵列孔的形成有很大影响,加入表面活性剂后形成的孔才具有一定的规整性以及深宽比.     

电化学阳极氧化条件对多孔硅及其光催化性能的影响研究

在HF/乙醇电解液中,采用恒电压电化学阳极氧化法,将P型硅片制备成了多孔硅催化剂。以甲基橙模拟废水为目标物,分析了电化学阳极氧化条件对多孔硅光催化甲基橙脱色率的影响。结果表明:随着HF浓度、阳极氧化时间、电流密度和光照时间的增加,甲基橙的脱色率逐渐增大。当V(HF)∶V(乙醇)=1∶1、阳极氧化时间为30min、电流密度为10mA/cm2以及光照时间为60min时,对甲基橙废水的脱色率较好。用十二烷基苯磺酸钠修饰的多孔硅对甲基橙废水有更高的脱色率。同直接催化相比,光催化甲基橙废水的脱色率提高到45.32%。同时对多孔硅表面形貌进行了表征。     

阳极氧化电流密度和时间对多孔硅形貌和电子发射特性的影响

为了应用于场发射显示器,采用电化学阳极氧化,快速热氧化和磁控溅射等方法制备出了金属/多孔硅/硅基底/金属结构的多孔硅电子发射体,并运用扫描电子显微镜观察了多孔硅的微观形貌,结果发现多孔硅的孔径随着电化学阳极氧化电流密度的增加而增加,多孔硅层的厚度随着阳极氧化电流密度和时间乘积的增加而增加。在真空系统中测量了多孔硅的电子发射特性,电子发射的阈值电压Vth随着多孔硅层厚度的增加而增加;最大的发射效率η为7.5‰,此效率出现在孔径6~16 nm,多孔硅层厚度为11.06μm的样品中,对应的器件电压Vps为30V。     

近规整多孔硅电化学制备与表征

电化学阳极氧化条件对多孔硅孔排列的规整度有着显著的影响.提出了一种不需阳极氧化铝模板或预图案化而直接制备近规整多孔硅的电化学方法,分析了氧化时间、电解液组成、HF浓度对多孔硅形态的影响.结果表明,随着阳极氧化时间的增加,多孔硅孔的深度逐渐加大,孔径则呈先增大后稳定的趋势.当氢氟酸(40%)与N-N-二甲基甲酰胺(DMF...     

图案化厚膜多孔硅制备与表征

图案化多孔硅是微电子、微机械、光电子器件的重要组成部分.实验以含Si3N4保护层的光刻单晶硅片为基底,采用电化学阳极氧化法制备图案化厚膜多孔硅,分析阳极氧化前后Si3N4保护层表面形貌变化特征和光刻尺寸对图案化多孔硅宽度、膜层厚度的影响规律,表征图案化多孔硅的结构、组成与发光性能.结果表明,氧化前Si3N4保护层局部区域出现枝晶,阳极氧化后形成不均匀孔状结构;制备的图案化多孔硅膜厚62～83μm,其横向扩展程度和膜层厚度均随光刻尺寸增大呈减小趋势;图案化多孔硅微结构含大量不规则裂纹和硅柱,新鲜制备的表面含Si-Hx键,其光致发光峰值波长650nm.     

用脉冲电化学法在低HF浓度下制备多孔硅的研究

用脉冲电化学阳极氧化的方法在5％的低HF浓度下获得多孔硅。多孔硅的形成和脉冲电场的施加、去除过程中与电解液－硅半导体体系中物理化学过程的变化有关。在施加电场的间隙，由于Si／电解液界面处HF的补充，SiO2的溶解增强，使得在低HF浓度下Si的溶解速率比其氧化速率高，从而导致多孔硅的形成。同时，在高电场作用下，由于产生了高浓度的空穴，使得氧化层变厚，导致在低HF浓度或大电流密度下多孔硅的平均孔径增大。     

Al-Li合金阳极氧化膜的制备与性能

Al-Li合金在潮湿和盐雾环境中易发生晶间腐蚀、剥落腐蚀和应力腐蚀等形式的破坏。为了提高Al-Li合金的耐蚀性,采用阳极氧化的方法,在15%硫酸溶液中在Al-Li合金表面制备了一层Al_2O_3阳极氧化膜,通过测厚仪及显微硬度计测试了膜层厚度及硬度,通过扫描电镜、电化学测试和腐蚀试验等方法,研究了电流密度、氧化时间等对阳极氧化膜耐蚀性的影响。结果显示:所得氧化膜表面呈多孔状结构,厚度在3~13μm之间,硬度在80~200 HV之间;当电流密度为2.0 A/dm~2、氧化时间为60 min、沸水封孔处理20 min时制备的阳极氧化膜耐蚀性最优。     

阳极氧化法制备TiO_2和Al_2O_3有序多孔阵列

采用阳极氧化法制备了TiO2和Al2O3有序多孔阵列,并通过X射线衍射(XRD)、场发射扫描电子显微镜(FESEM)、莱茨光学显微镜对制备的TiO2和Al2O3有序多孔阵列进行表征。结果表明,随着氧化电压的增大,TiO2和Al2O3纳米孔的直径增加,孔密度减小。随着氧化时间的延长,TiO2和Al2O3多孔膜厚度增加,到一定时间后膜厚不变。同时讨论了阳极氧化机理,无论是制备TiO2还是Al2O3有序多孔阵列,阳极氧化过程主要由3个阶段组成:阻挡层的形成、阻挡层的溶解、多孔层的稳定生长。     

用化学腐蚀制备多孔硅太阳电池减反射膜的研究

采用HF HNO3溶液化学腐蚀 ,在硅片上制备减反射效果优良的多孔硅太阳电池减反射膜 ,借助原子力显微镜 (AFM)和X光电子谱 (XPS)对其表面形貌和成分进行观察 ,发现该膜与电化学阳极腐蚀得到的多孔硅具有相似性 ,其主要成分为非化学配比的硅的氧化物SiOx(X <2 )。采用带积分球的光度分光计 ,测得形成多孔硅减反射膜后 ,硅片表面反射率大大下降 ,,在波长 330～ 80 0nm范围反射率只有 1 5～ 2 9%。研究指出这种强减反射作用 ,与多孔硅具有合适的折射率及其多孔特性的光陷阱作用有关     

微弧氧化时间对AZ61镁合金陶瓷膜形貌及性能的影响

用现有的微弧氧化方法制备的镁合金陶瓷膜厚度有限,且属于多孔结构。采用电流密度0.4 A/dm2,在AZ61镁合金表面制备了陶瓷膜;研究了不同微弧氧化时间(30,50,70,90,120,160 m in)对陶瓷膜微观性能的影响。结果表明:在电流密度一定的条件下,处理时间对陶瓷膜微观组织和性能有着较大的影响,随氧化时间延长,阳极电压、陶瓷膜厚度和粗糙度增大;孔隙率先增大后减小,最大值出现在70 m in时,陶瓷膜表面熔融物颗粒和孔隙尺寸增大且分布不均;50 m in时陶瓷膜耐蚀性最好。     

The dependence of hydrofluoric acid concentration during anodization on photoluminescence of porous silicon

The mixture of hydrofluoric (HF) acid and ethanol is used as an electrolyte during anodization of silicon. We investigated the effect of the ratio of HF acid to ethanol on photoluminescence. It is concluded that porous silicon anodized with the electrolyte containing 35 or 40% HF acid provides strong photoluminescence. The fact implies the existence of a chemical reaction including ethanol during anodization other than electrochemical reaction.     

The dependence of hydrofluoric acid concentration during anodization on photoluminescence of porous silicon

The mixture of hydrofluoric (HF) acid and ethanol is used as an electrolyte during anodization of silicon. We investigated the effect of the ratio of HF acid to ethanol on photoluminescence. It is concluded that porous silicon anodized with the electrolyte containing 35 or 40% HF acid provides strong photoluminescence. The fact implies the existence of a chemical reaction including ethanol during anodization other than electrochemical reaction.     

Hydrogen isotopic substitution experiments in nanostructured porous silicon

Nanostructured porous silicon is usually prepared by electrochemical anodization of monocrystalline silicon using a fluorine-rich electrolyte. As a result of this process, the silicon atoms conserve their original crystalline location, and many of the dangling bonds appearing on the surface of the nanostructure are saturated by hydrogen coming from the electrolyte. This work presents an IR study of the effects produced by partial substitution of water in the electrolytic solution by deuterium oxide. The isotopic effects on the IR spectra are analyzed for the as-prepared samples and for the samples subjected to partial thermal effusion of hydrogen and deuterium. We demonstrate that, although deuterium is chemically indistinguishable from hydrogen, it presents a singular behaviour when used in porous silicon preparation. We found that deuterium preferentially bonds forming Si-DH groups. A possible explanation of the phenomenon is presented, based on the different diffusivities of hydrogen and deuterium.     

Morphology of porous silicon structures formed by anodization of heavily and lightly doped silicon

By computer simulation the growing process of porous silicon under p⁻-Si and p⁺-Si anodization in HF solution is studied. The model of electrochemical etching of p⁺-Si includes the relief selective mechanism, which allows one to establish the relationship between anodization conditions (current density, HF concentration, temperature and doping level) and the topological characteristics of porous silicon (PS). The simulation of p⁻-Si dissolution is based on the model of diffusion limited aggregation (DLA), taking into account the thermal generation of holes and the quantum confinement effect. The various morphology of simulated PS structures exhibits a close resemblance to that of experimental ones formed in p⁺-Si and p⁻-Si wafers. For simulated p⁻-Si-based PS layers the porosity profiles and fractal dimension are calculated. It is shown that PS in p⁻-Si is multifractal with fractal dimension varying monotonously from 0.1 to 3 with size increase.     

Fabrication of silicon-based template-assisted nanoelectrode arrays and ohmic contact properties investigation

A convenient fabrication technology for large-area, highly-ordered nanoelectrode arrays on silicon substrate has been described here, using porous anodic alumina (PAA) as a template. The ultrathin PAA membranes were anodic oxidized utilizing a two-step anodization method, from Al film evaporated on substrate. The purposes for the use of two-step anodization were, first, improving the regularity of the porous structures, and second reducing the thickness of the membranes to 100-200 nm we desired. Then the nanoelectrode arrays were obtained by electroless depositing Ni-W alloy into the through pores of PAA membranes, making the alloy isolated by the insulating pore walls and contacting with the silicon substrates at the bottoms of pores. The Ni-W alloy was also electroless deposited at the back surface of silicon to form back electrode. Then ohmic contact properties between silicon and Ni-W alloy were investigated after rapid thermal annealing. Scanning electron microscopy (SEM) observations showed the structure characteristics, and the influence factors of fabrication effect were discussed. The current-voltage (I-V) curves revealed the contact properties. After annealing in N2 at 700 degrees C, good linear property was shown with contact resistance of 33 omega, which confirmed ohmic contacts between silicon and electrodes. These results presented significant application potential of this technology in nanosize current-injection devices in optoelectronics, microelectronics and bio-medical fields.     

Effects of porous silicon morphology on ballistic electron emission

Porous silicon ballistic electron emission source with a structure of metal/porous silicon/Si/metal is obtained by anodization, rapid thermal oxidation, and sputtering. The microstructures of porous silicon layers are characterized by means of scanning electron microscope. The results show that disordered pores are formed at anodization current densities of 15 mA/cm2, 30 mA/cm2, and 45 mA/cm2 for 5 min, respectively. However, straight pores are formed at anodization current densities of 60 mA/cm2, and 75 mA/cm2 for 5 min, respectively. The electron emission characteristic of porous silicon ballistic electron emission sources is measured in vacuum. The results show that electrons emitted into the vacuum from the porous silicon samples with disordered pores. Under a bias condition, injected electrons from the substrate are accelerated by the strong electric field on the surfaces of the Si nanocrystallites in disordered pores, and then emitted into the vacuum through Pt film. However, no electron emission is observed in porous silicon samples with straight pores. It attributes to the lack of Si nanocrystallites in straight pores. So there is not accelerating tunnels enough for electrons. According to disordered or straight pores, we can estimate whether PS samples emit electrons or not.     

A multilayer model for describing hardness variations of aged porous silicon low-dielectric-constant thin films

This paper reports on the micro-instrumented indentation of a porous silicon structure obtained by anodization of a highly p⁺-doped (100) silicon substrate aged over 1 week. The three-layer structure obtained consists of oxidized porous silicon (cap-layer), porous silicon (inner-layer) and silicon substrate. The hardness curve has the typical “U shape” of low-dielectric-constant films when the indentation depth rises: the early decrease in hardness, due to the soft inner layer, is followed by an increase, due to the hard substrate. A multilayer model is developed to account for hardness variation with respect to the applied load. This model considers the crumbling of the cap-layer and of the inner porous structure. As a result, it is shown that considering the minima in the U shape gives an over-estimated value when it comes to assessing the coating hardness. In our experiment, this minimum depends on both the hardness and the thickness of the oxidized cap layer, but not on the mechanical properties of the substrate, even for indentation depths slightly lower than the film's thickness.     

直流电化学腐蚀法制备多孔硅的表面形貌研究

采用正交实验，直流电化学腐蚀法制备多孔硅。用原子力显微镜对表面进行观察，研究电化学腐蚀参数对其表面形貌的影响。氢氟酸浓度（CHF）升高，使临界电流密度（JPS）增大，有利于多孔硅的形成。电流密度（J）增大，多孔硅的孔隙率和孔径随之变大，而其纳米粒径将变小。腐蚀时间（t）越长，孔径越大，孔越深。