适用于强化液体相变换热的纳米结构的制备与调控

液体相变换热是高热流密度器件冷却的有效方式。本文提出了一种适用于强化液体相变换热的纳米结构的制备与调控方法。通过热溶液法生长出的氧化锌纳米线阵列结晶优良、物质纯净,并且可以通过不同的磁控溅射方式沉积种子层实现生长不同形貌的纳米线,进而改变表面的润湿性。多步生长的方法被用来调控纳米线阵列的尺寸,实现了对表面粗糙状况、核态沸腾核化点以及表面润湿性的进一步调控。本文同时利用氧化锌独特的光敏性质实现了从改变表面化学特性的角度调控表面润湿性。     

溶液蒸发冻结过程中冰体发展的分形模拟研究

根据溶液在蒸发冻结过程中的复杂性以及液面冰体分布的不规则,结合分形有限扩散聚集(DLA)理论,建立了湿度差作用下溶液蒸发冷冻过程中液面冰体生成、发展过程的数学模型,模拟分析了气流湿度差和气流流速对溶液表面冰体生成、发展的影响.结果表明,利用分形方法可以对溶液蒸发冻结过程中冰体的生成发展进行预测,同时也为研究溶液蒸发冻结和冰体生长提供了新的思路和方法.     

Ag微米管阵列修饰的聚合物光子晶体光纤制备工艺研究

以聚合物光子晶体光纤空气孔阵列为模板,制备了Ag微米管阵列修饰的聚合物光子晶体光纤.讨论了银氨溶液和葡萄糖溶液浓度以及反应时间和温度对银微米管形貌的影响.在Ag(NH3)+2与C6H6O浓度比为2,反应时间为20 min,温度为65℃条件下光纤孔洞表面获得了规则的Ag微米管状结构,并对Ag的生长机理进行了讨论.     

TiO_2一维纳米阵列电极表面氧气泡发展规律研究

光电化学分解水反应驱动的氧气泡生长,是发生在固液表面典型的物理化学过程。本文通过搭建的光电化学分解水反应体系,利用显微拍摄系统,探究了氧气泡在光电极表面的发展规律,结果表明气泡大小与生长时间遵循关系;并通过改变反应溶液的浓度和激发光源的光照强度,总结了溶液浓度和光照强度对气泡的生长时间与脱离直径的影响规律。     

不同制备条件对聚偏氟乙烯纳米线生长的影响

为提高铁电聚合物聚偏氟乙烯(PVDF)的压电性能,利用纳米限域效应,采用模板直接浸润法,将多孔氧化铝(AAO)模板在不同浓度的PVDF的DMF溶液中自然浸润,并添加聚乙烯吡咯烷酮(PVP)作为表面修饰剂,制备了一维材料PVDF纳米线。分别研究了浸润温度、溶液浓度及表面修饰剂等因素对PVDF纳米线生长过程的影响。通过FTIR、SEM、XRD等对样品的形貌结构及性能进行了表征,进一步讨论了AAO模板中PVDF纳米线的生长机制。结果表明:模板法生长的PVDF纳米线形貌主要受溶液浓度的影响,并且当浓度为0.10 g/m L时形貌较优,其平均长度为50μm,平均直径为180 nm,与AAO模板孔径尺寸相当;表面修饰剂PVP可在一定程度上防止纳米线团聚并且优化其尺寸均一性;AAO模板中生长的PVDF纳米线由于纳米限域效应优先向β晶相结晶,并且在生长过程中PVDF并未参与任何化学反应。     

PTFE、FEP涂层表面CaCO3污垢特性的实验研究

实验室里进行了PTFE与FEP表面CaCO3污垢的对比实验.采用直接称重法获得污垢生长曲线,研究了在不同流速、温度、浓度条件下PTFE和FEP两种表面污垢特性.实验结果表明:在相同流速、浓度和温度条件下,FEP比PTFE有更好的阻垢性能;溶液流速、温度和浓度对CaCO3污垢沉积有较大影响:增大溶液流速、降低溶液的温度和浓度都会使这两种材料表面的污垢渐近值减小.     

亲疏水共型表面升温过程中气泡生长行为研究

本工作以引发式化学气相沉积技术制备共型表面,不改变受热表面粗糙程度,仅改变亲疏水性。进而在不同浓度的NaCl溶液和加有表面活性剂的溶液中,可以实时对比气泡在升温的固液接触表面亲疏水区域的产生、生长、脱离等行为特征。实验结果表明,共型疏水区域总是比原表面亲水区域易于产生气泡,且附着的气泡直径大于同一时刻亲水侧气泡直径。溶液的表面张力越大,接触表面气泡越难产生,且同一温度下气泡直径越小。溶液表面张力和受热表面亲疏水性都影响着成核的难易度和气泡大小,但溶液表面张力对成核数量即气泡数量的影响不大。亲疏水共型表面上的气泡行为,将有助于界面传热传质的深入研究。     

单晶硅表面均匀小尺寸金字塔制备及其特性研究

表面织构是一种通过有效的光俘获增加短路电流从而提高太阳电池效率的主要途径之一.在加入间隙式超声和NaClO添加剂的碱性四甲基氢氧化铵(TMAH)溶液中对单晶硅表面进行织构化处理,研究超声与NaClO在织构过程中对金字塔成核和生长的影响,以及金字塔大小对高温工艺之后的单晶硅少子寿命的影响.研究表明,通过在织构溶液中加入间隙式超声控制气泡停留在硅片表面的时间和脱离硅片表面速度,增强了小尺寸金字塔的均匀分布.织构之后硅片在AM1.5G光谱下的加权平均反射率能够达到12.4%,在高温扩散和氧化之后少子寿命的大小与金字塔大小之间存在近似于指数衰减函数的关系. 关键词： 表面织构化 反射率 少子寿命 单晶硅太阳电池     

ZnO纳米线薄膜的合成参数、表面形貌和接触角关系研究

水浴法合成ZnO纳米线薄膜的工艺参数直接影响其表面形貌, 并使其接触角及润湿性能发生变化. 本文仿真分析了轮廓算数平均偏差、偏斜度、峭度、相关长度等特征参数对随机粗糙表面特性的影响规律; 改变生长时间、种子层溶液和生长液的浓度, 批量制备了表面形貌不同的ZnO纳米线薄膜; 提出了取样长度的确定方法, 并基于扫描电镜图像和Matlab图像处理算子对ZnO纳米线薄膜表面形貌的特征参数进行了提取; 将表面形貌高度和水平方向的特征参数引入Wenzel模型, 分析了合成参数、表面形貌特征参数与接触角的影响关系. 结果表明, 合成参数变化时, 选择取样长度5.0 μm为宜; 生长液浓度大于0.125 mol/L时, ZnO纳米线之间发生重结晶, 并呈现疏水性; 改变种子层溶液浓度和生长时间, 均得到超亲水表面. 上述结论可用于不同氧化酶、细胞等在ZnO纳米线薄膜上的有效吸附及相应传感器测试性能的进一步提高. 关键词： ZnO纳米线 水浴合成 表面形貌 接触角     

碲、硒碲合金纳米线的可控合成

"采用一种新的化学溶液法合成了具有不同形貌的碲、硒碲合金纳米线．用十二烷基苯磺酸钠作为表面活性剂实现了对纳米线的可控合成,通过控制反应过程可以弯曲状、"V"字型的硒碲纳米线,利用XRD、TEM以及HRTEM对纳米线的形貌结构特征进行表征;以实验结果为依据讨论了纳米线的生长机理．"     

A stochastic model of three-dimensional crystal growth

This paper describes a stochastic model of crystallization from a gas or dilute solution. The model is limited to a crystal of rectangular symmetry whose surface has nonzero Miller indices. By a mapping into the modified KDP model, the kinetic growth coefficient can be given approximately as an analytic function of the Miller indices of the surface. Numerical simulations indicate that the aproximation is accurate within a few percent at all surface orientations.     

Stationary states of crystal growth in three dimensions

A new Markov process describing crystal growth in three dimensions is introduced. States of the process are configurations of the crystal surface, which has a terrace-edge-kink structure. The states are continuous along edges but discrete across edges, in accordance with the very different rates for the two types of captures of particles. Stationary distributions, describing steady crystal growth, are found in general. To our knowledge, these are the first examples of stationary distributions for layered crystal growth in three dimensions. The steady growth rate and other quantities are obtained explicitly for two interacting edges. For many interacting edges, growth behavior is determined (a) in various asymptotic regimes including thermodynamic limits, (b) via simulations, and (c) using series (cluster) expansions in the slope of the surface, the first three coefficients being computed. The theoretical growth rates show a marked dependence on surface dimensions. This may contribute to the size dependence and dispersion in the observed growth rate of small crystals.     

Study of the surface cleaning of GOI and SGOI substrates for Ge epitaxial growth

An effective wet cleaning process, optimized for low temperature Ge epitaxial growth on thin Ge or SiGe structures with reduced surface roughening, is proposed. It is found that HF + HCl cleaning is the most effective wet cleaning method that is applicable to the low temperature thermal cleaning. It is also found that temperature of the thermal cleaning appropriate to 25-30 nm thick germanium on insulator (GOI) or silicon-germanium on insulator (SGOI) substrates is approximately 450 °C. Moreover, it is also found that the temperatures of Ge epitaxial growth even in lattice-matched systems must be reduced to around 400 °C to prevent surface roughening and those in lattice-mismatched systems also must be reduced sufficiently (300 °C for strained Ge growth on SGOI (X_eff = 0.6)) to prevent lattice relaxation as well as surface roughening. Finally, the successful formation of the compressively strained GOI structures is demonstrated by applying these wet cleaning and low temperature thermal cleaning processes and low temperature Ge epitaxy to thin SGOI substrates.     

Studies on the growth,structural, optical and laser damage threshold properties of 4-aminopyridinium p-aminobenzenesulfonate p-ammoniobenzenesulfonate monohydrate crystal

An organic nonlinear optical crystal 4-aminopyridinium 4-aminobenzenesulfonate 4-ammoniobenzenesulfonate monohydrate (4APABS) was grown by slow evaporation solution growth technique. The cell parameters of grown crystal were confirmed by single crystal X-ray diffraction analysis. High resolution X-ray diffraction studies revealed the crystalline perfection of grown crystal. The functional groups present in title compound were confirmed by FTIR spectral studies. UV–vis spectral studies revealed that the grown crystal is transparent in the entire visible region. Single and multiple shots laser induced surface damage threshold values of the grown crystal were measured using Nd:YAG laser. The relative second harmonic generation efficiency of grown crystal was found to be 2.2 times that of KDP crystal.     

椭圆偏振技术研究VHF-PECVD高速沉积微晶硅薄膜的异常标度行为

采用VHF-PECVD技术高速沉积了不同生长阶段的微晶硅薄膜,通过椭圆偏振技术研究了生长过程中微晶硅薄膜表面粗糙度的演化.实验结果表明,沉积气压P_g=300 Pa时,β=0.81,其超出标度理论中β最大值为0.5范围,出现异常标度行为.这表明微晶硅薄膜高速生长中还存在其他粗糙化增加的因素,此粗糙化增加的因素与阴影作用有关. 关键词： 微晶硅薄膜 椭偏光谱法 生长机制 表面粗糙度     

刻蚀AlN缓冲层对硅衬底N极性n-GaN表面粗化的影响

研究了等离子体刻蚀AlN缓冲层对硅衬底N极性n-GaN表面粗化行为的影响. 实验结果表明, 表面AlN缓冲层的状态对N极性n-GaN的粗化行为影响很大, 采用等离子体刻蚀去除一部分表面AlN缓冲层即可以有效提高N极性n-GaN在KOH溶液中的粗化效果, AlN缓冲层未经任何刻蚀处理的样品粗化速度过慢, 被刻蚀完全去除AlN缓冲层的样品容易出现粗化过头的现象. 经X射线光电子能谱分析可知, 等离子体刻蚀能够提高样品表面AlN缓冲层Al 2p的电子结合能, 使得样品表面费米能级向导带底靠近, 原子含量测试表明样品表面产生了大量的N空位, N空位提供电子, 使得材料表面费米能级升高, 这降低了KOH溶液和样品表面之间的肖特基势垒, 从而有利于表面粗化的进行. 通过等离子体刻蚀掉表面部分AlN缓冲层, 改善了N极性n-GaN在KOH溶液中的粗化效果, 明显提升了对应发光二级管器件的出光功率.     

Preparation and growth mechanism of micro spherical ammonium dinitramide crystal based on ultrasound-assisted solvent-antisolvent method

Micro-sized spherical ammonium dinitramide (ADN) crystals are successfully prepared by a facile ultrasound-assisted solvent-antisolvent recrystallization method without introducing any additives. The influences of the volume ratio of solvent to antisolvent, the antisolvent temperature and the ultrasound power on the micro-morphologies and properties of ADN crystals are studied systematically. The changes of morphology, particle size, crystal structure and melting point of the ADN crystals are characterized through scanning electron microscopy (SEM), laser particle size analyzer (LPSA), X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The results show that the optimal experimental parameters for the ADN crystal of spherical morphology are as follows: the volume ratio of solvent to antisolvent is 1:50, the antisolvent temperature is 20 ℃, and the ultrasound power is 70 W. The predicted hexagonal-flake and spherical morphologies for the ADN are close to the experimental morphologies. The growth mechanism of the spherical ADN crystal changes with supersaturation of the ADN solution. As the degree of supersaturation increases, the growth models of the spherical ADN change from the spiral growth to the rough growth, and the morphologies of ADN change from the large-sized ADN ball to the small-sized ADN ball.     

多晶薄膜表面粗化与生长方式转变

采用原子力显微镜研究了磁控溅射多晶薄膜表面粗化行为对归一化沉积温度T_s/T_m(T_s是沉积温度，T_m是材料熔点)的依赖性与薄膜生长方式转变行为.随着T_s/T_m增加，薄膜表面粗糙度增加，而表征粗糙度随时间演化特征的生长指数β历经了先减小再增加的过程.β对T_s/T_m的依赖关系反映了薄膜生长方式的转变行为，即薄膜生长依次由随机生长方式向表面扩散驱动生长方式与异常标度行为生长方式转变.在低于体扩散控制薄膜生长的温度时，晶界扩散机理导致多晶薄膜的表面粗化的异常标度行为. 关键词： 多晶薄膜 表面粗化 温度 生长     

The mass transfer process and the growth rate of NaCl crystal growth by evaporation based on temporal phase evaluation

The mass transfer process and the crystal growth rate have been proved to be very important in the study of crystal growth kinetics, which influence the crystal quality and morphological stability. In this paper, a new method based on temporal phase evaluation was presented to characterize the mass transfer process in situ and determine the crystal growth rate. The crystallization process of NaCl crystal growth by evaporation was monitored in situ by a Mach-Zehnder interferometer, and the absolute concentration evolution, the evaporation rate and the real-time supersaturation of solution were obtained using temporal phase analysis, which acted as a novel technique to extract phase variation along time axis recently. Based on the evaporation rate and the absolution concentration, a new method to calculate mass transfer flux during the crystal growth without the knowledge of the mass transfer coefficient was proposed, and then the crystal growth rate could also be retrieved under the hypothesis of cubic crystals. The results show that the crystal growth rate increases with the supersaturation linearly. It is in agreement with the diffusion theories, which presume that matter is deposited continuously on a crystal face at a rate proportional to the difference in concentration between the points of deposition and the bulk of solution. The method is applicable to the research of crystallization process based on evaporation or vapor diffusion of which the precise conditions of nucleation and supersaturation are usually unknown because of the complexity of the evaporation rate and crystal growth rate.     

Monte carlo simulation of transitions related to growth on (001) faces of Si and Ge

Based on Monte Carlo simulations for molecular beam epitaxy, three types of growth related transitions on the Si(001) and Ge(001) surfaces have been studied. In the thermal roughening simulations on a Ge(001) surface, a different type of transition from the Kosterlitz and Thouless type is obtained. The simulated result is consistent with the experimental x-ray diffraction data, at least qualitatively. In the growth simulations, a transition in the shape of growing islands is shown at the very initial stage of the homoepitaxial growth on a Si(001)-2x1 flat surface. During the transition, the step density variations as a function time show different behaviors at various temperatures. In the homoepitaxial growth on Si(001)-2x1 vicinal surfaces, the growth mode transition from two-dimensional island formation to the step-flow mode is reproduced by increasing the system temperature, which agrees qualitatively with the observed results. At the intermediate temperature, a transient growth mode is obtained, in which the two-dimensional island formation and the step flow growth modes coexist on two types of terraces on the surface.