外延在蓝宝石衬底上的非掺杂GaN研究

采用改变生长条件的方法制备GaN薄膜,在(0001)面蓝宝石衬底上利用金属有机物化学气相沉积技术制备了不同样品,并借助X射线双晶衍射仪(XRD)、PL谱测试仪和光学显微镜对材料进行了分析。XRD(0002)面和(1012)面测试均表明TMGa流量为70 cm3/min时样品位错密度最低。利用该TMGa流量进一步制备了改变生长温度的样品。XRD和PL谱测试结果表明,提高生长温度有利于提高GaN样品的晶体质量和光学性能。最后,利用光学显微镜对样品的表面形貌进行了分析。     

高质量胶体晶体薄膜的快速制备及表征

通过控制温度和湿度，用垂直沉积法（vertical deposition method）快速制备出了可精确控制样品的厚度、在较大范围呈现好的有序性的密排结构的聚苯乙烯（PS）胶体晶体 薄膜.利用透射电子显微镜直观准确地确定了样品为面心（fcc）密排结构.通过控制样品干燥速度和加温处理，胶体颗粒排列更加有序,并且克服了胶体晶体干燥后易碎和在水等溶 剂中容易再分散等缺点，为胶体晶体实际应用创造了条件. 关键词： 胶体晶体薄膜 垂直沉积法 面心密排结构 再分散     

AlN缓冲层对ZnO薄膜质量的影响

采用脉冲激光沉积法以AlN为缓冲层在Si(100)衬底上制备了ZnO薄膜,并测量了样品的XRD谱、SEM图和PL谱.结果表明,AlN缓冲层可以提高Si衬底上外延生长ZnO薄膜的晶体质量.改变缓冲层的生长温度(50～500 ℃)所制备样品的测量结果表明,较低温度下生长的AlN缓冲层有利于制备高质量的ZnO外延层薄膜,其中AlN缓冲层生长温度为100 ℃时外延生长ZnO薄膜晶体质量最好.     

基片温度对磁控溅射HfO2薄膜结构和性能影响分析

在纯氧条件下,采用直流磁控溅射技术在单晶硅基片上沉积氧化铪（HfO2）薄膜,并研究了沉积过程中基片温度对薄膜结构和性能的影响规律。利用X射线衍射仪（XRD）和X射线能谱（XPS）表征了薄膜的晶体结构和组分,利用原子力显微镜（AFM）观察薄膜表面形貌,利用纳米力学测试系统表征了薄膜的纳米硬度和弹性模量。结果表明:磁控溅射制备的HfO2薄膜样品呈(111)择优生长,其晶粒尺寸随着基片温度的升高而增大,但其晶型并不发生转变。随着基片温度的增加,基片中的硅元素向薄膜内扩散,影响了薄膜的化学计量比。沉积薄膜的表面形貌和力学性能亦受到其结构和组分变化的影响。在200 ℃条件下制备的HfO2薄膜纯度高,O、Hf元素化学计量达到了1.99,其表面质量和力学性能均达到了最佳值,随着基片温度升高至300 ℃以上,薄膜纯度下降,表面质量和力学性能均产生劣化。     

感应耦合等离子体增强射频磁控溅射沉积ZrN薄膜及其性能研究

利用感应耦合等离子体(ICP)增强射频磁控溅射技术在Si(111)片和M2钢表面制备了ZrN薄膜，研究了基片的温度和ICP功率对ZrN薄膜的结构以及性能影响.研究发现：在基片温度≤300℃沉积的ZrN薄膜择优取向为(111)；基片温度达到450℃时薄膜出现ZrN(200)衍射峰，ZrN(111)晶面的织构系数明显降低.传统磁控溅射沉积薄膜为柱状结构，当ICP为200 W，基片温度为300℃时沉积薄膜中柱状晶体消失；随着基片温度的升高，N/Zr元素比例降低，并且薄膜的电阻率下降；相对于传统溅射，ICP增强射 关键词： 感应耦合等离子体 磁控溅射 ZrN 微结构     

Co-SiO2颗粒膜的巨磁电阻效应

采用离子束溅射方法在玻璃基片上制备了一系列的Co-SiO2颗粒膜样品,并对样品的巨磁电阻效应进行了研究.在Co35(SiO2)65(体积百分比)颗粒膜样品中,观测到室温下近4%的巨磁电阻效应.研究了不同基片温度对巨磁电阻效应的影响并发现,随着基片温度的升高样品的巨磁电阻效应下降.根据样品的电阻率-温度关系曲线分析,在铁磁金属-非磁绝缘介质颗粒膜中,除了电子自旋相关隧穿效应外,可能还存在其他的导电机制.     

隔热材料的纳米成型与性能分析

经不同工艺和过程制备二氧化硅气凝胶,初步摸索出制备温度、溶剂、催化剂、反应时间最佳参数.在分析气凝胶干燥开裂的原因后,以三甲基氯硅烷(TMCS)为表面修饰剂,正己烷为干燥介质的表面改性工艺,一定程度控制了气凝胶的干燥收缩和开裂.在室温、常压下的通过不同的改性方案制备出四种不同气凝胶样品,揭示了改性条件、干燥温度对于气凝胶孔隙分布、微观结构的影响.     

高质量三维光子晶体的实验制备及理论分析

对压强控制自组装法进行了改进,采用了密封硅胶颗粒的强吸水装置,为光子晶体样品的制备提供了一个稳定的温度、湿度和压强环境.将温度、压强分别控制在35 ℃、45 mmHg,利用直径为260 nm的聚苯乙烯胶体球进行了高质量三维光子晶体样品的制备.从理论计算和实验测量等方面对制备的光子晶体样品的结构、质量和性能进行了对比分析,结果表明,利用该实验装置进行光子晶体样品的制备时,可重复性高;制备的光子晶体样品具有较为完美有序的密堆结构,质量较好;在光子晶体样品的Г L方向有深且窄的光子带隙和陡峭的带隙边沿.光子带隙深度为83%,宽度为0.073,带隙边沿陡峭度为8%/nm,这为超快全光开关等先进的光学设备的研究奠定了基础.     

Co SiO2颗粒膜的巨磁电阻效应

采用离子束溅射方法在玻璃基片上制备了一系列的Co－SiO\-2颗 粒膜样品,并对样品的巨磁电阻效应进行了研究.在Co35(SiO\-2)65(体积 百分比)颗粒膜样品中,观测到室温下近4%的巨磁电阻效应.研究了不同基片温度对巨磁电 阻效应的影响并发现,随着基片温度的升高样品的巨磁电阻效应下降.根据样品的电阻率温度关系曲线分析,在铁磁金属- 非磁绝缘介质颗粒膜中,除了电子自旋相关隧穿效应外, 可能还存在其他的导电机制. 关键词：     

梯度铝镓氮缓冲层对氮化镓外延层性质的影响

采用金属有机物化学气相沉积系统在硅面碳化硅衬底的(0001)面上生长氮化铝缓冲层,并通过改变3层梯度铝镓氮(Al_xGa_(1-x)N:x=0.8,0.5,0.2)缓冲层的生长温度和氨气流量,制备出了高质量的氮化镓外延层。分别采用X射线衍射、原子力显微镜、光致发光谱和拉曼光谱对氮化镓外延层进行表征。实验结果表明,随着氮化镓外延层中张应力的降低,样品的晶体质量、表面形貌和光学质量都有显著提高。在最优的梯度铝镓氮缓冲层的生长条件下,氮化镓外延层中的应力值最小,氮化镓(0002)和(1012)面的摇摆曲线半峰宽分别为191 arcsec和243 arcsec,薄膜螺位错密度和刃位错密度分别为7×10~7cm~(-2)和3.1×108cm~(-2),样品表面粗糙度为0.381 nm。这说明梯度铝镓氮缓冲层可以改变氮化镓外延层的应力状态,显著提高氮化镓外延层的晶体质量。     

Strongly accelerated and humidity-independent drying of nanochannels induced by sharp corners

Measurements are shown indicating that the drying rate of nanochannels can be enhanced by up to 3 orders of magnitude relative to drying by vapor diffusion, and that the drying rate is independent of the relative humidity of the environment up to a relative humidity of more than 90%. Micromachined Pyrex glass nanochannels of 72 nm height and with sharp corners (corner angles 7 degrees) were used. Available theory shows that the sharp corners function as a low-resistance pathway for liquid water, siphoning (wicking) the water to a location close to the channel exit before it evaporates. The described phenomena are of importance for the understanding of drying processes in industry and agriculture. The introduction of sharp corners or grooves can furthermore be beneficial for the functioning of microheat pipes and capillary-pumped loops.     

基于Nafion-结晶紫传感膜的光纤湿度传感器研究

通过研究基于荧光和可见光吸收的两种湿度传感方法,从数种湿度分子探针中优选出结晶紫为分子识别器,包埋于Nafion溶胶中,制备成基于可见光吸收原理的光纤化学湿度传感膜。该传感膜与电荷耦合二极管阵列检测器等构成的光纤湿度传感器,于640nm波长处对30%~100%范围内的相对湿度(rela-tivehumidity,RH)具有较快的响应时间(<2min)、较高的灵敏度(≤5%RH)、选择性和良好的可逆性(RSD≤2.6%)。     

Temperature dependence of the photonic bandgap and the orientational order parameter for a cholesteric photonic crystal

The reflection spectra of a cholesteric photonic crystal have been measured. The experimental spectra are described by a theoretical expression that follows from the analytical solution of the Maxwell equations. The photonic bandgap width Δν has been determined. The photonic bandgap width changes abruptly as the position of the diffraction band changes. The temperature dependence of the relative bandgap width Δν/ν₀ and the order parameter for a photonic crystal are described by Landau’s theory of phase transitions.     

Birefringence sensitivity to temperature of polarization maintaining photonic crystal fibers

In this paper, we investigate the birefringence of polarization maintaining photonic crystal fibers (PM-PCFs) under thermal effect. Modeling and simulation of PM-PCFs under thermal effect are conducted. Birefringence in a PM-PCF as a function of the temperature is measured experimentally. The experimental results are in agreement with theoretical calculation, and show that the relative temperature dependent birefringence coefficient of the PM-PCF, dΔn/dT/Δn, is 2.93×10^?5/°C, which is typically ～35 times less than that of conventional panda fibers. The insensitivity of polarization properties in PM-PCFs to temperature is demonstrated. These findings have important benefits in fiber optic systems and sensors, especially in fiber optic gyroscopes (FOG) where it translates into a lower polarization error and thus a higher measurement precision.     

Enhancement of convective drying by application of airborne ultrasound – A response surface approach

Drying is one of the oldest and most commonly used processes in the food manufacturing industry. The conventional way of drying is by forced convection at elevated temperatures. However, this process step often requires a very long treatment time, is highly energy consuming and detrimental to the product quality. Therefore, an investigation of whether the drying time and temperature can be reduced with the assistance of an airborne ultrasound intervention is of interest.Previous studies have shown that contact ultrasound can accelerate the drying process. It is assumed that mechanical vibrations, creating micro channels in the food matrix or keeping these channels from collapsing upon drying, are responsible for the faster water removal. In food samples, due to their natural origin, drying is also influenced by fluctuations in tissue structure, varying between different trials. For this reason, a model food system with thermo-physical properties and composition (water, cellulose, starch, fructose) similar to those of plant-based foods has been used in this study.The main objective was, therefore, to investigate the influence of airborne ultrasound conditions on the drying behaviour of the model food. The impact of airborne ultrasound at various power levels, drying temperature, relative humidity of the drying air, and the air speed was analysed. To examine possible interactions between these parameters, the experiments were designed with a Response Surface Method using Minitab 16 Statistical Software (Minitab Inc., State College, PA, USA). In addition, a first attempt at improving the process conditions and performance for better suitability and applicability in industrial scale processing was undertaken by non-continuous/intermittent sonication.     

The two-dimensional superconducting photonic crystal

The band structure of a two-dimensional superconducting photonic crystal is studied. The temperature dependence of the photonic band structure in a wide temperature region below the superconducting transition is analyzed. It is found that the photonic crystal has two full band gaps and two incomplete band gaps, which are shifted to the high frequency region with decreasing temperature.     

Ambient effect on optical absorption of Au nanoparticles dispersed within pores of mesoporous SiO2

A gold nanoparticles/monolithic mesoporous silica assembly was synthesized by ultrasonic irradiation of monolithic porous silica presoaked with precursor solution. Subsequent exposure to ambient air (ageing) and then drying at 120°C induce a new optical absorption peak around 470?nm (falling into the range from 460 to 475?nm) which is stable at room temperature, in addition to the normal surface plasmon resonance (SPR) of Au nanoparticles. Further drying results in the decline and disappearance of this peak, accompanied by increase of the normal SPR. If the sample, in which the new peak has disappeared due to long drying at 120°C, is exposed to the ambience once more, this peak will appear again after subsequent drying at 120°C, showing reversibility. Further experiments indicate that ambient ageing for a certain time plays a crucial role in the appearance of the new peak after subsequent drying at 120°C. Increased ageing time increases this peak. In addition, the ambient relative humidity and temperature during exposure are also important to the appearance of this peak. This peak may be associated with Au clusters with a size less than 1.5?nm. Based on the porous structure of the assembly and hydrophilicity of its pore wall, a nanodroplet formation and evaporation model is presented which can well explain all evolution behaviours of this peak. The model predicts the existence of the peak at 470?nm in the Au/silica assembly prepared by methods other than ultrasonic irradiation, which has also been confirmed by further experiments.     

BP神经网络PID控制算法在农作物干燥控制系统中的应用研究与设计

针对传统PID控制算法对于农作物烘干控制方法存在的不足,以实现对农作物高效、节能的干燥为目的,设计了一种新型农作物干燥控制系统。系统采用DS18B20、SHT10为信息采集源,将采集到的温湿度信息传递到以C8051F340单品机为核心的控制器进行整个干燥过程的控制决策。系统应用了BP神经网络PID控制算法调节温湿度。     

Graphene oxide thin film coated quartz crystal microbalance for humidity detection

In this paper, we demonstrated that chemically derived graphene oxide (GO) thin film as a humidity sensitive coating deposited on quartz crystal microbalances (QCMs) for humidity detection. By exposing GO thin film coated QCMs to various relative humidity (RH) environments at room temperature, the humidity sensing characteristics of the QCMs such as sensitivity and linearity, response and recovery, humidity hysteresis were investigated. The experiment results show that GO thin film coated QCMs exhibit an excellent humidity sensing performance. Moreover, the possible humidity sensing mechanism of GO thin film coated QCMs was also investigated by monitoring the crystal's motional resistance change. It is suggested that the frequency response of the QCMs is dependent on water molecules adsorbed/desorbed masses on GO thin film in the low RH range, and on both water molecules adsorbed/desorbed masses on GO thin film and variations in interlayer expansion stress of GO thin film derived from swelling effect in the high RH range.