茂金属化合物Cp2ZrCl2与硅胶表面相互作用分子模拟

利用分子力学、分子动力学和基于密度泛函理论的量子力学从头计算方法对茂金属化合物Cp_2ZrCl_2与含有不同基团的硅胶表面之间的相互作用进行了研究,发现茂金属化合物Cp_2ZrCl_2在双羟基表面的物理吸附最强,在单羟基表面的吸附强度次之,在硅氧烷基表面的吸附最弱。Cp_2ZrCl_2在双羟基作用下,中心金属原子与茂环之间的距离增加,导致茂环脱落,这是茂金属化合物直接负载到硅胶表面后活性较低的主要原因。     

Fe2O3/SnO2和SnO2/Fe2O3双层薄膜的XPS分析

用X光光电子能谱(XPS),结合Ar~+刻蚀对Fe_2O_3/SnO_2及Fe_20_3/SnO_2双层薄膜进行分析.结果表明:Fe_2O_3/SnO_2膜表面,晶格氧的结合能为529.85eV,热处理前有大量吸附氧存在,在600℃退火后,大部分羟基、羰基形态的吸附氧解吸;SnO_2/Fe_2O_3膜表面,热处理前后都只有少量的吸附氧,经热处理后表面吸附氧却略有增加.双层薄膜中锡向氧化铁层的扩散较铁向氧化锡层的扩散强.扩散的结果,形成了一个数十纳米的过渡层,对元件的气敏性质产生一定的影响.     

煤表面对多种气体分子混合吸附的微观机理

应用量子化学密度泛函理论,在6-311 g水平上对建立的吸附模型进行全优化.结果表明,煤的表面能够与多组分气体发生混合吸附.煤表面吸附氧、氮和二氧化碳分子组成的吸附态中,氧分子和氮分子在煤表面的侧链吸附,CO2则在苯环的上方.煤表面氨基上的C原子和N原子的电子向氧分子中的氧原子转移.煤表面吸附了二氧化碳和氮分子,氧分子所得的电子减少,表明如果煤表面吸附其它种类分子,则削弱了吸附氧的作用.吸附后O2的频率变化较大,N2和CO2的频率变化很小.煤表面与矿井采空区各种气体发生吸附时的亲和顺序为:氧气>水>二氧化碳>氮气>一氧化碳>甲烷.     

掺锆SnO_2陶瓷的乙醇气敏特性研究

在研究SnO_2乙醇气体敏感陶瓷中,比较添加物,发现ZrO_2对乙醇气体有较高的灵敏度。进而从工艺上研究了添加ZrO_2时的最佳烧结温度和预烧温度。分析了烧结温度与测试初始电阻的关系。总结出不同条件下乙醇的分解物不同。提出ZrO_2的催化机理是活化表面羟基,释放占有的电子,释放表面的吸附位,从而提高氧离子的效率。     

还原性气体对SnO_2表面势垒的影响

建立了SnO_2表面势垒与表面氧化—还原过程的定量关系,其中考虑了氧的O~-形式吸附和还原性气体的电离吸附。其结果表明,还原性气体的电离是SnO_2表面化学物理过程的关键步骤之一。     

催化剂在MOS 气敏传感器中的作用

1 概述 MOS气敏传感器是在含氧丰富的空气中使用的,在MOS表面存在吸附氧。温度不同,MOS表面吸附氧的形态也不同。例如,SnO_2表面的吸附氧有三种形态:常温～150℃吸脱附的α氧(O_2、O_2~-),400～500℃分解的化学吸附β氧(O~-)以及晶格中的离子氧(O~(2-)),构成升温脱附谱。 β氧的脱附将导致电导变化二个数量级;β氧与还原性气体反应,将得到还原性特强的产物,将电子释放给导带,让气体产物脱附:     

双层气敏薄膜的Ar~+刻蚀及电学行为

制备包含α-Fe2O3与SnO2的双层气敏薄膜，研究发现：Ar＋刻蚀可同时除去薄膜表面的物理吸附氧和化学吸附氧，剩下晶格氧，因而O1s的XPS谱图变得对称．     

MgO(001)表面掺杂金属Au/Pt吸附CO的密度泛函研究

采用密度泛函理论DFT/B3LYP方法研究掺杂了Au和Pt原子的MgO(001)表面吸附CO分子的吸附性质,通过对吸附体系几何构型的优化、能量和电子性质等的计算,结果表明,对于MgO(001)完美表面,掺杂Pt原子比Au更容易吸附CO分子;在MgO(001)表面不同氧缺陷位(O_(5c)/O_(4c)/O_(3c)),掺杂了Au和Pt原子后吸附CO分子的能力依次分别为:O_(3c)O_(5c)O_(4c)和O_(5c)O_(3c)O_(4c),其中掺杂了Pt原子的O_(5c)位吸附能最低。由此可知Pt原子的掺杂及具有氧缺陷的MgO(001)表面,均有利于吸附CO分子。     

氧在SnO2（110）面吸附机理的研究

用ＥＨＭＯ方法计算了ＳｎＯ２（１１０）面原子簇模型，并计算了表面存在氧空位和氧原子吸附的情况，计算结果表明，表面本配位锡原子是吸附中心，因电子得失而引起的原子净电荷变化是完全定域的。     

氧SnO2在面吸附机理的研究

用方法计算了面原子簇模型, 并计葬了表面存在氮空位和氧原 于吸附的情况计界结果表明, 表面四配位锡原予是吸附中心, 因电于得失而引起的原予 净电待变化是完全定城的四酗位锡原子的净电荷变化很明显, 而五配位锡原予吸附的净 电荷变化很小     

The effects of temperature, relative humidity and reducing gases on the ultraviolet response of ZnO based film bulk acoustic-wave resonator

This study investigated the influence of temperature, relative humidity and reducing gases on the ultraviolet (UV) response of ZnO based film bulk acoustic-wave resonator (FBAR). As temperature increased, the UV response of the FBAR degraded. This was attributed to the softening of the ZnO film with increasing temperature. Water molecules can replace adsorbed oxygen on the ZnO surface. At high relative humidity, more oxygen was replaced by water. In this way, the density of the ZnO film increased and less oxygen was left on the surface to be desorbed by UV, both of which contributed to a lower UV response. Reducing gases, such as acetone, can react with the surface adsorbed oxygen and reduce the density of the ZnO film, resulting in UV response degradation.     

TiO_2表面氧吸附模拟与氧敏特性研究

根据经典的统计理论,并结合麦克斯韦速率分布律得出吸附过程中O2吸附量的理论模型,从而获得氧吸附面密度与温度、氧分压的理论变化规律。在活化能Ea=0.30 eV的情况下,TiO2对氧气吸附的温度敏感区域在120~410K之间,最佳吸附温度为370K,这与由金红石相TiO2所制成氧敏元件的最佳灵敏度所处的工作温度(378K)相近。并由模拟理论推测O2在半导体表面的吸附面密度与氧分压呈线性增加。     

Influence of oxygen backgrounds on hydrogen sensing with SnO2 nanomaterials

The influence of different oxygen backgrounds on the sensing of hydrogen with SnO₂ nanomaterials was investigated and a model was proposed. It is based on two hydrogen reaction mechanisms at the surface of tin oxide that can take place simultaneously; the weight of each mechanism depends on the concentration of oxygen in the ambient atmosphere. In the absence of oxygen the adsorbed hydrogen builds surface donors (rooted hydroxyl groups). In the presence of oxygen the reaction between hydrogen and pre-adsorbed oxygen ions dominates. Due to the fact that this behavior is present for very different nanomaterials, the model probably describes a SnO₂ specific feature.     

Growth and gas sensing characteristics of p- and n-type ZnO nanostructures

ZnO nanoparticles (NPs) of 5-15 nm size and nanowires (NWs) of 50-100 nm dia., exhibiting p and n-type characteristics, respectively, have been synthesized using simple chemical process. ZnO NW-films exhibited good sensitivity and selectivity towards H₂S in ppm range with fast response and recovery times. Interestingly, ZnO NP-films showed p-type conductivity that has been obtained for the first time without intentional doping while NW-films showed n-type conduction as has also been reported in various earlier studies. The p- and n-type conductivities in NP- and NW-films have been confirmed using hot probe and Kelvin probe measurements. The n-type behavior of NW-films is attributed to oxygen vacancies, whereas the p-type nature of NP-films is attributed to the zinc vacancy, surface acceptor levels created by the adsorbed oxygen and/or the unintentional carbon doping in ZnO.     

Metal to semiconductor conversion by hydrogenation in guanine functionalized SWCNT

Conversion of the metallic SWCNT to semiconducting SWCNT was achieved by band structure engineering of the nanotube by functionalization of the DNA nucleobase, guanine. The band structure analysis revealed that metallic SWCNT (6, 0), when surface engineered with guanine nucleobase with H-atom attachment as the functional group, is converted to a semiconductor one by opening a narrow bandgap with a value of 0.08 eV. This phenomenon was brought about by strong chemisorption due to hydrogenation by inducing partial sp³ hybridization in the nanotube structure. No bandgap openings were observed when guanine was adsorbed on the pristine nanotube surface by its nitrogen site and oxygen site respectively. Related zero-bias transmission spectra and IV-curve supported the result also. The entire study was done at room temperature using ATK-VNL simulation software.

     

Adsorption of phenol molecules by sodium dodecyl sulfate (SDS) surfactants deposited on solid surfaces: A computer simulation study

Adsorption studies of phenol molecules on a sodium dodecyl sulfate (SDS) micelle were investigated by molecular dynamics simulations. Simulations were carried out in bulk and on three distinct solid surfaces, silicon dioxide, titanium dioxide and graphite. It was observed that different surfactant micellar shapes were formed on the surfaces. For the silicon dioxide and titanium dioxide surfaces the surfactants were adsorbed by their headgroups whereas for the graphite surface they were adsorbed mainly by their tail groups. It was found that the amount of phenol adsorbed on the SDS micelle was altered by the surfactant shape deposited on the solid surface. However, the best phenol adsorption was obtained by the surfactant modified silicon dioxide surface. Moreover, in all cases, from structural investigations, it was determined that the phenol molecules were located inside the surfactant micelle with their hydroxyl groups close to the SDS headgroups.     

SnO_2/ZnO双层膜的表面界面及气敏特性

用溅射法制备了SnO_2/ZnO薄膜,采用XPS,AFS,SEM,等手段研究了薄膜的表面及界面,发现在薄膜中,锌与锡存在不同深度的相互扩散,从SEM的断面观察可看到有一个明显的界面存在。XRD分析则表明:ZnO极易沿(002)面择优取向生长。并且SnO_2/ZnO膜具有良好的气敏性质。     

Quantifying adsorbed water monolayers on silicon MEMS resonators exposed to humid environments

This study investigated the influence of temperature and humidity on the adsorbed water layer on micron-scale monocrystalline silicon (Si) films in air, using a Si-MEMS kHz-frequency resonator. Both temperature and relative humidity induced a reversible change in resonant frequency, attributed to the temperature-dependent properties of Si and to a change in adsorbed water layer. The excellent precision in resonant frequency measurement (0.02 Hz, or 0.5 ppm) allowed precise calculation of the changes in adsorbed water layer thickness over the specimen surface. The increase in water thickness with relative humidity was a function of temperature and could not be described with simple multimolecular adsorption theories such as the BET theory. A likely explanation is the presence of hydrocarbon contaminants on the Si surface. Guidelines are provided to accurately measure the influence of temperature and relative humidity on the adsorbed water layer thickness on micron-scale Si surfaces, using this technique.     

金属／YSZ电极对氧传感器性能的影响

借助交流阻抗谱测试技术和扫描电镜,对Pt,Au,Ag,Ag—Pt,Ag—Pd电极浆料所制金属／YSZ电极的界面电阻、激活能进行了研究,并计算了由其构成的氧传感器达到90％响应量所需时间。研究表明：400-600℃时,02在Ag／YSZ电极上反应速率最快,激活能最低,为91kJ·mol^-1;Pt／YSZ电极激活能最高,为183kJ·mol^-1,电极反应速率控制步骤为吸附氧原子在电极表面的扩散过程;Ag—Pt,Ag—Pd／YSZ电极激活能均较Ag／vsz电极高,Pd含量增大时,Ag—Pd／YSZ电极激活能亦增大;400-450℃时,Ag／YSZ氧传感器响应时间最短,450-600℃时,Ag-1％Pd／YSZ氧传感器响应最快。