钛酸锶晶体退火过程中氧扩散的有限元分析

针对钛酸锶晶体退火过程中氧原子的扩散问题建立了二维有限元模型,研究了温度、晶体尺寸、退火时间时氧原子扩散状态的影响规律.结果表明:氧在短时间内以大通量从晶体表面扩散,然后以小通量比较稳定地向内部缓慢扩散,温度越高,氧扩散到中心时间越短,在700 K、800 K、900 K条件下退火50 h,氧从晶体表面扩散到中心的时间分别为8h、5h和3h,退火深度分别为1 mm、3mm和退透.     

退火温度对等离子体增强化学气相沉积方法生长的ZnO薄膜质量的影响

研究ZnO薄膜质量与退火温度的关系,为了获得高质量的晶体薄膜,采用PECVD方法在硅(100)衬底上生长ZnO薄膜,生长温度为120℃,然后分别在氧气环境下退火(600℃～1000℃)1 h.X射线衍射谱和原子力显微镜(AFM)照片结果表明随着退火温度的升高,晶体择优取向明显,晶粒平均尺寸增大,到900℃时,晶粒平均尺寸达到38 nm.光致发光谱的结果表明,随着退火温度的升高,发光峰的半高宽(FWHM)逐渐地变窄,到900℃时,达到92meV,晶体质量得到了明显提高.通过对变温光谱的拟合计算,得到激子束缚能为59 meV,表明紫外发射来自于自由激子辐射复合.     

Mn掺杂ZnO稀磁半导体的化学合成及磁性研究

采用化学方法制备了名义组分为Zn0.993Mn0.007O的Mn掺杂ZnO稀磁半导体材料,并研究了退火温度(Ts＝400,600,800℃)对其结构和磁性的影响.结果表明:在退火温度低于600℃条件下,合成的样品为单一纤锌矿结构的ZnO颗粒材料;当退火温度为800℃时,合成的样品中除了纤锌矿结构ZnO外还观察到ZnMnO3第二相的存在.磁性研究表明:经过600℃退火后的样品,其室温铁磁性最强,而经过800℃退火后的样品,其铁磁性几乎消失,并表现为增强的顺磁性.结合对样品的Raman光谱和紫外-可见吸收光谱的分析,表明Mn元素进入了ZnO晶格中并替代了ZnO中的Zn离子. 样品的室温铁磁性是源于(Zn,Mn)O的本征特性,并排除了样品中第二相导致其具有室温铁磁性的可能性.     

衬底离子束表面氮化对ZnO薄膜性质的影响

采用射频磁控溅射法在抛光硅片上沉积了一系列ZnO薄膜样品.通过对薄膜样品X射线衍射谱的分析、原子力显微图的观察、吸收光谱和荧光光谱的研究,发现Si衬底的离子束表面氮化对ZnO薄膜的晶体结构、表面形貌和光学性质有重要影响.在衬底温度为200℃、高纯氩氧比例为3:1、压强为1.5Pa的条件下,在经离子束表面氮化预处理的Si衬底上溅射沉积的ZnO薄膜,经450℃真空退火,成为高(0002)晶面取向的ZnO薄膜,并具有良好的光学性质.     

自燃/球磨法制备NiZn系铁氧体

以金属硝酸盐和柠檬酸为原料,用溶胶凝胶自燃烧法制备NiZn系铁氧体前驱体粉末(Ni0.4Zn0.6Fe2O4,Ni0.2Zn0.6Cu0.2Fe2O4,Ni0.33Zn0.59Cu0.11Fe1.97O4(Bi2O3)0.002和Ni0.33Zn0.59Cu0.11 Fe1.97O4(Bi2O3)0.002(MnO2)0.02),然后经30小时高能球磨,从X-ray衍射谱中发现前驱体粉末虽然基本上是尖晶石结构,但是还有一些杂相,经过球磨,杂相明显减少,结构更加完整,颗粒减小.前驱体粉末Ni0.33Zn0.59Cu0.11Fe1.97O4(Bi2O3)0.002经30小时球磨后,在空气中退火,退火温度分别为400℃,600℃,800℃,900℃,1000℃.用X-ray衍射谱分析其物相,发现在800℃退火得到单相的尖晶石结构,无杂相.该样品的最佳退火温度低于1000℃.用振动样品磁强计分别测量制备态和退火态样品粉末的磁性,可以看出,随退火温度的升高,比饱和磁化强度σs逐渐增大,矫顽力Hc逐渐减小,当900℃退火后,比饱和磁化强度已接近块状NiZn系铁氧体.1000℃退火后,上述四种样品中Ni0.4Zn0.6Fe2O4具有最高的比饱和磁化强度σs=65.09emu/g.本文为NiZn铁氧体的低温烧结提供了有用的实验数据.     

不同煅烧温度对溶胶-凝胶合成的纳米ZnO光催化效果的影响

采用溶胶-凝胶工艺,以醋酸锌为前驱体,二乙醇胺为稳定剂,不同煅烧温度退火改性得到颗粒分布均匀的ZnO纳米粉体。测试发现,450℃退火得到的ZnO粉体催化效果最好,经紫外光照射240min后可完全降解甲基橙,其速率常数(k)为0.0163min-1。XRD、TEM、XPS、SEM、PL、UV-vis检测表明,温度从350℃上升到650℃,所有ZnO样品均呈六角纤锌矿结构,颗粒从不均匀扁平圆形生长为均匀球状,晶粒尺寸增大,团聚现象明显减少,样品结晶性随温度升高明显变好。另一方面,随着温度的升高,晶格氧所占的比例增大,空位氧浓度减小并产生体缺陷。结合光催化结果发现,适当的结晶度、比表面积和适量的氧缺陷对光催化降解更有利。     

反应源温度对ZnO纳米线阵列定向性及发光性能的影响

以Au薄膜为催化剂、ZnO与碳混合粉末为反应源,采用碳热还原法在单晶Si衬底上制备了ZnO纳米线阵列.通过扫描电子显微镜( SEM)、X射线衍射仪(XRD)、荧光分光光度计对样品的表征,研究了反应源温度对ZnO纳米线阵列的定向性和光致发光性能的影响.样品在源温度920℃条件下沿(002)方向择优生长,定向性最好,温度过低不利于ZnO纳米线阵列密集生长,而温度过高导致Zn原子二次蒸发,因而也不利于纳米线阵列的定向和择优生长;样品在源温度880℃有最强的近紫外带边发射,表明温度过高和过低都不利于ZnO晶体结构的优化;由于ZnO纳米线在缺氧氛围下生长,氧空位是缺陷存在的主要形式,因此所有样品都有较强的绿光发射.温度升高导致纳米线生长速度提高而增加了氧空位缺陷数量,从而使样品绿峰强度增强并在源温度920℃时达最大值,但温度的进一步升高可导致ZnO纳米线表面Zn元素的蒸发而降低氧空位缺陷的数量,从而抑制绿峰强度.     

氮硫共掺杂碳纳米管的制备及其催化性能研究

采用非原位掺杂方式,将化学气相沉积法生长的碳纳米管阵列在含氮和含硫的气氛下,700~900℃退火,制备了氮硫共掺杂的碳纳米管(NS-CNT)。X射线光电子能谱仪测试证明,通过非原位掺杂方式成功实现了氮和硫在碳纳米管上的掺杂。通过电化学测试研究退火温度对氧还原反应催化活性的影响,电化学测试结果表明,800℃退火所制备样品的氧还原峰电位和起始电位分别为0.873,0.771V,表现出最好的催化活性。通过旋转环盘电极测试发现,样品NS-CNT-800在反应过程中的反应电子数为3.7,说明该样品的反应机理是二电子和四电子反应同时进行,但以四电子反应过程为主,并研究了样品的长时间稳定性。与商业燃料电池所用的Pt/C催化剂相比,NS-CNT-800的稳定性更好,用于燃料电池有明显的优势。     

ZnO薄膜中与Zn原子缺陷相关的发光特性研究

ZnO薄膜中可见光的发射与缺陷有关,为了研究ZnO薄膜中与Zn原子缺陷相关的发光特性,将不同Zn缓冲层厚度的ZnO薄膜沉积在Si衬底上,且所有样品在400℃下真空中退火1 h,采用X射线衍射谱(XRD)、吸收谱和光致发光谱(PL)表征了样品的晶体结构和光学特性。结果表明,随着Zn缓冲层溅射时间的增加,ZnO薄膜中的紫光峰向长波段发生了红移,且所有的发光峰强度逐渐增加;缓冲层和真空中退火都使得样品中有过量的Zn原子缺陷出现,薄膜中所有的发光峰与Zn原子缺陷相关。     

表面热处理对氮化硼薄膜场发射特性的影响

用RF磁控溅射的方法在最佳沉积条件下在Si(100)基底上沉积了纳米氮化硼薄膜,然后对薄膜在真空度低于5×10-4Pa、温度分别为800℃和1000℃条件下进行了表面热处理,分别用红外光谱、原子力显微镜以及不同退火温度的场发射试验对薄膜进行了研究,结果表明表面热处理对BN薄膜的表面形貌没有明显影响,样品场发射特性的变化可能与表面负电子亲和势有关,未进行热处理的样品阈值电场较低,可能归因于表面负电子亲和势效应,阈值电场为8V/μm,发射电流为80μA,热处理温度为800℃时,负电子亲和势仍然存在,直到热处理温度达到1000℃时,表面负电子亲和势才消失.     

热处理对Ag-ZnO异质结构光催化性能的影响

用溶胶-凝胶法制备纯ZnO和Ag修饰ZnO复合光催化剂,并分别对其进行了400℃、450℃、500℃保温2 h的热处理。使用XRD、SEM、TEM、XPS、PL、BET等手段对其进行了表征。结果表明,纯ZnO和Ag修饰ZnO均为六方纤锌矿晶型,Ag颗粒沉积在ZnO表面形成了Ag-ZnO异质结构。以罗丹明B为目标污染物研究了样品的光催化活性。结果表明,热处理温度对纯ZnO的光催化性能的影响较大,在450℃热处理后光催化效果最佳;热处理温度对Ag修饰ZnO的光催化性能没有显著的影响;Ag修饰ZnO比纯ZnO的光催化活性均有所提高,因为Ag修饰提高了ZnO表面羟基的含量并抑制了光生电子与空穴的复合。在500℃热处理后Ag修饰ZnO对罗丹明B的60 min降解率达到98%,其反应速率常数为0.063 min^-1。     

温度对爆轰法合成纳米氧化铝晶型及晶粒度的影响

用爆轰法合成了纳米γ氧化铝粉体。对粉体分别进行从室温加热到600℃、800℃、900℃、1000℃、1100℃和1300℃的煅烧处理,对煅烧样品进行了X射线衍射分析,研究了不同煅烧温度下,纳米氧化铝的晶粒度。结果表明,随煅烧温度的升高,纳米氧化铝经历了从γ型转变成δ型,再转变成θ型,最后完全转变成α型纳米氧化铝的过程。随着加热温度的升高,纳米氧化铝出现了晶粒细化现象,且晶粒细化有两个过程,细化程度最大的温度区间为800~1000℃。     

Low-temperature synthesis and photocatalytic properties of ZnO nanotubes by thermal oxidation of Zn nanowires

A low-cost and catalyst-free two-step approach has been developed to produce ZnO nanotubes (ZNTs) by simple thermal oxidation of Zn nanowires under 20?Pa at a low temperature of 400?°C. The growth mechanism of ZNTs is discussed in detail. The formation of these tubular structures is closely linked to the oxidation pressure and temperature, which involves a process consisting of the deposition of Zn nanowires, cracking of the Zn nanowires and sublimation of the Zn cores, and subsequent oxidation to ZNTs. The optical properties were studied by using Raman and photoluminescence spectra, where a strong green emission related to the single ionized oxygen vacancy appears. The photocatalytic activity measurement indicates an enhanced photocatalytic activity of the prepared ZNTs due to their high surface-to-volume ratios and abundant oxygen vacancies near the surfaces of the ZNTs. This type of high surface area structural ZNTs could find promising potential for optoelectronic and environmental applications.     

Effect of substrate temperature on (<Emphasis Type="Italic">00l</Emphasis>) oriented growth of ZnO nanostructures on fused quartz substrate by PLD

A simple and novel catalyst free (00l) oriented zinc oxide (ZnO) nano-structures were synthesized on quartz substrate by pulsed laser deposition (PLD). The effects of substrate temperature on structural and optical properties of these nanostructures were investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and spectroscopic ellipsometry. XRD showed that the ZnO nanostructures had c-axis oriented hexagonal wurtzite crystal structure. Crystallite sizes were found to increase as substrate temperature increases. An AFM measurement confirms the grain formation and increase in surface roughness at higher substrate temperature. Optical band gap of these ZnO nanostructures was calculated using transmittance spectra in UV–Vis region and found to decrease from 3.24 to 3.21 eV as substrate temperature is increased from 500 to 800?°C. PL spectra show that all the peaks in UV region around 389 nm; 3.18 eV. The decrease in band gap may be attributed to decrease in oxygen vacancies at higher substrate temperature and may be useful for different applications.     

退火温度对多孔阳极氧化铝膜形貌的影响

采用二次阳极氧化法制备了有序的氧化铝膜,于800℃、900℃和1000℃对氧化铝膜进行退火处理,经X射线衍射检测发现,其晶相结构由γ-Al2O3向θ-Al2O3结构转变,而且由于相变不彻底导致多晶相结构并存。比较了3种不同的退火温度对氧化铝膜表面有序孔的影响,提出了对于内嵌入氧化铝膜的前驱体材料的退火条件,即退火温度不宜太高,退火时间不宜太长。     

Influence of spray flux density on the photocatalytic activity and certain physical properties of ZnO thin films

This paper reports the effect of spray flux density on the photocatalytic activity of sprayed ZnO thin films towards the Rhodamine B (RhB) degradation, for the first time. In addition, the influence of annealing on the photocatalytic activity of ZnO film is studied and reported. It was found that, the change in spray flux density helps in tuning the surface morphology, crystalline quality and the concentration of oxygen vacancies (V_O) and zinc interstitials (Zn_i) which are crucial factors that can control the photocatalytic activity of deposited samples. The photocatalytic study shows that the samples prepared from higher spray flux density possess high efficiency for degradation of RhB. As these samples require only lower deposition time, this result may be useful in reducing the time consumed in large area production of photocatalytic thin films.     

燃料对溶液燃烧合成ZnO纳米棒微观形貌和光催化性能的影响

以蔗糖、柠檬酸、乙二醇和尿素为燃料, Zn(NO₃)₂为氧化剂/锌源, 采用溶液燃烧法合成ZnO纳米棒。借助XRD、SEM、比表面分析和光谱吸收等测试方法, 考察了不同燃料对粉体的物相组成、微观形貌、比表面积和光催化性能的影响。结果表明: 在点燃温度500℃下, 各燃料配制的前驱体溶液均可发生燃烧反应合成六方相ZnO纳米棒, 其平均径向尺寸小于100 nm, 且以尿素为燃料合成的ZnO晶形更完整, 以蔗糖为燃料合成的ZnO粉体具有最大的比表面积(24.83 m²/g)。光催化实验表明, 以蔗糖为燃料合成的ZnO粉体光催化能力最佳, 在高压汞灯照射60 min条件下, 其对甲基橙溶液(10 mg/L)的降解率可达98.2%, 且光催化反应符合一级动力学方程。     

The correlation among morphology,oxygen vacancies and properties of ZnO nanoflowers

Despite numerous reports have investigated the effect of morphology on the properties of nanomaterials, its role in tuning nanomaterials properties is still not clear to date. This work introduces a unique attempt to explore the correlation among morphology, surface defects (oxygen vacancies), and properties of nanomaterials. To achieve this task, three different morphologies of ZnO nanoflowers were prepared via hydrothermal method by varying the concentration of diethylamine. It was observed that a change in ZnO nanoflowers morphology results in changes in their optical, photocatalytic, and antibacterial properties. Photoluminescence and X-ray photoelectron spectroscopy analyses reveal the presence of oxygen vacancies (V_O) in ZnO nanoflowers with a concentration varies with respect to morphology. V_O concentration plays a key role in tuning ZnO band gap and the concentration of reactive oxygen species and thereby tuning optical, photocatalytic, and antibacterial properties of ZnO nanoflowers. Our results suggest that V_O concentration, morphology, and properties of ZnO nanoflowers are correlated.     

Roles of photo-generated holes and oxygen vacancies in enhancing photocatalytic performance over CeO2 prepared by molten salt method

A series of CeO₂ photocatalysts were synthesized through the molten salt method. The photocatalytic activity was evaluated through the degradation of methyl orange (MO). Systematic characterizations including X-ray diffraction, Scanning electron microscopy, Fourier transformed infrared, X-ray photoelectron spectroscopy, Raman spectroscopy, electron spin-resonance spectroscopy, UV–vis diffuse reflectance spectroscopy, photoluminescence spectrometry, photocurrent response and electrochemical impedance spectroscopy were conducted to study the as-prepared CeO₂ samples. It was found that, under ultraviolet light irradiation, the apparent rate constants of CeO₂ prepared at 800 °C for degradation of MO was about 3.4 times higher than CeO₂ prepared at 500 °C. CeO₂ prepared at 800 °C held the higher oxygen vacancies concentration. According to the trapping experiments, it was demonstrated that photo-generated holes played a dominant role in this photocatalytic system. Furthermore, the possible photocatalytic mechanism which showed the roles of photo-generated holes and oxygen vacancies was proposed.