光退火制备多晶硅薄膜的量子态现象

用PECVD法直接沉积的非晶硅(a-Si:H)薄膜在中温情况下光退火,然后用XRD、Raman光谱和SEM分析,发现晶粒大小随退火温度和退火时间呈现量子态现象.平均晶粒大小为30nm左右.     

常规退火与光退火固相晶化的对比

为研究传统炉子退火与光退火固相晶化的不同特点,用石英玻璃作衬底,在室温、350℃和450℃下用PECVD法直接沉积非晶硅(a-Si:H)薄膜,把沉积的样品分别在850℃下用传统炉子退火3h、用光快速热处理(RTP)5min,然后用Raman、XRD和SEM分析对比,发现传统炉子退火后的晶粒分布不均匀,光退火后的晶粒分布均匀.XRD分析发现两种方法晶粒尺寸均为30nm左右.     

多晶硅薄膜结晶团晶化机理的研究

本文用PECVD法在石英玻璃上沉积非晶硅薄膜,然后用快速光退火和传统电阻炉退火方法晶化生长多晶硅薄膜,用拉曼光谱仪、XRD和场发射扫描电镜观察分析薄膜,发现在制备的多晶硅薄膜表面存在结晶团现象,并对这一现象的晶化机理进行了分析.     

碲锌镉单晶体的正电子寿命研究

用正电子湮没技术(PAT)研究了原料富Cd改进布里奇曼法生长的碲锌镉单晶样品退火前后的缺陷.刚生长的样品缺陷寿命值较高,其内部存在的点缺陷主要是占优势的Cd空位,用富Cd同成份源Cd1-xZnxTe气氛对样品在不同温度下等时退火后,发现样品的正电子寿命参数对退火温度表现出很强的依赖关系,通过对样品退火过程中空位的迁移、聚集及消失情况分析,得出较适宜的退火温度约为700℃.     

PbTiO3-CoFe2O4复合薄膜的溶液法制备及其微观结构研究

以乙二醇甲醚为溶剂,采用溶液法成功制备了致密的、铁电相和铁磁相共存的0-3型磁电复合薄膜.采用X射线衍射(XRD)、原子力显微镜(AFM)、X射线能潜分析(EDAX)、压电响应力显微镜(PFM)分析了退火时间对两相结构、晶粒大小、薄膜形貌、电畴及磁畴的影响.结果表明,退火20 min 对于 PbTiO3相晶粒的生长已经足够,随着退火时间的延长,CoFe2O4相的品粒逐渐长大,薄膜的均方根粗糙度有所提高;同时因为磁件相品粒的长大复合薄膜电畴的取向发生了极大地变化.复合薄膜中同时存在的电畴和磁畴证明了其同时具有的铁电性和磁性.     

基于直流磁控溅射室温制备ZnO薄膜研究

采用直流磁控溅射法在P型<100>晶向单晶硅衬底上室温制备ZnO薄膜,对室温制备的ZnO薄膜分别在500℃、600℃、700℃进行高温退火,通过采用X射线衍射(XRD)、拉曼光谱和场发射扫描电子显微镜(SEM)、HP4145B型半导体参数测试仪分析不同退火温度对室温生长ZnO薄膜微结构、表面形貌和,Ⅰ-Ⅴ特性影响.实验结果表明,室温生长的ZnO薄膜为非晶态,随退火温度增加,ZnO薄膜出现(002)、(100)、(101)晶面衍射峰且逐渐增强,晶粒大小相对增加,在700℃退火后,呈高度c轴择优取向,晶粒间界明显,拉曼光谱E2模增强.     

用快速光热退火制备多晶硅薄膜的研究

用等离子体增强型化学气相沉积先得到非晶硅(a-Si:H)薄膜,再用卤钨灯照射的方法对其进行快速光热退火(RPTA),得到了多晶硅薄膜.然后,进行XRD衍射谱、暗电导率和拉曼光谱等的测量.结果发现,a-Si:H薄膜在RPTA退火中,退火温度在750℃以上,晶化时间需要2min,退火温度在650℃以下,晶化时间则需要2.5h;晶化后,晶粒的优先取向是(111)晶向;退火温度850℃时,得到的晶粒最大,暗电导率也最大;退火温度越高,晶化程度越好;退火时间越长,晶粒尺寸越大;光子激励在RPTA退火中起着重要作用.     

硅薄膜晶化机制的光学分析

采用拉曼光谱和分光光度计等测试手段,对快速光热过程(RTP)和常规炉过程(CFP)退火后的硅薄膜结构性能和光学性能进行了研究。用Avrami-Mehl-Johnson和Monte Carlo晶体生长模型和黑体辐射理论分析得出,RTP法退火温度低、速度快的原因,是RTP中不仅存在“光量子效应”,而且还存在“光热相长效应”。由光学带隙的计算得知,RTP退火法可使带隙约为1.7eV的非晶硅薄膜变为带隙约为1.28eV的微晶硅薄膜,说明RTP退火达到了较好的结晶效果。     

退火温度对Zn0.93Fe0.07O薄膜微结构和铁磁性能的影响

用射频磁控溅射方法在硅片上制备了Zn0.93Fe0.07O薄膜,并在空气中用不同温度进行热处理,利用X射线衍射仪和扫描电子显微镜对其微结构、表面和断面形貌进行测试.结果表明,薄膜沿c轴方向择优生长,呈六角纤锌矿结构,空气中450℃退火的样品XRD谱中出现最强的(002)衍射峰,晶粒尺寸变大,薄膜结晶和取向明显变好.用振动样品强磁计对样品铁磁特性进行测试,发现当退火温度的升高时,饱和磁化强度有所增加,并经分析认为这可能是薄膜中晶粒间的晶界缺陷引起的.     

温度对快速热退火制备多晶硅薄膜结构与电学性能的影响

采用快速热退火方法对热丝CVD沉积的非晶硅薄膜进行了晶化处理.利用傅里叶红外光谱研究了非晶硅薄膜脱氢处理前后Si-Hx含量的变化;用X射线衍射(XRD),拉曼(Raman)光谱和扫描电子显微镜研究了硅薄膜的结构性能与退火温度的关系;利用电导率测试研究了硅薄膜的电学性能对退火温度的依赖性.研究发现,脱氢处理可以有效的抑制快速热退火引起的硅薄膜中微裂纹的出现.随着退火温度由700℃升高至1100℃,硅薄膜的结晶性逐渐升高,在1100℃下快速热退火15 s制备的多晶硅薄膜的晶化率高达96.7;.同时,硼掺杂硅薄膜的电导率也由700℃退火的1.39×10-6 S·cm-1提高至1100℃退火的16.41 S·cm-1,增大了7个数量级.     

Crystal growth of cyclodextrin‐based metal‐organic framework with inclusion of ferulic acid

The crystallization of γ‐cyclodextrin‐based metal‐organic framework (CD‐MOF) with inclusion of ferulic acid (FA) was carried out through vapor diffusion of methanol to the aqueous solution of γ‐cyclodextrin (γ‐CD), KOH and FA. Although the crystallization of pure CD was limited in highly basic solution of KOH (pH>13.0), the CD‐MOF with inclusion of FA (FA/CD‐MOF) was able to be formed at pH 6.8 after the neutralization of KOH by FA. The inclusion behavior of FA in CD‐MOF was studied by using differential scanning calorimetry. The data indicate the formation of the stable association between FA and γ‐CD in FA/CD‐MOF.     

Effect of P2O5 on the early stage crystallization of K-fluorrichterite glass-ceramics

The addition of 2 mol% P₂O₅ to stoichiometric K-fluorrichterite (KNaCaMg₅Si₈O₂₂F₂, KFR) has been reported to enhance the mechanical properties and improve the in vitro biocompatibility of this glass-ceramic by promoting the formation of enstatite and fluorapatite (FA). Here, the effect of further increasing the P₂O₅ concentration on phase evolution of KFR has been investigated. XRD data showed that mica crystallized in samples with 4 and 5 mol% P₂O₅ (GP4 and GP5, respectively) at 650 °C, but no diopside was detected at higher temperatures, in contrast with the general phase evolution in KFR based glass-ceramics. More importantly, however, the addition of ?4 mol% P₂O₅ induced phase separation of the glass into a silica glass matrix and phosphate rich droplets prior to crystallization. EDS traces taken from samples heat-treated at 600 °C, revealed that the silica glass matrix was deficient in Mg and unlikely to be the host for crystallization of mica. Conversely, the P₂O₅ rich regions contained excess Mg and were considered to be the host for the formation of mica and FA.     

Calcite growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic calcite formation

Increases in ocean surface water dissolved carbon dioxide (CO₂) concentrations retard biocalcification by reducing calcite supersaturation (Ω_c). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and Ω_c=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10^?4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a calcite growth-rate inhibitor as FA. Calcite growth rate in the presence of both FA (0.5 mg/L) and Mg (10^?4 M) is reduced to 5% of the control rate. Mg inhibits calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.     

Metal contamination detection in nickel induced crystallized silicon by spectroscopic ellipsometry

In this paper a new approach is presented for the simulation of spectroscopic ellipsometry (SE) data to estimate the level of nickel (Ni) contamination in silicon crystallized by metal induced crystallization (MIC). The method employs the addition of Ni as reference for a Bruggemann effective medium approximation (BEMA) to simulate the optical response of the crystallized silicon. This new approach is sensitive to changes in the initial average metal thickness used on the crystallization process to thickness values as low as 0.05 nm. This corresponds to a volume fraction of 0.24%, confirmed by Rutherford backscattering spectrometry (RBS) where it was observed that the Ni volume fraction detected by SE varies linearly with the metal amount inside the crystallized films determined by RBS.     

The Peculiarities of the Optical Absorption of Monocrystalline Fluorene and Its Heteroanalogues in the Energy Range Between 3.5 eV and 8.5 eV

Electronic absorption spectra of carbazole, dibenzofuran and fluorene were obtained in all three crystallographic directions (energy range 3.5-8.5eV). All electronic transitions with transition dipoles at oblique angles to a and b crystallographic axes can be traced to parental molecular states.

Crystal transitions with parallel transition dipoles can be traced to parental molecular states for thin (0.1-0.2μ) crystals, slow crystallized from melt under uniaxial pressure. For sublimation flakes and crystals fast crystallized from melt, these transitions cannot be traced to parental molecular states since their spectra have continuous, essentially uniform intensity distribution except for such transition at the onset of absorption.     

Pressure-induced crystallization in a bulk amorphous Zr-based alloy

Crystallization of multi-component on amorphous Zr-based alloy (Zr₄₁Ti₁₄Cu_12.5Ni₉Be_22.5C₁) is investigated at different pressures and temperatures. We have previously found that the primary crystallization temperature decreases with increasing pressure below 6 GPa, and the crystallization follows a different process under high pressure when compared to that at ambient pressure. In this work, pressure-induced crystallization is observed by in situ X-ray diffraction (XRD) using synchrotron radiation in a diamond anvil cell at ∼25 GPa and room temperature. This phase transition between amorphous and crystalline is reversible and the crystallized sample returns to the amorphous state during decompression. The mechanism for pressure-induced crystallization is discussed. We suggest that the crystallized phases under high pressure are interstitial solid solution phases formed from the amorphous matrix without long-range atomic rearrangements.     

Dynamic process of crystallization of Sb2Se3 from Sb50Se50 amorphous film

Dynamics of crystallization of amorphous antimony-selenium film deposited on carbon substrate have been studied by the high-resolution transmission electron microscopy. The amorphous film was suddenly crystallized at 200°C by heating in vacuum. By the electron beam irradiation crystallization occurred at the focused electron beam region in the amorphous film. The growth process of crystallization by electron beam irradiation was recorded on a video image at the atomic resolution mode. The growth front of crystallization showed nano-concave and -convex shapes. The recrystallization with the different orientation at the first grown crystal have been found, and discussed as the influence of remaining antimony crystallites at the first crystallized film region.     

Phase separation and crystallization of borosilicate glass enriched in MoO3, P2O5, ZrO2, CaO

Borosilicate glasses with high molybdenum, phosphorus, calcium and zirconium oxide concentrations are partially crystallized. Their final microstructure reveals the contribution of microphase separation and crystallization phenomena during cooling. Rapid quenching of melts between copper rollers and by air blowing was investigated at various melting temperatures. The microstructure of glass specimens was characterized by transmission electron microscopy (TEM) and scanning electron microscope (SEM) coupled with and EDS analyzer. Glass transformation mechanisms during cooling are proposed: initial microphase separation at high temperature probably occurring though a nucleation and growth mechanism, followed by coalescence of the separated droplets.     

Single crystal growth,structural, optical,mechanical, dielectric and thermal studies of formic acid doped potassium dihydrogen phosphate crystal for NLO applications

Optically transparent formic acid (FA) doped potassium dihydrogen phosphate (KDP) crystal of dimension 21×15×9 mm³ has been grown by slow evaporation solution technique (SEST). The X‐ray diffraction (XRD) technique was used to confirm the cell parameters and the shifts in peak positions of identified reflecting planes. The incorporation of FA in KDP has been qualitatively analyzed by fourier transform infrared analysis. The UV‐visible absorption spectrum of crystals has been recorded in the range of 200 to 900 nm and the doped KDP crystal is found to have improved optical parameters than pure KDP. The color centered photoluminescence emission spectrum of grown crystal has been illustrated in visible region. The mechanical behavior of pure and doped KDP crystal has been investigated using the Vicker's microhardness analyzer and hardness parameters have been calculated. The effect of FA on thermal stability of KDP crystal was examined by means of thermogravimetric and differential thermal analysis. The temperature dependent dielectric behavior of crystals was studied.     

Thermo-mechanical behavior of uniaxially drawn and crystallized poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) films

Thermo-mechanical properties of poly(ethylene naphthalene-2,6-dicarboxylate) (PEN) films in the amorphous state, uniaxially stretched and thermally crystallized were compared and show different microstructure–property relationships. The glass transition temperature shifts to higher temperatures when films are stretched above T_g at 160 °C, in relation with a crystallinity increase and subsequent confinement effects of the amorphous phase, but films stretched below T_g at 100 °C show an opposite trend while drawing. This is discussed in relation with the highly mobile structural state arising from plastic deformation of the amorphous phase. The confinement effects were particularly assessed by the estimation of a ‘rigid amorphous fraction’ (RAF). Crystallinities and RAF were estimated from DSC data for the uniaxially drawn and thermally crystallized films respectively. It was observed that the RAF was higher in thermally crystallized films than in uniaxially drawn samples in relation to a lamellar semi-crystalline morphology. In addition to this detailed thermo-mechanical characterizations, low stress creep measurements were carried out during heating scans. They can be related to the microstructure and thermal transitions of the films. In particular, for the uniaxially stretched films, the measured shrinkage decreases when the draw ratio increases because the crystalline entities developed during the draw process are locking the chain motions.