Gd_(3)(Al,Ga)_(5)O_(12):Ce闪烁晶体扭曲生长、组分偏析与性能研究

新型闪烁晶体Gd_(3)(Al,Ga)_(5)O_(12):Ce(简写为GAGG:Ce)在制备过程中易出现多晶扭曲生长、组分偏析等问题,严重影响晶体的性能。为了得到大尺寸高质量的GAGG:Ce晶体,采用X射线衍射(XRD)、电感耦合等离子体发射光谱(ICP-OES)和X射线激发发射谱(XEL)等手段,结合熔体特性分析了GAGG:Ce晶体多晶扭曲生长、组分偏析的形成机制。通过调整温场、抑制组分挥发等方法生长出φ50 mm×120 mm的GAGG:Ce晶体,并重点研究了GAGG:Ce晶体的光谱特性与闪烁性能。结果表明:GAGG:Ce晶体的光输出达58000 ph./MeV,能量分辨率为6.4%@662 keV,在550~800 nm波长区间的透过率约为82%。晶体闪烁衰减快分量为126 ns(83%),慢分量为469 ns(17%)。晶体的发射峰中心波长在550 nm左右,与硅光电倍增管的接收波长匹配,且发光峰值处的透过率EWLT(Emission Weighted Longitudinal Transmittance)值高达79.8%。GAGG:Ce晶体兼具高光输出与高能量分辨率,在中子和伽马射线探测领域具有广阔的应用前景。

大尺寸H-ZSM-5表面上MFI型沸石膜的合成

利用原位水热法合成了大尺寸的H-ZSM-5,并在其表面上合成了MFI型沸石膜。采用X射线衍射,光学显微镜,扫描电镜和Uv-vis紫外漫反射等方法对合成的结果进行了表征。表征结果表明,在大尺寸H-ZSM-5表面上生长MFI型沸石膜的机理是多晶生长。在MFI型沸石膜的生长过程中,大尺寸H-ZSM-5的加入方式以及对大尺寸H.ZSM-5表面的预处理方式都会在很大程度上影响MFI型沸石膜在大尺寸H.-ZSM-5表面的生长结果。

Phase-field simulation of forced flow effect on random preferred growth direction of multiple grains

The random distribution problem of dendrite preferred growth direction was settled by random grid method.This method was used to study the influence of forced laminar flow effect on multiple grains during solidification.Taking high pure succinonitrile （SCN） undercooled melt as an example,the forced laminar flow effect on multiple grains was studied by phase-field model of single grain which coupled with flow equations at non-isothermal condition.The simulation results show that the random grid method can reasonably settle the problem of random distribution and is more effective.When the solid fraction is relatively low,melt particles flow around the downstream side of dendrite,and the flow velocity between two dendrite arms becomes high.At the stage of solidification time less than 1800Δt,every dendrite grows freely;the upstream dendrites are stronger than the downstream ones.The higher the melt flow rate,the higher the solid fraction.However,when the solid fraction is relatively high,the dendrite arm intertwins and only a little residual melt which is not encapsulated can flow;the solid fraction will gradually tend to equal to solid fraction of melt without flow.

Growth interface of CdMnTe crystal by traveling heater method

The growth interfaces of CdMnTe（CMT） crystals grown by traveling heater method（THM） were studied. Two types of polycrystalline CMT feed ingots synthesized in a traditional rocking furnace and vertical Bridgman（VB） furnace were adopted in THM growth, and the effects of the polycrystalline feed on the growth interface were revealed. The morphology of the growth interface of CMT crystal（CMT2） grown from the feed by vertical Bridgman was smoother with lower curvature compared with that of CMT crystal（CMT1） from the feed by rocking furnace. The radial Mn composition and Te inclusion distribution of the CMT wafers were analyzed and correlated to the growth interface. The Mn segregation along the radial direction and Te inclusion density of CMT2 were lower than those of CMT1. The VB method synthesized polycrystalline feed could improve the growth interface morphology, which is beneficial for decreasing the Te inclusions and Mn segregation in CMT wafers.

Effects of growth interruption on the properties of InGaN/GaN MQWs grown by MOCVD

InGaN/GaN MQWs structures were grown by MOCVD. The effects of the growth interruption time on the optical and structural properties of InGaN/GaN MQWs were investigated. The experimental results show that the growth interruption can improve the interface quality, increase the intensity of photoluminescence (PL) and electroluminescence (EL); but if the interruption time was too long, the well thickness and the average In composition of MQWs decreased, and the EL intensity also decreased due to poor interface quality and impurities derived from growth interruption.

Rapid synthesis of CNTs@MIL-101(Cr) using multi-walled carbon nanotubes(MWCNTs) as crystal growth accelerator

In this work,hybrid material CNTs@MIL-101(Cr) was synthesized in 2 h using multi-walled carbon nanotubes(MWCNTs) as the crystal growth accelerator with hydrothermal method.The characteristic differences between the crystals of CNTs@MIL-101(Cr) and MIL-101 were investigated by N_2 adsorption–desorption isotherms,X-ray diffraction(XRD),scanning electron microscope(SEM) and thermogravimetric analyzer(TGA).The results showed that MWCNTs embedding in the hybrid material provide more mesoporous volumes than that of MIL-101.Moreover,the fast synthesized crystals of CNTs@MIL-101(Cr) still preserve the octahedral shape like MIL-101 and have a larger size ranging from 1.5 to 2.0 μm which were approximately three times larger than that of MIL-101.In the proposed mechanism,the roles of MWCNTs played in the crystallization were discussed where MWCNTs can be seen as coaxial cylindrical tubes composed of multi-layer graphenes and the place where nucleation and crystal growth processes occur at the tubes' out surface.Then,a crystal seeding layer bonding with the MWCNTs may be easily formed which accelerates the growth rate of MIL-101 crystals.Thus,larger crystals of CNTs@MIL-101(Cr) were formed due to the faster crystal growth rate of MIL-101.

Polycrystalline ZnSx Se1—x thin films deposited on ITO glass by MBE

MBE growth of ZnS_xSe_1-x thin films on ITO coated glass substrate s were carried o ut using ZnS and Se sources with the substrate temperature ranging from 270℃ to 330℃. The XRD θ/2θ spectra resulted from these films indicated that the as-gro wn polycrystalline ZnS_xSe_1-x thin films had a preferred orientat ion along the (1 11) planes. The evaluated crystal sizes as deduced from the FWHM of the XRD laye r peaks showed strong growth temperature dependence, with the optimized temperat ure being about 290℃. Both AFM and TEM measurements of these thin films also in dicated a similar growth temperature dependence. High quality ZnS_xSe_1- x thin fil m grown at the optimized temperature had the smoothest surface with lowest RMS v alue of 1.2 nm and TEM cross-sectional micrograph showing a well defined column ar structure.

Synergistic improvement of perovskite film quality for efficient solar cells via multiple chloride salt additives

Perovskite crystal film quality is critical for obtaining efficient perovskite solar cells. Anti-solvent processing was used for fast crystallization of perovskite precursor film, which can form dense perovskite film. However, the crystals from this method are usually small due to the fast crystal growth process, which could lead to grain boundary recombination. Here, element chloride is introduced to enhance the perovskite layer crystallinity via slowing down the perovskite crystallization process by simultaneous introduction of methylammounium chloride （MACI） and cesium chloride （CsCl） into precursor solution. As a result, we achieve high quality of pin-hole free perovskite film with large crystal size. A power conversion efficiency of 21.55% with free of hysteresis of the device is obtained, which is among the highest efficiency of planar structure perovskite solar cells.

Shape-controlled growth of SrTiOz polyhedral submicro/ nanocrystals

A series of SrTiO3 polyhedral submicro/nanocrystals with systematic morphology evolution from cubic to edge-truncated cubic and truncated rhombic dodecahedra have been synthesized by using a series of alcohol molecules with different acidities as surfactants. The concentration and pKa value of the alcohols both play important roles in determining the size and shape of the SrTiO3 polyhedral submicro]nanocrystals. The adsorption energy of alcohol molecules on SrTiO3 [110] facets depends on their pKa values, which are therefore critical for morphology control. Using the same strategy, a series of BaTiO3 polyhedral submicro/nanocrystals with systematic morphology evolution have also been successfully prepared.