Specific features of the behavior of oxygen in Sn-doped silicon

The influence of Sn on the absorption spectra of Si and the formation of low-temperature quenched-in donors (T=450°C) in Si was investigated. The effects of Ge and C were compared. It was found that Sn-doping of Si, similarly to Ge-and C-doping, leads to a decrease in the efficiency of the formation of quenched-in donors. It was demonstrated that the inhibition effect of the formation of quenched-in donors depends on the elastic stresses induced by isovalent impurities in Si. The higher the deformational charge of the impurity, the lower the concentration required for a comparable effect.     

Formation of electrically active centers in silicon irradiated with electrons and then annealed at temperatures of 400–700°C

The effect of irradiation with electrons on the formation of quenched-in donors in silicon is studied. It is found that n-and p-type regions are formed in the bulk of single-crystal silicon as a result of irradiation with electrons and subsequent annealing at a temperature of 450°C. The concentration of charge carriers in the regions of both types increases as the radiation dose and the annealing duration increase, which indicates that not only quenched-in donors but also quenched-in acceptors are formed. Nonuniformity in the distribution of the acceptor and donor centers correlates with fluctuations of the oxygen concentration in silicon.     

Relaxation of a defect subsystem in silicon irradiated with high-energy heavy ions

The relaxation of a silicon defect subsystem modified by the implantation of high-energy heavy ions was studied by varying the electrical properties of irradiated Si crystal annealed at a temperature of 450°C. It is shown that quenched-in acceptors are introduced into Si crystals as a result of irradiation with comparatively low doses of Bi ions and subsequent relatively short annealing (no longer than 5 h); the distribution of these quenched-in acceptors has two peaks located at a depth of about 10 μm and at a depth corresponding approximately to the ions’ projected range (43.5 μm). The peaks in the distribution of quenched-in acceptors correspond to the regions enriched with vacancy-containing defects. As the heat-treatment duration increases, the acceptor centers are transformed into donor centers with the centers’ spatial distribution remaining intact. Simultaneously, an almost uniform introduction of quenched-in donors occurs in the entire crystal beyond the depth corresponding to the projected range of ions. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 37, No. 5, 2003, pp. 565–569. Original Russian Text Copyright ? 2003 by Smagulova, Antonova, Neustroev, Skuratov.     

Eutectic Microstructure and Thermoelectric Properties of Mg2Sn

Ingots of undoped and Ag-doped Mg₂Sn were prepared from the melt using a rocking Bridgman furnace at different cooling rates: slow cooling (0.1 K/min), moderate cooling (1 K/min), and rapid quenching. The ingots show very different microstructure and thermoelectric properties. Slow-cooled ingots consist of large Mg₂Sn crystals with minor inclusions. Moderate-cooled ingots show significant variation in composition and microstructure, with Mg-rich material at the topmost section of the ingot and Sn-rich material at the bottom surface of the ingot. Rapid quenching results in ingots with finely dispersed Mg + Mg₂Sn eutectic microstructure in the form of lamellae 200 nm to 500 nm in thickness. Measurements of the Seebeck coefficient and electrical conductivity in the temperature range of T = 80 K to 700 K were carried out to establish correlations between the microstructure and the thermoelectric properties.     

Optical and Structural Properties of Composite Si:Au Layers Formed by Laser Electrodispersion

Composite Si–Au layers prepared by laser electrodispersion with different Si:Au ratios are studied. The microscopic structure of the layers is established and their Raman spectra and optical transmission and reflectance spectra are investigated. It is demonstrated that the sputtering of a two-component Si–Au target radically changes the layer morphology. With increasing Au content in the target, the layers become inhomogeneous and a large number of inclusions arise, which contain silicon nanocrystals and a certain amount of gold. Upon the sputtering of a two-component target, inclusions are most likely formed from large molten droplets, which are ejected from the target and do not manage to divide into nanoparticles. The nanocrystalline structure of the inclusions is attributed to the slow inhomogeneous cooling of particles on the substrate. It is concluded that variations in the photosensitivity spectra of heterostructures with the investigated layers are caused by the formation of inclusions containing silicon nanocrystals with the addition of gold.     

Characterization of the heat loading of Nd-doped YAG, YOS, YLF, andGGG excited at diode pumping wavelengths

The parameter ξ (xi) is proposed as an alternative to the traditional solid-state laser media heating parameter, χ (chi). ξ is the ratio of heat produced to energy absorbed, and χ is the ratio of heat produced to the maximum stored energy in the upper laser level. The parameter ξ is particularly relevant to diode pumped systems. We demonstrate an experimental ξ characterization based on the determination of the steady state cooling rate (hence heating rate) of small sample crystals subjected to pump laser heating. Using measured fluorescent lifetimes of the samples and near zero doping (intrinsic) values, the doping independent (zero doping or zero quenching) parameters χφ and ξφ are determined. The results for all samples are in excellent agreement with calculations based solely on energy defect and nonradiative quenching of the upper level     

Quenched-in centers in silicon p+n junctions

Silicon p⁺n junctions heat treated at high temperatures (1200°C) for a long time (2–20 hr) and then quenched to room temperatures or below shows two deep donor levels (E_C?264meV andE_C?542meV) in the n-type side of the junction depletion layer which appear to originate from the same imperfection center. The concentration of these levels ranges from 10¹³ to 10¹⁴ cm^?3. The junction leakage current comes from carrier generation at the deeper level in the depletion region. Phosphorus gettering was found ineffective in reducing the concentration of these quenched-in levels, but they are annealed out by very slow cooling (25°C/hr to 650°C then quench to room temperatures). The thermal emission and capture rates of electrons and holes at these levels are measured as a function of temperature and electric field by the junction high frequency capacitance and d.c. leakage current transient techniques. It is demonstrated that the detailed balance relationship does not hold. The origin of this double donor center is yet to be identified.     

用于高功率CO2激光器反射镜的研究

本文讨论了一种用于高功率CO2激光器反射镜的设计、制备、测试及冷却,比较了反镜基底材料的优劣。应用表明:这种反射镜远优于铜基底镀金的反射镜。     

激光手术中喷嘴尺寸对制冷剂闪蒸喷雾冷却表面传热特性的影响

制冷剂闪蒸喷雾冷却(CSC)已经成为激光治疗葡萄酒色斑等皮肤病手术中的标准冷却辅助手段。为优化喷嘴设计,进一步增进冷却效率和改善治疗效果,搭建了制冷剂闪蒸瞬态喷雾冷却实验台,设计了8个不同内径和长度的直管型喷嘴,采用先进的磁控溅射沉积薄膜热电偶测温方法,应用杜哈梅尔定理计算表面热流密度,定量研究了不同喷嘴对冷却表面传热特性的影响,并对其传热规律和雾化特性进行了系统的分析比较。此外,提出了评价喷嘴冷却效率标准,给出了采用不同几何尺寸喷嘴时冷却表面换热量随喷雾距离的变化规律。     

Evaporation-condensation cooling systems for electronic equipment

The paper shows that heat pipes with metal-fibrous capillary structures and evaporation-condensation cooling system based on heat pipes are highly efficient means of providing optimal thermal conditions for different electronic instruments and devices. Such cooling system combining the functions of effective heating conduit (equivalent heat conductivity is much higher than the heat conductivity of the best heat-conducting materials) and effective radiator with the possibility of passive heat dissipation is characterized by a high heat transport ability, low thermal resistance, relatively small size and weight, reliable performance at different orientation in space under exposure to mass forces action. The paper presents examples of developed designs and investigations of heat pipes and evaporation-condensation systems with metal-fibrous capillary structures aimed at cooling the different heat generating items of electronic equipment. In this case, special types and designs of systems are discussed. These systems operate under different conditions of heat removal to absorbing medium and feature both a high heat transport ability and specific dielectric properties. In addition, the thermotechnical characteristics of proposed cooling systems are also presented.     

半导体激光器非典型宏通道水冷散热系统设计

针对大功率半导体激光器散热系统展开设计研究。首先，对水冷散热系统的流体通道中的冷却液进行了流体分析，结果表明在传统矩形流体通道结构中，冷却液在进液口处和弯度较小处容易产生湍流空洞。湍流空洞不仅会产生空泡腐蚀效应，还会导致靠近热源的上层冷却液填充不充分，降低系统的散热效率；其次，在传统流体通道结构的基础上，提出了一种非典型宏通道结构的优化模型。采用有限元分析软件Fluent分别对散热模型的分布和激光器模块器件的分布进行了数值模拟，流场结果表明优化模型中冷却液流动时没有湍流空洞产生，散热系统可靠性更高，冷却液在流体通道的上层填充效果更好，同时解决了传统模型中流体在局部流道中流速缓慢的问题，使散热系统具备更良好的散热性能。接着又通过温度场仿真结果得出，优化模型搭建的散热系统工作时激光器最高温度可降低2 ℃，且热源1上温度更均匀，热源3上温度降低1.25 ℃；最后，在激光器满功率输出情况下进行的散热实验对比，获得的实验数据与仿真结果基本一致。     

Kinetics of production of oxygen-containing quenched-in donors in silicon and their nonuniform distribution: An analytical solution

The kinetics of production of oxygen-containing quenched-in donors in silicon, when atomically dissolved oxygen intensely forms the bound states (complexes), is considered. An analytical time-dependent homogeneous solution of the corresponding nonlinear kinetic equations is obtained. The uniform distribution of oxygen atoms and their complexes is shown to become unstable for certain parameters of the problem owing to their interaction, and a spatially periodic distribution is developed with a period in the range of 10–1000 Å.     

机载电子设备的散热设计

通过分析散热器翼片中空气流动的形式(层流流动或湍流流动),讨论了散热器散热效率不同的原因,提出了优化散热器翼片的设想;由机载电子设备常用的散热方案(自然冷却和强制风冷却),提出了机载电子设备散热的设计思路和计算方法.     

热容激光器冷却过程的热力学数值模拟

为了研究热容激光器冷却过程中激光介质的热力学特性,建立了激光介质热力学理论模型.该模型将介质表面的换热作为瞬态导热微分方程的热源,得到冷却过程中热传导模型.获得了激光介质在冷却过程中的瞬态温度场,进一步得到介质的热应力.利用数值模拟,得到了YAG介质和GGG介质在不同冷却条件下的冷却时间、温差和热应力.表面换热系数从0.1 W?cm-2?K-1增加到0.5 W?cm-2?K-1,冷却时间明显缩短;表面换热系数从0.5 W?cm-2?K-1增加到1 W?cm-2?K-1,冷却时间缩短不明显.对于相同体积、相同初始温度场的YAG介质和GGG介质,YAG介质的冷却时间少于GGG介质的冷却时间.在相同冷却条件下,YAG介质的温差小于GGG介质的温差,YAG介质的最大等效应力小于GGG介质的最大等效应力.     

基于CFD的电子器件散热最优间距的数值研究

为研究高发热功率电子器件散热的机理,采用CFD技术对小空间内电子器件的散热状况进行了研究,模拟了以空气为冷却流体多种电子器件间距条件下小空间的温度场及速度场.以电子器件冷却后的温度水平、平均换热系数、流动阻力为主要因素,并结合场协同理论提出一种评价电子器件冷却效果的评判公式,进而以它为指标得出电子器件散热效果的最优间距.     

Effect of cooling rate on growth of the intermetallic compound and fracture mode of near-eutectic Sn-Ag-Cu/Cu pad: Before and after aging

Several near-eutectic solders of (1) Sn-3.5Ag, (2) Sn-3.0Ag-0.7Cu, (3) Sn-3.0Ag-1.5Cu, (4) Sn-3.7Ag-0.9Cu, and (5) Sn-6.0Ag-0.5Cu (in wt.% unless specified otherwise) were cooled at different rates after reflow soldering on the Cu pad above 250°C for 60 sec. Three different media of cooling were used to control cooling rates: fast water quenching, medium cooling on an aluminum block, and slow cooling in furnace. Both the solder composition and cooling rate after reflow have a significant effect on the intermetallic compound (IMC) thickness (mainly Cu₆Sn₅). Under fixed cooling condition, alloys (1), (3), and (5) revealed larger IMC thicknesses than that of alloys (2) and (4). Slow cooling produced an IMC buildup of thicker than 10 μm, while medium and fast cooling produced a thickness of thinner than 5 μm. The inverse relationship between IMC thickness and shear strength was confirmed. All the fast- and medium-cooled joints revealed a ductile mode (fracture surface was composed of the β-Sn phase), while the slow-cooled joints were fractured in a brittle mode (fracture surface was composed of Cu₆Sn₅ and Cu₃Sn phases). The effect of isothermal aging at 130°C on the growth of the IMC, shear strength, and fracture mode is also reported.     

改善大功率LED散热的关键问题

考虑热导率与散热方式的影响,使用大型有限元软件ANSYS10．0模拟并分析了大功率LED热分布。通过分析不同封装、热沉材料及散热方式对LED热分布与最大散热能力的影响,指出解决LED散热问题的关键不是寻找高热导率的材料,而是改变LED的散热结构或者散热方式。     

一种均温板加速条件下性能试验研究

针对机载电子设备散热应用条件,研究热管均温板在机载加速环境下的传热性能。为提高热管散热稳定性,将热源布置在热管中部,热管两端作为散热端。试验中试验单元安装在离心加速机上,模拟机载加速环境,测试了不同加速度条件下热管传热性能,得到热管均温板当量导热系数变化曲线,分析了加速度对热管当量导热系数的影响。试验结果表明:在0 ~13g加速条件下,热管均温板均能正常工作。结合试验结果给出热管均温板用于机载电子设备散热的设计建议。     

Cryopreservation in the Era of Cell Therapy: Revisiting Fundamental Concepts to Enable Future Technologies

Cryopreservation strives to maximize the viability and biofunctionality of cells and tissues by cooling them to a subzero temperature to facilitate storage and delivery. This technology has enabled clinics and labs to preserve rare and crucial samples and is poised to become more important with rising interest in cell therapy. Here, the biological impact of cooling rates on different cellular components is first described, paying special emphasis on the differences between slow cooling and vitrification with a heat transfer perspective based on the Biot number. This is followed by an overview of various classes of chemical-based cryoprotective agents including small molecules, antifreeze proteins, hydrogels, and cryoprotective nanomaterials. Most importantly, fundamental concepts of cryopreservation including Mazur's “two-factor hypothesis” are revisited, gaps in them are highlighted, and experiments to validate reported claims to deepen mechanistic understanding of cryoprotection are proposed. A matric is also introduced to assess the suitability of biomaterials for use in cell therapy to support manufacturers in making strategic choices for storing clinical samples. It is believed that this review would inspire readers to scrutinize fundamental concepts in cryopreservation to facilitate the development of new cryoprotective materials and technologies to support the emerging cell manufacturing and therapy industry.     

TC4激光立体成形中基材热影响区组织性能优化研究

激光立体成形技术是一项基于同步送粉激光熔覆的先进制造技术。激光立体成形和修复过程中沉积层、热影响区以及基体材料组织、性能的差异将对最终零件的性能,尤其是疲劳性能产生重要影响。为改善基体、热影响区(HAZ)的组织、性能差异,针对TC4合金,提出在激光沉积前对基材表面进行多次激光重熔扫描预处理,从而优化基材热影响区组织性能。基于此,通过研究不同工艺条件下,多次激光重熔处理对热影响区组织性能的影响。结果表明:首先,多次激光重熔将引起的基材热影响区总体冷却速率下降,从而有效的消除热影响区的急冷组织;其次,重熔处理产生的多次热循环对基材热影响区的时效处理对于热影响区的组织、性能(硬度)也有一定的影响。通过在多层沉积前对基材进行适当的激光多次重熔扫描处理有效改善了沉积区、热影响区以及基材性能的大幅波动,实现了均匀渐变。