Effect of the doping level on temperature bistability in a silicon wafer

The influence of the doping level on the effect of the temperature bistability in a silicon wafer upon radiative heat transfer between the wafer and the elements of the heating system is studied. Theoretical transfer characteristics are constructed for a silicon wafer doped with donor and acceptor impurities. These characteristics are compared with the transfer characteristics obtained during heating and cooling of wafers with the hole conduction (with dopant concentrations of 10¹⁵, 2 × 10¹⁶, and 3 × 10¹⁷ cm^?3) and electron conduction (with impurity concentrations of 10¹⁵ and 8 × 10¹⁸ cm^?3) in a thermal reactor of the rapid thermal annealing setup. It is found that the width and height of the hysteresis loop decrease with increasing dopant concentration and are almost independent of the type of conduction of the silicon wafer. The critical value of the impurity concentration of both types is 1.4 × 10¹⁷ cm^?3. For this concentration, the loop width vanishes, and the height corresponds to the minimal value of the temperature jump (～200 K). The mechanism of temperature bistability in the silicon wafer upon radiative heat transfer is discussed.     

真空铟焊的负电子亲和势砷化镓光阴极实验研究

大功率激光加载会使负电子亲和势(NEA)砷化镓(GaAs)光阴极的温度迅速升高,较高的温度对NEA GaAs 光阴极的激活层造成了破坏,从而使其量子效率迅速下降。探索了基于FEL-THz装置的NEA GaAs 光阴极的真空铟焊工艺,搭建了GaAs真空铟焊平台,并进行了真空铟焊后的GaAs光阴极激光与束流加载实验。研究表明,真空铟焊使GaAs与金属阴极托之间形成了紧密连接,增强了阴极与阴极托之间的热传导,减缓了阴极的温升速率,并在数瓦平均功率激光加载时将注入器中NEA GaAs 光阴极的工作寿命提高了一个量级以上。     

真空铟焊的负电子亲和势砷化镓光阴极实验研究

大功率激光加载会使负电子亲和势(NEA)砷化镓(GaAs)光阴极的温度迅速升高,较高的温度对NEA GaAs光阴极的激活层造成了破坏,从而使其量子效率迅速下降。探索了基于FEL-THz装置的NEA GaAs光阴极的真空铟焊工艺,搭建了GaAs真空铟焊平台,并进行了真空铟焊后的GaAs光阴极激光与束流加载实验。研究表明,真空铟焊使GaAs与金属阴极托之间形成了紧密连接,增强了阴极与阴极托之间的热传导,减缓了阴极的温升速率,并在数瓦平均功率激光加载时将注入器中NEA GaAs光阴极的工作寿命提高了一个量级以上。     

Target heating during ion implantation and related problems

We have undertaken a general analysis of wafer heating during implantation and first, we present general considerations of this problem with respect to amorphization doses extracted from Morehead and Crowder theory. Then, radiative properties of silicon wafers are measured: a law of variation of the emissivity with temperature is given; a comparison is made with values found in the literature. Dependence with experimental conditions (heat reflector, conductive losses) is also studied. Three methods for temperature measurement are used: temperature coefficient of a small resistor vacuum deposited on a face, thermocouple measurement and infrared detection. We compare the three kinds of results which are in good agreement and we make some comments about the temperature measurements using infrared detection.     

Transient heat transfer in a spherical protective material, submitted to flux and mixed boundary conditions: an investigation on zirconia

An analytic solution is presented for describing combined radiation and conduction heat transfer in a spherical fiber thermal protection exposed to combined radiative and convective heating. The solution includes the equation of radiative transfer within the material, coupled to a transient energy equation that contains both radiative and convective terms. At elevated temperatures radiative transfer becomes important, and if several hot surfaces view each other, the radiation exchange process must be considered carefully. Some thermal protections are partially transparent to thermal radiation. Hence, an exchange process is complicated by radiation penetrating into and coming out of material. The radiation leaving an area depends on the temperature distribution inside that area and that is unknown and is affected by the exchange process to other areas. The analysis has allowed for unlimited spectral detail but assumes that the various material properties do not vary significantly with temperature. Transient temperature distributions are obtained for the boundary conditions of external radiation and convection. The present analysis includes the influence of reflectivity, surface radiative properties and spectral properties on the temperature distributions.     

Extension of Planck’s law to steady heat flux across nanoscale gaps

Recent experiments report that the radiative heat conductance through a narrow vacuum gap between two flat surfaces increases as the inverse square of the width of the gap. Such a significant increase of thermal conductivity has attracted much interest because of numerous promising applications in nanoscale heat transfer and because of the lack of its theoretical explanation. It is shown here that the radiative heat transport across narrow layers can be described in terms of conventional theory adjusted to non-equilibrium structures with a steady heat flux.     

The energy release and temperature field in the ultracold neutron source of the WWR-M reactor at the Petersburg Nuclear Physics Institute

Results of calculations of energy releases and temperature fields in the ultracold neutron source under design at the WWR-M reactor are presented. It is shown that, with the reactor power of 18 MW, the power of energy release in the 40-L volume of the source with superfluid helium will amount to 28.5 W, while 356 W will be released in a liquid-deuterium premoderator. The lead shield between the reactor core and the source reduces the radiative heat release by an order of magnitude. A thermal power of 22 kW is released in it, which is removed by passage of water. The distribution of temperatures in all components of the vacuum structure is presented, and the temperature does not exceed 100°C at full reactor power. The calculations performed make it possible to go to design of the source.     

Inverse radiation problem of temperature distribution in one-dimensional isotropically scattering participating slab with variable refractive index

In this paper, an inverse analysis is performed for estimation of source term distribution from the measured exit radiation intensities at the boundary surfaces in a one-dimensional absorbing, emitting and isotropically scattering medium between two parallel plates with variable refractive index. The variation of refractive index is assumed to be linear. The radiative transfer equation is solved by the constant quadrature discrete ordinate method. The inverse problem is formulated as an optimization problem for minimizing an objective function which is expressed as the sum of square deviations between measured and estimated exit radiation intensities at boundary surfaces. The conjugate gradient method is used to solve the inverse problem through an iterative procedure. The effects of various variables on source estimation are investigated such as type of source function, errors in the measured data and system parameters, gradient of refractive index across the medium, optical thickness, single scattering albedo and boundary emissivities. The results show that in the case of noisy input data, variation of system parameters may affect the inverse solution, especially at high error values in the measured data. The error in measured data plays more important role than the error in radiative system parameters except the refractive index distribution; however the accuracy of source estimation is very sensitive toward error in refractive index distribution. Therefore, refractive index distribution and measured exit intensities should be measured accurately with a limited error bound, in order to have an accurate estimation of source term in a graded index medium.     

Transient coupled radiative and conductive heat transfer in a semitransparent layer of ceramic

This work considers transient radiative and conductive heat transfer in a semitransparent layer of ceramic, submitted to several thermal and radiative boundary conditions. Each side of the layer is exposed to hot or cold radiative surroundings, while each boundary is heated or cooled by convection. The solution procedure must provide accurate temperature distribution in the layer, so a nodal analysis based on Hottel's zonal method extended by ray tracing method is carried out. A finite difference method with non-uniform space and time increments is used to solve the transient energy equation, including a radiative heat source, coupled to a equation of radiative transfer. Variable spacing was used to concentrate grid points in regions with large temperature gradients. The influence of refractive index, optical thicknesses and conduction-radiation parameters is investigated.     

A concept of multi-scale modeling for radiative heat transfer in particle polydispersions

To take the local thermal nonequilibrium between particles and the nonuniformity of temperature within a single particle into account, a concept of multi-scale modeling of radiative transfer is presented. Particles are considered to interact with thermal radiation on both micro-scale of a single particle and meso-scale of a particle cell to produce radiative source term at the local or meso-scale level of a particle cell for the modeling of radiative transfer at macro-scale of overall particle system. The accurate modeling of radiative transfer in particle polydispersions are related to the modeling of radiative transfer in following three different scales: macro-scale of the overall particle system, meso-scale of particle cell, and micro-scale of single particle. Two examples are taken to show the necessity of multi-scale modeling for radiative transfer in particle polydispersions. The results show that omitting local thermal nonequilibrium and nonuniformity will result in errors for the solution of radiative heat transfer to some extent, and the multi-scale modeling is necessary for the radiative transfer in particle system with large local thermal nonequilibrium and nonuniformity.     

用于热光伏系统的近场辐射光谱控制表面结构

为提升近场热光伏发电系统的能源转换效率和发电功率,设计了Ⅲ-Ⅴ族半导体表面的矩形光栅结构,以实现从热发射器到热光伏电池的近场辐射热流选择性调制.使用在近红外波段具有表面等离子体激元特性的掺杂氧化锌作为热发射器,在GaSb热光伏电池表面添加亚微米二维光栅结构,在近场间距下形成与表面波耦合的陷光效应,由此有选择性地增强了电池能带内的光谱辐射热流.有别于以往类似研究中常用的等效近似方法,开展了时域有限差分方法模拟,能够严格考虑周期性结构细节,结合以涨落耗散理论为基础的Langevin方法,直接计算了复杂结构参与的近场辐射传热问题,以此揭示表面结构影响近场辐射传热的物理机理.结果显示使用带表面结构的薄膜GaSb电池,可使辐射热流的光谱峰值达到同温度远场黑体辐射源情况下的2.84倍,且热流增益区集中在波长略短于电池能带的窄波段区间,适应高效率、高功率热光伏系统对辐射传热设计的要求.     

Thermal stress cleaving of silicon wafer by pulsed Nd：YAG laser

The applied laser energy absorbed in a local area in laser thermal stress cleaving of brittle materials using a controlled fracture technique produces tensile thermal stress that causes the material to separate along the moving direction of the laser beam. The material separation is similar to crack extension, but the fracture growth is controllable. Using heat transfer theory, we establish a three-dimensional （3D） mathematical thermoelastic calculational model containing a pre-existing crack for a two-point pulsed Nd：YAG laser cleaving silicon wafer. The temperature field and thermal stress field in the silicon wafer are obtained by using the finite element method （FEM）. The distribution of the tensile stress and changes in stress intensity factor around the crack tip are analyzed during the pulse duration. Meanwhile, the mechanism of crack propagation is investigated by analyzing the development of the thermal stress field during the cleaving process.     

Uniformity principle of temperature difference field in heat transfer optimization

The uniformity principle of temperature difference field is very useful in heat exchanger analyses and optimizations.In this paper, we analyze some other heat transfer optimization problems in the thermal management system of spacecrafts,including the cooling of thermal components, the one-stream series-wound heat exchanger network, the volume-to-point heat conduction problem, and the radiative heat transfer optimization problem, and have found that the uniformity principle of temperature difference field also holds. When the design objectives under the given constraints are achieved, the distributions of the temperature difference fields are uniform. The principle reflects the characteristic of the distribution of potential in the heat transfer optimization problems. It is also shown that the principle is consistent with the entransy theory. Therefore, although the principle is intuitive and phenomenological, the entransy theory can be the physical basis of the principle.     

A Monte Carlo implementation to solve radiation heat transfer in non-uniform media with spectrally dependent properties

This paper presents the application of the Monte Carlo method to solve the radiative heat exchange in non-homogeneous, non-isothermal gases with spectrally dependent properties. Among others models, the absorption-line blackbody (ALB) distribution function, originally defined and derived for the spectral line-based weighted-sum-of-gray-gases (SLW) model, allows an immediate, simple implementation of the Monte Carlo method to account the spectral dependence of the radiative properties. This work shows how the Monte Carlo method can be combined to the ALB distribution function, and provides results for heat transfer in a mixture of water vapor, carbon dioxide and nitrogen that have satisfactory agreement with the SLW method and with line-by-line integration. Finally, the solution technique is employed to solve two examples aiming at demonstrating the effect of the absorbing species concentration on the thermal radiative exchanges. The method is of great interest for the computation of radiative transfer in combustion systems where the chemical species concentration and the temperature are not uniform.     

辐射(火积)耗散与空间辐射器温度场均匀化的关系

(火积)理论是针对传热优化发展起来的,并获得了越来越多的应用。本文基于辐射(?)原理,对空间辐射器散热过程中的散热量分布、发射率分布和散热面积分布问题进行了分析。对于以上三类优化分布问题,理论分析和数值计算均表明,辐射器最小的辐射(?)耗散和辐射热阻均对应于散热表面均匀的温度场。因此,辐射(?)原理可用于空间辐射器的温度场均匀化设计。     

球形微粒子近场辐射换热研究

从偶极辐射理论出发,结合普朗克黑体辐射分布,推导出近场区热辐射分布。采用MC法模拟了两个纳米球形 村子的辐射换热,考察相天参数对近场辐射换热的影响。表明其辐射热流可比黑体辐射高8个数量级。其热流随间距的增 大急剧减小。小研究对于纳米粒子群的传热研究有积极意义。     

Monte Carlo ray-tracing simulation for radiative heat transfer in turbulent fluctuating media under the optically thin fluctuation approximation

The Monte Carlo ray-tracing method (MCRT) based on the concept of radiation distribution factor is extended to solve radiative heat transfer problem in turbulent fluctuating media under the optically thin fluctuation approximation. A one-dimensional non-scattering turbulent fluctuating media is considered, in which the mean temperature and absorption coefficient distribution are assumed and the shape of probability density function is given. The distribution of the time-averaged volume radiation heat source is solved by MCRT and direct integration method. It is shown that the results of MCRT based on the concept of radiation distribution factor agree with these of integration solution very well, but results of MCRT based on the concept of radiative transfer coefficient do not agree with these of integration solution. The solution of time-averaged radiative transfer equation by the concept of radiative transfer coefficient should be treated with caution.     

Une nouvelle méthode calorimétrique périodique de mesure de l'émissivité des matériaux opaques à température ambiante

This paper presents a new calorimetric periodic technique for measuring emissivity of opaque materials at room temperature, without surface temperature measurement. The sample is in a vacuum chamber, so the thermal losses are only radiative. The presented technique requires thermal modulation of one side of the sample (the front side). The measured signals are the sample's front side temperature and the infrared flux of the other side (back side). Experimental data and a heat conduction model are compared, yielding the Biot number which characterizes the thermal losses. Using the identified value of the Biot number, it is possible to access the total hemispherical emissivity. Measurements have been carried out on a PVC sample (5 mm thick) coated with black paint and on a PVC sample coated with aluminium paint. The results are concordant with the expected ones ; the repeatability error is about 3 %.     

Efficient inverse radiation analysis in a cylindrical geometry using a combined method of hybrid genetic algorithm and finite-difference Newton method

An inverse radiation problem was considered to estimate boundary conditions such as temperature distribution and emissivity in axisymmetric absorbing, emitting, and scattering medium, given the measured incident radiative heat fluxes. The finite-volume method was employed to solve a direct radiative transfer equation for a two-dimensional axisymmetric geometry. Various parameter estimators, such as conjugate-gradient method, hybrid genetic algorithm, and finite-difference Newton method, were employed to solve the inverse problems, while discussing their performances in terms of estimation accuracy and computational efficiency. Based on this, we proposed, as a best inverse analysis tool, a new combined method that adopted the hybrid genetic algorithm as an initial value selector and used the finite-difference Newton method as a parameter estimator.