沟槽型X射线两次衍射单色器研究

为获得高能量分辨率、高准直的同步辐射光,应用X射线衍射动力学原理,并依据上海光源小角散射线站光学参数,设计并加工了两次衍射的单晶硅(111)面沟槽型单色器。测量了两反射面平行度、斜切角及摇摆曲线,并对摇摆曲线的测量值进行了误差分析。理论模拟与实验数据对比分析显示:有效减小晶体加工过程中的残余应力导致的晶格畸变、改善晶体形貌、调整斜切角与增加衍射级次可降低晶体的衍射角宽,进而提高出射光的准直性和能量分辨率。经计算,在同步辐射光能量为10keV条件下,单晶硅(111)面沟槽型单色器的本征能量分辨率为1.452×10~(-4)。     

用时间分辨反射率技术研究硅的固相外延

用时间分辨反射率技术实时测量了Ｓｉ＋、Ａｓ＋注入单晶硅的固相外延生长速率和外延层厚度，并与背散射沟道方法测得的非晶层厚度进行了比较。介绍了测量原理，分析了实验结果．     

砷注入硅背散射沟道研究

我们对能量从40keV～150keV,剂量从1×10~(15)离子/cm~2～1×10~(16)离子/cm~2砷离子注入〈111〉单晶硅,进行了H~+和He~+背散射沟道测量。样品经600℃、700℃、825℃热退火后,都未能满意地消除损伤,而经红宝石脉冲激光退火之后,能满意地消除损伤。对40keV剂量为1×10~(16)离子/cm~(275)As~+注入的硅样品,分别进行900℃、30分钟热退火和红宝石脉冲激光退火,而后分别测量了〈111〉轴向和〈110〉轴向背散射沟道谱,砷原子的替位率分别为90％和95％以上,同时对两种退火方式的样品,测量了〈111〉轴向的角分布,观察到在热退火情况下,杂质砷原子的角分布有变窄的现象,大约窄0.2°;脉冲激光退火杂质砷原子的角分布与硅原子的角分布重合得相当好。我们又在连续打七个激光脉冲的斑点上测量了表面砷原子浓度的横向分布,其形状近似于高斯分布。     

用背散射方法分析硅中注入砷的深度分布

用离子注入方法能快速地将一种杂质元素射入到半导体材料中,而杂质元素在材料中的浓度随深度的分布直接影响了材料的性能,因此准确测定它们是十分必要的。我们用背散射分析法分析了注入砷的硅样品。 1.实验方法和数据处理 样品是电阻率为7～15Ω·cm、〈111〉晶向的p型单晶硅。为避免沟道,约倾斜7°注入,经严格清洗后在氮气保护下,在不同退火条件下恒温退火。背散射实验工作是在原子能所静电加速器上进行的,选用     

高通量工程试验堆堆内单晶硅旋转体温度测量

本文论述了高通量工程试验堆堆内单晶硅旋转体温度测量装置,介绍了在反应堆各种功率下单晶硅辐照样品温度的测量结果,并且根据温度测量值估算了单晶硅的 γ 发热率,进行了误差分析,同时作者还进行了单晶硅温度与轴流泵转速关系的试验.测量结果表明,在高通量堆首炉工况下单晶硅辐照装置内部冷却水不会沸腾.     

带有AlN插入层的GaN薄膜的结构及应变研究

利用金属有机化学汽相沉积（MOCVD）法在硅衬底上生长具有AlN插入层的GaN外延膜，采用高分辨X射线衍射（HRXRD）和卢瑟福背散射/沟道（RBS/Channeling）技术研究分析其结构和应变性质。从RBS<0001>沟道谱可知，该外延膜具有良好的结晶品质，χ_min=2.5%。利用不同方位角上XRD摇摆曲线测量，可得出GaN（0001）面与Si（111）面之间的夹角β=1.379°。通过对GaN（0002）和GaN（1015）衍射面的θ-2θ扫描，可以得出GaN外延膜在垂直方向和水平方向的平均弹性应变分别为-0.10%±0.02%和0.69%±0.09%。通过对{1010}面内非对称<1213>轴RBS角扫描可得出由弹性应变引起的四方畸变e_T在近表面处为0.35%±0.02%。外延膜弹性性质表明GaN膜在水平方向具有张应力(e∥>0)、在垂直方向具有压应力(e^⊥<0)，印证了XRD的结果。四方畸变是深度敏感的，通过对不同深度的四方畸变计算可知，AlN插入层下面的GaN外延膜弹性应变释放速度比AlN层上面的GaN层弹性应变释放快，说明AlN层的插入缓解了应变释放速度。     

热中子诱发239Pu裂变的85Krm、87Kr和88Kr产额测量研究

中子诱发²³⁹Pu裂变的⁸⁵Kr^m、⁸⁷Kr和⁸⁸Kr的产额是重要的核参数,目前国外实验数据较少而国内尚未见实验报道。基于西安脉冲堆跑兔系统辐照Pu靶开展了热中子诱发²³⁹Pu裂变的⁸⁵Kr^m、⁸⁷Kr和⁸⁸Kr的产额测量研究。纯化后的钚溶液通过滴定后阴干的方式制靶,靶辐照后结合γ无损分析和气-固分离制源测量等方式测量裂变产物。采用有机玻璃扁平面源等效石英管源、不锈钢大面源等效气体源,并结合蒙特卡罗模拟实现了3类实验样品的γ能峰探测效率曲线的等效法刻度。以相同方式制备的²³⁵U靶开展气-固分离制源实验验证了钚靶中⁸⁵Kr^m、⁸⁷Kr和⁸⁸Kr气体释放率的一致性。根据实测目标产物与⁹⁹Mo的相对产额,以ENDF/BⅧ.0评价数据库中^...     

CZT探测器前端读出电子学设计

针对碲锌镉阵列探测器设计了一种前端读出电子学。采用N沟道JFET共源共栅输入缓冲电路和集成运算AD8066构成低噪声电荷灵敏前置放大器,使用Sallen-Key滤波器实现对核脉冲信号的准高斯成形。在室温下对¹⁵²Eu进行能谱测量,其能量分辨率可达到13.2%121 keV,本设计为后续EAST硬X射线实时二维强度成像及能谱诊断系统研究奠定了重要的实验基础。     

沟道的经典近似及其应用

本文主要讨论沟道的经典近似,引入了连续模型和静态平均势概念。用经典轨迹图象的方法,近似地处理了沟道问题,其结果与实验值吻合较好。利用沟道技术分析了中子辐照硅材料生成的缺陷与中子注量率的线性关系。最后结合实验工作,介绍了沟道技术的几个方面的应用。     

硅中注氢热退火在晶体中产生的应力及其对晶体结构的影响

用X射线四晶衍射仪测量了不同温度下退火的注氢单晶硅的摇摆曲线,分析了不同温度退火后晶格内应力产生及消失的过程。并与离子背散射沟道分析进行了比较。结果表明,在400℃左右,氢注入形成的氢复合体分解,形成氢分子,氢分子在晶格中聚集,生成氢气,在高温下膨胀,引起晶格形变,并产生缺陷;当退火温度达到500℃以后,氢气的膨胀已超过晶体的屈服强度,产生了大量的缺陷、位错。同时在硅晶体内形成气泡,并在硅晶体表面造成砂眼、剥离等现象。     

Channeled ion beam synthesis: a new technique for forming high-quality rare-earth silicides

High dose ¹⁶⁶Er or ¹⁶⁰Gd implantations are used to form rare-earth (RE) silicides in Si. After implanting 0.8−2.0 × 10¹⁷ at./cm² with 90 keV into Si(111) substrates kept at 450 to 530°C, we found that using conventional non-channeled implantation (tilted over 7°), it is impossible to form a continuous RESi_1.7 layer. On the contrary, using channeled implantation, a continuous epitaxial ErSi_1.7 layer with very good crystalline quality can be synthesized; a lowest χ_min value of 1.5% for a surface ErSi_1.7 layer is obtained. This different behaviour is explained using a model based on the difference in implantation depth, defect density and sputtering yield between random and channeled implantation, and the results are compared with Monte Carlo simulations. Such a high-quality RESi_1.7/Si system offers a rare opportunity to study the structure, orientation and strain comprehensively using Rutherford backscattering and channeling spectrometry, X-ray diffraction and TEM. We found that the azimuthal orientation of the hexagonal RESi_1.7 layer to the cubic Si substrate is RESi_1.7[0001]/t|Si[111] and RESi_1.7{11 0}/t|Si{110}. It is further observed that the ErSi_1.7 epilayer is compre strained and quasi-pseudomorphic. In the case of GdSi_1.7, the most difficult rare-earth silicide to form, and enhanced stabilization of the hexagonal over the orthorhombic phase is observed.     

X-ray yields from high-energy heavy ions channeled through a crystal: their crystal thickness and projectile dependences

X-rays emitted from Ar¹⁷⁺, Fe²⁴⁺ and Kr³⁵⁺ ions of about 400 MeV/u transmitting through a thin Si crystal of about 20 μm thickness have been measured in a planar channeling condition and compared with those in a random incident condition. We have found that the X-ray yield from Ar¹⁷⁺ ions is larger for the channeling condition than for the random incidence, while those from Fe²⁴⁺ and Kr³⁵⁺ ions are rather smaller. Such tendencies are explained by considering the projectile dependences of excitation and ionization probabilities together with X-ray emission rates. A crude simulation has qualitatively reproduced these experimental results. When the crystal thickness is small, the X-ray yield is smaller in the channeling condition than in the random incident condition, because excitation is depressed. However, for thicker crystals, the X-ray yield is larger, since the survived population of projectile-bound electrons is larger due to small ionization probabilities under the channeling condition. This inversion occurs at a specific crystal thickness depending on projectile species. Whether the thickness of the used crystal is smaller or larger than the inversion thickness determines enhancement or depression of the X-ray yield in the channeling condition.     

Diffusion and strain relaxation in Si/Si1−xGex/Si structures studied with Rutherford backscattering spectrometry

The thermal stability of strained Si/Si_1−xGe_x/Si structures grown by molecular beam epitaxy was investigated by resistive heating and in situ Rutherford backscattering spectrometry. Ge profiles obtained from a 50 nm Si_1−xGe_x layer on a Si(100) substrate capped with 50 nm Si were evaluated for different Ge concentrations after sequential heating periods at a particular temperature between 850 and 1010° C. The diffusion coefficients, calculated from the increase in signal in the tail of the Ge profile, proved to be comparable to the value for Ge in bulk Si. A more pronounced decrease of the signal at the center of the Ge profile indicated a faster diffusion within the SiGe layer which was confirmed by analysis of the FWHM of the Ge profile. Ion channeling measurements were used to characterize tetragonal strain in the buried SiGe layers. Angular scans through the 111 direction were interpreted with Monte Carlo channeling calculations and used to study strain relaxation in dislocation-free and partially relaxed layers.     

A note on obtaining symmetrical angular yield curves in MeV ion channeling

Planar channeling effects can distort the angular yield (dip) curve measured about an axial channeling direction. Two methods for minimizing distortion due to planar channeling are discussed: 1) varying the angles θ and φ of a two-axis goniometer together during the angular scan, and 2) remounting the sample so that a scan of only θ produces an undistorted symmetric dip curve. In practice, remounting the sample is preferred in order to minimize effects due to the mechanical limitations of the goniometer.     

On the useful range of application of molecular dynamics simulations in the recoil interaction approximation

The validity of the binary collision (BC) approximation and of the so-called recoil interaction approximation (RIA) in ion–solid interactions at low energies is investigated by comparison with molecular dynamics (MD) simulations. The systems studied are channeling through a (1 1 0) oriented layer of Si, implantation into a (1 0 0)-Si target, and reflection from (1 0 0)-Si. It is found that the BC approximation does not introduce significant errors in the case of channeling simulations even at very low energies. Under non-channeling conditions an upper limit to the break-down energy of the BC approximation in Si is given by 30M₁^0.55 eV, taking 5% deviation in the projected range as the criterion.     

Radiation damage induced by 5 keV Si ion implantation in strained-Si/Si0.8Ge0.2

The damage distributions induced by ultra low energy ion implantation (5 keV Si⁺) in both strained-Si/Si_0.8Ge_0.2 and normal Si are measured using high-resolution RBS/channeling with a depth resolution better than 1 nm. Ion implantation was performed at room temperature over the fluence range from 2 × 10¹³ to 1 × 10¹⁵ ions/cm². Our HRBS results show that the radiation damage induced in the strained Si is slightly larger than that in the normal Si at fluences from 1 × 10¹⁴ to 4 × 10¹⁴ ions/cm² while the amorphous width is almost the same in both strained and normal Si.     

High resolution channeling contrast microscopy and channeling analysis of SiGe quantum well structures

High resolution channeling contrast microscopy (CCM) and channeling measurements were carried out to characterize SiGe quantum well structures on micron thick graded layers (i.e. virtual substrates). The virtual substrates were grown by gas source molecular beam epitaxy at a pressure of 10⁻⁵ mbar and low pressure chemical vapor deposition at 10⁻² mbar on boron doped Si(0 0 1) substrates respectively. A homoepitaxial silicon buffer layer was grown prior to the deposition. The nominal structure is a 20 nm Si_0.75Ge_0.25 layer at the surface, followed by 10 nm pure Si, 500 nm Si_0.75Ge_0.25 and a 1000 nm thick graded SiGe (0–26%) layer. RBS was used to measure the depth profiles, and angular scans around the (1 0 0) axis were carried out to assess crystal and interface quality. CCM was used to acquire depth resolved images of micron-sized lateral inhomogenities (‘cross-hatch') present on both samples.     

Effect of MeV beams on the interface structure of metal(adlayer)-silicon (crystal substrate) systems

The influence of MeV ion beams on the measured intensity of the surface peak (SP) in channeling studies has been examined for Ag and/or Au covered Si(111), and Pd covered Si(111) systems with film thicknesses up to several monolayers. A simple phenomenological model is introduced to analyse the observed increase in atomic displacements induced by probing He ions of 1 MeV. For the Ag and Pd cases, effects attributable to the deposited metal was small while for Au an appreciable enhancement of the beam sensitivity was observed which increases with increasing Au thickness for beam doses of ? 3.1 × 10¹⁶ ions/cm². The observe differences cannot be explained by the difference in mass and atomic number of the overlayer atoms. The model suggests that the chemical nature of atomic bonds near the interface affects the damage threshold energy.