Determination of the thickness of a gold layer deposited onto silicon via reflected electron spectroscopy

The energy spectra of electrons reflected from a gold layer deposited onto a silicon substrate have been measured when the energy losses are comparable with the energy of a probe electron beam (5 keV) and the elastic energy losses correspond to an electron-beam energy of 14 keV. A subsequent theory for calculating the energy spectra of electrons and light ions reflected from a multilayer target, which is used to interpret the energy spectra measured in the wide range of energy losses, has been developed. It is found that the elastic scattering processes in the gold layer (the thickness of which is tens of monolayers) substantially affect formation of the energy spectra. The Au layer thicknesses calculated by means of the developed theory are compared with those determined from the spectra of elastically reflected electrons. The errors of the Au layer thickness measurements via the proposed method are discussed.     

椭偏透射法测量氢化非晶硅薄膜厚度和光学参数

针对多角度椭偏测量透明基片上薄膜厚度和光学参数时基片背面非相干反射光的影响问题,报道了利用椭偏透射谱测量等离子增强化学气相沉积法(PECVD)制备的a-Si:H薄膜厚度和光学参数的方法,分析了基片温度T_s和辉光放电前气体温度T_g的影响.研究表明,用椭偏透射法测量的a-Si:H薄膜厚度值与扫描电镜(SEM)测得的值相当,推导得到的光学参数与其他研究者得到的结果一致.该方法可用于生长在透明基片上的其他非晶或多晶薄膜. 关键词： 椭偏测量 透射法 光学参数 氢化非晶硅薄膜     

Width determination of SiO2-films in Si-based devices using low-loss EFTEM: image contrast as a function of sample thickness

Energy filtering transmission electron microscopy (EFTEM) has become one of the most efficient tools for specimen characterization at nanometer length scales. EFTEM imaging is most often carried out in the core-loss region but image intensity becomes more and more a limiting factor with decreasing feature size. Alternatively, it is possible to record EFTEM images in the low-loss region, where intensities are essentially higher and where in many cases the images contain material specific contrasts. In this paper we investigate the influence of the important parameters on the material contrast between silicon and silicon dioxide, e.g. specimen thickness, specimen orientation, energy-loss and energy selecting slit width. We show that sample thickness plays an important role and present two methods to calculate material contrast as a function of energy-loss and sample thicknesses. The first method uses spectra taken from both materials at different sample thickness by electron energy-loss spectroscopy, the second calculates contrast directly from a series of energy filtered images. From the results we determine the ideal acquisition parameters for the Si/SiO(2) system and demonstrate imaging at sufficient resolution below 2nm with a test sample of thin SiO(2) layers on Si.     

Joint experimental and computational study of aluminum electron energy loss spectra

Experimental reflection electron energy loss (REEL) spectra are measured from aluminum for primary energies ranging from 130 eV to 2 keV. A Monte Carlo simulation is shortly described and used to calculate the same spectra. The focus is on reproducing the variable weight of surface and bulk losses as the surface sensitivity of spectra changes by changing the primary electron energy. The intensity of surface losses in the simulations is modulated by the thickness of the region where surface excitations occur. Simulations based either on a constant or an energy-dependent thickness for this layer are considered. In both cases, simulated spectra reproduce the experimental trend as a function of energy, though the correct surface-to-bulk intensity ratio for each energy is either underestimated or overestimated.     

Adsorption and electron properties of thin nickel films on W(110) surface

The evolution of the properties of ordered nickel films with thicknesses increasing from one to three atomic monolayers (ML) adsorbed on the W(110) single crystal surface is studied under ultrahigh vacuum conditions by the methods of reflection-absorption infrared spectroscopy (RAIRS) and ultraviolet photoelectron spectroscopy (UPS). The film structure corresponds to that of the Ni(111) single crystal face. The RAIRS technique is used to study the vibrational properties of the probing NO molecules adsorbed on the nickel films studied. In the course of the nickel film growth, whereby its thickness increases from 1 to 3 ML, both the vibrational and photoelectron spectra exhibit significant variation, which is indicative of a change in the adsorption and electron properties of the film. Stabilization of the IR and photoelectron spectra at a film thickness of 3 ML indicates that this thickness corresponds to the formation of the main adsorption and electron properties of the deposit. At the same time, the vibrational spectra of NO molecules adsorbed on a monoatomic nickel film exhibit features typical of adsorption on the W[110] surface of a massive tungsten crystal.     

Investigation of the protective properties of a subnanometer diamond-like carbon film

The influence of diamond-like carbon coatings on the corrosion resistance of zirconium is investigated. Zirconium films with a thickness of 20 nm and different thicknesses of carbon protective films are examined. The chemical state of atoms on the surface is characterized using the measured photoelectron, electron energy loss, and Auger electron spectra. The results obtained demonstrate that the diamond-like carbon coating with a thickness of approximately 1 nm almost completely protects the metal film against oxidation. These protective properties of the diamond-like carbon coatings are explained by their high chemical inertness and uniformity over the thickness.     

Thickness Determination for a Two-Layered Composite of a Film and a Plate by Low-Frequency Ultrasound

We present an ultrasonic method for determining the thickness of a composite consisting of a soft thin film attached to a hard plate substrate, by resonance spectra in the low frequency region, The interrogating waves can be incident only to the two-layered composite from the substrate side. The reflection spectra are obtained by FFT analysis of the compressive pulsed echoes from the composite, and the thicknesses of the film and the substrate are simultaneously inversed by the simulated annealing method from the resonant frequencies knowing other acoustical parameters in prior. The sensitivity of the method to individual thickness, its convergence and stability against experimental noises are studied, Experiment with interrogating wavelength 4 times larger than the film thickness in a sample of a polymer film （0.054mm） on an aluminium plate （6.24mm） verifies the validity of the method. The average relative errors in the measurement of the thicknesses of the film and the substrate are found to be -4.1% and -0.62%, respectively.     

10-25 keV电子致厚W,Au靶韧致辐射谱的测量

测量了10-25 keV电子碰撞厚W, Au靶产生的韧致辐射谱, 并与Monte Carlo程序PENELOPE模拟的X射线谱进行了比较, 除在3 keV前实验谱略低于理论谱外, 整体上两者符合得很好. 在模拟电子与靶材料相互作用产生韧致辐射时, PENELOPE程序中只包含有普通韧制辐射的截面数据. 我们的实验结果表明, 在电子与固体靶相互作用时, 没有明显的极化韧致辐射产生, PENELOPE程序能够可靠地描述电子与固体厚靶相互作用产生的韧致辐射.     

利用轫致辐射谱回推超热电子温度

超短超强激光打靶产生的超热电子与固体靶相互作用时会产生轫致辐射X射线。利用蒙特卡罗方法,对电子在固体靶中传输产生的轫致辐射X射线进行了模拟。1 MeV电子束与固体靶作用产生的轫致辐射谱模拟结果表明,轫致辐射谱高能段斜率受靶厚度及靶材料的影响不明显。麦克斯韦分布的电子束及单能电子束与30 m铜靶作用的模拟结果显示,两种电子源产生的轫致辐射谱在电子束能量或温度较高时基本一致。给出了一种利用轫致辐射谱斜率反推超热电子温度的定标方法。模拟了不同温度下超热电子产生的轫致辐射光子的能量角分布及光子数角分布,结果显示辐射光子能量通量和光子数随着电子温度的提高越来越向前倾,并给出了另外一种由轫致辐射能量角分布反推超热电子温度的定标关系。     

In插入层对硅衬底外延InN晶体质量和光学特性的影响

在Si（111）衬底上分别预沉积0,0.1,0.5,1 nm厚度的In插入层后,采用等离子辅助分子束外延法制备了纤锌矿结构的InN材料,结合X射线衍射（XRD）、扫描电子显微镜（SEM）、吸收谱及光致发光谱研究了不同厚度的In插入层对外延InN晶体质量和光学特性的影响。XRD和SEM的测试结果表明,在Si衬底上预沉积0.5 nm厚的In插入层有利于改善外延InN材料的形貌,提高材料的晶体质量。吸收谱和光致发光谱测试表明,0.5 nm厚In插入层对应的InN样品吸收边蓝移程度最小,光致发射谱半峰宽最窄,并且有最高的带边辐射复合发光效率。可见,引入适当厚度的InN插入层可以改善Si衬底上外延InN材料的晶体质量和光学特性。     

微腔有机发光器件中的电致发光光谱

设计了结构为Glass/DBR/ITO/TPD/Alq3/Ag的微腔有机发光器件。从理论上详细地研究了腔内各层结构对器件电致发光谱性能的影响。结果表明:随着腔长厚度的增加,器件的归一化电致发光谱强度不断减小;在可见光区,器件的EL谱随发光层厚度的增加出现振荡变化。空穴传输层和发光层的界面位置对器件电致发光谱的影响也很大。最后得到,在设计微腔时发光层厚度要尽量窄,并且中心发光区域应位于谐振腔中电场的峰值位置。     

Applicability of magic angle for angle-resolved X-ray photoelectron spectroscopy of corrugated SiO2/Si surfaces: Monte Carlo calculations

In several earlier works, the “magic angle” has been introduced in overlayer thickness estimation from angle-resolved X-ray photoelectron spectra as a practical tool for suppressing experimental errors induced by surface corrugation. We analyse the applicability of the “magic angle” in Monte Carlo calculations of random as well as non-random corrugated silicon surfaces covered by thin silicon dioxide films, accounting for (a) electron inelastic and elastic scattering events, (b) the shadowing of photoelectrons, and (c) the differences between microscopic and macroscopic electron emission geometry. It is shown that the “magic angle” value varies with the type of surface roughness, overlayer thickness, surface contamination, an uneven overlayer thickness and electron inelastic surface excitations.     

Manifestation of empty electron states in the total current spectra of silver

A combined analysis is made of the low-energy total current and secondary electron emission spectra at the initial stage of formation of a silver coating on a W(110) surface. It is shown that the features observed in the spectra are related to the energy structure of the density of empty states lying above the vacuum level. The dynamics of changes in these features in the total current spectra as the film thickness increases indicates that at the initial stage the silver coating is characterized by the Ag(111) orientation, but as the thickness increases, the Ag(110) orientation predominates. Zh. Tekh. Fiz. 69, 99–102 (July 1999)     

基于波长选择的纸页厚度太赫兹时域光谱检测新方法

光谱数据的波长选择是太赫兹光谱定量分析的关键。以纸页厚度检测为例,提出了一种基于波长选择的纸页厚度太赫兹相位谱检测新方法。首先采用离散离子群算法进行太赫兹相位信号优选,并应用偏最小二乘法建立纸页厚度定量模型,以模型的预测均方根误差作为太赫兹相位信号优选的评价标准,选择出预测效果最优的太赫兹相位信号,进行纸页厚度预测。最后将本文方法的预测结果与采用全谱和单频相位信号的预测结果进行比较,结果表明,提出的方法预测结果最好。     

Modification of electronic properties during adsorption of conjugate organic molecules on the surface of polycrystalline SnO<Subscript>2</Subscript>

The modification of the electronic structure during adsorption of ultrathin copper phthalocyanine (CuPc) and 3, 4, 9, 10 perylene-tetracarboxylic-dianhydride (PTCDA) coatings on the surface of polycrystalline tin dioxide is traced. Auger electron spectroscopy is employed to find changes in the atomic composition of the surface. It is found with the help of low-energy electron total current spectroscopy using a testing beam of electrons with energies up to 30 eV that the total current spectra typical of organic films are formed when the thickness of the coating being deposited is 2–7 nm. The formation of an interface layer 1.5–2.0 nm in thickness is detected, in which the intensity of the structure of the total current spectra decreases and the effect of interaction of PTCDA molecules with the SnO₂ surface is manifested.     

Measurement of velocity variations along a wave path in the through-thickness direction in a plate

In this paper there is given a method to predict ultrasonic wave velocity variations along a wave path in the through-thickness direction in a plate from thickness resonance spectra. Thickness resonance spectra are numerically calculated and two simple rules used to predict the entire ultrasonic wave velocity variation are derived. In the calculation, the wave path is assumed to be straight along the thickness direction and the velocity variation is assumed to be either as a parabolic curve dependence or a linear dependence with respect to the distance from the surface and to be symmetric with respect to the plate center. To see if the numerical calculation method is reliable, thickness resonance frequencies of a sample with three-layers were measured by EMAT (electromagnetic acoustic transducer) with a good agreement between the measured and the calculated frequencies. This method can be applied to the ultrasonic measurement of material characteristics, internal stress or various other properties of plate materials.     

Parametric x-ray radiation generated by 5.7-MeV electrons in a pyrolytic-graphite crystal

Parametric x-ray radiation is observed in a mosaic pyrolytic-graphite crystal irradiated with a 5.7-MeV electron beam. The first-order (002) reflection of parametric x-ray radiation is detected in Bragg geometry. In the measured spectra, there is a peak at about 8 keV. The detector used is arranged at an angle of Θ_D=2Θ_B=27° with respect to the electron beam, where Θ_B is the Bragg angle. The target thickness is 0.3 mm. The spectra of parametric x-ray radiation are measured at various angles of target orientation with respect to the axis of the incident-electron beam.     

Cerenkov losses: a limit for bandgap determination and Kramers-Kronig analysis

Measuring low energy losses in semiconductors and insulators with high spatial resolution becomes attractive with the increasing availability of modern transmission electron microscopes (TEMs) equipped with monochromators, C(s) correctors and energy filters. In this paper, we demonstrate that Cerenkov losses pose a limit for the interpretation of low energy loss spectra (EELS) in terms of interband transistions and bandgap determination for many materials. If the velocity of a charged particle in a medium exceeds the velocity of light, photons are emitted leading to a corresponding energy loss of a few electronvolt. Since these losses are strong for energies below the onset of interband transitions, they change the apparent loss function of semiconductors and insulators, with the risk of erroneous interpretation of spectra. We measured low energy losses of Si and GaAs with a monochromated TEM demonstrating the effect of sample thickness on Cerenkov losses. Angle resolved EELS and energy filtered diffraction patterns (taken without a monochromator) show the extremely narrow angular distribution of Cerenkov losses. The latter experiment provides a method that allows to decide whether Cerenkov radiation masks the very low loss signal in EELS.     

Ultrathin Fe layers on Ag (1 0 0) surface

Iron layers (0.15-10 ML thick) deposited on Ag (1 0 0) substrates were investigated by conversion electron Mössbauer spectrometry over a broad temperature range. The layers were characterized by scanning tunneling microscopy. Different forms of the layers, depending on their thickness, were observed. Minimum roughness of the layers were found at 0.15 and 10 ML thickness values. The Mössbauer spectra showed systematic thickness dependence. At low thickness values, broad doublets were observed, while above 6 ML, magnetic split spectra appeared at room temperature. At low temperatures, magnetically split spectra appeared with parameter values characteristic of Fe-Ag and Fe-Fe atomic interactions. The hyperfine split spectra indicated magnetic anisotropy and an enhanced saturation hyperfine magnetic field of ?40 T. The latter value is the highest ever measured for iron in thin layers.