Absolute atomic densities determined by auger electron spectroscopy

The secondary electron distributionN(E) obtained with a spherical grid retarding field analyser is stored in a multichannel analyser. The experimental intensities of Auger lines are accurately determined by numerically substracting the background in theN(E) distribution and taking the area under the resulting peaks. Broadening of the lines due to several experimental factors, the multiple structure of the lines and the characteristics energy losses are taken into account. The absolute atomic densities on the surface are deducted from the Auger line intensities by a simple theoretical model. A comparison is made with atomic densities on the surface which are known either from the crystal structure (cleaved muscovite) or from Rutherford backscattering experiments (thin layer of Ag) or simply from the specific weight in the case of bulk materials (C, Cu, Ag). The maximum deviation is smaller than a factor of 2. Generally, the values differ by about 30%, which shows that AES, performed in this way, can give reliable quantitative results for densities ranging from a fraction of a monolayer to the bulk material.     

The surface composition of platinum-palladium alloys determined by auger electron spectroscopy

Pt-Pd alloys were prepared as powders by a chemical reduction method and as films by evaporating the specpure metals onto a quartz substrate. Results were evaluated by means of the Gallon equation; the parameters of this equation — the signal intensity of a monolayer and of the bulk material — were determined experimentally for all relevant Auger peaks. The backscattering factor for the alloy system was evaluated from experiments in which a layer of one metal was evaporated on top of the other. The value determined in this way was compared with results obtained in the literature on similar systems. The theoretical surface compositions are calculated for several models and compared with the experimental results. Experimental results reveal surface enrichment in Pd, in good agreement with the theoretical calculations. Interactions of alloys with carbon monoxide and propane are discussed and a possible explanation of the effects observed is suggested.     

New trends in the conversion electron spectroscopy

The method of investigation of an electronic structure of chemical compounds and solids by high resolution measurement of internal conversion electron spectra for low-energy isomeric transitions is described.     

Depth analysis by combination of conversion electron,conversion X-ray and γ-ray Mössbauer spectroscopy

Conversion electrons, conversion X-rays and transmitted γ-rays were used to determine magnetic structures. The penetration depths of these radiations allow the material to be scanned.     

Spin values of the low lying nuclear levels of201Hg

Gamma-gamma directional correlations have been investigated for the cascades of 135-30 keV and 135-32 keV in²⁰¹Hg from the decay of²⁰¹Tl. A combination of NaI (Tl) and Si (Li) detectors was used for the experiments. Spin values ofI=1/2, 3/2 and 1/2 have been assigned to 1.58, 32.19 and 167.49 keV energy levels. In addition, the relative intensities of theγ rays have been measured with a Ge (Li) detector system. The results are 2.2±0.2, 2.2±0.2, 26.5±1.3, 1.6±0.1 and 100 for theγ rays of 30.60, 32.19, 135.34, 165.88 and 167.43 keV energies, respectively.     

Polarity and inverse boundary of Sn-doped ZnO bicrystal nanobelts determined by electron energy-loss spectroscopy

Polarity in Sn-doped ZnO bicrystal nanobelts has been investigated using electron energy-loss spectroscopy. The nanobelts are composed of two domain boundaries extending along the axial direction. It is confirmed that the nanobelts are Zn terminated at both sides. Examinations of high-resolution transmission electron microscopy and electron energy-loss spectroscopy show that one domain boundary results from a stacking fault, and the other originates from Sn-ion insertion, which leads to an inverse domain boundary. A possible atomic stacking model is proposed.     

In-beam conversion electron spectroscopy using the SACRED array

Conversion electron studies of medium-heavy to heavy nuclear mass systems are important where the internal conversion process begins to dominate over gamma-ray emission. The use of a segmented detector array sensitive to conversion electrons has been used to study multiple conversion electron cascades from nuclear transitions. The application of the Silicon Array for ConveRsion Electron Detection (SACRED) for in-beam measurements has successfully been implemented.     

Structure and magnetism of Fe mono‐ and multi‐layer systems as seen by conversion electron Mössbauer spectroscopy at atomic scale

The characteristic magnetic phenomena of ultrathin films are attributed to their reduced dimensionality and increased importance of the interfacial properties originated at their boundaries. The loss of nearest neighbor interactions at the interfaces, band hybridization, expansion or contraction of the atomic spacing occur, resulting in local changes of the energy band structure. Recent technical developments make it now possible to grow ultrathin films in a strictly layer‐by‐layer mode and to produce large areas of flat surfaces. Nevertheless, small structural perturbations in the local atomic configuration can still exist and result in significant changes of the global magnetic properties. Conversion Electron Mössbauer Spectroscopy (CEMS) determines the hyperfine interaction parameters which are sensitive to the arrangement at the atomic scale. In particular, depth selectivity at a monolayer level has been achieved in Fe films with one atomic layer replaced by the Mössbauer isotope ⁵⁷Fe. This contribution reviews the experimental work on magnetic phenomena of bcc, fcc and hcp Fe ultrathin films (including monolayer and multilayer structures), epitaxially grown by condensation from molecular beam under ultrahigh vacuum conditions. Since the structural and magnetic information can be achieved by using one method only, Mössbauer spectroscopy is pointed out as being an extremely effective and convenient tool for such purposes.     

利用时间分辨 Ar的K壳层发射光谱诊断内爆靶丸芯区电子温度的时间演化过程

在神光Ⅱ装置上的内爆实验中,通过在充氘气（D2）的靶丸中掺入氩（Ar）元素,利用晶体谱仪配条纹相机测量得到了内爆停滞阶段Ar 的K壳层发射光谱随时间的变化。在实验中,观测到Ar的Heα,Heβ以及Lyα线发射,持续时间大约200 ps。用Heα线与Lyα线强度比值来推断靶丸芯区电子温度。利用碰撞辐射模型,从理论上计算出Heα线与Lyα线强度比值随电子温度、数密度的变化。通过将实验上观测到的Heα线与Lyα线强度比与理论计算值相比较,获得了芯区电子温度随时间的演化。并计算比较了不同电子密度条件下推断出来的电子温度的差异,证明诊断电子温度的方法对电子数密度的变化不敏感。利用逃逸因子修正了自吸收效应,从计算的结果可以看出在目前的实验中Heα线和Lyα线是光学薄的。     

利用时间分辨Ar的K壳层发射光谱诊断内爆靶丸芯区电子温度的时间演化过程

在神光Ⅱ装置上的内爆实验中,通过在充氘气(D2)的靶丸中掺入氩(Ar)元素,利用晶体谱仪配条纹相机测量得到了内爆停滞阶段Ar的K壳层发射光谱随时间的变化。在实验中,观测到Ar的Heα,Heβ以及Lyα线发射,持续时间大约200ps。用Heα线与Lyα线强度比值来推断靶丸芯区电子温度。利用碰撞辐射模型,从理论上计算出Heα线与Lyα线强度比值随电子温度、数密度的变化。通过将实验上观测到的Heα线与Lyα线强度比与理论计算值相比较,获得了芯区电子温度随时间的演化。并计算比较了不同电子密度条件下推断出来的电子温度的差异,证明诊断电子温度的方法对电子数密度的变化不敏感。利用逃逸因子修正了自吸收效应,从计算的结果可以看出在目前的实验中Heα线和Lyα线是光学薄的。     

Investigation of atomic structures of diamond-like amorphous carbon by electron energy loss spectroscopy

Research into amorphous carbon films has been developed to such an extent that the film property can be fine tuned to mimic that of the crystalline counterparts, be it diamond, graphite, or even fullerene-like. This flexibility makes such films ideal for a wide range of applications from anti-abrasive window coating to lubricating layers on the surface of magnetic hard-disk. Not only are their mechanical properties interesting, electrically the diamond-like amorphous carbon films are also easier to dope than crystalline diamond, making them potentially a better alternative to amorphous silicon for photovoltaic devices. We will show that electron energy loss spectroscopy, in particular the carbon 1s core absorption spectroscopy, has been instrumental in revealing the nature of the bonding between carbon atoms. Such information allows microstructure models to be developed for proper understanding of the observed properties and providing scientific basis for future improvement.     

Band transitions in wurtzite GaN and InN determined by valence electron energy loss spectroscopy

Valence electron energy loss spectroscopy (VEELS) was applied to determine band transitions in wurtzite InN, deposited by molecular beam epitaxy on (0001) sapphire substrates or GaN buffer layers. The GaN buffer layer was used as VEELS reference. At room temperature a band transition for wurtzite InN was found at (1.7±0.2 eV) and for wurtzite GaN at (3.3±0.2 eV) that are ascribed to the fundamental bandgap. Additional band transitions could be identified at higher and lower energy losses. The latter may be related to transitions involving defect bands. In InN, neither oxygen related crystal phases nor indium metal clusters were observed in the areas of the epilayers investigated by VEELS. Consequently, the obtained results mainly describe the properties of the InN host crystal.     

Scintilation detectors in conversion electron Mössbauer spectroscopy

Results of CEMS measurements performed in vacuum applying a channeltron and a low-noise thin-layer scintillation detector equipped with different types of thin-layer scintillators (e.g. P-47 CsI(Tl) of different thickness) are reported here. The experimental merits of different detectors for different Mïossbauer isotopes of samples are evaluated.     

Magnetic properties of H+ implanted bubble garnet films by means of depth selective conversion electron Mössbauer spectroscopy

Bubble garnet films before and after 50 keV H⁺ implantation have been studied by means of DCEMS. The spintilt angle of the films as grown after etching off 1000 å was measured to be 30±2? relative to the surface normal at the top of the surface. The doses of implanted H⁺ ions were 2, 4 and 8×10¹⁶ ions/cm². Mössbauer spectra were measured after successive etching of the implanted layer. The magnetic hyperfine field was obtained as a function of depth. The implanted hydrogen distribution was also measured by the¹H(¹⁵N, αγ)¹²C reaction.     

Experimental techniques for conversion electron Mössbauer spectroscopy

Conversion electron Mössbauer spectroscopy has grown during the last decade as a new tool of surface science. High sensitivity, depth selectivity and capabilities of the method in non-destructive backscattering analysis are essential features of CEMS. These virtues made the method advantageous in various applications and stimulated considerable progress in experimental techniques. The latter is the subject of the present paper.