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[en] In 1977, the Methodist Hospital of Lubbock, Texas, sold a 14 year old Picker C-3000 therapy unit to Mexican Centro de Juarez, instead of taking up the Picker option of dismantling, removal and safe storage. The device was never used for research or treatment, and the resulting accident after its dismantling and dispersion of the parts by unknown persons in November 1983 is described in outline. (U.K.)
[en] Results of annealing experiments of boron-doped zinc oxide (ZnO:B) layers prepared by low pressure chemical vapor deposition method on polished Si, soda-lime glass for windows, and AF45 Schott alkali free thin glass substrates are presented. It is shown that short annealing of samples at 150 °C and 300 °C in air causes serious surface degradation of samples prepared on Si and soda-lime glass substrate. The characteristic feature of degradation is the creation of bubbles and craters on the sample surface which fully destroy the continuity of zinc oxide layers. The results of depth distribution mapping of elements indicate that the formation of bubbles is linked to increase in hydrogen concentration in the layer. The surface degradation was not noticed on samples deposited on AF45 Schott alkali free thin glass which has a SiO_2 diffusion barrier layer on the surface, only much fewer and smaller bubbles were visible. The results indicate the important role of hydrogen outgassing from the substrate induced by a thermal shock
[en] Complete text of publication follows. Secondary neutral mass spectrometry (SNMS) is a well known destructive method for depth profiling in material science. The depth resolution can achieve several nanometers. Study of surfaces and interfaces in layered structures by depth profile analysis (DPA) help to understand the behaviour of adjacent layers or doping elements. It is also an excellent method to investigate materials and compounds even at nanometer scale. To achieve such results, a correct interpretation of the acquired spectrum is required. The knowledge of depth concentrations of constituents of layered structures is very important for research and technological developments. An accurate method for the quantitative analysis of depth composition profiles with high depth resolution is essential for investigating the formation conditions, growth kinetics, and stability of thin-film systems with possible concentration gradients. Determination of depth distributions of constituents often uses mathematical methods which are based on approximations. These calculations are based on theoretical estimations for some well defined sample groups or measurements. The Mixing-Roughness-Information-depth (MRI) model of S. Hofmann makes it possible also to reconstruct the depth concentration profile determined by AES and SIMS. Its disadvantage is that the MRI model is only applicable partially for SNMS technique. Though AES and SIMS depth profiling yield a good depth resolution, they can have several artefacts as atomic mixing at the sputter surface, preferential sputtering of the specimen components, and implantation. Using high energy ions for sputtering, the effect of these undesirable phenomena increases. Since SNMS strictly separates the emission and ionisation of sputtered constituents, it is an excellent sputtering technique for DPA. In ion sputtering processes the sputtered elements mostly remain in neutral state, only less than 1% is ionised. The ionization happens in the matrix before the particles escape from the sample surface, and the ionization of degree depends on the matrix material. This is called as matrix effect. Contrary to the direct detection of secondary ions, the analysis of neutral particles can effectively eliminate the matrix effect. After a subsequent postionization of neutral particles, they are ideally suited for quantitative elemental and DPA of any material. Minimal matrix effect renders a very accurate material analysis possibility. Since models used to reconstruct depth concentration profiles measured by SIMS or AES are not fully applicable for SNMS analyses, a mathematical model based on statistical and probability calculations of surface morphology is required. Surface roughness, sputtered crater shape, detection rate of different constituent elements, and some other complex nanoscale physical behaviours must be taken into account and studied systematically for sufficient mathematical analysis. The goal is to develop and apply a new procedure for DPA of the samples having high surface roughness. Our experience shows that the depth resolution is mainly determined by the surface roughness and the crater shape.
[en] Complete text of publication follows. Optical diffraction grating and micro Fresnel zone plate type structures were fabricated in relatively thin poly(dimethylsiloxane) (PDMS) layers using proton beam writing technique and the performance of these optical devices was tested. Micro-optics is a key technology in many fields of common applications like, for example, data communication, lighting technology, industrial automation, display technology, sensing applications and data storage. It enables new functionalities and applications previously inaccessible and improves performance of the already available products with reduced cost, volume and weight. There are a few different fabrication techniques to produce refractive or diffractive micro-optical devices such as X-ray lithography, UV-lithography, e-beam lithography, laser writing, plasma etching, proton beam writing. In general, three different kinds of materials are used for micro-optics, such as glass, polymers and crystal. PDMS is a commonly used silicon-based organic polymer, optically clear, generally considered to be inert, non-toxic and biocompatible and it has been used as a resist material for direct write techniques only in very few cases. In this work, PDMS was used as a resist material; the structures were irradiated directly into the polymer. We were looking for a biocompatible, micropatternable polymer in which the chemical structure changes significantly due to proton beam exposure making the polymer capable of proton beam writing. We demonstrated that the change in the structure of the polymer is so significant that there is no need to perform any development processes. The proton irradiation causes refractive index change in the polymer, so diffraction gratings and other optical devices like Fresnel zone plates can be fabricated in this way. The observed high order diffraction patterns prove the high quality of the created optical devices . This technique may be a useful tool for designing micro-optics for various applications like microfluidics, lab-on-a-chip systems. Acknowledgements This work was supported by the EU cofunded Economic Competitiveness Operative Programme (GVOP-3.2.1.-2004-04-0402/3.0)
[en] Complete text of publication follows. The soccer ball shaped carbon molecule consisting of 60 carbon atoms (C60, fullerene) was discovered in 1985. Since that time the fullerene has become intensively studied. This special molecule has much potential in medical care, biotechnology and nanotechnology. We are motivated to produce special type fullerenes, so called endohedral fullerenes (some alien atoms are encapsulated inside the fullerene cage). The spring of our motivation is that the Fe at C60 could be applied as a contrast material for MRI (Magnetic Resonance Imaging) or microwave heat therapy. One way to make X at C60 is the surface production using an ECRIS (Electron Cyclotron Resonance Ion Source). An evaporated or preprepared fullerene layer is irradiated by ions to form a new material during the implantation. By this method several kinds of atomic species, such as Li, Na, K, Rb, Xe were encapsulated into the fullerenes. However evidence for the Fe at C60 has not been found yet. During the analysis of the irradiated samples three questions must be answered. 1. Are there iron atoms in the layer and where? 2. Does the iron bond to the fullerene? 3. How does the iron bond to the fullerene, inside or outside? Using different investigation tools, SNMS (Secondary Neural Mass Spectrometer), MALDI-TOF (Matrix Assisted Laser Desorption Ionization Time of Flight), XPS (Xray Photoelectron Spectroscopy) or HPLC (High-Performance Liquid Chromatography), all these questions could be clarified step by step. In this paper we made the first steps to answer the first question: fullerene layers irradiated by iron ion beam delivered by the ATOMKI-ECRIS have been analyzed by the ATOMKI-SNMS. The evaporated 90 - 120 nm thick fullerene layers on Si holder were irradiated by Fe5+ and Fe+ ion beams produced from Ferrocene vapor. Samples were irradiated with two different doses (5 1018 ion/cm3 and 1022 ion/cm3) at four ion energies (65 keV, 6.5 keV, 0.2 keV and two of these samples at four energies from 4 keV up to 65 keV). The samples were investigated by SNMS and depth profiles were recorded. The continuous line in Fig. 1. shows the iron distribution in the fullerene film at 6.5 keV irradiation energy. The well-known SRIM (Stopping and Range of Ions in Matter) code was used to check the curve measured experimentally. Longitudinal distribution of 105 iron ions was simulated at fullerene (dots in Fig. 1) Good agreement was found between the measurements (SNMS) and simulations (SRIM) for all the investigated samples. New irradiations with higher Fe-dose are planned to be carried out soon in order to use other methods (e.g. XPS) for answering the second and third questions.
[en] The thermal behaviour of sputtered Cu/Ta bilayer films on Si-substrate (Cu is the top layer) was investigated in the temperature range of 563-713 K. Samples were heated in ultra high vacuum conditions, while the Auger intensities were monitored. The time evolution of the Ta and Cu Auger signals was interpreted as Ta grain boundary diffusion through the Cu film and Ta accumulation on the copper surface. On the basis of the method developed by Hwang and Baluffi, the activation energy of the Ta grain boundary diffusion in copper was determined (Q=0.7±0.2 eV). At 713 K a 10-h heat treatment caused a complete degradation of the sample, silicon appeared on the top surface and silicide formation was detected
[en] Amorphous Si/Ge multilayers of 10-40 nm repeat length were prepared by DC magnetron sputtering and annealed at 683 K. Rutherford backscattering spectrometry (RBS) with increased depth resolution was applied to study the intermixing of the elements. The interdiffusion coefficient was determined by measuring the intensity of the first Ge peak in the RBS spectrum as a function of annealing time. An attempt was made to observe the theoretically predicted change of dimensions of the Si/Ge layers caused by the diffusion asymmetry
[en] Complete text of publication follows. In the case of solar cells, to optimize the properties of photovoltaic (PV) modules one of the important issues is the diffusion of sodium from the glass substrate into the layered structure. There are many discussions about the role of the Na during preparation of PV modules: i) selenisation of Mo interlayer between the ZnO and active layers to obtain a lower series electrical resistance without changing the transmittance of the ZnO layer; ii) the diffusion of Na from glass substrate to a-Si:H/c- Si or Cu(In,Ga)Se2 (CIGS) layer. In certain cases the ZnO layers must be annealed in air or in hydrogen atmosphere to improve electrical conductivity. At the same time, the annealing temperature induces diffusion of Na. Thus, detailed investigation of appropriate layered materials is required. Present work was initiated in the framework of developing the solar cell technology. The goal was to investigate suitable substrates appropriate for desirable Na diffusion. Borondoped ZnO layers were prepared by Low Pressure Chemical Vapour Deposition (LPCVD) method on three different types of substrate: soda-lime windows glass (s1) and Schott AF-45 alkali-free thin glass (s2) were selected for our experiments. Polished Si substrate (s3) was used as a reference sample. After sample preparation procedure, the samples were annealed in air at 300 deg C. As it can seen in Fig.1, significant structural changes occurred at the surface of boron-doped ZnO layers in the form of bubble formation. We experienced that Na diffusion directly connected with hydrogen precipitation. Formation of bubbles observed was most probably due to enhanced hydrogen accumulation from the ZnO:B structure or decomposition of physisorbed precursor. After the annealing, the bubbles on the sample surface were blown up and cracked, i.e. were destroyed on polished Si and Soda-lime glass substrates. However, the samples prepared on AF 45 Schott alkali-free thin glass substrate had visually much less bubbles originated from the ZnO film. Acknowledgements. This work was supported by the National Office for Research and Technology (Grant nos. OTKA 73424 and TFSOLAR2).
[en] The nature of the Ge satellite structure and the contributions from extrinsic and intrinsic processes were investigated using the ESA-31 electron spectrometer. These measurements are providing the first high energy resolution Ge KLL data. The intensity ratio of the plasmon peaks induced by intrinsic and extrinsic excitation processes is found. (R.P.)
[en] Complete text of publication follows. The layered Fe/V heterostructures are widely used in solid state physics research. Variety of fields where these systems are involved is primarily due to the crystallographic 'similarity' of lattice parameters of the vanadium and iron crystals. Both metals in bulk are bcc crystals, having difference in crystal parameters not exceeding several percents, which allows to growth epitaxial heterostructures. Iron in bulk is ferromagnetic with the critical temperature 770 deg C. Exchange coupling in Fe can be effectively suppressed by alloying with vanadium. Vanadium, in contrary, is not magnetic, but several studies have shown that near the interface with iron it is polarized antiparallel to the magnetization of the iron (the size of the polarized area in order of 1 nm). Magnitude of the magnetic moments depends on the quality of the interface and makes value (0.1/1)μB. In addition, it is worth to mention the indirect exchange interaction of iron layers through the vanadium spacer which can lead, at certain thicknesses of vanadium spacers, to the antiferromagnetic coupling of two neighboring Fe layers. This coupling can be affected by absorption of the hydrogen which leads to the effective change of the thicknesses of V layer. In this work experimental study of structural and magnetic properties of two Fe(d)/V(d) (d=3nm and 5nm) periodic structures have been done. Studies identified a number of structural features of systems that affect their magnetic properties. It was shown that ferromagnetic islands are formed on the interfaces of Fe and V. These islands have different magnetic properties as sub-layers of pure iron. Synchrotron diffuse scattering and magnetometry data indicate on the presence of the in-plane anisotropy of structural and magnetic properties in periodic Fe/V structures. In addition, magnetometry data indicate the presence of two magnetic phases in both samples. On this basis, we propose the following model which qualitatively describes our data. It is a well-known fact that the deposition of Fe/V structures with thicknesses of V greater than 2 nm goes in a 3D mode. It means that on the interface between Fe and V layers the formation of islands take place. The presence of steps on the hysteresis loop suggests that the magnetic properties of these islands, especially coercive force, different from those of sub-layer of pure iron. At thicknesses of 2-3 nm of V layer islands are quite isotropic, which is confirmed by magnetometry and synchrotron diffuse scattering. At the further growth of the V layer islands are quite isotropic, which is confirmed by magnetometry and synchrotron diffuse scattering. At the further growth of the V layer, islands stretch along one direction. Due to the shape anisotropy, islands are only can be magnetized applying magnetic field along one of the axis of the islands.