1D X-ray Beam Compressing Monochromators

Both Sb-doped Germanium and Ge-Si solid solution single crystals with resistivity from 1.5 to 7 Ω·cm were grown using the Czochralski method. The optical transmission of single crystals and the stability of their optical properties were studied by infrared Fourier spectroscopy at a wavelength of 10.6 μm and temperature range from 25 to 60 °C. It was found that decreasing the background impurities concentration leads to the reduction of the infrared absorption at room temperature while not affecting the thermal stability of the optical properties. Thermal stability of the optical properties of Sb-doped germanium single crystals increases by adding from 0.2 to 0.8 at % of silicon.

With the aim to improve the reliability of calculating and thus predicting the thermal deformation of cryogenically cooled silicon monochromators for intense synchrotron x-ray beams, we have measured the thermal conductivity of several specimen with different purities: float zone (FZ), Czochralski (CZ) single crystal materials and a Si99.3Ge0.7 (SG) crystal between 85 K and room temperature with 1% accuracy. We have shown by finite element analysis that a measured 30% increase of conductivity between the FZ and the CZ crystals leads to an increase of 30 to 40% of the thermal slope. Whereas the performances of these two materials were just acceptable, the 9 times reduced thermal conductivity of the SG crystal turned out to increase the thermal slope error by a factor 19 to a prohibitive value of 143 (mu) rad, as compared to 7.6 (mu) rad for the FZ crystal. Therefore, the application of SG crystals to cryogenic cooling cannot be recommended. In addition, we determined the thermal conductivity of germanium single crystals in the same temperature range. For the silicon FZ and the germanium materials, excellent agreement with recommended values was found. Moreover, we detected a small, but non-negligible dependence of thermal conductivity on the crystallographic direction (a few % at 85 K) that, to our knowledge, has not been published in previous papers.

Supplemental shielding of BMIT SOE-1 at the Canadian Light Source

An analytical model was constructed of a single silicon crystal monochromator. This model was used to examine the heat transfer processes within the monochromator. It was discovered that extracting heat from the top surface of the monochromator could cause the peak temperature to be below the surface of the crystal; this dislocation was shown to be approximately 10% of the thickness of the crystal when 20% of the input power was extracted from the top surface.

Anomalous effects of dopant distribution in Ge single crystals grown by FZ-technique aboard spacecrafts

An improved buffer rod-specimen unit is described for measuring longitudinal wave velocities in solids at temperatures up to 350°C. The method is particularly useful in determining elastic moduli of single crystals since very small path lengths in any prescribed direction can be employed. The use of molten metals to provide coupling at still higher temperatures is discussed. Several high-temperature techniques involving mode conversion at an impedance discontinuity for generating shear waves will be detailed, with particular interest in application to crystalline media. The various methods are illustrated with data for fused silica and single crystal germanium.

We have performed fluorescence x-ray absorption fine-structure (XAFS) measurements from 20-200 K on a 5000 \AA, c-axis film of YBa_2Cu_3O_{7-\delta} (YBCO) on MgO (Tc=89 K) using photons polarized perpendicular to the film. These data are compared to YBCO data from a single crystal and from a film on LaAlO_3 with the same Tc. The main difference between the single crystal and the film data is that while the single crystal data is well described by a two-site axial oxygen [O(4)] distribution, we see no evidence for such a distribution in either thin film sample. We place an upper limit on the size ofan axial oxygen splitting for the film on MgO at < 0.09 \AA. Therefore, the magnitude of the splitting is not directly related to Tc. Fits to the temperature dependent data from the YBCO film on MgO indicate that all bonds show a smooth change of their broadening factor \sigma, except the Cu-O(4) bonds, which show an increase in \sigma in the vicinity of Tc, followed by a decrease of the same magnitude. Such a feature does not occur in diffraction measurements. Since XAFS measurements of \sigma include any correlation between the atoms in a given bond, we conclude that the O(4) position becomes less correlated with the Cu positions near Tc. Correlation measurements of these and several further near-neighbors are also reported.

In the preceding paper, Paper I, we described an analytical technique, based on ion-induced x-ray yields, for detecting low-Z impurities in medium-Z targets. In this paper, Paper II, we report the application of this method to the lattice location of impurity atoms. Two systems have been examined to test the method, viz., P and S implants in Ge single crystals. The channeling effect was applied to the phosphorus and sulfur K x-ray yields excited by 0.5-MeV protons. Some 93% of implanted 31P (0.7 × 1015 atoms cm−2, room-temperature implant, 450°C anneal), were found to occupy substitutional sites; the fraction dropped to [inverted lazy s] 63% for an implant dose of 2.7 × 1015 atoms cm−2. Channeling effect results in 〈110〉, 〈111〉, and 〈100〉 directions for Ge(S), implanted at room temperature and annealed at 450°C, prescribe a preferred off-lattice (&amp;gt; 0.3 Å) site for the sulfur, necessarily different from the regular tetrahedral or hexagonal interstitial sites. For hot (220°C) implantation conditions, poorer crystal annealing and weaker channeling effects were observed.

The dislocation dissociation after the reverse motion along a slip plane in Ge single crystals have been investigated. It has been established that the dissociation width as well as the constriction density were independent on the motion direction. The results obtained have been used to clarify the role of the dislocation splitting in the formation of the phenomenon of the dislocation mobility asymmetry.

Nuclear interactions for 15 GeV/ c protons and pions under random and channeling conditions in germanium single crystals

A comparative study has been made for the defect induced room temperature ferromagnetism of single crystal, poly-crystal, and nanorod zinc oxide (ZnO), based on the magnetic properties and electronic properties by means of X-ray absorption near edge structure spectroscopy (XANES), X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy (UPS), valence band photoemission spectroscopy (VB-PES), and SQUID-type magnetometry. Magnetic measurement demonstrates the defect-induced ferromagnetic nature at room temperature in different ZnO films and a strong correlation between their electronic properties and magnetic responses. The higher ferromagnetic behaviour in polycrystalline ZnO is attributed to the increasing number of surface defects and native defect sites (oxygen vacancies and zinc interstitials) present in ZnO. XANES studies reveal that the number of unoccupied p states in polycrystalline ZnO is higher than single crystal ZnO as well as nanorod ZnO. The more amount of oxygen vacancy causes the highest intensity the O 1 s peak to appear in the XANES spectra of polycrystalline ZnO. In polycrystalline ZnO, the binding energy of the Zn 2p3/2 core level peak shifted to lower energy that further confirms the increase of the valence band maximum (VBM) position. The VBM of single crystal, poly-crystal, and nanorod-ZnO is 3.64 eV, 3.99 eV, and 3.71 eV, respectively, obtained from UPS (He-I) measurements. VB-PES studies confirm that the number of electrons in the valence band of O 2p - Zn 4sp hybridized states of poly-crystal ZnO is higher than single crystal and nanorod-ZnO.

Silicon and germanium single crystals (bent and ground) can be used as focusing X-ray monochromators with great success. In contrast to the mosaic-like behaviour of the commonly used quartz crystals, for Si and Ge which are available as nearly perfect crystals the dynamical theory of diffraction holds. The properties of perfect-crystal monochromators will be considered. Experiments on some prototype Si and Ge monochromators (with Cu Kα1 radiation) show the advantages of these new monochromators.

Tensoresistance in single crystals of germanium and silicon with different dopants but under practically equal charge carrier concentrations have been investigated. The features of ρX /ρ₀ = f(X) function, which depend on individual physical-chemical properties of dopants, have been discussed in this paper.

A HARD indenter pressed into the surface of a ductile solid such as a metal will produce a permanent indentation. The mean pressure over the indentation is known as the hardness of the solid and is a measure of its yield or flow stress1. With many relatively brittle materials such as glass and rock salt, it is possible to form plastic indentations at low loads. This is because the indentation process involves a very large component of hydrostatic stress which inhibits brittle failure: the material then yields by flow and the hardness is again a measure of the (ductile) yield stress of the solid2–4. At high loads the indentation is usually accompanied by appreciable cracking. Crack-free hardness indentations may also be made at low loads in single crystals of germanium and silicon (C. A. Brookes and our unpublished data) and it is suggested here that this may be due at least in part, to a different mechanism.

Optical interference and x-ray analysis methods are used to determine the mechanical stresses in single crystals of germanium and paratellurite, which cause local distortions of the wavefronts due to the photoelastic effect. The dislocation structure of the crystals close to optical anomalies is studied. The effect of high-temperature annealing on stress relaxation in germanium and paratellurite is investigated. © 2005 Optical Society of America