Solid Germanium Research Articles

On the thermodynamic properties of germanium-iodide compounds

The syntheses of high purity GeI 2 and GeI 4 from the elements are described. The vapour pressure over solid germanium (II) iodide has been measured by the static method with a membrane-gauge manometer from T=550 K to T=650 K and the molar enthalpy and entropy of sublimation calculated by second-law and third-law methods. Enthalpy differences for solid and liquid GeI 2 were measured in the temperature interval (330 to 770) K by drop calorimetry. The temperature, enthalpy and entropy of melting of germanium (II) iodide were determined. The values of the standard molar thermodynamic properties for solid and liquid GeI 2 are presented from T=298.15 K to T=781 K. We have used the maximum likelihood method in the treatment of the data obtained together with previous reported values. On the basis of this work we recommend a set of standard enthalpies of formation and absolute entropies for the Ge–I compounds.

Description of the thermodynamic properties of a nonmetallic solid (germanium): A self-consistent thermodynamic approach

An algorithm is proposed for constructing a Debye-type self-consistent model of a nonmetallic isotropic solid. Using germanium as an example, it is demonstrated that the thermodynamic quantities can be adequately described over a wide range of temperatures even under significantly simplifying assumptions about the thermodynamic parameters.

The First Determination of Spin–Lattice Relaxation Times (T1) of 73Ge in the Solid State

Abstract Spin–lattice relaxation times (T1) of 73Ge nuclei of tetraphenylgermane (1) and some other organogermanes in solid state and metallic germanium were determined under the high-resolution condition. T1 values were found in the order of s in agreement with the reported value for metallic germanium determined in the static condition.

Vacuum ultraviolet single photon versus femtosecond multiphoton ionization of sputtered germanium clusters.

Neutral atoms and clusters desorbed from a solid germanium surface by ion bombardment are detected by laser postionization and time-of-flight mass spectrometry. Two different photoionization schemes are compared which are generally believed to be candidates for the 'soft' ionization of polyatomic species without significant photon induced fragmentation. First, a single photon ionization process is employed using an F2 laser as an intense VUV source with a photon energy in excess of all relevant ionization potentials. It is shown that the available laser pulse energy is sufficient to saturate the ionization of Ge atoms and all detected Ge(n) clusters. The resulting mass spectra are compared to those obtained with a non-resonant multiphoton ionization process using a high intensity laser delivering pulses of 250 femtoseconds duration at a wavelength of 267 nm. Also in this case, the ionization process can apparently be driven into saturation. The mass spectra measured under these conditions are found to be almost identical to those obtained using single photon ionization. We take this as an indication that the results obtained with both postionization techniques closely reflect the true cluster sputtering yields and, in particular, are not dominated by photon induced fragmentation.

Effect of phonon scattering by isotope impurities on the thermal conductivity of dielectric solids

By an iteration method which has recently been applied to perfect rare gas crystals, the phonon Boltzmann equation is solved for a dielectric isotropic solid subjected to a thermal gradient and containing isotope scattering centres. The solution avoids the use of the relaxation time approximation for three phonon collisions, and consequently provides a rigorous description of the interference effects between these collisions and Rayleigh scattering due to point impurities. Good agreement is found between theory and experiment for solid krypton, germanium and silicon.

The changing phase of liquid metals

Most elements are metals. These elements remain metallic when they are heated through their melting point at normal pressure. Perhaps more surprisingly, two elements that are non-metallic in their solid form, silicon and germanium, also become metallic on melting. Indeed, if we consider the extremes of temperature and pressure found in many geophysical and astrophysical settings – some of which are now accessible in terrestrial laboratories – even more non-metallic elements become metallic in the fluid state. This includes fluid hydrogen, which has recently been shown to be metallic at high enough temperatures and pressures.

Thermochemistry of (germanium + sulfur): IV. Critical evaluation of the thermodynamic properties of solid and gaseous germanium(II) sulfide GeS and germanium(IV) disulfide GeS 2, and digermanium disulfide Ge 2S 2(g). Enthalpies of dissociation of bonds in GeS(g), GeS 2(g), and Ge 2S 2(g)

This is a critical evaluation of the thermodynamic properties of the known solid and gaseous compounds of (germanium + sulfur): GeS(cr), GeS(g), GeS 2(cr), GeS 2(g), and Ge 2S 2(g). The heat capacity of GeS(cr) at low and moderate temperatures was evaluated from all the information available in the literature, and the properties: C p,m °( T), { H m°( T) − H m°( T′)}, S m°( T), and Φ m°( T) = (Δ T 0 S m°− Δ T T′ H m°/ T), where T′ = 298.15 K, were computed to T= 930 K, close to the melting temperature, above which decomposition to a (germanium + sulfur) eutectic and uncombined germanium is believed to occur. On the basis of our recent value for Δ f H m°(GeS, cr, 298.15 K) ( J. Chem. Thermodynamics 1994, 26, 727), Δ f H m°( T) and Δ f G m( T) were also calculated over the same temperature range. A critical assessment of the enthalpy of sublimation Δ sub H m° yielded Δ f H m°(GeS, g, T). In another part of the present series ( J. Chem. Thermodynamics 1995,27, 99), we determined Δ f H m°(GeS 2, cr, 298.15 K); the corresponding Δ f H m°(GeS 2, cr, T) is tabulated in the present paper to T= 1000 K. Ab initiomolecular-orbital calculations showed the cyclic (C 2ν) arrangement to be the most stable for Ge 2S 2(g), and the predicted structure and vibrational wavenumbers were used in calculations of its thermodynamic properties as a function of temperature by means of statistical mechanics. A similar treatment of the linear GeS 2(g) is described. The assessed Δ f H m°(GeS, g, T→ 0) is in harmony with our reinterpreted molar enthalpy of dissociation D m°(GeS) from spectroscopy; and the enthalpies of dissociation of the bonds in GeS 2(g) and Ge 2S 2}(g) are also discussed. In summary, the molar enthalpy of dissociation of the (triple) bond in GeS, 535 kJ·mol −1, is the largest for any Ge-to-S linkage, and the mean molar enthalpy of dissociation of the (double) bonds in GeS 2, 404 kJ·mol −1, is greater by 110 kJ·mol −1than 〈 D m°(Ge 2S 2)〉 because, presumably, Ge 2S 2(g) has essentially single Ge-S bonds only. The molar enthalpy of dissociation of the “primary” bond D m°(S-GeS) is of comparable magnitude to the mean molar dissociation enthalpy of the Ge-S bonds in Ge 2S 2(g).

Structural study of molten germanium by energy-dispersive X-ray diffraction

An energy-dispersive X-ray diffraction study on molten germanium has been carried out at temperatures of 1253 and 1503 K. The interference and atomic distribution functions were compared with model ones by considering the characteristic features found in crystal structures of solid germanium. It has been established that over the temperature interval presently investigated the essential structural features of molten germanium are likely to be described by the atomic arrangement of the tetrahedral type encountered in the high-pressure form of solid germanium with minor modification.

Resolution of the discrepancy between temperature indicated interface and radiographically determined interface in a vertical Bridgman furnace

The melt-solid interface position was measured during the Bridgman growth of germanium both by X-ray imaging and by temperature measurements. X-ray imaging displayed an interface location through a change in image intensity representing the difference in density between liquid and solid germanium. The temperature measurements were obtained with thermocouples inserted into a centerline capillary tube in the germanium sample and translated to varying positions. The temperature profile indicated an interface location at the change in slope of temperature representing the difference in thermal conductivity between liquid and solid germanium. Comparisons between these measurement techniques showed a 3 mm difference in position of the interface. The position measured via radiography was lower (i.e. colder) than that measured by the temperature profile. The measured temperature was expected to be lower due to conduction of heat along the thermocouples but a spatial shift of the gradient discontinuity was not anticipated. The temperature field of the ampoule, growth material and measurement thermocouples was analyzed via numerical analysis. It was found that both the lower temperature and the spatial shift of the discontinuity in temperature gradient were a result of an end effect in the thermocouples. This end effect is caused by the low heat flux to the thermocouples which causes the temperature gradient at the tip of the thermocouples to be significantly lower than the temperature gradient of the environment. With this insight, a simple extension was made to the heat equation for a thin cylindrical rod in a temperature gradient. This analytical solution provided a good fit to both the numerical solution and the radiography data. This work provides a new insight into temperature measurement in a high gradient region.

M2,3M4,5M4,5 super-Coster-Kronig spectra of solid Ge and resonance effects around the 3p threshold.

${\mathit{M}}_{2,3}$${\mathit{M}}_{4,5}$${\mathit{M}}_{4,5}$ super-Coster-Kronig spectra of solid germanium have been measured using monochromatized synchrotron radiation. ${\mathit{M}}_{2}$${\mathit{M}}_{4,5}$${\mathit{M}}_{4,5}$ and ${\mathit{M}}_{3}$${\mathit{M}}_{4,5}$${\mathit{M}}_{4,5}$ transitions have been separated from each other. Resonance features were found at the 3p threshold corresponding to excitation of core excitons followed by resonant super-Coster-Kronig decay, which leaves two 3d holes and an excited electron in the conduction band. As opposed to normal Auger lines, these resonance features shift linearly with photon energy.

The 147 nm photodecomposition of monogermane

The 147 nm photolysis of GeH 4 results in the formation of H 2, Ge 2H 6, Ge 3H 8, Ge 4H 10 and a solid hydridic germanium film or powder. Two primary processes are involved: (a) GeH 4 + hv → GeH 2 + 2H and (b) GeH 4 + hv → GeH 3 + H, with π a = 0.66 and π b = 0.34. The quantum yields depend rather strongly on the partial pressure of GeH 4, but at 2 Torr are Φ(−GeH 4) = 9.0 ± 0.4 and Φ(Ge 2H 6) = 2.6 ± 0.7. The quantum yields of Ge 3H 8 and Ge 4H 10 were not measured at 2 Torr, but the average values found at lower pressures were 0.10Φ(Ge 2H 6) and 0.02Φ(Ge 2H 6) respectively; Φ(H 2) was not measured. A mechanism is proposed, which incorporates the known reactions of hydrogen atoms, GeH 2 radicals and GeH 3 radicals with GeH 4 and each other, and is shown to be in reasonable accord with the experimental facts.

Diffusion, solubility, and thermodynamic properties of gold in solid germanium studied by means of radiotracer and spreading-resistance analysis

Diffusion profiles of gold in germanium were measured using the radiotracer as well as the spreading-resistance technique. Diffusion coefficients from both experimental methods show a good agreement and are described by an activation energy of 147±2 kJ mol−1 and a preexponential factor in the range (1–2)×10−6 m2 s−1. The results are interpreted within a generalized dissociative model allowing for interstitial-substitutional exchange with the aid of vacancies or interstitial Au-vacancy pairs. Solubility data taken from the boundary concentration of the penetration profiles reveal nonsignificant differences between the total Au concentration and that of substitutional Au atoms. Basic thermodynamic quantities were calculated from the temperature dependence of the solid solubility using data from the Au-Ge phase diagram.

Elastic scattering of low-energy positrons by bound silicon and germanium

Elastic scattering differential and total cross sections for low-energy positron collisions with bound silicon and germanium atoms have been computed using partial wave analysis with static and polarization potentials. The calculations are performed at incident positron energies ranging from 0.2 to 500 eV. For each impact energy, an appropriate number of phase shifts are obtained by numerically integrating the radial wave equation to ensure convergence of the scattering amplitude. A simple parametrization of the total cross section in terms of the screened Rutherford cross section is also presented for use in Monte Carlo codes. Due, in part, to the lack of reliable experimental data, relatively little theoretical work has been done to calculate the inelastic and elastic differential cross sections (DCS) and total cross sections (TCS) for positron scattering. Most of the measurements were made on noble gases where it is observed that low-energy positrons exhibit a Ramsauer–Townsend (RT) minimum for helium, neon, and possibly argon (for electrons, the RT minimum occurs for heavier noble gases).1,2 Calculations of the positron TCS for these atoms agree with the observations. The RT effect has also been identified in a number of other free atoms and molecules for electrons.3,4 Recently, Meredith et al. computed the electron elastic scattering cross sections in solid silicon and germanium.5 In this work we calculate the DCS and TCS for positrons elastically scattered by silicon and germanium atoms which are bound in an amorphous solid using partial waves and the optical model. The results are presented for incident positron energies ranging from 0.2 to 500 eV. Simple fits to each TCS are given for use in Monte Carlo scattering simulations. For the static potential VS, Salvat and Parellada used Dirac–Hartree–Fock–Slater (DHFS) calculations to accurately fit analytic screening functions for atoms.6 They also imposed Wigner–Seitz boundary conditions (WSBC) on their wave functions to simulate atoms bound in a solid. The functional form of the static potential is (in atomic units)

Raman microprobe scattering of solid silicon and germanium at the melting temperature.

Raman microprobe spectroscopy is used to study c-Si and c-Ge heated to the melting point by a tightly focused cw laser beam. At their respective melting temperatures, the Raman shifts of solid Si and Ge are 481.7\ifmmode\pm\else\textpm\fi{}0.4 and 281.4\ifmmode\pm\else\textpm\fi{}0.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and the linewidths are 24.3\ifmmode\pm\else\textpm\fi{}0.3 and 14.1\ifmmode\pm\else\textpm\fi{}0.5 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. Optical-phonon coupling both to two and to three phonons is necessary to explain the Raman linewidths measured here at the melting temperature and those measured elsewhere at lower temperatures. Coupling to two phonons is important in determining anharmonic corrections to the Raman energy shift, while coupling to three phonons of lower energy is relatively less important. Polarization analysis of the Raman spectra has been used to differentiate the contributions from partially melted and nonmelted regions.

Calculation of inelastic mean free path of photoelectrons in some solids

The method of independent atomic centre approximation for the calculation of inelastic mean free paths of electrons in solids is described. To this end, the atomic ground and exited wave functions and the total cross sections of electron scattering on C, O, Al, Si, and Ge atoms were calculated in Hartree-Fock approximation and first Born approximation, respectively. Results for the application of the method to the six solid media amorphous carbon, silicon, germanium, Al2O3, SiO2, and GeO2; are presented. Agreement between calculated mean free paths and experimental attenuation lengths indicates that the approximation of independent atomic centres provides a useful method in the electron energy range from 200 to 4000 eV.

Anomalous behaviour of the knightshift on impurity atoms in glass-forming alloys

TDPAD (time dependent Perturbation of Angular distribution) technique has been used to measure the Knightshift of69mGe in liquid Ge and the solute Knightshift for73mAs in solid and liquid Germanium and the Ge alloys Ge−As, Ge−Se and Ge−Te. In the Ge−Te alloy the As Knightshift could hardly be explained by the magnetic properties of the alloy. The anomaly is discussed taking the glass forming properties of the Ge−As−Te system into account.

Calculated stopping cross sections for diamond and solid silicon and germanium

The Bethe stopping cross section of diamond, Si and Ge for protons has been calculated using the kinetic theory of stopping and valence electron momentum densities derived from experimental Compton profiles. Trends along the isovalent, isostructural series are discussed, and comparison with experimental stopping cross sections lead to mean excitation energies of the order I(Ge) = 310 eV, I(Si) = 173 eV and I(diamond) = 96 eV. It is also shown that care should be exercized when using graphite data for des the stopping of diamond.

Photoemission from liquid germanium and silver-germanium alloys

Abstract Low-energy photoemission spectra for liquid and solid germanium are presented and discussed in terms of the structural changes that accompany the crystalline-amorphous and crystalline-liquid transitions. The derived optical density of states of liquid germanium is compared with the results of theoretical calculations. Photoelectron spectra of liquid silver-germanium alloys are also presented and discussed with reference to structural properties and models for glass formation.

Diagramme de phase du système chrome-germanium

The Cr-Ge system has been completely reinvestigated by thermal analysis, X-ray diffraction, microhardness and electron microprobe. The five known intermetallic phases melt incongruently: Cr 3Ge at 1564 °C (homogeneous from 20.5 up to 25 at.% Ge) and Cr 5Ge 3 at 1262 °C (37.4 − 38.2 at.% Ge) with an allotropic transformation at 1002 °C; the three other phases Cr 11Ge 8 (melting at 1170 °C), CrGe (998 °C) and Cr 11Ge 19 (928 °C) are stoichiometric. The solubility of germanium in solid chromium varies from 4 at.% (800 °C) up to 11 at.% (1564 °C). Chromium is practically insoluble in solid germanium at any temperature. The system is compared with other binary alloys of germanium with transition metals.

Etude des systèmes SiAs‐halogènes et GeAs‐halogènes par spectrométrie Raman de gaz à haute température

AbstractRaman spectroscopy, because it is the most convenient method of determining the components of gaseous mixtures in equilibrium at high temperature, is well fitted for a systematic study of crystal growth mechanisms of inorganic solids by chemical transport.We have shown that the reaction between chlorine, bromine, or iodine and solid silicon or germanium arsenide is irreversible and complete between 150 and 400 °C, resulting in the formation of arsenic and the appropriate tetrahalide of silicon or germanium. At higher temperatures the tetrahalide vapour reacts with the arsenide in excess forming arsenic and the appropriate dihalide. This equilibrium reaction effects the chemical transport. The dihalides show resonance Raman scattering involving either the symmetric stretching or bending vibration.