The application of FIB milling for specimen preparation from crystalline germanium

The effectiveness of focused ion beam (FIB) for preparation of crystalline germanium specimens has been studied. FIB milling results in strong cellular relief of the germanium surfaces on bulk specimens. This cellular relief, associated with the generation of high densities of point defects during interaction of the specimen with the high-energy gallium beam, can be reduced by using either a lower ion beam currents or a lower beam energy. Even under these milling conditions the cellular relief is, however, still evident on the surface of the TEM specimens as evidenced by so-called 'curtaining' relief. Nevertheless good quality specimens for both conventional and high-resolution imaging may be prepared using FIB milling if low currents are employed for final milling.     

Nanorelief formation under ion irradiation of germanium and silicon surfaces

The surface topography of silicon and germanium single crystals formed under 10-keV Ar⁺ and Ne⁺ irradiation was studied experimentally. A relief with typical nanometer-scale dimensions is detected using atomic-force microscopy. It is established that the average height of the nanorelief formed depends on the silicon doping levels. It is also shown that the average height is determined by the parameters of ion irradiation.     

Formation of ultrasmall germanium nanoislands with a high density on an atomically clean surface of silicon oxide

The experimental results of an investigation into the initial stages of growth of a germanium film on an atomically clean oxidized silicon surface are reported. It is shown that the growth of the germanium film in this system occurs through the Volmer-Weber mechanism. Elastically strained nanoislands with a lateral size of less than 10 nm and a density of 2 × 10¹² cm^?2 are formed on the oxidized silicon surface. In germanium films with a thickness greater than 5 monolayers (ML), there also arise completely relaxed germanium nanoislands with a lateral size of up to 200 nm and a density of 1.5 × 10⁹ cm^?2.     

Removal of pyramidal germanium nanoislands from the silicon (001) surface as a result of deposition/sputtering of a gold nanolayer

Optimal conditions for selective removal of pyramidal germanium nanoislands from the silicon (001) surface by sequential ion-beam deposition/sputtering of a gold layer with a nanoscale thickness are determined experimentally; it is important that the sizes of large domelike germanium nanoislands change only slightly as a result of the ion-beam treatment.     

Neutron interactions as seen by a segmented germanium detector

The GERmanium Detector Array (GERDA) is designed for the search for “neutrinoless double-beta decay” ( 0ν2β with germanium detectors enriched in ⁷⁶Ge . An 18-fold-segmented prototype detector for GERDA Phase II was exposed to an AmBe neutron source to improve the understanding of neutron-induced backgrounds. Neutron interactions with the germanium isotopes themselves and in the surrounding materials were studied. Segment information is used to identify neutron-induced peaks in the recorded energy spectra. The Geant4-based simulation package MaGe is used to simulate the experiment. Though many photon peaks from germanium isotopes excited by neutrons are correctly described by Geant4, some physics processes were identified as being incorrectly treated or even missing.     

Electron-stimulated desorption of cesium atoms from cesium layers deposited on a germanium-coated tungsten surface

The yield and energy distribution of Cs atoms from cesium layers adsorbed on germanium-coated tungsten were measured, using the time-of-flight technique with a surface-ionization-based detector, as a function of the energy of bombarding electrons, germanium film thickness, the amount of adsorbed cesium, and substrate temperature. The threshold for the appearance of Cs atoms is ～30 eV, which correlates well with the germanium 3d-level ionization energy. As the electron energy increases, the Cs atom yield passes through a broad maximum at ～120 eV. For germanium film thicknesses from 0.5 to 2 monolayers, resonance Cs yield peaks were observed at electron energies of 50 and 80 eV, which can be related to the tungsten 5p and 5s core-level ionization energies. As the cesium coverage increases, the Cs atom yield passes through a flat maximum at monolayer coverage. The energy distribution of Cs atoms follows a bell-shaped curve. With increasing cesium coverage, this curve shifts to higher energies for thin germanium films and to lower energies for thick films. The Cs energy distribution measured at a substrate temperature T = 160 K exhibits two bell-shaped peaks, namely, a narrow peak with a maximum at ～0.35 eV, associated with tungsten core-level excitation, and a broad peak with a maximum at ～0.5 eV, deriving from the excitation of the germanium 3d core level. The results obtained can be described within a model of Auger-stimulated desorption.     

Structure,microhardness, and strength of a directionally crystallized Al-Ge alloy

The structure, microhardness, and strength of binary directionally crystallized aluminum alloys with 35, 43, 53, 57, and 64 wt % germanium have been investigated. It has been shown that the eutectic microhardness is constant in the composition region under study. The microstrength of primary crystals of the solid solution of germanium in aluminum with the dendrite structure increases with increasing germanium concentration. However, the difference in the microhardnesses of the eutectic and dendrites, which was determined for each of compositions on the same specimen, does not exceed the measurement error. It has been assumed that the change in the strength of the alloy having the composition in the hypoeutectic region is determined by the redistribution of the volume fractions of the eutectic (α-Al and eutectic germanium) and the domains of primary crystals of the solid solution. This dependence can be described by the mixture rule. Above the eutectic composition, the alloy decomposes in a brittle manner; its strength is likely dependent not only on the content of the components, but also on the form and orientation of primary germanium crystals.     

Structural and optical properties of germanium-doped zinc oxide nanorods as a function of annealing temperature

Zinc oxide nanorods with germanium doping were prepared by ion implantation and annealing treatment method, the microstructural and optical properties of which were studied by means of the X-ray diffraction, photoluminescence, and transmission electron microscopy measurements. The pristine sample exhibited a remarkable ultraviolet emission owing to the band edge emission from the zinc oxide matrix, indicated a good crystalline quality. Three emission peaks appeared after germanium ions were doped into zinc oxide nanorods. The 513?nm photoluminescence peak was ascribed to the transition between the vacancy defect in zinc oxide matrix. Photoluminescence peaks located at 548 and 778?nm were ascribed to germanium ions luminescence center in zinc germanate grain and germanium monoxide luminescence center. The light emission tuning was obtained by germanium doping and annealing treatment, which may help the development of the practical optoelectronic devices based on zinc oxide nanomaterials.     

Hexagonal germanium formed via a pressure‐induced phase transformation of amorphous germanium under controlled nanoindentation

We have studied the stable end phase formed in amorphous germanium (a‐Ge) films that have been subjected to a pressure‐induced phase transformation under indentation loading using a large (20 µm) spherical indenter. After indentation the samples have been annealed at room temperature to remove any residual unstable R8 and BC8 phases. Raman spectroscopy indicates a single broad peak centred around 292 cm^–1 and we have used first principles density functional perturbation theory calculations and simulated Raman spectra for nano‐crystalline diamond cubic germanium (DC‐Ge) to help identification of the final phase as hexagonal diamond germanium (HEX‐Ge). Transmission electron microscopy and selected area diffraction analysis confirmed the presence of a dominant HEX‐Ge end phase. These results help explain significant inconsistencies in the literature relating to indentation‐induced phase transitions in DC‐ and a‐Ge. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and thermal properties of a Bi nano-plane embedded in amorphous germanium

The synthesis by pulsed laser deposition of a bismuth nano-plane embedded in an amorphous germanium matrix is reported. The structural changes were studied by Raman spectroscopy as a function of temperature. Upon heating, the Bi nano-plane melts and, as the sample is cooled, it re-crystallizes at a temperature well below the melting point. The results show a broad melting–solidification hysteresis cycle (170 K) that is compared to the ones obtained earlier on nanoparticles. Furthermore, a metal-induced crystallization effect was also observed in the germanium matrix. PACS 81.15.Fg; 05.70.Fh; 78.30.En     

Optical charging of real surface of germanium over a wide range of temperatures

A study is made of the charging of a real germanium surface under the effect of light. Mechanisms of electron and hole transport from germanium to the oxide layer are discussed. Conclusions are drawn as to the nature of the deep electron and hole traps in the oxide.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 36–41, May, 1979.In conclusion the authors wish to thank V. F. Kiselev for his discussion of the paper and his useful comments.     

霍尔离子源辅助制备长波红外碳化锗增透膜

为了提高锗基底的透过率和环境适应性,镀制了增透保护膜。应用电子枪蒸发加霍尔离子源辅助的方法沉积了碳化锗(Ge_1-xC_x)薄膜。通过固定霍尔离子源参数,控制沉积速率的工艺得到了不同光学常数的碳化锗薄膜。X射线衍射(XRD)测试表明,所制备的碳化锗薄膜在不同的沉积速率下均为无定形结构。采用傅立叶变换红外(FTIR)光谱仪测量了试片的透过率,使用包络法获得了相应工艺条件下的光学常数。在锗基底上双面镀制碳化锗增透膜后,长波红外7.5～11.5 μm波段的平均透过率T_ave>85%。经过环境实验之后的碳化锗膜层完好,证明碳化锗增透膜具有良好的环境适应性。     

Appearance of ductility in germanium single crystals as a result of slow loading

The effect of slow loading (350 g/mm² per h) on the deformation resistance of n- and p-type germanium single crystals is studied. In the presence of a smoothly-increasing load, germanium single crystals undergo up to 22% deformation at 400°C without rupture. Germanium crystals subjected to preliminary slow loading yield in a plastic manner on subsequent subjection to ordinary tensile tests, even in the temperature range corresponding to the brittle fracture of the original samples.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 86–90, February, 1973.     

Resonant Raman scattering by strained and relaxed germanium quantum dots

This paper reports on the results of resonant Raman scattering investigations of the fundamental vibrations in Ge/Si structures with strained and relaxed germanium quantum dots. Self-assembled strained Ge/Si quantum dots are grown by molecular-beam epitaxy on Si(001) substrates. An ultrathin SiO₂ layer is grown prior to the deposition of a germanium layer with the aim of forming relaxed germanium quantum dots. The use of resonant Raman scattering (selective with respect to quantum dot size) made it possible to assign unambiguously the line observed in the vicinity of 300 cm^?1 to optical phonons confined in relaxed germanium quantum dots. The influence of confinement effects and mechanical stresses on the vibrational spectra of the structures with germanium quantum dots is analyzed.     

Comments on the Lock-Crisp-West theorem with experimental examples

The application of the Lock-Crisp-West (LCW) theorem to positron-annihilation angular-correlation data for copper and germanium as well as to Compton profile data for germanium is presented and discussed. Deviations from the LCW prediction are observed for copper and for germanium, attributable to the positron's presence. In germanium the Compton results indicate near agreement with the LCW expectation; the sensitivity of the theorem is analyzed.     

3D microoptical elements formed in a photostructurable germanium silicate by direct laser writing

We present our investigations into the fabrication of three-dimensional microoptical elements by the direct femtosecond laser writing of a germanium–silicon photosensitive hybrid material. Germanium glass composites are very interesting for optical applications as they are photosensitive, and maintain high optical transparency in the visible and near-infrared bands of the spectrum. Here, we have used a germanium containing hybrid material to make nanophotonic structures and microoptical elements such as photonic crystal templates, prisms and spatial polarization plates, both on flat surfaces and fiber tips. Our results show that this germanium silicate composite is an excellent material for microoptics fabrication.     

Calculations on two phonon bound states in diamond and germanium

A careful numerical calculation is reported searching for two phonon bound states in diamond and germanium. Using the experimental phonon dispersion in germanium and an improved force model for diamond we examined the two phonon Green function for a bound state pole, working in a formulation in which Rayleigh's theorems can be used. Our results are consistent with the possibility of a bound state in diamond and germanium.     

Fast surface states activated by silver ions on a germanium-neutral electrolyte interface

The activation peculiarities and fast surface state (FSS) parameters, including the recombination centers (RC) caused by adsorption of silver ions on a germanium surface in contact with a neutral electrolyte and oriented along the three main cristallographic planes (111), (110), and (100), were investigated. It has been detected that the anisotropy of the FSS and RC parameters differs from that found earlier for a pure germanium surface or for gold-doped germanium under analogous conditions, but agrees with the anisotropy of the potential distribution on the Ge-electrolyte interface and is apparently governed thereby, exactly as in later cases. The surface state parameters are quite close in all cases. The singularities in the kinetics of surface state activation are associated with the higher migration capability of the silver ions under the effect of polarization. It is shown that successive adsorption of gold and silver ions does not result in the effect of neutralizing the RC which is observed on a dry germanium surface in such a situation.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 91–96, August, 1975.     

Brittle-plastic relaxation of misfit stresses in the Si(001)/Si1 ? xGex system

It is found that stressed luminescent samples of Si(001)/Si_{1 − x} Ge _x /Si with a germanium concentration of up to 16% contain microcracks. In contrast to ordinary cracks, microcracks are characterized by partial cracks of the substrate that are not perpendicular to the plane of the plate and are detected by specially designed X-ray analysis techniques. In a 60-nm-thick layer of SiGe with a germanium concentration of 5%, individual microcracks arise in samples near the edges of the same type, and the traces of these microcracks coincide with the ripple profiles of the corrugated growth surface. As the germanium concentration increases, first, the number of microcracks near the edges of a sample increases, while the corrugated growth relief nearly completely disappears, and then microcracks appear even in the central region of the sample, thus leading to the vanishing of the curvature of the structure in this region without visible signs of plastic relaxation. At the same time, even a thin (20 nm) layer of SiGe exhibits a layered structure, and diffuse scattering near the peak of the SiGe layer increases, which points to the presence of fragments of the layer that are misoriented by ±0.015°; the intensity of the diffuse scattering may amount to 0.5% of the layer intensity. A spatial analysis of the luminescence of samples with microcracks shows that the emergence of microcracks hardly affects the peak position and the half-width of the emission line of the SiGe layer. At the same time, the intensity of exciton emission from both the SiGe layer and the bulk of silicon is significantly (several times) changed when passing to the regions with microcracks. All the phenomena observed can be accounted for under the assumption that, between the stages of the loss of the plane crystallization front and the development of plastic relaxation of misfit stresses, there exists an earlier unknown stage of growth in which the concentration of nonequilibrium vacancies increases by four to five orders of magnitude and then the vacancies condensate into micropores.     

Photo-thermal ionization in a copper-doped germanium detector

The spectral response of a copper-doped germanium photo-conductive detector has been examined. Two series of sharp photo-thermal neutral acceptor excitations are observed; one is identified with copper impurities while the other is of unknown origin.