Growth of Mn5Ge3 ultrathin film on Ge（111）

The growth of Mn5Ge3 ultrathin films with different thicknesses, prepared by solid phase epitaxy, is studied. The results of scanning tunnelling microscopy and low energy electron diffraction studies show that the film can be formed and it is terminated with a （√3 × √3） R30° surface reconstruction when the thickness of Mn exceeds 3 monolayers. The magnetic properties show that the Curie temperature is about 300 K and the T^2-dependent behaviour is observed to remain up to 220 K.     

Photoconductivity in amorphous thin films of Ge22Se78−xBix

Temperature and intensity dependence of photoconductivity is studied in amorphous thin films of Ge₂₂Se_78−x Bi_x with x = 0, 2 and 10. Transient photoconductivity measurements have also been made on the same samples. Our results show that photosensitivity decreases as Bi concentration is increased from x = 0 to x = 2. However, at high concentration of Bi(x = 10), photosensitivity again increases. Transient photoconductivity also show a different behaviour at low and high concentration of Bi. Results have been explained in terms of defect states produced due to Bi incorporation in GeSe system.     

Amorphous Ge1−ySey alloys: ESR study of gap states

We have measured the ESR spectra of evaporated amorphous Ge_1−ySe_y alloy films. We find that with the addition of Se to aGe the spin density drops, the g-value decreases from 2.0233 ± 0.0007 to 2.012 ± 0.002 and there is an increase in asymmetry and linewidth. The results indicate that the Fermi level shifts into the conduction band tail with the addition of as little as 5 at. % Se and that the introduction of Se permits a significant reduction in the dangling bond density.     

Anomalies of the static dielectric constant of Pb1−x Ge x Te

The static dielectric constant of Pb_1–x Ge _x Te (0x0.05) has been determined from differential capacitance measurements on Schottky-barriers in the temperature range of 4.2–300 K. A comparison with data deduced from the phonon frequencies via the Lyddane-Sachs-Teller relation shows substantial discrepancies which are attributed to lattice defects.Work supported by Jubiläumsfonds der Österreichischen Nationalbank     

Structural transformation of Ge dimers on Ge（001） surfaces induced by bias voltage

Scanning tunnelling microscopy is utilized to investigate the local bias voltage tunnelling dependent transformation between （2×1） and c（4×2） structures on Ge（001） surfaces, which is reversibly observed at room temperature and a critical bias voltage of -0.80 V. Similar transformation is also found on an epitaxial Ce islands but at a slightly different critical bias voltage of -1.00V. It is found that the interaction between the topmost atoms on the STM tip and the atoms of the dimers, and the pinning effect induced by Sb atoms, the nacancies or the epitaxial clusters, can drive the structural transformation at the critical bias voltage.     

Effect of Bias on Content of GeC in Ge1-xCx Films

Ge1-x Cx films with GeC content up to 11.6% can be prepared by using a medium frequency magnetron sputtering technique in our study. X-ray photoelectron analysis for these Ge1-x Cx films shows that the Ge1-x Cx films consist of C, Ge, GeC and GeOy. The content of GeC increases from 10.7% at 0 V to 11.6% at 250 V, and decreases to 9.6% at 350 V, and then increases again to 10.4% at 450 V. The Raman analysis confirms the result of XPS for checking GeC in the deposited Ge1-x Cx films. The related mechanism is discussed.     

Photoelectric properties of Pb1−x−y Sn x Ge y Te:In epitaxial films

Pb_1–x–y Sn _x Ge _y Te:In epitaxial films are examined in a wide temperature interval and at various background fluxes. These films have high sensitivity to infrared radiation in the spectral range <20m. The lifetime depends exponentially on temperature and varies from several seconds at T=10 K to 10^–2 s at T=20 K. The two-electron model of Jahn-Teller centers is proposed to explain the results. Multielement photoresistors based on these films are fabricated and D*=1.7×10¹³ cm Hz^1/2 W^–1 at T=25 K is achieved. Noise of the photoresistors is independent of background flux when it varies from 10¹² cm^–2 s^–1 to 10¹⁸ cm^–2 s^–1. As compared with Si:Ga and Ge:Hg photoresistors, the responsitivity is several orders larger at the operating temperature 25–30 K.     

Influence of CO 3 2− and OH− groups on dielectric losses of NaCl crystals

The results of measuring the dielectric losses of NaCl crystals with a different concentration of Na₂CO₃ and NaOH admixtures in the melt are given in the present paper. From a comparison of the curves found for the dielectric losses of the crystals studied it can be seen that the course of tan and the positions of the relaxation maxima, corresponding to the measured specimens with CO ₃ ^2– or OH^– admixtures, hardly differ. From these measurements and from a comparison with the results of other authors it follows that the admixture is probably the same in both groups of crystals.In conclusion the author thanks Dr. A. Bohun for discussions on the results and for his continuous interest in this work.     

Interplay of the doped Ge atoms and the N vacancies with the negative thermal expansion of M3(Cu1−x Ge x )N1−y

The giant negative thermal expansion (NTE) found in the anti-perovskite manganese nitride could be controlled by the content of the doped Ge and the vacancies of N. In this paper, the origin of such a tunable thermal expansion behavior is systematically studied. Our calculations indicate that the doped Ge atoms enhance the NTE property of the compound, and the existing N vacancies have a weak influence on the NTE property. Furthermore, the change of the exchange parameters between Mn ions with the content of the doped Ge as well as with the N vacancies in the compound is revealed, from which the relative stabilities of different magnetic phases in the concerned compounds can be explained.     

Ferromagnetic resonance study of Y3−z Ca z Fe5−x−y Co x Ge y O12 films

Conclusions It has been found that the character of the magnetic anisotropy changes markedly when the Co + Ge YIG films are doped with calcium. For the induced uniaxial and in-plane anisotropy we observe an increasing departure from the predictions based on the two-parameter model and for the cubic anisotropy the constantK ₁ becomes dependent on the growth direction. As a source for the latter effect the octahedral or tetrahedral preference of Co ions depending on the growth direction may be considered. The measured linewidth proportional to frequency indicates the presence of a relaxation mechanism which is, probably, connected with octahedral Co³⁺ ions.The authors express their thanks to Dr. P. Görnert and M. Neviva for preparation of the LPE films and to Dr. P. Novák for valuable discussions.Dedicated to Jan Kaczér DrSc on the occasion of his 65th birthday.     

Positron annihilation studies on the electronic structure of Pd−Ag−H system

Angular Correlation of Annihilation Radiation (ACAR) is shown to be useful to examine the electronic structure of -phase Pd_1–y Ag _y H _x system. Hydrogen absorption by Pd_1–y Ag _y alloys results in the increase of both nearly free andd-localized electron numbers in compliance with the KKR-CPA calculation outcomes. The investigation of -phase systems, PdH _x hydrides as well as Pd_1–y Ag _y H _x materials, failed because of a high concentration of lattice defects.     

Effect of temperature on the band structure of MnxHg1−xSe

The band structure of the solid solutions Mn_xHg_1–xSe is constructed on the basis of the band parameters obtained from the electrophysical and optical investigations of these solid solutions. It is shown that the band structure of Mn_xHg_1–xSe and the dynamics of the bands as a function of the composition and temperature are analogous to those for Cd_xHg_1–xTe. It is shown that the variation of the nonparabolicity of the band spectrum of Mn_xHg_1–xSe as a function of the temperature greatly affects the temperature coefficient of the change of the width of the optical forbidden band (d_gop/dT).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 40–44, April, 1991.     

Effects of the dielectric discontinuity on the photodetachment of H− ion

Using the closed orbit theory, we studied the effects of dielectric discontinuity on the photodetachment of H^? ions. The photodetachment cross-section of H^? in a medium with dielectric discontinuity was derived and calculated. The results have shown that the relative dielectric constants of the medium have a significant influence on the photodetachment of H^?. If H^? is kept in a medium with a relative small dielectric constant, the photodetachment cross-section of H^? becomes oscillating only in a small region above the ionization threshold. However, if H^? is kept in a medium with a relative large dielectric constant, the oscillation in the photodetachment cross-section becomes much stronger. Besides, the distance between H^? and the dielectric dividing interface also influences the photodetachment of H^?. For a given dielectric medium, the oscillation in the cross-section decreased with increasing distance between H^? and the dielectric dividing interface. Therefore, we can control the photodetachment of a negative ion by changing the dielectric constant and the ion–interface distance. This study provides a new understanding of the photodetachment process of negative ions in the presence of a dielectric medium.     

Investigation on Ge5−x Sb x Te5 phase-change materials by first-principles method

The structure stability and chemical bonding of Ge_5?x Sb _x Te₅ (x=0,1,2) phase-change alloys were studied by ab initio calculations. By analyzing formation energies, density of states and electron localization function, we have shown that the chemical bonding character of Ge₄Sb₁Te₅ is quite similar to that of GeTe and hence a NaCl crystalline state is expected. The introduction of extra electrons by Sb in Ge₄Sb₁Te₅ and Ge₃Sb₂Te₅ results in states at the Fermi Level. With increasing Sb contents as in Ge₃Sb₂Te₅, the chemical bonding becomes rather inhomogeneous.     

Influence of annealing temperature on the performance of Ge film and photon-counting imaging system

<正>Compared with the traditional image intensifier with phosphor screen readout,the photon-counting imaging detector with charge induction readout is more beneficial in several aspects(e.g.,good imaging properties and time resolution) to astronomy,reconnaissance,bioluminescence,and materials research.However, the annealing temperature during the tube-making process can affect the properties of the Ge film,and consequently impair the performance of the detector.Therefore,the influence of annealing temperature on Ge film and on the detector is studied in order to determine the crucial parameters.The Ge films are prepared on ceramic and quartz glass by the use of an electron gun.They are analyzed by scanning electron microscope(SEM),high-resistance meter,and X-ray diffraction(XRD).The results show that the optimum substrate and annealing temperature are ceramic plate and 250℃,respectively.     

Influence of germanium incorporation on the structural and electrical properties of boron-doped ultrathin poly-Si1−x Ge x films deposited by chemical vapour deposition

A few properties of polycrystalline silicon germanium (poly-Si_1?x Ge _x ) films can be tailored by modulating the germanium incorporation. In this paper, the structural, mechanical and electrical properties of heavily doped ultrathin (~100 nm) poly-Si_1?x Ge _x films (0.84 ≤ x ≤ 0.88) fabricated by low-pressure chemical vapour deposition were investigated. For a boron concentration of ~2.2 × 10²¹ atoms/cm³, a slight increase of germanium fraction significantly enhances the deposition rate, crystallinity and Hall mobility while having negligible influence on the Young’s modulus and hardness. The grain size increases from ~6 to ~12 nm while the grain structure becomes more columnar. In addition, the resistivity decreases from 7.4 to 1.1 m Ω cm with a corresponding increase in the Hall mobility from ~0.9 to ~4.2 cm² V^?1 s^?1. However, the Young’s modulus (~101 GPa) and hardness (~8.8 GPa) are virtually unaffected within the range of germanium fraction explored. In practice, poly-SiGe layer having low resistivity, high modulus, high mobility and low surface roughness can be successfully applied for resonators, biosensors and nanoswitches among others.     

Dielectric matrix imposed stress–strain effect on photoluminescence of Ge nanocrystals

Ge nanocrystals embedded in SiO₂ and Lu₂O₃ matrices were fabricated using the pulsed laser deposition method and investigated using high-resolution transmission electron microscopy, X-ray diffractometry and photoluminescence spectroscopy. X-ray diffractometry and Fullprof computer program clearly revealed the bond lengths of Ge nanocrystals embedded in Lu₂O₃ matrix is smaller than that in SiO₂ matrix, which can be attributed to the greater compressive stress exerted on Ge nanocrystals by the Lu₂O₃ matrix. The greater compressive stress will lead to much more defects induced at the interface of Ge nanocrystals and thus enhance the intensity of photoluminescence. The findings presented here indicate that the matrix environment of the nanocrystals plays a significant role in the photoluminescence property.     

Radiation-stimulated changes in the transmission of chalcogenide glasses of As2S3−Ge2S3

The radiative-optical properties of chalcogenide glass-like semiconductors of the As₂S₂−Ge₂S₃ system in the region of a topological 2D-3D-phase transition are investigated. It is shown that γ-irradiation of samples by an absorbed dose of 4.4 · 10⁶ Gy leads to a longwave shift of their optical-transmission edge in the spectrum. The effect observed depends on the structural type of the glasses investigated and changes considerably near the 2D-3D-phase transition. Two components of the transmission-edge shift are detected: a static component, which remains unchanged for a long time after irradiation of the samples, and a dynamic one, which gradually fades in 2–3 months. It is suggested that the microstructural mechanism of these changes is attributable to processes of coordination defect formation in the structural skeleton of the samples. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, pp. 657–660, September–October, 1999.     

Effects of Er substitution for Nd on structural and magnetic properties of Nd1−xErxMn2Ge2 (0⩽x⩽1)

The structure and magnetic properties of Nd_1−xEr_xMn₂Ge₂ (0.0⩽x⩽1) were studied by X-ray powder diffraction and magnetization measurements. All compounds crystallize in the ThCr₂Si₂-type structure with space group I4/mmm. Substitution of Er for Nd led to a linear decrease in the lattice constants and the unit cell volume. Increasing substitution of Er for Nd in NdMn₂Ge₂ shows a depression of ferromagnetic ordering and the gradual development of antiferromagnetic ordering. A typical SmMn₂Ge₂-like behaviour is observed for the x=0.4 sample. The results are summarized in α preliminary magnetic phase diagram.