Electrical properties of p-type ZnGeP2 irradiated by H+ ions

The properties of p-type ZnGeP₂ [p₀=(5–10)·10¹⁰ cm^–3, ₀=(2–5)·10^–7 (·cm)^–1], irradiated with H⁺ ions [E=5 MeV, T_irr=300 K, D=(1·10¹²–1.7·10¹⁶) cm^–2] are studied. An increase in the resistivity (to gr_max - 5·10¹¹ ·cm) and subsequent reduction in for large currents of H⁺ ions ( - 9·10⁸ ·cm for D - 1.7·10¹⁶ cm^–2), is observed in irradiated crystals. The resistivity of irradiated p-type ZnGeP₂ is found to be very sensitive to hydrostatic pressure [(4–5)·10^–5 bar^–1]. The annealing of radiation defects in the temperature interval (20–600) °C is examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 91–93, October, 1991.     

Recombination channels of molecular ions He 2 + and electrons

The dependence of the intensities of atomic lines and molecular bands emitted in the afterglow of a helium discharge on the electron temperature is used to identify the processes in which states of He and He ₂ ^* are populated. It is established that the formation of He^* atoms (n = 3, 4) in decaying helium plasma occurs principally on account of the associative recombination of vibrationally excited He ₂ ⁺ ions and electrons. Analysis of the experimental reuslts leads to the conclusion that the distribution of the molecular ions He ₂ ⁺ over vibrational states is strongly nonequilibrium.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 67–72, February, 1984.It remains to thank N. P. Penkin for discussions and for his interest in the work.     

Electrical properties of GaAs layers irradiated by H4 ions

The quantities(D) and(T) are studied in n- and p-GaAs, irradiated at T = 300°K by H⁺ ions (5 MeV). It is shown that the resistance of lightly doped GaAs specimens increases from original values of ₀ to 10⁹ ·cm upon irradiation by H⁺ ions (5 MeV) to integral fluxes up to D^* – 10¹⁵ H⁺/cm². For D > D^* the layer resistance decreases from 10⁹ ·cm to 1 ·cm at 300°K. It was found that all the GaAs specimens intensely irradiated by H⁺ ions had p-type conductivity near 300°K. Isochronic annealing of radiation defects was studied in the temperature interval 20–700°C.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 39–43, January, 1982.     

”Reverse” annealing mechanism in ion-doped silicon layers subjected to electron beam heating

The annealing of silicon layers doped by high doses (10¹⁵-10¹⁶ cm^–2) of P⁺, As⁺, or Sb⁺ ions by means of an electron beam applied for 10–20 sec is studied. It is established that when a certain specimen temperature is exceeded, reverse annealing of the ion-implanted layers commences- a decrease in the degree of activation of the impurity introduced. The mechanism of reverse annealing in Si+> and Si+> layers is related to exit of P⁺ and As⁺ ions into interstices with their subsequent sublimation. In the case of heating of an Si+> layer reverse annealing is caused by exit of Sb⁺ ions into interstices and formation of impurity-defect complexes.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 97–102, August, 1989.     

Slow and monoenergetic (3Heμ−)+ beam production and novel applications

Based upon the recent discovery at UT MSL/KEK, a new idea is proposed for producing a slow and monoenergetic (3.2 keV) (³He^–)⁺ ion beam by using particle decay of the (d³He) muon molecule formed during the (d) to³He transfer reaction. The proposed intense (³He) beam as well as the less intense (⁴He) beam will open up way to various new types of important CF experiments.     

IR Reflection of Thin Bi4Ge3O12 Films

The spectra of IR reflection of the systems thin Bi₄Ge₃O₁₂ film–substrate made of molten -SiO₂ quartz in the region 10–1600 cm^–1 at 295 K are investigatedterpretation of fundamental vibrations in the region 10–800 cm^–1 and two phonon processes in the region 800–1600 cm^–1 are considered.     

Neutralizing a high-aperture metal-ion beam

It is found that secondary electrons ejected by the ions from the collector are responsible for neutralizing 300 sec pulses of wide-aperture ion beams (about 100–300 cm²) formed by various metals and having current densities ji of about 10^–2 A/cm² and energy _i 100 keV. A negative potential _ee=–500 V applied to the extracting electrode relative to the grounded collector improves substantially not only the beam neutralization in the transport section but also the ion generation efficiency in the accelerating gap.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 53–56, April, 1990.     

Electrical and optical properties and stabilization of the Fermi level in GaP crystals irradiated by electrons and H+ ions

Electrical and optical properties and Fermi level stabilization are studied in GaP crystals irradiated by electrons (E2.2 MeV, D1·10¹⁹ cm^–2) and H⁺ ions (E5 MeV, D1.7·10¹⁶ cm^–2). It is shown that the limiting position of the Fermi level (F_limE_G/2±0.2 eV) is independent of the initial GaP parameters and the type of bombarding particle, but is determined by the condition of local neutrality of the defective GaP. Resistivity values for the irradiated specimens of _max(D)1·10¹³ ·cm were obtained at 300 K. At maximum integral particle fluxes a decrease in crystal resistivity to (3–6)·10⁹ ·cm was observed. The readjustment of GaP absorption spectra in the region hvE_G upon irradiation is related to recharging of gap states by radiation defects upon motion of the Fermi level toward F_lim.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 37–42, December, 1994.     

Superconductivity in simple cubic Te—Au alloys produced by ion irradiation

Superconducting simple cubic Te_100–x Au _x films (10<x<90) were produced by He⁺-irradiation at low temperatures as well as at room temperature. After low temperature irradiation the as-irradiated disordered samples forx<60 at % Au are in a semiconducting state which becomes unstable at about 230 K, and then transform into the s.c. superconducting phase. The resistivity of the s.c. phase displays a negative temperature coefficient for residual resistivity values larger than 100 cm. In comparison to splat cooled foils, the s.c. Te—Au phase in the He⁺-irradiated films is more homogeneous. The observed variation of the transition temperature to the superconducting state with Au content is explained as an interaction of the Fermi-surface with several Bragg-planes.     

Determination of the strain potential constant by means of the p-InSb photoconductivity spectra under uniaxial compression

The influence of uniaxial pressure (0 < P < 2600 kg/cm2) on the intrinsic photoconductivity (PC) spectrum of p-InSb at 93 and 15°K is investigated. At 77°K the carrier concentration and mobility in the specimens were, respectively, (1.4–3.2)·10¹⁴ cm^–3 and 7000 cm²/V. sec. It is established that the maximum in the PC(E_m) spectra under compression is shifted towards higher energies. In the low-compression range E_m/P=5·10^–6eV·cm²/kg, while E_m/P=1·10^–6eV·cm²/kg for P > 1000 kg/cm². It is shown that the shift of the maximum of the intrinsic PC spectra with pressure is due to the growC;th in the forbidden bandwidth (E_g), and the change in parameters characterizing carrier diffusion in the specimen bulk (the diffusion coefficient, lifetime, surface recombination velocity) plays no part. The change in E_m/P with pressure is explained by the influence of valence band splitting. The deformation potential constants of the valence band |b|=(1.7±0.3) eV and |d|=(4.4±0.8)eV are calculated on the basis of a comparison between experimentally obtained data and theoretical results.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 159–162, February, 1976.     

Femtosecond-pulse laser ablation of human corneas

A femtosecond pulse laser in the visible spectral region shows promise as a potentially new powerful corneal sculpting tool. It combines the clinical and technical advantages of visible wavelengths with the high ablation quality observed with nanosecond-pulse excimer lasers at 193 nm. A femtosecond and a nanosecond dye laser with pulse durations of 300 fs and 7 ns, and centre wavelengths at 615 nm and 600 nm, respectively, both focused to an area of the order of 10^–5 cm², have been applied to human corneal ablation. Nanosecond laser pulses caused substantial tissue disruption within a 30–100 m range from the excision edge at all fluences above the ablation threshold of F _th60 J cm^–2 (I _th9 GW cm^–2). Completely different excisions are produced by the femtosecond-pulse laser: high quality ablations of the Bowman membrane and the stroma tissue characterised by damage zones of less than 0.5 m were observed at all fluences above ablation threshold of F _th1 J cm^–2 or I _th3 TW cm^–2 (3×10¹² W cm^–2). The transparent cornea material can be forced to absorb ultrashort pulses of extremely high intensity. The fs laser generates its own absorption by a multiphoton absorption process.     

Electrophysical properties of ionic alloys of GaAs obtained by implanting Zn+ (150 keV) with subsequent annealing at 500–1000°C

A study is made of the electrophysical properties (N_s, _eff) of ionic alloys of GaAs obtained by implanting 150-keV Zn ions at 20 and 300°C. The ion dose D=5·10¹³–10¹⁶ ions/cm²; the alloys were subsequently annealed for 10 min in an H₂ atmosphere with temperatures in the range 500–1000°C. The optimal parameters of the ionic alloys are obtained for T_i=300°C and T_a=700°C. Thermal acceptance of the GaAs under a SiO₂ film (d0.2–0.3 m) is observed for T_a>700°C. The limiting concentration of thermal acceptors N_s(TA)3·10¹³ cm^–2) for T=1000°C and t=10 min.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 22–26, March, 1979.     

Ions trapped near the free surface of superfluid helium: A review

Suitable ions or other charged particles can be trapped electrostatically just below the free surface of superfluid⁴He. Examples of such particles are the socalled negative ion, which is an electron in a bubble, and the so-called positive ion, which is a⁴He⁺ ion surrounded by a small region (snowball) of solid helium. The trapping mechanism can be used to create two-dimensional pools of ions. Three types of experiment can be carried out with such pools: those that relate to the ionic structure; those in which the ions are used as probes of the properties of the superfluid helium; and those in which the pools are studied as examples of simple two-dimensional fluids or solids. Experiments that have been carried out so far are reviewed, and prospects for the future are assessed.     

Investigation of the radiation damage to a single crystal of KCl using the method of backward scattering and chaneling of hydrogen and helium ions

The method of channeling and backward scattering of H⁺ and He⁺ ions has been used to analyze the radiation defects in a single crystal of KCl when the crystal is irradiated with H⁺ and He⁺ ions with energies of 1 MeV. The position of the displaced atoms in the crystal lattice was determined and the value of the cross section for the formation of radiation defects and their rate of formation as a function of the radiation dose and orientation of the bombarded beam with respect to the 100 crystallographic axes of the crystal are found. The effect of an external electric field on the formation of the radiation defects was investigated. The effects of irradiation with H⁺ and He⁺ ions are compared with one another. It is shown that mechanisms connected with ionization and excitation of the crystal atoms make the main contribution to the formation of defects.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 49–53, March, 1980.     

The effect of low-temperature electron irradiation on the transition temperature of YBa2Cu3O7−δ superconductors

Measurements of the complex susceptibility =–i of electron-irradiated YBa₂Cu₃O_7– show a strong influence of the electron irradiation dose, ·t on the transition temperatureT _c . For irradiation doses of ·t=2.2·10¹⁹ e^–/cm² we find a damage rate of T _c /(·t)=–1.6·10^–19 K/(e^–/cm²). It is assumed that the decrease ofT _c is mainly a bulk effect due to the production of atomic defects like vacancies and interstitials in the Cu–O–Cu chains and in the basal planes of the unit cells.     

μ −SR-Spectroscopy on light neutral muonic atoms

In the past few years ^–SR-spectroscopy has been successfully applied to the simple muonic atoms, namely muonic helium: He ^–e^–. Here the theoretical and experimental progress in understanding this atomic system consisting of a nucleus, a muon and an electron is reviewed. The various effects contributing to the ground state hyperfine structure are explained. The experiments are described and are compared with the theoretical calculations.     

Baryon decays and gamma-spectroscopy of hypernuclei

The applicability of (K ^–,^–) - and (K ^–,^– N)-reactions on^13,14C and^14,15N nuclei to the study of -transitions in primary and daughter -hypernuclei is discussed. The intensity of -deexcitation of ¹³C state |S ¹²C(15·11 MeV; 1⁺1): 1/2⁺ has been shown to be comparable with the intensity of baryon decay. Isospin selection rules are used to distinguish excitation energy ranges of primary hypernuclei, where the identification of the secondary -lines is probable.Presented at the symposium Mesons and Light Nuclei, Bechyn, Czechoslovakia, May 27–June 1, 1985.     

Optical and electron spin resonance spectra ofZ 2(Eu) centers in alkali halide crystals

The ESR spectra ofZ ₂(Eu)-centers in KBr and KCl are presented and correlated to the optical absorption and the electron spin resonance of the Europium vacancy complex. The fine structure of theZ ₂ spectra can be described by a Spin-Hamiltonian with an axialb ₂ ⁰ -parameter only. At room temperature it amounts to 1,761 10^–4 cm^–1 for KBr, 1,854 10^–4 cm^–1 for KCl and 1,453 10^–4 cm^–1 for RbCl. Accordingly theZ ₂(Eu)-center must posses a strict axial 100-symmetry in these crystals.     

Negative muon precession in nuclei with spin

Polarized negative muons were stopped in various materials containing nuclei with nonzero spin. The TF-SR precession signal of theF ⁺ hyperfine state (frequencyv ₊ > 0) was pronounced for ^–Li and ^–Be, faint for ^–Cl (in NiCl₂), and undetectable for ^–F (in CaF₂ or NiF₂) and ^–P. TheF ^– signal (frequencyv _– < 0) was observed clearly for ^–Be, ^–Al and ^–Na, marginally for ^–K, ^–V and ^–Nb, and not at all for ^–Ga (at 4 kOe) or ^–Co (ferrromagnetic, zero field). In the heavier elements theF ^– signal is fed by transitions from theF ⁺ to theF ^– state at a rateR, as long asR(v ₊ –v _–). [See separate paper on ^–Al in these Proceedings, p. 879.]I am grateful to Alex Schenck and Bruce Patterson for the loan of equipment and samples, to Fred Gygax for helping set up the apparatus, to Jun Imazato for help with the experiment, and to Toshi Yamazaki and Tak Suzuki for valuable comments. I am also indebted to SIN for several weeks of free ^– beam time and to SIN, BOOM, and the University of Tokyo for free time on their VAX computers, which were kept busy for several months in the analysis.     

Effective Stimulated Emission Cross-Sections of Poly(Phenylene Vinylene) Copolymers in Toluene Solution

We report optical gain measurements in four different copolymers polyp-phenylene-co-[2,5-dioctyloxy-p-phenylene-bis-2(4-nonyl phenyl) vinylene]nonyl-PpPV, polym-phenylene-co-[2,5-dioctyloxy-p-phenylene-bis-2(4-methyl phenyl) vinylene]methyl-PmPV, polyp-phenylene-co-[2,5-dioctyloxy-p-phenylene-bis-2(4-methyl-phenyl) vinylene]methyl-PpPV, polyp-phenylene-co-[2,6-naphthylene-bis-2(4-nonyl phenyl) vinylene]nonyl-PpPV-NV in toluene. The copolymers are related to poly(phenylene vinylene) and have been synthesized via Horner–Emmons polycondensation reaction. The optical gain determined from the amplified spontaneous emission (ASE) intensity is dependent on the excited stripe length. The net optical gain coefficients are found to vary between 0.1 cm^–1 in nonyl-PpPV to 2.5 cm^–1 in methyl-PmPV under nanosecond pulse excitation. The gain for Rodamine 6G was also measured under the same experimental condition and was used to determine the stimulated emission cross-sections for the four polymers and found to be _SE(peak)= 6.7 × 10^–20 cm² for nonyl-PpPV, _SE(peak)= 1.7 × 10¹⁸ cm² for methyl-PmPV, _SE(peak)= 1.4 × 10^–18 cm² for methyl-PpPV, and _SE(peak)= 1.5 × 10^–18 cm² for nonyl-PpPV-NV.