对单晶硅里双碳中心经退火后的光谱研究

对区熔和直拉单晶硅中双碳中心的热退火行为进行研究,并观测到新的硅光致发光谱线。这些谱线与硅中的碳、氧等点缺陷有关。实验已发现,双碳中心化学键断裂不是双碳中心退化的唯一原因,其他缺陷也会产生影响。我们认为双碳中心位于951.16(7671),952.98(7686),956.91meV(7717cm^-1的子带谱线是由于间隙硅原子而不是由空位造成的。     

Neutron irradiation-induced enhancement of electronic carrier transport in ZnO

Irradiation of ZnO single crystals by thermal neutrons with a dose up to 7×10¹⁷ cm^?2 and subsequent annealing at 400 °C for 1 h leads to a significant increase in majority carrier mobility and concentration in this material, with the corresponding decrease of its sheet resistance. Additionally, cathodoluminescence spectra taken before and after neutron irradiation are consistent with the growing carrier lifetime. The observed effects are attributed to irradiation-induced formation of electrically active species of interstitial Zn and improvement of lattice crystallinity due to annealing.     

Pairs of F centres and CN− molecules in KCl: An ENDOR analysis

Abstract

Pair defects consisting of F centres and CN^? molecules as substitutional impurity anions (F_H(CN^?) centres) exhibit a strong coupling between the F centres and the CN^? molecules. This leads to an optical pumping of the CN^? vibrations via the F centre absorption band. We performed an Electron Nuclear Double Resonance (ENDOR) investigation in order to analyse the microscopic structure of these aggregate centres. The CN^? molecule occupies a [110] nearest anion position with respect to the F centre in two dynamic dipole orientations even at low temperature.     

Infrared studies of single crystals of polycaprolactam

Infrared studies of the α-crystalline form of polycaprolactam (nylon 6) have confirmed the assignment of the 1288 and 1210-cm^?1 bands to a unique fold conformation. The γ-crystalline phase has a band at 1212 cm^?1 which overlaps the 1210-cm^?1 fold band in samples containing both α and γ phases. The 1288-cm^?1 band was, therefore, used to monitor regular fold content. No unique fold bands were detected in the γ form. Irregular folds present in solution-grown crystals regularize to the unique fold conformation upon annealing. Crystals which originally exhibit slight differences in regular folding as a result of different crystallization history have similar amounts of regular folds upon annealing at 220°C. Crystals grown from solutions of very dilute concentrations of polymer have different amounts of regular folding. The annealing behavior of crystals prepared from two different solution concentrations reflect the processes of regularization and long period increase.     

Studies on the 1831 cm−1 SiH band in NTD c-Si containing H

Abstract

The dose dependence and annealing behavior of the 1831 cm^?1 SiH band in NTD c-Si containing H have been studied via FTIR. The annealing kinetics has been found to be of first order with the activation energy equal to 1.45⁺ _? 0.1 eV. The possible models for this SiH band have been discussed.     

Influence of irradiation on the thermal decomposition of lithium perchlorate

Abstract

Infrared absorption measurements were made before and after 90 °K electron irradiations of silicon samples which contained either dispersed oxygen, carbon, or carbon plus oxygen. Irradiation-produced absorption bands associated with two distinctly different defects are observed depending on the oxygen and carbon content of the silicon. One center is the well-known vacancy-oxygen A-center defect (836-cm^?1 band) and is formed on irradiation in oxygen-containing silicon with a magnitude which is independent of the carbon content. Measurements have correlated the formation of one A-center with the loss of one interstitial oxygen atom, thereby indicating that A-center formation occurs by vacancy trapping at interstitial oxygen atoms. A second center (922-and 932-cm^?1 bands) is formed only in silicon crystals which contain both oxygen and carbon. The results indicate that this center is formed by the trapping of a silicon interstitial at a carbon-oxygen complex.     

The infrared spectrum of OH-compensated defect sites in C-doped MgO and CaO single crystals

The IR spectra of OH-compensated point defects in MgO (and CaO) single crystals of various purity grades were reinvestigated. Three distinct groups of IR bands appear in the O-H stretching region: A, B and C around 3550 cm^?1 (3650 cm^?1), 3300 cm^?1 (3450 cm^?1) and 3700cm^?1 (3750cm^?1). They are assigned as follows: band A to the fully compensated, band B to the half compensated and band C to the overcompensated cation vacancies, [O?V”_catH?]^×, [O?V”_cat], and [O?O?V”_catH?$\text{]}\text{?}$, respectively.Upon cooling to 80 K the band A shows a complex behavior partly due to the formation of Ha molecules by charge transfer and concommittant O^? formation: [? (H₂)”_cat?]^×. The O^? represent defect electrons or positive holes in the O^2? matrix.Bands A and B show a characteristic multiplet splitting which is caused by local lattice strains coming from carbon atoms on near-by interstitial position. The intensity ratios between the multiplet components remain constant regardless of temperature pretreatments up to 1470 K, but strong variations of the integral intensities are observed. These are caused by the highly mobile C atoms entering and leaving reversibly the cation vacancy sites as a function of temperature and of the quenching speed. When the C atoms push the H₂ molecules onto interstitial sites, an H-H stretching signal appears around 4150cm^?1.     

Investigation of the dynamical behaviour of the FH(CN−) centre in KCl with temperature dependent endor spectroscopy

Abstract

The temperature dependence of the electron nuclear double resonance (ENDOR) spectra of F_H(CN^?) centres in KCl was investigated in the temperature range between 10–220 K. At the lowest temperature of 10 K only one CN^? orientation with respect to the F centre electron is present, in which the nitrogen is thought to be nearer to the F-electron than the carbon. With the very small thermal activation energy of 2.9 meV the opposite orientation is occupied. The superhyperfine interactions of those first shell K nuclei nearest to CN^? and of the ¹³C interaction of the CN^? molecule are strongly temperature dependent between 10 and 60 K, following an exponential law with a thermal activation energy of 4.2 meV. It is assumed that a soft local mode involving those two nearest K nuclei and the CN^? is causing the strong temperature dependence. The shf interactions of ¹⁴N nuclei have not been seen, probably because of the dynamical effects.     

Resonant and localised modes due to boron in gallium arsenide

Silicon-doped n-type GaAs crystals pulled from a melt encapsulated with boric oxide exhibit an IR absorption band at 123 cm^?1 as well as a number of localised-mode bands associated with boron and silicon. Evidence is presented which leads us to attribute the band at 123 cm^?1 to a resonant mode associated with isolated B atoms on Ga sites. Other crystals containing high concentrations of silicon or phosphorous did not show such an absorption band. The results are discussed briefly in terms of the simple mass defect model for impurity vibrations.     

Location of self-interstitial atoms in boron-implanted silicon by means of rutherford backscattering of channelled ions

Abstract

For locating self-interstitial atoms in silicon by means of Rutherford backscattering of channelled ions, boron has been implanted at room temperature and at the temperature of liquid nitrogen. The employed implantation doses were 2. 10¹⁴ cm^?2 and 7. 10¹³ cm^?2, respectively. The experiments have been performed at 300 K and at 120 K to reduce ionization-stimulated annealing. The beam of 1.4 MeV He⁺-ions was highly collimated.

To obtain the configuration of implantation-induced self-interstitial atoms symmetry considerations have been performed.

The location experiments presented indicate the existence of isolated self-interstitial atoms in silicon. Under the conditions of these experiments the interstitial atoms assume a (110) split configuration of orthorhombic symmetry.     

Damage and lattice location studies in Hg implanted Hg1–xCdxTe

Abstract

Rutherford backscattering (RBS) and ion induced X-ray (PIXE) channeling experiments have been used to study the damage accompanying Hg and Al implantations into Hg_0.8Cd_0.2 Te and its annealing as well as to determine the location of Hg in the crystal.

The damage induced by the implantation of 300 keV Hg and 250 keV Al ions at room temperature was found from RBS channeling studies to reach a saturation level at doses of 1 × 10¹⁴ cm^?2 and 3 × 10¹⁴ cm^?2 respectively. The damage resembles that characteristic for extended defects and it anneals at ≈ 300°C.

The location of the constituents of Hg implanted Hg_0.8 Cd_0.2 Te was studied by PIXE channeling observing the characteristic X-rays for each element. Angular scans indicate that the channels are mostly blocked by Hg atoms for both unannealed and, to a lesser extent, annealed crystals. This observation supports the suggestion that interstitial Hg atoms may be responsible for the conductivity of Hg implanted Hg_1–x Cd_g Te.     

Irradiation and heating effects in amethyst crystals from brazil

Abstract

In this work we report optical absorption spectroscopy study of thermal and irradiation effects on samples of amethyst from Minas Gerais and Rio Grande do Sul, Brazil. Three bands were studied: 10500 cm^?1 (k), 18300 cm^?1 (θ) and 28000 cm^?1 (ζ). Thermal and irradiation effects shows that the θ and ζ bands belongs to a same center and the k band to another center. The isothermal decay and irradiation growth of these band reveal a complex kinetics. The optical absorption bands of amethyst from Minas Gerais do not recover the prmitive absorbance after being bleached at 470°C and irradiated. This sample heated at 470°C in highly reducing atmosphere gets a yellow-brown color. The amethyst from Rio Grande do Sul treated at 400°C gets, also, a yellow-brown color. We suggest this color is probalbly due to the formation of Fe₂O₃ submicroscopc segregate crystals due to the diffusion of Fe ions and oxygen vacancies.     

Electron microscopy studies of void swelling and annealing of voids in aluminium irradiated with aluminium ions

Abstract

MgO single crystals implanted with Au⁺ ions (180 keV, 6 10¹⁶-10¹⁷ ions cm^?2) and annealed at temperatures between 25°C and 1100°C, have been analysed—by optical spectrophotometry—by Rutherford back-scattering (to confirm the effective presence and to study the distribution profile of Au atoms), and by TEM and X-ray diffraction (to identify the phases precipitated by thermal treatment).

Thermal annealing between 550°C and 1100°C produced an optical absorption band located between 565 nm and 600 nm. This band can be attributed to a fee Au precipitate with diameter varying from 50 to 200 Å. Larger metallic colloids 1000 Å are in simple orientation with the matrix.

Annealing at temperatures higher than 500°C produces a supplementary optical absorption located at 425 nm. This band can be attributed to Au plasma resonance.

After annealing for 15 min at 1100°C, a new phase is detected by X-ray diffraction and TEM and identified as Au₃Mg alloy with hexagonal structure.     

Letters to the editor

Abstract

Optical absorption spectra of TeO₂ crystals, irradiated at room temperature by up to 2·10¹⁸ cm^?2 10-MeV electrons and subsequently annealed to 575K, are studied. The dependence of Urbach absorption edge parameters in TeO₂ on the electron beam fluence is discussed. The irradiation-induced near-edge broad (2.5–3.5eV) absorption band is shown to be related to oxygen vacancies, annealing at 475–525K.     

Infrared Study of the Hydrogen Bond Complexes Between N-Methylsuccinimide and Phenols

Abstract

The hydrogen bonded complexes between N-methylsuccinimide and phenols (pKa = 10.2 → 6) are investigated by infrared spectrometry. The thermodynamic parameters for the 1–1 complexes are determined in carbon tetrachloride-. The formation constants at 298 K range from 15 to 150 dm³ mol^?1, the enthalpies of complex formation from - 20 to - 30 kJ mol^?1, the changes of entropy from - 22 to - 40 J K^?1 mol^?1 and the frequency shifts of the v(OH) stretching vibration from 170 to 340 cm^?1. The complexes are weaker than those involving the monocarbonyl bases. The decrease of the force constant of the bonded carbonyl group ranges from 0.48 to 0.65 N cm^?1. The force constant of the free C=O group slightly increases upon complex formation, in agreement with the cooperatively theory.     

Positron annihilation in electron-irradiated n-type gap crystals

Abstract

The defects in n-GaP crystals irradiated by 2.3 MeV electrons up to 1 × 10¹⁹ cm^?2 at RT were studied by means of positron annihilation (angular correlation) and electrical property measurements. It was found that positrons are trapped in some radiation-induced vacancy-type defects (acceptors) but that the effect saturates at high electron fluences (D1 × 10¹⁸ cm^?2). The trapping rate in irradiated samples increases with temperature in the range 77–300 K. Post-irradiation isochronal annealing reveals the positron traps clustering at about 200–280°C. All positron sensitive radiation-induced defects disappear upon annealing up to 500°C.     

Effect of absorbing microinhomogeneities on optical damage to Alkali-Halide crystals

Micropores up to 30?C100 ??m in size (bulk density ??10⁵ cm^?3) are obtained in NaCl, KCl, KBr, and RbI via the effect of a pulse of a CO₂ laser with power density 10⁶?C10⁷ W cm^?2 up to 5 ??s long. When a pore appears, plasma formation is initiated. The average temperature is ??5500 K and the pressure is ??10⁴ kg cm^?2. The dependence of the average weight of the material removed from the pore on the energy of the crystal lattice is found. Pore formation occurs mainly via the effect of the radiation pulse, due to evaporation at the absorption wave front (velocity, 5 m s^?1) and plastic deformation. The annealing kinetics of micropores and the effect of the ionizing radiation on the bulk pore formation in NaCl crystals are investigated.     

TEM study of ion implanted GaAs after pulsed electron beam annealing

Abstract

(001) GaAs single crystals were implanted with 150 keV Cr⁺ ions using a dose of 5 × 10¹⁵ ions cm^?2. The amorphized surface layers were subjected to pulsed electron beam annealing at energy densities in the range 0–1.3 J cm^?2. A detailed TEM investigation of the damaged and annealed surface layer was conducted. These observations were correlated with backscattering results.     

Experimental evidence of the vibrational coupling of nearest neighbours in 1D spin crossover polymers of rigid bridging ligands

The nuclear inelastic scattering signatures of the low spin centres of the methanosulphonate, tosylate and perchlorate salts of the spin crossover polymer ([Fe(II)(4-amino-1,2,4-triazole)₃]⁺²) _n have been compared for the pure low-spin phase, for the mixed high-spin and low-spin phases, as well as for Zn(II) diluted samples. Within this series a change in the spectral pattern in the 320–500 cm^?1 region is observed involving the decrease of the intensities of a band at ～320 cm^?1 and those over 400 cm^?1 as the molar fraction of the low-spin centres decreases. On the basis of the DFT calculations (B3LYP/CEP-31G) this effect is interpreted in terms of vibrational coupling of the iron centres of the same spin.