A compton profile study of tantalum

We report the results of Compton profile study on polycrystalline tantalum. Measurements have been made using 59.54 keV gamma-rays. The results are compared with the APW band structure calculations of Papanicolaouet al and other available data. In contrast to the work of Changet al the overall agreement is better with the APW band structure which worsens on incorporating the electron correlation correction. Estimates of the errors due to the contribution from bremsstrahlung, non-validity of impulse-approximation and anomalous dispersion are also briefly discussed.     

Anisotropy in the compton profile of copper

Directional Compton profiles of high statistical accuracy are measured by means of a 412 keV gamma-ray Compton spectrometer. The experimental anisotropies are in very satisfactory agreement with earlier measurements and there is good qualitative agreement between the experimental data and a recent band structure calculation. Quantitatively, however, the experimental anisotropy is significantly smaller than predicted by theory.A simple model calculation based on the Seitz approximation, in which higher order Fermi surface volumes all of spherical shape are taken into account in obtaining the momentum density, demonstrates that the major contribution to the Compton profile anisotropy in copper is due to the hybridization which has mixedd-electrons and nearly-free electrons in the top band. Any fine structure in the theoretical anisotropy due to the detailed shape of the Fermi surface cannot be resolved in the present experiment.The potential of analysing the electronic structure of transition metals in terms ofB(r), the Fourier transform of the momentum density, is discussed in detail. The major contribution to the anisotropy arises from localised peaks inB(r) centered on the sites of the translational lattice. Within the Seitz approximation it could be shown that these secondary maxima are caused by the presence of localisedd-electrons in the highest partly occupied band. In conclusion we anticipate that a proper treatment of electron correlation would produce a marked quantitative improvement in the agreement between the present experimental data and the Compton profiles obtained from current band structure calculations.     

OPW calculation of the compton profile of beryllium

Compton profile of beryllium is calculated by OPW method using the potential constructed by Loucks and Cutler which had given good agreement with Fermi surface data. However, the computed profile compares poorly with the experiment.     

The experimental compton profile of deuterium in NbD0.6

The Compton profiles of Nb and NbD_0.6 single crystals have been measured using 412 keV gamma-radiation from a¹⁹⁸Au source. In the region of low momentum the difference between the two profiles provides a sensitive probe of the electronic structure of hydrogen in niobium. The result for this deuteride clearly supports the protonic model in which the electrons from the deuterium fill empty states in the conduction band of the host metal. In addition, the two profiles are in excellent agreement at high momentum, which indicates that the niobium core electrons are unaffected by the introduction of deuterium into the crystal lattice.     

Electronic structure of hafnium: A compton profile study

In this paper, we report the first-ever isotropic Compton profile of hafnium measured at an intermediate resolution, with 661.65 keV γ-radiation. To compare our experimental data, the theoretical computations have also been carried out within the framework of pseudopotential using CRYSTAL03 code and the renormalized-free-atom (RFA) model. It is found that the present experimental profile is in better agreement with the RFA calculations if the outer electronic configuration is chosen as 5d^3.26s^0.8. The cohesive energy of Hf is also deduced from the experimental data and is compared with the available data. On leave from Hindu College, Sonepat 131 001, India     

Band structure,optical properties,and compton profile of copper

A self-consistent calculation of the band structure of copper has been performed using a basis of gaussian orbitals and a local exchange-correlation potential. Results are also presented for the optical conductivity and the Compton profile.     

Structural information from directional compton profile measurements on Si and Ge

Compton profile measurements on single crystals can reveal effects on the valence electron distribution arising both from local atomic interactions and from the long-range ordering of the atoms in the crystal. In order to separate those features relating primarily to the structure, we have analysed the long-range autocorrelations of the electronic wave functions obtained directly from the Fourier transform of the Compton profile. New experimental results for Si and Ge, measured along 〈110〉, clearly illustrate the expansion of the valence electron wave functions which follows the 4% change in the lattice constant. In particular, the autocorrelations display zero passages which arise from the lattice translational symmetry, and these features provide a basic test of the quality of experimental data.     

ODMR studies of antisite-related luminescence in GaP

By the use of ODMR, we have detected and identified two different antisite defects which contribute to newly-reported infrared luminescence observed in GaP. The antisite proper, P_Ga, gives rise to a spin-$\text{1}\text{2}$ resonance; the associated luminescence originates in the DA pair recombination of an electron trapped at the deep double donor P⁺_Ga with a distant shallow acceptor. An impurity-associated centre of the form P_Ga · Y_P is observed in a spin-triplet state via a distinct luminescence band which originates in electron-hole recombination localised at the defect.     

Positron annihilation studies in alpha-irradiated n-type GaP

The positron annihilation technique has been used to study the defect recovery in 22.0 MeV alpha-irradiated n-type GaP. The increase in the lineshape parameter S along with defect specific parameter R between 200 and 350°C indicates the migration of vacancies and the formation of vacancy clusters. The defects start disappearing between 350 and 600°C.     

Electron-damage studies in GaP at low temperature

The defects introduced in p-type Zn doped GaP by beta particle irradiation, of 1 MeV average energy, at low temperatures are monitored by bridge measurements of capacitance and delectric losses of a capacitor. The results of measurements, between 15 and 65 K, are attributed, in two different temperature regimes, to a GaP capacitor with losses arising from (a) an a.c hopping conduction process, below 45 K, and (b) a band conduction, above 45 K. Electron irradiation affects both hopping and band conduction as well as the transition temperature.     

Neutron transmutation doping of GaP: optical studies

An unambiguous proof for successful neutron transmutation doping (NTD) of GaP is presented on the basis of optically detected magnetic resonance (ODMR). GaP:S samples grown by the liquid encapsulated Czochralski method were irradiated with thermal neutrons and subsequently annealed at 800°C. In the ODMR experiments the transmuted Ge substitutional on Ga sites was detected. The NTD process was also found to create deep acceptors, the nature of which will be tentatively discussed.     

Electron state in TiO studied by measurements of compton profile and scattering factors

Compton profileswere measured on TiO_1.25 and TiO_0.82 with an SSD and γ-ray source. The results were compared with the profiles calculated from isolated ions and also with the scattering factor values obtained with the critical voltage effect.     

Directional reconstruction and anisotropy studies

The incident directions of cosmic ray particles at the highest energies are readily measured by modern detectors. Provided that there are sufficient data, the interpretation of such directions should give strong information on the origin of cosmic rays. However, the choice of statistical methods used in such an analysis can be of paramount importance in the reliability of the interpretation. This article summarizes the conclusions which may be drawn from the present data, and proposes methods needed to interpret statistically the large quantities of data which will become available in the near future. To cite this article: R.W. Clay et al., C. R. Physique 5 (2004).     

Self-consistent LCAO local density determination of anisotropic compton profile and X-ray structure factors in diamond

Our newly developed fully Self-Consistent Numerical Discrete Variational Method (which exactly treats all non-spherical parts of the crystal potential) yields X-ray scattering factors and anisotropies in the Compton profile of diamond in very good agreement with experiment.     

implantation of Bi into GaP. II. channeling studies

The channeling technique has been used to investigate the properties of Bi-implanted Gap. Measurements of the crystal disorder for 100 keV room temperature implants indicate a damage vs dose curve corresponding to ～13000 displacements/ion in the linear region and saturation at ～1.5 × 10¹³ Bi ions/cm². Annealing of the radiation damage has been observed and indicates two annealing steps at ～450°C for light damage and ～750°C for implants in the 1 × 10¹⁴/cm² range. Difficulties associated with the thermal decomposition of the implanted area have been overcome with the use of SiO _x coatings. The experimental details associated with the use of the SiO _x layer and with the use of a C¹² beam to obtain better depth and mass resolution in the backscattering spectrum are discussed. The lattice location measurements of the Bi impurity show ～50 per cent of the Bi atoms to be along the 〈110〉 string after a 900°C anneal for a 7.5 × 10¹³/cm² implant. In addition, the spectra show ～25 per cent of the Bi atoms have diffused to the surface. Correlations of these lattice location results with measurements of the photoluminescent intensity of the GaP (Bi) isoelectronic trap show an agreement in trend with anneal temperature but indicate a factor of ～10 more substitutional ions in the channeling measurement as compared to the photoluminescence results.     

The compton current

The secondary electrons produced by penetrating X-rays and gamma rays move preferentially in the forward direction. In an insulator absorption of the photon beam is therefore accompanied by an electron current. The current can be measured by a suitable receiver that collects the electrons and absorbs the photons. In this paper an approximate expression for the Compton current is established. Results of preliminary measurements are given and found to be in satisfactory agreement with the theory.     

Ellipsometric studies of chemisorption on GaP(110) single crystals

Ellipsometry has been used to study the room temperature adsorption of H₂, O₂, Cl₂, Br₂, HCl, HBr, HI, H₂S, CH₃SH, H₂Se, NH₃, PH₃ and AsH₃ on GaP(110) surfaces; CO, CO₂ and CH₄ did not adsorb. Initial sticking coefficients were determined from the change in the ellipsometric angle Δ with time at a constant gas pressure and found to lie between I and 10 ^?5. The change in both Δ and ψ at monolayer coverage was measured as a function of wavelength in the visible and near UV for several gases. The observed structure was at variance with theoretical expectation for non-absorbing layers and, further, appeared similar for each adsorbate. This is attributed to small changes in the optical properties of the substrate arising from the removal of intrinsic surface states by chemisorption. Analysis of the data reveals GaP surface states with a maximum interband transition probability at a greater than band gap energy of 3.5eV. The optical constants of film-free GaP were also measured between 2 and 5.5eV, and direct interband transitions between bulk states were located at 3.76 and 5.05eV.     

Multiphoton stimulated compton scattering

The processes of multiphoton Compton scattering of relativistic electrons are considered in a special one-dimensional geometry. The multiphoton parameter and the energy distribution of scattered electrons are found. The nonlinear behaviour of the gains of the two external electromagnetic waves is investigated in the saturation region. The multiphoton parameter is shown to be of order of one and the perturbation theory is shown to be inapplicable at very weak fields. For saturation of the gains much stronger fields are required which however are much weaker than those which are necessary for appearance of multiphoton processes in the spontaneous Compton scattering.     

Separate measurement of compton profile due to 1s electrons in Fe,Ni and Cu by coincidence method

The use of a solid state detector has enabled us to measure the contribution from 1s electrons separately by the coincidence technique. The discrepancy between the measured profile and the corresponding calculated ones shows that the approximations used in the calculations are poor.