Diamond Band Research Articles

Microscopic optical fields in diamond and germanium: Molecular-orbital approach

Using the bonding and antibonding orbitals for the valence and conduction bands in germanium and diamond, the nonresonant part of the microscopic dielectric matrix, the local dielectric function, and the microscopic fields induced by a transverse optical field are calculated self-consistently. It is found that the secondary fields are appreciable in both germanium and diamond.

Vibronic spectra in diamond

The temperature dependence of some of the more important vibronic bands in diamond is investigated. Spectra of the N3, ND1, 640 nm, H3, 3.188 eV and 594 nm bands are given, together with detailed measurements of the intensity, peak energy and width of most of the zero phonon lines over the temperature range of typically 20 to 350K. These data, and published data on the N9 band, are analysed in terms of coupling of the electrons to vibrational modes that are totally symmetric in the point group of the optical centres. It is shown that the shapes of the N3, ND1, 640 nm, 3.188 eV, 594 nm and N9 bands may be closely described by the theory and yield effective densities of coupled phonon states. These densities of states predict, to a high accuracy, the temperature dependence of the respective zero phonon intensities. It is shown that the long-wavelength modes dominate the temperature dependence of the zero phonon energy, and so, after allowing for lattice expansion effects, the peak energy may be fitted using the densities of states.

X-ray photoemission studies of diamond, graphite, and glassy carbon valence bands

The high-resolution x-ray photoemission spectra (XPS) of the total valence bands of atomically clean diamond, graphite, and glassy carbon, obtained with monochromatized Al K ..cap alpha.. radiation, are reported and discussed. By comparing valence-band and carbon-1s photoelectron kinetic energies, the XPS valence-band spectra I'E) of diamond and graphite were rigorously affixed to the same energy scale as earlier K x-ray emission spectra i(E). The two spectra - I'(E) and i(E) - have very different energy dependencies of intensity because selection rules and cross-section ratios render i(E) sensitive only to 2p character and I'(E) far more sensitive to 2s character. Taken together, I'(E) and i(E) show that the fractional p character in the diamond valence band increases from approx. 16% at the bottom of the band to approx. 92% at the top, with an average hybridization of approx. s/sup 1/ /sup 2/p/sup 2/ /sup 8/. The spectra agree well with the density of states of Painter et al, but indicate a valence-band width of 24.2(10) eV rather than their 20.8 eV. The C(1s) binding energy of 284.68(20) eV in graphite agrees well with a recent theoretical estimate of 284.4(3) eV by Davis and Shirley. Analysis of I'(E) i(E) for graphite resolvesmore » the valence bands cleanly into sigma and ..pi.. bands, with the spectrum I'(E) of the former resembling that of diamond, but with a stronger 2s admixture (sp/sup 2/ vs sp/sup 3/). The XPS cross section of the (p/sub z/)..pi.. bands was very low, as expected by symmetry. The bandwidth of 24(1) eV somewhat exceeded Painter and Ellis's calculated value of 19.3 eV. Glassy carbon showed an I'(E) between that of diamond and graphite, consistent with an amorphous lattice containing both trigonal and tetrahedral bonds. 8 figures, 3 tables.« less

An APW calculation of the energy band in diamond using different approximations for the exchange energy

The valence and conduction bands of diamond were calculated by the augmented plane wave (APW) method for the points of higher symmetry of the Brillouin zone. The calculations were carried out for four different approximations to the exchange energy. The convergence of the method was studied, and a limited study of the self- consistency in the potential was made. Very good results were obtained using a non-muffin-tin potential between APW spheres, instead of a constant. The correlation effects appear to be of importance, and very good results were obtained making an approximate self- consistency in the dielectric constant. On the other hand, self-consistency in the crystal potential was shown to be of minor importance for diamond.

Determination of the occupancy of valence bands in graphite, diamond and less-ordered carbons by X-ray photo-electron spectroscopy

Download options Please wait... Article information DOI https://doi.org/10.1039/TF9716701875 Article type Paper Download Citation Trans. Faraday Soc., 1971,67, 1875-1886 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Determination of the occupancy of valence bands in graphite, diamond and less-ordered carbons by X-ray photo-electron spectroscopy J. M. Thomas, E. L. Evans, M. Barber and P. Swift, Trans. Faraday Soc., 1971, 67, 1875 DOI: 10.1039/TF9716701875 To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Search articles by author J. M. Thomas E. L. Evans M. Barber P. Swift

The electronic energy bands in diamond

A calculation of the valence bands for diamond using a linear combination of bond orbitals is described. The method of calculation is basically that of Cohan, Pugh and Tredgold (1963). Improvements in the method of calculating the interaction integrals have been made and non-orthogonality terms are included.

Structure of the conduction band in diamond and silicon in the semiempirical tight binding method

Structure of the conduction band in diamond and silicon in the semiempirical tight binding method

Infra-red electro-optical effects in diamond

The anisotropy of the electric field-induced, one-phonon transverse-optical absorption band in diamond, and the quadratic dependence of the integrated absorption on the applied field E are found to agree with theoretical predictions. The band is centred at (1332·2±0·2) cm-1 irrespective of|E| up to 1·14 × 105 v cm-1. The results are compared with some previous measurements by other authors.

Energy Bands in Diamond

Calculations of the valence and conduction bands of a covalent crystal by the augmented-plane-wave (APW) method are carried out in the case of diamond for 256 points in the first Brillouin zone. The bands show an unexpected gap between the first conduction bands and those that lie immediately above them. The calculated position in the Brillouin zone of the conduction-band minimum agrees with that determined experimentally by Warren, Wenzel, and Yarnell by the inelastic scattering of neutrons. It proved necessary to use the average potential between the APW spheres as a disposable parameter in order to obtain a satisfactory energy gap for the bands.

Determination of Parameters of Complex Energy Bands in Semiconductors from Studies of Free Carrier Faraday Rotation, Voigt Effect, and Transport Properties

AbstractSimultaneous measurements of magneto‐optical and transport properties can be used to obtain fundamental parameters of semiconductors with complex band structures. The derived formulae are applied to the case of the valence band in diamond and germanium.

Direct calculation of modes modified by a point imperfection

Abstract Lattice vibrations modified by a point imperfection can be usefully investigated using a model in which all crystal atoms except those in N shells round the imperfection are either held fixed or (for low frequency modes) forced to move according to an elastic continuum solution. By making full use of symmetry and using an electronic computer to calculate the relevant matrices as well as to diagonalize them, one can make N large enough to get sufficient information about modified lattice modes to treat most problems concerning their interaction with the centre. For an imperfection in an alkali halide we have considered the “spherical” vibrations of an 11-shell model and all the modes of vibration of a 4-shell model. The results have been applied to a discussion of the temperature dependence of the breadth of the F-band, and applications to calculations of entropies of formation and of localized modes are outlined. The spherical modes round a vacancy in diamond are determined for a 60-shell model. Work now completed on applying these results to explaining the Mossbauer-like structure of some optical absorption bands in diamond is mentioned. Possible applications to thermal conductivity and relaxation time calculations are indicated.

The electronic properties of tetrahedral intermetallic compounds II. Conduction band in diamond

A set of plane waves, made orthogonal to the 1 s band and to the approximate valence band, is used to calculate the conduction band in diamond. This is a modification of the usual orthogonalized plane-wave method where the plane waves are made orthogonal only to the 1 s band. The approximate valence-band wave functions are obtained by assuming that the equivalent orbitals, employed by Hall to discuss the valence band in diamond, can be written as linear combinations of atomic hybrid orbitals. The following results are obtained: The lowest conduction b and level at k = 0 is antibonding and threefold degenerate. The minimum of the conduction band is not at k = 0 but is about half-way along the (1, 0, 0) direction.

A New Absorption Band in Diamond and its Likely Cause

A New Absorption Band in Diamond and its Likely Cause

Infrared Lattice Absorption Bands in Germanium, Silicon, and Diamond

Infrared absorption bands characteristic of the crystal lattice were investigated for germanium and silicon. The absorption was found to be insensitive to lattice imperfections due to impurities (\ensuremath{\sim}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) and due to disorders (\ensuremath{\sim}${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) produced by nucleon irradiation. It did vary with temperature in the same way as the calculated mean-square displacement of the atoms. Variations of absorption with temperature were also studied for two specimens of type I diamond. The bands characteristic of type II diamonds showed similar temperature dependence, whereas the long-wavelength bands were temperature insensitive. It appears that the observed absorption in germanium and silicon corresponds to the absorption characteristic of type II diamond and is made possible by the thermal vibration of the atoms. The long-wavelength bands in type I diamonds may be due to impurities.