Identification of Semiconductive Patches in Thermally Processed Monolayer Oxo‐Functionalized Graphene

The thermal decomposition of graphene oxide (GO) is a complex process at the atomic level and not fully understood. Here, a subclass of GO, oxo‐functionalized graphene (oxo‐G), was used to study its thermal disproportionation. We present the impact of annealing on the electronic properties of a monolayer oxo‐G flake and correlated the chemical composition and topography corrugation by two‐probe transport measurements, XPS, TEM, FTIR and STM. Surprisingly, we found that oxo‐G, processed at 300 °C, displays C?C sp³‐patches and possibly C?O?C bonds, next to graphene domains and holes. It is striking that those C?O?C/C?C sp³‐separated sp²‐patches a few nanometers in diameter possess semiconducting properties with a band gap of about 0.4 eV. We propose that sp³‐patches confine conjugated sp²‐C atoms, which leads to the local semiconductor properties. Accordingly, graphene with sp³‐C in double layer areas is a potential class of semiconductors and a potential target for future chemical modifications.     

XPS Analysis of Bridgman-grown CuInTe2 and of its Native Oxide

X-ray excited photoelectron spectroscopy is used to analyse the near-surface properties of CuInTe₂ single crystals grown by the vertical Bridgman method. It is found that keeping the crystals at room temperature in air for relatively short times is sufficient for the formation of an oxide layer which consists mainly of TeO₂. No detectable amounts of copper or indium oxides could be observed.     

Thermal Analysis of LiGaO2 and NaGaO2

The high-temperature thermal properties of the ternary oxides LiGaO₂ and NaGaO₂ are studied by simultaneous differential thermal analysis and thermogravimetry between room temperature and about 1700 °C. For the melting temperature of LiGaO₂ a value of 1595 ± 10 °C is determined. NaGaO₂ undergoes a solid state phase transition at 1280 ± 10 °C and melts at 1395 ± 10 °C.     

On Measuring Impurity Absorption Spectra of Semiconductors by Photoacoustic Spectroscopy

Theoretical relations are derived for the amplitude of the photoacoustic signal of a gas-coupled cell for thick semiconductor samples including the influence of multiple reflections of light within the sample. It is shown that in the range of low absorption coefficients characteristic of impurity absorption spectra the sensitivity of the cell can be enhanced by using a highly reflecting metal as backing material. Numerical estimates for CuInSe₂ are given to illustrate this effect.     

Characterization of the Microhardness of Ion-implanted GaP

Implantation induced changes of the microhardness are studied in GaP single crystals which were bombarded with ions in the range of mass numbers M = 1–40. It is observed that point defects and incorporated hydrogen have a stronger hardening effect. The effect of defect complexes is lower, and amorphized layers are softer than crystalline layers.     

Infrared Optical Characterization of Thermally Oxidized CuInSe2 Single Crystals

Infrared reflectivity spectra of thermally oxidized CuInSe₂ single crystals are measured at room temperature in the wavenumber range from 180 to 4000 cm⁻¹. A Kramers-Kronig analysis of the spectra reveals seven vibrational modes with frequencies which agree with mode frequencies in In₂O₃. No vibrational modes due to Cu–O and Se–O bonds could be observed. The results obtained are compared with previous studies of oxidized CuInSe₂ crystals.     

Lattice Vibrations and Interatomic Forces in AIIB2IIIC4VI Defect-Chalcopyrite Compounds (I) Keating Model Considerations

The lattice vibrations of the A^IIB^III₂C^VI₄ semiconductors with defect-chalcopyrite structure are treated in a simplified version of the Keating model considering only interaction with nearest neighbours and assuming that all anions occupy their ideal lattice sites. It is found that in this model the frequencies of the nonpolar and polar modes with highest energy are determined by the properties of the B^III–C^VI sublattice alone. The frequencies of all the other optical modes depend not only on the A^II–C^VI and B^III–C^VI interactions but are also influenced by the presence of the ordered array of vacancies. The results obtained are compared with previous model considerations.