Raman spectroscopy of graphene and graphite: Disorder, electron phonon coupling, doping and nonadiabatic effects

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

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Diamond-like amorphous carbon

Fluorescent carbon nanoparticles or carbon quantum dots (CQDs) are a new class of carbon nanomaterials that have emerged recently and have garnered much interest as potential competitors to conventional semiconductor quantum dots. In addition to their comparable optical properties, CQDs have the desired advantages of low toxicity, environmental friendliness low cost and simple synthetic routes. Moreover, surface passivation and functionalization of CQDs allow for the control of their physicochemical properties. Since their discovery, CQDs have found many applications in the fields of chemical sensing, biosensing, bioimaging, nanomedicine, photocatalysis and electrocatalysis. This article reviews the progress in the research and development of CQDs with an emphasis on their synthesis, functionalization and technical applications along with some discussion on challenges and perspectives in this exciting and promising field.

Carbon quantum dots and their applications

We review the physical properties of diluted magnetic semiconductors (DMS) of the type AII1−xMnxBVI (e.g., Cd1−xMnxSe, Hg1−xMnxTe). Crystallographic properties are discussed first, with emphasis on the common structural features which these materials have as a result of tetrahedral bonding. We then describe the band structure of the AII1−xMnxBVI alloys in the absence of an external magnetic field, stressing the close relationship of the sp electron bands in these materials to the band structure of the nonmagnetic AIIBVI ‘‘parent’’ semiconductors. In addition, the characteristics of the narrow (nearly localized) band arising from the half‐filled Mn 3d5 shells are described, along with their profound effect on the optical properties of DMS. We then describe our present understanding of the magnetic properties of the AII1−xMnxBVI alloys. In particular, we discuss the mechanism of the Mn++‐Mn++ exchange, which underlies the magnetism of these materials; we present an analytic formulation for the magnetic susc...

Diluted magnetic semiconductors

The complex dielectric function \ensuremath{\epsilon}(\ensuremath{\omega}) of GaAs was measured from 20 to 750 K with a scanning rotating-analyzer ellipsometer. The structures observed in the 1.3\char21{}5.5-eV photon-energy region, attributed to transitions near the \ensuremath{\Gamma} point of the Brillouin zone (${E}_{0}$, ${E}_{0}$+${\ensuremath{\Delta}}_{0}$, ${E}_{0}^{\mathcal{'}}$), along the \ensuremath{\Lambda} direction (${E}_{1}$, ${E}_{1}$+${\ensuremath{\Delta}}_{1}$), and near the X point (${E}_{2}$), are analyzed by fitting the second-derivative spectrum ${d}^{2}$\ensuremath{\epsilon}(\ensuremath{\omega})/d${\ensuremath{\omega}}^{2}$ to analytic critical-point line shapes. The ${E}_{0}^{\mathcal{'}}$ and ${E}_{2}$ critical points are best fitted in the whole temperature region by a two-dimensional line shape, whereas the ${E}_{1}$ and ${E}_{1}$+${\ensuremath{\Delta}}_{1}$ transitions are best fitted up to room temperature by a Lorentzian interacting with a continuum of interband transitions (Fano line shape). The excitonic character of the ${E}_{1}$ and ${E}_{1}$+${\ensuremath{\Delta}}_{1}$ transitions is discussed within several theoretical approaches. The experiments indicate that up to room temperature the localized Lorentzian interacting with the continuum is dominant, whereas at higher temperatures the modification of the two-dimensional Van Hove singularity due to the electron-hole attractive perturbation is a better description of the measurements. For all critical points, the energy decreases with increasing temperature while the broadening increases. This dependence on temperature is analyzed in terms of averaged phonon frequencies which cause a renormalization of the energies and a broadening of the band gaps.

Interband critical points of GaAs and their temperature dependence

Ellipsometric measurements of the dielectric constant of undoped Ge were performed between 1.25 and 5.6 eV in the temperature range of 100 to 850 K. The dependence of the ${E}_{1}$, ${E}_{1}+{\ensuremath{\Delta}}_{1}$, ${E}_{0}^{\ensuremath{'}}$, and ${E}_{2}$ critical energies on temperature was obtained. It can be represented either with Varshni's empirical formula or with an expression proportional to the Bose-Einstein statistical factor of an average phonon. Broadening parameters, amplitudes, and phase angles for the corresponding critical points were also obtained. A decrease of the excitonic interaction with increasing temperature was found. The results are discussed in the light of recent calculations of the effect of temperature on the band structure of Ge containing Debye-Waller and self-energy contributions.

Temperature dependence of the dielectric function of germanium

We investigate the electronic properties of nanocrystalline cerium oxide $({\mathrm{CeO}}_{x})$ films, grown by various techniques, and we establish universal relations between them and the film structure, composition, and morphology The nanocrystalline ${\mathrm{CeO}}_{x}$ films mainly consist of ${\mathrm{CeO}}_{2}$ grains, while a considerable concentration of trivalent ${\mathrm{Ce}}^{3+}$ is distributed at the ${\mathrm{CeO}}_{2}$ grain boundaries forming amorphous ${\mathrm{Ce}}_{2}{\mathrm{O}}_{3}$ A small portion of ${\mathrm{Ce}}^{3+}$ is also located around O-vacancy sites The optical properties of the ${\mathrm{CeO}}_{x}$ films are considered, taking into account the reported band-structure calculations The fundamental gap ${E}_{g}$ of ${\mathrm{CeO}}_{x}$ is due to the indirect $\mathrm{O}2\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{Ce}4f$ electronic transition along the L high-symmetry lines of the Brillouin zone and it is correlated with the $[{\mathrm{Ce}}^{3+}]$ content, explaining the redshift of ${E}_{g}$ in nanostructured ${\mathrm{CeO}}_{x},$ which is due to the ${\mathrm{Ce}}^{3+}$ at the grain boundaries and not due to the quantum-size effect itself We also correlate the energy position of the $\mathrm{O}2\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{Ce}4f$ electronic transition, which varies up to 160-meV wide, with the lattice constant of the ${\mathrm{CeO}}_{2}$ grains We also show that the higher-order transitions are more sensitive to film composition The refractive index, far below ${E}_{g},$ is explicitly correlated with the film density, independently of the ${\mathrm{Ce}}^{3+}/{\mathrm{Ce}}^{4+}$ and O concentrations, grain size, and lattice parameter The density is also found to be the major factor affecting the absolute value of the ${\ensuremath{\varepsilon}}_{2}$ peak, which corresponds to the $\mathrm{O}2\stackrel{\ensuremath{\rightarrow}}{p}\mathrm{Ce}4f$ electronic transition

Structure-dependent electronic properties of nanocrystalline cerium oxide films

The research for the development of flexible organic electronic devices (FEDs) is rapidly increasing worldwide, since FEDs will change radically several aspects of everyday life. Although there has been considerable progress in the area of flexible inorganic devices (a-Si or solution processed Si), there are numerous advances in the organic (semiconducting, conducting and insulating), inorganic and hybrid (organic–inorganic) materials that exhibit customized properties and stability, and in the synthesis and preparation methods, which are characterized by a significant amount of multidisciplinary efforts. Furthermore, the development and encapsulation of organic electronic devices onto flexible polymeric substrates by large-scale and low-cost roll-to-roll production processes will allow their market implementation in numerous application areas, including displays, lighting, photovoltaics, radio-frequency identification circuitry and chemical sensors, as well as to a new generation of modern exotic applications. In this work, we report on some of the latest advances in the fields of polymeric substrates, hybrid barrier layers, inorganic and organic materials to be used as novel active and functional thin films and nanomaterials as well as for the encapsulation of the materials components for the production of FEDs (flexible organic light-emitting diodes, and organic photovoltaics). Moreover, we will emphasize on the real-time optical monitoring and characterization of the growing films onto the flexible polymeric substrates by spectroscopic ellipsometry methods. Finally, the potentiality for the in-line characterization processes for the development of organic electronics materials will be emphasized, since it will also establish the framework for the achievement of the future scientific and technological breakthroughs.

Flexible organic electronic devices: Materials, process and applications

Spectroscopic ellipsometry (SE) was employed to get insights on the optical, electronic, and transport properties of nanocrystalline titanium nitride (TiNx) films with respect to their microstructure and stoichiometry. The films’ properties can be tailored by varying the energy of bombarding ions during sputter deposition and the substrate temperature (Td). The best metallic behavior of TiNx (resistivity 40 μΩ cm and conduction density 5.5×1022 electrons/cm3) has been observed in films developed with energy above 100 eV and Td⩾400 °C. A redshift of the optical gaps has been observed for overstoichiometric films, suggesting it as a sensitive probe to investigate the TiNx stoichiometry. The energy, strength, and broadening of the interband transitions were studied with respect to the energy of ions and Td and they were explicitly correlated with the TiNx crystal cell size and grain orientation. On the other hand, the study of intraband absorption has provided the conduction electron density with respect to ...

Stergios Logothetidis

Papers

Interband critical points of GaAs and their temperature dependence

Temperature dependence of the dielectric function of germanium

Structure-dependent electronic properties of nanocrystalline cerium oxide films

Flexible organic electronic devices: Materials, process and applications

Optical, electronic, and transport properties of nanocrystalline titanium nitride thin films