Through a systematic structural search we found an allotrope of carbon with Cmmm symmetry which we predict to be more stable than graphite for pressures above 10 GPa. This material, which we refer to as Z-carbon, is formed by pure sp(3) bonds and it provides an explanation to several features in experimental x-ray diffraction and Raman spectra of graphite under pressure. The transition from gra...

Since its discovery, graphene has held great promise as a two-dimensional (2D) metal with massless carriers and, thus, extremely high-mobility that is due to the character of the band structure that results in the so-called Dirac cone for the ideal, perfectly ordered crystal structure. This promise has led to only limited electronic device applications due to the lack of an energy gap which pre...

Despite manifold interests on the wide band gap (3.37 eV) semiconductor properties of zinc oxide (ZnO) material and its varied optoelectronic applications [1,2], much remains to be explored when its material perspective is sought in the context of nanotechnology and biomedicine. ZnO is generally known to be nontoxic and biocompatible substance [3]. It is also realized that ZnO nanomaterials wit...

Nanocrystalline materials may be considered as the challenge of this age. Intensive investigations were stimulated for several applications for these new classes of materials. Zinc oxides of particle size in nanometer range have been paid more attention for their unique properties. They are widely used for solar energy conversion, non-linear optics, catalysis, varistors, pigments, gas sensors, ...

A concept of doping that permits for the first time the freedom to design the desired activation energy of a dopant in a semiconductor is introduced and demonstrated. This doping engineering (DE) may also offer the possibility of achieving dopings in semiconductors in which a normally employed doping process is not successful, such as in wide band-gap IIVI semiconductors. Experimentally, we dem...

Zinc oxide, a wide-band-gap semiconductor with many technological applications, typically exhibits n-type conductivity. The cause of this conductivity has been widely debated. A first-principles investigation, based on density functional theory, produces strong evidence that hydrogen acts as a source of conductivity: it can incorporate in high concentrations and behaves as a shallow donor. This...

Zinc oxide (ZnO) is a wide band gap II–VI semiconductor with optical, electronic, and mechanical applications. Nitrogen is a promising acceptor dopant. Nitrogen–hydrogen (N–H) complexes were introduced into ZnO during chemical vapor transport (CVT) growth, using ammonia as a doping source. The N–H bond-stretching mode gives rise to an infrared (IR) absorption peak at 3151 cm 1 at liquidhelium t...

Since the discovery of mesostructured materials in the early 1990s a great deal of effort has been devoted to developing new structures, compositions, and functionalities. The ability to synthesize semiconducting singleor multicomponent metal-oxide mesostructured materials with controlled morphologies has been a major step towards functional materials with potential applications in sensing, cat...