Zinc oxide, a wide-gap semiconductor, typically exhibits n-type conductivity even when nominally undoped. The nature of the donor is contentious, but hydrogen is a prime candidate. We present ab initio calculations of the migration barrier for H, yielding a barrier of less than approximately 0.5 eV. This indicates isolated hydrogen is mobile at low temperature and that thermally stable H-related donors must logically be trapped at other defects. We argue this is also true for other oxides where H is a shallow donor.

We use local density function theory to study the electronic properties of tetrafluoro-tetracyanoquinodimethane (F4-TCNQ) deposited on a graphene surface. We show that charge transfer of 0.3 holes/molecule between graphene and F4-TCNQ occurs, which makes graphene p-type doped. These results are in agreement with experimental findings on F4-TCNQ.

Nitrogen is ubiquitous in both natural and laboratory-grown diamond, but the number and nature of the nitrogen-containing defects can have a profound effect on the diamond material and its properties. An ever-growing fraction of the supply of diamond appearing on the world market is now lab-grown. Here, we survey recent progress in two complementary diamond synthesis methodshigh pressure high temperature (HPHT) growth and chemical vapour deposition (CVD), how each is allowing ever more precise control of nitrogen incorporation in the resulting diamond, and how the diamond produced by either method can be further processed (e.g. by implantation and/or annealing) to achieve a particular outcome or property. The burgeoning availability of diamond samples grown under well-defined conditions has also enabled huge advances in the characterization and understanding of nitrogen-containing defects in diamondalone, and in association with vacancies, hydrogen and transition metal atoms. Amongst these, the negatively charged nitrogen-vacancy (NV −) defect in diamond is attracting particular current interest on account of the many new and exciting opportunities it offers for, e.g., quantum technologies, nanoscale magnetometry and biosensing. 2 Laboratory Based Synthesis of Diamond and Nitrogen-Containing Diamond 2.1 High Pressure High Temperature (HPHT) Methods. Nature was the inspiration for the HPHT method, by which diamond growth was demonstrated by Swedish company ASEA in 1953 (though not reported at that time) and subsequently by US company General Electric in 1955. 14 , 15 Most present-day HPHT synthesis exploits the temperature-gradient growth (TGG) method developed later in that decade. 16 However, it took many further years before the design and control of HPHT reactors yielded diamonds of

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Nitrogen impurities form complexes with native defects such as vacancies and self-interstitials in silicon which are stable to high temperatures. These complexes can then suppress the formation of large vacancy and self-interstitial clusters. However, there is little known about their properties. We use first-principles densityfunctional theory to the determine the local vibrational modes, electrical levels and stability of a range of nitrogen-interstitial and vacancy complexes. Tentative assignments of the ABC photoluminescence line and the trigonal SL6 EPR center are made to substitutional-nitrogen pair and the substitutional-nitrogen-vacancy complex.

The chemical termination of diamond has a dramatic impact on its electrical and chemical properties, where hydrogen and oxygen termination produce negative and positive electron affinities, respectively. However, the impact of halogen termination is not fully understood. We show that for low-index surfaces, 100% fluorinated surfaces exhibit chemically stable positive electron affinities in the 1.17 to 2.63 eV range, whereas 100% chlorination is energetically unfavorable. At lower coverage the positive electron affinity is smaller, being a combination of halogen-terminated and unterminated sites. For mixed halogen and hydrogen termination, a wide range of negative and positive electron affinities can be achieved by varying the relative concentrations of adsorbed species. © 2011 American Physical Society

A global model of a radiofrequency (rf) inductively coupled H 2 plasma discharge in the Deuterium Negative Ion Source Experiment (DENISE) has been developed using the numerical code 'Global Model Solver' (GMS). The volume-averaged energy and particle balance equations, along with the quasi-neutrality condition, are numerically solved to determine the averaged densities of all the species included in the model and the electron temperature. The effects of the multicusp magnetic field and of the asymmetry of the source chamber are considered in the model. The values of the volume-averaged electron density and the average electron temperature obtained are compared to experimental measurements in the pressure and input power ranges of interest and a reasonably good agreement is found.

Hydrogen is a ubiquitous impurity in diamond but in contrast to other group IV materials the microscopic structure adopted in bulk material has largely remained elusive. It has therefore been the role of modelling to predict the properties of H in bulk diamond, as well as the interactions with impurities and other defects. Presented here is an account of the current theoretical understanding of hydrogen in diamond. Contents1. Introduction 552 2. Theoretical approaches 554 2.1. Hartree-Fock based methods 554 2.2. Density functional methods 555 2.3. Tight-binding approaches 555 2.4. Basis sets and Brillouin zone sampling 556 2.5. Classical versus quantum mechanical treatment of the H atoms 556 2.6. Summary 556 2.7. Calculation of experimental observables 557 3. Muonium and interstitial hydrogen 561 3.1. Muonium hyperfine coupling constants 563 3.2. Electrical activity of isolated hydrogen 564 3.3. Vibrational modes of interstitial H 565 3.4. Diffusion of interstitial hydrogen 565 3.5. Solubility of bond-centred hydrogen 567 3.6. Hydrogen in near-surface region 567 4. Di-hydrogen aggregates 568 5. Hydrogenated lattice vacancies 569