In this Letter, the photoinduced switching of the single nitrogen-vacancy (NV) center between two different charge states, negative (NV(-)) and neutral (NV(0)), is studied under resonant excitation at liquid helium temperature. We show that resonant conversion of NV(0) to NV(-) significantly improves spectral stability of the NV(-) defect and allows high fidelity initialization of the spin qubit. Based on density functional theory calculations a novel mechanism involving an Auger ionization of NV(-) and charge transfer of an electron from the valence band to NV(0) is discussed. This study provides further insight into the charge dynamics of the NV center, which is relevant for quantum information processing based on an NV(-) defect in diamond.

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.

SummaryMany potential applications of graphene require its precise and controllable doping with charge carriers. Being a two-dimensional material graphene is extremely sensitive to surface adsorbates, so its electronic properties can be effectively modified by deposition of different atoms and molecules. In this paper, we review two mechanisms of graphene doping by surface adsorbates, namely electronic and electrochemical doping. Although, electronic doping has been extensively studied and discussed in the literature, much less attention has been paid to electrochemical doping. This mechanism can, however, explain the doping of graphene by adsorbates for which no charge transfer is expected within the electronic doping model. In addition, electrochemical doping is in the origin of the hysteresis effects often observed in graphene-based field effect transistors when operating in the atmospheric environment.

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