Impurities in diamond

At the top of systems proposed for processors of quantum computers, there are systems in which electronic and nuclear spins of various defects and impurities in diamond are used as stationary qubits [1,2]. Single NV-centers having electronic spin S=1 in the ground electronic state are the most promising [3]. To improve optical read-out of such spin-states, various three-dimensional nanostructures in diamond such as micro resonators, waveguides, photon-crystal structures, etc. [1,4,5] are being developed. Besides, the methods of NV-center... 

R. J. Graham, T. D. Moustakas, and M. M. Disko, Cathodoluminescence imaging of defects and impurities in diamond films grown by chemical vapor deposition,... 

Aside from the filament stability and its hydrogen dissociation capability the incorporation of evaporated filament material into the growing diamond films is one aspect which has to be taken into account in HF-CVD Quantitative determinations of filament-related impurities in diamond films have been carried out for rhenium, tantalum and tungsten filaments. For filament temperatures between 1900°C and 2350°C the amount of incorporated Re increases by three orders of magnitude to a maximum of about 0.1 at-% [10]. Using Rutherford backscattering... 

We start by considering a single three-level impurity in diamond dressed by a coupling field and a probe field as shown in Fig. 5. In the limit of a weak probe, the steady state off-diagonal density... 

Nitrogen. Nitrogen impurity in diamond is detected and characterized by IR absorption and paramagnetic resonance. The majority of nitrogen atoms within the diamond structure are arranged in pairs as shown in Fig. 

Photoluminescence as well as the shape of the Raman diamond line were also the principal parameters in a detailed study of stresses and impurities in diamond films on silicon substrates by Bergman and Nemanich [20]. Diamond films were found to be under net compressive stress. The stress magnitude correlated with the concentration of the graphitic phase. The line shape of the photoluminescent nitrogen band at 25.14 eV (yellow) can be indicative of a uniform distribution of nitrogen centers. 

Diamond is sp hybridized with a C-C bond of 1.54 A and has very low intrinsic conductivity, considered a wide-bandgap semiconductor (5.5 eV). Doping is required to increase the conductivity to a level sufficient to support electrochemical measuranents. Boron, a p-type dopant, is the most common element used, but nitrogen is also used as an n-type dopant. Doped diamond materials, such as boron-doped diamond (BDD), are chemically inert and can often display a wider potential window than other carbon electrodes. NanocrystaUine diamond (NCD) contains significant sp character due to defects, which increase the material s conductivity without additional doping. The Raman band at 1332 cm is associated with the sp diamond lattice. The intensities of the sp band and the D-band for sp carbons at 1360 cm" can be used to determine the relative amounts of sp impurities in diamond, but the cross section for the D-band is approximately 50 times larger than that for diamond. ... 

The total energy of the system is one of the most important results obtained from any of the calculational techniques. To study the behavior of an impurity (in a particular charge state) in a semiconductor one needs to know the total energy of many different configurations, in which the impurity is located at different sites in the host crystal. Specific sites in the diamond or zinc-blende structure have been extensively studied because of their relatively high symmetry. Figure 1 shows their location in a three-dimensional view. In Fig. 2, some sites are indicated in a (110) plane... 

In diamond, Sahoo et al. (1983) investigated the hyperfine interaction using an unrestricted Hartree-Fock cluster method. The spin density of the muon was calculated as a function of its position in a potential well around the T site. Their value was within 10% of the experimental number. However, the energy profiles and spin densities calculated in this study were later shown to be cluster-size dependent (Estreicher et al., 1985). Estreicher et al., in their Hartree-Fock approach to the study of normal muonium in diamond (1986) and in Si (1987), found an enhancement of the spin density at the impurity over its vacuum value, in contradiction with experiment this overestimation was attributed to the neglect of correlation in the HF method. 

The color of diamond due to nitrogen impurities has been described in Section 9.6.3 It has been found that nitrogen impurities that are located next to a carbon vacancy in diamond thin films endow the solid with quite new properties, somewhat similar to the properties of a solid containing FLi centers compared with ordinary F centers. The diamond structure is built up of carbon atoms each surrounded by four... 

Figure 9.27 A (N-V) center in diamond, consisting of a carbon atom vacancy and a neighboring nitrogen atom impurity.

The last explanation, i.e. the development of 111 due to impurity adsorption, can be easily refuted on the basis of the anisotropy involved in diamond structure (PBC analysis). The likelihood of (2) and (3) being true is also remote. 

C. T. Pillinger. There are no metal impurities in these diamonds high enough to give that kind of response. 

After a few years scientists from Japan, Israel, France, USA, and other countries followed these studies. Whereas in the first papers the diamond electrodes, although of very good crystallinity, were not intentionally doped (their conductance was attributed to some unidentified impurities or point defects imparted by special thermal treatment), turning to boron-doped diamond samples [12] gave impetus to further progress in diamond electrochemistry. The number of laboratories involved in the studies of diamond electrodes is ever increasing in the last few years. 

Recently, approximate MO theories have been applied to a wide range of solid-state phenomena in addition to those reviewed in this paper. A short review of some of these problems indicates its versatility. Messmer and Watkins (3) have used EH to predict the position of N impurity levels in diamond using a 35-atom C lattice. Their calculations indicated the presence of a Jahn-Teller effect in accordance with electron paramagnetic resonance (EPR) experiments. The calculation was successful in explaining the deepening of the N donor level as due to Jahn-Teller distortion. 

---