Asaf Bolker

Diamond processing by focused ion beam—surface damage and recovery

The nitrogen vacancy color center (NV−) in diamond is of great interest for photonic applications. Diamond nano-photonic structures are often implemented using focused-ion-beam (FIB) processing, leaving a damaged surface which has a detrimental effect on the color center luminescence. The FIB processing effect on single crystal diamond surfaces and their photonic properties is studied by time of flight secondary ion mass spectrometry and photoluminescence. Exposing the processed surface to hydrogen plasma, followed by chemical etching, drastically decreases implanted Ga concentration, resulting in a recovery of the NV− photo-emission and in a significant increase of the NV−/NV0 ratio.

3D Graphene-Infused Polyimide with Enhanced Electrothermal Performance for Long-Term Flexible Space Applications.

Polyimides (PIs) have been praised for their high thermal stability, high modulus of elasticity and tensile strength, ease of fabrication, and moldability. They are currently the standard choice for both substrates for flexible electronics and space shielding, as they render high temperature and UV stability and toughness. However, their poor thermal conductivity and completely electrically insulating characteristics have caused other limitations, such as thermal management challenges for flexible high-power electronics and spacecraft electrostatic charging. In order to target these issues, a hybrid of PI with 3D-graphene (3D-C), 3D-C/PI, is developed here. This composite renders extraordinary enhancements of thermal conductivity (one order of magnitude) and electrical conductivity (10 orders of magnitude). It withstands and keeps a stable performance throughout various bending and thermal cycles, as well as the oxidative and aggressive environment of ground-based, simulated space environments. This makes this new hybrid film a suitable material for flexible space applications.

Transfer doping of single isolated nanodiamonds, studied by scanning probe microscopy techniques.

The transfer doping of diamond surfaces has been applied in various novel two-dimensional electronic devices. Its extension to nanodiamonds (ND) is essential for ND-based applications in many fields. In particular, understanding the influence of the crystallite size on transfer doping is desirable. Here, we report the results of a detailed study of the electronic energetic band structure of single, isolated transfer-doped nanodiamonds with nanometric resolution using a combination of scanning tunneling spectroscopy and Kelvin force microscopy measurements. The results show how the band gap, the valence band maximum, the electron affinity and the work function all depend on the NDs size and nanoparticle surface properties. The present analysis, which combines information from both scanning tunneling spectroscopy and Kelvin force microscopy, should be applicable to any nanoparticle or surface that can be measured with scanning probe techniques.

Accurate carrier-type determination of nonhomogenously doped diamond

Electrical properties of B-doped homoepitaxialy grown diamond are characterized with and without mesa structures by Hall effect measurements as function of temperature in the as-grown state and following oxygen reactive ion etching (RIE). The extracted carrier type, concentration, and mobility are found to depend on the measurement contact configuration. For measurements performed without mesa major differences, even in carrier type, are found following the RIE treatment, however no changes what so ever are observed when measuring with a mesa structure. Finite element simulation confirms that carrier concentration or/and mobility inhomogeneities in the regions surrounding the contacts in Hall effect measurements using the Van der Pauw configuration can result in wrong assignments of carrier type, concentration and mobility.

Temperature dependence of reversible switch-memory in electron field emission from ultrananocrystalline diamond

Temperature dependence of reversible hysteretic switching in electron field emission from surface transfer doped ultrananocrystalline diamond (UNCD) thin films is reported. Sharp jumps (up to 3 orders of magnitude) of the current, at specific ramp up and down extracting electric field values, are found. The memory-window, i.e., hysteresis widths, of the emitted current is controllable by heating (50 °C to 250 °C). The temperature dependence of the hysteresis is explained as being due to conductivity properties of the transfer doped UNCD film namely, by the electrons supply to emission sites. These results may find application in memory-switch devices with tunable properties.