B. He

Fabrication of diamond nanopillars and their arrays

High-density, uniform diamond nanopillar arrays were fabricated by employing bias-assisted reactive ion etching in a hydrogen/argon plasma. Gold nanodots were employed as etching masks. The formation of nanopillar structure is associated with the directional physical etching/sputtering by ion bombardment and selective chemical etching of sp2 carbons by reactive hydrogen atoms and ions. The density and geometry of the nanopillars depend on the initial structure of diamond films and reactive ion etching conditions. The nanopillars with high aspect ratio and large surface area may have potential applications in high-efficiency and high-sensitivity diamond-based biomedical and chemical sensors and in mechanical and thermal management.High-density, uniform diamond nanopillar arrays were fabricated by employing bias-assisted reactive ion etching in a hydrogen/argon plasma. Gold nanodots were employed as etching masks. The formation of nanopillar structure is associated with the directional physical etching/sputtering by ion bombardment and selective chemical etching of sp2 carbons by reactive hydrogen atoms and ions. The density and geometry of the nanopillars depend on the initial structure of diamond films and reactive ion etching conditions. The nanopillars with high aspect ratio and large surface area may have potential applications in high-efficiency and high-sensitivity diamond-based biomedical and chemical sensors and in mechanical and thermal management.

Room temperature fabrication of p-channel Cu2O thin-film transistors on flexible polyethylene terephthalate substrates

The effects of growth temperature on the microstructure evolution and electrical transport properties of Cu2O films were investigated. Nanocrystalline Cu2O films with modest p-type semiconducting properties (Hall mobilities ∼20 cm2/Vs, hole concentrations ∼1016u2009cm−3) were successfully prepared at room temperature without post-annealing. Bottom gate and top contact p-channel Cu2O thin-film transistors (TFTs) were constructed on flexible polyethylene terephthalate substrates at room temperature, which shows superior transfer performance (field effect mobility ∼2.40u2009cm2/Vs and current on/off ratio ∼3.96u2009×u2009104). The low processing temperature and the good electrical performance of the p-type Cu2O TFTs suggest their good potential for applications in high-throughput and low-cost electronics.

Electrical properties of Be-implanted polycrystalline cubic boron nitride films

P-type conductivity of polycrystalline cubic boron nitride (cBN) films was achieved by implantation of beryllium ions. The effects of implantation doses and annealing on the phase composition and electrical properties of cBN films were studied. A reduction in resistivity by seven orders of magnitude was observed. Hall measurement revealed a corresponding hole concentration of 6.1×1018cm−3 and mobility of 3cm2∕Vs. The activation energy was estimated to be 0.20±0.02eV from the temperature dependence of resistance. The electrical properties of Be-implanted films are comparable to that of Be-doped cBN single crystals synthesized by high-pressure and high-temperature method.

Energy band engineering and controlled p‐type conductivity of CuAlO2 thin films by nonisovalent Cu‐O alloying

The electronic band structure and p‐type conductivity of CuAlO2 films were modified via synergistic effects of energy band offset and partial substitution of less‐dispersive Cu+ 3d10 with Cu2+ 3d9 orbitals in the valence band maximum by alloying nonisovalent Cu‐O with CuAlO2 host. The Cu‐O/CuAlO2 alloying films show excellent electronic properties with tunable wide direct bandgaps (∼3.46–3.87u2009eV); Hall measurements verify the highest hole mobilities (∼11.3–39.5 cm2/Vs) achieved thus far for CuAlO2 thin films and crystals. Top‐gate thin film transistors constructed on p‐CuAlO2 films were presented, and the devices showed pronounced performance with Ion/Ioff of ∼8.0u2009×u2009102 and field effect mobility of 0.97 cm2/Vs.

Preparation of superhydrophobic nanodiamond and cubic boron nitride films

Superhydrophobic surfaces were achieved on the hardest and the second hardest materials, diamond and cubic boron nitride (cBN) films. Various surface nanostructures of nanocrystalline diamond (ND) and cBN films were constructed by carrying out bias-assisted reactive ion etching in hydrogen/argon plasmas; and it is shown that surface nanostructuring may enhance dramatically the hydrophobicity of ND and cBN films. Together with surface fluorination, superhydrophobic ND and cBN surfaces with a contact angle greater than 150° and a sliding angle smaller than 10° were demonstrated. The origin of hydrophobicity enhancement is discussed based on the Cassie model.

p-type conduction in beryllium-implanted hexagonal boron nitride films

p-type conduction in hexagonal boron nitride (hBN) films was achieved by beryllium implantation and subsequent rapid thermal annealing treatment. The dependence of phase composition and electrical properties of hBN films on the implantation fluence and annealing was studied. A maximum resistivity reduction by six orders of magnitude was demonstrated. Hall measurements revealed a corresponding hole concentration of 3×1019u2002cm−3 and mobility of 27u2002cm2/Vu2009s. The activation energy of Be ions was estimated to be 0.21 eV. It is suggested that hBN is a promising wide bandgap semiconductor for applications in high-temperature electronic devices and transparent conductive coatings.

The fabrication of cubic boron nitride nanocone and nanopillar arrays via reactive ion etching

High-density (2 x 10(9) cm(-2)) uniform arrays of cubic boron nitride (cBN) nanocones and nanopillars with a high aspect ratio were fabricated by employing sequential growth and bias-assisted reactive ion etching using gold nano-dots as an etching mask. The mechanism of formation of the nanopillar and nanocone morphologies was discussed in terms of the relative action of ion bombardment etching and chemical etching due to activated hydrogen plasma constituents. The presented method enabled nanostructuring of cBN surfaces over large areas with great uniformity and reproducibility with a controlled aspect ratio. The unique morphology of the nanostructures offers diverse application opportunities in microelectromechanical devices.

Electronic structure and electrical transport in ternary Al-Mg-B films prepared by magnetron sputtering

Nanostructured ternary Al-Mg-B films possess high hardness and corrosion resistance. In the present work, we study their electronic structure and electrical transport. The films exhibit semiconducting characteristics with an indirect optical-bandgap of 0.50u2009eV, as deduced from the Tauc plots, and a semiconductor behavior with a Fermi level of ∼0.24u2009eV below the conduction band. Four-probe and Hall measurements indicated a high electrical conductivity and p-type carrier mobility, suggesting that the electrical transport is mainly due to hole conduction. Their electrical properties are explained in terms of the film nanocomposite microstructure consisting of an amorphous B-rich matrix containing AlMgB14 nanoparticles.

Study of in-plane orientation of epitaxial AlN films grown on (111) SrTiO3

Substrate temperature and chemical etching were demonstrated to be dominant factors in determining the in-plane orientation of AlN films grown epitaxially on SrTiO3 (STO) (111) substrates by magnetron sputtering. Single-domain epitaxial AlN films were grown at moderate temperatures of 270–370°C with a sharp interface and orientation relationship of [21¯1¯0]AlN∥[01¯1]STO and (0002)AlN∥(111)STO. At temperature above 470°C, an additional 30° in-plane-rotated AlN domain appeared, and increased in percentage with increasing temperature. A model based on the reconstruction of STO (111) surfaces from (1×1) to (3×3)R30° was proposed to account for the formation of this new domain.

Electrical properties and electronic structure of Si-implanted hexagonal boron nitride films

Si ion implantation with a set of ion energies and ion doses was carried out to dope hexagonal boron nitride (hBN) thin films synthesized by radio-frequency magnetron sputtering. Hall effect measurements revealed n-type conduction with a low resistivity of 0.5 Ω cm at room temperature, corresponding to an electron concentration of 2.0u2009×u20091019u2009cm−3 and a mobility of 0.6 cm2/V s. Temperature-dependent resistivity measurements in a wide temperature range from 50 to 800u2009K demonstrated two shallow donor levels in the hBN band gap induced by Si doping, which was in consistence with the theoretical calculation by density function theory.