Search

Hexagonal boron nitride (hBN) nanowalls were deposited by unbalanced radio frequency sputtering on (100)-oriented silicon, nanocrystalline diamond films, and amorphous silicon nitride (Si 3 N 4 ) membranes. The hBN nanowall structures were found to grow vertically with respect to the surface of all of the substrates. To provide further insight into the nucleation phase and possible lattice distortion of the deposited films, the structural properties of the different interfaces were characterized by transmission electron microscopy. For Si and Si 3 N 4 substrates, turbostratic and amorphous BN phases form a clear transition zone between the substrate and the actual hBN phase of the bulk nanowalls. However, surprisingly, the presence of these phases was suppressed at the interface with a nanocrystalline diamond film, leading to a direct coupling of hBN with the diamond surface, independent of the vertical orientation of the diamond grain. To explain these observations, a growth mechanism is proposed in which the hydrogen terminated surface of the nanocrystalline diamond film leads to a rapid formation of the hBN phase during the initial stages of growth, contrary to the case of Si and Si 3 N 4 substrates. [ABSTRACT FROM AUTHOR]

A detailed investigation of electron emission from a set of chemical vapour deposited (CVD) diamond films is reported using high-resolution PeakForce-controlled tunnelling atomic force microscopy (PF-TUNA). Electron field emission originates preferentially from the grain boundaries in low-conductivity polycrystalline diamond samples, and not from the top of features or sharp edges. Samples with smaller grains and more grain boundaries, such as nanocrystalline diamond, produce a higher emission current over a more uniform area than diamond samples with larger grain size. Light doping with N, B or P increases the grain conductivity, with the result that the emitting grain-boundary sites become broader as the emission begins to creep up the grain sidewalls. For heavy B doping, where the grains are now more conducting than the grain boundaries, emission comes from both the grain boundaries and the grains almost equally. Lightly P-doped diamond samples show emission from step-edges on the (1 1 1) surfaces. Emission intensity was time dependent, with the measured current dropping to ∼10% of its initial value ∼30 h after removal from the CVD chamber. This decrease is ascribed to the build-up of adsorbates on the surface along with an increase in the surface conductivity due to surface transfer doping. [ABSTRACT FROM AUTHOR]