Origin of a needle-like granular structure for ultrananocrystalline diamond films grown in a N₂/CH₄ plasma

Abstract

Microstructural evolution as a function of substrate temperature (T S) for conducting ultrananocrystalline diamond (UNCD) films is systematically studied. Variation of the sp2 graphitic and sp3 diamond content with T S in the films is analysed from the Raman and near-edge x-ray absorption fine structure spectra. Morphological and microstructural studies confirm that at T S = 700 °C well-defined acicular structures evolve. These nanowire structures comprise sp3 phased diamond, encased in a sheath of sp2 bonded graphitic phase. T S causes a change in morphology and thereby the various properties of the films. For T S = 800 °C the acicular grain growth ceases, while that for T S = 700 °C ceases only upon termination of the deposition process. The grain-growth process for the unique needle-like granular structure is proposed such that the CN species invariably occupy the tip of the nanowire, promoting an anisotropic grain-growth process and the formation of acicular structure of the grains. The electron field emission studies substantiate that the films grown at T S = 700 °C are the most conducting, with conduction mediated through the graphitic phase present in the films.

Structural properties of highly conductive ultra-nanocrystalline diamond films grown by hot-filament CVD

“…3,4 Different morphologies have been achieved by variations of the gas mixture and pressure, which leads to homogenous flat films, but also clustered surfaces and also needle like diamond grains 9 are presented, resulting in total a broad difference, ranging from insulating films of σ < 10 −9 (S/cm) up to high conducting ones with a mail address corresponding author: michael.mertens@uni-ulm.de σ = 10 3 (S/cm). In contrast, nanocrystalline diamond films grown by HFCVD usually possess high electrical resistivity.…”

Structural modification of nanocrystalline diamond films via positive/negative bias enhanced nucleation and growth processes for improving their electron field emission properties

“…The existing model proposes that the alteration of the granular structure of diamond films is related closely with the presence of the C 2 and CH species in the plasma. 22,41 That the C 2 species can nucleate diamond clusters easily [7][8][9] is the main factor resulting in the formation of ultra-small grains in UNCD films. In contrast, the presence of sufficient amount of CH species in the plasma is necessary for retaining the small size of the diamond grains, 41 as the CH species can encapsulate the newly nucleated diamond clusters, thereby preventing them from growing bigger.…”

The microstructural evolution of ultrananocrystalline diamond films due to P ion implantation and annealing process-dosage effect

“…Dosage of P-ions (10 13 800°C-annealed samples and as 16.87 V/μm for e-UNCD, which were 1 × 10 15 ions/cm 2 P-ion implanted/800°C-annealed, even though the surface resistivity of these films is markedly smaller than the other films (i.e.,σ b-UNCD = 7.05 × 10 6 , σ c-UNCD = 3.14 × 10 6 , σ d-UNCD = 5.85 × 10 4 and σ e-UCND = 2.66 × 10 3 Ω/squares). The EFE parameters are also listed in Table 1.…”

“…Incorporation of N 2 into the growth plasma of UNCD films gives rise to the conversion of a-C phase to graphite phase at the grain boundaries, increasing the number of conduction paths in the material and hence efficiently advancing the electrical conductivity and EFE properties of the films. [10][11][12][13] However, N 2 incorporation via the addition of N 2 gas to the growth plasma requires high growth temperature (700°C) [13]. On the other hand, ion implantation has long been utilized to amend the properties of materials through controlled doping, using select dopants [14][15][16][17].…”