Effect of pretreatment bias on the nucleation and growth mechanisms of ultrananocrystalline diamond films via bias-enhanced nucleation and growth: An approach to interfacial chemistry analysis via chemical bonding mapping

Abstract

The effect of pretreatment bias on the nucleation and growth mechanisms of the ultrananocrystalline diamond ͑UNCD͒ films on the Si substrate via bias-enhanced nucleation and bias-enhanced growth ͑BEN-BEG͒ was investigated using cross-sectional high-resolution transmission electron microscopy, chemical bonding mapping, and Raman spectroscopy. The mirror-polished substrate surface showed the formation of a triangular profile produced by a dominant physical sputtering mechanism induced by ion bombardment of ions from the hydrogen plasma accelerated toward the substrate due to biasing and a potential hydrogen-induced chemical reaction component before synthesizing the UNCD films. The BEN-BEG UNCD films grown on the Si substrate with biased and unbiased pretreatments in the hydrogen plasma were compared. In the case of the bias-pretreated substrate, the SiC phases were formed at the peaks of the Si surface triangular profile due to the active unsaturated Si bond and the enhanced local electrical field. The UNCD grains grew preferentially at the peaks of the triangular substrate surface profile and rapidly covered the amorphous carbon ͑a-C͒ and oriented graphite phases formed in the valley of the surface profile. In the case of the substrate with unbiased pretreatment, the SiC phases were formed via the reactions between the hydrocarbon species and the active Si atoms released from the substrate with assistance of the hydrogen plasma. The UNCD grains nucleated on the nucleating sites consisting of the SiC, a-C, and graphite phases. Growth mechanisms for the BEN-BEG UNCD films on both Si substrates were proposed to elucidate the different nucleation processes. Applying bias on the Si substrate pretreated in the hydrogen plasma optimized the nucleation sites for growth of UNCD grains, resulting in the low content of the nondiamond phases in UNCD films.

Origin of graphitic filaments on improving the electron field emission properties of negative bias-enhanced grown ultrananocrystalline diamond films in CH4/Ar plasma

“…[21][22][23][24][25][26] The application of negative bias voltage in CH 4 / H 2 plasma attracts the positively charged species, such as H þ , CH 3 þ , CH þ and expels the electrons that markedly alter the plasma chemistry near the substrates. [21][22][23][24][25][26] Shigesato et al 48 found that negative biasing increased the concentration of atomic hydrogen in the CH 4 /H 2 plasma and proposed that this could cause preferential etching of sp 2 -bonded C. On the other hand, Robertson et al 49 proposed that ion subplantation due to applied negative bias causes deposition of nanocrystalline graphitic C, and that diamond nucleates where the graphitic planes are locally oriented perpendicular to the surface. Zhong et al 25 described that during negative bias in CH 4 /H 2 plasma, the diamond grains were formed easier than on graphitic phases, so the diamond grains grow rapidly covering the graphitic phases, minimizing the influence of the nucleation sites of the graphitic phases on the subsequent growth process of the diamond grains.…”

“…A few earlier reports [21][22][23][24][25] observed that the application of bias voltage in the CH 4 /H 2 plasma-based microwave plasma enhanced CVD (MPECVD) process not only facilitated the growth of diamond, but also efficiently reduced the size of the grains, resulting in diamond films with nanosized granular structure. In addition, Teng et al 26 reported the enhanced EFE behavior of bias-enhanced grown (BEG) nanocrystalline diamond (NCD) films using CH 4 CH 4 /H 2 plasma and the feasibility of bias enhanced growth of UNCD films using CH 4 /Ar plasma has not been reported yet.…”

Fast growth of ultrananocrystalline diamond films by bias-enhanced nucleation and growth process in CH4/Ar plasma

“…8 The application of bias voltage in the CH 4 /H 2 plasma using microwave plasma enhanced chemical vapor deposition (MPECVD) system not only facilitated the growth of diamond but also efficiently reduced the size of the grains. 9,10 Moreover, Teng et al reported the enhanced EFE behavior for the BEG grown diamond films in CH 4 /H 2 plasma and proposed that BEG process can convert the a-C into nanographite phases. 11 Nevertheless, whether the same BEN-BEG process can be applied in CH 4 /Ar plasma for growing the UNCD films has not been reported yet.…”

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

“…This is efficient in reducing the size of the diamond grains. 37,38 Zhong et al 38 describe that when using a negative bias in the CH 4 /H 2 plasma, the diamond grains easily form on the graphitic phases, thereby rapidly covering them and minimizing the influence of the nucleation sites of the graphitic phases during the subsequent growth process of the diamond grains. In addition, Shigesato et al 39 find that negative biasing increases the concentration of atomic hydrogen in the CH 4 /H 2 plasma and propose that this can cause preferential etching of sp 2 -bonded C. On the other hand, Robertson et al 40 propose that ion sub-plantation due to applied negative bias causes deposition of nanocrystalline graphitic C, and that diamond nucleates at places where the graphitic planes are locally oriented perpendicular to the surface.…”