Study of Atomic Hydrogen Concentration in Grain Boundaries of Polycrystalline Diamond Thin Films

Abstract

This paper describes research focused on investigating the effect of hydrogen (H) atom insertion into the grain boundaries of polycrystalline diamond (PCD) films. This is required in order to understand the key morphological, chemical, physical, and electronic properties of the films. The PCD films were grown using the hot filament chemical vapor deposition (HFCVD) process, with flowing Ar gas mixed with CH4 and H2 gases to control film growth into microcrystalline diamond (MCD, 0.5–3 µm grain sizes), nanocrystalline diamond (NCD, 10–500 nm grain sizes), and ultrananocrystalline diamond (UNCD, 2–5 nm grain sizes) films depending on the Ar/CH4/H2 flow ratios. This study focused on measuring the H atom concentration of the PCD films to determine the effect on the properties indicated above. A simple model is presented, including a hypothesis that the two dangling bonds per unit cell of C atoms serve as the site of hydrogen incorporation. This correlates well with the observed concentration of H atoms in the films. Dangling bonds which are not passivated by hydrogen are postulated to form surface structures which include C double bonds. The Raman peak from these surface structures are the same as observed for transpolyacetyline (TPA). The data reveal that the concentration of H atoms at the grain boundaries is around 1.5 × 1015 atoms/cm2 regardless of grain size. Electrical current measurements, using a conductive atomic force microscopy (CAFM) technique, were performed using an MCD film, showing that the current is concentrated at the grain boundaries. Ultraviolet photo electron spectroscopy (UPS) confirmed that all the PCD films exhibited a metallic behavior. This is to be expected if the nature of grain boundaries is the same regardless of grain size.

Growth of Nitrogen Incorporated Ultrananocrystalline Diamond Coating on Graphite by Hot Filament Chemical Vapor Deposition

“…The Raman spectrum reveals peaks at 1345 cm −1 , which encapsulates the 1332 cm −1 peak correlated with sp 3 C atoms bonds characteristic of diamond in the grains, and sp 2 bonds of C atoms in the grain boundaries, expected for N-UNCD films, as shown in those grown by MPCVD [ 16 ]. The Raman spectrum shown in Figure 3 c and Figure 4 c,d are considered N-UNCD thin films, since they show the TPA peaks at 1150 ane1480 cm-1 characteristic of UNCD films [ 17 ], although the D and G peaks are a bit sharper and higher than the peaks observed in thick N-UNCD films produced by MPCVD [ 5 , 6 ] or thicker N-UNCD films grown recently by HFCVD [ 8 , 18 ] on Si substrate. This may be due to the laser beam reaching the underlying graphite layer used as substrate.…”

“…As was initially expected, the seeding process carried out, before N-UNCD film growth, is necessary for the nucleation of N-UNCD films on NG/Cu anodes, since HFCVD requires to have a high density of nucleation sites for the growth of UNCD films [ 17 , 20 ]. The Raman spectrum of samples without seeding (not shown) showed no difference compared to that of the virgin NG/Cu anode ( Figure 2 a).…”

“…Regarding information on sp2 C-bonds in grain boundaries available for N atoms chemical bonding, the reader is encouraged to read the article recently published by our group, which provides valuable quantitative information on bonds in grain boundaries of UNCD films [ 17 ].…”

Полученные плазменно-химическим осаждением a-C : ND покрытия: взаимосвязь эмиссионных свойств и фазового состава

“…5, b и с: осаждение углеводородов на поверхности пленки является источником материала для ее роста. Вытравливание же водорода с поверхности растущей пленки происходит главным образом при взаимодействии −C x H y -радикалов с атомарным водородом [47], что схематически показано данный процесс, как правило, не удается описать в рамках простых соображений [50]. В свою очередь, для плазменно-ассистированного CVD, проводимого в содержащей аргон рабочей атмосфере, может играть роль и проявление процессов, связанных с взаимодействием частиц аргона с поверхностью.…”

Transitions in polycrystalline diamond probed by steady state, modulated and transient surface photovoltage spectroscopy

“…Structural defects at grain boundaries lead to a large fraction of sp 2 bonded carbon atoms and disorder in diamond [16][17][18]. The concentration of hydrogen correlates with the grain size what gives evidence for passivation of dangling bonds (dbs) at grain boundaries of diamond [19]. In nanocrystalline diamond, defects at grain boundaries dominate electronic transitions from defect states in the bandgap.…”