Effects of hydrogenation on thermal conductivity of ultrananocrystalline diamond/amorphous carbon composite films prepared via coaxial arc plasma deposition

Abstract

Ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) composite (UNCD/a-C:H) and UNCD/non-hydrogenated amorphous carbon (a-C) composite (UNCD/a-C) films were prepared via coaxial arc plasma deposition, and their thermal conductivity and interfacial conductance in grain boundaries were measured using a time-domain thermoreflectance method. The interfacial conductance was estimated to be 1,010 and 4,892 MW/(m 2 &K) for UNCD/a-C:H and UNCD/a-C films, respectively. The reasons for the hydrogenated film having lower interfacial conductance than the non-hydrogenated film are 1) the reduced number of carriers that contribute to heat transport and 2) the hydrogen atoms, which are preferentially located at the grain boundaries and enhance phonon scattering.

Evidence of hydrogen termination at grain boundaries in ultrananocrystalline diamond/hydrogenated amorphous carbon composite thin films synthesized via coaxial arc plasma

“…Or the amount of dopedboron might be too small to be reflected on the spectra. The values of sp 3 / (sp 2 +sp 3 ) range from 55 to 59 %, which are situated between the values of 64 and 41 % in case of UNCD / a-C: H and UNCD / a-C films by CAPD, reported recently [23].…”

“…2(a), in spite of a control of the applied voltages that showed vivid variations of electrical characteristics [33]. In the meantime, some of the previous works certainly detected the relative increase of sp 3 -bonded carbons by means of hydrogenation that were conducted by changing base pressure of hydrogen in a chamber [18,23]. The reason for it is unclear at present.…”

“…All of the spectra are deconvoluted by Voigt curves consisting of Gaussian and Lorentzian functions, after the backgrounds are subtracted by Shirley's method [45,46]. The references of the peak positions describing sp 2 -and sp 3 -hybridized carbons and C−O−X at 284.5, 285, 286 eV, in order are employed to decompose the spectra, which successfully deconvoluted the spectra of the films synthesized under the most similar conditions by CAPD in a recent work [23]. As shown in Figs.…”

“…sp 3 and sp 2 bonds, which largely affect the physical properties of the films. UNCD / a-C and UNCD / a-C:H films synthesized by CAPD have been studied up to the present, by taking the advantages of conventional diamonds, toward the applications not only to hard coatings [18][19][20][21][22] and thermoelectric conversion elements [23], but also to optoelectronic devices such as photovoltaics [24][25][26][27][28][29][30][31][32][33][34][35][36]. As mentioned above, UNCD / a-C:H films prepared by CAPD include more a-C and/or a-C:H fractions and GBs that would act as generation sources of photo-induced carriers, which might be a cause of extremely large light absorption coefficients excessing 10 5 cm −1 in the photon energy range of 3 to 6 eV [15].…”

Maximizing visible Raman resolution of nanodiamond grains fabricated by coaxial arc plasma deposition through oxygen plasma etching optimization

“…The preferential incorporation of atomic hydrogen at nanodiamond grain boundaries terminates the dangling bonds to suppress the progression of the sp 2 carbon matrix in the film. 14 With these possessing priorities for nanodiamond fabrication using CAPD, it has been never reported about their application concerning the visible radiation excitation of the embedded nanodiamonds. In addition, limited employment of visible Raman spectroscopy for nanodiamond signature distinction has been reported in recent years.…”