Atomic structure modifications of diamond-like nanocomposite films: Observation by Raman spectroscopy, FTIR and STM Page: 2 of 6
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I
[(C2Hs)3SiO[CH3C.H5SiO],Si(CH),]. The Cr-DLN and Pt-DLN films were synthesized in a
combined process of DLN deposition and dc magnetron sputtering of the metal target (400-500
V, 0.2-2.0 A in Ar). The <100> Si substrate wafers were cleaned in situ by Ar plasma etching
prior to deposition. The thicknesses of the DLN, Cr-DLN and Pt-DLN films were in the range
0.2-1.0 pm, 0.7-1.2 m, and 0.7-1.2 pm, respectively. The sheet resistance (p,) of the Cr-DLN
was 1800 0/0. Two types of Pt-DLN films were studied: samples A and B with p, = 1500
0/C and p, - 1x10' 0/0, respectively. Some films were annealed in vacuum at 450C for 2
hrs.
The Fourier Transform Infrared (FTIR) spectra were taken with a Mattson Cygnus 100
with DTGS detector. The Raman measuremens were made using the 515 nm, 488 rm, or 475
nm lines of an Ar-ion laser as an excitation source. The laser power on the sample was about
1 Watt. No change in the lineshape with respect to laser intensity was found. All measurements
were taken in the backscattering geometry. The instrumental resolution was about 6 cm1.
The Raman spectra, I(a), were fitted by an equation which contains a low frequency,
aymmetric (P) and a Lorentzian (G) term [12]:
I(C) .Io + In- (2-X41Wd)4 + _______________ (1)
where To is the background, I1 is the integrated intensity, w, is the peak position and At is the
full width at half maximum of the Pa feature, respectively.
All STM images were taken in the constant current mode, with the set current around
1 nA and the tip bias voltage around -200 mV (tip negative with respect to the sample). STM
tips were mechanically formed from Pt90/Ir10 wires.
EXPERIMENTAL RESULTS
The FTIR spectra of as-deposited DLN films formed at different rf bias voltages (V) are
displayed in Fig 1. No arbitrary scaling factors were introduced and curves are displaced for
clarity. It can be seen that an increase from Vf = 0 to Vf - 1000 V causes the disappearance
of the broad C-H stretching vibration band at 2900 cm' [9,10] and a considerable decrease of
the peaks at 1600 cm (C-C sp stretching vibrations [11]) and 1000 c=1. The nature of this
latter feature is not clear. However, the complete absence of the C-H stretch vibration causes
us to believe that the properties of this film are not conditioned by hydrogen incorporation. After
thermal annealing the film with Vf 0 was destroyed. Annealing the films deposited with V,
= 300 V and V, = 1000 V did not change significantly the peak intensities but it did increase
film transparency.
Figure 2 shows the FTIR spectra of the various Pt-DLN films. The spectrum of sample
A is less transparent in relation to sample B because of the higher metal concentration (the
correlation between p, and metal concentration is presented in [8]). Thermal annealing of the Pt-
DLN films causes some increase in the intensity of the peak at 1600 cm' . The appearance of
the 1600 cm I peak after annealing at 3900C was observed by Grill et al.[l ], and explained as
the organization of the carbon atoms in the graphite coordination. The FTIR spectrum of Cr-
DLN remained almost unchanged after annealing and is similar to that of as-grown sample A.
The first order Raman spectra for both crystalline forms of carbon, i.e., graphite (with
threefold coordination symmetry) and diamond (with fourfold coordination symmetry) are well
known [12,13]. The first order Raman spectrum of diamond consists of a single sharp line ati/ .
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Dorfman, B.; Abraizov, M.; Pollak, F. H.; Yan, D.; Strongin, M.; Yang, X. Q. et al. Atomic structure modifications of diamond-like nanocomposite films: Observation by Raman spectroscopy, FTIR and STM, article, June 1, 1994; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc1341759/m1/2/: accessed May 16, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.