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We fabricated large area bilayer graphene by hot filament chemical vapor deposition (HFCVD) on Cu foil. The HFCVD technique can represent a significant advantage over other techniques for industrial scaling at low cost. We performed systematic experiments to determine the best parameters to obtain uniform graphene coverage over an area of ~ 16 cm 2 . The experimental growth parameters are grouped into two distinct regions according to the products obtained: (A) continuous bilayer graphene with low defect density and (B) continuous bilayer graphene with high defect density. The optimum graphene films obtained are uniform bilayer with low defect density, greater than 90% transmittance in the visible region, and no gaps. The high quality of the bilayer graphene was confirmed by Raman spectroscopy mapping. The results show that the ratio of 2D to G peak intensities ( I 2D / I G ) is in the 0.9–1.6 range over 90% of the area. Moreover, we employed the static cling property of polyethylene terephthalate (PET) to preserve the integrity of the as-grown graphene films in the transfer process, showing that the graphene films become well attached to the SiO 2 /Si substrates while the PET films were completely peeled off.

We report enhancement of photovoltaic properties of highly oriented BiFeO3 (BFO) thin films. The single phase rhombohedral R3c space group structure was confirmed by XRD and Raman spectra in the films grown on SrTiO3 (111) substrates using RF magnetron sputtering. The films of BFO were characterized in planar geometry with top Pt electrodes having 200μm diameter, ∼40nm thickness and at a regular spacing of ∼150μm deposited by DC sputtering process. For photovoltaic studies the current voltage characteristic of as grown and poled samples were studied under the white light illumination having energy density of ∼1kW/m2. The as grown films showed open circuit voltage (Voc) of ∼3.9V which increased up to ∼17.8V on poling with 200V. This enhancement in Voc by poling was attributed to increase in net polarization due to alignment of domains in the direction of applied electric field and hence potential barriers between the domains.

We report a new method for the synthesis of boron nitride nanostructures (nBN) using laser chemical vapor decomposition (LCVD). Borazine was used as precursor and excited with two simultaneous radiations, the fundamental and second YAG laser harmonics. If only one of the two radiations is employed, no reaction takes place. Abundant BN powder is obtained after one hour of laser radiation. The BN yield obtained with the LCVD technique is about 83% by weight. The BN material was characterized using scanning electron microscopy, transmission electron microscopy, electron energy loss spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. They all indicate that the BN powder consists of a mixture of hexagonal and cubic BN nanostructures. No other BN phases or stoichiometries were found. The size of the resulting BN nanostructures is in the range of 20–100 nm and their B : N composition is 1 : 1. A simplified mechanism involving laser-excited states followed by photoinduced removal of hydrogen is proposed to understand the synthesis of BN nanopowder by LCVD of borazine.

ZnO nanowires with high density are grown over zinc foil by thermal evaporation process at relatively low temperature. Electron microscopy studies confirmed that the as-grown nanowires are of single crystal hexagonal wurtzite structure, growing preferentially in the c -axis direction. The Raman spectrum of the ZnO nanowires shows an optical-phonon E 2 mode at 440 cm −1 confirming good crystallinity for the grown nanowires. The field emission measurement indicated that ZnO nanowires have a turn-on field of 9.1 V/μm at current density of 0.001 μA/cm 2 .

Spontaneously detaching self-standing diamond films were successfully fabricated using saturated hydrocarbon polymers as seeding source by hot filament chemical vapor deposition (HFCVD) technique. X-ray diffraction confirmed the crystal structure of diamond. The microcrystalline morphology of the diamond films was analyzed by atomic force microscopy (AFM) and scanning electron microscopy. Raman spectra from the front and back sides of the films show the characteristic diamond band at 1332 cm − 1 and no carbide layer. EELS spectra also show the signature features of diamond. The use of hydrocarbon polymers as seeding source will improve the cost-effectiveness of the fabrication of diamond wafers by simplifying the fabrication process.

We present a scalable, reproducible and economic process for the fabrication of diamond and diamond-graphene hybrid films using paraffin wax as a seeding source for diamond. The films were characterized using Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). Raman spectra show the characteristic band of diamond at 1332 cm-1 and the D, G, and 2D bands of graphene at 1360, 1582 and 2709 cm-1, respectively. Electron microscopy confirms the microcrystalline nature of the diamond films with crystal size in the range of 0.5 μm to 1.0 μm, and the hybrid film consists of microcrystalline diamond attached to thin, semi-transparent graphene flakes. The graphene-diamond hybrid films exhibit a turn-on field of about 3.6 V/μm with a prolonged current stability of at least 135 h.

A dual stage technique employing hot filament chemical vapor deposition (HFCVD) and radio frequency sputtering was used to synthesize SiN/BCNTs (bamboo like carbon nanotubes) on copper substrates. The films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Electron field emission studies (EFE), charge–discharge, and cyclic voltammetry. The comprehensive characterization is consistent with a nanolayer of amorphous SiN on BCNTs. Field emission experiments confirm the excellent contact of the SiN nanolayer with the surface of the BCNTs necessary for fabrication of a coin cell. Electrochemical testing shows that SiN/BCNT electrode can deliver an initial discharge capacity of 2000 mAh g −1 which is higher than the capacity of graphite and the reversible capacity after ten cycles is 300 mAh g −1 . The cyclic voltammetry results suggest good reversibility with Li during cycling.

We report the new results on the direct synthesis of nanostructured silicon carbide (SiC) materials using the pulsed laser deposition technique. Scanning electron microscopy images revealed that SiC nanoholes, nanosprouts, nanowires, and nanoneedles were obtained. The crystallographic structure, chemical composition, and bond structure of the nanoscale SiC materials were investigated using X-ray diffraction, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman scattering spectroscopy. The transverse optical mode and longitudinal optical mode in Raman spectra were found to become sharper as the substrate temperature was increased, while the material structure evolved from amorphous to crystalline.

A dual stage process of depositing bamboo-like carbon nanotubes (BCNTs) by hot filament chemical vapor deposition (HFCVD) and coating Si using Radio frequency sputtering (RFS) technique. The films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron field emission studies (EFE). SEM results suggest a dense network of homogeneous silicon-coated BCNTs. From the comprehensive analysis of the results provided by these techniques emerges the picture of Si encapsulated BCNTs.

Sulfur-assisted hot-filament chemical vapor deposition (HFCVD) was employed to grow nanocrystalline diamond at low substrate temperature, ∼ 300 °C, on molybdenum (Mo), and ∼ 250 °C, on polyimide film. The polyimide films remained flexible and strong after the deposition, clearly indicating that they did not experience temperatures near or above the glass transition temperature at ∼ 360 °C. The relative intensity of the diamond peak in the Raman spectra increases when the substrate temperature is decreased from ∼ 500 to ∼ 300 °C, a result that is inverted with respect to HFCVD without sulfur. This behavior was employed to obtain microcrystalline diamond on Mo at ∼ 270 °C. Profound changes induced to the gas phase chemistry and surface reactions when a trace amount of H2S is added to the HFCVD process seem to enable these results.

Structural evolutions of tungsten oxide(WO3) samples on different substrates are studied using Raman spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, x-ray diffraction and x-ray photoelectron spectroscopy. The WO3 samples are prepared using hot-filament CVD techniques. The focus of the study is on the evolutions of nano structures at different stages following deposition time. The experimental measurements reveal evolutions of the surface structures from uniform film to fractal-like structures, and eventually to nano particles, and crystalline structures from mono (0 1 0) crystalline thin film to polycrystalline thick film developments. The effect of high temperature on the nanostructured WO3 is also investigated. Well-aligned nanoscale WO3 rod arrays are obtained at a substrate temperature of up to 1400 °C. Further increasing the substrate temperature yields microscale crystalline WO3 particles.

AlN films are synthesized by using hollow cathode discharge sputtering technique. Typical transverse optical and longitudinal optical modes in Raman spectrum of AlN sample are observed at the gas pressures of 200 Pa and 500 Pa discharge sputtering deposition, respectively. The results show evidence that the structures of the films can be controlled by variations of discharge gas pressures. High discharge electric field used for sputtering deposition of AlN film causes transverse optical mode in Raman spectrum shift toward relatively low wave numbers. After annealing at 600 °C for 5 h in air at atmospheric pressure, the profile of the Raman longitudinal optical band appears narrow, probably indicating better quality of the film.

Boron carbonitride nanotubes (BCNNTs) were grown with high yield by DC arc discharge without catalyst particles or pre-grown template nanostructures. Two types of nanotubes (NTs) were formed: thin NTs with diameters of 10–15 nm and thick NTs with diameters of 25–50 nm. Transmission electron microscopy, electron energy loss spectroscopy, and Raman spectroscopy analyses indicate that the thin NTs are carbon NTs (CNTs) while the thick NTs are BCNNTs wrapped around CNTs. The growth kinetic appears to be faster for CNTs than for BCNNTs. Through the concerted substitution of B and N for C in the in situ grown CNTs, template growth of BCNNTs follows the CNTs growth without causing topological changes.

Device quality hydrogenated amorphous silicon (a-Si:H) thin films were grown by hot wire chemical vapor deposition (HWCVD) on glass (Corning 7059) using silane under high hydrogen dilution as a function of substrate temperature (TS) ranging 50–515 °C. As a consequence of variation of TS, the hydrogen concentration [CH] varied from 20.0% to 0.2%. They are optically examined ex situ using Raman spectroscopy (RS) and spectroscopic phase modulated ellipsometry (SPME) from near IR to near UV (1.5–5.0 eV) obtaining their vibration frequencies and pseudo-dielectric function, respectively for analyzing network disorder. The ellipsometry raw data (〈er(E)〉, 〈ei(E)〉) were modeled using Bruggeman effective medium theory (BEMT) and the dispersion relations for the amorphous semiconductors comprising a two-layer model consisting of a top surface roughness layer (dS) containing an effective medium mix of 50% a-Si:H and 50% voids and a single “bulk” layer (dB) of a-Si:H to simulate the data reasonably well. We performed these simulations by non-linear least-square regression analysis based on Marquardt–Levenberg algorithm and it was possible to estimate the true dielectric function of a-Si:H thin films and the energy band gap (Eg), besides film thickness (dSE), bulk void fraction, surface roughness layer (dS), and the confidence limits (χ2). Moreover, it is shown that the Tauc–Lorentz (TL) model fits the ellipsometry data much better than Forouhi and Bloomer (FB) and help elucidate the layered structure of a-Si:H thin films. We also compared the optical band gap (Eg) determined using ellipsometry modeling and the Tauc gap (ET) using conventional approach. We discuss the possible physical meaning and the variation of the deduced parameters in terms of role of TS (T-role) or of hydrogen (H-role) in the dispersion model abovementioned. The bandgap was found to decrease systematically with increasing TS, reconfirming the role of hydrogen as alloy in conjunction with network relaxation, which is in agreement with excitation dependent Raman spectroscopy (i.e. strongly versus weakly absorbing) results interpreted in terms of the variation of three “order parameters” relating the short- and medium-range order with respect to substrate temperature. This is since, previous Raman scattering studies in various hydrogenated amorphous silicon (a-Si:H) materials resulted in contradicting conclusions as to the role of hydrogen on the atomic-network order. Hereby, we elucidated these contradictions using the abovementioned optical probes by establishing that the surface and the bulk of HW a-Si:H films behave differently due to their different hydrogen concentrations. Micro-Raman spectroscopy (RS) and atomic force microscopy (AFM) were used to validate the simulations also. Further consequences of these findings are also discussed in terms of other optical and structural properties. These analyses led to a correlation between the films’ microstructure (or network disorder) and their electronic properties for several technological applications, in general, and for solar cells applications, in particular.

The structural bonding in a series of nanocrystalline carbon thin films grown under different substrate biasing conditions was analyzed using Raman spectroscopy in both the visible and ultraviolet (uv) regimes of the spectrum. The nanocrystalline carbon thin films studied were deposited by the hot-filament chemical vapor deposition (HFCVD) technique using a 2% concentration of methane in hydrogen. The films were deposited on molybdenum substrates under various substrate biasing conditions. A positive bias (forward) produced a continuous flow of electrons from the filament on to the substrate, whereas a negative bias (negative) caused the substrate to be bombarded with positive ions. Films were also grown under no bias, for comparison. Differences in the Raman spectra obtained with visible (λL = 514.5 nm) and uv (λL = 244.0 nm) excitation sources were investigated. Apart from the basic features consisting of D and G bands at around 1360 and 1580 cm−1 in the case of visible Raman spectra, an extra feature at around 1060 cm−1, denoted a T band, appeared in the uv Raman spectra only. Hence, uv Raman scattering measurements clearly revealed the presence of sp3-bonded carbon atoms. The position and its intensity ratio with respect to the G peak [(I(T)/I(G)] were used to provide a reliable means to measure the sp3 C bonding fraction, which is both semi-quantitative and non-destructive. The sp3 content estimated within the microstructure of n-C thin films was found to be around 60–80%. Further, probing the samples with two different photons (visible and uv) allowed us to estimate qualitatively the amount and clustering of sp2 sites. This technique provided a fast and reliable microstructural characterization of disordered carbons. The dispersion in the Raman features is specific to each carbon system and, therefore, can be used as a fingerprint. These findings point at the similarities of bias-assisted HFCVD nanocrystalline carbon (n-C) materials and the tetrahedrally bonded amorphous carbon (ta-C) materials grown by ion-beam assisted deposition (IBAD). Copyright © 2003 John Wiley & Sons, Ltd.

Sulfur incorporated nanocrystalline carbon (n-C:S) thin films were grown on molybdenum substrates by a hot-filament chemical vapor deposition technique using gas mixtures of methane, hydrogen, and a range of hydrogen sulfide (H2S) concentrations (100–500 ppm with an interval of 100 ppm) at a fixed substrate temperature of 900 °C. They were optically characterized using Raman spectroscopy (RS) and ex situ spectroscopic phase modulated ellipsometry from near-infrared to near UV (1.5–5.0 eV) obtaining their vibrational frequencies and pseudodielectric function, respectively, as a function of [H2S]. The ellipsometry data [〈er(E)〉,〈ei(E)〉] were modeled using Bruggeman effective-medium theory and dispersion relations for the amorphous semiconductors: Forouhi and Bloomer (FB) parameterization model. A simplified two-layer model consisting of a top layer comprising an aggregate mixture of sp3C+sp2C+void and a bulk layer (L2), defined as a dense amorphized FB-modeled material, was found to simulate the data reason...

We report for the first time the fabrication of single-crystal metastable manganese sulfide nanowires (γ-MnS NWs) conformally coated with graphitic carbon via chemical vapor deposition technique using a single-step route. Advanced spectroscopy and electron microscopy techniques were applied to elucidate the composition and structure of these NWs at the nanoscale, including Raman, XRD, SEM, HRTEM, EELS, EDS, and SAED. No evidence of α-MnS and β-MnS allotropes was found. The γ-MnS/C NWs have hexagonal cross-section and high aspect ratio (∼1000) on a large scale. The mechanical properties of individual γ-MnS/C NWs were examined via in situ uniaxial compression tests in a TEM-AFM. The results show that γ-MnS/C NWs are brittle with a Young's modulus of 65 GPa. The growth mechanism proposed suggests that the bottom-up fabrication of γ-MnS/C NWs is governed by vapor-liquid-solid mechanism catalyzed by bimetallic Au-Ni nanoparticles. The electrochemical performance of γ-MnS/C NWs as an anode material in lithium-ion batteries indicates that they outperform the cycling stability of stable micro-sized α-MnS, with an initial capacity of 1036 mAh g(-1) and a reversible capacity exceeding 503 mAh g(-1) after 25 cycles. This research advances the integration of carbon materials and metal sulfide nanostructures, bringing forth new avenues for potential miniaturization strategies to fabricate 1D core/shell heterostructures with intriguing bifunctional properties that can be used as building blocks in nanodevices.

Tin dioxide-carbon nanotube (SnO2-CNT) composite films were synthesized on copper substrates by a one-step process using hot filament chemical vapor deposition (HFCVD) with methane gas (CH4) as the carbon source. The composite structural properties enhance the surface-to-volume ratio of SnO2demonstrating a desirable electrochemical performance for a lithium-ion battery anode. The SnO2and CNT interactions were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared-attenuated total reflectance (ATR-FTIR) spectroscopy. Comprehensive analysis of the structural, chemical, and electrochemical properties reveals that the material consists of self-assembled and highly dispersed SnO2nanoparticles in CNT matrix. The process employed to develop this SnO2-CNT composite film presents a cost effective and facile way to develop anode materials for Li-ion battery technology.

Nanocrystalline carbon thin films were deposited by hot-filament chemical vapor deposition using a 2% concentration of methane in hydrogen. The films were deposited on molybdenum substrates under various substrate biasing conditions. A positive bias produced a continuous flow of electrons from the filament onto the substrate, while a negative bias caused the substrate to be bombarded with positive ions. Films were also grown under no bias, for comparison. Differences in the electron field emission properties (turn-on fields and emitted currents) of these films were characterized. Correspondingly, microstructural differences were also studied, as characterized with atomic force microscopy and Raman spectroscopy. Films grown under electron bombardment showed lower turn-on fields, smoother surfaces, and smaller grains than those grown under ion bombardment or no bias. A correlation between the enhanced emission properties and the nanocrystalline carbon material produced by the low-energy particle bombardment...

Photoluminescence (PL) and Raman spectra of thermochemically reduced and untreated cubic calcia-stabilized zirconia (CaSZ) have been investigated. The effect of the reduction process results in a decrease in Raman activity in the acoustic mode region and a shift in the maximum of the excitation (EX) spectra. These variations can be related to a broad absorption band centered at ∼365 nm. The results point out the oxygen vacancies, their aggregates and associated complex defects as the main defect involved in the reduction process.

Raman spectroscopy is an excellent technique for characterization of the crystalline quality of diamond films and the amount of graphite and amorphous carbon impurities in them. Most publications on diamond include Raman spectra to show the quality of the films through a measurement of the bandwidth (FWHM) of the feature at ca. 1332.5 cm−1 characteristic of diamond. These measurements are often done directly on the spectra without correcting them for the instrumental contribution to the bandwidth. This can lead to meaningless comparisons of diamond bandwidth measurements across research groups. In order to show to what extent interpretations based on such raw measurements can be misled, we have characterized five CVD diamond films and a natural type IIa diamond using four different sets of instrumental parameters. We present a fitting procedure to obtain the Raman bandwidth corresponding to the material under study independent of the experimental parameters. This method permits absolute comparisons among Raman bandwidths obtained under different experimental conditions, providing they are corrected for the instrumental contribution.

The network disorder of amorphous Si 1 − x C x :H films, containing carbon concentrations below 25 at.%, has been studied by means of Raman spectroscopy. Two different radiations were employed to excite the Raman scattering of these materials, one that is strongly (458 nm) absorbed and another that is weakly (581 nm) absorbed. The variation in probed depth attained with these excitation radiations together with the significant differences observed in the Raman spectra excited with them indicate the existence of silicon network disorder inhomogeneities at the short-range (bond angle) and intermediate-range (dihedral angle) levels along the axis perpendicular to the films which are considerably larger than those existing in device-quality a-Si:H. Such inhomogeneities are observed to develop abruptly at the smallest carbon concentration. The findings explain the various previous conflicting reports in the literature regarding the behavior of the Si-network disorder in these alloys. When excited with strongly absorbed radiations (e.g., 514 and 488 nm), the Raman spectra do not show a definite trend as a function of carbon concentration, although it can still be concluded that there is less order than in a-Si:H. On the other hand, the Raman spectra excited with weakly absorbed radiation show that the order actually improves in the bulk of Si-rich a-SiC:H films. The above findings indicate that silicon is forming compact clusters in the interior of the films on this compositional regime. Besides, our results show that hydrogen dilution of the gas mixture during film growth helps improve the short-range order in the bulk of the films with the smallest carbon concentrations, but has no definite effect over the intermediate-range order or over the short-range order at the near surface. It is also found that the spectral intensity enhancement observed in these materials with increasing carbon content is due to a scattering volume effect.

We have carried out a comprehensive study of the Raman spectra of a‐Si:H films produced by the glow discharge (GD) and radio frequency sputtering (RFS) deposition techniques. The results show that the short‐range disorder (bond‐angle deviation), as measured by the width of the TO band (ΓTO), is larger in RFS than in GD a‐Si:H films. The intermediate‐range disorder (dihedral angle deviation), as measured by the ratio of the intensity of the TA band to that of the TO band (ITA/ITO), is generally larger in RFS than in GD a‐Si:H films. However, while the ITA/ITO values of RFS films remain relatively close to those of GD films when the interior is probed, the near surface of RFS films shows much larger values evidencing the existence of a significant disorder gradient along the growth axis. Together, these results indicate that the network order and homogeneity of RFS amorphous silicon is lower than those of GD for substrate temperatures that produce the hydrogenated material. These structural differences are ...

We report the optical and electrical properties of chemically-doped bilayer graphene stack by tetracyanoethylene, a strong electron acceptor. The Tetracyanoethylene doping on the bilayer graphene via charge transfer was confirmed by Raman spectroscopy and Infrared Fourier transform spectroscopy. Doped graphene shows a significant increase in the sheet carrier concentration of up to 1.520 × 1013 cm−2 with a concomitant reduction of the sheet resistance down to 414.1 Ω/sq. The high optical transmittance (ca. 84%) in the visible region in combination with the low sheet resistance of the Tetracyanoethylene-doped bilayer graphene stack opens up the possibility of making transparent conducting electrodes for practical applications.

We report the tuning of the internal Mn photoluminescence (PL) transition of magnetically-ordered Sr-doped lanthanum manganite (LSMO)/Mn-doped zinc sulfide (ZnS:Mn) nanocomposites (NCs) by applying a static magnetic field in the range of 0-1 T below the critical temperature of ∼225 K. To do that, we have systematically fabricated LSMO/ZnS:Mn at different concentrations (1:1, 1:3, 1:5 and 1:10 wt%) via a straightforward solid-state reaction. X-ray diffraction and Raman analyses reveal that both phases coexist with a high degree of crystallinity and purity. Electron microscopy indicates that the NCs are almost spherical with an average crystal size of ∼6 nm, and that their surfaces are clean and smooth. The bifunctional character of LSMO/ZnS:Mn was evidenced by vibrating sample magnetometry and PL spectroscopy analyses, which show a marked ferromagnetic behavior and a broad, intense Mn orange emission band at room temperature. Moreover, the LSMO/ZnS:Mn at 1:3 wt% exhibits magneto-luminescent (ML) coupling below 225 K, and reaches the largest suppression of Mn-band PL intensity (up to ∼10%) at 150 K, when a magnetic field of 1.0 T is applied. The ML effect persists at magnetic fields as low as 0.2 T at 8 K, which can be explained by evoking a magnetic-ordering-induced spin-dependent restriction of the energy transfer to Mn states. No ML effect was observed in bare ZnS:Mn nanoparticles under the same experimental parameters. Our findings suggest that this NC can be considered as a new ML compound, similar to FeCo/InGaN-GaN and LSMO/ZnO NCs, useful as q-bits for quantum computation. The results presented here bring forth new avenues to better understand the interaction between semiconductors and perovskites, and exploit their synergistic effects in magneto-optics, spintronics and nanoelectronics.

The room-temperature electrical conductivity of sulfur-incorporated microcrystalline diamond (μc-D:S) thin films synthesized by hot-filament chemical vapor deposition was investigated as a function of sulfur concentration. The films were prepared using a 0.3% CH4/H2 gas mixture and hydrogen sulfide (H2S) as dopant source on intrinsic Si(001) substrates. The μc-D:S films exhibited an increase in n-type conductivity with increase in H2S concentration from 0 to 200 ppm, followed by a decrease in conductivity and sign reversal for the films grown with 500 ppm of H2S. These films were also characterized using scanning electron microscopy, atomic force microscopy, and Raman spectroscopy techniques. The findings are discussed in terms of the role of sulfur in the films. The films grown at the highest [H2S] possess the highest carrier concentration (∼1.07×1017/cm3) and the lowest carrier Hall mobility (0.01 cm2 V−1 s−1). Since the conductivity is affected by carrier concentration and crystallinity, the relatively...

Oxygenated CdTe films prepared by r.f. sputtering have been shown to have band gap energies between 1.48 and 3.35 eV, depending on the amount of oxygen incorporated in the CdTe matrix. Samples with oxygen concentrations above 7 at.% are amorphous, whereas those with oxygen concentrations below 7 at.% are polycrystalline, as determined by x-ray and Raman measurements. The Raman spectra of the polycrystalline samples show that there is ca. 4 at.% Te in the form of inclusions under high pressure, which is relatively easy to detect owing to the enhanced Raman cross-section of Te. The Raman spectra of the amorphous samples is dominated by a single broad band at 159 cm −1. The fact that tellurates in general show a similar band, in spite of their different vibrational density of states, indicates that it corresponds to TeTe bonds in the amorphous matrix.

The electron field emission properties of sulfur-incorporated nanocomposite carbon thin films grown by hot-filament chemical vapor deposition were investigated as a function of film microstructure. The in-plane correlation length (La) of the sp2 C clusters in these films was determined from the intensity ratio of the D and G bands [I(D)/I(G)] in the visible Raman spectra using a phenomenological model. The turn-on field was found to decrease with increasing sp2 C cluster size in the range of 0.8–1.4 nm. The lowest turn-on field found was 4.0 V/μm corresponding to films having sp2 C clusters of around 1.4 nm and conductivity of 30 Ω−1 cm−1. These findings are discussed in terms of a reduced field emission barrier brought about by the incorporation of sulfur and the need for relatively longer conductive paths capable of withstanding the relatively large emission currents.

Results are reported on the electron field emission properties of sulfur-incorporated nanocrystalline carbon (n-C:S) thin films grown by hot-filament chemical vapor deposition technique. The lowest turn-on field values observed were around 4.0–4.5 V/μm, which are about half of those measured for films grown without sulfur. Associated to the effect of addition of sulfur on field emission properties, there are interesting microstructural changes, as characterized with scanning electron microscopy, atomic force microscopy, and Raman spectroscopy techniques. The sulfur-incorporated films show smoother and finer-grained surfaces than those grown without sulfur. These results are similar to those found for the introduction of nitrogen, but different to those produced by oxygen addition to the chemical vapor deposition process. These findings are attributed to changes in the electronic band structure.

Temperature-dependent first-order Raman scattering studies in the range 30–290 K were carried out in LiCsSO4 in order to investigate its phonon spectra in relation to the phase transitions in the crystal. Complete spectra were obtained for the z(xx)y and z(xz)y geometries. A careful analysis of the spectra shows that both the low- and high-energy Raman modes exhibit variations either in frequency or intensity or both with temperature of the crystal, indicating that the D2k normal phase undergoes a transition at the Ti (202 K) and one to the commensurate phase at ca 160 K (Tc). Below the Tc, in the C2ν phase, the lattice mode at 44 cm−1 was observed to be a soft phonon with its frequency decreasing to 32 cm−1 at 30 K, indicating the possibility of a new structural phase transition of unlocking type in the crystal at a temperature Tu below 20 K. Another observation is the oscillating behaviour of Rayleigh scattering near the phase transition at the Ti.

Polarized first-order Raman spectra of BeO crystal were recorded at various temperatures to study the variations in frequencies and intensities associated with some of the phonons. At 35 K five modes were assigned to be fundamentals at 338.1 682.6, 726.7 and 1085.8 cm−1. The different scattering geometries were utilized to study the directional dependence of the dipolar phonons. Two peaks at 703.6 and 1093.7 cm−1. were the quasi-TO and LO modes, respectively. Both the frequency and the intensity of the phonons increase with decreasing temperature. The mode at 682.6 cm−1 was examined in more detail at several temperatures.

Previous Raman scattering studies of the effect of hydrogen on the atomic network disorder in various hydrogenated amorphous silicon (a-Si:H) materials resulted in contradicting conclusions. We resolve these contradictions by showing that the surface and the bulk of a-Si:H films can behave differently due to their different hydrogen contents. In particular, we establish that hydrogen has a relatively moderate effect in improving the short-range order but a profound effect in improving the intermediate-range order of the atomic network.

Films of bamboo-like carbon nanotubes (BCNTs) were grown directly on copper substrates by sulfur-assisted hot filament chemical vapor deposition (HFCVD). The effects of substrate temperature and growth time over the BCNT structure were investigated. The films were characterized by scanning electron microscopy (SEM), Raman spectroscopy (RS), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and electron field emission (EFE) studies. SEM and Raman characterization indicate a transition from the growth of microcrystalline diamond to the growth of a dense entangled network of carbon nanotubes or fibers as the substrate temperature is increased from 400 to900°Cthat is accounted for by the base growth model. TEM images show that the nanotubes have regular arrays of nanocavities. These BCNTs show good electron field emission properties as other carbon films.

We report here a study of the Raman spectra of ternary Cu–In–S and Cu–In–Se polycrystalline film compounds as a function of the x=[In]/{Cu]+[In]} ratio. Using these spectra we were able to identify, with high resolution in x, the phases present in the films. We found that the single phase of chalcopyrite CnInSe2 exists over the fairly wide composition range of 0.48⩽x⩽0.55, and that the lattice disorder increases with the increase of In content. No such single phase range was found for the Cu–In–S films. Considering the electrical properties of these materials around x=0.5, it is concluded that the native defect model accounts for the electrical properties of the Cu–In–Se films but does not account simply for the electrical properties of the Cu–In–S films.

Boron carbonitride nanotubes (BCNNTs) were grown with high yield by arc discharge without catalyst particles or pre-grown template nanostructures. Two types of nanotubes (NTs) were formed: thin NTs with diameters of 10–15 nm and thick NTs with diameters of 25–50 nm, all multiwall. Transmission electron microscopy, electron energy loss spectroscopy, and Raman spectroscopy analyses indicate that the thin NTs are carbon NTs (CNTs) while the thick NTs are BCNNTs wrapped around CNTs. The growth kinetic appears to be faster for CNTs than for BCNNTs. Through the concerted substitution of B and N for C in the in situ grown CNTs, template growth of BCNNTs follows the CNTs growth without causing topological changes.

Nanocrystalline diamond (NCD) thin films offer applications in various fields, but the existing synthetic approaches are cumbersome and destructive. A major breakthrough has been achieved by our group in the direction of a non-destructive, scalable, and economic process of NCD thin-film fabrication. Here, we report a cheap precursor for the growth of nanocrystalline diamond in the form of paraffin wax. We show that NCD thin films can be fabricated on a copper support by using simple, commonplace paraffin wax under reaction conditions of Hot Filament Chemical Vapor Deposition (HFCVD). Surprisingly, even the presence of any catalyst or seeding that has been conventionally used in the state-of-the-art is not required. The structure of the obtained films was analyzed by scanning electron microscopy and transmission electron microscopy. Raman spectroscopy and electron energy-loss spectroscopy recorded at the carbon K-edge region confirm the presence of nanocrystalline diamond. The process is a significant step towards cost-effective and non-cumbersome fabrication of nanocrystalline diamond thin films for commercial production.

We have studied diamond films grown by electron cyclotron resonance-assisted chemical vapor deposition (ECR-CVD) at low pressure (1.0 Torr) and temperatures (550–700 °C). These films were grown on seeded Si (111) substrates with different diamond seed densities (0.225, 1.5, 2.3, and 3.1 × 109 nuclei/cm2). Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy (RS) were employed to investigate the crystalline quality, diamond yield, and stresses developed in the films as a function of seeding density. Thermal interfacial stress, interactions across grain boundaries, and internal stress were considered in order to account for the total stress observed from the Raman band. We present correlations among seed density, relative amount of non-sp3 phase, O/C ratio, and total intrinsic stress.

We employed in situ ellipsometry to monitor and study the nucleation and growth processes of diamond thin films fabricated by chemical vapor deposition. The films were grown on Si substrates in a hot filament chemical vapor deposition (HFCVD) system. We monitored the effective extinction coefficient (k) at 1.96 eV of the diamond films during growth through ellipsometry. The behavior of this parameter was found to be reproducible, making it suitable as a basis for dividing the deposition process into intervals. The film growth was aborted at various k values yielding diamond film samples that represent snapshots of the growth process at different stages. These films were removed for ex situ characterization using Raman spectroscopy and scanning electron microscopy (SEM). These characterizations were used to correlate the ellipsometric data with film microstructure, enabling us from now on to monitor the diamond film growth in real time and to design experiments targeted at modifying the film microstructure by changing growth parameters in the middle of film fabrication.

We studied the effects of low-energy electron bombardment during diamond growth over the film crystalline quality and morphology. The film growth was monitored via the effective extinction coefficient (k) at 1.96 eV with in situ ellipsometry, in order to determine the developmental stage of the film in real time. Taking advantage of this in situ monitoring, we triggered the electron bombardment over the growing surface at different growth stages and studied the corresponding induced changes in film morphology and crystalline quality. Ex situ Raman spectroscopy and scanning electron microscopy (SEM) were also employed to evaluate the crystalline quality and the morphology of the grown films, respectively. We found that electron bombardment can be used to control the surface morphology of the films (triangular, pyramidal, square, amorphous). The results also indicate that applying the electron bombardment over the diamond film during the whole time of growth is detrimental to its crystalline quality and favors the formation of non-sp3 carbon. However, when the electron bombardment is triggered just after high quality scattered diamond crystallites have formed, the resulting film is of similar quality as those grown without bombardment. Therefore, properly chosen and triggered electron bombardment during diamond growth by chemical vapor deposition (CVD) can be used to control the film morphology while maintaining the film crystalline quality.

Electron field emission measurements have been performed on thin film cold cathode materials grown, on molybdenum, by a modified MPACVD diamond process. Specifically the modification is due to the addition of nitrogen and oxygen, in varying ratios, during the diamond growth phase. Characterization using Raman spectroscopy shows features at 1190, 1330 and 1550 cm−1. A simple triode device was fabricated for electron emission characterization. KAPTON® film is used as the insulating layer and a Mo mesh is used as the extraction gate electrode. The collector is an indium tin oxide (ITO) coated glass plate which is positively biased with respect to the gate electrode. Field emission characteristics have shown current measurements of greater than I microamp for fields of 40 V/micron. Gate currents are typically 1000 times greater than the emitted current. Issues currently being addressed include improvement in the total emitted current, current stability and device failure. We also present field emission measurements on diamond films grown by HFCVD.

Hydrogenated amorphous silicon (a-Si:H) films prepared by the glow discharge (GD) technique show superior optoelectronic properties over those prepared by rf sputtering (RFS). To find out whether this is associated to structural differences in the amorphous network, we have carried out a comprehensive comparison of the Raman spectra of the two types of films grown at different substrate temperatures. The use of two properly chosen excitation radiations allowed the observation of the Raman spectra from the near surface versus that from the bulk of the films. The results show that the short-range order in the bulk of GD films is close to that of the ideal tetrahedral network, having an rms bond angle deviation (Δθ) of ≈9°. In contrast, the smallest value of Δθfound in the RFS films was ≈15°. There is also a short-range order inhomogeneity in both sets of materials that can be reduced significantly by selecting the appropriate substrate temperature. The intermediate-range disorder is relatively small and uniform in GD films, while large differences exist in this parameter between the surface and bulk of RFS films. In general, the results indicate that the short-range order and the inhomogeneity in intermediate-range order present in the RFS films cannot be improved to equal those of GD materials by annealing at temperatures low enough that no substantial hydrogen effusion occurs. These structural differences are argued to be the reasons for the superior phototransport properties of GD over RFS materials and are interpreted in terms of the differences between the two deposition processes.

Nano-size barium strontium titanate Ba0.7Sr0.3TiO3 (BST) maize-bead?like structures were conformally coated on bamboo-like carbon nanotubes (BCNTs) grown on copper substrates. Initially BCNTs were fabricated by hot-filament chemical vapor deposition (HF-CVD) techniques on Cu substrates. Later, BST was deposited on BCNT/Cu by pulsed laser deposition (PLD) techniques. Surface morphology, cross-sectional image and topography of the BCNTs and BCNT-BST maize-like nanostructures were investigated by X-ray, field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy and tunneling electron microscopy (TEM) techniques. BST-BCNT hybrid structures provide an additional degree of freedom to interconnect the oxides, which in turn provides [3D] geometry for functionality. There had been a popular misconception that oxides cannot grow on CNT at high temperature; this long-standing problem has now been solved. The present unregistered nanostructures can be used as sensors; however, if these structures are made as registered arrays, they can be used as nonvolatile memory elements and high-energy density capacitors.

Free standing graphene-diamond hybrid films have been fabricated using saturated hydrocarbon polymers as seeding material by hot filament chemical vapor deposition technique. The films are characterized with x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). The XRD shows the characteristic diffraction peaks of both diamond and graphene. The Raman spectrum shows the characteristic band of diamond at 1332 cm−1 and D, G, and 2D bands of graphene at 1349, 1592, and 2687 cm−1, respectively. Both SEM and TEM depict the presence of diamond and graphene in the films. The EELS recorded in the carbon K-edge region also shows the signature peaks of diamond and graphene. The free standing hybrid films exhibit a remarkably low turn-on field of about 2.4 V/μm and a high emission current density of 0.1 mA/cm2. Furthermore, emission currents are stable over the period of 7 days. The superior field emission...

We synthesized sp3-rich crystalline tubular structures, referred to as diamond nanotubes (DNTs), by hot-filament chemical vapor deposition and characterized them using SEM, TEM, EELS, and Raman spectroscopy. The images and spectra indicate the formation of DNTs with internal diameter of about 7–10 nm and external diameter of about 20–30 nm. During the fabrication process, CNTs form first and give way to the synthesis of DNTs. The DNTs show good field emission properties and enhanced temporal stability as compared to CNTs.

The room-temperature photosensitivity of sulfur-doped micro-, submicro-, and nano-crystalline diamond films synthesized by hot-filament chemical vapor deposition was studied. The structure and composition of these diamond materials were characterized by Raman spectroscopy, scanning electron microscopy, and x-ray diffraction. The ultraviolet (UV) sensitivity and response time were studied for the three types of diamond materials using a steady-state broad UV excitation source and two pulsed UV laser radiations. It was found that they have high sensitivity in the UV region (as high as 109 s−1 mV−1 range), a linear response in a broad spectral range below 320 nm, photocurrents around ∼10−5 A, and a short response time better than 100 ns, which is independent of fluency intensity. A phenomenological model was applied to help understand the role of defects and dopant concentration on the materials’ photosensitivity.

Diamond has many potential electronic applications, but the diamond seeding methods are generally harsh on the substrates rendering them unsuitable for integration in electronics. We report a non-abrasive, scalable and economic process of diamond film seeding using kitchen-wrap polyethylene employing hot filament chemical vapour reaction of H2S/CH4/H2 gas mixtures on Cu substrates. The fabricated diamond films were characterized with scanning electron microscopy, transmission electron microscopy and Raman spectroscopy, which confirm that the deposited film consists of a microcrystalline diamond of size in the range 0.5–1.0 µm. The synthesized diamond films exhibit a turn-on field of about 8.5 V µm−1 and long-term stability. Diamond film synthesis using polyethylene will enable the integration of diamond heat sinks into high-power and high-temperature electronic devices.

Films of bamboo-like carbon nanotubes (BCNTs) were grown directly on Cu substrates by hot filament chemical vapor deposition requiring no catalysts for growth. This is an efficient technique that yields a large density of active sites on the battery electrode. The thin films were characterized by scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The electrochemical properties of these BCNTs were studied by cyclic voltammetry (CV) and charge-discharge measurements. CV results indicate the formation of a solid electrolyte interface. The initial discharge capacity was found to be 880 μAh cm -2 μm -1 , which is greater than the volumetric theoretical capacity of graphite, i.e., 84 μAh cm -2 μm -1 . The reversible capacity remains at 205 μAh cm -2 μm -1 after ten cycles. The nanocavities of the BCNTs appear to have a significant role in the large capacity for reversible Li insertion.

We have studied a set of diamond films grown at low temperatures and pressures by electron cyclotron resonance (ECR)-assisted chemical vapor deposition (CVD). These films were grown on Si (100) substrates at temperatures ranging between 550 and 710 °C and pressures ranging between 1 and 2 Torr. Raman spectroscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were employed to investigate the crystalline quality, diamond yield, and stresses developed in these films. Our Raman lineshape analysis indicates that most of the diamond films exhibit a net compressive stress. An estimate of the net stresses developed in these films was made by adding the thermal interfacial stress component to the calculated stress developed at the grain boundaries from the X-ray analysis. It was found that the residual stress is compressive in nature, but less compressive than that calculated from the Raman shift. The net stress exhibits a strong correlation with the relative amount of non-sp3 phase, thus implying that the non-sp3 phase is causing the measured excess compressive stress. However, the crystalline quality of the diamond phase improves as the overall non-sp3 component increases, thus indicating a process analogous to phase segregation within the films. These results indicate that the source of the excess compressive stress is non-sp3-bonded carbon accumulated at the grain boundaries.

Photoluminescence, optical absorption and Raman techniques have been used to study the defects generated by the thermochemical reduction in calcia stabilized zirconia (CaSZ) and yttria stabilized zirconia (YSZ) single crystals. The results point out the oxygen vacancies, their aggregates and associated complex defects as the main defects involved in the reduction process.