Structure of the silver containing diamond like carbon films: Study by multiwavelength Raman spectroscopy and XRD

In the present study structure of silver containing diamond like carbon (DLC:Ag) films deposited by reactive magnetron sputtering was investigated by X-ray diffractometry (XRD) and multiwavelength Raman spectroscopy. In the case of the DLC:Ag films containing low amount of silver, crystalline silver oxide prevails over silver. While at higher Ag atomic concentrations formation of the silver crystallites of the different orientations was observed. Surface enhanced Raman scattering (SERS) effect was detected for high Ag content in the films. For UV excited Raman spectra sp³ bonded carbon related Raman scattering T peak at ~ 1060 cm^− 1 was detected only for the films with the highest amount of silver (34.3 at.%). The dependence of the Raman scattering spectra parameters such as position of the G peak, G peak full width at half maximum (FWHM(G)), D/G peak area ratio on Ag atomic concentration in DLC:Ag film as well as Raman scattering spectra excitation wavelength were studied. The dependence on Ag amount in film was more pronounced in the case of the Raman scattering spectra excited by higher wavelength laser beam, while in the case of the spectra excited by 325 nm and 442 nm laser beams only weak dependence (or no dependence) was observed. Overall tendency of the decrease of the dispersion of the G peak with the increase of Ag atomic concentration was found. Thus sp³/sp² bond ratio in DLC:Ag film decreased with the increase of Ag atomic concentration in the films.     

Sp3/sp2 character of the carbon and hydrogen configuration in micro- and nanocrystalline diamond

Hot filament and microwave plasma CVD micro- nanocrystalline diamond films are analysed by visible and ultra-violet excitation source Raman spectroscopy. The sample grain size varies from 20 nm to 2 μm. The hydrogen concentration in samples is measured by SIMS and compared to the grain size, and to the ratio of sp² carbon bonds determined by Raman spectroscopy from the 1332 cm^− 1 diamond peak and the sp² 1550 cm^− 1 G band. Hydrogen concentration appears to be proportional to the sp² bonds ratio. The 3000 cm^− 1 CH_x stretching mode band intensity observed on the Raman spectra is decreasing with the G band intensity. Thermal annealing modifies the sp² phase structure and concentration, as hydrogen outdiffuses.     

X-ray photoemission spectroscopy of nitrogen-doped UNCD/a-C:H films prepared by pulsed laser deposition

Nitrogen-doped ultrananocrystalline diamond (UNCD)/hydrogenated amorphous carbon (a-C:H) films were deposited by pulsed laser deposition (PLD). Nitrogen contents in the films were controlled by varying a ratio in the inflow amount between nitrogen and hydrogen gases. The film doped with a nitrogen content of 7.9 at.% possessed n-type conduction with an electrical conductivity of 18 Ω^? 1 cm^? 1 at 300 K. X-ray photoemission spectra, which were measured using synchrotron radiation, were decomposed into four component spectra due to sp², sp³ hybridized carbons, C=N and C–N. A full-width at half-maximum of the sp³ peak was 0.91 eV. This small value is specific to UNCD/a-C:H films. The sp²/(sp³ + sp²) value was enhanced from 32 to 40% with an increase in the nitrogen content from 0 to 7.9 at.%. This increment probably originates from the nitrogen incorporation into an a-C:H matrix and grain boundaries of UNCD crystallites. Since an electrical conductivity of a-C:H does not dramatically enhance for this doping amount according to previous reports, we believe that the electrical conductivity enhancement is predominantly due to the nitrogen incorporation into grain boundaries.     

Structure and friction properties of laser-patterned amorphous carbon films

In the paper we report on laser surface modification of super hard micrometer-thick tetrahedral amorphous carbon (ta-C) films in the regime of single-shot irradiation with KrF laser pulses (wavelength 248 nm, pulse duration 20 ns), aimed at investigations of the laser-induced changes of the structure and surface properties of the ta-C films during graphitization and developing ablation processes. Based on the analysis of surface relief changes in the laser-irradiated spots, characteristics of the single-shot graphitization and ablation of the 2-μm-thick ta-C film are determined. Using Raman spectroscopy, it is found that during the graphitization regime the structure transformation and growth of graphitic clusters occur according to the relationship I(D)/I(G) ∝ L_a², but after reaching the ablation threshold the Tuinstra-Koenig relationship I(D)/I(G) ∝ 1/L_a describes further growth of the graphitic cluster size (L_a) during developing ablation of the ta-C film with nanosecond pulses. The maximal size of graphitized clusters is estimated as L_a = 4–5 nm. The studies of nanomechanical properties of laser-patterned ta-C films using the lateral force microscopy and force modulation microscopy have evidenced lower friction forces (between diamond-coated tips and film surface) and lower stiffness in the laser-graphitized areas. The laser-produced graphitic layer acts as a solid lubricant during sliding of the diamond-coated tips on the ta-C film surface in ambient air (~ 50% RH); the lubricating role of adsorbed water layers is suggested to be significant at low loads on the tips. The results of this work demonstrate that the UV laser surface texturing in the regime of graphitization is a promising technique to control the friction and surface elasticity of super hard amorphous carbon films on the micro and nanoscale.     

Ultraviolet and visible Raman spectroscopies of the graphitic BCx phases

Ultraviolet (UV) Raman and visible Raman spectroscopies were applied to study the graphitic BC_x (g-BC_x) phases. The Raman spectra of the g-BC_x phases excited with UV laser at 244 nm have one main peak: a G peak (approximately at 1590 cm^? 1), and do not have the D peak (around 1350 cm^? 1) characteristic for Raman spectra of disordered graphitic phases. The D peak can be detected in all g-BC_x phases when green (534 nm) or near-infrared (785 nm) lasers are used for Raman scattering excitation. The positions of the G and D peaks were found to be independent (within the experimental errors) of the B/C ratio. The pattern of the peaks in UV Raman spectra of g-BC_2.1 phase indicates that the additional peaks centered at 1089 cm^? 1 should be assigned to the E_g mode of B₄C vibration rather than to the T mode characteristic to amorphous graphite. The high signal-to-noise (S/N) ratio and lack of fluorescence of the UV Raman spectra allow an accurate measure of bandwidth and frequency of the G peaks.     

Crystal structure,luminescent properties and white light emitting diode application of Ba3GdNa(PO4)3F:Eu2+ single-phase white light-emitting phosphor

A series of single-phase white-light-emitting phosphors, Eu²⁺-activated Ba₃GdNa(PO₄)₃F phosphors were synthesized by solid-state reactions. The crystal structure of Ba₃GdNa(PO₄)₃F was been identified by Rietveld refinement of X-ray diffraction pattern. The Eu²⁺-activated Ba₃GdNa(PO₄)₃F phosphors exhibit broad excitation spectra from 250 to 420 nm, which matched well with the n-UV LED chips. Under the excitation of 365 nm, the emission spectrum almost covered the entire visible region including two emission bands peaked at 472 nm and 640 nm. Three different Eu²⁺ emission centers in Ba₃GdNa(PO₄)₃F:Eu²⁺ phosphor were confirmed by their fluorescence decay lifetimes. The optimal concentration of Eu²⁺ in Ba₃GdNa(PO₄)₃F:xEu²⁺ was 3 mol% and the corresponding concentration quenching mechanism was verified to be exchange coupling interaction. Furthermore, the white light-emitting diode fabricated with Ba₃GdNa(PO₄)₃F:0.05Eu²⁺ phosphor and a 370 nm UV chip has a CIE of (0.3267, 0.2976) with a color-rendering index of 78.4 at the CCT of 5287 K.     

Blue light emission from barium doped zinc sulfide nanoparticles

ZnS nanoparticles with Ba²⁺doping have been prepared at room temperature through chemical route, namely the chemical precipitation method. The nanostructures of the prepared nanoparticles have been analyzed using X-ray diffraction (XRD) for phase analysis, Field emission scanning electron microscope (FESEM) for the morphological characterization, UV–Vis–NIR spectrophotometer for determining band gap energy and fluorescence spectroscopy for determining the emission wave length. The sizes of as prepared nanoparticles are found to be in 9–10 nm range. FESEM morphology shows the formation of nanostructure of ZnS samples. The value of optical band gap has been found to be in range 4.10–4.63 eV. Room temperature photoluminescence (PL) spectrum of the undoped sample exhibits emission in the blue region with multiple peaks under UV excitation. On the other hand, the Ba²⁺ doped ZnS samples exhibit visible light emissions under the same UV excitation wavelength of 310 nm.     

Hydrogen incorporation,bonding and stability in nanocrystalline diamond films

The hydrogen concentration in hot filament and microwave plasma CVD nanocrystalline diamond films is analysed by secondary ion mass spectrometry and compared to the film grain size. The surface and bulk film carbon bonds are analysed respectively by X-ray photoelectron spectroscopy (XPS) and ultra-violet Raman spectroscopy. XPS results show the presence of the hydrogenated p-type surface conductive layer. The respective intensities of the 1332 cm^− 1 diamond peak, of the G and D bands related to sp² phases, and of the 3000 cm^− 1 CH_x stretching mode band, are compared on Raman spectra. The samples are submitted to thermal annealing under ultra-high vacuum in order to get hydrogen out-diffusion. XPS analysis shows the surface desorption of hydrogen. Thermal annealing modifies the sp² phase structure as hydrogen out diffuses.     

Optical properties of impact diamonds from the Popigai astrobleme

Impact diamonds from Popigai astrobleme were found to consist of different carbon phases: cubic and hexagonal diamond with sp³ bonding according to X-ray structural analysis as well as amorphous, crystalline and disordered graphite with sp²-bonding (Raman scattering). The sizes of graphite domains vary from 10 to 100 nm. Fundamental absorption edge for Popigai impact diamonds is shifted ~ 0.5 eV to lower energies in comparison with kimberlite diamonds (5.47 eV) as a result of the lonsdaleite input, in good agreement with ab initio calculations (E_g = 5.34 and 4.55 eV for 3C cubic and 2H hexagonal diamonds, respectively). Yellowish color of impact diamonds is due to Rayleigh light scattering on structural defects whereas graphite is responsible for gray to black coloring. In the mid-IR region there is a multi-phonon absorption of 3C diamond in the 1800 to 2800 cm^− 1 range and some new bands at 969, 1102, 1225, and 1330 cm^− 1 in the one-phonon region. Micro-Raman study shows inclusions of side noncarbon minerals (quartz, magnetite, and hematite) some of which contain Cr^3 + impurity. The vibration modes of cubic diamond and lonsdaleite exhibited in the Raman spectra were elucidated by the first-principles studies. Popigai impact diamonds demonstrate a broad-band luminescence in 2.1, 2.38, and 2.84 eV components similar to that for nanocrystal polycrystalline 3C diamond. All emissions are excited at band-to-band transitions whereas the last two are observed also at excitation into 2.4 and 3.0 bands supposedly as a result of intracenter processes within the H3(NVN) and NV⁰ centers.     

Mechanical and electrical properties of micron-thick nitrogen-doped tetrahedral amorphous carbon coatings

The effect of nitrogen doping on the mechanical and electrical performance of single-layer tetrahedral amorphous carbon (ta-C:N) coatings of up to 1 μm in thickness was investigated using a custom-made filtered cathode vacuum arc (FCVA). The results obtained revealed that the hardness and electrical resistance of the coatings decreased from 65 ± 4.8 GPa (3 kΩ/square) to 25 ± 2.4 GPa (10 Ω/square) with increasing nitrogen gas ratio, which indicates that nitrogen doping occurs through substitution in the sp² phase. Subsequent AES analysis showed that the N/C ratio in the ta-C:N thick-film coatings ranged from 0.03 to 0.29 and increased with the nitrogen flow rate. Variation in the G-peak positions and I(D)/I(G) ratio exhibit a similar trend. It is concluded from these results that micron-thick ta-C:N films have the potential to be used in a wide range of functional coating applications in electronics.     

Enhanced cycling stability of Ni-MH battery by depositing amorphous carbon film on the Ti1.4V0.6Ni negative electrode

Amorphous carbon (a-C) films with various thicknesses depending on the reaction time are deposited on the surface of Ti_1.4V_0.6Ni alloy electrodes for Ni-MH (nickel-metal hydride) battery by radio frequency plasma enhanced chemical vapor deposition (RF-PECVD). With the increasing deposition time, the Raman spectra show a gradually disordered sp²-bonding change of the films and the changing trend of sp²/sp³ is obtained by X-ray photoelectron spectroscopy. The a-C film of depositing for 30 min with the thickness of 400 nm shows a favorable stability in alkaline electrolyte, the capacity is enhanced by 36.2% after 50 cycles than the bare electrode, and the charge voltage is 80 mV lower than the bare one. The a-C film with high sp²-bonded carbon content effectively reduces the charge transfer resistance, and as a coating layer, the dissolution of V of the alloy is also inhibited. In particular, to get a proper discharge voltage and a stable capacity simultaneously, covering completely and an appropriate thickness of the a-C film are crucial for an expected performance.     

Electro-optical and electrochemical properties of an ionic polyacetylene derivative with azobenzene anisole moieties

An ionic polyacetylene derivative with azoanisole moieties was prepared by the activated polymerization of 2-ethynylpyridine by using 4-[4-(9-bromononyloxy)phenylazo]anisole without any additional initiator or catalyst in high yield. The chemical structure of poly[2-ethynyl-N-(p-methoxyphenylazophenyl)oxynonylpyridinium bromide] (PEMPB) was characterized by instrumental methods such as NMR (¹H and ¹³C), IR, UV–vis spectroscopies to have a conjugated polymer backbone system with the designed azobenzene moieties as substituents. This polymer was completely soluble in organic solvents and well processible. The electrochemical and electro-optical properties of PEMPB were studied. The cyclovoltammograms of this polymer exhibited the irreversible electrochemical behaviors between the oxidation and reduction peaks. The oxidation current density of PEMPB versus the scan rate is approximately linear relationship in the range of 30 mV/s–120 mV/s. The exponent of scan rate, x value of PEMPB, is found to be 0.6. The absorption spectrum starts around 700 nm and shows a characteristic absorption band at visible region of 464 nm due to the π → π* interband transition of the polymer backbone, which is a peak of the conjugated polyene backbone. The photoluminescence spectrum showed that the PL peak is located at 539 nm corresponding to the photon energy of 2.30 eV.     

Synthesis and photoluminescence properties of the high-brightness Eu3+-doped Sr3Y(PO4)3 red phosphors

A series of red-emitting phosphors Eu³⁺-doped Sr₃Y(PO₄)₃ have been successfully synthesized by conventional solid-state reaction, and its photoluminescence properties have been investigated. The excitation spectra reveal strong excitation bands at 392 nm, which match well with the popular emissions from near-UV light-emitting diode chips. The emission spectra of Sr₃Y(PO₄)₃:Eu³⁺ phosphors exhibit peaks associated with the ⁵D₀ → ⁷F_J (J = 0, 1, 2, 3, 4) transitions of Eu³⁺ and have dominating emission peak at 612 nm under 392 nm excitation. The integral intensity of the emission spectra of Sr₃Y_0.94(PO₄)₃:0.06Eu³⁺ phosphors excited at 392 nm is about 3.4 times higher than that of Y₂O₃:Eu³⁺ commercial red phosphor. The Commission Internationale de l’Eclairage chromaticity coordinates, the quantum efficiencies and decay times of the phosphors excited under 392 nm are also investigated. The experimental results indicate that the Eu³⁺-doped Sr₃Y(PO₄)₃ phosphors are promising red-emitting phosphors pumped by near-UV light.     

Raman spectroscopy investigation of the H content of heated hard amorphous carbon layers

We revisit here how Raman spectroscopy can be used to estimate the H content in hard hydrogenated amorphous carbon layers. The H content was varied from 2 at.% to 30 at.%, using heat treatments of a a-C:H, from room temperature to 1300 K and was determined independently using ion beam analysis. We examine the correlation of various Raman parameters and the consistency of their thermal evolution with thermo-desorption results. We identify a weak band at 860 cm^− 1 attributed to H bonded to C(sp²). We show that the H_D/H_G parameter (height ratio between the D and G bands) is quasi-linear in the full range of H content and can thus be used to estimate the H content. Conversely, we show that the m/H_G parameter (ratio between the photoluminescence background, m, and the height of the G band), often used to estimate the H content, should be used with care, first because it is sensitive to various photoluminescence quenching processes and second because it is not sensitive to H bonded to C(sp²).     

Optimization,synthesis and characterization of vanadium-substituted thick-walled three-dimensional SBA-16

A systematic study was carried out to examine the viable synthesis condition at high acidic condition for the direct incorporation of a high level of vanadium into the 3D cubic arrangement of SBA-16 molecular sieves. The extent of mesopore structural ordering was determined by X-ray diffraction, N₂ physisorption, SEM and TEM analysis. The coordination and nature of the V sites were characterized by FT-Raman, electron spin resonance, ²⁹Si nuclear magnetic resonance spectroscopy, UV–visible diffuse reflectance spectroscopy and NH₃–TPD analysis. The surface area of calcined V-SBA-16 was ～1000 m²/g, while the mesopore volume of the SBA-16 cage ranged from 0.3 to 0.6 cm³g^?1. The pore size distribution was ～3.0 nm with a wall thickness of ～9.7 nm at the maximum. The Si/V ratios as determined by ICP-OES technique was varied from 438 to 8, respectively. The calcined samples exhibited promising catalytic activity in the oxidation of styrene with tert-butyl hydroperoxide as an oxidant.     

Substrate temperature effects on the microhardness and adhesion of diamond-like thin films

Diamond-like films were deposited on silicon substrates by r.f. plasma-enhanced chemical vapor deposition from gas methane. In this study, the substrate temperature, T_S, was varied in a wide range from 20 to 370°C while maintaining fixed other important process parameters such as r.f. power (70 W) or pressure (2.5 Pa). The increase of T_S causes an increase of the sp²/(sp²+sp³) bonded carbon ratio and a decrease of the hydrogen content. These changes produce a great modification of the mechanical properties: microhardness, friction coefficient and adhesion. The variations of mechanical properties with T_S correlate well with the sp²/(sp²+sp³) bonded carbon ratio and the hydrogen content in the films showing a gradual transformation of the diamond-like structure into a more sp²-rich one.     

Effects of diamond-like carbon in TPD-Alq3 doped PVK organic light-emitting devices

Effects of an ultrathin (~ 1 nm) diamond-like carbon (DLC) layer in single-layer organic light-emitting devices (OLEDs) that consist of ITO/(TPD-Alq₃ doped PVK)/Al were investigated. DLC layers deposited by using Nd:YAG laser at laser wavelengths of 355 nm were high in sp³ content and resistivity (DLC_UV) while that of 1064 nm laser were lower in sp³ content and resistivity (DLC_IR), as characterized by Raman spectroscopy and resistivity measurements. Although emission were obtained for all the devices, only the device of ITO/DLC_UV/(TPD-Alq₃ doped PVK)/Al exhibited enhanced current density and brightness with lower turn-on voltage as compared to a standard device. Devices of ITO/DLC_IR/(TPD-Alq₃ doped PVK)/Al and ITO/(TPD-Alq₃ doped PVK)/DLC_UV/Al showed poor current and brightness characteristics but failed at higher applied voltage. The enhance performance of device with high resistivity/sp³ DLC film suggests the mechanisms of barrier reduction by sufficiently thin insulating layer which increase the probability of tunneling of carriers at ITO and PVK interface.     

A novel 3D silver(I) coordination polymer exhibiting unprecedented μ3- and μ4-bonding modes of 2-aminopyrazines

The unprecedented μ₃- and μ₄-bonding modes of NH₂pyz (NH₂pyz = 2-aminopyrazine) are observed for the first time in a novel 3D Ag(I) coordination polymer [Ag₇(NHpyz)₆(ClO₄)]_n (1) which was obtained by reaction of Ag₂O, NH₂pyz and NaClO₄ in H₂O/CH₃OH/NH₃ media under ultrasonic treatment. Compound 1 is a 3D framework with infinite 1D Ag belts incorporating diverse Ag···Ag interactions. Moreover, 1 exhibits photoluminescence maximized at 494 nm upon 300 nm excitation at room temperature, which may be mainly assigned to ligand-to-metal charge transfer (LMCT) mixed with metal-centered (d-s/d-p) transitions. Semiconducting behavior of 1 was also measured at room temperature with σ value of 6.78 × 10^?6 S cm^?1.     

The production of carbon particles of different shapes produced by the chlorination of Cr(C5H5)2

Carbon particles have been obtained by the chlorination of chromocene (Cr(C₅H₅)₂). Changes in their morphology and micro-nanostructure have been monitored at two different temperatures. At 400 °C, filled materials (tubes and spheres) and agglomerated round particles are formed, whereas at 900 °C closed-end tubes, hollow and solid spheres were produced. Transmission electron microscopy shows that these particles are formed of highly disordered graphene-like layers, which is confirmed by the absence of the 2D and 2G bands in the Raman spectrum. The calculated in-plane correlation length of these graphene-like layers is 1.2 ± 0.1 nm. In all the carbon particles, electron energy-loss spectroscopy shows a very similar sp² carbon bonding content (89–98%) and mass density ranging from 1.6 to 1.8 g/cm³, both below standard graphite. Textural studies performed on the sample prepared at 900 °C show Type II adsorption isotherms with a surface area of 694 m²/g.     

Effect of substrate temperature on microstructure and optical properties of nanocrystalline alumina thin films

Aluminum oxide (Al₂O₃) thin films were deposited on silicon (100) and quartz substrates by pulsed laser deposition (PLD) at an optimized oxygen partial pressure of 3.0×10^?3 mbar in the substrate temperatures range 300–973 K. The films were characterized by X-ray diffraction, transmission electron microscopy, atomic force microscopy, spectroscopic ellipsometry, UV–visible spectroscopy and nanoindentation. The X-ray diffraction studies showed that the films deposited at low substrate temperatures (300–673 K) were amorphous Al₂O₃, whereas those deposited at higher temperatures (≥773 K) were polycrystalline cubic γ-Al₂O₃. The transmission electron microscopy studies of the film prepared at 673 K, showed diffuse ring pattern indicating the amorphous nature of Al₂O₃. The surface morphology of the films was examined by atomic force microscopy showing dense and uniform nanostructures with increased surface roughness from 0.3 to 2.3 nm with increasing substrate temperature. The optical studies were carried out by ellipsometry in the energy range 1.5–5.5 eV and revealed that the refractive index increased from 1.69 to 1.75 (λ=632.8 nm) with increasing substrate temperature. The UV–visible spectroscopy analysis indicated higher transmittance (>80%) for all the films. Nanoindentation studies revealed the hardness values of 20.8 and 24.7 GPa for the films prepared at 300 K and 973 K respectively.