Friction force microscopy study of annealed diamond-like carbon film

In this paper we introduce mechanical and structural characteristics of diamond-like carbon (DLC) films which were prepared on silicon substrates by radio frequency (RF) plasma enhanced chemical vapor deposition (PECVD) method using methane (CH₄) and hydrogen (H₂) gas. The films were annealed at various temperatures ranging from 300 to 900 °C in steps of 200 °C using rapid thermal processor (RTP) in nitrogen ambient. Tribological properties of the DLC films were investigated by atomic force microscopy (AFM) in friction force microscopy (FFM) mode. The structural properties of the films were obtained by high resolution transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The wettability of the films was obtained using contact angle measurement. XPS analysis showed that the sp³ content is decreased from 75.2% to 24.1% while the sp² content is increased from 24.8% to 75.9% when the temperature is changed from 300 to 900 °C. The contact angles of DLC films were higher than 70°. The FFM measurement results show that the highest friction coefficient value was achieved at 900 °C annealing temperature.     

Field emission enhancement of carbon nitride films by annealing with different durations

Magnetron sputtered carbon nitride films (CN_x) were annealed at 750 °C for periods from 30 to 120 min. Effects of annealing with different durations on the field emission of CN_x films were investigated and related to the variations of chemical bonding and surface morphology induced by annealing. The results show that annealing effectively enhances field emission ability of the CN_x films and that the threshold field was lowered from 13 to 5 V/μm. The measurements of Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) indicated that annealing leads to a loss of N content and to formation of more graphite-like sp² C clusters in the films, and simultaneously the film surface becomes rougher after annealing, all of which is attributed to the increased film field emission. A large number of sp² C clusters with good conductivity enables tunneling in the film, making electron emission easier, and moreover, a rougher surface also improves the field enhancement factor of the films. However, continuing to increase annealing time eventually lowers the field emission of the films.     

Synthesis of carbon nano-fibers on p-Si having improved temperature sensing capability

Synthesis of an innovative material for temperature sensor based on carbon nano-fibers (CNFs) on p-Si substrates has been demonstrated. The CNF films were characterized by SEM, Raman and FTIR studies. First order Raman spectra indicated a G band at ～1597 cm^?1 corresponding to the E_2g tangential stretching mode of an ordered graphitic structure with sp² hybridization and a D band located ～1350 cm^?1 originated from disordered carbon. Gold fingers were deposited on the p-Si/CNF surface for resistance measurement. Temperature sensing properties were also investigated critically. Resistance changes with temperature (ΔR/R) in p-Si/CNF films are found to be significantly large 30–60% Very stable, reproducible and improved temperature sensing properties would make this material superior to commonly available temperature sensors.     

The effects of annealing temperature on characteristics of UBMS sputtered CNx films for protective coatings

The carbon nitride (CNx) films have been prepared by unbalanced magnetron sputtering (UBMS) at room temperature. The deposited CNx films have been post-annealed at temperatures ranging from 300 °C to 700 °C in increments of 200 °C using rapid thermal annealing (RTA) equipment in vacuum ambient. We investigated the effects of rapid thermal annealing on the structural, surface, and physical properties of CNx films for application of protective coatings. As the result, the increasing annealing temperature led to a decline in physical properties of CNx films such as hardness, elastic modulus, adhesion, frication coefficient, and surface roughness, however it is attributed to the improvement of the residual stress in the film. These results are related to the ordering of sp² bonded clustering and the increase of disordered graphite domain by the desorption of N contents in the films, Specially, high annealing temperature over 700 °C is attributed to the graphitization of film.     

Performances of a-Si:H films produced by hot wire plasma assisted technique

This work reports on the performances of undoped and doped amorphous/nanocrystalline silicon films grown by hot wire plasma assisted technique. The structure (including the presence of several nanoparticles with sizes ranging from 5 nm to 50 nm), composition (oxygen and hydrogen content) and transport properties of the films are highly dependent on the temperature of the filament and on the hydrogen dilution. The undoped films grown under low r.f. power (≈4 mWcm⁻²) and filament temperatures around 1850 K present dark conductivities below 10⁻¹⁰ Scm⁻¹, optical gaps of about 1.6 eV and photosensitivities above 10⁵, (under AM1.5 light intensities), with almost no traces of oxygen content. For the n- and the p-doped silicon films also fabricated under the same conditions the conductivities obtained are of about 10⁻² Scm⁻¹ and 10⁻⁵ Scm⁻¹, respectively.     

Flame synthesis of carbon nano onions using liquefied petroleum gas without catalyst

Densely agglomerated, high specific surface area carbon nano onions with diameter of 30–40 nm have been synthesized. Liquefied petroleum gas and air mixtures produced carbon nano onions in diffusion flames without catalyst. The optimized oxidant to fuel ratio which produces carbon nano onions has been found to be 0.1 slpm/slpm. The experiment yielded 70% pure carbon nano onions with a rate of 5 g/h. X-ray diffraction, high-resolution electron microscopy and Raman spectrum reveal the densely packed sp² hybridized carbon with (002) semi-crystalline hexagonal graphite reflection. The carbon nano onions are thermally stable up to 600 °C.     

Spectroscopic studies on DLC/TM (Cr,Ag, Ti,Ni) multilayers

The hydrogen-free diamond-like carbon (DLC) films with transition metal (TM = Cr, Ag, Ti, Ni) interlayer (bilayer and multilayer) were deposited on to stainless steel and silicon substrates using pulsed laser deposition technique. Secondary ion mass spectroscopy (SIMS) confirmed that the films were hydrogen free. Incorporation of chromium inter layer reduced the stress value by about 3 GPa as determined by micro Raman spectroscopy. Incorporation of the TM inter layer enhanced the photoluminescence (PL) intensity as compared to the monolithic DLC films. The optical band gap determined by spectroscopic ellipsometry for DLC/TM films was found to be in the range of 1.56–1.67 eV.     

Deposition of B4C/BCN/c-BN multilayered thin films by r.f. magnetron sputtering

Thin films of cubic boron nitride (c-BN) and B₄C/BCN/c-BN multilayers, were deposited by r.f. (13.56 MHz) multi-target magnetron sputtering from high-purity (99.99%) h-BN and a (99.5%) B₄C targets, in an Ar (90%)/N₂ (10%) gas mixture. Films were deposited onto silicon substrates with (100) orientations at 300 °C, with r.f. power density near 7 W/cm². In order to obtain the highest fraction of the c-BN phase, an r.f. substrate bias voltage between − 100 and − 300 V was applied during the initial nucleation process and − 50 to − 100 V during the film growth. Additionally, B₄C and BCN films were deposited and analyzed individually. For their deposition, we varied the bias voltage of the B₄C films between − 50 and − 250 V, and for the BCN coatings, the nitrogen gas flow from 3% to 12%. A 300-nm-thick TiN buffer layer was first deposited to improve the adhesion of all samples. X-ray diffraction patterns revealed the presence of c-BN (111) and h-BN phases. FTIR spectroscopy measurements indicate the presence of a peak at 780 cm^− 1 referred to as “out-of-plane” h-BN vibration mode; another peak at 1100 cm^− 1 corresponds to the c-BN TO mode and the “in-plane” vibration mode of the h-BN at 1400 cm^− 1. BN films deposited at 300 °C at a pressure of 4.0 Pa and under − 150 V of nucleation r.f. bias, applied for 35 min, presented the highest c-BN fraction, near 85%. By using 32 layers, it was possible to deposit a 4.6-μm-thick c-BN film with adequate mechanical properties and good adhesion to the substrate.     

Large “Pillow” Fullerenes Hydrogenated at the Inter‐sheet “Seam”

Abstract

In a previous paper on large “pillow” fullerenes, various systems were described with 12 pentagons connecting 2 parallel hexagonal arrays of benzenoid rings (graphene fragments functioning as the faces of the “pillow”) on top of each other. Additional bonds between these identical arrays formed only from sp²‐hybridized carbon atoms gave rise to hexagons and 12 pentagons along the “seam” or “rim.” High steric strain was associated with curvature around the pentagons due to connections between the 2 pillow faces involving bonds between 2 sp²‐hybridized carbon atoms. The present paper examines similar “quasi‐graphitic” structures in which some carbon atoms of the rim between the two raphene faces have hydrogen atoms attached to them, i.e., have sp³‐hybridization, alleviating thereby some strain.     

The influence of nanosecond pulse laser irradiation on the properties of a-C:H films

Plasma-deposited amorphous hydrogenated carbon (a-C:H) films are determined both by the carbon sp³/sp² bonding ratio and the hydrogen content. As the energy of the bonds C-H (C-C) is considerably smaller than that of CC or CC bonds, so the hydrogen concentration and the physical properties of a-C:H films can be varied by laser irradiation. The properties of produced films were investigated by Rutherford backscattering (RBS) and elastic recoil detection (ERD) spectroscopy, null-ellipsometry, and Raman spectroscopy (RS). It was found that films with higher hydrogen concentration are more sensitive to nanosecond pulse laser irradiation.     

Studying the high-field electron conduction of tetrahedral amorphous carbon thin films by conducting atomic force microscopy

The high-field electron conduction of tetrahedral amorphous carbon (ta-C) thin films substrate has been studied using a conducting atomic force microscope (C-AFM). The ta-C thin films with a high concentration of sp³ bonding (80–90%) were deposited on Si by field arc deposition (FAD). The high-field “conductance” and surface morphology were mapped simultaneously. At low bias, the “conductance” exhibits inhomogeneities on a large scale, presumably due to thickness variations or interface defects. However, at high bias, the small difference in “conductance” due to thickness variations or interface defects was buried by the high intrinsic “conductivity.” It has also been shown that high field causes electric breakdown in these films by converting sp³ bonding to sp² at high electric field.     

Biopolymer-manganese oxide nanoflake nanocomposite films fabricated by electrostatic layer-by-layer assembly

Bio-nanocomposite films based on chitosan and manganese oxide nanoflake have been fabricated via the layer-by-layer (LBL) self-assembly technique. UV–vis absorption spectra showed that the subsequent growth of the nanocomposite film was regular and highly reproducible from layer to layer. X-ray photoelectron spectroscopy (XPS) spectra confirmed the incorporation of chitosan and manganese oxide nanoflake into the films. Scanning electron microscopy (SEM) images revealed that the nanocomposite film had a continuous surface and a layered structure. A sensitive hydrogen peroxide (H₂O₂) amperometric sensor was fabricated with the chitosan–manganese oxide nanoflake nanocompoite film. The sensor showed a rapid and linear response to H₂O₂ over the range from 2.5 × 10^? 6 to 1.05 × 10^? 3 M, with a sensitivity of 0.038 A M^? 1 cm^? 2.     

Structural and optical properties of neodymium-doped lutetium fluoride thin films grown by pulsed laser deposition

Neodymium-doped lutetium fluoride (Nd³⁺:LuF₃) thin films were successfully grown on MgF₂ (0 0 1) substrates by pulsed laser deposition (PLD). It is void of cracks that are otherwise prevalent due to structural phase transitions in Nd³⁺:LuF₃ during thin film deposition and bulk crystal growth. Cathodoluminescence (CL) spectra revealed multiple emission peaks, with a dominant peak in the vacuum ultraviolet (VUV) region at 179 nm. This peak has a decay time of 6.7 ns. The ability to grow high quality Nd³⁺-doped fluoride thin films would enable fabrication of VUV light-emitting devices that will enhance applications requiring efficient VUV light sources.     

Biomolecular urease thin films grown by laser techniques for blood diagnostic applications

Matrix assisted pulsed laser evaporation (MAPLE) was used for growing urease thin films designed for bio-sensor applications in clinical diagnostics. The targets exposed to laser radiation were made from a frozen composite manufactured by dissolving biomaterials in distilled water. We used a UV KrF* (λ = 248 nm, τ_FWHM ? 30 ns, ν = 10 Hz) excimer source for multipulse laser irradiation of the frozen targets cooled with Peltier elements. The laser source was operated at an incident fluence of 0.4 J/cm². Urease activity and kinetics were assayed by the Worthington method that monitors urea hydrolysis by coupling ammonia production to a glutamate dehydrogenase reaction. A decrease in absorbance was measured at 340 nm and correlated with the enzymatic activity of urease. We show that the urease films obtained by MAPLE techniques remain active up to three months after deposition.     

The low temperature synthesis of Al doped ZnO films on glass and polymer using pulsed co-magnetron sputtering: H2 effect

It has been reported that a small amount of hydrogen in argon plasma induces an increase in the crystallite size of the as-deposited films. In addition, control of the hydrogen partial pressure is expected to improve the carrier mobility by increasing the crystallinity of the film (larger crystal size and lower grain boundary effects). Al doped ZnO (AZO) films were deposited by co-CFUBM (closed field unbalanced magnetron) sputtering. The ultimate aim was to deposit transparent films on a polymer substrate with a low electrical resistivity. Therefore, the structural, optical and electrical properties of AZO films were investigated as a function of the hydrogen partial pressure. A minimum resistivity and maximum transparency of 8 × 10^− 4 Ω cm and 88.1% were obtained, respectively. A critical P_H2 was expected to improve the carrier mobility by increasing the crystallinity of the film. However, above this value, conductivity reduced due to the formations of oxides such as ZnO and Al₂O₃ in the AZO films.     

Eggshell- and fur-like microstructures of yttrium silicate film prepared by laser chemical vapor deposition

Yttrium silicate (Y–Si–O) films with eggshell- and fur-like microstructures were prepared by laser chemical vapor deposition using a Nd:YAG laser, and tetraethyl orthosilicate (TEOS) and yttrium dipivaloylmethane (Y(dpm)₃) precursors. Amorphous Y–Si–O films were prepared at deposition temperature below 1200 K. The crystalline Y–Si–O films with mixtures of Y_4.67(SiO₄)₃O and α-Y₂Si₂O₇ phases were obtained at deposition temperature above 1200 K. y-Y₂Si₂O₇ and X1-Y₂SiO₅ minor phases were also formed at a higher deposition temperature. At deposition temperature ranging between 1285 and 1355 K, a dome-like structure covered with fine fur-like projections was formed under a total pressure of 3.5 kPa, whereas an eggshell-like structure 200–300 μm in diameter and 10–20 μm in shell thickness was formed at 7.5 kPa. The deposition rate for the Y–Si–O films with fur- and eggshell-like microstructures reached 300 and 1000 μm h^?1, respectively.     

High-speed deposition of dense,dendritic and porous SiO2 films by Nd: YAG laser chemical vapor deposition

Dense, dendritic and porous SiO₂ films were prepared by laser chemical vapor deposition (LCVD) using a high-power continuous-wave mode Nd: YAG laser (206 W) and a TEOS (tetraethyl orthosilicate) precursor. The effects of laser power (P_L) and total chamber pressure (P_tot) on the microstructure and deposition rate (R_dep) were investigated. Amorphous SiO₂ films were obtained independent of P_L and P_tot. Flame formation was observed between the nozzle and the substrate at P_L > 160 W and P_tot > 15 kPa. At P_L = 206 W, dense, dendritic and porous SiO₂ films were obtained at P_tot < 20 kPa, P_tot = 23 kPa and P_tot > 25 kPa, respectively. The R_dep increased thousands of times under flame formation conditions, the highest R_dep being reached at 1200 μm h^?1, 22,000 μm h^?1 and 28,000 μm h^?1 for the dense, dendritic and porous SiO₂ films, respectively.     

Defects in TiO2 films on p+-Si studied by positron annihilation spectroscopy

Variable-energy positron annihilation spectroscopy has been applied to the study of defects in TiO₂/p⁺-Si structures, in the as-grown state and after annealing in vacuum and in hydrogen, to investigate whether annealing (and film thickness) resulted in an increase of vacancy-type defects in the oxide films. It was found that the concentration of such defects remained unchanged after vacuum annealing for all films studied, but after H₂ annealing more than doubled for 150 nm-thick films, and increased by an order of magnitude for 100 nm-thick films. The nature of the vacancies was examined further by measuring high-precision annihilation lines and comparing them with a reference Si spectrum. The changes observed in the ratio spectra associated with oxygen electrons suggest that the defects are oxygen vacancies, which have been shown to enhance electroluminescence from TiO₂/p⁺-Si heterostructure-based devices.     

Oxygen partial pressure dependence of the structural properties of CdO thin films deposited by a modified reactive vacuum evaporation process

Thin films of cadmium oxide were thermally deposited on glass substrates at partial pressures of oxygen, pO₂ in the range 1.33×10⁻² to 0.133 Pa at a substrate temperature of 160 °C. Energy dispersive analysis of X-ray fluorescence (EDAX) revealed that the CdO films deposited at pO₂ value of 4.00×10⁻² Pa were nearly stoichiometric. X-ray diffractometry (XRD) confirmed the polycrystalline nature of the film structure. All the films showed an fcc structure of the NaCl-type, as the dominant phase. The films exhibited preferred orientation along the (1 1 1) diffraction plane. The texture coefficients calculated for the various planes at different oxygen partial pressures (pO₂) indicated that the maximum preferred orientation of the films occurred along the (1 1 1) plane at an oxygen partial pressure of 4.00×10⁻² Pa. This was interpreted in terms of oxygen chemisorption and desorption processes. The lattice parameters determined from the diffraction peaks were in the range 4.655–4.686 Å. The average lattice parameter a₀ found by extrapolation using the Nelson–Riley function was 4.696 Å. Both the lattice parameter and the crystallite size were found to increase with increased partial pressure of oxygen. On the other hand, the strain and dislocation density were found to decrease as the partial pressure of oxygen was raised. A maximum (80%) in the optical transmittance at λ=600 nm and minimum in the electrical resistivity (9.1×10⁻⁴ Ω cm) of the films occurred at an optimum partial pressure of oxygen of 4.00×10⁻² Pa. The results are discussed.     

Crystal growth and photoluminescence characteristics of Ca2MgSi2O7:Eu3+ thin films grown by pulsed laser deposition

Ca₂MgSi₂O₇:Eu³⁺ films were deposited on Al₂O₃ (0 0 0 1) substrates by pulsed laser deposition. The films were grown at various oxygen pressures ranging from 100 to 400 mTorr. The crystallinity and surface morphology of the films were examined by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. XRD and AFM respectively showed that the Ca₂MgSi₂O₇:Eu³⁺ films had a zircon structure and consisted of homogeneous grains ranging from 100 to 400 nm depending on the deposition conditions. The radiation emitted was dominated by a red emission peak at 620 nm. The maximum PL intensity of the Ca₂MgSi₂O₇:Eu³⁺ films grown at 300 mTorr was increased by a factor of 1.3 compared to that of Ca₂MgSi₂O₇:Eu³⁺ films grown at 100 mTorr. The crystallinity, surface roughness and photoluminescence of the thin-film phosphors were strongly dependent on the deposition conditions, in particular, the oxygen partial pressure.