The RF plasma surface chemical modification of nanodiamond films grown on glass and silicon at low temperature

Glass slides (standard 1 × 3 in. size) coated with nanocrystalline diamond were successfully tested for DNA immobilization. The nanodiamond films were grown on glass substrates at temperature below 400 °C, while keeping the excellent material properties of diamond, such as low background luminescence and high optical transparency. The nanodiamond surface to which proteins were attached was functionalized by ultra-thin amino-polymer film in the radio-frequency (RF) plasma discharge of vaporized organosilane coupling agent N-(6-aminohexyl) aminopropyl trimethoxysilane (AHAPS). Several different IR spectroscopy methods (transmission and reflection–absorption spectroscopy (IRRAS), attenuated total reflectance (ATR) and grazing angle reflectance (GAR)) are discussed with respect of their ability of detecting the functional groups on bio-functionalized diamond surface. The IR absorbance spectra of just a few nm thick RF plasma polymer films deposited on nanodiamond surface are presented.     

Characterization of spray pyrolytically deposited high mobility praseodymium doped CdO thin films

Praseodymium (Pr) doped CdO thin films with high transparency and high mobility were deposited, using a homemade spray pyrolysis setup, on micro-slide glass substrates preheated at 300 °C. Polycrystalline nature and Cd-O bond vibration of deposited films were confirmed by X-ray diffraction, micro-Raman and Fourier transform infrared spectroscopy analyses. The oxidation state of Cd²⁺, O²⁻, and Pr³⁺ was confirmed by X-ray photoelectron spectroscopy analysis. The highest average particle size (92 nm-FESEM) and high RMS (13.48 nm-AFM) values are obtained for 0.50 wt% Pr doped CdO thin film. The optical band gap is varied between 2.38 eV and 2.52 eV, depending on the Pr doping concentration. Photoluminescence spectra revealed that Pr doped CdO thin film exhibits strong green emission at 582 nm. High mobility (82 cm²/V s), high charge carrier concentration (2.19×10²⁰ cm⁻³) and high transmittance (83%) were observed for 0.50 wt% Pr doped CdO film. A high figure of merit (9.79×10⁻³ Ω⁻¹) was obtained for 0.50 wt% Pr doped CdO thin films. The mechanism behind the above results is discussed in detail in this paper.     

Effects of additive LiF on the synthesis of cBN in the system of Li3N–hBN at HPHT

High-quality cBN single crystals were successfully synthesized in the system of Li₃N–hBN with additive LiF at high pressure and high temperature (HPHT). The lowest synthetic conditions of cBN decreased to 4.6 GPa, 1320 °C by employing 3 wt.% LiF, and it didn't change anymore though more than 3 wt.% LiF had been added. The quality of cBN crystals improved markedly. The cBN crystals and other products were examined by X-Ray diffraction and scanning electron microscopy. The X-Ray analysis reveals that the “graphitization index” (GI) of hBN increased by adding 3 wt.% LiF into the system of Li₃N–hBN at HPHT. The SEM photographs show that different growth steps were formed on the cBN crystal surface in systems of Li₃N–hBN and Li₃N–LiF–hBN, respectively.     

Effects of time-dependent substrate biasing and gas composition on the nucleation of cubic boron nitride thin films

Boron nitride (BN) thin films were deposited on silicon and sapphire substrates by an inductively coupled plasma chemical vapor deposition technique with time-dependent control of the substrate dc bias (Vdc). Turbostratic BN films were deposited on sapphire when the bias reduction rate, ·Vdc, was optimized specifically for cBN growth on silicon. This difference depending on the substrates was explained by a potential drop in the dielectric substrate. By reducing ·Vdc at the early stage of deposition, the cBN phase was successfully deposited on both substrates. We also found that the chemical composition of BN varied from B/(B + N) = 0.48 to 0.57 upon changing the gas ratio of diborane to nitrogen. The gas ratio for film nonstoichiometry resulted in a thicker initial layer, i.e., the delayed nucleation of cBN.     

A superhard diamond-like carbon film

A superhard hydrogen-free amorphous diamond-like carbon (DLC) film was deposited by pulsed arc discharge using a carbon source accelerator in a vacuum of 2×10⁻⁴ Pa. The growth rate was about 15 nm/min and the optimum ion-plasma energy was about 70 eV. The impact of doping elements (Cu, Zr, Ti, Al, F(Cl), N) on the characteristics of DLC films deposited on metal and silicon substrates was studied aiming at the choice of the optimum coating for low friction couples. The microhardness of thick (≥20 μm) DLC films was studied by Knoop and Vickers indentations, medium thick DLC films (1–3 μm) were investigated using a ‘Fischerscope’, and Young's module of thin films (20–70 nm) was studied by laser induced surface acoustic waves. The bonds in DLC films were investigated by electron energy loss spectroscopy (EELS), X-ray excited Auger electron spectroscopy (XAES), and X-ray photoelectron spectroscopy (XPS). The adhesion of DLC films was defined by the scratch test and Rockwell indentation. The coefficient of friction of the Patinor DLC film was measured by a rubbing cylinders test and by a pin-on-disk test in laboratory air at about 20% humidity and room temperature. The microhardness of the Patinor DLC film was up to 100 GPa and the density of the film was 3.43–3.65 g/cm³. The specific wear rate of the Patinor DLC film is comparable to that of other carbon films.     

Densification of SiO2–cBN composites by using Ni nanoparticle and SiO2 nanolayer coated cBN powder

Cubic boron nitride (cBN) powder was coated with Ni nanoparticle and SiO₂ nanolayer (abbreviated as cBN/Ni and cBN/SiO₂, respectively) by rotary chemical vapor deposition (RCVD), and compacted with SiO₂ powder by spark plasma sintering at 1473–1973 K for 0.6 ks. The effects of Ni and SiO₂ coatings on the densification, phase transformation of cBN and hardness of SiO₂–cBN composites were compared. The phase transformation of cBN to hBN was identified at 1973 K in SiO₂–cBN/SiO₂ composites, 300 K higher than that in SiO₂–cBN/Ni composites, indicating that SiO₂ retarded the transformation of cBN. The relative density of SiO₂–cBN/SiO₂ with 50 vol% cBN sintered at 1873 K was 99% with a hardness of 14.5 GPa.     

Structural,optical and methanol sensing properties of sprayed In2O3 nanoparticle thin films

Indium oxide (In₂O₃) nanoparticle thin films were grown on cleaned glass substrates by the chemical spray pyrolysis technique using the precursor solution of indium nitrate (In (NO₃)₃). The XRD studies confirm that the films are polycrystalline In₂O₃, possessing cubic structure with lattice parameters, a = b = c = 10.17 Å. The optical studies show a direct optical band gap of 3.32 eV and an indirect band gap of 2.6 eV in the prepared films. The films exhibit high optical transparency >80% in the visible region, reaching a maximum of 85% at 684 nm wavelength. Further, the gas sensing properties of the films have been investigated for various concentrations of methanol in air at different operating temperatures. At 300 °C the film exhibits a very high response 99% to methanol vapor at a concentration of 40 ppm in air, which is ideal to be used as a methanol sensor. The film shows fast response and recovery to methanol vapor at higher operating temperatures. A possible methanol sensing mechanism has been proposed.     

Preparation of tetrahedral amorphous carbon films by filtered cathodic vacuum arc deposition

Tetrahedrally bonded amorphous carbon (ta-C) and nitrogen doped (ta-C:N) films were obtained at room temperature in a filtered cathodic vacuum arc (FCVA) system incorporating an off-plane double bend (S-bend) magnetic filter. The influence of the negative bias voltage applied to substrates (from −20 to −350 V) and the nitrogen background pressure (up to 10⁻³ Torr) on film properties was studied by scanning electron microscopy (SEM), electron energy loss spectroscopy (EELS), Raman spectroscopy, X-ray photoemission spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and X-ray reflectivity (XRR). The ta-C films showed sp³ fractions between 84% and 88%, and mass densities around 3.2 g/cm³ in the wide range of bias voltage studied. In contrast, the compressive stress showed a maximum value of 11 GPa for bias voltages around −90 V, whereas for lower and higher bias voltages the stress decreased to 6 GPa. As for the ta-C:N films grown at bias voltages below −200 V and with N contents up to 7%, it has been found that the N atoms were preferentially sp³ bonded to the carbon network with a reduction in stress below 8 GPa. Further increase in bias voltage or N content increased the sp² fraction, leading to a reduction in film density to 2.7 g/cm³.     

Reactive sintering cBN-Ti-Al composites by spark plasma sintering

When synthesizing polycrystalline cubic boron nitride (PcBN) at normal pressure, cBN had a trend of hexagonal transformation, which reduces the hardness and strength of PcBN. The cBN-Ti-Al composite was prepared by spark plasma sintering with introducing Ti and Al to absorb hexagonal boron nitride (hBN) transformed from cBN. By the results of X-ray diffraction (XRD), Ti and Al reacted with BN and forming TiN, TiB₂, and AlN, which combined cBN as the binder by chemical bonding. The mechanical properties of the prepared composite increased as the increment of sintering temperature. The threshold temperature for preparing composite without hBN phase was at 1400 °C. The composite with optimal mechanical properties was prepared at 1400 °C, and the relative density, the bending strength, hardness, and fracture toughness were 98.9 ± 0.1%, 390.7 ± 4.4 MPa, 14.1 ± 0.5 GPa, and 7.6 ± 0.1 MPa·m^0.5, respectively.     

cBN reinforced Y-α-SiAlON composites

Dense α-Sialon–cBN composites were produced by FAST/SPS–sintering at 1575–1625 °C. The hardness of the materials increases only up to 21 GPa for materials with 10 vol.% cBN. On the other hand the fracture toughness increases up to nearly 8 MPa m^0.5 with 30 vol.% cBN. The reason for the increase in fracture toughness is attributed to crack deflection at cBN grains due to the weak bonding of the grains in the matrix. The weak interfaces are also responsible for the moderate increase in hardness. Detailed investigation of the interface between cBN and the matrix was carried out by TEM.     

Room temperature synthesis of boron nitride thin films by dual-ion beam sputtering deposition

Boron nitride (BN) films are prepared by dual-ion beam sputtering deposition at room temperature (~25 °C). An assisting argon/nitrogen ion beam (ion energy E_i=0–300 eV) directly bombards the substrate surface to modify the properties of the BN films. The effects of assisting ion beam energy on the characteristics of BN films were investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, Raman spectra, atomic force microscopy, and optical transmittance. The density of the B–N bond in the film increased with the increase in assisting ion beam energy. The highest transmittance of more than 95% in the visible region was obtained under the assisting ion beam energy of 300 eV. The band gap of BN films increased from 5.54 eV to 6.13 eV when the assisted ion-beam energy increased from 0 eV to 300 eV.     

Characterization of crystallinity of a large self-standing homoepitaxial diamond film

We have investigated the crystallinity of a self-standing homoepitaxial diamond film grown at a high rate using a polarized optical microscope, X-ray rocking curves and X-ray topographs. The self-standing film was made by removing a synthetic type-Ib(001) substrate after the film growth using a “lift-off process”. The cross-nicol optical microscope image demonstrated that there exists strain spreading at a relatively large area in the film and the strain inherits over that in the substrate. From cross-sectional X-ray topographs, the dominant defects, observed as dotted patterns in plan-view topographs and micrographs, are dislocations extending along the film growth direction 〈001〉 and generating at the interface between the film and the substrate. The density of such defects counted from these measurements was ~ 1 × 10³ cm^? 2. The dotted patterns observed in X-ray topographs of (220), (? 220) and (400) diffraction planes are almost the same with each other, suggesting that dominant line defects along 〈001〉 are mixed dislocations with a burgers vector directing between 〈001〉 and in-plane of the sample. The high resolution X-ray rocking curve showed that the peak is very sharp with full width at half maximum of 7.56″, which indicates that imperfection of our single-crystal diamond plate is almost the same as that of high-quality high-pressure high-temperature, synthetic type-Ib diamond.     

Crystallinity of freestanding large undoped single crystal diamond plates produced using pre-ion-implanted substrates and lift-off processes

Crystallinity of freestanding large (size: ～ 9 × 9 mm) undoped single crystal (SC) diamond films grown by plasma chemical vapor deposition (CVD) was investigated using optical transmission spectroscopy, polarized optical microscope, X-ray rocking curves, X-ray topographs and photoluminescence. The production of the freestanding film was performed by elimination of the substrates using a so-called “lift-off method” after the growth of a homoepitaxial thick-film on a pre-ion-implanted substrate. The remarkable optical absorption in the wavelength from ultraviolet to near-infrared region (220–2500 nm) was not seen, similarly to a high-pressure, high-temperature (HPHT) synthetic type-IIa diamond. The cross-nicol optical microscope image demonstrated that there are patchy white regions and many dotted patterns, originating from internal strain and threading dislocations, respectively, over the entire area of the sample. The dotted patterns, corresponding to threading dislocations observed in the cross-nicol image, were also observed in X-ray topographs. The full width at half maximum (FWHM) of the X-ray rocking curve was 19.8″. In photoluminescence spectra at room temperature, a strong sharp peak around 235 nm corresponding to the recombination emission of free exciton was observed, while there were no remarkable emission peaks related to various defects typically observed in the visible region.     

Transparent and high infrared reflection film having sandwich structure of SiO2/Al:ZnO/SiO2

New transparent and high infrared reflection films having the sandwich structure of SiO₂/Al:ZnO(AZO)/SiO₂ were deposited on the soda-lime silicate glass at room temperature by radio frequency (R.F.) magnetron sputtering. The optical and electrical properties of SiO₂ (110 nm)/AZO (860 nm)/SiO₂ (110 nm) sandwich films were compared with those of single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. The results show that these sandwich films exhibit high transmittance of over 85% in the visible light range (380–760 nm), and low reflection rate of below 4.5% in the wavelength range of 350–525 nm, which is not shown in the conventional single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. Further these sandwich films display a low sheet resistance of 20 Ω/sq by sheet resistance formula and high infrared reflection rate of above 80% in the wavelength range of 15–25 μm. In addition, the infrared reflection property of these sandwich films is determined mainly by the AZO film. The outer SiO₂ film can diminish the interference coloring and increase transparency; the inner SiO₂ film improves the adhesion of the coating to the glass substrate and prevents Ca²⁺ and Na⁺ in the glass substrate from entering the AZO film.     

Densification and mechanical properties of cBN–TiN–TiB2 composites prepared by spark plasma sintering of SiO2-coated cBN powder

cBN–TiN–TiB₂ composites were fabricated by spark plasma sintering at 1773–1973 K using cubic boron nitride (cBN) and SiO₂-coated cBN (cBN(SiO₂)) powders. The effect of SiO₂ coating, cBN content and sintering temperature on the phase composition, densification and mechanical properties of the composites was investigated. SiO₂ coating on cBN powder retarded the phase transformation of cBN in the composites up to 1873 K and facilitated viscous sintering that promoted the densification of the composites. Sintering at 1873 K, without the SiO₂ coating, caused the relative density and Vickers hardness of the composite to linearly decrease from 96.2% to 79.8% and from 25.3 to 4.4 GPa, respectively, whereas the cBN(SiO₂)–TiN–TiB₂ composites maintained high relative density (91.0–96.2%) and Vickers hardness (17.9–21.0 GPa) up to 50 vol% cBN. The cBN(SiO₂)–TiN–TiB₂ composites had high thermal conductivity (60 W m⁻¹ K⁻¹ at room temperature) comparable to the TiN–TiB₂ binary composite.     

Large-size graphene microsheets as a protective layer for transparent conductive silver nanowire film heaters

A new strategy is reported for the fabrication of silver nanowire (AgNW) film heaters using reduced small/or large-size graphene oxide (rSGO or rLGO) sheets as an over-coating protective layer. The results show that ultrathin rLGO microsheets provide the best combination of protective effect and electrical properties on AgNW networks and thus could enable the design of high-performance transparent film heaters. As a consequence, good optical transparency and electrical conductivity, good oxidation resistance and thermal stability, and good heating performances are achieved with as-made rLGO/AgNW film heaters. Specifically, the rLGO/AgNW hybrid film annealed at 700 °C shows a low sheet resistance of 27 Ω sq⁻¹ and a good optical transparency of 80%. Furthermore, it exhibits good heating characteristics and defrosting performance at low voltages. The results presented here may pave the way for a new promising application of rLGO/AgNW hybrid film in transparent film heaters and other electrical devices.     

Quantitative linear correlations between the cBN synthesis parameters and the structural features of the hBN precursor

Seven selected hBN powders previously characterized by X-ray diffraction were subject to cBN synthesis tests at 1500 °C and 5.2GP using MgB₂ as a solvent-catalyst. Attempts have been made to establish quantitative linear correlations involving the conversion yield and the kinetic parameters (nucleation rate and linear growth rate) obtained in the cBN synthesis and the X-ray revealed features of the hBN precursor to disclose definite hereditary influences in the hBN → cBN conversion. The aspect ratio of the hBN crystallites seems to have an influence on the conversion yield and nucleation rate only if considered jointly with the graphitizing index and special lattice defects such as nanoarches and mid-plane point defects of chemical origin. The model of Sung and Tai for the catalytic synthesis of diamond was used to explain the obtained correlations.     

Fabrication of highly efficient TiO2/Ag/TiO2 multilayer transparent conducting electrode with N ion implantation for optoelectronic applications

Fabrication of highly conductive and transparent TiO₂/Ag/TiO₂ (referred hereafter as TAT) multilayer films with nitrogen implantation is reported. In the present work, TAT films were fabricated with a total thickness of 100 nm by sputtering on glass substrates at room temperature. The as-deposited films were implanted with 40 keV N ions for different fluences (1×10¹⁴, 5×10¹⁴, 1×10¹⁵, 5×10¹⁵ and 1×10¹⁶ ions/cm²). The objective of this study was to investigate the effect of N⁺ implantation on the optical and electrical properties of TAT multilayer films. X-ray diffraction of TAT films shows an amorphous TiO₂ film with a crystalline peak assigned to Ag (111) diffraction plane. The surface morphology studied by atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) revealed smooth and uniform top layer of the sandwich structure. The surface roughness of pristine film was 1.7 nm which increases to 2.34 nm on implantation for 1×10¹⁴ ions/cm² fluence. Beyond this fluence, the roughness decreases. The oxide/metal/oxide structure exhibits an average transmittance ~80% for pristine and ~70% for the implanted film at fluence of 1×10¹⁶ ions/cm² in the visible region. The electrical resistivity of the pristine sample was obtained as 2.04×10⁻⁴ Ω cm which is minimized to 9.62×10⁻⁵ Ω cm at highest fluence. Sheet resistance of TAT films decreased from 20.4 to 9.62 Ω/□ with an increase in fluence. Electrical and optical parameters such as carrier concentration, carrier mobility, absorption coefficient, band gap, refractive index and extinction coefficient have been calculated for the pristine and implanted films to assess the performance of films. The TAT multilayer film with fluence of 1×10¹⁶ ions/cm² showed maximum Haacke figure of merit (FOM) of 5.7×10⁻³ Ω⁻¹. X-ray photoelectron spectroscopy (XPS) analysis of N 1s and Ti 2p spectra revealed that substitutional implantation of nitrogen into the TiO₂ lattice added new electronic states just above the valence band which is responsible for the narrowing of band gap resulting in the enhancement in electrical conductivity. This study reports that fabrication of multilayer transparent conducting electrode with nitrogen implantation that exhibits superior electrical and optical properties and hence can be an alternative to indium tin oxide (ITO) for futuristic TCE applications in optoelectronic devices.     

Conversion of pyrazoline to pyrazole in hydrazine treated N-substituted reduced graphene oxide films obtained by ion bombardment and their electrical properties

An efficient method for the conversion of pyrazoline to pyrazole in hydrazine treated N-substituted reduced graphene oxide (N-rGO) films at room temperature has been reported. This method comprises the Ar⁺ ion bombardment of the N-rGO films that are prepared by drop casting method. The X-ray photoelectron spectroscopy (XPS) data in association with the X-ray diffraction, Ultra-violet spectroscopy and Raman spectroscopy data reveal that the addition of hydrazine removes the epoxy and hydroxyl groups of graphite oxide largely, and the reaction of hydrazine with carbonyl groups at 1,3-position of GO yields the pyrazoline moiety at the edge of the exfoliated carbon network. Further, the XPS data of the bombarded N-rGO films at the threshold applied potential of ∼3 keV for 10 min show that the position of the N1s XPS peak shifts from 400.05 to 398.6 eV due to the bombardment, indicating a conversion occurs from non-aromatic pyrazoline to aromatic pyrazole moiety. The electrical results reveal that the conductivity of the N-rGO/pyrazole film (47,600 S/m) is higher than the N-rGO/pyrazoline film (25,000 S/m) by virtue of the enhancement in the length of the conjugation π bond. The conversion of pyrazoline to pyrazole is discussed based on the activation energy.     

The role of substrate temperature on the properties of nanocrystalline Mo doped ZnO thin films by spray pyrolysis

Transparent conducting molybdenum (2 at.%) doped zinc oxide (MZO) films were prepared with various substrate temperatures by spray pyrolysis technique on glass substrates. The effect of substrate temperature on the structural, surface morphological, electrical, optical and photoluminescence properties of these films were studied. The X-ray diffraction analysis revealed that the films are polycrystalline in nature having a wurtzite structure with a preferred grain orientation in the (0 0 2) direction. The average crystallite size of the films increases from 17 nm to 28 nm with the increase of substrate temperature from 573 K to 623 K, thereafter it slightly decreases with further increase of substrate temperature to 723 K. Analysis of structural parameters indicates minimum strain and stress values for films deposited at a substrate temperature of 673 K. From atomic force microscopy (AFM) analysis, it is found that rms roughness of the films deposited at 623 K is a minimum, indicating better optical quality. The scanning electron microscopy (SEM) measurements showed that the surface morphology of the films changes with substrate temperature. Optical parameters such as optical transmittance, reflectance, refractive index, extinction coefficient, dielectric constant and optical band gap have been studied and discussed with respect to substrate temperature. Room temperature photoluminescence (PL) spectra show the deep-level emission in the MZO thin films. The films exhibit a low electrical resistivity of 6.22 × 10^?2 Ω cm with an optical transmittance of 75% in the visible region at a substrate temperature of 623 K.