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.     

Deposition of carbon nitride films by reactive pulsed-laser ablation at high fluences

The effects of high laser fluence on the properties of CN_x thin films prepared by reactive pulsed laser (KrF excimer laser, λ=248 nm, τ_FWHM=30 ns) ablation at two different N₂ gas pressures were investigated. A variety of analytical techniques have been used to characterize the structure and properties of the deposited films: X-ray photoelectron spectroscopy; X-ray diffraction; scanning electron microscopy; energy dispersive X-ray spectroscopy; Fourier transform infrared; and Rutherford backscattering spectroscopy. Analysis of these data shows the existence of a certain amount of covalent C–N single bonds and a nitrogen content up to 44%. The results also show the presence of covalent C≡N triple bonds in the film deposited at high nitrogen pressure (50 Pa).Comparison with the films deposited by XeCl excimer laser (λ=308 nm, τ_FWHM=30 ns), at the same experimental conditions, will also be presented.     

Optical properties of graphitic carbon nitride films prepared by evaporation

Graphitic carbon nitride (g-C₃N₄) consists of two-dimensional sheets of carbon and nitrogen atoms. Films of g-C₃N₄ were prepared by evaporating guanidine carbonate at four different substrate temperatures. The optical absorption band of the films appears at 3.3 eV and the optical energy gaps are calculated to be 2.83–2.90 eV. Band intensity increases with increasing substrate temperature, but the energetic band position does not shift. The photocurrent of g-C₃N₄ films can be observed by irradiation with monochromatic light. While the photosensitivity spectra are in almost complete correspondence with the optical absorption spectra, it is also found that the photocurrent is generated by irradiation at photon energies below the optical energy gap down to 2.5 eV.     

Deposition of nanocomposite CNx/SiO2 films in inductively coupled r.f. discharge

Hard films were deposited in an inductively coupled r.f. discharge at a frequency of 3.5 MHz by the chemical transport of carbon from a graphite target in a nitrogen atmosphere combined with evaporation from a quartz tube. The nitrogen flow was varied from 1.0 to 4.0 sccm. The r.f. power supplied was in the range 2.5–3.5 kW. Silicon substrates were placed on the graphite holder whose temperature was 700–800°C. In the emission spectra the CN, N₂ and C₂ molecular bands and the silicon, carbon, oxygen and nitrogen atomic lines were observed. The ratio of nitrogen to carbon in the films ranged from 0.1 to 0.55 while the ratio of oxygen to silicon was about 2 for all the films studied. The films had a maximum hardness of 35 GPa and they showed a high elasticity up to 88%, good fracture toughness and adhesion to the substrate. Unlike carbon nitride films the CN_x/SiO₂ films were almost non-absorbing in the visible range.     

Electrical contacts to nitrogen incorporated nanocrystalline diamond films

The effect of surface plasma treatment on the nature of the electrical contact to the nitrogen incorporated nanocrystalline diamond (n-NCD) films is reported. Nitrogen incorporated NCD films were grown in a microwave plasma enhanced chemical vapor deposition (MPECVD) reactor using CH₄ (1%)/N₂ (20%)/Ar (79%) gas chemistry. Raman spectra of the films showed features at ∼ 1140 cm^− 1, 1350 cm^− 1(D-band) and 1560 cm^− 1(G-band) respectively with changes in the bonding configuration of G-band after the plasma treatment. Electrical contacts to both untreated and surface plasma treated films are formed by sputtering and patterning Ti/Au metal electrodes. Ohmic nature of these contacts on the untreated films has changed to non-ohmic type after the hydrogen plasma treatment. The linear current–voltage characteristics could not be obtained even after annealing the contacts. The nature of the electrical contacts to these films depends on the surface conditions and the presence of defects and sp² carbon.     

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.     

The microstructure and properties of energetically deposited carbon nitride films

The intrinsic stress, film density and nitrogen content of carbon nitride (CN_x) films deposited from a filtered cathodic vacuum arc were determined as a function of substrate bias, substrate temperature and nitrogen process pressure. Contour plots of the measurements show the deposition conditions required to produce the main structural forms of CN_x including N-doped tetrahedral amorphous carbon (ta-C:N) and a variety of nitrogen containing graphitic carbons. The film with maximum nitrogen content (~ 30%) was deposited at room temperature with 1.0 mTorr N₂ pressure and using an intermediate bias of − 400 V. Higher nitrogen pressure, higher bias and/or higher temperature promoted layering with substitutional nitrogen bonded into graphite-like sheets. As the deposition temperature exceeded 500 °C, the nitrogen content diminished regardless of nitrogen pressure, showing the meta-stability of the carbon–nitrogen bonding in the films. Hardness and ductility measurements revealed a diverse range of mechanical properties in the films, varying from hard ta-C:N (~ 50 GPa) to softer and highly ductile CN_x which contained tangled graphite-like sheets. Through-film current–voltage characteristics showed that the conductance of the carbon nitride films increased with nitrogen content and substrate bias, consistent with the transition to more graphite-like films.     

Copper–cobalt heterobimetallic ceramic oxide thin film deposition: Synthesis,characterization and application of precursor

Thin films of halide free Cu–Co mixed metal oxide have been prepared at 390 °C from the heterobimetallic complex Co₄(THF)₄(TFA)₈(μ-OH)₂Cu₂(dmae)₂ · 0.5C₇H₈ (1) [dmae = N,N-dimethylaminoethanol ((CH₃)₂NCH₂CH₂O⁻), TFA = triflouroacetate (CF₃COO⁻), THF = tetrahydrofurane (C₄H₈O)] which was prepared by the reaction of [Cu(dmae)Cl]₄ and Co(TFA)₂ · 4H₂O. The precursor was characterized for its melting point, elemental composition, FTIR and X-ray single crystal structure determination. Thin films grown on glass substrate by using AACVD out of complex 1 were characterized by XRD and SEM. TGA and AACVD experiments reveal it to be a suitable precursor for the deposition of halide free Cu–Co mixed-metal oxide thin films at relatively low temperatures.     

Thermal conversion synthesis of Cu2O photocathode and the promoting effects of carbon coating

Simplifying the synthesis of cuprous oxide (Cu₂O) photocathode has turned out to be critical for scalable application. Herein, we present a novel thermal conversion approach to synthesize a shell/core structured Cu₂O/Cu photocathode. In this method a shell comprising a mixture of CuO and Cu₂O is obtained by heating Cu mesh at 500 °C in air beforehand, and subsequent annealing in N₂ atmosphere converts the unwanted CuO into Cu₂O gradually, which results in the desired Cu₂O/Cu structure. A slightly viscous starch sol coats the Cu₂O shell as carbon source, after carbonizing under N₂ atmosphere, the Cu₂O/Cu is covered with compact carbon films, i.e. C/Cu₂O/Cu. Photoelectrochemical experiments reveal that the introduction of carbon layers on Cu₂O enhances the photocurrent density from − 1.5 to − 2.75 mA·cm^− 2 at 0 V vs. reversible hydrogen electrode (RHE). Moreover, the deposition of carbon films on Cu₂O in this work has little effect on improving the stability.     

Effect of the type of plasma on the polydimethylsiloxane/collagen composites adhesive properties

Polydimethylsiloxane (PDMS) films were treated with either oxygen (O₂), nitrogen (N₂) or argon (Ar) plasma between 40 W and 120 W for 5–15 min and their surface properties studied by contact angle measurements, infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Lower contact angles and increases in surface roughness, assessed by SEM and AFM, were observed for all used gases when plasma power and time increased, with argon treatment being the one that showed the most significant change in roughness.PDMS/collagen type I composites obtained after treating PDMS with oxygen at 80 W for 13 min or nitrogen and argon at 80 W for 14 min showed a peel strength of 0.1N/mm (oxygen plasma), 0.08 N/mm (nitrogen plasma) and 0.09 N/mm (argon plasma). In all cases, peel strength was higher than that measured for the untreated bilayer composite. An increase in adhesion strength, after oxygen and nitrogen plasma, was mostly attributed to chemical interaction between functional groups introduced on the PDMS surface and the functional groups on collagen as detected by FTIR. In contrast, the high peel strength observed on PDMS treated with argon plasma was attributed to its increased roughness which in turn increased mechanical interlocking. The properties of these composites render them suitable for adhesive free skin substitutes.     

Influence of nitrogen overpressure on the nitridation,densification and formation of β-SiAlONs produced by silicothermal reduction

β-SiAlON materials (with z = 1) with 2 mol% DyAG have been synthesised by silicothermal reduction under different nitrogen pressures. The possibility of rapidly nitriding silicon and forming the SiAlON phase has been investigated through its reaction sequence of formation under different pressures. β-SiAlONs were fully nitrided (degree of nitridation greater than 93%) and formed after a 1-h hold at 1400 °C, or after a straight ramp to 1500 °C under 0.7 MPa of nitrogen. This was not achievable under static nitrogen at atmospheric pressure where the degree of nitridation was only 43% and β-SiAlON phase represented only about 60% of the crystalline phase assemblage at the same temperature. The formation of β-SiAlON depended on the formation of Si₃N₄ whose reaction rate was enhanced by nitrogen overpressures.     

Simultaneous catalytic removal of NOx and soot particulates over CuMgAl hydrotalcites derived mixed metal oxides

A series of CuMgAl hydrotalcites derived oxides were prepared by co-precipitation and calcination methods and tested for the simultaneous catalytic removal of NOx and soot. The obtained samples were characterized by XRD, N₂ adsorption-desorption, H₂-TPR and ICP-AES techniques. The crystal phases, porous structures and redox properties of the catalysts were strongly influenced by Cu substitution contents and calcination temperatures. The CuMgAl mixed oxides with mesoporous properties exhibit high activity for the simultaneous NOx-soot removal. Among the tested catalysts, 3.0Cu-800 sample shows the best performance with the ignition temperature of soot = 260 °C and the total amounts of N₂ = 6.0 × 10^− 5 mol. Based on the experimental work, a primitive kinetics analysis was carried out from the non-steady (dynamic) TPR measurements. Linear Arrhenius plots of rates of CO₂, N₂ and N₂O formation were observed around the onset of formation curves where the substantial amount of the soot still remains in the soot/catalyst mixture and the effective area of the soot/catalyst contact can be regarded as constant. Finally, a compensation effect was found for the formation of CO₂, N₂ and N₂O over CuMgAl mixed oxides with CuO as the predominant phase.     

Impact of nitrogen doping of carbon nanospheres on the nickel-catalyzed hydrogenation of butyronitrile

Three nickel catalysts supported on carbon and nitrogen-doped carbon nanospheres have been prepared by deposition-precipitation (DP) with urea (ca. 2% w/w). The nanospheres were prepared by thermal pyrolysis of benzene (CNS_B), aniline (CNS_A) and nitrobenzene (CNS_N) and characterized by transmission electron microscopy (TEM), N₂ adsorption–desorption, temperature-programmed oxidation (TPO), X-ray diffraction (XRD), elemental (CHN) analysis, X-ray photoelectron spectroscopy (XPS), temperature-programmed decomposition (TPD) and acid/base titrations, revealing different graphitic characteristics and different distribution of nitrogen (when present) functionalities. Upon Ni introduction, the catalysts were characterized by temperature-programmed reduction (TPR), XRD and TEM. Surface area weighted mean Ni particle diameters (post activation at 603 K) were in the range 10.5–18.2 nm. Ni particle size exhibited a big dependence on CNS nitrogen doping, where nitrogen introduction, essentially in the quaternary form, enhanced metal sintering by enriching the surface electron density of the support. The catalysts were tested in the gas phase hydrogenation of butyronitrile (T = 493 K). Extracted specific reaction rates in the steady state followed the sequence: Ni/CNS_B < Ni/CNS_A < Ni/CNS_N. When the active metal was physically mixed with the support, the following sequence was obtained: Ni + CNS_B < Ni + CNS_A < Ni + CNS_N. Our results demonstrate that doping carbon nanospheres with nitrogen strongly impacts on reactant adsorption and metal sintering, both critical aspects in the hydrogenation of nitriles. Selectivity was not sensitive to the support (or the physical mixture) employed and was in all cases close to 100% to the primary amine.     

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.     

Novel three-dimensional microfluidic device for process intensification

Microchannel heat exchangers and chemical reactors have extensive applications in process industries, especially in electronics cooling, air conditioning, and chemical industries. Microchannel devices provide enhanced heat and mass transfer characteristics by controlled flow conditions and high surface-to-volume ratios. The different designs of microchannels are based on planar structures from various fabrication technologies. In the present study a novel three-dimensional micro-structured device, the micro coiled flow inverter (MCFI) with 0.38–0.8 mm internal diameter, has been numerically investigated as a micro heat exchanger. In comparison micro helical coil (MHC) and straight tube of same heat transfer area (d_t = 0.5 mm, A = 3.9 × 10⁻⁴ m²) has been studied, too. The Reynolds and Prandtl numbers are varied from 25 to 1200 and 0.74 to150, respectively. The MCFI offers a four-fold heat transfer enhancement as compared to straight tube of same heat transfer area at N_Re = 1200 and N_Pr = 7. Furthermore, the heat transfer coefficient in MCFI augments by 38.5% as compared to MHC, with slight increase (5–16%) in friction factor. New design correlations are developed for Nusselt number and friction factor in MCFI. The MCFI device offers 1.15–1.7-folds higher thermal merit as compared to micro straight tube.     

First example of PMMA-supported and highly luminous color-purity red-light metallopolymer based on a tris-β-diketonate Zn2 +-Eu3 +-complex

Through the copolymerization of a complex monomer [Zn(L)(4-vinyl-Py)Eu(TTA)₃] (2; H₂L = N,N′-bis(salicylidene)cyclohexane-1.2-diamine; 4-vinyl-Py = 4-vinyl-pyridine and HTTA = 2-thenoyltrifluoroacetonate) with MMA (methyl methacrylate), the first example of PMMA-supported and highly luminous (Ф_Eu^L = 63.1%) color-purity red-light metallopolymer poly(MMA-co-2) based on a tris-β-diketonate Zn^2 +-Eu^3 +-complex is obtained.     

Highly active and selective ethylene oligomerization catalysts: Asymmetric 2,6-bis(imino)pyridyl iron (II) complexes with alkyl and halogen substitutients

A series of asymmetric 2,6-bis(arylimino)pyridines with alkyl and halogen substitutients on different iminoaryl rings and corresponding iron (II) complexes ([2-(Ar₁N = CCH₃)-6-(Ar₂N = CCH₃)C₅H₃N]FeCl₂, 3a–3j) are synthesized and characterized. These Fe(II) complexes are highly active for ethylene oligomerization with high selectivity for linear α-olefins. The oligomer distributions can be tuned by the synergism of alkyl-steric effect and halogen electronic effect, and the production of C₆–C₁₆ can reach more than 80% with the highest selectivity being 87.5% for 3 g (Ar₁ = 2-ethylphenyl, Ar₂ = 2-fluorophenyl), which is 15–30% higher than that catalyzed by their methyl or fluoro-substituted symmetric counterparts.     

Substrate temperature effects on the electron field emission properties of nitrogen doped ultra-nanocrystalline diamond

For the purpose of improving the electron field emission properties of ultra-nanocrystalline diamond (UNCD) films, nitrogen species were doped into UNCD films by microwave plasma chemical vapor deposition (MPCVD) process at high substrate temperature ranging from 600° to 830 °C, using 10% N₂ in Ar/CH₄ plasma. Secondary ion mass spectrometer (SIMS) analysis indicates that the specimens contain almost the same amount of nitrogen, regardless of the substrate temperature. But the electrical conductivity increased nearly 2 orders of magnitude, from 1 to 90 cm^− 1 Ω^− 1, when the substrate temperature increased from 600° to 830 °C. The electron field emission properties of the films were also pronouncedly improved, that is, the turn-on field decreased from 20 V/μm to 10 V/μm and the electron field emission current density increased from less than 0.05 mA/cm² to 15 mA/cm². The possible mechanism is presumed to be that the nitrogen incorporated in UNCD films are residing at grain boundary regions, converting sp³-bonded carbons into sp²-bonded ones. The nitrogen ions inject electrons into the grain boundary carbons, increasing the electrical conductivity of the grain boundary regions, which improves the efficiency for electron transport from the substrate to the emission sites, the diamond grains.     

Formation and characteristics of undoped and doped tetrahedral amorphous carbon films

Synthesis of undoped and doped tetrahedral amorphous carbon (ta-C) films has been achieved using magnetic field filtered plasma stream system in an ambient gas of pure Ar and Ar with N₂, respectively. The optical and electrical properties of these films as a function of the substrate bias voltages (V_b) or nitrogen partial pressures (P_N) have been studied using UV-visible optical absorption spectroscopy, Fourier-transform infra-red spectroscopy (FTIR) and measurements of electrical conductivity. The results show that ta-C films with a high sp³ fraction were formed when the V_b was in the range of −10 to −50 V. The optical band gap of such ta-C films was found to be larger than 3 eV. The incorporation of nitrogen into the ta-C films deposited at low P_N (P_N<25%), results in a slight drop in activation energy, which indicates that there is evidently some doping effect of nitrogen. The configurations of N atoms in ta-C network are identified and discussed.     

New [2 × 2] cyclic framework that induces distortions from square planar to tetrahedral around the copper(II) centers

A new tetracopper(II) complex [Cu₄(bsbd)₄] (bsbd = bis(N-salicylidene)benzene-1,4-diamine) has been prepared and structurally characterized. The complex constructs a [2 × 2] cyclic coordination framework, which inhibits formation of square planar copper(II) centers, and induces distortion to a tetrahedral structure. The effects of the distortions on the absorption spectra are characterized.