Se-precursor effect on ZnSe films grown by OMVPE

The growth of ZnSe by organometallic vapor phase epitaxy (OMVPE) was investigated for diallyl selenide (DASe) and methylallyl selenide (MASe), combined with dimethylzinc: triethylamine (DMZn: NEt₃). The allyl selenide compounds are shown to reduce the growth temperature relative to that needed with diethyl selenide (DESe). The surface morphology of the grown ZnSe films varies on growth temperature and VI/II ratios. Secondary ion mass spectrometry (SIMS) measurements show increasing carbon incorporation with the VI/II ratio, and for a value of VI/II =~4 in MASe and VI/II=~1 in DASe. The amount of incorporated carbon abruptly jumps to concentrations of 10²¹ cm³, whereupon the films become polycrystalline. The results are interpreted in terms of dominant intramolecular decomposition pathways compared to homolysis pathway.     

Interfacial phase formation during growth of ferromagnetic CdCr2Se4 on AlGaAs and ZnSe/AlGaAs

Microstructure and interfacial phase formation of CdCr₂Se₄ thin films deposited by molecular beam epitaxy on GaAs, Al_0.1Ga_0.9As and ZnSe/Al_0.1Ga_0.9As have been investigated with high-resolution transmission electron microscopy, fine-probe energy-dispersive spectroscopy and Z-contrast imaging. For CdCr₂Se₄ grown epitaxially on GaAs and/or Al_0.1Ga_0.9As, Cr tends to segregate to the interface forming either a layer enriched with Cr or trapezoidal-shaped Cr-rich precipitates. On ZnSe, CdCr₂Se₄ grows epitaxially at temperatures >300 °C, but when grown at 350 °C, the interface is quite rough or wavy. When the CdCr₂Se₄ is grown at 300 °C, the CdCr₂Se₄/ZnSe interface is more planar, but the CdCr₂Se₄ film is only epitaxial up to a thickness of about 5 nm, and then becomes polycrystalline as the thickness of the film increases. An interfacial phase, Cd_xZn_1−xSe, forms at the CdCr₂Se₄/ZnSe interface, the thickness of which is determined by specific growth conditions.     

Two-phase nanostructured carbon nitride films prepared by direct current magnetron sputtering and thermal annealing

Two-phase nanocrystalline/amorphous carbon nitride films have been successfully prepared by direct current magnetron sputtering and the following thermal annealing at 1000 K. The analysis of Raman spectra supports the existence of sp³-hybridized C-N bonds in the films. The results obtained from X-ray photoelectron spectroscopy (XPS) indicate that the fractional concentration of the tetrahedral bonded crystalline phase in the carbon nitride films is 40%, and the ratio of N:C in the tetrahedral bonded crystalline phase is 1.12:1. Transmission electron microscopy (TEM) investigations indicate that the films contain a very dense and homogenous distribution of nanocrystalline grains, and the lattice parameters of these crystalline phases are in good agreement with the theoretically predicted β-C₃N₄ lattice constant. The films deposited on Si substrates have a high hardness of 40 GPa, and the correlations between the microstructure of the films and their mechanical properties are discussed.     

Thermal stability of diamond-like carbon films with added silicon

Diamond-like carbon (DLC) films with added silicon content from 0 to 19.2 at.% were deposited using r.f. PECVD (radio frequency plasma enhanced chemical vapor deposition). Fourier transform IR (FTIR) spectrometry, Raman spectrometry and X-ray photoelectron spectrometry (XPS) were used to determine the structural change of the annealed DLC films in ambient air. By increasing the annealing temperature the CH_n and Si–H groups in the FTIR spectra decrease because of hydrogen evolution, whereas the intensities of CO and Si–O peaks increase owing to oxidation. From Raman spectra, the integrated intensity ratio I_D/I_G of the pure DLC films and the silicon-doped films increases at 300 and 400 °C, respectively, whereas the observable shoulder of the D band occurs at 400 and 500 °C, respectively, which indicates that the addition of silicon improves the thermal stability of DLC films. Using XPS analysis, a surface reaction for the annealed films is investigated.     

Surface plasmon resonance and electrical properties of RF: magnetron sputtered carbon–nickel composite films at different annealing temperatures

In this work, the optical absorption spectra of carbon–nickel films annealed at different temperatures(300–1000 °C) with a special emphasis on the surface plasmon resonance(SPR) were investigated. The films were grown on quartz substrates by radio-frequency(RF)magnetron co-sputtering at room temperature with a deposition time of 600 s. The optical absorption peaks due to the SPR of Ni particle are observed in the wavelength range of 300–330 nm. With annealing temperature increasing up to 500 °C due to the increase in Ni particle size, the intensity of the SPR peaks increases, but weakens with annealing temperature increasing over 500 °C. The Ni nanoparticle size, the dielectric function of carbon matrix(ε_m) and the plasma frequency of the free electrons(ω_p) at500 °C have the maximum values of 21.63 nm, 0.471 and5.26 9 10~(15)s~(-1), respectively. The absorption peak shows a redshift trend up to 500 °C and then turn to blueshift with annealing temperature increasing over 500 °C. These observations are in a good agreement with the electrical measurements in temperature range of 15–520 K and the Maxwell–Garnett(M–G) effective medium theory(EMT).     

Characterization and analysis of DLC films with different thickness deposited by RF magnetron PECVD

Diamond-like carbon (DLC) films have excellent mechanical and chemical properties similar to those of crystalline diamond giving them wide applications as protective coatings. So far, a variety of methods are employed to deposit DLC films. In this study, DLC films with different thicknesses were deposited on Si and glass substrates using RF magnetron PECVD method with C4H10 as carbon source. The bonding microstructure, surface morphology and tribological properties at different growing stages of the DLC films were tested. Raman spectra were deconvoluted into D peak at about 1370 cm-1 and G peak around 1590 cm-1, indicating typical features of the DLC films. A linear relationship between the film thickness and the deposition time was found, revealing that the required film thickness may be obtained by the appropriate tune of the deposition time. The concentration of sp3 and sp2 carbon atoms in the DLC films was measured by XPS spectra. As the films grew, the sp3 carbon atoms decreased while sp2 atoms increased. Surface morphology of the DLC films clearly showed that the films were composed of spherical carbon clusters, which tended to congregate as the deposition time increased. The friction coefficient of the films was very low and an increase was also found with the increase of film thickness corresponding to the results of XPS spectra. The scratch test proved that there was good bonding between the DLC films and the substrates.     

Hydrogen-free carbon thin films prepared by new type surface-wave-sustained plasma (SWP)

In this paper is described the simple structure of a new type surface-wave-sustained plasma (SWP) source without a magnetic field surrounding the chamber wall. In the source, the plasma is excited and sustained by 2.45 GHz microwaves, and the plasma density is measured by a single Langmuir probe in the target direction. The results indicate that the electron density obtained in this system is as high as 9 × 10¹¹ cm^− 3 even at a low pressure of 2.8 Pa. A graphite target (99.998%) and argon (99.999%) are used for depositing hydrogen-free amorphous carbon films by the new SWP source. The Raman spectra of the carbon films were obtained, and the results denote that the structure of the carbon films prepared by SWP is typical of diamond-like carbon; the Raman intensity ratio I_D/I_G is 2.97. The surface morphology was investigated by using an atomic force microscope (AFM). The images demonstrate that the hydrogen-free carbon films deposited by SWP have a very smooth surface, with a grain size of about 20 nm and surface roughness R_a of about 0.778 nm.     

Sublimation sandwich route to ultralong zinc-blende ZnSe nanowires and the cathodoluminescence properties of individual nanowires

Sublimation sandwich method (SSM) was developed to fabricate ZnSe nanowires assisted by Au-catalytic vapor-liquid-solid (VLS) process. The ZnSe nanowires have zinc-blende structure and the length is ultralong, up to tens of micrometers. High-resolution transmission electron microscopic (HRTEM) investigations reveal that there are two types of nanowires: well crystalline nanowires and poor crystalline nanowires with high density of bulk defects e.g. stacking faults, dislocations and twinning defects. The cathodoluminescence spectra indicate significant difference in optical properties of these two types of nanowires. We deduce that V_Zn and Zn_i are the main reason for the deep defects related green-red emission observed in well crystalline nanowires, while the bulk defects in the poor crystalline nanowires should be responsible for the deep defects related emissions centered at 515 and 604 nm.     

Effects of growth temperature on structure and electrical properties of dielectric (Ba,Sr)TiO3 capacitors with transparent conducting oxide electrodes

200 nm-thick BST thin films were grown on Zr-doped In₂O₃/SrTiO₃ (1 0 0) substrates at 550-750 °C. X-ray diffraction results show that the as-deposited BST films were polycrystalline with random crystallographic orientations. X-ray diffraction patterns reveal that the BST film grown at 650 °C had the best crystalline quality of all the deposition temperatures. Atomic force microscopy and secondary ion mass spectrometry showed that the surface and interface structures of the BST films became rough as the growth temperature increased. The BST film grown at 650 °C showed the best electrical properties, with a dielectric constant of 420 at 1 MHz, dielectric tunability of 32.1%, dielectric loss of 0.015 at 300 kV/cm, and a mean optical transmittance in visible wavelength of 71.3%.     

Effect of annealing and O2 pressure on structural and optical properties of pulsed laser deposited TiO2 thin films

In this paper, effect of annealing and O₂ pressure on the structural and optical properties of pulsed laser deposited thin films of TiO₂ is reported. XRD, FTIR spectra and SEM images confirm that at high annealing temperatures, the rutile phase and crystalline quality of thin films increases. Higher pressure of O₂ during deposition improves the rutile phase and favors the rod like growth of TiO₂ thin film. The red shift in photoluminescence (PL) spectra of TiO₂ thin films with annealing temperature is reported. Contact angle measurement data for the thin films reveals the hydrophobic nature of the films. The very low reflectivity (～10%) reported in this paper may be promising for anti-reflection coating applications of pulsed laser deposited TiO₂ thin films.     

Epitaxial PMN-PT thin films grown on buffered Si substrates using ceramic and single-crystal targets

Epitaxial 0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (PMN-PT) thin films were deposited on LSCO/CeO₂/YSZ tri-buffered Si substrate by pulsed laser deposition (PLD) using sintered ceramic and single-crystal targets. The PMN-PT films deposited using both targets were single crystalline and exhibited cube-on-cube growth epitaxy with the substrate. The films deposited using the single-crystal target showed higher crystallinity and a smoother surface morphology than those grown using the ceramic target. The crystallinity of films can be affected by the in-plane lattice mismatch of PMN-PT/LSCO interfaces. The low density and low absorption coefficient of the sintered ceramic target were responsible for the severe compositional deviation from the desired stoichiometry of the PMN-PT films. Dielectric constants of approximately 1926 and 1540 at 10 kHz were obtained for the films deposited using the single-crystal and sintered ceramic target, respectively. In addition, the PMN-PT films fabricated using the single-crystal target exhibited well-developed polarization hysteresis loops with a remnant polarization of 11.9 μC/cm². Single-crystal targets are an indispensable candidate for the growth of epitaxial PMN-PT films with high crystallinity and good electrical properties.     

Diamond-like carbon thin films produced by femtosecond pulsed laser deposition of fullerite

Diamond-like carbon films have been deposited from a fullerite target by ultra-short pulsed laser deposition technique. The results indicate that the films morphology and structure, determined by scanning electron microscopy, atomic force microscopy and energy dispersive X-ray diffraction, depend strongly on the substrate temperature. X-ray photoelectron, X-ray Auger electron, Raman and surface enhanced Raman scattering spectra indicate that the fs-DLC films composition involves a mixed sp, sp² and sp³ carbon network consisting of aromatic rings and sp³ diamond-like structures linked by chains of different lengths and composition. The films deposited at room temperature, presenting the higher content of sp³ carbon (48%), also contain C₆₀ crystalline phase and show a very high hardness of 49 GPa.     

High enhanced magnetization in carbon-doped Mn3Ga thin films

Carbon-doped Mn₃Ga thin films were grown on Si/SiO₂ substrates using rf magnetron sputtering technique. The tetragonal D0₂₂–type crystalline structure of ferrimagnetic Mn₃Ga is preserved on the Mn₃GaC_x films upon carbon concentrations up to x = 0.5, whereas higher concentrations lead to the formation of the antiperovskite Mn₃GaC phase. Geometry optimization calculations using the density functional theory were performed on a 2 × 2 × 2 Mn₃GaC_0.25 supercell with C in different positions in order to find that the most stable position for the C is interstitial octahedral site. Magnetic M(H) loops show that saturation magnetization M_s of Mn₃GaC_0.25 is enhanced to 200 kAm⁻¹ (from M_s = 90 kAm⁻¹ for undoped films). The increase of the C concentration leads to a reduction of the Curie temperature from 770 K to ∼420 K at the same time that the lattice cell suffers an expansion. The enhancement of M_s is explained in terms of a 90° ferromagnetic superexchange Mn-C-Mn interaction.     

Influence of substrate temperature on the preparation of GaP thin films

Gallium phosphide (GaP) was prepared by treating specpure gallium with AnalaR grade Zn₃P₂ in an argon atmosphere. Thin films of GaP were evaporated onto glass substrates at various substrate temperatures under vacuum. Films evaporated onto substrates at and above 250°C were polycrystalline in nature. Films of various thicknesses were grown. The conductivity of these films in the dark and in white light is presented for the temperature range 100–300 K. Optical absorption spectra for films grown at substrate temperatures T_s = 90, 180 and 250°C were also recorded in the range 0.5–2.5 eV. All the features are attributed to the structural disorder which probably occurs during evaporation onto the glass substrates.     

Structural and optical study of samarium doped cerium oxide thin films prepared by electron beam evaporation

Samarium doped cerium oxide films were grown on the glass substrate using e-beam deposition technique and then characterized using different techniques: X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Raman spectroscopy and UV-visible spectroscopy measurements. XRD analysis shows that all the films have cubic structure and the crystallite size decreases from 18 to 13 nm as the samarium (Sm) concentration increases. The FE-SEM images indicate that all the films have columnar growth. UV-visible measurements reflect that the films have high transparency (>80%) in the visible region. From the Raman spectra, we have observed two peaks at 466 and 565 cm⁻¹. The peak at 466 cm⁻¹ is assigned to the F_2g mode of cerium oxide (CeO₂) whereas the peak at 565 cm⁻¹ is due to the presence of the oxygen vacancies. The increase in the intensity of the peak at 565 cm⁻¹ indicates that the oxygen vacancy increases with Sm doping.     

Preparation of a BiFeO3/LaNiO3 multiferroic oxide superlattice structure by RF magnetron sputtering

Artificial superlattices consisting of multiferroic BiFeO₃ (BFO) and conductive LaNiO₃ (LNO) were grown epitaxially on a Nb-doped SrTiO₃ (STO) (001) single-crystal substrate at temperatures in a range 560–810 °C with a RF magnetron sputtering system. The superlattice contained 30 periods of symmetric BFO/LNO bilayers with a thickness of 2 nm of each individual layer. Ferroelectric and conductive superlattice materials of this type can serve for an investigation of the strain dependence of ferroelectric properties of BFO layers in superlattice structures.Measurements of X-ray reflectivity and X-ray diffraction at high resolution were employed to characterize the microstructure of these films. The formation of a superlattice structure was confirmed by the appearance of Bragg peaks separated by Kiessig fringes in the X-ray reflectivity curve and a diffraction pattern. The clearly discernible main feature and satellite features on both sides of the substrate feature about the (002) STO Bragg peak indicate the high quality of the BFO/LNO artificial superlattice structure formed on a STO substrate at all deposition temperatures.X-ray measurements show that these superlattice films become subject to greater compressive strain in the in-plane direction, and possess increased crystalline quality when increasing the deposition temperature to 660 °C. The measurement of hysteresis loops shows that the largest remanent polarization (P_r) occurs at 660 °C.     

Hydrothermal synthesis and characterization of mesoporous zinc selenide agglomerates by nitrogen bubble templates

Mesoporous coral-like and litchi-like zinc selenide agglomerates were successfully synthesized with sodium selenite and zinc acetate dihydrate as precursors by adding hydrazine hydrate using the hydrothermal method. The experimental parameters were varied and hard agglomerates of small nanoparticles were observed. Increasing amounts of hydrazine hydrate were added to control the pH values of the reaction system. The effective control of the morphology and size of the ZnSe nanopores agglomerates by varying the pH was also demonstrated. The N₂ bubble templates produced provided the aggregation centers during the reaction, and then result in agglomerates of the small ZnSe nanoparticles with mesopores. The litchi-like zinc selenide has two different morphologies, including hollow spherical agglomerates comprising of 4-8 nm diameter nanoparticles and 15-25 nm diameter nanorods. The coral-like ZnSe mesoporous structure has a very high specific surface area of 129 m²/g and an emission band at 626 nm as measured by a photoluminescence (PL).     

Infrared optics applications of thin polyaniline emeraldine base films

The use of polyaniline emeraldine base films as antireflection coating for near and middle IR optics elements was studied. The optical quality of ZnSe substrates spin-coated with thin PANI EB layers were studied using a Linnik interferometer. The spectral properties of PANI coated ZnSe plates were investigated with FTIR spectrometer. It was shown that PANI coating allows a significant decrease of Fresnel losses in the near and middle IR bands (1.0–6.25 μm). The coating allowed continuous transmission of high power density (up to 3 W/mm²) of IR radiation produced by CO₂ laser. The laser irradiation damage threshold of the PANI EB coating was studied at a wavelength of 1.5 μm. Microhardness of the coated ZnSe is established as satisfactory.     

Influence of GaCl carrier gas flow rate on properties of GaN films grown by hydride vapor-phase epitaxy

The influence of GaCl carrier gas flow rate on GaN films grown by hydride vapor-phase epitaxy (HVPE) was investigated. The symmetric (0 0 0 2) and asymmetric (10-12) ω scans were detected to estimate the quality of GaN films. Optical properties were studied by room temperature photoluminescence spectra. Raman spectroscopy was employed to analyze the residual stress in the samples. The surface morphology of the GaN films was investigated by atomic force microscopy (AFM). On the basis of process optimization the optimal GaCl carrier gas flow rate for growth of high quality GaN films in our system was obtained as 1.3 L/min.     

Epitaxial SrRuO3 thin films deposited on SrO buffered-Si(001) substrates for ferroelectric Pb(Zr0.2Ti0.8)O3 thin films

SrRuO₃ thin film electrodes are epitaxially grown on SrO buffered-Si(001) substrates by pulsed laser deposition. The optimum conditions of the SrO buffer layers for epitaxial SrRuO₃ films are a deposition temperature of 700 °C, deposition pressure of 1 × 10^?6 Torr, and thickness of 6 nm. The 100 nm thick-SrRuO₃ bottom electrodes deposited above 650 °C on SrO buffered-Si (001) substrates have a rms (root mean square) roughness of approximately 5.0 Å and a resistivity of 1700 µω-cm, exhibiting an epitaxial relationship. The 100 nm thick-Pb(Zr_0.2Ti_0.8)O₃ thin films deposited at 575 °C have a (00l) preferred orientation and exhibit 2P_r of 40 µC/cm², E_c of 100 kV/cm, and leakage current of about 1 × 10^?7 A/cm² at 1 V. The silicon oxide phase which presents within PZT and SrRuO₃ films, influences the crystallinity of the PZT films and the resistivity of the SrRuO₃ electrodes.