Defects in nanocrystalline Nb films: Effect of sputtering temperature

Thin niobium (Nb) films (thickness 350-400 nm) were prepared on (1 0 0)Si substrate in a UHV chamber using the cathode beam sputtering. The sputtering temperature T_s was varied from 40 up to 500 °C and the influence of the sputtering temperature on the microstructure of thin Nb films was investigated. Defect studies of the thin Nb films sputtered at various temperatures were performed by slow positron implantation spectroscopy (SPIS) with measurement of the Doppler broadening of the annihilation line. SPIS was combined with transmission electron microscopy (TEM) and X-ray diffraction (XRD). We have found that the films sputtered at T_s = 40 °C exhibit elongated, column-like nanocrystalline grains. No significant increase of grain size with T_s (up to 500 °C) was observed by TEM. The thin Nb films sputtered at T_s = 40 °C contain a high density of defects. It is demonstrated by shortened positron diffusion length and a high value of the S parameter for Nb layer compared to the well-annealed (defect-free) bulk Nb reference sample. A drastic decrease of defect density was found in the films sputtered at T_s ≥ 300 °C. It is reflected by a significant increase of the positron diffusion length and a decrease of the S parameter for the Nb layer. The defect density in the Nb layer is, however, still substantially higher than in the well-annealed reference bulk Nb sample. Moreover, there is a layer at the interface between the Nb film and the substrate with very high density of defects comparable to that in the films sputtered at T_s < 300 °C. All the Nb films studied exhibit a strong (1 1 0) texture. The films sputtered at T_s < 300 °C are characterized by a compressive macroscopic in-plane stress due to lattice mismatch between the film and the substrate. Relaxation of the in-plane stress was observed in the films sputtered at T_s ≥ 300 °C. The width of the XRD profiles of the films sputtered at T_s ≥ 300 °C is significantly smaller compared to the films sputtered at lower temperatures. This is most probably due to a lower defect density which results in reduced microstrains in the films sputtered at higher temperatures.     

Influence of temperature on structure as well as adhesion and friction and wear behavior of hydrogenated carbon nitride films prepared on silicon substrate

Hydrogenated-carbon nitride (CN_x:H) films were synthesized on silicon substrate in a large quantity by the pyrolysis of ethylenediamine in a temperature range of 700-950 °C. The influence of temperature on the morphology, structure, adhesion to substrate, and friction and wear behavior of CN_x:H films was investigated. It has been found that CN_x:H films obtained at 700 °C and 800 °C are amorphous, and those prepared at 900 °C and 950 °C consist of carbon nitride nanocrystal. Besides, CN_x:H film sample obtained at 700 °C has the maximum N content of 9.1 at.% but the poorest adhesion to Si substrate, while the one prepared at 900 °C has the lower N content and the highest adhesion to substrate. As a result, nanocrystalline CN_x:H (nc-CN_x:H) film synthesized at 900 °C possesses the best wear resistance when slides against stainless steel counterpart. N atom is incorporated into the graphitic network in three different bonding forms, and their relative content is closely related to temperature, corresponding to different adhesion as well as friction and wear behavior of the films obtained at different temperatures. Furthermore, the friction coefficient and antiwear life of as-deposited CN_x:H films vary with varying deposition temperature and thickness, and the film with thickness of 1.3 μm, obtained at 900 °C, has the longest antiwear life of over 180,000 s.     

Crystallization and surface morphology evolution of erbium fluoride films on different substrates

Erbium fluoride (ErF₃) films were thermally deposited on Ge(1 1 1), Si(0 0 1) and copper mesh grid with different substrate temperature. X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the structure and morphology of the films. The structure of ErF₃ films deposited on germanium and silicon changed from amorphous to crystalline with increasing the substrate temperature, while the crystallization temperature of the films on silicon is higher than that of on germanium. The infrared optical properties of the films change greatly with the evolution of crystal structure. It is also found that the morphology of ErF₃ film on Ge(1 1 1) at 200 °C is modulated by the stress between the substrate and film. The SEM and TEM results confirmed that the ErF₃ films on copper mesh grid were crystalline even at 100 °C. Interestingly, the ErF₃ films show flower-like surface morphology when deposited on copper mesh at 200 °C. The crystallization temperature (T_c) of ErF₃ films on the three substrates has the relation which is which is induced by the wetting angle of ErF₃ films on different substrates.     

Formation of silicon nanodots from dysprosium-doped amorphous SiCxOy films grown by hot-filament assisted chemical vapor deposition of CH3SiH3 and Dy(DPM)3 gas jets

We report on Si nanodot formation by chemical vapor deposition (CVD) of ultrathin films and following oxidation. The film growth was carried out by hot-filament assisted CVD of CH₃SiH₃ and Dy(DPM)₃ gas jets at the substrate temperature of 600 °C. The transmission electron microscopy observation and X-ray photoelectron spectroscopy analysis indicated that ∼35 nm Dy-doped amorphous silicon oxycarbide (SiC_xO_y) films were grown on Si(1 0 0). The Dy concentration was 10-20% throughout the film. By further oxidation at 860 °C, the smooth amorphous film was changed to a rough structure composed of crystalline Si nanodots surrounded by heavily Dy-doped SiO₂.     

Nanostructure of photocatalytic TiO2 films sputtered at temperatures below 200 °C

The article reports on correlations between the process parameters of reactive pulsed dc magnetron sputtering, physical properties and the photocatalytic activity (PCA) of TiO₂ films sputtered at substrate surface temperature T_surf ≤ 180 °C. Films were deposited using a dual magnetron system equipped with Ti (Ø50 mm) targets in Ar + O₂ atmosphere in oxide mode of sputtering. The TiO₂ films with highly photoactive anatase phase were prepared without a post-deposition thermal annealing. The decomposition rate of the acid orange 7 (AO7) solution during the photoactivation of the TiO₂ film with UV light was used for characterization of the film PCA. It was found that (i) the partial pressure of oxygen pO₂ and the total sputtering gas pressure p_T are the key deposition parameters influencing the TiO₂ film phase composition that directly affects its PCA, (ii) the structure of sputtered TiO₂ films varies along the growth direction from the film/substrate interface to the film surface, (iii) ∼500 nm thick anatase TiO₂ films with high PCA were prepared and (iv) the structure of sputtered TiO₂ films is not affected by the substrate surface temperature T_surf when T_surf < 180 °C. The interruption of the sputtering process and deposition in long (tens of minutes) pulses alternating with cooling pauses has no effect on the structure and the PCA of TiO₂ films and results in a decrease of maximum value of T_surf necessary for the creation of nanocrystalline nc-TiO₂ film. It was demonstrated that crystalline TiO₂ films with high PCA can be sputtered at T_surf ≤ 130 °C. Based on obtained results a phase zone model of TiO₂ films was developed.     

Bimodal growth of manganese silicide on Si(1 0 0)

Two different growth modes of manganese silicide are observed on Si(1 0 0) with scanning tunneling microscopy. 1.0 and 1.5 monolayer Mn are deposited at room temperature on the Si(1 0 0)-(2 × 1) substrate. The as-grown Mn film is unstructured. Annealing temperatures between room temperature and 450 °C lead to small unstructured clusters of Mn or Mn_xSi_y. Upon annealing at 450 °C and 480 °C, Mn reacts chemically with the Si substrate and forms silicide islands. The dimer rows of the substrate become visible again. Two distinct island shapes are found and identified as MnSi and Mn₅Si₃.     

Influence of substrate temperature in BiFeO3-CoFe2O4 nanocomposites deposited on SrTiO3 (0 0 1)

BiFeO₃-CoFe₂O₄ epitaxial nanocomposites have been deposited on SrTiO₃ (0 0 1) substrates by pulsed laser deposition. We present here a study of the influence of the deposition temperature (T_S), in the 550-800 °C range, on the film composition, morphology and microstructure. Electron-probe microanalysis shows strong reduction of the Bi content in the films when increasing T_S. Films prepared at T_S=750 °C and above are virtually Bi-free. X-ray diffraction (XRD) data show that, due to the volatility of Bi, there is a progressive reduction in the amount of BiFeO₃. The deposition temperature and the concomitant presence of Fe_xO_y spurious phases in the nanocomposites grown at high temperature promote radical changes in film morphology and magnetization. It thus follows that a temperature range suitable for controlled modification of nanocomposites morphology would be extremely narrow.     

Fabrication of textured SnO2:F thin films by spray pyrolysis

Transparent conductive SnO₂:F thin films with textured surfaces were fabricated on soda-lime-silica glass substrates by spray pyrolysis. Structure, morphology, optical and electrical properties of the films were investigated. Results show that the film structure, morphology, haze, transmittance and sheet resistance are dependent on the substrate temperature and film thickness. An optimal 810 nm-thick SnO₂:F film with textured surface deposited at 520 °C exhibits polycrystalline rutile tetragonal structure with a (2 0 0) orientation. The sheet resistance, average transmittance in visible region, and haze of this film were 8 Ω/□, 80.04% and 11.07%, respectively, which are suitable for the electrode used in the hydrogenated amorphous silicon solar cells.     

Effect of substrate temperature and annealing temperature on the structural, electrical and microstructural properties of thin Pt films by rf magnetron sputtering

Influence of both substrate temperature, T_s, and annealing temperature, T_a, on the structural, electrical and microstructural properties of sputtered deposited Pt thin films have been investigated. X-ray diffraction results show that as deposited Pt films (T_s = 300, 400 °C) are preferentially oriented along (1 1 1) direction. A little growth both along (2 0 0) and (3 1 1) directions are also noticed in the as deposited Pt films. After annealing in air (T_a = 500-700 °C), films become strongly oriented along (1 1 1) plane. With annealing temperature, average crystallite size, D, of the Pt films increases and micro-strain, e, and lattice constant, a₀, decreases. Residual strain observed in the as deposited Pt films is found to be compressive in nature while that in the annealed films is tensile. This change in the strain from compressive to tensile upon annealing is explained in the light of mismatch between the thermal expansion coefficients of the film material and substrate. Room temperature resistivity of Pt films is dependant on both the T_s and T_a of the films. Observed decrease in the film resistivity with T_a is discussed in terms of annihilation of film defects and grain-boundary. Scanning electron microscopic study reveals that as the annealing temperature increases film densification improves. But at an annealing temperature of ∼600 °C, pinholes appear on the film surface and the size of pinhole increases with further increase in the annealing temperature. From X-ray photoelectron spectroscopic analysis, existence of a thin layer of chemisorbed atomic oxygen is detected on the surfaces of the as deposited Pt films. Upon annealing, coverage of this surface oxygen increases.     

Silicon carbonitride by remote microwave plasma CVD from organosilicon precursor: Physical and mechanical properties of deposited Si:C:N films

Silicon carbonitride (Si:C:N) films produced by the remote microwave hydrogen plasma chemical vapor deposition (RP-CVD) using bis(dimethylamino)methylsilane as single-source precursor and hydrogen as an upstream gas for plasma generation, were examined in terms of their physical (density) and mechanical (hardness, elastic modulus, friction coefficient, and “plasticity index”) properties. The effect of substrate temperature (varied in the range of 30-400 °C) on the properties of Si:C:N films is presented. A reasonable compositional and structural dependencies of film properties were determined using, respectively, the XPS atomic concentration ratios N/Si and C/Si, as well as the relative integrated intensities of the IR absorption bands from the SiN and SiC bonds (controlled by deposition temperature), evaluated in the first part of this work. In view of their good mechanical properties, Si:C:N films seem to be useful coatings for improving surface mechanics of engineering materials.     

The influence of substrate temperature and annealing on the properties of pulsed laser-deposited YIG films on fused quartz substrate

Yttrium iron garnet (YIG) thin films were deposited on fused quartz substrate at different substrate temperatures (T_s) varying from room temperature (RT) to 850 °C using pulsed laser deposition (PLD) technique. All the films in the as-deposited state were X-ray amorphous and non-magnetic at RT. The film deposited at RT after annealing at temperatures T_a?700 °C showed both X-ray peaks and the magnetic order. The films deposited at higher T_s (500–850 °C) and then annealed at 700 °C resulted in better-quality films with higher 4πM_s value. The highest value of magnetization was for the sample deposited at 850 °C and annealed at 700 °C, which is 68% of the bulk 4πM_s value.     

Growth and characterization of polycrystalline Ge1−xCx by reactive pulsed laser deposition

Polycrystalline thin films of Ge-C were grown on Si (1 1 1) substrates by means of reactive pulsed laser deposition with methane pressure of 100 mTorr. Effect substrate temperature, T_s, on C incorporation to substitutional sites (x) in Ge_1−xC_x was investigated systematically by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyzes. The substrate temperatures were ranging from 250 to 400 °C. The substitutional C composition x in the films by XRD were estimated using the Vegard's linear law. The maximum value of x calculated by XRD was 0.032 for T_s of 350 °C. The position of the C 1s peak at 283.4 eV in the XPS spectrum confirmed the germanium-carbon alloys. XRD measurements indicated that x increased with T_s from 250 °C to 350 °C. At T_s = 400 °C, the estimation of x was lowered. However, the C content calculated by XPS analyzes increased with T_s being more these values than substitutional C composition x. XPS and XRD analyzes demonstrate that the remaining C atoms are incorporated to interstitial sites. The use of the T_s plays important roles in the incorporation of substitutional C and in restraining C-cluster formation in the reactive pulsed laser deposition growth of Ge-C/Si.     

Interaction of copper with sulfur on the sulfur-terminated Si(1 1 1)-(7 × 7) surface

The adsorption of S₂ on the Si(1 1 1)-(7 × 7) surface and the interaction of copper and sulfur on this sulfur-terminated Si(1 1 1) surface have been studied using synchrotron irradiation photoemission spectroscopy and scanning tunneling microscopy. The adsorption of S₂ at room temperature results in the passivation of silicon dangling bonds of Si(1 1 1)-(7 × 7) surface. Excessive sulfur forms S_n species on the surface. Copper atoms deposited at room temperature directly interact with S-adatoms through the formations of Cu-S bonds. Upon annealing the sample at 300 °C, CuS_x nanocrystals were produced on the sulfur-terminated Si(1 1 1) surface.     

Study of electronic structures for Fe thin films deposited on Si- and C-faces of 4H-SiC substrates by soft X-ray emission spectroscopy

Silicon carbide (SiC) is a candidate material for electronic devices to operate upon crucial environment. Electronic states of silicides and/or carbide/graphite formed in metal/SiC contact system are fundamentally important from the viewpoint of device performance.We study interface electronic structure of iron thin film deposited on silicon (Si)- and carbon (C)-face of 4H-SiC(0 0 0 1) by using a soft X-ray emission spectroscopy (SXES). For specimens of Fe (50 nm)/4H-SiC (substrate) contact systems annealed at 700 and 900 °C, the Si L_2,3 emission spectra indicate different shapes and peak energies from the substrate depending on thermal-treated temperature. The product of materials such as silicides is suggested. Further, from comparison of Si L_2,3 emission spectra between Si- and C-face for the same annealing temperature at 700 °C, it is concluded that the similar silicides and/or ternary materials are formed on the two surfaces. However for those of 900 °C, the film on substrate is composed of the different silicide and/or ternary materials.     

Effects of oxygen partial pressure and substrate temperature on the structure and optical properties of MgxZn1−xO thin films prepared by magnetron sputtering

Deposited with different oxygen partial pressures and substrate temperatures, Mg_xZn_1−xO thin films were prepared using a Mg_0.6Zn_0.4O ceramic target by magnetron sputtering. The structural and optical properties of the prepared thin films were investigated. The X-ray diffraction spectra reveal that all the films on quartz substrate are grown along (2 0 0) orientation with cubic structure. The lattice constant decreases and the crystallite size increases with the increase of substrate temperature. Both energy dispersive X-ray spectroscopy and calculated results suggest the ratio of Mg/Zn increases with increasing substrate temperature. The thin film deposited with T_s = 500 °C has a minimal rms roughness of 7.37 nm. The transmittance of all the films is higher than 85% in the visual region. The optical band gap is not sensitive to the oxygen partial pressure, while it increases from 5.63 eV for T_s = 100 °C to 5.95 eV for T_s = 700 °C. In addition, the refractive indices calculated from transmission spectra are sensitive to the substrate temperature. The photoluminescence spectra of Mg_xZn_1−xO thin films excited by 330 nm ultraviolet light indicate that the peak intensity of the spectra is influenced by the oxygen partial pressure and substrate temperature.     

In situ growth stresses during the phase separation of immiscible FeCu thin films

This paper addresses the in situ growth stress evolution and post-growth stress relaxation during the phase separation of immiscible Fe_0.51Cu_0.49 thin films at various in situ deposition temperatures. Each film was sputter-deposited onto a 10 nm Si₃N₄ underlayer that was grown on top of Si [0 0 1] substrate at 25 °C, 145 °C, 205 °C, 265 °C or 325 °C. The thin film stress was measured using a wafer curvature technique. The in situ growth stress increased in compression with increasing substrate temperature. The stress relaxation of the Fe_0.51Cu_0.49 was found to have a linear increase with the inverse grain size for films deposited at temperatures greater than 205 °C. The stress state was correlated to the films’ phase and morphology by X-ray diffraction, (scanning) transmission electron microscopy and atomic force microscopy techniques.     

Four-fold magnetic anisotropy in a Co film on MgO(0 0 1)

The development of devices based on magnetic tunnel junctions has raised new interests on the structural and magnetic properties of the interface Co/MgO. In this context, we have grown ultrathin Co films (≤30 Å) by molecular-beam epitaxy on MgO(0 0 1) substrates kept at different temperatures (T_S). Their structural and magnetic properties were correlated and discussed in the context of distinct magnetic anisotropies for Co phases reported in the literature. The sample characterization has been done by reflection high energy electron diffraction, magneto-optical Kerr effect and ferromagnetic resonance. The main focus of the work is on a sample deposited at T_S=25 °C, as its particular way of growth has enabled a bct Co structure to settle on the substrate, where it is not normally obtained without specific seed layers. This sample presented the best crystallinity, softer magnetic properties and a four-fold in-plane magnetic anisotropy with Co〈1 1 0〉 easy directions. Concerning the samples prepared at T_S=200 and 500° C, they show fcc and polycrystalline structures, respectively and more intricate magnetic anisotropy patterns.     

The influence of substrate temperature variation on tungsten oxide thin film growth in an HFCVD system

Tungsten oxide (WO₃) thin films were deposited by a modified hot filament chemical vapor deposition (HFCVD) technique using Si (1 0 0) substrates. The substrate temperature was varied from room temperature to 430 °C at an interval of 100 °C. The influence of the substrate temperature on the structural and optical properties of the WO₃ films was studied. X-ray diffraction and Raman spectra show that as substrate temperature increases the film tends to crystallize from the amorphous state and the surface roughness decreases sharply after 230 °C as confirmed from AFM image analysis. Also from the X-ray analysis it is evident that the substrate orientation plays a key role in growth. There is a sharp peak for samples on Si substrate due to texturing. The film thickness also decreases as substrate temperature increases. UV-vis spectra show that as substrate temperature increases the film property changes from metallic to insulating behavior due to changing stoichiometry, which was confirmed by XPS analysis.     

Effect of oxidation temperature on microstructure, mechanical behaviors and surface morphology of nanocomposite Ti-Cx-Ny thin films

Two nanocomposite Ti-C_x-N_y thin films, TiC_0.95N_0.60 and TiC_2.35N_0.68, as well as one pure TiN, were deposited at 500 °C on Si(1 0 0) substrate by reactive unbalanced dc-magnetron sputtering. Oxidation experiments of these films were carried out in air at fixed temperatures in a regime of 250-600 °C with an interval of 50 °C. As-deposited and oxidized films were characterized and analyzed using X-ray diffraction (XRD), microindentation, Newton's ring methods and atomic force microscopy (AFM). It was found that the starting oxidation temperature of nanocomposite Ti-C_x-N_y thin films was 300 °C irrespective of the carbon content; however their oxidation rate strongly depended on their carbon content. Higher carbon content caused more serious oxidation. After oxidation, the film hardness value remained up to the starting oxidation temperature, followed by fast decrease with increasing heating temperature. The residual compressive stress did not show a similar trend with the hardness. Its value was first increased with increase of heating temperature, and got its maximum at the starting oxidation temperature. A decrease in residual stress was followed when heating temperature was further increased. The film surface roughness value was slightly increased with heating temperature till the starting oxidation temperature, a great decrease in surface roughness was followed with further increase of heating temperature.     

Proton NMR relaxation study of the CsHSO4 solid acid system

At 141 °C the solid acid CsHSO₄ is known to undergo transition to a superprotonic phase that is characterized by dramatic (several-order-of-magnitude) increases in hydrogen ion conductivity. Proton NMR spin-spin relaxation time T₂ measurements reported here for CsHSO₄ also reveal substantial increases (factors of 20-30) in the vicinity of the transition temperature. In the temperature range just below the transition (70-136 °C), T₂ increases by a factor of order 10 relative to the rigid-lattice regime, suggesting motional narrowing of the NMR resonance line. In the regime of motional narrowing, the activation energy barrier to diffusion is 0.40 eV, as determined from the present T₂ results. NMR spin-lattice relaxation T₁ measurements also show behavior consistent with transition to a regime of rapid hydrogen motion. In particular, proton T₁'s decrease with temperature (from 80 to 120 °C), and then drop sharply near the transition temperature. Above the transition temperature, T₁ exhibits a minimum in which the correlation time is found to be ∼2 ns.