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1.
Ricardo S. Schrebler Paula Grez Eduardo C. Muñoz Ricardo A. Córdova Enrique A. Dalchiele 《Thin solid films》2010,518(23):6844-6852
In this work morphological, structural and photoelectrochemical properties of n-type α-Fe2O3 (hematite) thin films synthetized by means of two different electrochemical procedures: potential cycling electrodeposition (PC) and potential pulsed electrodeposition (PP) have been studied. The X-ray diffraction measurements showed that the films obtained after a thermal treatment at 520 °C present a nanocrystalline character. Scanning electron microscopy allowed finding that hematite films obtained by PP technique exhibit nanostructured morphology. The electrochemical and capacitance (Mott-Schottky and parallel capacitance) measurements showed that when in the PC and PP procedures the anodic limit Eλ,A is being made more anodic, a decrease of the majority carriers concentration (ND) and the surface states number has been observed. The photovoltammetry measurements indicated that the hematite films formed with the PP technique present a photocurrent one order of magnitude higher than the ones exhibited by the iron oxide films formed by PC. For instance, PP hematite films exhibit photovoltaic conversion efficiencies of 0.96% which are 2.5 times higher than the corresponding to the PC ones (0.38%). The maximum incident photon-to-current efficiency measured at λ = 370 and 600 nm was observed for hematite films grown by the PP procedure. By means of the photocurrent transient technique a decrease in the recombination process for those samples synthesized by PP was observed. The results obtained are discussed considering the influence of the anodic limit of the potential employed during the preparation of the iron oxyhydroxide (β-FeOOH) precursor film, all of this related to a decrease of the oxygen defects in this material and to a decrease of Fe(II) amount that is formed during the electrodeposition process. 相似文献
2.
Nitrogen ions were implanted into [1 0 0] oriented α-Fe thin films on MgO (1 0 0) substrates at room temperature. The films
were annealed at a low temperature of 473 K. α″-Fe16N2 and α′-martensite phases were formed and the volume fractions of these nitride phases were estimated from the X-ray diffraction
patterns. When the film thickness was 250 nm, α″-Fe16N2 was formed directly by ion implantation and the maximum volume fraction was about 12%. For the case of 50 nm thick films,
no α″-Fe16N2 but α′-martensite was formed after nitrogen-ion implantation, and the volume fraction of the martensite exceeded 90%. By
post annealing at 473 K, α″-Fe16N2 was formed, when the implanted specimens were coated with gold or copper films. The volume fraction of α″-Fe16N2 reached about 36%. A SQUID magnetic measurement showed that the saturation magnetization of the nitrogen-implanted 250 nm
thick iron films was a few per cent larger than that of unimplanted iron films.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
3.
Thin films of Al-Sb of varying compositions and thickness have been formed on glass substrates employing three-temperature
method. Electrical resistivity (ρ) and activation energy (ΔE) have been studied as a function of composition, thickness (d) and temperature of the film. Films of Al-Sb system with aluminium < 50 at.%, ∼ 50 at.% and > 50 at.% exhibit metallic, semiconducting
and metallic to semiconducting behaviours respectively. Activation energy (ΔE) of semiconducting films found to vary inversely with thickness, is attributed to combined effects of change in barrier height
due to the size of grains and stoichiometry in the films. 相似文献
4.
Deok-kee Kim 《Thin solid films》2012,520(21):6571-6575
Hillock formation in Al thin films with varying thicknesses of SiO2 as a passivation layer was investigated during thermal cycling. Based on the stress measurements and the number of hillocks, 250 nm thick SiO2 was thick enough to suppress the hillock formation and the suppression of hillock at 250 nm passivation and the lack of suppression at thinner passivation is related to the presence/absence of protection against the diffusive flow of atoms from the surrounding area to the surface due to the biaxial compressive stresses present in the film through the weak spots in the passivation layer. The stress state of Al films measured during annealing (the driving force for hillock formation) did not vary much with SiO2 thickness. A small number of hillocks formed during the plasma enhanced chemical vapor deposition of SiO2 overlayers at 300 °C. 相似文献
5.
The paper analyses, at nanoscale levels, the chemical composition and mechanical properties of the anodic oxide films formed on Ti-6Al-4V alloy by galvanostatic polarization at maximum final voltages of 12-100 V. For the investigations Auger Electron Spectroscopy, Photoelectron Spectroscopy and nanoindentation measurements have been used. The results have shown that anodizing the Ti-6Al-4V alloy produces an oxide film whose thickness depends on the final voltage. The chemical composition is not significantly dependent on the thickness, the film consists of TiO2 and Al2O3. However, the best insulating properties of the films, determined from the growth parameter nm/V, are achieved with a final voltage between 30 and 65 V. Nanohardness and Young's modulus measurements have shown that the anodic films formed by different voltages exhibit similar mechanical properties which is consistent with the results of the surface analysis. 相似文献
6.
Irine Banu Lucy 《Journal of Materials Science》2007,42(14):5875-5879
Capacitance and dielectric loss measurements were carried out using an Al/Cu–GeO2/Al sandwich structure for 0 to 10 vol% Cu films, 120–400 nm thick, deposited at 0.4–1.5 nm/s in the frequency and temperature
range 1–106 Hz and 90–573 K, respectively. The variation of capacitance and dielectric loss with frequency and temperature follows the
Goswami and Goswami model. Capacitance decreases slowly with increasing thickness and also varies with the change in deposition
rate of the cermet film. 相似文献
7.
Magnetron sputtered Ni thin films on both oxidised Si (100) and α-Al2O3 (0001) substrates of thickness 150–1000 nm were tested thermomechanically with a wafer curvature system, as well as in situ
in a transmission electron microscope. The films on oxidised Si have a {111}-textured columnar microstructure with a mean
grain size similar to the film thickness. On (0001) α-Al2O3 a near single crystal epitaxy with two growth variants is achieved leading to a significantly larger grain size. The thermomechanical
testing was analysed in terms of the room temperature/high temperature flow stresses in the films and the observed thermoelastic
slopes. It was found that the room temperature flow stresses increased with decreasing film thickness until a plateau of ∼1100 MPa
was reached for films thinner than 400 nm. This plateau is attributed to the present experiments exerting insufficient thermal
strain to induce yielding in these thinner films. At 500 °C the compressive flow stresses of the films show a competition
between dislocation and diffusion mediated plasticity. A size effect is also observed in the thermoelastic slopes of the films,
with thinner films coming closer to the slope predicted by mismatch in thermal expansion coefficients. It is put forward here
that this is due to a highly inhomogeneous stress distribution in the films arising from the grain size distribution. 相似文献
8.
Ahmed M. El-Naggar 《Journal of Materials Science: Materials in Electronics》2012,23(4):972-976
GaN films with different thicknesses were grown on Si(111) substrates by Plasma—Assisted Molecular Beam Epitaxy (PA-MBE).
The optical properties of the films were investigated using spectrophotometric measurements of the reflectance in the wavelength
range 200–3,300 nm. With increasing film thickness, the refractive index (n) increased slightly, while the optical energy
gap (Eg) changed with no specific trend. The structural properties of the grown films were studied at (002) reflections using two
types of rocking curve measurements; normal rocking curve (ω-scan) and triple axis rocking curve (ω/2θ-scan). The Full Width
at Half Maximum (FWHM) of rocking curve decreased with increasing film thickness. Hall effect measurements showed that all
the samples were n-type with carrier concentrations decreasing from 8.025 × 1018 to 5.65 × 1017 cm−3, and mobility increasing from 14 to 110 cm2 V−1 s−1 as increasing the film thickness from 590 to 1,420 nm, respectively. Photoluminescence (PL) spectra for the grown GaN films
with different thicknesses were measured at room temperature. PL spectra for all the samples exhibited band edge (BE) emissions
at peak energies of 3.24 eV, with peak intensities increased with increasing the film thickness. 相似文献
9.
N. V. Lyanguzov V. E. Kaydashev E. M. Kaidashev K. G. Abdulvakhidov 《Technical Physics Letters》2011,37(3):193-196
The influence of thicknesses of a ZnO sublayer and a copper catalyst film on the morphology of ZnO nanorods grown by carbothermal
synthesis on α-Al2O3(11–20) substrates has been studied. An increase in the Cu catalyst film thickness leads to a growth in the diameters, heights,
and surface density of nanorods. As the ZnO sublayer thickness is increased, the average diameter of nanorods also increases,
while their lengths and surface density decrease. The effect of elevated temperatures on the thermal decomposition of ultrathin
Cu films deposited on α-Al2O3 substrates has been studied. The photoluminescence characteristics of nanorod arrays have been measured at high levels of
optical pumping. An increase in the pumping level to 250–280 kW/cm2 leads to superluminescence of the nanorods. 相似文献
10.
Alternating current (a.c.) electrical properties of thermally evaporated amorphous thin films of SnO2 sandwiched between aluminium electrodes have been investigated for temperature during electrical measurements, film thickness,
substrate temperature and post-deposition annealing. The a.c. conductivity, σ(ω), is found to vary with frequency according
to the relation σ(ω) ∝ ωs, indicating a hopping process at low temperature. The conduction is explained by single polaron hopping process as proposed
by Elliott. The increase in electrical conductivity with increase in temperature during electrical measurements is ascribed
to the increase in the formation and high mobility of doubly ionized oxygen vacancies. The increase in conductivity with increase
in film thickness is caused by the increase in interstitial tin, oxygen vacancies and defects produced due to deviation from
stoichiometry. The increase in conductivity with increase in substrate and annealing temperature may be due to the formation
of singly or doubly ionized oxygen vacancies and tin species of lower oxidation state. Measurements of capacitance C as a function of frequency and temperature show a decrease in C with increasing frequency and increase in C with increasing temperature. The increase in capacitance in the high-temperature low-frequency region is probably due to
space charge polarization induced by the increasing number of free carriers as a result of increasing temperature. 相似文献
11.
M.V. Popa P. Drob E. Vasilescu J.C. Mirza-Rosca A. Santana Lopez C. Vasilescu S.I. Drob 《Materials Chemistry and Physics》2006,100(2-3):296-303
This paper presents the results regarding the pigments effect on the protective properties of alkyd films in 3% natrium chloride solution. The films were realized on carbon steel substrate from an alkyd resin using the pigments of metallic, mineral and organic type. Dry films thickness in 30–35 μm range was obtained. Electrochemical techniques (electrochemical impedance spectroscopy (EIS) and stepwise polarization) were used. The interpretation of the impedance spectra (Nyquist and Bode diagrams) with the immitance analysis Equivcrt. Programme established two electrical equivalent circuits (with two and four time constants) for the carbon steel/alkyd film systems in electrolyte solution, fitted to the experimental data. The electric capacitance and resistance of the alkyd films were monitored with the immersion time to establish the water and ions permeability of these paint films. The electrochemical parameters of alkyd coated carbon steel from the anodic potentiostatic polarisation curves were determined. The correlation of all experimental results established that the tested pigments except the green organic pigment increase the protective performances of alkyd coatings. Best protection of the carbon steel was found for the alkyd film with aluminum powder pigment. 相似文献
12.
A. Hardy S. Van Elshocht C. De Dobbelaere J. Hadermann G. Pourtois S. De Gendt V.V. Afanas’ev M.K. Van Bael 《Materials Research Bulletin》2012,47(3):511-517
Ultrathin bismuth titanate films (Bi2Ti2O7, 5–25 nm) are deposited onto SiO2/Si substrates by aqueous chemical solution deposition and their evolution during annealing is studied. The films crystallize into a preferentially oriented, pure pyrochlore phase between 500 and 700 °C, depending on the film thickness and the total thermal budget. Crystallization causes a strong increase of surface roughness compared to amorphous films. An increase of the interfacial layer thickness is observed after anneal at 600 °C, together with intermixing of bismuth with the substrate as shown by TEM-EDX. The band gap was determined to be ~3 eV from photoconductivity measurements and high dielectric constants between 30 and 130 were determined from capacitance voltage measurements, depending on the processing conditions. 相似文献
13.
Shaohua Shen Coleman X. Kronawitter Jiangang Jiang Samuel S. Mao Liejin Guo 《Nano Research》2012,5(5):327-336
Hematite (α-Fe2O3) nanorod films with their surface tuned by W6+ doping have been investigated as oxygen-evolving photoanodes in photoelectrochemical cells. X-ray diffraction, field emission scanning electron microscopy, UV-visible absorption spectroscopy, and photoelectrochemical (PEC) measurements have been performed on the undoped and W6+-doped α-Fe2O3 nanorod films. W6+ doping is found to primarily affect the photoluminescence properties of α-Fe2O3 nanorod films. Comparisons are drawn between undoped and W6+-doped α-Fe2O3 nanorod films, WO3 films, and α-Fe2O3-modified WO3 composite electrodes. A close correlation between dopant concentration, photoluminescence intensity, and anodic photocurrent was observed. It is suggested that W6+ surface doping promotes charge transfer in α-Fe2O3 nanorods, giving rise to the enhanced PEC performance. These results suggest surface tuning via ion doping should represent a viable strategy to further improve the efficiency of α-Fe2O3 photoanodes. 相似文献
14.
The beneficial effect of nitrogen alloying on the corrosion resistance of stainless steels has been attributed to the increase of the local pH within the active sites and the enhanced repassivation of the metastable pits. In order to better understand the effect of nitrogen alloying, in situ capacitance measurements and potentiostatic polarization were conducted for 316L and 316LN stainless steels with different nitrogen contents in deaerated 0.1 M Na2SO4 and 0.1 M NaCl aqueous solutions. The Mott–Schottky plots obtained from the in situ capacitance measurements offered information on the donor concentration and the thickness of the space charge region within the passive film. The metastable pitting susceptibility was investigated by performing potentiostatic polarization tests. The results showed that nitrogen alloying decreased the donor densities and the number of metastable pits, while the absorption of chloride ions on the passive film had the opposite effect. Auger electron spectroscopy (AES) analysis demonstrated that nitrogen alloying enriched the chromium within the passive film. The relationship between the semiconducting properties of the passive film and the metastable pitting susceptibility was elucidated. 相似文献
15.
Lee TM 《Journal of materials science. Materials in medicine》2006,17(1):15-27
The aim of the present study was to investigate the effects of passivation treatment (34% nitric acid passivation, 400 ∘C heated in air, and aged in 100 ∘C de-ionized water) and surface modification (2 hr and 8 hr vacuum-brazed treatments) on the ion dissolution and nano-surface
characteristics of Ti-6Al-4V exposed in Hank's solution with 8.0 mM ethylene diamine tetra-acetic acid (EDTA) at 37 ∘C. The results indicated that the original nano-surface characteristics and microstructure would influence the ion dissolution
but not change the capability of the Ca and P adsorption upon immersion. Of the three passivated treatments, 400 ∘C thermal treatment for both 2 hr brazed Ti-6Al-4V (B2) and 8 hr brazed Ti-6Al-4V (B8) exhibits a substantial reduction in
the constituent release compared to the acid passivated and water aged treatment, because the thicker thickness and rutile
structure of surface oxide could provide the better dissolution resistance for 400 ∘C-treated specimens. Moreover, the reduced Ti2Cu and increased α -titanium structure in B8 specimen could also improve ion dissolution resistance in comparison with B2
specimen. After soaking in Hank/EDTA solution, the adsorbed non-elemental Ca and P for all groups of specimens were observed
by XPS analysis, and the AES depth-profile analysis indicate that the oxide films of all groups of specimens thicken with
the longer immersion periods. The increasing oxide thickness may be the factor in the improved dissolution resistance at the
longer immersion periods. The relation between lower dissolution rate and thicker oxide films were observed for all groups
of specimens. The results suggest that the dissolution kinetics was governed by the metal ion transport through the oxide
film in this study. 相似文献
16.
E. Şenarslan B. Güzeldir M. Sağlam 《Journal of Materials Science: Materials in Electronics》2017,28(11):7582-7592
In this paper, the V2O5 thin film has been grown on the both p-type semiconductor and glass substrate by the spray pyrolysis method. For optical and structural properties of thin film, the optical absorption, SEM, AFM and XRD measurements have been done. It is observed that films exhibit polycrystalline behavior. The effects of anodic passivation on the characteristic parameters of diodes have been investigated using current–voltage (I–V) characteristics. The I–V measurements of the diodes have been performed at the room temperature in the dark. The main electrical parameters such as ideality factor (n) and barrier height (Φ b ) of diodes have been calculated from the forward bias I–V characteristics. Likewise, the values of series resistance (R s ) of diodes have been obtained from Norde method. It is observed that while the ideality factor decreases with anodic passivation, the barrier height increases. 相似文献
17.
Cerium oxide (CeO2) thin films have been prepared by electron beam evaporation technique onto glass substrate at a pressure of about 6 × 10−6 Torr. The thickness of CeO2 films ranges from 140–180 nm. The optical properties of cerium oxide films are studied in the wavelength range of 200–850
nm. The film is highly transparent in the visible region. It is also observed that the film has low reflectance in the ultra-violet
region. The optical band gap of the film is determined and is found to decrease with the increase of film thickness. The values
of absorption coefficient, extinction coefficient, refractive index, dielectric constant, phase angle and loss angle have
been calculated from the optical measurements. The X-ray diffraction of the film showed that the film is crystalline in nature.
The crystallite size of CeO2 films have been evaluated and found to be small. The experimental d-values of the film agreed closely with the standard values. 相似文献
18.
M. Bleiweiss J. Amirzadeh M. Yin A. Lungu T. Datta 《Journal of Superconductivity and Novel Magnetism》2005,18(4):567-572
Synthesis and optical transmission of MgB2 thin films on optically transparent glass are reported. In the 400–1000 nm regime as deposited films show high metallic reflectivity
and very little transmission. After deposition, the films were annealedex situ and rendered superconducting withT
c of 38 K, approaching that of the bulk material. The reaction conditions where quite soft ∼ 10 min at 550°C. The optical absorption
coefficient,α and photon energy,E followed a Tauc-type behavior, (αE)1/2=β
T(E −E
g). The band gap (E
g) was observed to peak at 2.5 eV; but, the slope parameterβ
Tbehaved monotonically with reaction temperature. Our results indicate that an intermediate semiconducting phase is produced
before the formation of the superconducting phase; also optical measurements provide valuable information in monitoring the
synthesis of MgB2 from its metallic constituents. In addition these films have interesting optical properties that may be integrated into optoelectronics. 相似文献
19.
Shaily M. Bhola Rahul Bhola Brajendra Mishra David L. Olson 《Journal of Materials Science》2010,45(22):6179-6186
Electrochemical impedance spectroscopic characterization of the low modulus Ti–35.5Nb–7.3Zr–5.7Ta alloy has been performed
in phosphate buffer saline solution at 37 °C. Measurements were performed at various immersion intervals up to 720 h at OCP
and also at various anodic potentials up to 2 V. The alloy exhibits a two time constant impedance response at the OCP and
a one-time constant response at anodic potentials in the passive region. The thickness of the oxide film formed has been evaluated
and the electrochemical interpretation of the results has been reported. Cyclic potentiodynamic profile of the alloy displays
valve metal characteristics and the presence of a wide passive region that extends up to the maximum potential value of 2 V
studied. 相似文献
20.
The electrochemical behavior of nano and microcrystalline Fe–10Cr and Fe–20Cr alloys was determined using potentiodynamic polarization in 0.5 M H2SO4. Disks of the alloys were prepared by high-energy ball milling followed by compaction and sintering. In the current study, nanocrystalline Fe–Cr alloys reveal significantly different electrochemical characteristics, typified by lower anodic current densities and more negative passivation potentials, compared with their microcrystalline counterparts. In addition to the differences in grain boundary density, compositional characterization of corrosion films carried out by X-ray photoelectron spectroscopy indicates a higher Cr content in the film developed upon nanocrystalline Fe–Cr alloys. Mechanisms for observed enhancement in the corrosion performance of the nanocrystalline Fe–Cr alloys are discussed. 相似文献