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1.
ZnO thin film with strong orientation (0 0 2) and smooth surface morphology was electrosynthesized on ITO-coated glass substrate at room temperature under pulsed voltage. Photoluminescence (PL) shows two obvious peaks: violet band and strong green band. The former is due to the free-excitonic transition and the latter is believed to arise from the single ionized oxygen vacancy (VO+). Raman scattering reveals that the 580 cm−1 mode and the shoulder peak mode at 550 cm−1 originate from the N-related local vibration mode (LVM) and E1 (LO) mode, respectively.  相似文献   

2.
ZnO films were prepared using radio frequency magnetron sputtering on Si(1 1 1) substrates that were sputter-etched for different times ranging from 10 to 30 min. As the sputter-etching time of the substrate increases, both the size of ZnO grains and the root-mean-square (RMS) roughness decrease while the thickness of the ZnO films shows no obvious change. Meanwhile, the crystallinity and c-axis orientation are improved by increasing the sputter-etching time of the substrate. The major peaks at 99 and 438 cm−1 are observed in Raman spectra of all prepared films and are identified as E2(low) and E2(high) modes, respectively. The Raman peak at 583 cm−1 appears only in the films whose substrates were sputter-etched for 20 min and is assigned to E1(LO) mode. Typical ZnO infrared vibration peak located at 410 cm−1 is found in all FTIR spectra and is attributed to E1(TO) phonon mode. The shoulder at about 382 cm−1 appearing in the films whose substrates were sputter-etched for shorter time (10-20 min) originates from A1(TO) phonon mode. The results of photoluminescence (PL) spectra reveal that the optical band gap (Eg) of the ZnO films increases from 3.10 eV to 3.23 eV with the increase of the sputter-etching time of the substrate.  相似文献   

3.
ZnO films prepared from the ZnO target containing 2% AlN are transparent irrespective of radio frequency (RF) power. The obtained ZnO films have the carrier density of 3.8 × 1020 cm−3 or less and the low mobility of 5.3-7.8 cm2/(V s). In the case of 5% AlN target, ZnO films prepared at 40, 60 and 80 W are transparent, whereas ZnO films prepared at 100 and 120 W are colored. As RF power increases from 40 to 120 W, the carrier density increases straightforwardly up to 5.5 × 1020 cm−3 at 100 W and is oppositely reduced to 3.2 × 1020 cm−3 at 120 W. In the case of 10% AlN target, ZnO films prepared at 60 W or more are colored, and have the carrier density of 4 × 1020 cm−3 or less. The N-concentration in these colored films is estimated to be 1% or less. The Al-concentration in the ZnO films prepared from the 5 and 10% AlN targets is higher than 2%. The carrier density of the ZnO films containing Al and N atoms is nearly equal to that of ZnO films doped with Al atoms alone. There is no evidence in supporting the enhancement of the carrier density via the formation of N-AlxZn4−x clusters (4 ≥ x ≥ 2).  相似文献   

4.
Synthesis of large-quantity uniformly distributed ZnO hollow objects, i.e. cages and spheres have been performed on Si(1 0 0) and steel alloy substrates by the direct heating of metallic zinc powder in the presence of oxygen. Extensive structural observations revealed that the formed products are crystalline ZnO with the wurtzite hexagonal phases. The Raman-active optical phonon E2 modes, attributed to wurtzite hexagonal phase of ZnO, were observed at 437 cm−1 for the products grown on both the substrates. The room-temperature photoluminescence spectra showed a broad band in the visible region with a suppressed UV emission, indicating the presence of oxygen vacancies and structural defects in the as-grown structures. Additionally, post growth annealing was also carried out to further investigate the photoluminescence properties of the as-grown products. It was observed that the formation of hollow objects consists of several stages which include the formation of Zn clusters, oxidation on the sheath and sublimation/evaporation of the Zn from the interiors, resulted in the formation of hollow objects.  相似文献   

5.
Carbon nanofibers were grown by electrodeposition technique onto aligned zinc oxide (ZnO) nanorods deposited by hybrid wet chemical route on glass substrates. X-ray diffraction traces indicated very strong peak for reflections from (0 0 2) planes of ZnO. The Raman spectra were dominated by the presence of G band at about 1597 cm−1 corresponding to the E2g tangential stretching mode of an ordered graphitic structure with sp2 hybridization and a D band at about 1350 cm−1 originating from disordered carbon. Fourier transformed infrared studies indicated the presence of a distinct characteristic absorption peak at ∼511 cm−1 for Zn-O stretching mode. Photoluminescence spectra indicated band edge luminescence of ZnO at ∼3.146 eV along with a low intensity peak at ∼0.877 eV arising out of carbon nanofibers. Field emission properties of these films and their dependence on the CNF coverage on ZnO nanorods are reported here. The average field enhancement factor as determined from the slope of the FN plot was found to vary between 1 × 103 and 3 × 103. Both the values of turn-on field and threshold field for CNF/ZnO were lower than pure ZnO nanorods.  相似文献   

6.
The experimental results on the synthesis and characterization of tetraethoxysilane (TEOS) based hydrophobic silica aerogels using hexadecyltrimethoxysilane (HDTMS) as a hydrophobic reagent by two step sol-gel process, are described. The molar ratio of tetraethoxysilane (TEOS), methanol (MeOH), acidic water (0.001 M, oxalic acid) and basic water (10 M, NH4OH) was kept constant at 1:55:3.25:1.25 and the molar ratio of HDTMS/TEOS (M) was varied from 0 to 28.5 × 10−2. The organic modification was confirmed by infrared spectroscopic studies, and the hydrophobicity of the aerogels was tested by the contact angle measurements. The maximum contact angle of 152° was obtained for M = 22.8 × 10−2. The aerogels retained the hydrophobicity up to a temperature of 240 °C and above this temperature the aerogels became hydrophilic. The aerogels were characterized by the thermal conductivity, density, contact angle measurements, optical transmission and scanning electron micrographs.  相似文献   

7.
ZnO nanospheres were synthesized by a wet-chemical method. X-ray diffraction and field-emission scanning electron microscopy confirmed the formation of wurtzite-structured ZnO with regular sphere shape. Two Raman modes located at 333 cm−1 and 437 cm−1 with two additional Raman humps centered at 577 cm−1 and 1077 cm−1 were observed. Photoluminescence spectra showed ultraviolet, green, orange and red emissions, which changed significantly after the samples were annealed in air, oxygen, argon and forming gas four different ambiences. All the evidence indicates that surface states are responsible to orange and red emissions in addition to excitonic recombination (3.18 eV) and oxygen vacancy (2.25 eV) emission.  相似文献   

8.
Bifunctional magnetic-optical Fe3O4/ZnO nanocomposites with different molar ratio were successfully synthesized by a facile two-step strategy. Compared with the other methods, it was found to be mild, inexpensive, green, convenient and efficient. Fe3O4 nanocrystal was used as seed for the deposit and growth of ZnO nanoparticle. A series of the characterizations manifested that the combination of Fe3O4 with ZnO nanoparticles was successful. Photocatalytic activity studies confirmed that as-prepared nanocomposites had excellent photodegradating behavior to Methyl Orange (MO) compared to the pure ZnO nanoparticles. The results showed that the degradation percentage of MO was about 93.6% for 1 h when the amount of catalyst was 0.51 g L−1 and initial concentration of MO was 6 × 10−5 mol L−1 in the pH 7 solution. Moreover, the kinetics of photocatalytic degradation reaction could be expressed by the first-order reaction kinetic model. Furthermore, the Fe3O4/ZnO nanocomposites could be also served as convenient recyclable photocatalysts because of their magnetic properties.  相似文献   

9.
Solid-state reaction processing technique was used to prepare ZnxNb1−xO (0≤x≤0.02) polycrystalline bulk samples. In the present study, we find that their lattice parameters a and c tend to decrease with increasing amount of Nb additive. The electrical conductivity of all the Zn1−xNbxO samples increased with increasing temperature, indicating a semiconducting behavior in the measured temperature range. The addition of Nb2O5 to ZnO led to an increase in the electrical conductivity and a decrease in the absolute value of the Seebeck coefficient. The best performance at 1000 K has been observed for nominal 0.5 at% Nb-doped ZnO, with an electrical resistivity of about 73.13 (S cm−1) and Seebeck coefficient of ∼257.36 μV K−1, corresponding to a power factor (S2σ) of 4.84×10−4 Wm−1 K−2. The thermal conductivity, κ, of the oxide decreased as compared to pure ZnO. The figure of merit ZT values of ZnO-doped Nb2O5 samples are higher than the ZnO pure sample, demonstrating that the Nb2O5 addition is fairly effective for enhancing thermoelectric properties.  相似文献   

10.
We report on the growth of cubic spinel ZnCo2O4 thin films by reactive magnetron sputtering and bipolarity of their conduction type by tuning of oxygen partial pressure ratio in the sputtering gas mixture. Crystal structure of zinc cobalt oxide films sputtered in an oxygen partial pressure ratio of 90% was found to change from wurtzite Zn1−xCoxO to spinel ZnCo2O4 with an increase of the sputtering power ratio between the Co and Zn metal targets, DCo/DZn, from 0.1 to 2.2. For a fixed DCo/DZn of 2.0 yielding single-phase spinel ZnCo2O4 films, the conduction type was found to be dependent on the oxygen partial pressure ratio: n-type and p-type for the oxygen partial pressure ratio below ∼70% and above ∼85%, respectively. The electron and hole concentrations for the ZnCo2O4 films at 300 K were as high as 1.37×1020 and 2.81×1020 cm−3, respectively, with a mobility of more than 0.2 cm2/V s and a conductivity of more than 1.8 S cm−1.  相似文献   

11.
Fluorine and hydrogen co-doped ZnO:Al (AZO) films were prepared by radio frequency (rf) magnetron sputtering of ZnO targets containing 1 wt.% Al2O3 on Corning glass at substrate temperature of 150 °C with Ar/CF4/H2 gas mixtures, and the structural, electrical and optical properties of the as-deposited and the vacuum-annealed films were investigated. In as-deposited state, films with fairly low resistivity of 3.9-4 × 10−4 Ω cm and very low absorption coefficient below 900 cm−1 when averaged in 400-800 nm could be fabricated. After vacuum-heating at 300 °C, the minimum resistivity of 2.9 × 10−4 Ω cm combined with low absorption loss in visible region, which enabled the figure of merit to uplift as high as 4 Ω−1, could be obtained for vacuum-annealed film. It was shown that, unlike hydrogenated ZnO films which resulted in degradation upon heating in vacuum at moderately high temperature, films with fluorine addition could yield improved electrical properties mostly due to enhanced Hall mobility while preserving carrier concentration level. Furthermore, stability in oxidizing environment could be improved by fluorine addition, which was ascribed to the filling effect of dangling bonds at the grain boundaries. These results showed that co-doping of hydrogen and fluorine into AZO films with low Al concentration could be remarkably compatible with thin film solar cell applications.  相似文献   

12.
EPR study of the Cr3+ ion doped l-histidine hydrochloride monohydrate single crystal is done at room temperature. Two magnetically inequivalent interstitial sites are observed. The hyperfine structure for Cr53 isotope is also obtained. The zero field and spin Hamiltonian parameters are evaluated from the resonance lines obtained at different angular rotations and the parameters are: D=(300±2)×10−4 cm−1, E=(96±2)×10−4 cm−1, gx=1.9108±0.0002, gy=1.9791±0.0002, gz=2.0389±0.0002, Ax=(252±2)×10−4 cm−1, Ay=(254±2)×10−4 cm−1, Az=(304±2)×10−4 cm−1 for site I and D=(300±2)×10−4 cm−1, E=(96±2)×10−4 cm−1, gx=1.8543±0.0002, gy=1.9897±0.0002, gz=2.0793±0.0002, Ax=(251±2)×10−4 cm−1, Ay=(257±2)×10−4 cm−1, Az=(309±2)×10−4 cm−1 for site II, respectively. The optical absorption studies of single crystals are also carried out at room temperature in the wavelength range 195-925 nm. Using EPR and optical data, different bonding parameters are calculated and the nature of bonding in the crystal is discussed. The values of Racah parameters (B and C), crystal field parameter (Dq) and nephelauxetic parameters (h and k) are: B=636, C=3123, Dq=2039 cm−1, h=1.46 and k=0.21, respectively.  相似文献   

13.
Nitrogen-doped ZnO thin films have been prepared by reactive ion beam sputtering deposition utilizing a capillaritron ion source. X-ray diffraction (XRD) analysis of the as-deposited film exhibits a single strong ZnO (002) diffraction peak centred at 34.40°. Post-growth annealing causes increase of grain size and decrease of c-axis lattice constant. Micro-Raman spectroscopy analysis of the as-deposited film shows strong nitrogen-related local vibration mode at 275, 582, 640 and 720 cm−1, whereas the E2 mode of ZnO at 436 cm−1 can barely be identified. Annealing at 500-800 °C causes decrease of 275, 582, 640 and 720 cm−1 and increase of 436 cm−1 intensity, indicating out-diffusion of nitrogen and improvement of ZnO crystalline quality. Unlike un-doped ZnO, the surface roughness of nitrogen-doped ZnO deteriorates after annealing, which is also attributed to the out-diffusion of nitrogen. A nitrogen concentration of ∼1021/cm3 was observed while type conversion from n-type to p-type was not achieved, which is likely due to the formation of ZnI-NO or (N2)O that act as donor/double donors.  相似文献   

14.
P doped ZnO films were grown on quartz by radio frequency-magnetron sputtering method using a ZnO target mixed with 1.5 at% P2O5 in the atmosphere of Ar and O2 mixing gas. The as-grown P doped ZnO film showed n-type conductivity, which was converted to p-type after 800 °C annealing in Ar gas. The P doped ZnO has a resistivity of 20.5 Ω cm (p∼2.0×1017 cm−3) and a Hall mobility of 2.1 cm2 V−1 s−1. XRD measurement indicated that both the as-grown and the annealed P doped ZnO films had a preferred (0 0 2) orientation. XPS study agreed with the model that the PZn-2VZn acceptor complex was responsible for the p-type conductivity as found in the annealed P-doped ZnO. Temperature-dependent photoluminescence (PL) spectrum showed that the dominant band is located at 3.312 eV, which was attributed to the free electronic radiative transition to neutral acceptor level (FA) in ZnO. The PZn-2VZn acceptor complex level was estimated to be at EV=122 meV.  相似文献   

15.
Phosphorus (P)-doped ZnO thin films with amphoteric doping behavior were grown on c-sapphire substrates by radio frequency magnetron sputtering with various argon/oxygen gas ratios. Control of the electrical types in the P-doped ZnO films was achieved by varying the gas ratio without post-annealing. The P-doped ZnO films grown at a argon/oxygen ratio of 3/1 showed p-type conductivity with a hole concentration and hole mobility of 1.5 × 1017 cm−3 and 2.5 cm2/V s, respectively. X-ray diffraction showed that the ZnO (0 0 0 2) peak shifted to lower angle due to the positioning of P3− ions with a larger ionic radius in the O2− sites. This indicates that a p-type mechanism was due to the substitutional PO. The low-temperature photoluminescence of the p-type ZnO films showed p-type related neutral acceptor-bound exciton emission. The p-ZnO/n-Si heterojunction light emitting diode showed typical rectification behavior, which confirmed the p-type characteristics of the ZnO films in the as-deposited status, despite the deep-level related electroluminescence emission.  相似文献   

16.
It has been synthesized Mg/Al layered double hydroxide anionic clay (Mg/Al hydrotalcite) through direct precipitation by adding 0.5 M NaOH solution into a mixed solution containing Mg(NO3)2 and Al(NO3)3 with molar ratio of 0.1:0.05 until the medium acidity reached pH 10.1. The synthesized Mg/Al hydrotalcite was then utilized to remove dissolved humic acid in aqueous medium. The humic acid was isolated from peat soil taken in Gambut District, South Kalimantan, Indonesia using the recommended procedure of IHSS (International Humic Substances Society). The removal of humic acid was mostly occurred through simple sorption process without accompanied by significant intercalation. The sorption was optimum at pH 9.0, with the first order rate constant, capacity and energy of sorption were 5.50 × 10−3 min−1, 0.12 mmol g−1 (69 mg g−1), and 28.32 kJ mol−1, respectively.  相似文献   

17.
Aluminium-doped zinc oxide (ZnO:Al) films were prepared by magnetron sputtering at different radio-frequency powers (Prf) of 50, 100, 150 and 200 W. The properties of the films were characterised by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Raman microscopy, and spectrophotometry with the emphasis on the evolution of compositional, surface-morphological, optical, electrical and microstructural properties. XPS spectra showed that within the detection limit the films are chemically identical to near-stoichiometric ZnO. AFM revealed that root-mean-square roughness of the films has almost linear increase with increasing Prf. Optical band gap Egopt of the films increases from 3.31 to 3.51 eV when Prf increases from 50 to 200 W. A widening Egopt of the ZnO:Al films compared to the band gap (∼3.29 eV) of undoped ZnO films is attributed to a net result of the competition between the Burstein-Moss effect and many-body effects. An electron concentration in the films was calculated in the range of 3.73 × 1019 to 2.12 × 1020 cm−3. Raman spectroscopy analysis indicated that well-identified peaks appear at around 439 cm−1 for all samples, corresponding to the band characteristics of the wurtzite phase. Raman peaks in the range 573-579 cm−1 are also observed, corresponding to the A1 (LO) mode of ZnO.  相似文献   

18.
Preparation and characterization of CdS/Si coaxial nanowires   总被引:1,自引:0,他引:1  
CdS/Si coaxial nanowires were fabricated via a simple one-step thermal evaporation of CdS powder in mass scale. Their crystallinities, general morphologies and detailed microstructures were characterized by using X-ray diffraction, scanning electron microscope, transmission electron microscope and Raman spectra. The CdS core crystallizes in a hexagonal wurtzite structure with lattice constants of a=0.4140 nm and c=0.6719 nm, and the Si shell is amorphous. Five Raman peaks from the CdS core were observed. They are 1LO at 305 cm−1, 2LO at 601 cm−1, A1-TO at 212 cm−1, E1-TO at 234 cm−1, and E2 at 252 cm−1. Photoluminescence measurements show that the nanowires have two emission bands around 510 and 590 nm, which originate from the intrinsic transitions of CdS cores and the amorphous Si shells, respectively.  相似文献   

19.
The temperature dependence of the Raman modes in anatase TiO2 nanocrystals has been investigated over the temperature range 77-873 K. With increasing temperature, the frequency of the Eg mode at 639 cm−1 shifts sublinearly to the lower frequencies, however, the frequency of the lowest-frequency Eg mode shifts sublinearly to the higher frequencies from 138 cm−1 at 77 K to 152 cm−1 at 873 K and the frequency of the B1g mode at 397 cm−1 increases firstly and attains a maximum near 350 K. The linewidth of all of the three modes increases linearly with increasing temperature. The anharmonic effects contribute a lot to the temperature dependence behavior of the frequency and linewidth of Raman modes in anatase TiO2 nanocrystals.  相似文献   

20.
Infrared optical absorption has been used to study OHimpurities into congruent co-doped LiNbO3:Cr3+:ZnO crystals doped with different Zn2+ concentration. The OH IR absorption spectra present three bands that can be associated with different OH complex centres available in the lattice. For crystals with lower Zn2+ concentrations (<4.7%) only one IR absorption band centred at 2867 nm (3490 cm−1) is reported which is associated with the OH unperturbed vibration. For crystals with higher Zn2+ concentrations (>4.7%), two new bands associated with OHvibration in distortion environment are reported. These bands are centred at 2827 nm (3537 cm−1) and 2847 nm (3512 cm−1) and can be associated with OH-Zn2+ and Cr3+(Li+)-OH-Zn2+(Int.) complex centres, respectively. Electron paramagnetic resonance (EPR) has been used to identify the Cr3+ centres in the lattice of the doped LiNbO3:ZnO crystals.  相似文献   

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