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1.
ZnO nanoparticles, nanowires, and nanowalls were synthesized rapidly on Si via thermal decomposition of zinc acetate by a
modified chemical vapor deposition at a low substrate temperature of 200–250°C for the first time. The diameters of the synthesized
nanoparticles and nanowires are around 100 and 30 nm, respectively, and the thickness of nanowalls is around 20 nm. High-resolution
transmission electron microscopy shows that the nanowires as well as nanowalls are single-crystalline, and the nanoparticles
are highly-textured poly-crystalline structures. Room-temperature photoluminescence spectra of the nanostructures show strong
ultraviolet emissions centered at 368–383 nm and weak violet emissions at around 425 nm, indicating good crystal quality.
The study provides a simple and efficient route to synthesize ZnO diverse nanostructures at low temperature. 相似文献
2.
Chivalrat Masingboon Prasit Thongbai Santi Maensiri Teerapon Yamwong 《Applied Physics A: Materials Science & Processing》2009,96(3):595-602
Nanocrystalline CaCu3Ti4O12 powders were synthesized by a simple PVA sol–gel route and calcined at 700 and 800°C in air for 8 h. The diameter of the
powders ranges from 40–100 nm. The calcined CaCu3Ti4O12 powders were characterized by TG-DTA, XRD, FTIR, SEM, and TEM. Sintering of the powders was conducted in air at 1100°C for
16 h. The XRD results indicated that all sintered samples had a typical perovskite CaCu3Ti4O12 structure although the sintered samples contained some amount of CaTiO3. SEM of the sintered CaCu3Ti4O12 ceramics showed the average grain sizes of 13–15 μm. The samples exhibit a giant dielectric constant, ε′∼105 at 150 to 200°C with weak temperature dependence below 1 kHz in the sample sintered using the powders calcined at 700°C.
The Maxwell–Wagner polarization mechanism is used to explain the high permittivity in these ceramics. It is also found that
all sintered samples have the same activation energy of grains, which is ∼0.122 eV. 相似文献
3.
Sword-like (diameter ranging from 40 nm to 300 nm) and needle-like zinc oxide (ZnO) nanostructures (average tip diameter ∼40 nm)
were synthesized on annealed silver template over silicon substrate and directly on silicon wafer, respectively via thermal
evaporation of metallic zinc followed by a thermal annealing in air. The surface morphology, microstructure, chemical analysis
and optical properties of the grown samples were investigated by field emission scanning electron microscopy, X-ray diffraction,
energy dispersive X-ray analysis, room temperature photoluminescence and Raman spectroscopy. The sword-like ZnO nanostructures
grown on annealed silver template are of high optical quality compared to needle-like ZnO nanorods for UV emission and show
enhanced Raman scattering. 相似文献
4.
J. H. Thorat K. G. Kanade L. K. Nikam P. D. Chaudhari R. P. Panmand B. B. Kale 《Journal of nanoparticle research》2012,14(2):657-10
In this study, we report the synthesis of well-aligned nanocrystalline hexagonal zinc oxide (ZnO) nanoparticles by facile
solid-state and co-precipitation method. The co-precipitation reactions were performed using aqueous and ethylene glycol (EG)
medium using zinc acetate and adipic acid to obtain zinc adipate and further decomposition at 450 °C to confer nanocrystalline
ZnO hexagons. XRD shows the hexagonal wurtzite structure of the ZnO. Thermal study reveals complete formation of ZnO at 430 °C
in case of solid-state method, whereas in case of co-precipitation method complete formation was observed at 400 °C. Field
emission scanning electron microscope shows spherical morphology for ZnO synthesized by solid-state method. The aqueous-mediated
ZnO by co-precipitation method shows rod-like morphology. These rods are formed via self assembling of spherical nanoparticles,
however, uniformly dispersed spherical crystallites were seen in EG-mediated ZnO. Transmission electron microscope (TEM) investigations
clearly show well aligned and highly crystalline transparent and thin hexagonal ZnO. The particle size was measured using
TEM and was observed to be 50–60 nm in case of solid-state method and aqueous-mediated co-precipitation method, while 25–50 nm
in case of EG-mediated co-precipitation method. UV absorption spectra showed sharp absorption peaks with a blue shift for
EG-mediated ZnO, which demonstrate the mono-dispersed lower particle size. The band gap of the ZnO was observed to be 3.4 eV
which is higher than the bulk, implies nanocrystalline nature of the ZnO. The photoluminescence studies clearly indicate the
strong violet and weak blue emission in ZnO nanoparticles which is quite unique. The process investigated may be useful to
synthesize other oxide semiconductors and transition metal oxides. 相似文献
5.
Sujittra Daengsakul Charusporn Mongkolkachit Chunpen Thomas Sineenat Siri Ian Thomas Vittaya Amornkitbamrung Santi Maensiri 《Applied Physics A: Materials Science & Processing》2009,96(3):691-699
This study reports the new and simple synthesis of magnetic La0.7Sr0.3MnO3 (LSMO) nanoparticles by thermal decomposition method using acetate salts of La, Sr and Mn as starting materials. To obtain
the LSMO nanoparticles, thermal decomposition of the precursor is carried out at the temperatures of 600, 700, 800, 900, and
1000°C for 6 hours. The synthesized LSMO nanoparticles were characterized by XRD, FT-IR, TEM and SEM. Structural characterization
shows that the prepared particles consisted of two phases of LaMnO3 (LMO) and LSMO with crystallite sizes ranging from 18 to 55 nm. All the prepared samples have a perovskite structure which
changes from cubic to rhombohedral with the increase in the thermal decomposition temperature. Basic magnetic characteristics
such as saturation magnetization (M
S) and coercive field (H
C) are evaluated by sample vibrating magnetometry at room temperature (20°C). The samples show soft ferromagnetic behavior
with M
S values of ∼9–55 emu/g and H
C values of ∼8–37 Oe, depending on the crystallite size and thermal decomposition temperature. The relationship between the
crystallite size and the magnetic properties is presented and discussed. The cytotoxicity of synthesized LSMO nanoparticles
was also evaluated with NIH 3T3 cells and the result showed that the synthesized nanoparticles were not toxic to the cells
as determined from cell viability in response to the liquid extraction of LSMO nanoparticles. 相似文献
6.
H. Kim G. P. Kushto R. C. Y. Auyeung A. Piqué 《Applied Physics A: Materials Science & Processing》2008,93(2):521-526
Fluorine-doped tin oxide (FTO) thin films have been investigated as an alternative to indium tin oxide anodes in organic photovoltaic
devices. The structural, electrical, and optical properties of the FTO films grown by pulsed laser deposition were studied
as a function of oxygen deposition pressure. For 400 nm thick FTO films deposited at 300°C and 6.7 Pa of oxygen, an electrical
resistivity of 5×10−4 Ω-cm, sheet resistance of 12.5 Ω/□, average transmittance of 87% in the visible range, and optical band gap of 4.25 eV were obtained. Organic photovoltaic (OPV)
cells based on poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester bulk heterojunctions were prepared on FTO/glass electrodes and the device performance was investigated as a function of FTO
film thickness. OPV cells fabricated on the optimum FTO anodes (∼300–600 nm thick) exhibited power conversion efficiencies
of ∼3%, which is comparable to the same device made on commercial ITO/glass electrodes (3.4%). 相似文献
7.
Santi Maensiri Paveena Laokul Jutharatana Klinkaewnarong Chunpen Thomas 《Applied Physics A: Materials Science & Processing》2009,94(3):601-606
Room-temperature ferromagnetism was observed in Zn0.9Co0.1O nanorods with diameters and lengths of ∼100–200 nm and ∼200–1000 nm, respectively. Nanorods were synthesized by a simple
sol–gel method using metal acetylacetonate powders of Zn and Co and poly(vinyl alcohol) gel. The XRD, FT-IR and SAED analyses
indicated that the nanorods calcined at 873–1073 K have the pure ZnO wurtzite structure without any significant change in
the structure affected by Co substitution. Optical absorption measurements showed absorption bands indicating the presence
of Co2+ in substitution of Zn2+. The specific magnetization of the nanorods appeared to increase with a decrease in the lattice constant c of the wurtzite unit cell with the highest value being at 873 K calcination temperature. This magnetic behavior is similar
to that of Zn0.9Co0.1O nanoparticles prepared by polymerizable precursor method. We suggest that this behavior might be related to hexagonal c-axis being favorable direction of magnetization in Co-doped ZnO and the 873 K (energy of 75 meV) being close to the exciton/donor
binding energy of ZnO. 相似文献
8.
Huilian Liu Lianhua Fei Jinghai Yang Xin Jin Xiaoyan Liu Ming Gao 《Solid State Communications》2011,151(24):1864-1868
Zn0.95Cu0.02Cr0.03O powders have been synthesized by the sol-gel method and sintered in argon atmosphere under different temperatures. The structural, optical and magnetic properties of the powders were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and vibrating sample magnetometer (VSM). The XRD results demonstrated that Cr and Cu ions are incorporated into ZnO successfully when annealing temperatures were 600 and 700 °C. But when the samples were annealed at 500 °C, the crystallinity of the samples was not very good. However, when the annealing temperature was increased to 800 °C, the secondary phase of Cu and ZnCr2O4 appeared in the samples. The PL spectra revealed that the position of the ultraviolet (UV) emission peak of the samples showed a blue shift and the green emission peak enhanced significantly with the annealing temperature increasing from 600 to 700 °C. Magnetic measurements indicated that the room temperature ferromagnetism of Zn0.95Cu0.02Cr0.03O was intrinsic in nature. In addition, the saturation magnetization (Ms) increased from 0.0078 to 0.0088 emu/g with the annealing temperature increased from 600 to 700 °C. 相似文献
9.
Al-doped ZnO (ZnO:Al) thin films with c-axis preferred orientation were deposited on glass substrates using the radio frequency reactive magnetron sputtering technique. The effect of Al concentrations on the microstructure and the luminescence properties of the ZnO:Al thin films were studied by atomic force microscopy (AFM), X-ray diffraction (XRD), and fluorescence spectrophotometer. The results showed that the crystallization of the films was promoted by appropriate Al concentrations; the photoluminescence spectra (PL) of the samples were measured at room temperature. Strong blue peak located at 437 nm (2.84 eV) and two weak green peaks located at about 492 nm (2.53 eV) and 524 nm (2.37 eV) were observed from the PL spectra of the four samples. The origin of these emissions was discussed. In addition, absorption and transmittance properties of the samples were researched by UV spectrophotometer; the UV absorption edge shifted to a shorter wavelength first as Al was incorporated, and then to a longer wavelength with the increasing Al concentrations. The optical band gaps calculated based on the quantum confinement model are in good agreement with the experimental values. 相似文献
10.
B. P. Aduev D. R. Nurmukhametov A. V. Puzynin 《Russian Journal of Physical Chemistry B, Focus on Physics》2010,4(3):452-456
The temperature dependence of the probability of the explosion of pentaerythritol tetranitrate (PETN) with an admixture of
NiC particles (0.3 wt %) initiated by laser pulses (1064 nm, 20 ns) was studied over the temperature range 295–450 K. At 295–350
K, a weak temperature dependence was observed. The determining contribution to explosion initiation was made by the absorption
of laser radiation by nanoparticles. The threshold of explosive decomposition at 295 K decreased by ∼40 times compared with
samples free of NiC nanoparticles. Over the temperature range 400–450 K, the threshold of the explosive decomposition of samples
containing NiC nanoparticles decreased with the activation energy ∼0.4 eV. A decrease in the threshold of explosive decomposition
with a ∼0.4 eV activation energy over the temperature range 340–440 K was also observed for laser action on PETN samples not
containing NiC. A hypothesis was suggested according to which the absorption of a light quantum caused the transfer of an
electron from the valence band of the crystal to a level in the forbidden band with subsequent thermal positive ion dissociation
to the carbocation and NO3 radical. 相似文献
11.
《Current Applied Physics》2010,10(2):636-641
In this paper, a very simple procedure was presented for the reproducible synthesis of large-area SnO2 nanowires (NWs) on a silicon substrate by evaporating Sn powders at temperatures of 700, 750, and 800 °C. As-obtained SnO2 NWs were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. They revealed that the morphology of the NWs is affected by growth temperature and the SnO2 NWs are single-crystalline tetragonal. The band gap of the NWs is in the range of 4.2–4.3 eV as determined from UV/visible absorption. The NWs show stable photoluminescence with an emission peak centered at around 620 nm at room-temperature. The sensors fabricated from the SnO2 NWs synthesized at 700 °C exhibited good response to LPG (liquefied petroleum gas) at an operating temperature of 400 °C. 相似文献
12.
ZnO of different morphologies with controlled size and aspect ratio (l/d) such as dumbbell-like microrods, thick nanowires and thin nanowires were prepared by a hydrothermal method. Possible mechanisms for the formation of ZnO crystals with the different morphologies were discussed. Strong violet photoluminescence bands at~413 nm (3.0 eV) without band edge emission were observed from the dumbbell-like ZnO microrods and thick nanowires. Correspondingly, the thin nanowires showed a weak shoulder UV photoluminescence band at~390 nm. Such result indicates that the photoluminescence properties could be improved by the morphologies or aspect ratio (l/d) and the potential fabrication violet-light-emitting devices. 相似文献
13.
The pyrolytic decomposition of layered basic zinc acetate (LBZA) nanobelts (NBs) into nanocrystalline ZnO NBs is investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). We also report on the gas sensing response of the resulting ZnO nanomaterial to CO. The LBZA NBs are grown at 65 °C in an aqueous solution of zinc acetate dihydrate. AFM and SEM results show as-grown products possess the characteristic layered structure of the LBZA crystals. XRD and XPS results show that annealing as-grown products at 210 °C in air causes a transformation from zinc acetate to nanocrystalline ZnO NBs via thermal decomposition. The ZnO crystalline domain size increases with temperature from 9.2 nm at 200 °C to 94 nm at 1000 °C, as measured from XRD. SEM shows evidence of sintering at 600 °C. The thickness of the NBs, determined via AFM, ranges from 10 to 50 nm and remains approximately constant with annealing temperature. XPS confirmed the chemical transformation from zinc acetate to ZnO and showed a significant remaining zinc hydroxide component for the ZnO NBs consistent with published results. PL measurements at room temperature show a blue shift in peak emission as the nanobelts change from LBZA to ZnO at 200 °C. Above this transition temperature, the ZnO nanobelts possess strong band edge emission at 390 nm and little broad band emission in the visible region. The AFM and SEM images reveal that the crystallites within the nanobelts orientate in rows along the long axis during annealing. This structure provides a high surface area to volume ratio of aligned nanoparticles which is beneficial for gas sensing applications. Gas sensors fabricated from 400 °C annealed nanobelts showed a response of 1.62 when exposed to 200 ppm of CO in dry air at 400 °C, as defined by the ratio of resistance before and during exposure. This indicates that ZnO nanostructures obtained by thermal decomposition of LBZA NBs could provide a cost effective route to high sensitivity gas sensors. 相似文献
14.
This Letter reports on structural and photoluminescence properties of Zn1 − xMnxO nanocrystalline powders, which were synthesized by using oxalate precursor decomposition method. From the XRD features, we have noticed that all samples exhibit wurtzite crystal structure. The origin of photoluminescence properties of Mn doped and undoped ZnO have been discussed. 相似文献
15.
The luminescence properties of zinc oxide (ZnO) nanocrystals grown from solution are reported. The ZnO nanocrystals were characterized by scanning electron microscopy, X-ray diffraction, cathodo- and photoluminescence (PL) spectroscopy. The ZnO nanocrystals have the same regular cone form with the average sizes of 100-500 nm. Apart from the near-band-edge emission around 381 nm and a weak yellow-orange band around 560-580 nm at 300 K, the PL spectra of the as-prepared ZnO nanocrystals under high-power laser excitation also showed a strong defect-induced violet emission peak in the range of 400 nm. The violet band intensity exhibits superlinear excitation power dependence while the UV emission intensity is saturated at high excitation laser power. With temperature raising the violet peak redshifts and its intensity increases displaying unconventional negative thermal quenching behavior, whereas intensity of the UV and yellow-orange bands decreases. The origin of the observed emission bands is discussed. 相似文献
16.
P. Mandal S. S. Talwar R. S. Srinivasa S. S. Major 《Applied Physics A: Materials Science & Processing》2009,94(3):577-584
CdS nanocrystallites formed in ordered fatty acid LB multilayers exhibited strong surface states emission ∼550 nm and weak
excitonic emission ∼400 nm. Treatment with aqueous CdCl2 resulted in the suppression of surface states emission and enhancement of the blue excitonic emission. Subsequent annealing
in air at 200°C caused an order of magnitude enhancement of excitonic emission. The growth of nanocrystallites during annealing
as seen from the red-shift of excitonic absorption and emission is suppressed by the CdCl2 treatment. The hindered growth of nanocrystallites, the significant enhancement of excitonic emission from CdS, and the suppression
of surface states emission are attributed to surface passivation of CdS nanocrystallites by surface oxide formation. 相似文献
17.
A series of stoichiometric and nonstoichiometric copper–chalcogenide nanocrystallines with different morphologies, e.g., extremely
high aspect ratio nanofibers (Cu9S8), tubular structure (Cu
x
S (x=∼1.86–1.96), nanorods (CuS, Cu31S16), platelets (β-CuSe, Cu3Se2), rope-like Cu3Se2, as well as spherical nanoparticles (Cu7Se4, Cu2−x
Se), have been successfully synthesized in 20 vol% water and 80 vol% organic solvents mixture under mild conditions. The products
were characterized by various techniques, including X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission
electron microscopy (TEM), electronic diffraction (ED), and high-resolution transmission electron microscopy (HRTEM). The
studies of the optical properties revealed that the copper chalcogenides have a wide absorption in the range of about 400–700 nm,
with accessional IR band. Systematic studies showed that the mixture of 20 vol% water and 80 vol% organic solvents played
a key role in controlling the copper chalcogenides with different morphologies and phases. 相似文献
18.
I. Navas R. Vinodkumar V. P. Mahadevan?Pillai 《Applied Physics A: Materials Science & Processing》2011,103(2):373-380
We report on the synthesis of self-assembled hillock shaped MoO3 nanoparticles on thin films exhibiting intense photoluminescence (PL) by RF magnetron sputtering and subsequent oxidation.
MoO3 nanocrystals of size ∼29 nm are self-assembled into uniform nanoparticles with diameter ∼174 nm. The mechanism of the intense
PL behaviour from MoO3 nanoparticles is investigated and systematically discussed. The films exhibit two bands; a near-band-edge UV emission and
a defect related deep level visible emission. The enhancement in PL intensity with annealing is not only by the improvement
in crystallinity and grain size but also by the increase in the rms surface roughness and porosity of the films. The PL intensity
is thermally activated with activation energy 1.07 and 0.87 eV respectively for the UV and visible emissions. The UV band
exhibits a blue shift according to the band gap with increasing post-annealing temperatures, which suggests the possibility
to tune the UV photoluminescence band by varying the oxidation temperature. 相似文献
19.
Chao Liu Haiping He Luwei Sun Zheng Xu Zhizhen Ye 《Applied Physics A: Materials Science & Processing》2011,104(2):695-699
ZnO nanorod arrays and nanowires were grown by hydrothermal and vapor phase deposition methods, respectively. At low temperature,
the photoluminescence (PL) spectra of both samples are dominated by a broad peak around 3.34 eV. Combined with excitation
density-dependent PL spectra and surface passivation process, it is indicated from temperature-dependent PL results that the
3.34 eV emission could be attributed to free electron-to-neutral acceptor transitions. The acceptor level is estimated to
be ∼100 meV. 相似文献
20.
ZnS and SiO2-ZnS nanophosphors, with or without different concentration of Mn2+ activator ions, were synthesized by using a sol-gel method. Dried gels were annealed at 600 °C for 2 h. Structure, morphology and particle sizes of the samples were determined by using X-ray diffraction (XRD), highresolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). The diffraction peaks associated with the zincblende and the wurtzite structures of ZnS were detected from as prepared ZnS powders and additional diffraction peaks associated with ZnO were detected from the annealed powders. The particle sizes of the ZnS powders were shown to increase from 3 to 50 nm when the powders were annealed at 600 °C. An UV-Vis spectrophotometer and a 325 nm He-Cd laser were used to investigate luminescent properties of the samples in air at room temperature. The bandgap of ZnS nanoparticles estimated from the UV-Vis data was 4.1 eV. Enhanced orange photoluminescence (PL) associated with 4T1→6A1 transitions of Mn2+ was observed from as prepared ZnS:Mn2+and SiO2-ZnS:Mn2+ powders at 600 nm when the concentration of Mn2+ was varied from 2-20 mol%. This emission was suppressed when the powders were annealed at 600 °C resulting in two emission peaks at 450 and 560 nm, which can be ascribed to defects emission in SiO2 and ZnO respectively. The mechanism of light emission from Mn2+, the effect of varying the concentration on the PL intensity, and the effect of annealing are discussed. 相似文献