Characterization of dip-coated ITO films derived from nanoparticles synthesized by␣low-pressure spray pyrolysis

In₂O₃:Sn (Indium Tin Oxide; ITO) films were prepared from a sol solution with highly crystalline ITO nanoparticles (less than 20 nm in size with 10 at.% Sn) which had been prepared by low-pressure spray pyrolysis (LPSP) in a single step. The ITO sol solution was prepared by dispersing LPSP-prepared ITO nanoparticles into ultra pure water. The nanoparticle ITO film was deposited on a glass substrate using a dip-coating method and then annealed in air at various temperatures. The optical transmittances of the ITO films were measured by UV–Vis spectrometry, and the films were found to have a high transparency to visible light (in the case of a film thickness of 250 nm annealed at 400°C, the transparency was in excess of 95% over the range λ=450–800 nm, with a maximum value near 100% at wavelengths above λ=700 nm). The optical transmittances of the films were influenced by the size of the ITO particle used, the film thickness and the annealing temperature. The ITO films showed a minimum resistivity of 9.5×10⁻² Ω cm, and their resistivity was affected by both the ITO particle size and the annealing temperature used.     

Nanocrystalline oxide zinc materials studied by the Mössbauer effect, μSR and neutron diffraction

ZnO and ZnFe₂O₄ were investigated in nanocrystalline form using various hyperfine techniques in conjunction with neutron diffraction and bulk magnetic measurements. For the zinc oxide, the main interest was the influence of the nanocrystalline state on lattice dynamics and on the local symmetry of the Zn atom as reflected in its quadrupolar coupling, employing the high-resolution Mössbauer resonance of ⁶⁷Zn. Measurements were carried out on nanocrystalline materials with particle sizes between 4 and 25 nm. It was found that the asymmetry parameter increases drastically from η=0 in ZnO single crystals to η≈0.5 in nanostructured material, indicating an off-axis displacement of either Zn or O atoms in finite size grains. The dependences of the Lamb-Mössbauer factor on grain size and temperature are well described by a two-component model in which small crystallites are surrounded by a network of grain boundaries. For the zinc ferrite the question of changes in the magnetic properties stood in the foreground. Using the combination of techniques mentioned, the magnetic behavior of nanocrystalline ZnFe₂O₄, which had an average particle size of about 9 nm was compared to differently prepared crystalline samples. It was seen that the role of cation-site occupation, which changes substantially with nanocrystallinity, plays a decisive role for the magnetic properties.     

Crystallization annealing effects on ferroelectric properties of Al-Doped HfO2 thin film capacitors using indium–tin–oxide electrodes

To investigate the effect of indium-tin-oxide (ITO) electrode on the Al-doped HfO₂ (Al:HfO₂) ferroelectric thin films, we fabricated and characterized the ITO/Al:HfO₂/ITO and ITO/Al:HfO₂/TiN capacitors by changing the annealing conditions. The ferroelectric remnant polarization (2P_r) was obtained to be 13.25 μC/cm² for the ITO/Al:HfO₂/TiN capacitors with the post-deposition annealing, which was termed T1. The 2P_r decreased after the post-metallization annealing due to the interface degradation between the Al:HfO₂ and ITO electrode. Alternatively, the switching time and activation field of the T1 for the ferroelectric polarization switching were 1.25 μs and 1.15 MV/cm. These parameters were sensitively influenced by the interfacial dead layer formation and the amounts of ferroelectric orthorhombic phase. Furthermore, the fatigue endurance of the T1 were improved by preventing the crowding of oxygen vacancies at interfaces between the Al:HfO₂ and top electrodes, in which the polarization values did not experience marked variations even after the fatigue cycles of 10⁸.     

X-ray emission study of the electronic structure of nanocrystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Valence states of metal ions and the phase composition of nanocrystalline Al₂O₃ (of the original oxide and the oxide irradiated by high-energy Fe⁺ ions) are studied by using x-ray emission Al L_{2, 3} and O Kα spectra. It is established that the shape of the Al L_{2, 3} spectra strongly changes as one goes from the original (bulk) Al₂O₃ to nanocrystalline oxide, while the O Kα spectra remain practically unchanged. Moreover, irradiation by high-energy Fe⁺ ions results in slight additional changes in the x-ray spectral characteristics of the aluminum oxides under study. The obtained experimental data are compared with the results of theoretical calculations of the electronic structure of α and γ phases of Al₂O₃ performed using the LDA formalism. Using the results of x-ray spectral studies, electronic structure calculations, and x-ray diffraction analysis, it is shown that the revealed spectral differences between the nanocrystalline state of aluminum oxide and the bulk material can be interpreted as a phase transition from the α phase to the γ phase of Al₂O₃ with an addition of bayerite.     

New polymorphs of alumina

Abstract

We present the results of high-pressure, high-temperature studies on xerogel gamma alumina which is made up of nanocrystalline alumina and an amorphous phase. Not many studies of this type have been reported on xerogel materials. At about 5 GPa and 1400°C, the xerogel alumina transforms into a polymorphic mixture containing α Al₂O₃, B Al₂O₃ and C Al₂O₃ where the last two phases have B Ln₂O₃ and C Ln₂O₃ type structures respectively. Here Ln stands for the rare earths. The xerogel alumina containing 1 wt.% Cr₂O₃ under these conditions transforms into a polymorphic mixture containing Al₂O₃, k' Al₂O₃ and H Al₂O₃ where H Al₂O₃ has the H Ln₂O₃ type structure. For the first time, the observation of rare earth sesquioxide structures of alumina is reported. At about 5 GPa at 27°C, the xerogel aluminal transforms to an amorphous phase. The results are discussed using the free energy diagram for xerogels proposed by R. Roy (J. Amer. Cer. Soc., 52, 344, 1969; 67, 468, 1984).     

Study of structural, optical and electrical properties of ZnO and SnO2 thin films

The investigation of structure, optical and electrical properties of tin and zinc oxide films on glass substrates by using magnetron sputtering are carried out. X-ray data show the formation of textured tin oxides film during deposition and its transformation to SnO₂ polycrystalline film at low temperature (200 C) if the concentration of oxygen in the chamber is high (O₂ — 100%, Ar — 0%). Optimal conditions of SnO₂ polycrystalline film deposition (pressure of Ar–O₂ mixture in chamber — 2.7 Pa, concentration of O₂ — 10%) are determined. Low resistivity of as-deposited ZnO film and increasing ZnO crystallite sizes and phase volume at temperatures higher than the melting point of Zn (419.5 C) are explained by formation of conductive Zn and ZnO particle chains and their destruction, respectively.     

Observation of stimulated Raman scattering in Y3Al5O12 single crystals and nanocrystalline ceramics and in these materials activated with laser ions Nd3+ and Yb3+

High-order Raman parametric generation was excited in the visible and near-IR regions on the Stokes and anti-Stokes lines of Y₃Al₅O₁₂ single crystals and nanocrystalline ceramics. All generation components, as well as the χ⁽³⁾-active vibrational modes of these materials, were identified. In connection with the extensive use of the Nd³⁺-and Yb³⁺-doped Y₃Al₅O₁₂ crystals and, in recent years, nanocrystalline Y₃Al₅O₁₂: Nd³⁺ ceramics in laser physics and quantum electronics, the applied aspect of the observed nonlinear properties of these materials is outlined.     

XRD, HRTEM, magnetic and Mössbauer studies on chemically prepared Fe-doped nanoparticles of cerium oxide

Nanocrystalline samples of Fe-doped cerium oxide (Ce_0.90Fe_0.1O₂) are prepared by sol-gel method. The precursor materials used for the synthesis are ferric nitrate and cerium nitrate. The as-prepared samples is annealed at different temperatures to obtain the sample with different particle sizes. The crystallographic phases of the nanocrystalline materials have been confirmed by X-ray diffractograms (XRD). The sizes of the nanoparticles estimated from the peaks of the XRD patterns using Debye-Scherrer equation are in the range 6-58 nm. Results extracted from the high-resolution transmission electron microscopy (HRTEM) are in agreement with the findings obtained from XRD. The average magnetic susceptibilities of all the samples with different particle sizes are measured in the temperature range 300-14 K. The average susceptibilities of the samples annealed below ∼740 °C show paramagnetic behaviour. The susceptibilities of the samples annealed at and above ∼740 °C sharply decrease at ∼240 K and this sharp transition is quite likely due to the anti-parallel alignment of Fe³⁺ spins and is attributed to Morin transition of α-Fe₂O₃. Mössbauer spectra of the samples annealed at and above ∼740 °C give sextet patterns indicating the presence of exchange interaction among the Fe³⁺ ions of these samples and these sextets are also of typical nature of the α-Fe₂O₃ phase. The Mössbauer spectra of the samples annealed below ∼740 °C are doublets which may be attributed to either superparamagnetic and/or paramagnetic type nanoparticles.     

In situ observation of Ni–Mo–S phase formed on NiMo/Al2O3 catalyst sulfided at high pressure by means of Ni and Mo K‐edge EXAFS spectroscopy

To obtain direct evidence of the formation of the Ni–Mo–S phase on NiMo/Al₂O₃ catalysts under high‐pressure hydrodesulfurization conditions, a high‐pressure EXAFS chamber has been constructed and used to investigate the coordination structure of Ni and Mo species on the catalysts sulfided at high pressure. The high‐pressure chamber was designed to have a low dead volume and was equipped with polybenzimidazole X‐ray windows. Ni K‐edge k³χ(k) spectra with high signal‐to‐noise ratio were obtained using this high‐pressure chamber for the NiMo/Al₂O₃ catalyst sulfided at 613 K and 1.1 MPa over a wide k range (39.5–146 nm^?1). The formation of Ni–Mo and Mo–Ni coordination shells was successfully proved by Ni and Mo K‐edge EXAFS measurement using this chamber. Interatomic distances of these coordination shells were almost identical to those calculated from Ni K‐edge EXAFS of NiMo/C catalysts sulfided at atmospheric pressure. These results support the hypothesis that the Ni–Mo–S phase is formed on the Al₂O₃‐supported NiMo catalyst sulfided under high‐pressure hydrodesulfurization conditions.     

Er3+掺杂SiO2复合的Al2O3粉末结构及光致发光特性

采用溶胶-凝胶(sol-gel)工艺制备0.1 mol% Er³⁺掺杂Al₂O₃体系和SiO₂-Al₂O₃复合体系粉末. 实验结果表明：5 mol%的SiO₂复合加入Al₂O₃抑制γ→θ和θ→α相转变. 掺0.1 mol%Er³⁺:Al₂O₃体系粉末，900℃烧结，在1.47—1.63μm波段内光致发光(PL)谱为中心波长1.53 μm、半高宽56 nm的单一宽峰，1000—1200℃烧结，劈裂为多峰PL谱. 掺0.1 mol%Er³⁺:SiO₂-Al₂O₃复合体系粉末，在高达1200℃烧结，仍保持中心波长1.53 μm的单一宽峰PL谱，由于—OH更完全的脱除，PL强度较900℃烧结Al₂O₃体系，SiO₂-Al₂O₃复合体系均提高1个数量级. 关键词： 2-Al₂O₃复合体系')" href="#">SiO₂-Al₂O₃复合体系 掺铒 溶胶-凝胶工艺 光致发光     

Effect of Cu–Al double substitution on the electrical properties of Bi4V2O11

Bi₂Cu_0.1?xAl_xV_0.9O_5.35?x/2?δ, 0.02 ≤ x ≤ 0.08, were synthesized by standard solid-state reaction route. Structural and electrical properties of samples are characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), Fourier transform infrared (FT-IR) and alternating current (AC) impedance spectroscopy. The tetragonal γ′ phase structure is preserved to room temperature with compound x = 0.02. The stabilization of β orthorhombic phase is observed for compositions 0.04 ≤ x ≤ 0.05. As the Al content increases, the monoclinic α phase is evidenced for materials 0.06 ≤ x ≤ 0.08. The electrical investigation of Bi₂Cu_0.1?xAl_xV_0.9O_5.35?x/2?δ system has been performed in the frequency range from 20 Hz to 1 MHz using AC impedance spectroscopy. The impedance spectra indicate the two semicircle arcs associated with the bulk and grain boundary resistances at temperature below ～450 ^○C. The conductivity generally changes when Al is substituted. The highest conductivity at 300 ^○C (σ = 2.55 × 10^?4 S cm^?1) is shown for x = 0.02.     

X-ray determination of thermal expansion of cadmium fluoride and lead fluoride

The lattice parameters of CdF₂ andβ-PbF₂ have been determined over the temperature range 300–670 K. The coefficient of expansion at room temperature is 21·3 × 10⁻⁶ K⁻¹ and 25·4 × 10⁻⁶ K⁻¹ for CdF₂ and PbF₂ respectively and it increases linearly with temperature over the range of temperature covered. The Grüneisen parameter decreases with temperature in both the crystals.     

Laser power influence on Raman spectra of ZnO(Co) nanoparticles

Influence of laser power on nanocrystalline samples of ZnO(Co) prepared by commonly used wet chemistry method followed by calcination was investigated. Previous confirmation of the existence of ZnO and Co₃O₄ phases was based on the X-ray diffraction measurements. Here we report the experimental spectra of non-resonant Raman scattering in the range between 100 cm⁻¹ and 1600 cm^–1, for a series of samples irradiated with four different laser power densities. The laser power density has different influence on relative intensity of peaks that belong to ZnO phase than on those corresponding to Co₃O₄ phase. Both peak types show characteristic broadening and red shift toward lower frequencies. The laser power densities used in our study did not cause thermal destruction in any of the investigated samples. Laser-induced local heating effects in samples caused formation of cobalt dimers on the surface of Co₃O₄.     

Enhanced optical activation of Er in Er-doped Al2O3 powders by Y codoping in a sol-gel method

Enhanced photoluminescence (PL) mechanism of Er³⁺-doped Al₂O₃ powders by Y³⁺ codoping at wavelength 1.53 μm has been investigated through PL measurements of 0.1 mol% Er³⁺- and 0-20 mol% Y³⁺-codoped Al₂O₃ powders prepared at a sintering temperature of 900 °C in a non-aqueous sol-gel method. PL intensity and lifetime of Er³⁺-Y³⁺-codoped Al₂O₃ powders composed of γ-(Al,Er,Y)₂O₃ and θ-(Al,Er,Y)₂O₃ phases increased with increasing Y³⁺-codoping concentration. The 10-20 mol% Y³⁺ codoping in 0.1 mol% Er³⁺-doped Al₂O₃ powders intensified the PL intensity by about 20 times, with a PL lifetime prolonged from 3.5 to 5.8 ms. A maximal increase of the optical activity of Er³⁺ in 0.1 mol% Er³⁺-Y³⁺-codoped Al₂O₃ powders about one order was achieved by 10-20 mol% Y³⁺ codoping. It is found that the improved PL properties for Er³⁺-Y³⁺-codoped Al₂O₃ powders are mainly attributed to enhanced optical activation of Er³⁺ in the Al₂O₃ by Y³⁺ codoping, and to the slightly increased radiative quantum efficiency of Er³⁺ in the Al₂O₃.     

The structure and optical characters of the ZnO film grown on GaAs/Al2O3 substrate

In this paper ZnO films are grown on GaAs/Al₂O₃ substrates at different temperature by metal-organic chemical vapor deposition (MOCVD). The GaAs/Al₂O₃ substrates are formed by depositing GaAs layer (∼35 nm) on the Al₂O₃ substrate. The results of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) demonstrate that most of the Ga and As atoms form Ga-As bond and the GaAs layer does not present any orientation. The characters of the ZnO films grown on GaAs/Al₂O₃ substrates are investigated by XRD, photoluminescence (PL), atomic force microscopy (AFM) and Raman scattering. Compared with ZnO film grown on Al₂O₃ substrate, ZnO film prepared by our fabrication scheme has good crystal and optical quality. Meanwhile its grain size becomes bigger according to the AFM image. Raman analysis indicates that the intrinsic defects and the in-plane tensile stress are obviously reduced in ZnO/GaAs/Al₂O₃ samples.     

Red, green and blue (RGB) emission doped Y3Al5O12 (YAG) phosphors prepared by non-hydrolytic sol-gel route

An evolutionary optimization process involving combination chemistry was employed in an attempt to develop Y₃Al₅O₁₂ (YAG). The combination chemistry process utilized here consisted the doping of the YAG host with appropriate amounts of red (R), green (G), and blue (B) dopants in a single layer, for use in tricolor white light. The doped YAG was acieved by means of the non-hydrolytic sol-gel route. Four samples were prepared, three of which were mono-doped samples containing 1.0% of a certain lanthanide (Eu³⁺, Tb³⁺, or Tm³⁺) ion, while the fourth contained the three ions. The samples were characterized by X-ray diffractometry and photoluminescence. The diffraction pattern of the mono-doped samples synthered at 800 °C for 16 h displayed peaks corresponding to the Y₃Al₅O₁₂ (YAG) phase, while the sample doped with the three ions revealed the presence of a mixture of Y₃Al₅O₁₂ (YAG) and Y₄Al₂O₉ (YAM) phases. The emission spectra of the three mono-doped YAG samples displayed the typical bands of the blue, green, and red emission of the corresponding lanthanide ions. As for the sample doped with the three lanthanide ions; it simultaneously emitted R, G and B lights. The green emission (546 nm) was more intense and narrow in relation to the red and blue emissions, which may be due to differences in the size of the three incorporated ions.     

Structural, optical and electrical properties of ZnO and ZnO-Al2O3 films prepared by dc magnetron sputtering

ZnO and ZnO-Al₂O₃ thin films were prepared by dc magnetron sputtering and their structural, optical and electrical properties were studied comparatively. It is discovered that the ZnO-Al₂O₃ thin films remain transparent in a shorter wavelength range than the ZnO films, resulting from the increase of their band gap. Their resistivity decreases by seven orders of magnitude, which is caused by doping of Al to ZnO grains in the film. Preferential orientation of ZnO grains in the ZnO-Al₂O₃ thin films deteriorates because of the existence of Al₂O₃ impurity phase in the film. Received: 5 January 1999 / Accepted: 11 October 1999 / Published online: 8 March 2000     

Fabrication of nano-floating gate memories through atomic layer deposition incorporated with chemically-synthesized ZnO-nanocrystals

Nano-floating gate memories made of Al₂O₃/ZnO/Al₂O₃ nanostructures were fabricated with chemically-driven ZnO nanocrystals embedded into high-k Al₂O₃ thin films prepared through atomic layer deposition. The memory characteristics were analyzed through high-frequency capacitance–voltage measurement and current–voltage characteristics, along with high-resolution images of the aforementioned structures. The dotted ZnO nanocrystals function as charge-trapping/detrapping centers, inducing a very large memory window of 5.34 V. The defective nature of ZnO was optimally adjusted into the energy-band diagrams in combination with the tunneling and control layers of the robust Al₂O₃ thin films. The measured memory characteristics exhibited superior retention features derived from the charge-trapping/detrapping behaviors.     

Blue light emission from Eu ions in sol-gel-derived Al2O3-SiO2 glasses

Blue light-emitting glasses were successfully prepared by doping Eu²⁺ ions in the system Al₂O₃-SiO₂. The Al₂O₃-SiO₂ glasses doped with Eu³⁺ ions were synthesized using a sol-gel method, followed by heating in hydrogen gas atmosphere to reduce into the Eu²⁺ ions. The obtained glasses exhibited emission spectra with peak at ∼450 nm due to 4f⁶5d→4f⁷ (⁸S_7/2) transition, the intensities of which strongly changed depending on their glass composition and heating conditions. The emission quantum efficiency of 48% was achieved by heating the glass with the ratio of Al³⁺ to Eu³⁺ at about 6 at 1000 °C in hydrogen gas atmosphere. It was found that the Al₂O₃-SiO₂ glasses were appropriate not only for homogeneously doping the Eu³⁺ ions in glass structure but also reducing to Eu²⁺ ions, resulting in enhanced blue light-emission properties.     

The insert of zinc oxide thin film in indium tin oxide anode for organic electroluminescence devices

Zinc oxide films were prepared by rf magnetron sputtering on glass substrates with designed ZnO target using high-purity of zinc oxide (99.99%) powder. Systematic study on dependence of target-to-substrate distance (D_ts) on structural, electrical and optical properties of the as-grown ZnO films was mainly investigated in this work. XRD showed that highly preferred ZnO crystal in the [0 0 1] direction was grown in parallel to the substrate, while the D_ts did not effect to the peak position of XRD. With decreasing D_ts, the growth rate is increased while the electrical resistivity as well as crystal size in the ZnO films was decreased. The XPS data showed that the O/Zn ratio in ZnO films was increased with increasing D_ts in the films. The as-grown ZnO films have an average transmittance of above 85% at the visible region. The optical band gap of the as-grown ZnO films was changed from 3.18 to 3.36 eV with D_ts. With decreasing D_ts, the electrical resistivity was decreased, while the growth rate was increased.A bilayer is used as an anode electrode for organic electroluminescent devices. The bilayer consists of an ultrathin ZnO layer adjacent to a hole-transporting layer and an Indium tin oxide (ITO) outerlayer. We tried to bring low the barrier between the devices as deposited ZnO films on ITO substrates. We fabricated the organic EL structure consisted of Al as a cathode, Al₂O₃ as an electro transport layer, Alq₃ as a luminously layer, TPD as a hole transport layer and ZnO (1 nm)/ITO (150 nm) as an anode. The result of this experiment was not good compared with the case of using ITO, nevertheless, at this structure we obtained the lowest turn-on voltage as the value of 19 V and the good brightness (6200 cd/m²) of the emission light from the devices. Then the quantum efficiency was to be 1.0%.