Self-formation of dielectric layer containing CoSi2 nanocrystals by plasma-enhanced atomic layer deposition

Dielectric layer containing CoSi₂ nanocrystals was directly fabricated by plasma-enhanced atomic layer deposition using CoCp₂ and NH₃ plasma mixed with SiH₄ without annealing process. Synchrotron radiation X-ray diffraction and X-ray photoelectron spectroscopy results confirmed the formation of CoSi₂ nanocrystal. The gate stack composed of dielectric layer containing CoSi₂ nanocrystals with ALD HfO₂ capping layer together with Ru metal gate was analyzed by capacitance–voltage (C–V) measurement. Large hysteresis of C–V curves indicated charge trap effects of CoSi₂ nanocrystals. The current process provides simple route for the fabrication of nanocrystal memory compatible with the current Si device unit processes.     

Growth and characterization of c-plane AlGaN on γ-LiAlO2

This study demonstrates a pure c-plane AlGaN epilayer grown on a γ-LiAlO₂ (1 0 0) (LAO) substrate with an AlN nucleation layer grown at a relatively low temperature (LT-AlN) by metal-organic chemical vapor deposition (MOCVD). The AlGaN film forms polycrystalline film with m- and c-plane when the nucleation layer grows at a temperature ranging from 660 to 680 °C. However, a pure c-plane AlGaN film with an Al content of approximately 20% can be obtained by increasing the LT-AlN nucleation layer growth temperature to 700 °C. This is because the nuclei density of AlN increases as the growth temperature increases, and a higher nuclei density of AlN deposited on LAO substrate helps prevent the deposition of m-plane AlGaN. Therefore, high-quality and crack-free AlGaN films can be obtained with a (0 0 0 2) ω-rocking curve FWHM of 547 arcsec and surface roughness of 0.79 nm (root-mean-square) using a 700-°C-grown LT-AlN nucleation layer.     

Structure and growth morphology of Gd2O3-doped CeO2 thin films

Gd₂O₃-doped CeO₂ (Gd_0.1Ce_0.9O_1.95, GDC) thin films were synthesized on (1 0 0) Si single crystal substrates by a reactive radio frequency magnetron sputtering technique. Structures and surface morphologies were characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and one-dimensional power spectral density (1DPSD) analysis. The XRD patterns indicated that, in the temperature range of 200–700 °C, f.c.c. structured GDC thin films were formed with growth orientations varying with temperature—random growth at 200 °C, (2 2 0) textures at 300–600 °C and (1 1 1) texture at 700 °C. GDC film synthesized at 200 °C had the smoothest surface with roughness of R_rms=0.973 nm. Its 1DPSD plot was characterized with a constant part at the low frequencies and a part at the high frequencies that could be fitted by the f^−2.4 power law decay. Such surface feature and scaling behavior were probably caused by the high deposition rate and random growth in the GDC film at this temperature. At higher temperatures (300–700 °C), however, an intermediate frequency slope (−γ₂≈−2) appeared in the 1DPSD plots between the low frequency constant part and the high frequency part fitted by f⁻⁴ power law decay, which indicated a roughing mechanism dominated by crystallographic orientation growth that caused much rougher surfaces in GDC films (R_rms>4 nm).     

Hydride-assisted growth of GaN nanowires on Au/Si(0 0 1) via the reaction of Ga with NH3 and H2

High quality, straight GaN nanowires (NWs) with diameters of 50 nm and lengths up to 3 μm have been grown on Si(0 0 1) using Au as a catalyst and the direct reaction of Ga with NH₃ and N₂:H₂ at 900 °C. These exhibited intense, near band edge photoluminescence at 3.42 eV in comparison to GaN NWs with non-uniform diameters obtained under a flow of Ar:NH₃, which showed much weaker band edge emission due to strong non-radiative recombination. A significantly higher yield of β-Ga₂O₃ NWs with diameters of ≤50 nm and lengths up to 10 μm were obtained, however, via the reaction of Ga with residual O₂ under a flow of Ar alone. The growth of GaN NWs depends critically on the temperature, pressure and flows in decreasing order of importance but also the availability of reactive species of Ga and N. A growth mechanism is proposed whereby H₂ dissociates on the Au nanoparticles and reacts with Ga giving Ga_xH_y thereby promoting one-dimensional (1D) growth via its reaction with dissociated NH₃ near or at the top of the GaN NWs while suppressing at the same time the formation of an underlying amorphous layer. The higher yield and longer β-Ga₂O₃ NWs grow by the vapor liquid solid mechanism that occurs much more efficiently than nitridation.     

Fabrication of (1 1 1)-oriented Si layers on SiO2 substrates by an aluminum-induced crystallization method and subsequent growth of semiconducting BaSi2 layers for photovoltaic application

We have prepared (1 1 1)-oriented Si layers on SiO₂ (fused silica) substrates from amorphous-Si(a-Si)/Al or Al/a-Si stacked layers using an aluminum-induced crystallization (AIC) method. The X-ray diffraction (XRD) intensity from the (1 1 1) planes of Si was found to depend significantly on growth conditions such as the thicknesses of Si and Al, deposition order (a-Si/Al or Al/a-Si on SiO₂), deposition technique (sputtering or vacuum evaporation) and exposure time of the Al layer to air before the deposition of Si. The crystal orientation of the Si layers was confirmed by θ−2θ, 2θ XRD and electron backscatter diffraction (EBSD). The photoresponse properties of semiconducting BaSi₂ films formed on the (1 1 1)-oriented Si layers by the AIC method were measured at room temperature. Photocurrents were clearly observed for photon energies greater than 1.25 eV. The external quantum efficiencies of the BaSi₂ were also evaluated.     

Atomic layer deposition of Al2O3, ZrO2, Ta2O5, and Nb2O5 based nanolayered dielectrics

Ta₂O₅, Ta-Nb-O, Zr-Al-Nb-O, and Zr-Al-O mixture films or solid solutions were grown on Si(1 0 0) substrates at 300 °C by atomic layer deposition. The equivalent oxide thickness of Ta₂O₅ based capacitors was between 1 and 3 nm. In Zr-Al-O films, the high permittivity of ZrO₂ was combined with high resistivity of Al₂O₃ layers. The permittivity, surface roughness and interface charge density increased with the Zr content and the equivalent oxide thickness was between 2.0 and 2.5 nm. In the Zr-Al-Nb-O films the equivalent oxide thickness remained at 1.8-2.0 nm.     

The effect of PbF2 content on the microstructure and upconversion luminescence of Er-doped SiO2-PbF2-PbO glass ceramics

The Er³⁺ doped transparent oxyfluoride glass ceramics were obtained by appropriate heat treatment of the precursor glasses with composition (mol%) 50SiO₂-xPbF₂-(50 − x)PbO-0.5ErF₃. The microstructure and optical properties of the glasses and glass ceramics were determined by differential scanning calorimetry (DSC), X-ray diffraction (XRD), absorption spectra and luminescence spectra. The intensity of upconversion luminescence significantly increased in glass ceramics compared to that in precursor glass. The emission bands centered around 660 nm (⁴F_9/2 → ⁴I_15/2) and 410 nm (²H_9/2 → ⁴I_15/2) were simultaneously observed in glass ceramics but cannot be seen in the corresponding precursor glass. The influence of different PbF₂ content on the microstructure and upconversion luminescence of the samples was analyzed in detail. The results indicated that with the increase of PbF₂ content, the Ω₂ was almost the same and the ratios of red to green upconversion luminescence decreased in glass ceramics.     

Microstructure and dielectric properties of La2O3 films prepared by ion beam assistant electron-beam evaporation

Ultrathin La₂O₃ gate dielectric films were prepared on Si substrate by ion assistant electron-beam evaporation. The growth processing, interfacial structure and electrical properties were investigated by various techniques. From XRD results, we found that the La₂O₃ films maintained the amorphous state up to a high annealing temperature of 900 °C for 5 min. From XPS results, we also discovered that the La atoms of the La₂O₃ films did not react with silicon substrate to form any La-compound at the interfacial layer. However, a SiO₂ interfacial layer was formed by the diffusion of O atoms of the La₂O₃ films to the silicon substrate. From the atomic force microscopy image, we disclosed that the surface of the amorphous La₂O₃ film was very flat. Moreover, the La₂O₃ film showed a dielectric constant of 15.5 at 1 MHz, and the leakage current density of the La₂O₃ film was 7.56 × 10⁻⁶ A/cm² at a gate bias voltage of 1 V.     

Spectroscopic properties of Er-doped Na2O-Sb2O3-B2O3-SiO2 glasses

Spectroscopic properties of Er³⁺-doped Na₂O-Sb₂O₃-B₂O₃-SiO₂ glasses have been investigated for developing 1.5-μm broadband fiber amplifiers. An intense 1.5-μm near infrared emission with a broad full width at half maximum (FWHM) of 88 nm has been obtained for Er³⁺-doped 5Na₂O-20Sb₂O₃-35B₂O₃-40SiO₂ glass upon excitation with a 980 nm laser diode. The obtained emission cross-section of the ⁴I_13/2 → ⁴I_15/2 transition and the lifetime of the ⁴I_13/2 level of Er³⁺ ions are 6.8 × 10⁻²¹ cm² and 0.36 ms, respectively. It is noted that the product of the emission cross-section and the FWHM of the glass, σ_e × FWHM, is as great as 598.4 × 10⁻²¹ cm² nm, which is comparable or higher than that of Er³⁺-doped bismuth-based and tellurite-based glasses. These special optical properties encourage in identifying them as important materials for potential applications in high performance optics and optical communication networks.     

Composition dependent upconversion of Er-doped PbF2-TeO2 glasses

The upconversion properties of Er³⁺ ions were studied for heavy metal oxyfluoride tellurite glass hosts xPbF₂-(100−x)TeO₂ under 975 nm excitation. The intense green (529 and 545 nm) and relative weak red (657 nm) emissions corresponding to the transitions ⁴S_3/2 → ⁴I_15/2, ²H_11/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2, respectively, were simultaneously observed at room temperature. The PbF₂ content has an important influence on upconversion luminescence emission. With increasing PbF₂ content, the intensities of green (529 nm) and red (657 nm) emissions increase slightly, while the green (545 nm) emission increases significantly. These results indicate that PbF₂ has more influence on the green (545 nm) emission than the green (529 nm) and red (657 nm) emissions. The intense green emission observed suggest that Er³⁺-doped heavy metal oxyfluoride tellurite glasses can become candidates for developing upconversion optical devices.     

The effect of composition on UV-vis-NIR spectra of iron doped glasses in the systems Na2O/MgO/SiO2 and Na2O/MgO/Al2O3/SiO2

Glasses with the compositions xNa₂O · 10MgO · (90 − x)SiO₂, 10Na₂O · xMgO · (90 − x)SiO₂, 5Na₂O · 15MgO · xAl₂O₃ · (80 − x)SiO₂, xNa₂O · 10MgO · 10Al₂O₃ · (80 − x)SiO₂, 10Na₂O · 10MgO · xAl₂O₃ · (80 − x)SiO₂, 10Na₂O · 5MgO · 10Al₂O₃ · (80 − x)SiO₂ were melted and studied using UV-vis-NIR spectroscopy in the wavenumber range from 5000 to 30 000 cm⁻¹. At [Al₂O₃] > [Na₂O], the UV-cut off is strongly shifted to smaller wavenumbers and the NIR peak at around 10 000 cm⁻¹ attributed to Fe²⁺ in sixfold coordination gets narrower. Furthermore, the intensity of the NIR peak at 5500 cm⁻¹ increases. This is explained by the incorporation of iron in the respective glass structures.     

GaN-based nitride semiconductor films deposited on nitrified HfO2/Si substrate by molecular beam epitaxy

Nitrified HfO₂/Si substrate was used to grow GaN-based film with molecular beam epitaxy. Four-period InGaN/GaN layered structure and p/n junction were deposited on the nitrified HfO₂/Si. X-ray photoelectron spectroscopy (XPS) result shows that N was effectively incorporated into the HfO₂. The crystallographic relationship of the GaN/HfO₂/Si is GaN(0 0 0 2)∥HfO₂(1 1 1)∥Si(1 1 1). Temperature-dependent photoluminescence (PL), PL peak wavelength, PL peak intensity, and PL full-width at half-maximum of the p/n junction were investigated. Light-emitting diode was fabricated from the p/n junction. Red light was emitted at low voltage and yellow light was emitted when increasing the voltage.     

Structure of Ni/SiO2 films prepared by sol-gel dip coating

The sol-gel dip coating technique has been used to deposit composite oxide films (NiO)_x(SiO₂)_1−x with x = 0.1 on silicon wafers. Single and multilayer coatings allowed a variation of the film thickness from 70 to 400 nm. Film morphology, atomic structure and atomic composition have been investigated by transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS). The local environment of the Ni atoms was characterized by extended X-ray absorption fine structure (EXAFS). The samples were studied in the as-prepared state and after annealing in H₂ at 600 °C for 1 h. The structural and chemical state evolution of clusters present inside the silica matrix is discussed in terms of out-of-equilibrium reaction processes specific to low-dimensional objects and superficial effects.     

The structure and optical properties of GeO2-GeS2 glasses

Oxy-chalcogenide glasses with compositions of xGeO₂-(100 − x)GeS₂, where 0 ? x ? 100 mol%, have been prepared and studied in terms of their structures and optical properties. X-ray fluorescence spectroscopy shows that Ge:S ratio can deviate from GeS₂ by ∼10 at.%, depending critically upon the preparation conditions. Raman scattering spectroscopy suggests that stoichiometric GeO₂-GeS₂ glasses have a heterogeneous structure in the scale of 1-100 nm. The optical gaps are nearly constant at 3.0-3.5 eV for glasses with 0 ? x ? 80 mol% and abruptly increase to ∼6 eV in GeO₂. This dependence suggests that the optical gap is governed by GeS₂ clusters, which are isolated and/or percolated. Composition-deviated glasses appear as orange and brown, and these glasses seem to have more inhomogeneous structures.     

Optical properties of Ga3PO7 single crystals

Ga₃PO₇ crystal with size 18×15×12 mm³ and good optical quality has been grown by the top-seeded solution growth (TSSG) slow-cooling method from a Li₂O–3MoO₃ flux system. The Vickers microhardness and optical properties of the as-grown Ga₃PO₇ crystal have been carefully studied. The results show that the Ga₃PO₇ crystal belongs to the harder materials, and Meyer's index numbers for (1 1 0) and (0 0 1) planes were about 1.45 and 1.60, respectively. The Ga₃PO₇ crystal has a wide transmission range from 215 to 4300 nm. The smaller difference between the refractive indices values of n_o and n_e indicated that the Ga₃PO₇ crystal is an optically uniaxial negative crystal.     

Preparation of Sb2S3 nanomaterials with different morphologies via a refluxing approach

Single-crystalline antimony trisulfide (Sb₂S₃) nanomaterials with flower-like and rod-like morphologies were successfully synthesized under refluxing conditions by the reaction of antimony trichloride (SbCl₃) and thiourea with PEG400 and OP-10 as the surfactants. X-ray diffraction (XRD) indicates that the obtained sample is orthorhombic-phase Sb₂S₃ with calculated lattice parameters a=1.124 nm, b=1.134 nm and c=0.382 nm. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that the flower-like Sb₂S₃ is 9–10 μm in size, which is composed of thin leaves with thickness of 0.05–0.2 μm, width of 0.8–2.2 μm and length of 2.5–3 μm, and the rod-like Sb₂S₃ is 45–360 nm in diameter and 0.7–4 μm in length, respectively. UV–Vis analysis indicates that the band gap of Sb₂S₃ nanorods is 1.52 eV, suitable for photovoltaic conversion. A possible mechanism of formation was proposed. The effects of reaction time and surfactants on the growth of nanomaterials with different morphologies were also investigated.     

Anionic structure and elasticity of Na2O-MgO-SiO2 glasses

The structure and elastic properties of a series of xNa₂O · MgO · 4SiO₂ glasses have been studied using both Raman and Brillouin spectroscopy. Relative to Na₂O-SiO₂ glasses, the maximum abundance for phyllosilicate structural units in the present glasses shows a lag of 0.5 units in the number of non-bridging oxygen per silicon atom (NBO/Si). This phenomenon has been attributed to the decrease in the average coordination number of modifying cations due to the presence of Mg²⁺. It has also been found that the decomposition of both metasilicate and disilicate (dimerized SiO₄) anionic structural units in Na₂O-SiO₂ glasses are enhanced by the addition of MgO. However, the presence of Mg²⁺ does not cause a considerable effect on the decomposition of phyllosilicate structural unit. The acoustic data have revealed that both shear and Young’s moduli of the present glasses decrease with increasing NBO/Si (the variation in bulk modulus is reversed, however). The resistance to shear deformation for the anionic structural units in silicate glasses has been found to decrease in the following order: tectosilicate > phyllosilicate > metasilicate > disilicate > orthosilicate. The relative contribution of the various anionic structural units to the bulk modulus of a glass remains to be determined. The ideal mixing model using Makishima-Mackenzie’s relationship for predicting Young’s modulus is not applicable to the present glasses.     

Growth of polar axis oriented tetragonal Pb(Zr,Ti)O3 films on CaF2 substrates with transparent (La0.07Sr0.93)SnO3

Epitaxial (La_0.07Sr_0.93)SnO₃ [LSSO] films were deposited on CaF₂ substrates by pulse laser deposition. The (1 0 0)_c orientation of LSSO films was observed only on (1 1 0)CaF₂, whereas (1 1 0)_c orientation was found on (1 1 1)CaF₂ and (1 0 0)CaF₂. (0 0 1) polar axis oriented tetragonal Pb(Zr_0.35Ti_0.65)O₃ films were grown on the fabricated (1 0 0)_cLSSO∥(1 1 0)CaF₂ by pulsed metal organic chemical vapor deposition. The (0 0 1)Pb(Zr_0.35Ti_0.65)O₃∥(1 0 0)cLSSO∥(1 1 0)CaF₂ stack structure exhibited about 70% transparency with an adsorption edge of approximately 330 nm.     

Crystallization kinetics of Fe73.5−xMnxCu1Nb3Si13.5B9 (x = 0, 1, 3, 5, 7) amorphous alloys

In this study, we have investigated the effect of substituting Mn for Fe on the crystallization kinetics of amorphous Fe_73.5−xMn_xCu₁Nb₃Si_13.5B₉ (x = 1, 3, 5, 7) alloys. The samples were annealed at 550 °C and 600 °C for 1 h under an argon atmosphere. The X-ray diffraction analyses showed only a crystalline peak belonging to the α-Fe(Si) phase, with the grain size ranging from 12.2 nm for x = 0 to 16.7 nm for x = 7. The activation energies of the alloys were calculated using Kissinger, Ozawa and Augis-Bennett models based on differential thermal analysis data. The Avrami exponent n was calculated from the Johnson-Mehl-Avrami equation. The activation energy increased up to x = 3, then decreased with increasing Mn content. The values of the Avrami exponent showed that the crystallization is typical diffusion-controlled three-dimensional growth at a constant nucleation rate.     

Growth and microstructural features of laser ablated LiCoO2 thin films

Thin films of LiCoO₂ were prepared by pulsed laser deposition technique and the properties were studied in relation to the deposition parameters. The films deposited from a sintered composite target (LiCoO₂+Li₂O) in an oxygen partial pressure of 100 mTorr and at a substrate temperature of 300 °C exhibited preferred c-axis (0 0 3) orientation perpendicular to the substrate surface. The AFM data demonstrated that the films are composed of uniform distribution of fine grains with an average grain size of 80 nm. The grain size increased with an increase in substrate temperature. The (0 0 3) orientation decreased with increase in (1 0 4) orientation for the films deposited at higher substrate temperatures (>500 °C) indicating that the films’ growth is parallel to the substrate surface. The composition of the experimental films was analyzed using X-ray photoelectron spectroscopy (XPS). The binding energy peaks of Co(2p_3/2) and Co(2p_1/2) are, respectively, observed at 779.3 and 794.4 eV, which can be attributed to the Co³⁺ bonding state of LiCoO₂. The electrochemical measurements were carried out on Li//LiCoO₂ cells with a lithium metal foil as anode and LiCoO₂ film as cathode of 1.5 cm² active area using a Teflon home-made cell hardware. The Li//LiCoO₂ cells were tested in the potential range 2.6-4.2 V. Specific capacity as high as 205 mC/cm² μm was measured for the film grown at 700 °C. The growth of LiCoO₂ films were studied in relation to the deposition parameters for their effective utilization as cathode materials in solid-state microbattery application.