Characterization of the chemical bath deposited In(OH)xSy films: Effect of the growth conditions

The In(OH)_xS_y thin films were deposited by chemical bath deposition (CBD) using three different deposition procedures: ‘hot’: starting the deposition at 70 °C, ‘cold’: starting the deposition at room temperature and pre-treatment with In³⁺ ions prior the ‘hot’ deposition. The analysis of the deposited In(OH)_xS_y layers on glass revealed that modifications in the chemical bath deposition procedure provoked significant changes in the nucleation process, the growth rate, the layer elemental composition and the layer morphology. With an additional In³⁺ pre-treatment or starting from a cold solution, the formation of a dense bottom layer has been observed, resulting in In(OH)_xS_y films with more compact structure with refractive index values of 2.6. The comparison of the measured In/S ratio with a thicker layer suggests, that the In(OH)_xS_y deposition starts with an OH-rich layer. Assuming the indirect allowed band gap transition type, an E_g of 2.2 eV was found independent of the procedure type or deposition time.     

Polymorphous Fe/FexOy composites: One-step oxidation preparation,composition control,and static magnetic and electromagnetic characteristics

Polymorphous Fe/Fe_xO_y core–shell and urchin-like composites were synthesized via a facile oxidation process at relatively low temperatures (100–300 °C) in the absence of surfactants or an external magnetic field. The oxidation temperature plays a key role in determining the morphology, crystal size, and composition of the resulting products. The static magnetic and electromagnetic (EM) properties of Fe/Fe_xO_y composites are influenced by their morphology, crystal size, and composition. In this study, excellent soft magnetic properties and enhanced permeability were obtained from core–shell Fe/Fe_xO_y composites with low Fe_xO_y shell contents and low surface anisotropy. In contrast, high coercivity and dielectric performance were exhibited by urchin-like Fe/Fe_xO_y composites with high shape and surface anisotropy. This work provides insights into the absorption mechanism of urchin-like complex absorption materials.     

Blue-shifted stimulated emission from ZnO films deposited on SiO2 by atomic layer deposition

ZnO films were prepared by atomic layer deposition upon a SiO₂ layer on a Si substrate and treated by rapid thermal annealing. The optically-pumped random lasing actions with low threshold values were observed in the ZnO films on SiO₂/Si substrates. With the decrease in ZnO film thickness or the increase in post-annealing duration, the stimulated emission shifted toward the shorter wavelength and the lasing threshold increased. The results can be attributed to the inter-diffusion between ZnO and SiO₂, which causes the modification of bandgap renormalization in ZnO.     

Investigation of SiOxCy film as the encapsulation layer for full transparent OLED using hollow cathode discharge plasma at room temperature

The plasma polymer of SiO_xC_y film has attracted much attention because it could possess both the organic and inorganic properties simultaneously for wide range applications. In this work, a SiO_xC_y film with a gradient composition through tuning the N₂O/N₂O + Ar ratio from 0% to 100% was used for TOLED encapsulation using hollow cathode discharge plasma. In order to confirm whether the plasma damage was caused during the PECVD process, a ZnO buffer layer prepared using RF sputtering was deposited before encapsulation. Furthermore, the reference samples with glass lid encapsulation were also used for comparison. The results showed that the SiO_xC_y film with a gradient composition cooperated with the sputtering ZnO buffer layer was a simple and effective method for TOLED encapsulation.     

Properties of atomic layer deposited HfO2 thin films

The growth, composition and morphology of HfO₂ films that have been deposited by atomic layer deposition (ALD) are examined in this article. The films are deposited using two different ALD chemistries: i) tetrakis ethylmethyl amino hafnium and H₂O at 250° and ii) tetrakis dimethyl amino hafnium and H₂O at 275 °C. The growth rates are 1.2 Å/cycle and 1.0 Å/cycle respectively. The main impurities detected both by X-ray Photoelectron Spectroscopy and Fourier transform infrared spectroscopy (FTIR) are bonded carbon (~ 3 at.%) and both bulk and terminal OH species that are partially desorbed after high temperature inert anneals up to 900 °C. Atomic Force Microscopy reveals increasing surface roughness as a function of increasing film thickness. X-ray diffraction shows that the morphology of the as-deposited films is thickness dependent; films with thickness around 30 nm for both processes are amorphous while ~ 70 nm films show the existence of crystallites. These results are correlated with FTIR measurements in the far IR region where the HfO₂ peaks are found to provide an easy and reliable technique for the determination of the crystallinity of relatively thick HfO₂ films. The index of refraction for all films is very close to that for bulk crystalline HfO₂.     

UV-enhanced atomic layer deposition of ZrO2 thin films at room temperature

A UV-enhanced atomic layer deposition (UV-ALD) process was developed to deposit ZrO₂ thin films on poly(ethylene terephthalate) (PET) polymer substrates using zirconium tetra-tert-butoxide (ZTB) and H₂O as precursors with UV light. In the UV-ALD process, the surface reactions were found to be self-limiting and complementary enough to yield uniform, conformal, and pure ZrO₂ thin films on polymer substrates at room temperature. The UV light was very effective to obtain the high-quality ZrO₂ thin films with good adhesive strength on polymer substrates. The ZrO₂ thin films exhibit large-scale uniformity, sharp interfaces, and unique electrical properties.     

Characteristics of NixFe100−x films deposited on SiO2/Si(1 0 0) by DC magnetron co-sputtering

Ni_xFe_100−x films with a thickness of about 200 nm were deposited on SiO₂/Si(1 0 0) substrates at room temperature by DC magnetron co-sputtering using both Fe and Ni₈₀Fe₂₀ targets. Compositional, structural, electrical and magnetic properties of the films were investigated. Ni₇₆Fe₂₄, Ni₆₅Fe₃₅, Ni₆₀Fe₄₀, Ni₅₅Fe₄₅, Ni₄₉Fe₅₁ films are obtained by increasing the sputtering power of the Fe target. All the films have a fcc structure. Ni₇₆Fe₂₄, Ni₆₅Fe₃₅, Ni₆₀Fe₄₀ and Ni₅₅Fe₄₅ films grow with crystalline orientations of [1 1 1] and [2 2 0] in the direction of the film growth while the Ni₄₉Fe₅₁ film has the [1 1 1] texture structure in the direction of the film growth. The lattice constant of the film increases linearly with increasing Fe content. All of the films grow with thin columnar grains and have void networks in the grain boundaries. The grain size does not change markedly with the composition of the film. The resistivity of the film increases with increasing Fe content and is one order of magnitude larger than that of the bulk. For all the films the magnetic hysteresis loop shows a hard magnetization. The Ni₇₆Fe₂₄ film has the lowest saturation magnetization of 6.75×10⁻² T and the lowest saturation field of 8.36×10⁴ A/m while the Ni₄₉Fe₅₁ film has a largest saturation magnetization of 9.25×10⁻² T and the largest saturation field of 1.43×10⁵ A/m.     

Optimization of AlxOy/Pt/AlxOy multilayer spectrally selective coatings for solar-thermal applications

Spectrally selective Al_xO_y/Pt/Al_xO_y multilayer absorber coatings were deposited onto corning 1737 glass, Si (111) and copper substrates using electron beam (e-beam) vacuum evaporator at room temperature. The employment of ellipsometric measurements and optical simulation was proposed as an effective method to optimize and deposit multilayer solar absorber coatings. The optical constants (n and k) measured using spectroscopic ellipsometry, showed that both Al_xO_y layers, which used in the coatings, were dielectric in nature and the Pt layer was semi-transparent. The optimized multilayer coatings exhibited high solar absorptance α ∼ 0.94 ± 0.01 and low thermal emittance ? ∼ 0.06 ± 0.01 at 82 °C. The Rutherford backscattering spectroscopy (RBS) data of Al_xO_y/Pt/Al_xO_y multilayer absorber indicated the Al_xO_y layers present in the coating were nearly stoichiometry. The scanning electron microscope analysis (SEM) result indicated that the average diameter and inter-particles distance of Pt grains were statistically about 146 ± 0.17 nm and 6-10 ± 0.2 nm respectively.     

Goniocolorimetric study of aluminum oxide films deposited by atomic layer deposition

The interference colors resulting from thin films of Al₂O₃ deposited by atomic layer deposition (ALD) on silicon have been rigorously analyzed using a recently developed robotic gonioreflectometer. A series of eleven increasingly thick films was deposited, up to 1613 Å, and their reflectance values obtained for the visible spectrum. A comparison of these values with the predictions of computer simulations employing Fresnel equations has revealed that while there was generally good agreement between predicted and measured spectra, there are some spectral regions that exhibit large deviations from predicted reflectances, typically at near-normal measurement angles and shorter wavelengths. The effect of these discrepancies on color appearance was investigated in the CIE L*a*b* color space for the daylight illuminant D65. Large iridescence is both predicted and measured for most film thicknesses. Chroma and hue differences as large as 20 CIELAB units between the predicted and the measured color centers were obtained. Simulation also predicts larger iridescence than what is actually measured. A likely cause for the observed discrepancies is that the dielectric constants of the ALD films deviate from the literature values for the bulk material.     

Hysteresis-free HfO2 film grown by atomic layer deposition at low temperature

Hysteresis-free hafnium oxide films were fabricated by atomic layer deposition at 90 °C without any post-deposition annealing, and their structures and properties were compared with films deposited at 150 °C and 250 °C. The refractivity, bandgap, dielectric constant and leakage current density all increase with deposition temperature, while the growth rate and breakdown field decrease. All films are amorphous with roughly the same composition. Although the thin films deposited at the above-mentioned temperatures all show negligible hysteresis, only the 90 °C-deposited films remain hysteresis-free when the film thickness increases. The 90 °C-deposited films remain hysteresis-free after annealing at 300 °C. The hysteresis in films deposited at high temperatures increases with deposition temperature. Evidences show such hysteresis originates in the HfO₂ film instead of the interface. Based on a careful structure analysis, middle-range order is suggested to influence the trap density in the films. HfO₂ films deposited at low temperature with negligible hysteresis and excellent electrical properties have great potential for the fabrication and integration of devices based on non-silicon channel materials and in applications as tunneling and blocking layers in memory devices.     

Luminescence properties of Eu ions doped in Y2−xGdxO3 thin films grown by pulsed laser deposition method

Luminescence properties of Y_2−xGd_xO₃:Eu³⁺ (x = 0 to 2.0) thin films are investigated by site-selective laser excitation spectroscopy. The films were grown by pulsed laser deposition method on SiO₂ (100) substrates. Cubic phase Y₂O₃ and Gd₂O₃ and monoclinic phase Gd₂O₃ are identified in the excitation spectrum of the ⁷F₀ → ⁵D₀ transition of Eu³⁺. The emission spectra of the ⁵D₀ → ⁷F_J (J = 1 and 2) transition from individual Eu³⁺ centers were obtained by tuning the laser to resonance with each excitation line. The excitation line at around 580.60 nm corresponds to the line from Eu³⁺ with C₂ site symmetry of cubic phase. New lines at 578.65 and 582.02 nm for the C_S sites of Gd₂O₃ with monoclinic phase are observed by the incorporation of Gd in Y₂O₃ lattice. Energy transfer occurs between Eu³⁺ ions at the C_S sites and from Eu³⁺ ions at the C_S sites to those at the C₂ site in Y_2−xGd_xO₃.     

Cd1−xMnxTe thin films deposited by close-spaced sublimation for application in solar cells

High-quality Cd_1−xMn_xTe polycrystalline films with (1 1 1) preferred orientation were deposited by close-spaced sublimation (CSS) method. The XRD and optical absorption analysis indicated that the band gap of the film was about 1.6 eV. The as-grown Cd_1−xMn_xTe films exhibit quite low photovoltaic performance when used to make cells with CdS as the hetero-junction partner. The effect of various post-deposition treatments with vapors of chlorine-containing materials (CdCl₂ and/or MnCl₂), in Ar or H₂/Ar ambient, on the properties of Cd_1−xMn_xTe cells was studied.     

Growth studies and characterization of silicon nitride thin films deposited by alternating exposures to Si2Cl6 and NH3

We deposited silicon nitride films by alternating exposures to Si₂Cl₆ and NH₃ in a cold-wall reactor, and the growth rate and characteristics were studied with varying process temperature and reactant exposures. The physical and electrical properties of the films were also investigated in comparison with other silicon nitride films. The deposition reaction was self-limiting at process temperature of 515 and 557 °C, and the growth rates were 0.24 and 0.28 nm/cycle with Si₂Cl₆ exposure over 2 × 10⁸ L. These growth rates with Si₂Cl₆ are higher than that with SiH₂Cl₂, and are obtained with reactant exposures lower than those of the SiH₂Cl₂ case. At process temperature of 573 °C where the wafer temperature during Si₂Cl₆ pulse is 513 °C, the growth rate increased with Si₂Cl₆ exposure owing to thermal deposition of Si₂Cl₆. The deposited films are nonstoichiometric SiN, and were easily oxidized by air exposure to contain 7-8 at.% of oxygen in the bulk film. The deposition by using Si₂Cl₆ exhibited a higher deposition rate with lower reactant exposures as compared with the deposition by using SiH₂Cl₂, and exhibited good physical and electrical properties that were equivalent or superior to those of the film deposited by using SiH₂Cl₂.     

Hydrophobic properties of the ion beam deposited DLC films containing SiOx

Diamond like carbon (DLC) films received considerable interest due to outstanding mechanical and tribological properties as well as chemical inertness and hydrophobicity. That combination is particularly interesting for possible application of the DLC as anti-sticking layers in novel lithographic techniques such as nanoimprint lithography, because Si, quartz and Ni - the most often used materials for imprint stamp formation - have high surface energy and, as a result, bad anti-adhesive properties. In present study, SiO_x containing DLC thin films were synthesized from hexamethyldisiloxane vapor and hydrogen gas mixture by direct ion beam deposition. Anti-sticking properties of the grown DLC thin films were evaluated measuring surface contact angle with water. Chemical composition and structure of the deposited films were investigated by X-ray photoelectron spectroscopy and FTIR spectrometry. Morphology of the films was measured by atomic force microscopy. Effects of hexamethyldisiloxane flux on structure, anti-sticking properties and surface morphology of the SiO_x containing DLC thin films were defined.     

Effect of LaNiO3 electrodes and lead oxide excess on chemical solution deposition derived Pb(Zrx,Ti1 − x)O3 films

The effects of LaNiO₃ (LNO) and Pt electrodes on the properties of Pb(Zr_x,Ti_1 − x)O₃ (PZT) films were compared. Both LNO and PZT were prepared by chemical solution deposition (CSD) methods. Specifically, the microstructure of LNO and its influence on the PZT properties were studied as a function of PbO excess. Conditions to minimize the Pyrochlore phase and porosity were found. Remnant polarization, coercive field and fatigue limit were improved in the PZT/LNO films relative to the PZT/Pt films. Additionally, the PZT crystallization temperature over LNO was 500 °C, about ~ 50 °C lower than over Pt. The crystallization temperature reported here is amongst the lowest values for CSD-based PZT films.     

Sputter-assisted plasma CVD of polymer-like amorphous CNx:H films using supermagnetron plasma

By using a sputter-assisted chemical vapor deposition (CVD) of supermagnetron plasma, amorphous CN_x:H films were deposited on the lower part of two parallel electrodes. By applying rf power to the upper electrode (UPRF) at 5 W to 800 W, polymer-like a-CN_x:H films were deposited on substrates placed on the lower electrode with an rf power (LORF) of 10 W. The deposition rate increased as UPRF increased. The hardness was as low as about 6.5 GPa, which is less than that of glass (13.1 GPa). The refractive index changed only slightly as UPRF changed from 1.6 to 1.75. The FT-IR spectrum showed strong absorption bands of NH and CH bonds at high and low UPRFs, respectively. The optical band gap was as large as 2.1 to 2.5, and it decreased as UPRF increased. These a-CN_x:H films showed white photoluminescence (PL) with broadband. With the increase of UPRF from 5 W to 800 W, the PL peak energy shifted down from 2.3 eV to 1.9 eV.     

Electrode effect on resistive switching of Ti-added amorphous SiOx films

Ti-added amorphous SiO_x films were sputter-deposited into stacks of Pt/SiO_x/Pt and Cu/SiO_x/Pt. Optimally prepared Pt/SiO_x/Pt exhibits unipolar resistive switching over 10² cycles, resistance ratio ∼ 10³, yet wide voltage distribution (2 ∼ 7 V for SET, 0.5 ∼ 1.5 V for RESET). Cu/SiO_x/Pt exhibit similar endurance, resistance ratio up to 10⁷, and SET and RESET voltages reduced to 1.8 ∼ 4.2 V and 0.5 ∼ 1 V, respectively. Cu diffusion into SiO_x at the virgin state may play a role in resistive switching of Cu/SiO_x/Pt stack besides of filament conduction. Ti-added amorphous SiO_x films incorporating Cu electrode shows potential for resistive memory.     

On the initial growth of atomic layer deposited TiO2 films on silicon and copper surfaces

Atomic layer deposition (ALD) of TiO₂ using tetrakis(diethylamino)titanium precursor and H₂O was studied on silicon and copper surfaces in order to examine differences in nucleation. Both surfaces were patterned on the same substrate to assure identical deposition conditions. Spectral ellipsometry, X-ray photoelectron spectroscopy and surface profilometry were used to probe nucleation phenomena, growth rates, and surface morphology on both surfaces. The TiO₂ deposition on copper was found to exhibit a significant induction period of about 20-25 ALD cycles with no observable TiO₂ during the first 10-15 cycles on the copper side; in contrast, no such inhibited growth was observed in the TiO₂ deposition on silicon. This result opens up potential for selective ALD of TiO₂ films on silicon-based substrates patterned with a metal without the use of a mask, a self-assembled monolayer or soft lithography which is impractical for some nanoscale semiconductor fabrication processes. After film nucleation, the TiO₂ growth rate on both surfaces was found to be 0.10 nm/cycle.     

Structural study of Si1 − xGex nanocrystals embedded in SiO2 films

We have investigated the structural properties of Si_1 − xGe_x nanocrystals formed in an amorphous SiO₂ matrix by magnetron sputtering deposition. The influence of deposition parameters on nanocrystal size, shape, arrangement and internal structure was examined by X-ray diffraction, Raman spectroscopy, grazing incidence small angle X-ray scattering, and high resolution transmission electron microscopy. We found conditions for the formation of spherical Si_1 − xGe_x nanocrystals with average sizes between 3 and 13 nm, uniformly distributed in the matrix. In addition we have shown the influence of deposition parameters on average nanocrystal size and Ge content x.     

Effects of atomic layer deposited HfO2 compact layer on the performance of dye-sensitized solar cells

The performance of dye-sensitized solar cells (DSSCs) is limited by the back-reaction of photogenerated electrons from the photoelectrode back into liquid electrolyte. An atomic layer deposited (ALD) hafnium oxide (HfO₂) ultra thin compact layer was grown on the surface of the transparent conducting oxide (TCO) and its effects on the DSSC performance were studied with dark and illuminated current-voltage and electrochemical impedance spectroscopy measurements. It was found that this compact layer was effectively blocking the back-reaction of electrons from TCO to the liquid electrolyte, resulting in the overall photoconversion efficiency being enhanced by 66% compared to a DSSC with a conventional sol-gel processed TiO₂ compact layer. Reasons for the improved photovoltaic performance were attributed to passivation of the TCO surface, better electronic quality of the compact layer material and the higher compactness, shown by atomic force microscopic images, obtained from gas-based deposition methods. Also, an increased short-circuit current density suggests that the interfacial resistance for the injection of electrons from the porous nanoparticle network to TCO was reduced. Further, the theory of electron recombination at the TCO/compact layer/electrolyte interface was developed and used to explain the improved DSSC performance with an ALD HfO₂ compact layer.