Characterization of Al2O3/ZrO2 nano multilayer thin films prepared by pulsed laser deposition

Microstructural characterization of pulsed laser deposited Al₂O₃/ZrO₂ multilayers on Si (1 0 0) substrates at an optimized oxygen partial pressure of 3 × 10⁻² mbar and at room temperature (298 K) has been carried out. A nanolaminate structure consisting of alternate layers of ZrO₂ and Al₂O₃ with 40 bi-layers was fabricated at different zirconia layer thicknesses (20, 15 and 10 nm). The objective of the work is to study the effect of ZrO₂ layer thickness on the stabilization of tetragonal ZrO₂ phase for a constant Al₂O₃ layer thickness of 5 nm. The Al₂O₃/ZrO₂ multilayer films were characterized using high temperature X-ray diffraction (HTXRD) in the temperature range 298–1473 K. The studies showed that the thickness of the zirconia layer has a profound influence on the crystallization temperature for the formation of tetragonal zirconia phase. The tetragonal phase content increased with the decrease of ZrO₂ layer thickness. The cross-sectional transmission electron microscope (XTEM) investigations were carried out on a multilayer thin films deposited at room temperature. The XTEM studies showed the formation of uniform thickness layers with higher fraction of monoclinic and small fraction of tetragonal phases of zirconia and amorphous alumina.     

Characterization of thermally stable W/Ni multilayers by X-rays and cross-sectional transmission electron microscopy

W/Ni multilayer structures (MLS) composed of 5 and 10 bilayers, with composition W(15 Å)/Ni(55 Å), have been deposited on float glass substrate using ion-beam sputtering. X-ray reflectivity and wide-angle X-ray diffraction techniques have been used to study their interface characteristics, such as layer thickness, interface roughness and change in structural parameters. The fabricated MLS were found to be oriented along (111) of Ni having superlattice modulation perpendicular to the film plane. Thermal annealing studies on these multilayers showed that these were stable up to 500 °C. Cross-sectional transmission electron microscopy and selected area electron diffraction studies on as-deposited W/Ni MLS of 10 bilayers revealed well formed interfaces without any correlated roughness. The thicknesses of different layers were found to vary along the film thickness.     

Monocrystalline silicon surface passivation by Al2O3/porous silicon combined treatment

In this paper, we report on the effect of Al₂O₃/porous silicon combined treatment on the surface passivation of monocrystalline silicon (c-Si). Al₂O₃ films with a thickness of 5, 20 and 80 nm are deposited by pulsed laser deposition (PLD). It was demonstrated that Al₂O₃ coating is a very interesting low temperature solution for surface passivation. The level of surface passivation is determined by techniques based on photoconductance and FTIR. As a result, the effective minority carrier lifetime increase from 2 μs to 7 μs at a minority carrier density (Δn) of 1 × 10¹⁵ cm^?3 and the reflectivity reduce from 28% to about 7% after Al₂O₃/PS coating.     

ZnO/Cu/ZnO multilayer films: Structure optimization and investigation on photoelectric properties

A series of ZnO/Cu/ZnO multilayer films has been fabricated from zinc and copper metallic targets by simultaneous RF and DC magnetron sputtering. Numerical simulation of the optical properties of the multilayer films has been carried out in order to guide the experimental work. The influences of the ZnO and Cu layer thicknesses, and of O₂/Ar ratio on the photoelectric and structural properties of the films were investigated. The optical and electrical properties of the multilayers were studied by optical spectrometry and four point probe measurements, respectively. The structural properties were investigated using X-ray diffraction. The performance of the multilayers as transparent conducting coatings was compared using a figure of merit. In experiments, the thickness of the ZnO layers was varied between 4 and 70 nm and those of Cu were between 8 and 37 nm. The O₂/Ar ratios range from 1:5 to 2:1. Low sheet resistance and high transmittance were obtained when the film was prepared using an O₂/Ar ratio of 1:4 and a thickness of ZnO (60 nm)/Cu (15 nm)/ZnO (60 nm).     

Tribological and mechanical behaviors of TiN/CNx multilayer films deposited by magnetron sputtering

TiN/CN_x multilayer films with bilayer periods of 4.5-40.3 nm were deposited by direct-current magnetron sputtering. Layer morphology and structure of the multilayered films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy. The TiN/CN_x multilayers exhibited coherent epitaxial growth due to the mutual growth-promoting effect at small bilayer period and some crystalline regions going through the interface of TiN/CN_x. Nanoindentation tests showed that the hardness of the multilayers varied from 12.5 to 31 GPa, with the highest hardness being obtained with a bilayer period of 4.5 nm. The tribological properties of the films were investigated using a ball-on-disk tribometer in humid air, and the TiN/CN_x multilayer with a bilayer period of 4.5 nm also exhibited the lowest friction coefficient and the highest wear resistance.     

Effect of nitrogen partial pressure on the structure, physical and mechanical properties of CrB2 and Cr-B-N films

The investigation of structure and properties of Cr-B and Cr-B-N films deposited by direct current magnetron sputtering of CrB₂ target in argon and argon-nitrogen environments, respectively is presented. The nitrogen partial pressure was kept at 10, 15, and 25% of the total pressure. The microstructure, phase and chemical composition of Cr-B-(N) films were studied by means of X-ray diffraction, transmission- and scanning-electron microscopy, X-ray photoelectron spectroscopy, electron probe microanalysis and secondary neutral mass-spectrometry. The films were characterized in terms of their electrical resistivity, optical reflectivity and transmittance. Measurements of hardness and elastic modulus were performed by depth sensing nanoindentation. The results obtained show that the films deposited in pure Ar had a hexagonal AlB₂-type structure with crystallites, 15-17 nm in lateral size, elongated in the direction of film growth. The Cr-B-N films consisted of nanocrystalline nc-CrB₂ and amorphous a-BN phases. As the nitrogen content in films was raised, the volume fraction of the nc-CrB₂ phase decreased and a-BN phase increased. When nitrogen was added to the gas discharge during deposition, the nc-CrB₂ crystallite size decreased down to 3-5 nm. Without nitrogen, the films exhibited a columnar morphology. Nitrogen introduction suppressed the columnar growth of films because formation of a-BN intergranular layers. The films deposited under optimal parameters showed hardness in the range of 36-43 GPa and Young's modulus below 300 GPa. For all films, electrical resistivity values between approximately 200 and 700 µΩ cm were recorded.     

Multilayer films consisted of azulene-based dye molecules and polyelectrolyte: Preparation, characterization and photoluminescent property

Ultrathin multilayer films of two azulene-based (Az-based) dye molecules (Az), 3-methylazulene-1-carboxylic acid hydrazide (Az-1) and 5-(4-phenylamine)-2-(3-methylazulene-1-yl)-1,3,4-oxadiazoles (Az-2), and poly(sodium 4-styrenesulfonate) (PSS) have been prepared by layer-by-layer self-assembly and characterized by UV-vis spectroscopy, fluorescence spectroscopy, small-angle X-ray reflectivity measurements and atomic force microscopy (AFM) imaging. UV-vis spectra show that the characteristic absorbance values of the multilayer films increase almost linearly with the number of PSS/Az bilayers, suggesting that the deposition process is regular and highly reproducible from layer to layer. Average thicknesses for the PSS/Az-1 and PSS/Az-2 bilayers of the multilayer films are ca. 0.9 and 1.4 nm, respectively. AFM images provide the surface morphology of the PSS/Az films, indicating that the film surface is relatively uniform and smooth. The occurrence of photoluminescent activity conforms the potential for creating luminescent multilayer films with Az-based dye molecules.     

PLD growth of CuAlO2

Copper aluminium oxide, CuAlO₂ (“CAO”) films were deposited by pulsed laser deposition (“PLD”) on a variety of substrates. As-deposited films were X-ray amorphous. Films formed at 200 °C were insulating, whereas films formed on sapphire at 720 °C were conducting. Specific conductivity and light transmittance were optimized for CAO/sapphire. Best values for the conductivity of around 0.3 S/cm for 280 nm thick films on sapphire were obtained for 3.5 J/cm²/pulse, substrate to target distance 6.5 cm, 400 mTorr oxygen and 720 °C, deposition time 90 min at 10 Hz. Films obtained under these conditions were specular and had a refractive index around 2.1 as derived from reflectivity measurements. Transmission spectra showed an onset around 400 nm and a non-negligible unspecific absorption above.Annealing of as-deposited, X-ray amorphous films on sapphire at 1050 °C in air for 5 min led to crystallization in combination with disruption of film continuity (and therefore loss of conductivity) as seen by optical microscopy, where hexagonal platelets could be clearly distinguished. X-ray analysis showed highly preferential orientation (<003>, <006>, <009>, <0012>). Post-annealing in situ (15 min-8 h) at 720 °C had no effect on film properties.     

Influence of Ag thickness on electrical, optical and structural properties of nanocrystalline MoO3/Ag/ITO multilayer for optoelectronic applications

In this study, MoO₃/Ag/ITO/glass (MAI) nano-multilayer films were deposited by the thermal evaporation technique and then were annealed in air atmosphere at 200 °C for 1 h. The effects of Ag layer thickness on electrical, optical and structural properties of the MoO₃(45 nm)/Ag(5-20 nm)/ITO(45 nm)/glass nano-multilayer films were investigated. The sheet resistance decreased rapidly with increasing Ag thickness. Above a thickness of 10 nm, the sheet resistances became somewhat saturated to a value of 3(Ω/□). The highest transparency over the visible wavelength region of spectrum (85%) was obtained for 10 nm Ag layer thickness. Carrier mobility, carrier concentrations, transmittance and reflectance of the layers were measured. The allowed direct band-gap for an Ag thickness range 5-20 nm was estimated to be in the range 3.58-3.71 eV. The XRD pattern showed that the films were polycrystalline. X-ray diffraction has shown that Ag layer has a (111) predominant orientation when deposited. The figure of merit was calculated for MAI multilayer films. It has been found that the Ag layer thickness is a very important factor in controlling the electrical and optical properties of MAI multilayer films. The optimum thickness of the Ag layer for these films was determined. The results exhibit that the MAI transparent electrode is a good structure for use as the anode of optoelectronic devices.     

Performance and quality analysis of Mo-Si multilayers formed by ion-beam and magnetron sputtering for extreme ultraviolet lithography

Mo-Si multilayer structures were grown by ion-beam and magnetron sputtering to make high-performance mask blanks for practical use in extreme-ultraviolet (EUV) lithography. For ion-beam sputtering, the effect of using Ar or Xe as the sputtering gas, and the impact of the acceleration voltage of Ar or Xe ions on the EUV reflectivity of multilayers were evaluated. In the wavelength range of 12.5-14.5 nm, the peak EUV reflectivity was 60-63% for 40 Mo-Si bilayers grown by ion-beam sputtering, and 62-65% for those grown by magnetron sputtering. Transmission electron microscopy images of Mo-Si multilayers revealed interface layers between the Mo and Si layers. They were found to be composed of a mixture of Mo and Si and to be formed during sputtering. They had a thickness of 1.5-2.0 nm for the deposition sequence Mo-on-Si, and 0.5-1.0 nm for Si-on-Mo. In addition, they were 20-30% thicker for ion-beam sputtering than for magnetron sputtering. Calculations of the EUV reflectivity spectrum for 40 Mo-Si bilayers indicate that interface layer thickness plays a crucial role in determining the EUV performance of multilayers. Finally, an ion-implantation model was found to provide a better explanation of the mechanism of interface layer formation than a thermal-interdiffusion model.     

Irradiation induced effects on Ni3N/Si bilayer system

The irradiation effect in Ni₃N/Si bilayers induced by 100 MeV Au ions at fluence 1.5 × 10¹⁴ ions/cm² was investigated at room temperature. Grazing incidence X-ray diffraction determined the formation of Ni₂Si and Si₃N₄ phases at the interface. The roughness of the thin film was measured by atomic force microscopy. X-ray reflectivity was used to measure the thickness of thin films. X-ray photoelectron spectroscopy has provided the elemental binding energy of Ni₃N thin films. It was observed that after irradiation (Ni 2p_3/2) peak shifted towards a lower binding energy. Optical properties of nickel nitride films, which were deposited onto Si (100) by ion beam sputtering at vacuum 1.2 × 10⁻⁴ torr, were examined using Au ions. In-situ I–V measurements on Ni₃N/Si samples were also undertaken at room temperature which showed that there is an increase in current after irradiation.     

Layer-by-layer deposition of zirconia thin films from aqueous solutions

Thin films of ZrO₂ and Y₂O₃-doped ZrO₂ were deposited using a novel yet simple layer-by-layer technique by means of electrostatic assembling and surface precipitation via dipping substrates alternately in cationic and anionic precursor solutions. Uniform films have been made. A constant growth rate of 5.4 ± 0.3 nm per deposition cycle for the dehydrated nanocrystalline films was achieved. This generic technique can be adapted to make other oxide films and novel multilayers or functionally-graded coatings.     

Coherent growth and superhardness effect of heterostructure h-TiB2/c-VC nanomultilayers

TiB₂/VC nanomultilayers with different VC layer thicknesses have been prepared by a multi-target magnetron sputtering system. X-ray diffraction, high-resolution transmission electron microscopy and nanoindentation measurements were employed to investigate the microstructure and mechanical properties of these films. The results revealed that a metastable structure of VC has been formed in epitaxial TiB₂/VC multilayers with VC layer thickness ≤0.8 nm. Meanwhile, the multilayers exhibited coherent interface between layers resulting in a significantly enhanced hardness of the films, with a maximum value of 43.9 GPa. The stable cubic structure of VC was observed for VC layer thickness ≥1.3 nm, which causes a gradual disruption of the coherent interface of the multilayers, resulting in the quick decrease of hardness.     

Preparation of porous ZrO<Subscript>2</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> macrobeads from ion-exchange resin templates

In this work, we will report a method to prepare porous ZrO₂ and ZrO₂/Al₂O₃ macrobeads using cation-exchange resins with sulfonate groups as templates. The preparation process involves metal ion-loading, ammonia-precipitation, and calcination at an appropriate temperature. Several characterization methods, such as TGA, XRD, SEM with EDX, TEM and N₂ adsorption and desorption, were used to characterize the ZrO₂ and ZrO₂/Al₂O₃ macrobeads. The results showed that the porous structures of the resin templates were negatively duplicated in the two kinds of macrobeads. We found the following interesting results: (1) The ZrO₂/Al₂O₃ macrobeads are composed of tetragonal zirconia nanocrystals that are more technologically important, while the pure ZrO₂ macrobeads consist of a mixture of tetragonal and monoclinic zirconia. (2) In the ZrO₂/Al₂O₃ macrobeads, the size of ZrO₂ nanocrystals is about 5 nm smaller than that (about 19 nm) found in the pure ZrO₂ macrobeads. (3) The ZrO₂/Al₂O₃ macrobeads have more mesopores and, therefore, have a larger surface area than the pure ZrO₂ macrobeads. These oxide macrobeads will have potential applications in catalysis by taking advantage of their macrobeads shape and pores structure.     

Si nanocrystals in SiO2 films analyzed by small angle X-ray scattering

Amorphous SiO/SiO₂ multilayers were studied using grazing-incidence small-angle X-ray scattering (GISAXS). Such SiO/SiO₂ superlattices were prepared by alternately magnetron sputtering of 3 nm thin films of SiO and 3 nm of SiO₂ (10 layers each) on Si (100) substrate. Rotation of the Si substrate during evaporation ensures the homogeneity of the films over the whole substrate. After evaporation the samples were annealed at 1050 °C for 2 h in vacuum or in air. The analysis of the 2D GISAXS pattern has shown that Si nanocrystals are formed in the annealed samples. Using a Guinier approximation, the inter-nanocrystal distance (10.5 nm) and radius of gyration (2.3 nm) have been obtained for the samples annealed in vacuum. Samples annealed in air have shown similar peak values which were however, much wider distributed.     

Coherent growth and superhardness effect of heterostructure h-TiB2/c-VC nanomultilayers

TiB₂/VC nanomultilayers with different VC layer thicknesses have been prepared by a multi-target magnetron sputtering system. X-ray diffraction, high-resolution transmission electron microscopy and nanoindentation measurements were employed to investigate the microstructure and mechanical properties of these films. The results revealed that a metastable structure of VC has been formed in epitaxial TiB₂/VC multilayers with VC layer thickness ≤0.8 nm. Meanwhile, the multilayers exhibited coherent interface between layers resulting in a significantly enhanced hardness of the films, with a maximum value of 43.9 GPa. The stable cubic structure of VC was observed for VC layer thickness ≥1.3 nm, which causes a gradual disruption of the coherent interface of the multilayers, resulting in the quick decrease of hardness.     

Microstructure and properties of (Sr,Ca)CuO2/(Sr,Ca)RuO3 multilayers

Epitaxial multilayer thin films of “infinite-layer” (Sr, Ca)CuO₂ and perovskite (Sr, Ca)RuO₃ have been prepared on (100) SrTiO₃ substrates by multitarget rf magnetron sputtering. X-ray diffraction analyses revealed that the multilayer structure of (Sr, Ca)CuO₃/(Sr, Ca)RuO₃ was successfully fabricated with a minimum layer thickness of 20 Å. Transmission electron microscopy measurements of the multilayers indicated that there was no dislocation which normally exists in single-layer films with an infinite-layer structure. Resistivities of multilayer films at room temperature ranged from 1 to 10 mΩ cm and showed semiconductor-like dependence against the temperature.     

Microstructure and mechanical properties of nanolayered W/W–C thin films

The present study reports on the mechanical and structural properties of W/W–C multilayered thin films with bilayer periods Λ ranging from 2.5 to 100 nm. Films were grown by reactive sputtering radio frequency on Si (100) substrate. X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXRD) and X-ray reflectivity were used to globally characterise the multilayers structure. Hardness and Young modulus have been determined using nanoindentation with a Berkovich tip. The XRD and the GIXRD diagrams revealed the presence of three phases: WC_1−x randomly oriented, W₂C with (100) preferred orientation and W with (110) preferred orientation. An increase in hardness is observed with decreasing period Λ, reaching a maximum value of ~26 GPa at Λ = 2.5 nm.     

Pulsed laser deposition of crystalline ZrC thin films

ZrC thin films were grown on Si substrates by the pulsed laser deposition (PLD) technique under various conditions. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), X-ray diffraction and reflectivity, spectroscopic ellipsometry, and four point probe measurements were used to characterize the properties of the deposited films. It has been found that crystalline films could be grown only by using laser fluences higher than 5 J/cm² and substrate temperatures in excess of 500 °C. For a fluence of 10 J/cm² and a substrate temperature of 700 °C, cubic ZrC films (a = 0.469 nm) exhibiting a (200)-texture were deposited under vacuum or low pressure C₂H₂ atmosphere. These films were smooth, with surface roughness values below 1.0 nm and mass densities around the tabulated value of 6.7 g/cm³. AES depth profiling investigations showed oxygen contamination around 7% in the bulk region. Despite the relatively high levels of oxygen contamination, the deposited ZrC films were very conductive. The use of a low C₂H₂ pressure atmosphere during deposition had a small beneficial effect on crystallinity and stoichiometry of the films.     

Samarium-decorated ZrO2@SnO2 nanostructures,their electrical,optical and enhanced photoluminescence properties

In the present work, pure ZrO₂@SnO₂ and Samarium (Sm_x) (x?=?1%, 8% and 12%)-doped ZrO₂@SnO₂ nanoparticles (NPs) successfully synthesized by facile low-cost co-precipitation technique. As-synthesized nanostructures (NS) were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), UV–visible, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR), Brunauer–Emmett–Teller (BET) spectroscopic investigation. The tetragonal crystal phase of the as-synthesized Sm_x:ZrO₂@SnO₂ NS confirmed by XRD analysis. The observed peak shift in the XRD patterns confirmed incorporation of dopant into host lattice. The Sm_x:ZrO₂@SnO₂ NS present irregular spherical morphology and high agglomeration confirmed by FESEM microscope analysis. The presence of functional groups, chemical bonding, chemical constituents and valence state of the NS confirmed by FT-IR and XPS analysis. The Sm_x:ZrO₂@SnO₂ NS showed higher surface area and smaller optical band gap (454 cm²/g and 2.12 eV) than the pure ZrO₂@SnO₂ NS (189–196 cm²/g and 2.84 eV). Photoluminescence (PL) spectra of undoped ZrO₂@SnO₂ and Sm_x:ZrO₂@SnO₂ NS exhibited oxygen vacancies. Undoped ZrO₂@SnO₂ NS exhibited emission intensity at 370.6 nm (λ_excitation?=?300 nm) whereas, Sm_x:ZrO₂@SnO₂ NS showed emission intensities at 453.4 nm, 476.3 nm, 601.3 nm (λ_excitation?=?300 nm). Electrical property studies of Sm_x:ZrO₂:SnO₂ (1%, 8% and 12%) NS showed large variation in Hall constant (0.125?×?10⁶ cm²/coulomb to 0.647?×?10⁶ cm²/coulomb) with proportionately large variation in the resistivity (147.8 Ω-cm to 456.8 Ω-cm) for all the doped samples as compared with pure ZrO₂@SnO₂ NS. The Sm³⁺-doped ZrO₂@SnO₂ NS showed higher stability, intense PL emission and enhanced electrical properties.