Amorphous Quartz Substrates Research Articles

Plasma-enhanced atomic layer deposition of crystalline GaN thin films on quartz substrates with sharp interfaces

Polycrystalline hexagonal GaN films were deposited directly on amorphous quartz (fused glass) substrates at 250 °C by plasma-enhanced atomic layer deposition. An atomically sharp GaN/quartz interface is observed from transmission electron microscopy images, which is further demonstrated by x-ray reflectivity measurements. The atomic force microscopy image reveals a smooth surface of GaN. The concentrations of oxygen and carbon impurities in GaN are 6.3 and 0.64%, respectively, according to x-ray photoelectron spectroscopy analysis. The electron mobility measured by Hall is 1.33 cm2 V−1 s−1. The results show that high-quality GaN films are obtained on amorphous quartz substrates, and GaN/quartz can be used as a template for the fabrication of GaN-based devices.

Synthesis and Characterization of Nanoporous ZnO Films by Controlling the Zn Sublimation by Using ZnO/Zn Precursor Films.

A reliable process for the formation of nanoporous ZnO films supported on amorphous quartz and (100) silicon substrates via the processing of ZnO/Zn precursor films is reported. The process is based on the sublimation mechanism of Zn implemented in a novel ZnO/Zn precursor film to produce a nanoporous film. A scanning electron microscopy analysis of the nanoporous ZnO films’ surfaces revealed the presence of ZnO nano-features with round tips; in contrast, the nanoporous ZnO films supported on (100) Si substrates showed hexagonal nut-like nanostructures. The crystallite size of the nanoporous ZnO films decreased as the sublimation temperature was increased. X-ray photoelectron spectroscopy studies demonstrated that formations of oxygen vacancies were produced during the processing stages (as the main structural lattice defects in the ZnO nanoporous films). The analysis of the photoluminescence response confirmed that the active deep-level centers were also related to the oxygen vacancies generated during the thermal processing of the ZnO/Zn precursor films. Finally, a qualitative mechanism is proposed to explain the formation of nanoporous ZnO films on quartz and crystalline Si substrates. The results suggest that the substrates used have a strong influence on the nanoporous ZnO structures obtained with the Zn-sublimation-controlled process.

Lattice Orientation Heredity in the Transformation of 2D Epitaxial Films.

The ability to control lattice orientation is often an essential requirement in the growth of both 2D van der Waals (vdW) layered and nonlayered thin films. Here, a unique and universal phenomenon termed "lattice orientation heredity" (LOH) is reported. LOH enables product films (including 2D-layered materials) to inherit the lattice orientation from reactant films in a chemical conversion process, excluding the requirement on the substrate lattice order. The process universality is demonstrated by investigating the lattice transformations in the carbonization, nitridation, and sulfurization of epitaxial MoO2 , ZnO, and In2 O3 thin films. Their resultant compounds all inherit the mono-oriented crystal feature from their precursor oxides, including 2D vdW-layered semiconductors (e.g., MoS2 ), metallic films (e.g., MXene-like Mo2 C and MoN), wide-bandgap semiconductors (e.g., hexagonal ZnS), and ferroelectric semiconductors (e.g., In2 S3 ). Using LOH-grown MoN as a seeding layer, mono-oriented GaN is achieved on an amorphous quartz substrate. The LOH process presents a universal strategy capable of growing epitaxial thin films (including 2D vdW-layered materials) not only on single-crystalline but also on noncrystalline substrates.

Self-diffusion processes in stoichiometric iron mononitride

In this work, we studied atomic self-diffusion and structural phase transformation in a single phase iron mononitride (FeN) thin film deposited at an optimized substrate temperature (Ts) of 423 K. At this Ts, the FeN film exhibits a tetrahedral coordination between Fe and N atoms (ZnS-type structure with a lattice parameter of 4.28 Å). The structure of the FeN film was studied by combining x-ray diffraction with Fe and N K-edge x-ray absorption spectroscopy and conversion electron Mössbauer spectroscopy measurements. Self-diffusion of Fe and N was measured using secondary ion mass spectroscopy depth profiling in trilayer structures: [FeN(50 nm)/57FeN(2 nm)/FeN(50 nm)] and [FeN(50 nm)/Fe15N(2 nm)/FeN(50 nm)] deposited on an amorphous quartz substrate using reactive magnetron sputtering. It was found that atomic self-diffusion is strongly associated with thermal stability. Before reaching the phase decomposition temperature, the self-diffusion of N was found to be slower than Fe. Upon phase decomposition, both Fe and N diffuse rapidly, and at this stage, the self-diffusion of N takes over Fe. Within the thermally stable state, slower N diffusion indicates that Fe–N bonds are stronger than Fe–Fe bonds in FeN. This behavior was predicted theoretically and has been evidenced in this work.

Preferred‐oriented polycrystalline Y3Fe5O12 films grown on quartz with low microwave loss

AbstractYttrium iron garnet (YIG) is an ideal magnetic insulator for room temperature microwave and spintronic applications. The growth of high‐quality YIG films on substrates other than isostructural Gadolinium gallium garnet (GGG) is a primary requirement to integrate with current semiconductor electronics. Here, we are presenting the growth of highly oriented YIG films on amorphous quartz substrates using pulsed laser deposition. Structural characterization suggests the growth of pure polycrystalline garnet phase with preferred (100) orientation. The 430‐nm thick YIG film shows a saturation magnetization (4πMS) of 1620 (92% of the bulk value of YIG) with a very small coercive field of 6 Oe and a minimum value for ferromagnetic resonance linewidth of 78 Oe for the magnetic field applied perpendicular to the film plane. Estimated damping constant shows reasonably low value, beneficial for realizing the applications integrated with semiconductor technology. Importantly, the formation of YIG with preferred orientation could unveil enormous opportunities in the preparation of textured or single crystal materials on amorphous substrates.

Preparation of RF sputtered AZO/Cu/AZO multilayer films and the investigation of Cu thickness and substrate effects on their microstructural and optoelectronic properties

AZO/Cu/AZO multilayer films are deposited on glass and amorphous quartz substrates by RF magnetron sputtering in confocal configuration at room temperature. The effects of Cu thickness and substrate type on the microstructure and optoelectronics properties are investigated. The results show that the properties of the tri-layer films are strongly influenced by these parameters. For both substrates, all the films are polycrystalline and show an obvious ZnO (002) c-axis preferential growth. No diffraction peaks related to Cu are observed through X-ray diffraction analysis. The average transmittance in the visible region is in the range of 69–83%, while the optical band gap remains constant at 3.454 eV regardless of the Cu thickness and substrate type. With the increase of Cu thickness, the electrical properties of AZO/Cu/AZO tri-layer films on glass and quartz substrates are improved. The best figure of merit obtained is 1.97 × 10-3 Ω-1 for a Cu thickness of 13 nm on glass substrate with a low resistivity of 2.05 10-4 Ω cm and an acceptable average transmittance of 70%. These multilayer structures, with such good performances, are of great interest for potential thin film applications in optoelectronic devices in the visible and NIR region, in particular solar cells.

Synthesis and structural investigation of stoichiometric iron mononitride thin films

We report the synthesis of iron mononitride (FeN) thin films having zinc blende (ZB) type structure, deposited using a direct current magnetron sputtering process on amorphous quartz substrates. The effect of substrate temperature (Ts) on the structure of FeN thin films was systematically investigated by varying the Tsfrom 300 to 500 K(in close intervals of 25K). The long-range as well as the local structure of samples was studied using x-ray diffraction (XRD), x-ray absorption near edge spectroscopy (XANES) at N K-edge, Fe L and K-edge and extended x-ray absorption fine structure (EXAFS) at Fe K-edge. The lattice parameter (LP) obtained from XRD and the presence of an intense pre-edge feature in Fe K-edge XANES confirms the ZB-structure of FeN samples. It was found in this work that the stoichiometric FeN with a LP close to its theoretical value can only be obtained in a narrow temperature regime due to minimization of stresses generated during the growth near the thermodynamic equilibrium conditions. These findings were further validated by EXAFS results yielding Fe–N and Fe–Fe bond distances, in conformity with the theoretically predicted values for FeN in ZB type structure.

Zero field cooled exchange bias effect in nano-crystalline Mg-ferrite thin film

The Zero Field Cooled (ZFC) Exchange Bias (EB) effect in a single phase nanocrystalline Mg-ferrite thin film, deposited on an amorphous quartz substrate using pulsed laser ablation technique, is reported. The film showed a high ZFC EB shift (HE ∼ 190 Oe) at 5 K. The ZFC EB shift decreased with increasing temperature and disappeared at higher temperatures (T > 70 K). This Mg-ferrite thin film also showed the Conventional Exchange Bias (CEB) effect, but unlike many CEB systems, the film showed a decrease in coercivity (HC) under the Field Cooled measurements. The film also showed the training effect in ZFC measurements, which followed the frozen spin relaxation behavior. The observed exchange bias could be attributed to the pinning effect of the surface spins of frozen glassy states at the interface of large ferrimagnetic grains.

Structural and magnetic properties of FeN thin films grown on TiN

We studied the growth of iron mononitride (FeN) thin film on a titanium mononitride (TiN) underlayer. FeN samples with a zinc blende (ZB)-type structure were deposited using reactive magnetron sputtering with and without the TiN underlayer on an amorphous quartz substrate. Combining x-ray diffraction, conversion electron Mössbauer spectroscopy, nuclear forward scattering and N K-edge x-ray absorption near edge spectroscopy measurements, we probed the long range and the local structure in our samples. FeN films are known to exhibit structural and magnetic imperfections. With the TiN underlayer such imperfections get reduced to a large extent. By studying films of different thicknesses, the origin of imperfections present in FeN films has turned out to be correlated with the film growth process. Obtained results are presented and discussed in this work.

Bulk-like magnetization and improved microwave properties of polycrystalline YIG (Y3Fe5O12) films grown on quartz substrates by pulsed laser deposition

Yttrium iron garnet (YIG) thin films with thickness 110 nm ≤ t ≤ 530 nm were grown on amorphous quartz substrates using pulsed laser deposition (PLD). The films show an improved magnetic and microwave performance. The value of saturation magnetization (4πMS) and ferromagnetic resonance (FMR) linewidth were found to be dependent on the thickness (t) of the film. The film with t = 530 nm shows a 4πMS value of 1725 (98% of the bulk value of YIG) and a minimum value for FMR linewidth of 57 Oe and 78 Oe respectively for the magnetic field applied perpendicular and parallel to the film plane. An almost linear relation between linewidth and coercivity is observed, which suggests a positive correlation between magnetic anisotropy, coercivity, and linewidth. The results demonstrated that YIG films prepared on quartz substrates can be beneficial to the application of YIG films to semiconductor integrated devices.

Absence of ferromagnetism in transition metal (Co, Ni and Cu) doped ZnO films

Structural, optical and magnetic properties of oriented Zn0.95TM0.05O (TM = Co, Ni, Cu) films prepared on amorphous quartz substrate using RF magnetron sputtering have been studied. X-ray diffraction patterns show that all films are single phase and are preferably oriented in (002) direction. An analysis of transmission spectra shows that the optical band gap is reduced for all doped ZnO films with respect to that of bulk ZnO single crystal. With increase in thickness of Cu doped ZnO films, the band gap reduces further (3.00 eV for 200 nm film and 2.86 eV for 400 nm film). A strong absorption is observed at 665 nm for Co doped ZnO film due to transitions of tetrahedrally coordinated Co2+ from 4A2 (4F) → 2E (2G). A pre-edge peak observed in TM K-edge XANES spectra of each film confirms that TM ions get substituted in Zn site of ZnO hexagonal wurtzite structure. No room temperature ferromagnetism is observed in any of doped films.

Pyrite thin films on amorphous substrates: Interaction with the substrate and doping effects

Recent published literature dealing with FeS2 pyrite (thin films and single crystals) faces a few and relevant issues: the low photovoltage presented by pyrite (mainly related to the singular nature of its surface), the not yet clearly defined way of making available n and p type reliable samples and the relevance of their stoichiometry. To address the second and third issues, Fe thin films, Ti/Fe and Co/Fe bilayers deposited on sodalime glass and amorphous quartz substrates have been sulfurated at different temperatures (Ts) (Ts ≲ 600°C) during 20 h to obtain pyrite thin films. Seebeck coefficient and Hall Effect measurements have been carried out at room temperature with the sulfurated samples. It has been found that sulfurated Ti/Fe on sodalime glass presents a change of the Seebeck coefficient sign (from negative to positive) due to a strong interaction of the Ti layer with the substrate, which is not present in the Ti/Fe samples deposited on amorphous quartz. As a consequence of the interaction, a new TiO2 layer is formed between the sodalime glass substrate and the pyrite layer. Sulfurated Co/Fe bilayers on sodalime glass show a coherent behavior according to the obtained results and previously published works. They all appear to be n-type semiconductors when Ts ≳ 175°C. Non-intentionally doped Fe thin films on sodalime glass behave in a non-conclusive fashion from the point of view of their electrical transport characterization. The Seebeck coefficient (S) of the sulfurated films appear to be S > 0 for all values of Ts. However, the value and sign of the Hall constant behave in a non-reproducible way. Results are discussed on the light of present knowledge of synthetic pyrite thin films growth and doping.

Large Room Temperature Magnetic Moment in Mn${_{1-x}}$ Zn${x}$ Fe2O4 Thin Films for ${x \geq0.4 }$

Mn ${_{1-x}}$ Zn x Fe2O4 ( $0.1\le x\le 0.8$ ) thin films with nanocrystalline grains were deposited on amorphous quartz substrate using pulsed laser ablation technique, at a substrate temperature of 650 °C. For $x\le 0.3$ , the room temperature spontaneous magnetization ( $4\pi M_{S}$ ) of thin films was observed to be lower than the bulk composition. For $x=0.7$ , the room temperature $4\pi M_{S}$ value (~6.1 kG) is 7.5 times the bulk value for same x. This value is only 1.4 times of the bulk at 10 K, signifying a large enhancement in the exchange constant for thin films. The exchange stiffness constant (D) values were evaluated by fitting the $4\pi M_{S}$ data to the Bloch equation. The D values of thin films were always higher than that of the bulk. This result can be explained on the basis of occupancy of nonmagnetic Zn2+ on both the tetrahedral (A) and octahedral (B) sites. This is unlike in the bulk, where all the Zn2+ ions occupy only A site.

Scalable lattice-strain in preferentially oriented acceptor-doped cerium oxide film and its impact on oxygen ion transport kinetics

Fast ionic conduction through strain engineered heteroepitaxial film have been demonstrated well. However, this effect in the preferentially orientated film remains to be unexplored. Here, we report the effect of interatomic distance between cation-oxygen bonds on the oxygen ionic transport in preferetially (111) oriented Ce0.80Sm0.1M0.1O2-δ (M = Gd, Nd, Pr, La) film over an amorphous quartz substrate. With the increase in ionic radii of dopant cation, the films exhibited a substantial increase in tensile strain with a change in lattice constant (Δa) in the order of ∼1.14% (Δa: 1.14% (Sm3+ + La3+) > 1.04% (Sm3+ + Pr3+) > 0.69% (Sm3+ + Nd3+) > 0.14% (Sm3+) > 0.08% (Sm3+ + Gd3+)) has strong influence on defect association enthalpy (ΔHa) leading to the change in migration energy of oxygen ion during conduction process. Highest conductivity was observed from Ce0.85Sm0.1Nd0.1O2-δ, which is four times greater than that of Ce0.85Sm0.2O2-δ. As a consequence, it is clear that optimum co-dopant is needed to attain the critical ionic radii/tensile strain to achieve the maximum ionic conductivity in the preferentially oriented ceria-based thin film. This work demonstrates the importance of tuning the ionic radii of dopant cation, which can effectively facilitate the optimum expansion of lattice to attain the fast ionic conduction process in (111) oriented thin film based solid electrolyte.

Evaluation of Exchange Stiffness From Temperature-Dependent Magnetization in ZnFe2O4 Thin Films

Nano-crystalline magnetic ZnFe2O4 thin films were deposited in oxygen atmosphere at different substrate temperatures (T S ) on amorphous quartz substrate by pulsed laser deposition technique. The T S = 350 °C film was also annealed at different temperatures in air. X-ray diffraction patterns confirmed that all the samples were cubic spinel and the average grain size of the films increased with increasing T S and annealing temperatures (T A ). Spontaneous magnetization at different temperature was obtained from the $M$ – $H$ loops. The temperature dependence of magnetization data was fit using Bloch’s law. The value of exchange stiffness constant (D) was calculated using the fit values of Bloch’s constant. The obtained D values were found to gradually decrease with the increase of average grain size.

Anomalously large magnetic moment in nanocrystalline Co0.3Zn0.7Fe2O4 thin films

Co0.3Zn0.7Fe2O4 nanocrystalline thin films were deposited by pulsed laser ablation technique on amorphous quartz substrate. These films were as deposited at different substrate temperatures (TS) varying from room temperature (RT) to 750 °C. The RT deposited films were ex situ annealed at annealing temperatures (TA) ranging from 150 °C to 750 °C. The magnetic properties of the films were observed to depend on TA and TS. A spontaneous magnetization (4πMS) value higher than that of the bulk was observed in the as deposited film at TS = 750 °C. This film also showed a higher Curie temperature than bulk. These results were explained based on the grain growth and cation distribution in thin films.

Magnetic properties of pulsed laser deposited Co1−xZnxFe2O4 (0.10 ≤ x ≤ 0.70) thin films

The magnetic properties of pulsed laser deposited Co-Zn ferrite [Co1−xZnxFe2O4 (0.1≤x≤0.7)] nanocrystalline thin films have been investigated. The films were deposited on amorphous quartz substrate. The observed magnetic properties of the films depend on the deposition temperature (TS), the annealing temperature (TA) and the Zn content (x). A magnetization value higher than bulk was observed in a room temperature deposited Co rich (x=0.1) Co-Zn ferrite thin films, when the films were ex-situ annealed at TA=750°C. On the other hand, in Zn rich (x=0.7) Co-Zn ferrite, a magnetization value higher than bulk (x=0.7) was obtained in a film deposited at TS=750°C. The unusual magnetization values are explained on the basis of grain growth and the cation distribution in thin films.

Enhancing the oxygen ionic conductivity of (111) oriented Ce0.80Sm0.20O2-δ thin film through strain engineering

Several physicochemical properties can be tailored by tuning the lattice strain of the crystal. Here, we report the effect of lattice strain on oxygen ion conduction of oriented samarium doped ceria (SDC) films deposited over an amorphous quartz substrate. Lattice distortion was induced by varying the deposition rate in electron beam deposition technique (EB-PVD). Texture coefficient calculation and pole figure analysis confirms the (111) orientation in out‐off plane direction. Stress state was monitored using sin2Ψ method in tri-axial direction and the results indicate a reduction in compressive stress with an increase in deposition rate. A difference in the mean free path of adatom influences the surface morphology of SDC films with compressive stress leading to a significant impact on conductivity. Compared to higher compressive stress, thin film containing lower stress along (111) orientation exhibited a two order enhancement in conductivity. The faster ionic conductivity arises from the ease of oxygen ion hopping through the expanded lattice as compared to the highly-stressed crystal structure. Thus, the deposition rate in EB-PVD provides a valuable technique for engineering the strain to realize the potential enhancement in the efficiency of electrolyte for ITSOFC application.

Influence of O2 pressure on structural, morphological and optical properties of TiO2-SiO2 composite thin films prepared by pulsed laser deposition

In this work, TiO2-SiO2 composite films were grown on amorphous quartz substrate at different oxygen partial pressure by pulsed laser deposition technique. The influence of oxygen partial pressure on structural, optical and surface properties of films was examined. Grazing incidence X-ray diffraction showed the formation of TiO2 rutile phase and degree of crystallinity decreased with the increase of oxygen pressure. Energy band gap of the films increased from 3.3 to 3.6 eV with the increase of oxygen pressure from 13.33×10−3Pa to 20.00Pa. Variation of surface morphology of films with increasing oxygen partial pressure was studied by Atomic Force Microscopy (AFM). AFM images are showing that grain size of deposited films is increasing with increasing oxygen pressure. Field effect scanning electron microscopy images also shows the similar surface morphology. X-ray Photoelectron Spectroscopy shows the evidence of oxygen defect and related Ti3+ states in composite films. Composite films showed blue photoluminescence (PL) emission by the excitation of 350nm wavelength. Deconvoluted PL peaks showed emission originated from Ti3+ defect level associated with an oxygen vacancy. Oxygen vacancy decreased with increasing oxygen pressure. Intense blue emission with high luminous efficacy of radiation and maximum flux was achieved for 13.33×10−3Pa oxygen pressure. Deposited films might be used in the field of blue light emitting diode application.

Optical and Electrical Properties of (002)-Oriented ZnO Films Prepared on Amorphous Substrates by Sol-Gel Spin-Coating

Zinc oxide (ZnO) films were prepared on amorphous quartz substrates by sol-gel spin-coating using Zn(CH3COO)2•2H2O precursor. Isopropanol, ethanol and 2-methoxyethanol were used as solvents. The film drying temperature was kept constant at 200 oC and the annealing temperature was varied from 400 to 800 oC. Highly transparent and (002)-oriented hexagonal wurtzite-type ZnO films were obtained using isopropanol solvent. The ZnO films prepared at Tanneal = 600 oC showed the highest (002) preferential orientation, however it was not the significant feature to achieve low resistivity. The uniform and (002)-oriented ZnO films prepared at Tanneal = 400 oC display the highest transmittance (>93% in the visible region) and the lowest resistivity (7.1 Ω•cm).