Magnesium Oxide Substrates Research Articles

Nanomechanical and nanowear properties of Cr 3C 2 thin films deposited by rf sputtering

In this investigation, nanoindentation, nanoscratch and nanowear tests were done in order to study the nanomechanical and nanotribological properties of the chromium carbide nanostructured thin films. Chromium carbide films were synthesized by rf sputtering from a Cr 3C 2 target on magnesium oxide substrate. The samples were characterized by X-ray diffraction and grazing X-ray reflectivity. All the films have a thickness of 300 nm. A pyramidal Berkovich indenter diamond tip was used for nanomechanical testing. The residual wear depth of the samples was examined using an atomic force microscope (AFM). In this study, an experimental method adapted to the nanowear properties was explored. We have studied the influence of the substrate temperature on the structural, mechanical and tribological properties of chromium carbide films. We have shown that Cr 3C 2 films deposited at a substrate temperature up to 600 °C exhibit a better wear resistance and a hardness value higher than what is measured in the case of the films deposited at room temperature.

Non-destructive analysis of silver selenide films obtained by Pulsed Laser Deposition (PLD) with Micro-XRF

Thin films of silver selenide with varying composition have been deposited on magnesium oxide substrates with pulsed laser deposition and were investigated via micro-XRF. A calibration procedure was designed to determine the absolute thicknesses of the films. The lateral homogeneity was investigated by elemental mapping, thus delivering information about the deposition process. Wet chemical analysis was performed on the dissolved layers with ICP-OES and ICP-MS to determine the stoichiometry of the Ag x Se y . The results suggest a correlation between the composition of the layers and their thicknesses by showing a silver enrichment for thinner layers.

Growth of thin Fe(0 0 1) films for terahertz emission experiments

The electrical and magnetic properties of thin iron (Fe) films have sparked significant scientific interest. Our interest, however, is in the fundamental interactions between light and matter. We have discovered a novel application for thin Fe films. These films are sources of terahertz (THz) radiation when stimulated by an incident laser pulse. After intense femtosecond pulse excitation by a Ti:sapphire laser, these films emit picosecond, broadband THz frequencies. The terahertz emission provides a direct measure of the induced ultrafast change in magnetization within the Fe film. The THz generation experiments and the growth of appropriate thin Fe films for these experiments are discussed. Several criteria are used to select the substrate and film growth conditions, including that the substrate must permit the epitaxial growth of a continuous, monocrystalline or single crystal film, yet must also be transparent to the emitted THz radiation. An Fe(0 0 1) film grown on the (0 0 1) surface of a magnesium oxide (MgO) substrate makes an ideal sample. The Fe films are grown by physical vapor deposition (PVD) in an ultrahigh vacuum (UHV) system. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) are used to characterize the Fe(0 0 1) films. Two substrate surface preparation methods are investigated. Fe(0 0 1) films grown on MgO(0 0 1) substrates that are used as-received and films grown on MgO(0 0 1) substrates that have been UV/ozone-cleaned ex vacuo and annealed in vacuo produce the same results in the THz generation experiments. Either substrate preparation method permits the growth of samples suitable for the THz emission experiments.

Fe(001) thin films for x-ray diffraction and terahertz emission studies

Our interests in growing thin films of iron (Fe) are twofold. First, Fe(001) films are ideal targets for an ultrafast x-ray diffraction instrument designed to understand complex behavior, such as melting or solid-solid phase transitions, in shock-loaded materials. Second, we have discovered that thin iron films generate picosecond, broadband terahertz frequencies after intense femtosecond pulse excitation by a Ti:sapphire laser. Excluding film thickness, the criteria for samples used in both experiments are identical due to the similarities of the experiments. Iron films are grown in ultrahigh vacuum (UHV) conditions on (001)-oriented magnesium oxide (MgO) substrates. We have investigated the effects of substrate preparation on the film quality and have found that films grown in UHV on UV/ozone-cleaned and annealed MgO(001) have a better crystal quality than films grown on as-received MgO(001). However, both substrate preparation methods produce continuous, (001)-oriented thin films of iron.

Fabrication and Optical Properties of PLZT Photonic Crystals Using a Sol-Gel Process

Two-dimensional Pb0.865La0.09Zr0.65Ti0.35O3 (PLZT) photonic crystals with hexagonal arrays of air holes on (001) Pt-sputtered magnesium oxide substrates were fabricated using a sol-gel process with resist molds. The PLZT photonic crystals have a thickness of 200 nm, and the period of hexagonal array and the radius of air holes were 400 or 450 nm and 135 or 165 nm, respectively. The PLZT photonic crystals were primarily orientated along the c-axis. The strain hysteresis loop of the photonic crystals suggested that the photonic crystals are ferroelectric. Several peaks within range of wavelength between 500 nm and 1000 nm appeared in the optical reflection spectra from the cleaved facet of the photonic crystals. The peaks have polarization dependence and the frequency bands of the each peak were close to that of photonic band gaps (PBGs) expected by the calculations.

Characterization of MgO substrates for growth of epitaxial YBCO thin films

YBCO films were grown on magnesium oxide (MgO) substrates for fabricatingstep-edge junction SQUIDs and other Josephson junction-based devices. In-plane45° grain misorientation was frequently observed in films grown on degraded orcontaminated MgO substrates. The appearance of these misoriented grains results in adecrease of the thin-film critical-current density and reduces the device yield.In this work, we investigated the chemical properties of MgO substrates withvarious surface conditions due to different substrate preparation methods andenvironmental degradation, by using x-ray photoelectron spectroscopy (XPS). The XPScharacteristics of the surface are compared before and after a thermal annealing at760 °C resembling the thin-film deposition heating cycle. The MgO substrates, after lithographicprocessing or only weeks of exposure to the laboratory environment, showed surfacedegradation characterized by the presence of hydroxyl groups, carbonate, and other possiblecarbon compounds such as bicarbonate, alcohols and carboxyl. Heating of the substrates to760 °C improves the surface quality to a certain degree with the removal of some of the abovecontaminants, but is not sufficient to recover the MgO surfaces. A final Ar ion-beam etchcleaning process at low ion energy proved to be very effective in refreshing the MgOsubstrate surface that had been degraded due to lithographic processing or storage. Filmsgrown on MgO with this pre-treatment showed perfect grain alignment and highcritical-current densities.

Preparation and properties of two-dimensional PLZT photonic crystals using a sol–gel method

Lead lanthanum zirconate titanate (PLZT) film with an array of air-holes was successfully fabricated on a platinum-deposited (0 0 1) magnesium oxide substrate using a sol–gel method with a resist mold. A PLZT precursor solution was cast into a mold with resist pillars patterned using electron-beam lithography. After removing the resist pillars and applying a firing process, a PLZT ceramic film with air-holes was obtained. The patterned PLZT film was grown epitaxially on the substrate. Reflection peaks were also observed by optical measurement of PLZT film with a hexagonal array of air-holes. The frequency range of the reflection peaks coincided with that of the calculated photonic band structures. We consider that this periodic structure and process are suitable for preparing tunable photonic crystals.

Epitaxial Growth of Strontium Bismuth Tantalate/Niobate on Buffered Magnesium Oxide Substrates

AbstractEpitaxial films of strontium bismuth tantalate (SrBi2Ta2O9, SBT) and strontium bismuth niobate (SrBi2Nb2O9, SBN) were grown using solution deposition techniques on magnesium oxide (MgO) substrates buffered with a 100 nm layer of lanthanum manganate (LaMnO3, LMO). Film structure and texture analyses were carried out using x-ray diffraction. Theta-2theta diffraction patterns were consistent with a c-axis aligned structure for both the buffer layer and the solution deposited films. Theta-2 theta scans revealed (001)SBT, SBN //(001) LMO epitaxial relationships between the solution deposited films and the buffer layer. A pole figure about the SBT, SBN (115) reflection indicated a single in-plane epitaxy. Film quality was assessed using ω and φ scans. Nuclear Magnetic Resonance (13C) was used to characterized the methoxy-ethoxide solutions used for the deposition of the SBN and SBT films.

Optimization of Non-Fluorine Sol-Gel Derived YBCO Thin Films

Sol-gel deposition of thin film YBa2Cu3O7−δ (YBCO) is widely seen as the most cost effective means to manufacture long length HTS wires (A.P. Malozemoff, D.T. Verebelyi, S. Fleshler, D. Aized, and D. Yu, “HTS Wire: Status and Prospects,” Physica C, 386, 424 (2003)). We present a sol-gel technique for YBCO deposition using low cost starting materials and forming only benign by-products during processing. Optimization has concentrated on producing the correct stoichiometry in the final films. RBS measurements show that copper diffuses into the substrate due to its high mobility at the temperatures required to form the YBCO phase. Therefore a starting stoichiometry of 1:2:3 can produce a film highly copper deficient. In order to compensate for this we have made films with different excesses of copper in the precursor solution. The surface morphologies of these films have been examined by SEM and AFM, and the stoichiometry and cation depth profiles characterized by ion beam analysis. The effect of the varying copper stoichiometry is correlated with the superconducting properties and the surface morphology for films on lanthanum aluminate (LAO) and magnesium oxide (MgO) substrates. The residual carbon concentration in the films is measured by nuclear reaction analysis.

HTS Coplanar Meander-Line Resonator Filters With a Suppressed Slot-Line Mode

The design and experimental results of a four-pole coplanar waveguide (CPW) quasi-elliptic filter using high-temperature superconductor (HTS) films are presented. Quarter-wavelength meander-line resonators are used in the filter topology. Although the resonators are aligned in two lines, no bond-wire bridges are required to balance the ground planes in the design and measurement. The slot-line mode of the filter was shifted to be higher than its third harmonic. The filter is highly miniaturized and the performance is significantly improved by the use of superconductors. The main circuit of the filter only has an area of about 6.6 mm /spl times/ 2.4 mm on a magnesium oxide substrate, coated with 600-nm-thick YBCO HTS thin film on single side of the substrate. The 3-dB bandwidth is about 1.6% centered at 2.95 GHz. The performance measured at 30 K, without any tuning, gives an insertion loss of better than 0.4 dB and a return loss of about 12 dB in the passband. The first spurious mode is about triple the center frequency.

The contact angle between liquid iron and a single-crystal magnesium oxide substrate at 1873 K

The contact angle between liquid iron and a single-crystal magnesium oxide substrate at 1873 K

High critical current density of YBCO coated conductors fabricated by inclined substrate deposition

Inclined substrate deposition (ISD) has great potential for rapid production of high-quality template layers for YBCO-coated conductors. We have grown biaxially textured magnesium oxide (MgO) films on metallic substrates by ISD at deposition rates, 20–100 Å/s. Scanning electron microscopy of the ISD MgO films showed columnar grain structures with a roof-tile-shaped surface. X-ray diffraction and pole figure analysis revealed that the c-axis of the ISD MgO is tilted at an angle with respect to the substrate normal. A full width at half maximum (FWHM) of ≈10° was observed in the φ-scan for MgO films. Yttria-stabilized zirconia (YSZ) and ceria (CeO 2) buffer layers were epitaxially grown on ISD MgO by pulsed laser deposition (PLD) prior to YBCO deposition by PLD. The YBCO films grown on YSZ/CeO 2 buffered ISD MgO substrates were biaxially aligned with the YBCO c-axis normal to the substrate surface. A critical current density of J c>1.2×10 6 A/cm 2 was measured at 77 K in self-field.

Influence of MgO surface conditions on the in-plane crystal orientation and critical current density of epitaxial YBCO films

Abstract The effect of magnesium oxide (MgO) surface conditions on in-plane grain orientation and critical current density of epitaxial YBa 2 Cu 3 O 7 (YBCO) films was systematically investigated. The MgO substrates were either “as received” or stored for some time, cleaned using different methods and lithographically prepared for our step-edge junction devices. The YBCO films were grown via reactive thermal co-evaporation by Theva, GmbH. The surface characterisation of MgO substrates was studied using X-ray photoelectron spectroscopy (XPS). The in-plane grain orientation of the YBCO films was studied by means of X-ray diffraction (XRD) φ -scan and the critical current density was measured for the XRD scanned samples. The surface condition of the MgO substrates was found to have a strong influence on the in-plane grain orientation and the critical current density of the YBCO films. The MgO substrates with a degraded or contaminated surface gave rise to 45° grain misorientation in YBCO films and reduced the critical current density. A final process step using a low energy Ar ion beam etching (IBE) of the MgO substrates prior to the YBCO film deposition was found effective in removing the in-plane grain misorientation and promoting the growth of perfectly aligned c -axis YBCO films.

Processing and properties of Bi2Sr2CaCu2Ox thick films on polycrystalline magnesium oxide substrates

Abstract In this paper we report on the processing parameters and resulting critical current densities of Bi 2 Sr 2 CaCu 2 O x (Bi-2212) thick films on polycrystalline MgO substrates. Bi-2212 tapes were cast by the doctor blade technique and laminated onto flat MgO-ceramic substrates. The tapes were produced via the partial melt-process in a single cycle. Silver(I)oxide (Ag 2 O) was added to the powder and the maximum process temperature was varied in order to optimize the transport current density at 77 K in self-field. It was found that both parameters, maximum process temperature during partial melting and amount of Ag 2 O added have a strong influence on the critical current density at 77 K. The highest J c of 1900 A/cm 2 was achieved in the 130 μm thick films with an addition of 4 wt% Ag 2 O processed at a maximum temperature of 900 °C. In addition, large components were processed with 1 cm wide conductors meandering over 150 cm on 20 cm diameter MgO plates.

Microwave and magnetic properties of double-sided hexaferrite films on (111) magnesium oxide substrates

We have deposited hexaferrite films of BaFe12O19 on both sides of a magnesium oxide, (111) MgO, substrate by the liquid phase epitaxy (LPE) deposition technique. The procedure entailed the deposition of seed layers of BaFe12O19 onto the substrate by laser ablation deposition and then dipping of the substrate into a molten flux. Whereas the seed layers were the order of 0.5 μm, the total thickness after LPE deposition was ∼45 μm. The ferrimagnetic resonance linewidth at 60 GHz, 27 Oe, is as low as it has ever been measured before in BaFe12O19 to the best of our knowledge. The static field measurements of the saturation magnetization and anisotropy field were in agreement with previous measured bulk values.

Variation in material parameters for hexagonal barium ferrite films on (111) magnesium oxide as a function of oxygen pressure

This work examines the material characteristics and magnetic properties of hexagonal M-type barium ferrite (BaFe12O19) films deposited by pulsed laser ablation deposition onto (111) magnesium oxide substrates at different oxygen growth pressures. X-ray diffraction data showed the lattice constant of the film grown at 300 mTorr c=23.23 Å increased to c=23.30 Å for the film grown at 20 mTorr. The saturation magnetization ranged from 4.03 to 4.33 kG and the magnetic uniaxial anisotropy field ranged from 16.73 to 19.49 kOe as the oxygen pressure was varied from 10 to 300 mTorr. The narrowest ferrimagnetic resonance (FMR) linewidths (ΔH) for as-produced films were obtained for the 10 mTorr films, where ΔH=0.39 kOe. Films grown with oxygen pressure at 200 mTorr or higher showed two distinct resonance modes, which exhibited ΔH1⩾0.90 kOe and ΔH2⩾1.10 kOe at 59 GHz for a film deposited at 925 °C. The FMR linewidths for this film decreased to ΔH1=0.52 kOe and ΔH2=0.45 kOe after annealing the film at 1000 °C for 1 h. These results indicate that thick films grown at higher oxygen pressures have magnetic parameters closer to bulk values, but also show larger magnetic losses than films grown at lower oxygen pressures.

Phase stability, nitrogen vacancies, growth mode, and surface structure of ScN(0 0 1) under Sc-rich conditions

Rocksalt structure scandium nitride films have been grown on magnesium oxide (0 0 1) substrates by molecular beam epitaxy using a radio frequency plasma source for nitrogen. The case of Sc-rich growth conditions, which occurs when the scandium flux J Sc exceeds the nitrogen flux J N, is discussed. Despite the excess Sc during growth, reflection high-energy electron diffraction and X-ray diffraction (XRD) show that these films have only a single orientation which is (0 0 1), and ion channeling confirms the good crystallinity. Rutherford backscattering shows that these films are off-stoichiometric, and this is found to be directly related to variations in the nitrogen, not the scandium, content by secondary ion mass spectrometry. High-resolution XRD reciprocal lattice mapping shows that these variations in the nitrogen content are related to the existence of the N-vacancies. It is concluded that Sc-rich growth leads to the incorporation of N-vacancies into the crystal structure, the concentration of which depends on the Sc/N flux ratio. Additionally, excess scandium conditions at the surface are explored by in situ scanning tunneling microscopy. The observed wider terrace widths as compared to N-rich growth are due to an increased surface diffusion which is attributed to a Sc-rich, metallic surface structure. Combined with the large dislocation density, the enhanced diffusion results in a predominant spiral growth mode.

Enhanced coercive and remanence fields for CoFe2O4 and BaFe12O19 bilayers deposited on (111) MgO

High quality epitaxial bilayer films of spinel CoFe2O4 (CoF) and M-type hexagonal ferrite BaFe12O19 (BaM) were deposited onto (111) magnesium oxide (MgO) substrate by pulsed laser ablation deposition. X-ray diffraction patterns of both BaM/CoF and CoF/BaM films showed only (0001) BaM, (111) CoF, and (111) MgO peaks. The highest coercive field of Hc=1.4 kOe was obtained for a BaM/CoF film where the CoF layer was deposited at 400 °C, which was higher than typical Hc values of ∼0.4 kOe found for single layer BaM films on (111) MgO. This was less than the Hc∼3.0 kOe found for (111) CoF films deposited at 400 °C, probably due to in situ annealing effects during the growth of the overlying BaM film at 900 °C. This Hc enhancement for BaM/CoF bilayers as compared to BaM/MgO films may provide a means to combine large coercive fields with high quality hexaferrite films.

Ferroelectric Thin-Film-Based Electrically Tunable Bandpass Filters

We report on gold/Ba 0 . 5 Sr 0 . 5 TiO 3 (BST) ferroelectric thin film C-band tunable bandpass filters (BPFs) designed and fabricated on magnesium oxide substrates using three different structures: microstrip, coplanar waveguide (CPW), and conductor backed coplanar waveguide (CBCPW). The two-pole filters were designed for a center frequency of 5.89, 5.88, or 5.69 GHz with bandwidths of 3, 9, or 7%, respectively. The BST-based CPW filter offers a higher sensitivity parameter as well as a lower loss parameter compared to the BST tunable two-pole microstrip filter and CBCPW filter. With an applied voltage of 40 V, the tuning range for the BPF with CPW structure was determined to be 170 MHz.

Microwave Characterization Of Electro-Optic Polymers

ABSTRACTElectro-optic polymer thin-films were characterized at microwave frequencies, for possible applications in GHz modulators. Single layers of the polymers were spin coated on low loss magnesium oxide substrates for characterizing the polymers at microwave frequencies. Coplanar waveguide test structures were designed for evaluation of the relative dielectric permittivity as well as the loss-tangent of the polymers at microwave frequencies. A conformal mapping technique was used for the extraction of relative dielectric constant of the polymer films based on the microwave scattering parameter measurements. As an example, a DR1-PMMA polymer had a relative dielectric permittivity of 3.01 and a loss-tangent of 0.075 at 8 GHz. The design of the test structures, the procedure for the accurate determination of the dielectric permittivity and the loss-tangent of the polymer films are discussed in this paper.