MgO Thin Films Research Articles

X-ray absorption study of the local structure at the NiO/oxide interfaces

This work reports an X-ray absorption near-edge structure (XANES) spectroscopy study at the Ni K-edge in the early stages of growth of NiO on non-ordered SiO2, Al2O3 and MgO thin films substrates. Two different coverages of NiO on the substrates have been studied. The analysis of the XANES region shows that for high coverages (80 Eq-ML) the spectra are similar to that of bulk NiO, being identical for all substrates. In contrast, for low coverages (1 Eq-ML) the spectra differ from that of large coverages indicating that the local order around Ni is limited to the first two coordination shells. In addition, the results also suggest the formation of cross-linking bonds Ni-O-M (M = Si, Al, Mg) at the interface.

Preparation and optical properties of ZnO/Zn0.9Mg0.1O multiple quantum well structures with various well widths grown on c-plane sapphire

A series of 5-period ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs) with different well layer thicknesses in the range of 3–10nm have been fabricated on (0001) sapphire substrates by plasma-assisted molecular beam epitaxy (MBE) with combined MgO and low-temperature ZnO thin film as buffer layers. The good quality of ZnO/Zn0.9Mg0.1O MQWs is evidenced by the observation of readily resolved Pendellösung fringes and the small full-width at half-maximum (FWHM) value of exciton emission as low as 8.3meV, as well as the observation of high order phonon replicas. The dominated photoluminescence (PL) peak in the MQWs shows a systematic blueshift with decreasing well width, which is consistent with a quantum confinement effect. In order to clarify the thermal quenching behavior of exciton emission in the MQWs, temperature-dependent PL is investigated and the relevant activation energies are calculated.

Resolving oxide surfaces – From point and line defects to complex network structures

AbstractIn the following, we demonstrate the atomic‐scale analysis of oxide surfaces. Essential physical properties were extracted using noncontact atomic force microscopy (nc‐AFM) and scanning tunneling microscopy (STM). The main focus has been put on the determination of surface structures. A review of the recent achievements towards atomic‐scale resolution from highly crystalline to amorphous materials is provided. An overview of local probe microscopy and spectroscopy to get beyond the averaging character of diffraction methods is thereby summarized. In particular, surface defects of various dimensionality were investigated. Furthermore, acquisition of information on electronic properties is detailed. The presented material covers zero‐dimensional (0D) point defects, one‐dimensional (1D) line defects, and two‐dimensional (2D) random networks, i.e., amorphous structures. First, we present spectroscopy data taken on thin MgO films grown on Ag(001). Distance‐ and bias‐dependent nc‐AFM and STM measurements were recorded on these films. The local work‐function shift and electronic structure of color centers in the MgO surface were studied. In the next section, the structure determination of ultrathin alumina/NiAl(110) is shown. Atomically resolved nc‐AFM reveals a detailed picture of various line defects in the film. Finally, we discuss the atomic structure of a recently discovered ultrathin vitreous silica film on Ru(0001). The atomic arrangement in the 2D random network, resembling the classical picture of Zachariasen, is analyzed in terms of the pair correlation function and ring‐size distribution.

Highly conformal magnesium oxide thin films by low-temperature chemical vapor deposition from Mg(H3BNMe2BH3)2 and water

Pure, dense, and stoichiometric MgO thin films have been deposited at temperatures as low as 225 °C by chemical vapor deposition using a recently reported magnesium precursor, magnesium N,N-dimethylaminodiboranate, which has the highest room-temperature vapor pressure among known Mg-containing compounds, with water as a co-reactant. The films are characterized by x-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and spectroscopic ellipsometry. Conformal coating on a trench with 35:1 aspect ratio is achieved at a film growth rate of 2 nm/min. The growth rate can be tuned between 2–20 nm/min according to the requirement of the structure to be coated.

Measurement of Energy Band Structure of MgO, MgSrO and MgCaO Thin Film by their Secondary Electron Emission Coefficient due to Auger Neutralization

The energy band structure of MgO, MgSrO and MgCaO thin films has been investigated based on the Auger neutralization theory. Profiles of secondary electron emission from MgO, MgSrO and MgCaO thin films have been measured by gamma focused-ion-beam (γ-FIB) system. We have measured the energy band structure, fe(α), function in their respective valence band from the secondary electron emission characteristics by γ-FIB system with He ion beam whose energy is less than 200 eV in the surface of MgO, MgSrO and MgCaO thin films. For this work, we have employed a Fast Fourier Transform (FFT) and its Inverse-Fast Fourier Transform of the secondary electron current profile emitted from the thin films due to the Auger neutralization mechanism for the determination of the energy band structure fe(α).

Origin of room temperature ferromagnetism in MgO films

We report a systematic study of the crystallinity dependence of room-temperature ferromagnetism (RTFM) in pure MgO thin films prepared by pulsed laser deposition. A sequential transition from ferromagnetism to diamagnetism as a function of deposition temperature is observed. All the samples deposited from room temperature (RT) to 200 °C show clear RTFM, and the magnetization decreases monotonically with the increase of the substrate temperature, whereas the MgO film grown at 300 °C shows diamagnetism behavior like bulk MgO sample. The maximum saturation magnetization of 8 emu/cm3 is obtained for the MgO film deposited at RT, which degrades dramatically after crystallization under the annealing in both vacuum and air atmosphere. Further photoluminescence and X-ray photoelectron spectroscopies reveal that the ferromagnetism in the MgO thin films is correlated directly with the Mg vacancies.

Effect of O3 and Aqueous Ammonia on Crystallization of MgO Thin Film Grown by Mist Chemical Vapor Deposition

Mist chemical vapor deposition (CVD) has been applied to fabricate MgO thin films under atmospheric pressure. In this work, to fabricate highly crystalline MgO thin films at low temperature, the effects of ozone gas (O3), aqueous ammonia (NH3), and a combination of O3 and NH3 on the crystallization temperature were studied by comparing samples grown under a standard condition of inactive gas such as argon (Ar). It was clarified that the crystallization temperature was decreased from 450 to 400 °C by the assistance of O3 and the crystallinity was improved by the addition of NH3. The growth of higher crystallinity MgO thin films at temperatures above 400 °C was possible by the combination of O3 and NH3, which caused stronger enhancement of the crystallization temperature and crystallinity. The causes of these effects were analyzed thermodynamically, and it was clarified that the results were due to the activated oxygen sources and the stability level of precursor materials in the solution.

Microstructure and magnetic properties of L10 FePt–MgO/Fe–MgO thin films

The L10 FePt–MgO/Fe–MgO bilayers were fabricated on thermal oxide silicon substrate by using magnetron sputtering. The TEM image shows that the FePt–MgO single layer has small and uniform granular grain. In the FePt–MgO/Fe–MgO bilayer system, with increasing Fe layer thickness, the grain size become larger and the grain boundary become obscure, while the magnetization process transforms from a coherent magnetization to an exchange spring behavior, and finally a two-phase magnetization reversible process.

Epitaxial MgO/Fe(001) and Fe/MgO(001): Structures of the interfaces

The chemical, electronic and magnetic structures of the interfaces between Fe(001) and MgO(001) thin films were studied using conversion electron Mössbauer spectroscopy (CEMS). A 1 ML thick 57Fe probe located at either of the interfaces in the MgO/56Fe/MgO epitaxial structure enabled precise measurements of the interfacial hyperfine interactions. Analysis of the CEMS spectra showed that both the “MgO/Fe” and “Fe/MgO” interfaces are partially oxidized (63% and 86%, respectively), although, despite good crystallinity, no well-defined iron oxide phases were detected. At the “MgO/Fe” interface, 14% of the oxidized Fe sites were found to be defective (located at steps, corners or kinks). The “Fe/MgO” interface, from which the formation of 57Fe islands of at least 3 ML in height was inferred, was found to be almost defect-free. No modification of the hyperfine parameters of Fe atoms located away from the interface was detected for “Fe/MgO,” in contrast with the “MgO/Fe” interface. Approximately 6% of the probe layer diffused into the MgO films at both interfaces.

Metal Nanoparticles: Steering the Growth of Metal Ad‐particles via Interface Interactions Between a MgO Thin Film and a Mo Support (Adv. Funct. Mater. 1/2013)

The coincidence lattice formed between a Mo(001) surface and a MgO thin film is used to prepare Fe nanoparticle ensembles with high spatial uniformity. As reported by Jacek Goniakowski, Niklas Nilius, and co-workers on page 75, the ordered growth of Fe is initiated by regular work function modulations and geometric distortions of the oxide layer across the coincidence cell.

Local Structural Analysis of Dopants in MgO Thin Film

Local Structural Analysis of Dopants in MgO Thin Film

Si 基板上への(001)配向 MgO 薄膜の作製

We investigated the structural property of MgO thin films on Si(001) substrates by molecular beam epitaxy in order to obtain (001)-oriented MgO barrier for high spin polarization on Si substrate. The MgO layer deposited at 200℃ and deposition rate of 0.30 nm/min grew with (001)-orientation on Si(001) substrate. The (001)-orientation and crystallization of the MgO layer were enhanced by insertion of Mg layer into interface between Si substrate and MgO layer. It is considered that the Mg layer prevented oxidation of Si at interface and functioned as buffer layer.

Effects of Operating Frequency on Panel-Aging and Discharge Characteristics in AC Plasma Display Panel

This paper investigates the changes in the optical and discharge characteristics during the panel-aging process in ac plasma display panel as a parameter of the operating frequency. The resulting changes in the optical and discharge characteristics, including the firing voltage, dynamic voltage margin, three-dimensional IR emission, and SEM image, are then compared for the three different operating frequencies (10, 25, and 50 kHz) during the panel-aging process. Our experimental results confirm that the 50 kHz operating frequency is very effective in obtaining the uniform surface morphology of the MgO thin film during the panel-aging process.

YBCO-Buffered NdBCO Film with Higher Thermal Stability in Seeding REBCO Growth and Recycling Failed Bulk YBCO Superconductors

In this work, we report a strengthened super- heating effect caused by a buffering YBa2Cu3Oy (YBCO or Y123) layer in the Nd1+xBa2−xCu3O7−y (NdBCO or Nd123) thin film with MgO substrate (i.e., NdBCO/YBCO/ MgO thin film). In the cold-seeding melt-textured (MT) growth, the NdBCO/YBCO/MgO film presented an even higher superheating level, about 20 °C higher than that of nonbuffered NdBCO film (i.e., NdBCO/MgO film). Pole figure (X-ray Φ-scan) measurement reveals that the Nd- BCO/YBCO/MgO film has better in-plane alignment than the NdBCO/MgO film, which may be the main origin of the enhanced thermal stability. Using this NdBCO/YBCO/MgO film as the seed and under a maximum processing temper- ature (Tmax) up to 1120 °C, we succeeded in growing vari- ous RE1+xBa2−xCu3O7−y (REBCO, RE = Gd, Sm, Nd, RE refers to rare elements) bulk superconductors and recycling the failed REBCO (RE = Y) bulks in a simple and feasible process.

Catalytic growth of N-doped MgO on Mo(001)

A simple pathway to grow thin films of N-doped MgO (MgO:N), which has been found experimentally to be a ferromagnetic d0 insulator, is presented. It relies on the catalytic properties of a Mo(001) substrate using growth of Mg in a mixed atmosphere of O2 and N2. Scanning tunneling spectroscopy reveals that the films are insulating and exhibit an N-induced state slightly below the conduction band minimum.

Probing the luminescence of single Eu2O3nano-islands on MgO(001) with scanning tunneling microscopy

STM imaging and cathodoluminescence spectroscopy are used to explore the morphology and optical properties of Eu2O3 nano-islands grown on MgO(001) thin films. The global emission properties are governed by intense photon peaks at around 600 nm, arising from forced-dipole transitions in the 4f-state manifold of Eu3+ ions placed in a non-centrosymmetric crystal field. Local optical spectra obtained in the tunneling mode of the STM reveal that the Eu2O3 islands are responsible for the distinct optical response and not isolated Eu3+ ions inside the MgO matrix. Our work demonstrates that thin-film model systems can be used to elucidate fundamental properties of Eu-containing phosphors on the nanometer scale.

Pulsed LASER Deposition of MgO Thin Films

MgO thin films were deposited by Pulsed Laser deposition using different process parameter. The characteristics were investigated via X-Ray diffraction (XRD), Scanning Electron Microscope (SEM) and Digital Holographic Microscope (DHM). It is found that the thin film surface morphology and thickness are different. It was found that the different process parameters such as chamber gas pressure, substrate temperature, LASER energy and number of pulses greatly influence the characteristics of the thin films obtained. The thin films have very low thicknesses of 97, 187 and 193 nm.

Effects of incidence angle on the structure and properties of cathodic vacuum arc deposition MgO thin films

MgO thin films, as the protective layers for plasma display panels (PDP), were prepared by using cathodic vacuum arc deposition technique. The influences of deposition angle between −60° and 60° on film structure and properties were investigated. X-ray diffraction (XRD), ellipsometer, thermal field emission environment scanning electron microscopy (SEM) and UV-Visible spectrophotometry were used to study the properties of MgO thin films like crystallization, surface structures, thicknesses and refraction indices. Our results show that the thickness of MgO thin film decreases with the increase of incidence angle. This is confirmed by the transmittance spectra as well. The film deposited at 0° shows sharper diffraction peaks and smaller FWHMs (full width at half maximum) of both MgO (200) and (220), which means better crystallization quality of the film. The higher packing density is achieved on the 0° deposited film as well.

Study Of Surface Morphology And Grain Size Of Irradiated MgO Thin Films

Present work reports 200 MeV Ag 15+ irradiation induced effects on the surface morphology, grain size and local electronic structure in MgO thin films deposited by e-beam evaporation under ultra High vacuum. The grain size was found to decrease from 37 nm (pristine film) to 23 nm for the sample irradiated with fluence of 1×10 12 ions/cm 2 and thereafter it increases upto fluence of 5×10 12 ions/cm 2 . Similar changes with ion fluence were also observed for surface roughness. Shifting and disappearance of peaks in X-ray absorption spectra with irradiation shows the electronic structure modification after irradiation. The detailed analysis of observed results has been done on the basis of existing theories. Copyright © 2012 VBRI Press.

Comprehensive Approach for the Construction of New Material for Electronic Multipliers

Volatile Complexes Mg(thd)2(TMEDA) (1) and Cs[Y(ptac)4] (2) (Hthd = 2,2,6,6-Tetramethylheptane-3,5-Dione, TMEDA = N,N,N’,N’-Tetramethylethylenediamine, Hptac = 1,1,1- Trifluoro-5,5-Dimethylhexane-2,4-Dione) Were Synthesized and Characterized. Thermal Properties of (1) and (2) Were Investigated by TG. The Temperature Dependencies of Saturated Vapour Pressure of Compounds Were Measured by Static (for (1)) or Flow (for (2)) Method. The Obtained Data Were Used for Choosing Temperature Parameters of Deposition Mg- and Cs-Containing Films by CVD Using (1) and (2) as Volatile Precursors. MgO Thin Films Were Deposited on Si (100) by Low-Pressure CVD (LPCVD) and Pulse-CVD in Temperature Deposition Range 673-823K. Cs- and Mg,Cs-Containig Films Were Formed by LPCVD. The Deposited Films Were Studied by SEM and AFM, Correlations between Temperature Conditions of Deposition Processes and Film Characteristics Were Found.