scholarly journals Optical Properties of Rare Earth Nitrides

2021 ◽  
Author(s):  
◽  
Muhammad Azeem
Keyword(s):  
Thin Films ◽  
Rare Earth ◽  
Band Structure ◽  
Energy Gap ◽  
High Vacuum ◽  
Fundamental Absorption Edge ◽  
Ultra High Vacuum ◽  
Band Structure Calculation ◽  
Direct Energy ◽  
Valence Bands

<p>This experimental thesis uncovers the fundamental optical features of rare earth nitride compounds and relates them to their electronic structure. Experimental observations for the optical energy gaps for thin films of GdN, DyN, SmN and EuN are made for the first time. Thin films are grown by thermal evaporation in ultra high vacuum environment and are passivated by MgF₂ layers. Initial characterizations indicate the polycrystalline thin films of RENs are strongly textured along [111] direction.  Optical characterization techniques, Fourier transform infrared and conventional UV/Vis spectrometers are used in conjunction with SQUID magnetometer and DC electrical resistivity. Transmission and reflection spectra for rare earth nitride thin films were obtained in the photon energy range 0.5 – 5.5 eV in their paramagnetic and ferromagnetic phases. Paramagnetic GdN has a direct energy gap of 1.30±0.05 eV which coincides well with theoretically predicted energy gap. A red-shift in the fundamental absorption edge of ferromagnetic GdN is observed along with onset of absorption at higher energy attributable to the exchange splitting of conduction and valence bands of GdN. The spin split joint density of states is in remarkable agreement with theoretically calculated spin polarized band structure of GdN. Similarly for DyN a consensus is found between theory and experiment on the energy gap of 1.20±0.05 eV at room temperature. However, in the case of SmN, an energy gap of 1.30±0.1 eV is underestimated by theory to 0.81 eV. For EuN, the experimentally determined value of energy gap is 0.97±0.05 eV. This value is used to tune the band structure calculation by QSGW theory which returns a ferromagnetic semiconducting solution for EuN.</p>

scholarly journals Optical Properties of Rare Earth Nitrides

2021 ◽  
Author(s):  
◽  
Muhammad Azeem
Keyword(s):  
Thin Films ◽  
Rare Earth ◽  
Band Structure ◽  
Energy Gap ◽  
High Vacuum ◽  
Fundamental Absorption Edge ◽  
Ultra High Vacuum ◽  
Band Structure Calculation ◽  
Direct Energy ◽  
Valence Bands

<p>This experimental thesis uncovers the fundamental optical features of rare earth nitride compounds and relates them to their electronic structure. Experimental observations for the optical energy gaps for thin films of GdN, DyN, SmN and EuN are made for the first time. Thin films are grown by thermal evaporation in ultra high vacuum environment and are passivated by MgF₂ layers. Initial characterizations indicate the polycrystalline thin films of RENs are strongly textured along [111] direction.  Optical characterization techniques, Fourier transform infrared and conventional UV/Vis spectrometers are used in conjunction with SQUID magnetometer and DC electrical resistivity. Transmission and reflection spectra for rare earth nitride thin films were obtained in the photon energy range 0.5 – 5.5 eV in their paramagnetic and ferromagnetic phases. Paramagnetic GdN has a direct energy gap of 1.30±0.05 eV which coincides well with theoretically predicted energy gap. A red-shift in the fundamental absorption edge of ferromagnetic GdN is observed along with onset of absorption at higher energy attributable to the exchange splitting of conduction and valence bands of GdN. The spin split joint density of states is in remarkable agreement with theoretically calculated spin polarized band structure of GdN. Similarly for DyN a consensus is found between theory and experiment on the energy gap of 1.20±0.05 eV at room temperature. However, in the case of SmN, an energy gap of 1.30±0.1 eV is underestimated by theory to 0.81 eV. For EuN, the experimentally determined value of energy gap is 0.97±0.05 eV. This value is used to tune the band structure calculation by QSGW theory which returns a ferromagnetic semiconducting solution for EuN.</p>

scholarly journals Rare Earth - Fe2 Thin Films Study With Strata™

1996 ◽  
Vol 4 (6) ◽  
pp. 22-23
Author(s):  
J. M. Claude ◽  
J. F. Thiot ◽  
V. Oderno ◽  
C. Dufour
Keyword(s):  
Thin Films ◽  
Rare Earth ◽  
Room Temperature ◽  
Vacuum Chamber ◽  
High Vacuum ◽  
Growth Direction ◽  
Ultra High Vacuum ◽  
Laves Phases ◽  
20 Nm ◽  
The Rare Earth

The Rare-Earth Laves phases RE-Fe2 (RE represent the Rare-Earth) show large magnetostrictive properties, especially at room temperature. These materials are well characterized when in bulk form, but they have rarely been studied as thin films and one can expect some important effects due to epitaxial growth.A few single crystal layers of RE-Fe2 have been studied (YFe2, TbFe2, DyFe2, ErFe2: and Dy0.7Tb0.3Fe2 known as Terfenol-D). The thickness of these different layers are between 5 and 20 nm and with [110] as a growth direction have been epitaxied. They have been deposited with a Molecular Beam Epitaxy (MBE) in an ultra high vacuum chamber. A [1120] sapphire substrate is recovered by a [110] niobium buffer. The RE and the iron are then co-deposited on the substrate which is maintained at 500°C. Lastly, an Yttrium layer is deposited on the Rare Earth material at a temperature close to ambient.

TEM sample preparation of wear-tested room-temperature pulsed-laser-deposited thin films of MoS2 by ultramicrotomy

1993 ◽  
Vol 51 ◽  
pp. 1118-1119
Author(s):  
Pamela F. Lloyd ◽  
Scott D. Walck
Keyword(s):  
Thin Films ◽  
Sample Preparation ◽  
Room Temperature ◽  
High Vacuum ◽  
Pulsed Laser ◽  
Ultra High Vacuum ◽  
Wear Testing ◽  
Preparation Technique ◽  
Cross Sectional ◽  
Aerospace Applications

Pulsed laser deposition (PLD) is a novel technique for the deposition of tribological thin films. MoS2 is the archetypical solid lubricant material for aerospace applications. It provides a low coefficient of friction from cryogenic temperatures to about 350°C and can be used in ultra high vacuum environments. The TEM is ideally suited for studying the microstructural and tribo-chemical changes that occur during wear. The normal cross sectional TEM sample preparation method does not work well because the material’s lubricity causes the sandwich to separate. Walck et al. deposited MoS2 through a mesh mask which gave suitable results for as-deposited films, but the discontinuous nature of the film is unsuitable for wear-testing. To investigate wear-tested, room temperature (RT) PLD MoS2 films, the sample preparation technique of Heuer and Howitt was adapted.Two 300 run thick films were deposited on single crystal NaCl substrates. One was wear-tested on a ball-on-disk tribometer using a 30 gm load at 150 rpm for one minute, and subsequently coated with a heavy layer of evaporated gold.

scholarly journals The Growth of Semiconductor Thin Films Studied by RHEED

1990 ◽  
Vol 43 (5) ◽  
pp. 583
Author(s):  
GL Price
Keyword(s):  
Thin Films ◽  
Surface Science ◽  
High Vacuum ◽  
High Energy ◽  
Ultra High Vacuum ◽  
Large Area ◽  
Growth Modes ◽  
Semiconductor Thin Films ◽  
Wide Range ◽  
Recent Developments

Recent developments in the growth of semiconductor thin films are reviewed. The emphasis is on growth by molecular beam epitaxy (MBE). Results obtained by reflection high energy electron diffraction (RHEED) are employed to describe the different kinds of growth processes and the types of materials which can be constructed. MBE is routinely capable of heterostructure growth to atomic precision with a wide range of materials including III-V, IV, II-VI semiconductors, metals, ceramics such as high Tc materials and organics. As the growth proceeds in ultra high vacuum, MBE can take advantage of surface science techniques such as Auger, RHEED and SIMS. RHEED is the essential in-situ probe since the final crystal quality is strongly dependent on the surface reconstruction during growth. RHEED can also be used to calibrate the growth rate, monitor growth kinetics, and distinguish between various growth modes. A major new area is lattice mismatched growth where attempts are being made to construct heterostructures between materials of different lattice constants such as GaAs on Si. Also described are the new techniques of migration enhanced epitaxy and tilted superlattice growth. Finally some comments are given On the means of preparing large area, thin samples for analysis by other techniques from MBE grown films using capping, etching and liftoff.

scholarly journals Strain-Relief Patterns and Kagome Lattice in Self-Assembled C60 Thin Films Grown on Cd(0001)

2021 ◽  
Vol 22 (13) ◽  
pp. 6880
Author(s):  
Zilong Wang ◽  
Minlong Tao ◽  
Daxiao Yang ◽  
Zuo Li ◽  
Mingxia Shi ◽  
...  
Keyword(s):  
Thin Films ◽  
Self Assembly ◽  
High Vacuum ◽  
Ultra High Vacuum ◽  
Scanning Tunneling ◽  
Kagome Lattice ◽  
Tunneling Microscopy ◽  
Kagomé Lattice ◽  
Temperature Scanning ◽  
C60 Films

We report an ultra-high vacuum low-temperature scanning tunneling microscopy (STM) study of the C60 monolayer grown on Cd(0001). Individual C60 molecules adsorbed on Cd(0001) may exhibit a bright or dim contrast in STM images. When deposited at low temperatures close to 100 K, C60 thin films present a curved structure to release strain due to dominant molecule–substrate interactions. Moreover, edge dislocation appears when two different wavy structures encounter each other, which has seldomly been observed in molecular self-assembly. When growth temperature rose, we found two forms of symmetric kagome lattice superstructures, 2 × 2 and 4 × 4, at room temperature (RT) and 310 K, respectively. The results provide new insight into the growth behavior of C60 films.

AlN thin films fabricated by ultra-high vacuum electron-beam evaporation with ammonia for silicon-on-insulator application

2005 ◽  
Vol 239 (3-4) ◽  
pp. 327-334 ◽  
Author(s):  
Ming Zhu ◽  
Peng Chen ◽  
Ricky K.Y. Fu ◽  
Weili Liu ◽  
Chenglu Lin ◽  
...  
Keyword(s):  
Thin Films ◽  
Electron Beam ◽  
High Vacuum ◽  
Electron Beam Evaporation ◽  
Silicon On Insulator ◽  
Ultra High Vacuum

Ultra-high vacuum chemical vapor deposition and in situ characterization of titanium oxide thin films

1991 ◽  
Vol 6 (9) ◽  
pp. 1913-1918 ◽  
Author(s):  
Jiong-Ping Lu ◽  
Rishi Raj
Keyword(s):  
Thin Films ◽  
Chemical Vapor Deposition ◽  
Titanium Oxide ◽  
Vapor Deposition ◽  
Photoelectron Spectroscopy ◽  
High Vacuum ◽  
Chemical Vapor ◽  
Titanium Isopropoxide ◽  
Ultra High Vacuum

Chemical vapor deposition (CVD) of titanium oxide films has been performed for the first time under ultra-high vacuum (UHV) conditions. The films were deposited through the pyrolysis reaction of titanium isopropoxide, Ti(OPri)4, and in situ characterized by x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). A small amount of C incorporation was observed during the initial stages of deposition, through the interaction of precursor molecules with the bare Si substrate. Subsequent deposition produces pure and stoichiometric TiO2 films. Si–O bond formation was detected in the film-substrate interface. Deposition rate was found to increase with the substrate temperature. Ultra-high vacuum chemical vapor deposition (UHV-CVD) is especially useful to study the initial stages of the CVD processes, to prepare ultra-thin films, and to investigate the composition of deposited films without the interference from ambient impurities.

scholarly journals Enhanced Ionic Conduction at the Film/Substrate Interface in LiI Thin Films Grown on Sapphire(0001)

1993 ◽  
Vol 318 ◽  
Author(s):  
D. Lubben ◽  
F. A. Modine
Keyword(s):  
Thin Films ◽  
Film Thickness ◽  
Ionic Conduction ◽  
High Vacuum ◽  
Dislocation Motion ◽  
Ultra High Vacuum ◽  
Vacuum System ◽  
Substrate Interface ◽  
Interdigital Electrodes ◽  
Film Substrate

ABSTRACTThe ionic conductivity of LiI thin films grown on sapphire(0001) substrates has been studied in situ during deposition as a function of film thickness and deposition conditions. LiI films were produced at room temperature by sublimation in an ultra-high-vacuum system. The conductivity of the Lil parallel to the film/substrate interface was determined from frequency-dependent impedance measurements as a function of film thickness using Au interdigital electrodes deposited on the sapphire surface. The measurements show a conduction of ∼5 times the bulk value at the interface which gradually decreases as the film thickness is increased beyond 100 nm. This interfacial enhancement is not stable but anneals out with a characteristic log of time dependence. Fully annealed films have an activation energy for conduction (σT) of ∼0.47 ± .03 eV, consistent with bulk measurements. The observed annealing behavior can be fit with a model based on dislocation motion which implies that the increase in conduction near the interface is not due to the formation of a space-charge layer as previously reported but to defects generated during the growth process. This explanation is consistent with the behavior exhibited by CaF2 films grown under similar conditions.

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