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Article Overviews[edit | edit source]
Abstract: GdN thin films are deposited on MgO(100) by low-energy ion-beam-assisted molecular-beam epitaxy at elevated temperatures. Elemental analysis by secondary-ion mass spectrometry proves that a protective layer is imperative to avoid oxidation of the GdN films in air. In situ surface structural investigation of the growing GdN films by reflection high-energy electron diffraction reveals epitaxial film growth. This result is confirmed by x-ray diffraction structure and texture analysis. Accordingly, the GdN films on MgO(100) exhibit cube-on-cube epitaxy. Due to the epitaxial growth the crystalline quality of the films is by far higher than that of films previously reported of in literature.
Summary[edit | edit source]
This study's purpose was to produce high-quality GdN for the study of its electronic properties, which have a degree of uncertainty, with reported semiconducting, semimetallic, and insulating characteristics. The involves the growth of GdN by Ion Beam Assisted Molecular Beam Epitaxy (IBA-MBE)on a substrate of MgO (100) (lattice mismatch of 18.7%). Both materials crystallize in the NaCl structure. The IBA-MBE process involved the irradiation of the growth surface with nitrogen ions, which stimulated crystal growth. Comparisons to other qualities of GdN reported that the quality of GdN produced in this study surpassed that of previous attempts. The lattice parameter value of GdN to which the results were compared was a=0.4999 nm, as provided by The International Centre for Diffraction Data Powder Diffraction File; results showed a to be equal to 0.497±0.006 nm, and tending to the smaller end of that range. Twinning was present in the GdN layer, possibly caused by stacking faults, which commonly cause twinning in (100) oriented cubic thin films, but it was expected that optimization of the nitrogen ion to gadolinium atom flux ratio and growth temperature could further improve quality of the GdN surface.
GdN (111) heteroepitaxy on GaN(0001)by N2 plasma and NH3 molecular beam epitaxy [edit | edit source]
Abstract: We report on the heteroepitaxial growth of thin films of rocksalt GdN on c-plane (0001) wurtzite GaN by molecular beam epitaxy (MBE) using either an N2 plasma or NH3 as the nitrogen source. In both cases, epitaxial films with fully oriented GdN (111)||GaN (0001) were deposited as demonstrated by ϴ–2ϴ X-ray diffraction. ϕ scans of GdN peaks demonstrate 6-fold symmetry along the growth axis implying the presence of two 3-fold-symmetric GdN (111) crystal variants in-plane. Electrical transport and magnetometry measurements on films grown using N2 plasma show that these GdN films are ferromagnetic below TC= 70K and degenerately dope or metallic from 10 to 300 K with magnetotransport signatures associatedᶿ with TC.
Absract: This paper contains a summary of selected aspects of the epitaxial growth of rare-earth nitride thin films and the recent progress achieved in this field. The discussion is focussed on GdN, SmN, EuN compounds grown by both pulsed laser deposition and molecular beam epitaxy on different substrates including YSZ (001), c-plane (0001) AlN and GaN. While a N2 plasma cell is used as a nitrogen source for growing EuN, we take advantage of the catalytic breakdown of molecular nitrogen by rare-earth atoms to grow GdN and SmN in the absence of activated N2. The structural, magnetic and transport properties of the thin films are assessed by reflection high-energy electron diffraction, x-ray diffraction, Hall Effect, temperature-dependent magnetization and resistivity.
Abstract: We report on the epitaxial growth of the intrinsic ferromagnetic semiconductor GdN on Si (111) substrates buffered by a thick AlN layer, forming a heteroepitaxial system with promise for spintronics. Growth is achieved by depositing Gd in the presence of unactivated N2 gas, demonstrating a reactivity at the surface that is sufficient to grow near stoichiometric GdN only when the N2:Gd flux ratio is at least 100. Reflection high-energy electron diffraction and X-ray diffraction show fully (111)-oriented epitaxial GdN films. The epitaxial quality of the films is assessed by Rutherford backscattering spectroscopy carried out in random and channelling conditions. Magnetic measurements exhibit a Curie temperature at 65 K and saturation magnetisation of 7 mB/Gd in agreement with previous bulk and thin-film data. Hall effect and resistance data establish that the films are heavily doped semiconductors, suggesting that up to 1% of the N sites are vacant.
Abstract: The electronic structure of strained and unstrained Gd~0001! has been studied with photoemission, inverse photoemission, and spin-polarized photoemission. A shift of the occupied majority and unoccupied minority surface states has been observed as a result of the strain, consistent with the phase accumulation model. There is a strain induced shift of the minority spin surface state across the Fermi level.
Abstract: Epitaxial gadolinium nitride films with well-oriented crystallites of up to 30 nm have been grown on yttria-stabilized ziconia substrates using a plasma-assisted pulsed laser deposition technique. We observe that the epitaxial GdN growth proceeds on top of a gadolinium oxide buffer layer that forms via reaction between deposited Gd and mobile oxygen from the substrate. Hall effect measurements show the films are electron doped to degeneracy, with carrier concentrations of 4X1020 cm−3. Magnetic measurements establish a TC of 70 K with a coercive field that can be tuned from 200 Oe to as low as 10 Oe.
Abstract: The growth of strained thin films of gadolinium has been investigated with low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) and compared to the film growth of unstrained gadolinium. Strained thin films of gadolinium are distinct from the unstrained films by a substrate induced preferential domain growth direction, which is also reflected in the electronic structure.
Growth of rare earth single crystals by molecular beam epitaxy: The epitaxial relationship between hcp rare earth and bcc niobium [edit | edit source]
Abstract: High-quality rare-earth (RE) single-crystal films of yttrium (Y) and gadolinium (Od) were successfully grown with the metal molecular beam epitaxy technique on a bcc Nb single-crystal film which serves as a buffer layer to the sapphire substrates. With reflection high-energy electron diffraction, the hcp RE (0001) was found to grow epitaxially on the (110) Nb in the Nishiyama-Wasserman orientation. The regrowth of Nb on this RE (000 1) surface yielded the (110) orientation with 120· in-plane domains. These epitaxial relationships suggest the possibility of fabricating an ultrathin, coherent crystalline superlattice in the Nb ( 110) / RE (0001) system.
Abstract: Single-crystal holmium and gadolinium layers have been grown on yttrium substrates using the molecular beam epitaxy technique and their structures investigated using high resolution x-ray scattering. The experiments were performed using a Philips MRD diffractometer in Oxford, and with the XMaS facility at the ESRF. Holmium layers with a thickness below T'C= 115 Å give scattering that is characteristic of a pseudomorphic film structure with the same in-plane lattice parameter as the yttrium substrate to within 0.05%. For layers thicker than T'C, there is a sharp reduction in misfit strain due to the creation of edge dislocations. The transverse lineshape of the holmium peaks exhibits a two-component lineshape for thicknesses above T'C, but below about 500 Å. Above 500 Å the lineshape of the transverse scans becomes Gaussian and is characteristic of a mosaic crystal.
-Characterization of the Structural and Magnetic Properties of Gd -Relationship between morphology and magnetic behavior for Gd thin films on W(110)
References[edit | edit source]
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