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We attempted to grow a thin film of BiN by co-deposition of bismuth and nitrogen on rock-salt structure MgO (001) substrates. Furthermore, we studied the effect of variation of the growth temperature and the nitrogen to bismuth flux ratios on sample growth. For the samples grown and conditions used, we do not find strong evidence for the formation of a bulk Bi-N alloy. Even for very high nitrogen to bismuth flux ratio, we observed only bismuth and no nitrogen using bulk Rutherford back-scattering spectroscopy measurements, and only 1%–2% nitrogen was seen through surface Auger electron spectroscopy measurements. The in-plane lattice measurements show that the resulting Bi (110) samples are strained, which is presumably caused by lattice mismatch between the sample and the substrate when grown without any buffer layer. The use of a high-temperature buffer layer helps to release strain in the sample but only along one axis. Measurements of the atomic layer spacing using x-ray diffraction and also scanning tunneling microscopy confirm the Bi (110) thin film sample structure. [ABSTRACT FROM AUTHOR]

Structural phase transition is studied in high quality CrN thin films grown by molecular beam epitaxy on MgO(001) substrates. Cross-sectional transmission electron microscopy and x-ray diffraction reveal that the epitaxial relationship between CrN film and MgO substrate is [ 100 ] CrN / [ 100 ] MgO , [ 110 ] CrN / [ 110 ] MgO , and [ 001 ] CrN / [ 001 ] MgO . The films show tensile strain/compression at the CrN/MgO(001) interface, which relaxes gradually with the film growth. Temperature dependent x-ray diffraction measurements show a first-order structural phase transition. In addition to the experimental measurements, first-principles theoretical calculations have been carried out for finding a stable model for the CrN/MgO interface. These calculations determine two possible models for the interface, where a monolayer of chromium oxide is formed between the CrN and MgO layers. [ABSTRACT FROM AUTHOR]

The Kagome antiferromagnet Mn 3 Sn has garnered much attention due to the presence of exciting properties such as anomalous Hall and Nernst effects. This paper discusses the synthesis of crystalline Mn 3 Sn thin films, prepared on Al 2 O 3 (0001) substrates at 453 ± 5 ° C using molecular beam epitaxy. The growth is monitored in situ using reflection high energy electron diffraction and measured ex situ using x-ray diffraction, Rutherford back-scattering, and cross-sectional scanning transmission electron microscopy. Our analysis shows the in-plane lattice constants of a 1 , M = 4.117 ± 0.027 Å and a 2 , M = 4.943 ± 0.033 Å, which is a very unexpected result when compared to the bulk a -plane Mn 3 Sn. This indicates a strain in the film and makes it challenging to provide a straightforward explanation. In an effort to explain our results, we discuss two possible orientation relationships between the Mn 3 Sn films and the sapphire substrates. Samples prepared under these conditions appear to have smooth surfaces locally, but overall the film has a 3D island morphology. First-principles calculations provide atomic models of the Mn 3 Sn (11 2 ¯ 0) lattice on Al 2 O 3 (0001) high symmetry sites, indicating that the L3-R90 ° is the most stable configuration. A detailed discussion of the experimental data and theoretical results, as well as strain effects, is provided. [ABSTRACT FROM AUTHOR]

We describe the formation of a δ-doped manganese layer embedded within c-plane wurtzite gallium nitride using a special molecular beam epitaxy growth process. Manganese is first deposited on the gallium-poor GaN ([formula]) surface, forming a [formula] reconstructed phase. This well-defined surface reconstruction is then nitrided using plasma nitridation, and gallium nitride is overgrown. The manganese content of the [formula] phase, namely one Mn per each [formula] unit cell, implies that the MnGaN alloy layer has a Mn concentration of up to 33%. The structure and chemical content of the surface are monitored beginning from the initial growth stage up through the overgrowth of 20 additional monolayers (MLs) of GaN. An exponential-like drop-off of the Mn signal with increasing GaN monolayers, as measured by Auger electron spectroscopy, indicates that the highly concentrated Mn layer remains at the δ-doped interface. A model of the resultant δ-doped structure is formulated based on the experimental data, and implications for possible spintronic applications are discussed. [ABSTRACT FROM AUTHOR]

Cubic GaN has been grown under gallium (Ga)-rich growth conditions using radio frequency nitrogen plasma molecular beam epitaxy on MgO(001) substrates. Reflection high energy electron diffraction patterns indicate the smoothness of the c-GaN surface and show 2× and even 8× periodicities after the growth at sample temperature Ts<200 °C and 1×1 at higher temperatures. Scanning tunneling microscopy images reveal a sequence of variant surface reconstructions including c(4×12), 4×7, c(4×16), 4×9, c(4×20), and 4×11. These variant reconstructions correspond to slightly different Ga adatom coverages all less than 1/4 ML, with 4×11 having the highest, and c(4×12) the lowest Ga coverage. The electronic properties of these six variant reconstructions are investigated, and they are found to have a metallic nature. [ABSTRACT FROM AUTHOR]

The incorporation of manganese into semiconducting ScN, using radio frequency molecular beam epitaxy, has been investigated. X-ray diffraction and reflection high energy electron diffraction measurements show the face-centered tetragonal rocksalt-type crystal structure with Sc and Mn cations and N anions. In addition to the solute incorporation into the lattice, which is clear from the positions of the diffraction peaks, atomic force microscopy images show that the surface of the alloy grown at Ts&les; 518 °C contains dot-like features, indicating surface accumulation. The areal dot density is found to decrease as the growth temperature increases, whereas the Mn incorporation increases at 518 °C. This behavior is suggestive of a thermally activated process, and it is well explained by an Arrhenius law, giving an activation energy (diffusion barrier) of 0.67 eV. Increasing the growth temperature to 612 °C leads to an increased desorption rate, resulting in little Mn incorporation. It has been found that the growth is nearly optimized at Ts=518 °C for high Mn incorporation, smooth growth, and small accumulate density. The alloy is found to have lattice parameters which depend on the Mn/(Mn+Sc) bulk ratio. The alloy lattice constants follow Vegard's law depending on the Mn bulk fraction and the lattice constants of ScN and θ-phase MnN. The Mn incorporation and Mn incorporation coefficient for films grown at Ts= 518 °C increase as the Mn/(Mn+Sc) flux ratio increases. [ABSTRACT FROM AUTHOR]

The phase and orientation of manganese nitride grown on MgO(001) using molecular beam epitaxy are shown to be controllable by the manganese/nitrogen flux ratio as well as the substrate temperature. The most N-rich phase, θ phase (MnN), is obtained at very low Mn/N flux ratio. At increased Mn/N flux ratio, the next most N-rich phase, the η phase (Mn[sub 3]N[sub 2]), is obtained having its c axis normal to the surface plane. Further increasing the Mn/N flux ratio, the η phase (Mn[sub 3]N[sub 2]) having its c axis in the surface plane is obtained. Finally, the &Vegr; phase (Mn[sub 4]N) is obtained at yet higher Mn/N flux ratio. The structural phase variation with Mn/N flux ratio is due to the kinetic control of the surface chemical composition, which determines the energetically most favorable phase. For a given Mn/N flux ratio, the phase is also found to be a function of the substrate temperature, with the less N-rich phase occurring at the higher substrate temperature. The change of phase with temperature is attributed to the change in the chemical composition resulting from the diffusion of N vacancies. Since the magnetic properties of Mn[sub x]N[sub y] depend on the phase, the Mn/N flux ratio provides a way of directly controlling the magnetic properties. A phase diagram for molecular beam epitaxial growth is presented. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Scandium nitride (001) oriented layers have been grown on magnesium oxide (001) substrates by molecular beam epitaxy using a rf-plasma source and a scandium effusion cell. The Sc/N flux ratio is found to be critical in determining the structural, optical, and electronic properties of the grown epitaxial layers. A distinct transition occurs at the point where the Sc/N flux ratio equals 1, which defines the line between N-rich and Sc-rich growth. Under N-rich conditions, the growth is epitaxial, and the surface morphology is characterized by a densely packed array of square-shaped plateaus and four-faced pyramids with the terraces between steps being atomically smooth. The films are stoichiometric and transparent with a direct optical transition at 2.15 eV. Under Sc-rich conditions, the growth is also epitaxial, but the morphology is dominated by spiral growth mounds. The morphology change is consistent with increased surface diffusion due to a Sc-rich surface. Excess Sc leads to understoichiometric layers with N vacancies which act as donors. The increased carrier density results in an optical reflection edge at 1 eV, absorption below the 2.15 eV band gap, and a drop in electrical resistivity. c 2001 American Institute of Physics. [DOI: 10.1063/1.1388161]. [ABSTRACT FROM AUTHOR]

In addition to the usual set of the well-known reconstructions that have been observed on the N-polar GaN surface, namely 1 × 1, 3 × 3, 6 × 6, and c(6 × 12), an additional structure is occasionally seen at high Ga coverage, which can extend over a large area of the surface. This structure, which is referred to as trench line structure, is partially ordered and consists of parallel-running dark (trench) lines separating wide and narrow strips of atomically ordered regions. There are also randomly placed defects interrupting the ideal ordering. Reflection high energy electron diffraction and scanning tunneling microscopy in ultrahigh vacuum are applied to investigate this trench line structure on samples prepared using molecular beam epitaxy. It is found that the trench line structure results from annealing the Ga-rich c(6 × 12) at high temperature followed by quenching to room temperature. By careful comparison of the scanning tunneling microscopy images with those from neighboring c(6 × 12) regions, it is found that the trench line structure can be decomposed into subunits of the c(6 × 12). Using these subunits, some simple models for the trench line structure are created. It is proposed that the trench line structure is composed of two primary c(6 × 12) subunits consisting of first and second layer Ga adatoms and that the trench lines are regions devoid of Ga adatoms, going down to the Ga adlayer. [ABSTRACT FROM AUTHOR]

Ferromagnetic L10-MnGa thin films have been epitaxially grown on GaN, sapphire, and MgO substrates using molecular beam epitaxy. Using diffraction techniques, the epitaxial relationships are determined. It is found that the crystalline orientation of the films differ due to the influence of the substrate. By comparing the magnetic anisotropy to the structural properties, a clear correlation could be established indicating that the in-plane and out-of-plane anisotropy is directly determined by the crystal orientation of the film and could be controlled via selection of the substrates. This result could be helpful in tailoring magnetic anisotropy in thin films for spintronic applications. [ABSTRACT FROM AUTHOR]

Structural and electronic properties of stoichiometric single-phase CrN(001) thin films grown on MgO(001) substrates by radio-frequency N plasma-assisted molecular-beam epitaxy, are investigated. In situ room-temperature scanning tunneling microscopy clearly shows the 1×1 atomic periodicity of the crystal structure as well as long-range topographic distortions which are characteristic of a semiconductor surface. This semiconductor behavior is consistent with ex situ resistivity measurements over the range 285 K and higher, whereas below 260 K, metallic behavior is observed. The resistivity-derived band gap for the high-temperature region, 71 meV, is consistent with the tunneling spectroscopy results. The observed electronic (semiconductor/metal) transition temperature coincides with the temperature of the known coincident magnetic (para-antiferro) and structural (cubic-orthorhombic) phase transitions. [ABSTRACT FROM AUTHOR]

Face-centered tetragonal (fct) η-phase manganese nitride films have been grown on magnesium oxide (001) substrates by molecular-beam epitaxy. For growth conditions described here, reflection high energy electron diffraction and neutron scattering show primarily two types of domains rotated by 90° to each other with their c axes in the surface plane. Scanning tunneling microscopy images reveal surface domains consisting of row structures which correspond directly to the bulk domains. Neutron diffraction data confirm that the Mn moments are aligned in a layered antiferromagnetic structure. The data are consistent with the fct model of G. Kreiner and H. Jacobs for bulk Mn[sub 3]N[sub 2] [J. Alloys Compd. 183, 345 (1992)]. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

L10-structured MnGa(111) ultra-thin films were heteroepitaxially grown on GaN(0001) under lightly Mn-rich conditions using molecular beam epitaxy. Room-temperature scanning tunneling microscopy (STM) investigations reveal smooth terraces and angular step edges, with the surface structure consisting primarily of a 2 × 2 reconstruction along with small patches of 1 × 2. Theoretical calculations were carried out using density functional theory, and the simulated STM images were calculated using the Tersoff-Hamman approximation, revealing that a stoichiometric 1 × 2 and a Mn-rich 2 × 2 surface structure give the best agreement with the observed experimental images. [ABSTRACT FROM AUTHOR]

High quality scandium nitride films have been grown on magnesium oxide (001) substrates by molecular beam epitaxy using a rf plasma source for nitrogen. Both reflection high energy electron diffraction and x-ray diffraction confirm that these films have (001)-orientation. Atomic force microscopy reveals a surface morphology consisting of large plateaus and pyramids. The plateaus are found to be atomically smooth and have a 1x1 surface structure, as revealed by in situ scanning tunneling microscopy. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In advanced compound semiconductor devices, such as in quantum dot and quantum well systems, detailed atomic configurations at the growth surfaces are vital in determining the structural and electronic properties. Therefore, it is important to investigate the surface reconstructions in order to make further technological advancements. Usually, conventional semiconductor surfaces (e.g., arsenides, phosphides, and antimonides) are highly reactive due to the existence of a high density of group V (anion) surface dangling bonds. However, in the case of nitrides, group III rich growth conditions in molecular beam epitaxy are usually preferred leading to group III (Ga)-rich surfaces. Here, we use low-temperature scanning tunneling microscopy to reveal a uniform distribution of native gallium adatoms with a density of 0.3%-0.5% of a monolayer on the clean, as-grown surface of nitrogen polar GaN(0001) having the centered 6 × 12 reconstruction. Unseen at room temperature, these Ga adatoms are strongly bound to the surface but move with an extremely low surface diffusion barrier and a high density saturation coverage in thermodynamic equilibrium with Ga droplets. Furthermore, the Ga adatoms reveal an intrinsic surface chirality and an asymmetric site occupation. These observations can have important impacts in the understanding of gallium nitride surfaces. [ABSTRACT FROM AUTHOR]

The thin films of c -plane dominated hexagonal ζ - phase Mn 2 N were successfully grown on a cubic MgO (001) substrate directly using plasma-assisted molecular beam epitaxy. The surface was comprehensively studied through experimental and theoretical approaches. Reflection high energy electron diffraction revealed two pseudo-cubic domains along [100] MgO and [110] MgO , and one hexagonal domain, which is 30° apart from the [100] MgO direction. Scanning tunneling microscopy was used to image and resolve the high quality surface, revealing a distorted hexagonal surface structure. Furthermore, atomic resolution of the hexagonal domain with a 2 × 2 reconstructed surface is presented. For the c -plane surface, theoretical investigations were carried out using first-principle studies to determine the surface formation energy for various reconstructed surfaces. The theoretical study shows that the nitrogen terminated 2 × 2 structure with a manganese adatom on the surface is the most stable reconstruction that reproduces the experimental results. A corresponding simulated scanning tunneling microscopy model is also presented, providing strong support for the experimentally observed in-plane lattice structures. The manganese:nitrogen stoichiometry within the bulk and surface is in good agreement with the expected ratio of 2:1. [Display omitted] • Heteroepitaxial growth of Mn 2 N on cubic substrate. • Film grown on cubic substrate isn't always constrained to maintain cubic symmetry. • Crystal structure accommodated on symmetry mismatched substrate in various ways. • STM images reveal 2 × 2 reconstructed pseudo-cubic and hexagonal domains. • N-terminated Mn ad-atom model corresponds to the most stable Mn 2 N surface. [ABSTRACT FROM AUTHOR]

The (0 1 0) surface of η-phase Mn3N2 grown on MgO(0 0 1) by molecular beam epitaxy is studied using scanning tunneling microscopy. The images show that the surface is composed of rows with spacing of 6.07 Å. Two types of domains with their c-planes perpendicular are observed in which the domain boundary is oriented at ∼45° to the c-planes. In other cases, the angle between the c-planes of the two domains is closer to 87°, consistent with a twin model in which the two domains meet along a (1 0 1) plane. Atomic resolution images vary with the sample bias. At lower sample bias, primarily Mn1 atoms are observed. At higher sample bias, both Mn1 and Mn2 atoms can be resolved. The dependence of the atomic resolution image on sample bias is explained by the ratio of the integrated local density of states of Mn1 to that of Mn2, which are based on first-principles theory. Simulations of the STM atomic-scale height profiles using the integrated local densities of states vs. sample bias voltage are in excellent agreement with the experimental line profiles. [Copyright &y& Elsevier]

Single phase ε -Mn 4 N thin and ultrathin films are grown on MgO(001) using molecular beam epitaxy. Reflection high-energy electron diffraction and out-of-plane X-ray diffraction measurements are taken for each sample in order to determine the in- and out-of-plane strain for each sample. Vibrating sample magnetometry and superconducting quantum interference device measurements, which are performed on the thin and ultrathin films respectively, are used to plot the magnetization of each sample versus both in- and out-of-plane H → -fields and to determine the magnitude of perpendicular magnetic anisotropy in these films. Three significant components of perpendicular magnetic anisotropy are observed in these films and are attributed to sample strain (1 component) and shape (2 components). Among these components, the most significant component 0.8 – 4.9 Merg cm 3 is identified as a second term of shape anisotropy, which possesses a negative linear relationship with sample thickness over the range from 9 nm to 310 nm. Atomic (magnetic) force microscopy measurements show the presence of a surface localized magnetic polarization (22–82 % ), which increases with decreasing thickness, when the net magnetizations of the films are zero. The second term of shape anisotropy as well as the surface localized polarization, which each depend on sample thickness, are each regarded as a consequence of Ising domains overlapping out-of-plane in these films. [ABSTRACT FROM AUTHOR]

Single phase ε -Mn 4 N and ζ -Mn 10 N thin films are grown on MgO(001) using molecular beam epitaxy. The films are identified and characterized using reflection high-energy electron diffraction, x-ray diffraction, back scattered electron scanning electron microscopy, atomic/magnetic force microscopy and Rutherford backscattering spectrometry. These films are found to be highly smooth with root-mean-squared roughnesses 3.39 nm and below. The quality of ε -Mn 4 N grown is strongly dependent on substrate temperature during growth. Epitaxial growth of substantial grains composed of the antiferromagnetic η -phase Mn 3 N 2 side by side with ferrimagnetic ε -phase grains is observed when growth temperature is below 480 °C. Ising domains isolated within areas roughly 0.5 μm across are observed in the ferrimagnetic ε -phase grains of samples consisting of a mix of η - and ε -phase grains. Magnetic domains following semi-continuous paths, which are 0.7–7.2 μm across, are observed in single phase ε -Mn 4 N. Measurements of the ζ -phase detail the structure and magnetism of the material as high Mn content γ -type ζ -phase with a regular surface corrugation along the [100]-direction and antiferromagnetic. [ABSTRACT FROM AUTHOR]

We report structural, surface, and magnetic investigations of ferromagnetic Ga-rich MnGa thin and ultra-thin films grown on semiconducting GaN(0001) using molecular beam epitaxy. The Mn:Ga composition ratio is varied from ≈1 (stoichiometric) to ≈0.42 (very Ga-rich) for different samples. We find that the L1 0 MnGa phase is preserved down to a Mn:Ga ratio of ≈0.81. As the Ga concentration increases, we observe the coexistence of more Ga-rich phases, namely Mn 3 Ga 5 and Mn 2 Ga 5 . Room temperature scanning tunneling microscopy imaging reveals highly epitaxial films, with atomically smooth and highly reconstructed surfaces. Magnetic characterizations show how the magnetic properties evolve with changing composition and that giant perpendicular magnetic anisotropy is induced by reducing the size of our films. [ABSTRACT FROM AUTHOR]

A class of striped superstructures with local hexagonal ordering has been obtained by depositing submonolayer Mn on the GaN(0001) surface. Combining scanning tunneling microscopy and first-principles theory, we find that Mn atoms incorporate into the surface and form a high-density two-dimensional MnxGa1-x structure. The highly spin-polarized Mn d electrons are found to dominate the surface electronic states. For the narrowest stripes, we calculate a row-wise antiferromagnetic ground state, which is observed in real space at room temperature as a spin-induced asymmetry in the density of states. These two-dimensional magnetic structures on GaN can also be considered model systems for wide-band-gap magnet/semiconductor spin injectors. [ABSTRACT FROM AUTHOR]

Abstract: Ferromagnetic -phase manganese gallium layers with have been successfully grown on ScN(001) by molecular beam epitaxy, expanding possibilities for ferromagnetic layers on nitride semiconductors. The in-plane epitaxial relationship of manganese gallium with respect to scandium nitride is determined to be and . Vibrating sample magnetometry measurements indicate out-of-plane magnetization of the film, suggesting strong magnetic anisotropy along the manganese gallium -axis. [Copyright &y& Elsevier]

Abstract: We report a study of the growth of iron nitride on gallium nitride using molecular beam epitaxy with Fe e-beam evaporation and rf N-plasma growth. Thin iron nitride layers of thickness about 16nm were grown and monitored in situ using reflection high energy electron diffraction. The samples following growth were analyzed ex situ using a variety of techniques including X-ray diffraction, Rutherford Backscattering, and atomic force microscopy. By monitoring the structure, morphology, and lattice constant evolution of the iron nitride film, the crystal phase and orientation with respect to the GaN substrate are deduced; and from RBS data, the stoichiometry is obtained. The growth is discussed in terms of a 2-D to 3-D growth mode transition, and a critical thickness is estimated. [Copyright &y& Elsevier]

Abstract: Here, we report the influence of the growth conditions for CrGaN grown with the N-polarity on sapphire (0001) using radio frequency N plasma-assisted molecular beam epitaxy. Samples are grown under different Ga/N flux ratio of 0.65–1.0 at substrate temperatures of 650 and . The Cr/Ga flux ratio is set to either 3% or 5%. These growth parameters allow to vary over a range of growth conditions from N-rich to Ga-rich. It is shown that the surface condition during growth influences the surface morphology and magnetic properties of CrGaN. In particular, we show that N-rich and metal-rich growth conditions result in room temperature ferromagnetism. Also discussed are the influence of Cr on the surface reconstruction and also the influence of annealing on the properties of the CrGaN film. [Copyright &y& Elsevier]