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Complex morphology is observed in the GaAs:Bi cap layer of Ga(As,Bi) films grown on GaAs(001) substrates by low-temperature (LT) molecular beam epitaxy (MBE). The microstructure is dominated by the presence of V-shaped domains in the LT-GaAs cap layer and by the (unintentional) inhomogeneous incorporation of Bi from the underlying Ga(As,Bi) layer growth. Aberration-corrected scanning transmission electron microscopy techniques enabled two types of domain to be identified: (i) twinned domains and (ii) Bi-rich atomically ordered domains with triple periodicity. The observed microstructure is discussed in the context of LT-MBE growth in combination with the presence of a small amount of Bi, which seemingly alters adatom diffusivity. Surface processes and (surface) kinetic factors play a key role in the resultant morphology and explain the appearance of both types of domains. [ABSTRACT FROM AUTHOR]

We report a study of the magnetic domain structure of nanocrystalline thin films of nickel-zinc ferrite. The ferrite films were synthesized using aqueous spin-spray coating at low temperature (∼90 °C) and showed high complex permeability in the GHz range. Electron microscopy and microanalysis revealed that the films consisted of columnar grains with uniform chemical composition. Off-axis electron holography combined with magnetic force microscopy indicated a multigrain domain structure with in-plane magnetization. The correlation between the magnetic domain morphology and crystal structure is briefly discussed. [ABSTRACT FROM AUTHOR]

We have used electron holography to investigate the local magnetic behavior of isolated ferromagnetic nanowires (NWs) in their remanent states. The NWs consisted of periodic magnetic layers of soft, high-saturation magnetization CoFeB alloys, and non-magnetic layers of Cu. All NWs were fabricated by pulsed-potential electrodeposition in nanoporous alumina membranes. The NW composition and layer thicknesses were measured using scanning transmission electron microscopy and energy dispersive spectroscopy. The magnetization of individual NWs depended upon the thicknesses of the layers and the direction of an external magnetic field, which had been applied in situ. When the CoFeB was thicker than the diameter (50 nm), magnetization was axial for all external field directions, while thinner layers could be randomized via a perpendicular field. In some cases, magnetization inside the wire was detected at an angle with respect to the axis of the wires. In thinner Cu/CoFeB (<10 nm each) multilayer, magnetic field vortices were detected, associated with opposing magnetization in neighbouring layers. The measured crystallinity, compositions, and layer thicknesses of individual NWs were found to be significantly different from those predicted from calibration growths based on uniform composition NWs. In particular, a significant fraction of Cu (up to 50 at. %) was present in the CoFeB layers such that the measured magnetic induction was lower than expected. These results will be used to better understand previously measured effective anisotropy fields of similar NW arrays. [ABSTRACT FROM AUTHOR]

Magnetic remanent states in a rectangular array of 75×280-nm2 NiFe/Cu/Co thin-film pseudo-spin-valve elements are studied using off-axis electron holography in the transmission electron microscope (TEM). An approach based on focused ion-beam milling is used to minimize damage to the magnetic properties of the elements during preparation for TEM examination in plan-view geometry. Experimental electron holographic phase images are used to measure the switching fields of the Co and NiFe layers in each of three adjacent elements separately, and comparisons with micromagnetic simulations are used to infer the true magnetic thicknesses and widths of the layers. Demagnetizing fields are included in the discussion of the results, and the possibility that the conclusions may be affected by the procedure used to analyze the holograms is discussed. [ABSTRACT FROM AUTHOR]

We report a study of the magnetic switching behavior of nanoscale Co rings using off-axis electron holography. Arrays of 10 nm thick polycrystalline Co rings with 400 nm outer diameter (OD) and different inner diameter (ID) were fabricated by electron-beam lithography. The switching behavior of the rings was studied for different OD/ID ratios, and two kinds of reversal mechanism were identified. For OD/ID of 400 nm/250 nm and 400 nm/50 nm, the reversal started from the so-called onion (bidomain) state, proceeding to a stable vortex state, and finally to the reversed onion state. For intermediate OD/ID of 400 nm/150 nm, the reversal was instead accomplished via rotation of head-to-head domain walls around the rings to the reversed onion state without formation of a vortex state. The OD/ID ratio of the rings thus played the most important role in determining the switching process. Irrespective of the reversal mechanism, the coercive field of the rings and the range of the field needed to reverse their magnetization, both increased as the inner ring diameter was increased (i.e., narrower ring). The significance of different contributions to the total energy in causing these differences in switching behavior is briefly discussed. [ABSTRACT FROM AUTHOR]

Provides information on a study wherein an asymmetrical triangular quantum well was grown by molecular-beam epitaxy using a digital alloy composition grading methods. Methods; Results; Conclusion.

The microstructure of Ba(Cd1/3Ta2/3)O3 ceramics with boron additive was investigated by high-resolution and analytical electron microscopy. Superlattice reflections were present at positions of (h ± 1/3, k ± 1/3, 1 ± 1/3) away from the fundamental reflections in the [110] zone diffraction pattern for the pseudocubic perovskite unit cell. Lattice images showed a well-ordered structure with hexagonal symmetry. No boron segregation and amorphous phase was observed along grain boundaries. An amorphous phase rich in boron-oxide was observed to form pockets partially penetrating along multiple grain junctions. [ABSTRACT FROM AUTHOR]

Stress concentration at the boundary of Ge/Si(100) islands drives strain relief mechanisms activated at higher growth temperature, T. Si interdiffusion for T ≥ 550°C forms a reduced misfit alloy allowing specific cluster morphologies to exist at sizes greater than those for pure Ge islands. This interdiffusion also affects the pathway for island shape changes. Trenches formed at the island base result from diffusion of the most highly strained material to regions of lower strain and precede dislocation formation for T ≥ 600°C. [ABSTRACT FROM AUTHOR]

We describe the magnetic properties of nanoscale Fe shells grown on GaAs nanowires (NWs) by molecular beam epitaxy. The ferromagnetic character of these tubular Fe shells has been confirmed by dc magnetization measurements, and is further studied by ferromagnetic resonance (FMR), small-angle neutron scattering (SANS), and off-axis electron holography (EH). [ABSTRACT FROM AUTHOR]

Quantitative comparisons have been made of the In concentration, strain, and internal electric field present in a pseudomorphic InGaN/GaN quantum well. Z-contrast scanning transmission electron microscopy was used for mapping In concentration with atomic resolution, variations of the c-lattice parameter of the InGaN layer were measured from (0001) lattice fringes in high-resolution transmission electron micrographs, and the internal electric fields were determined by differentiating phase images obtained by electron holography. Based on these measurements, it was concluded that local fluctuations of In concentration caused inhomogeneities in the internal electric field across the quantum well. The band structure of the quantum well would thus be altered not only by quantum dot effects but also by the additional modulation of the internal electric field, leading to further broadening of the light emission. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

An approach based on the technique of convergent-beam electron diffraction (CBED) has been used to determine the elemental composition of a pseudomorphic GaN/In[sub x]Ga[sub 1-x]N/GaN quantum-well structure on the nanometer scale. Areas of triangles formed by intersecting higher order Laue-zone (HOLZ) lines are highly sensitive to lattice-parameter variations. By calculating the ratio of triangle areas, the local In concentration is estimated to within ±0.5% once lattice expansion in the growth direction has been taken into account. Moreover, shifts in the HOLZ-line positions as the CBED probe is moved along the quantum well provide a simple and rapid indication of local fluctuations in In content. The technique is applicable to other pseudomorphically strained epitaxial layers. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report a theoretical and experimental investigation of Cr-doped A1N. Density functional calculations predict that the isolated Crt[sub 2] defect level in AlN is 1/3 full, falls approximately at midgap, and broadens into an impurity band for concentrations over 5%. Substitutional A1[sub 1 - x]Cr[sub x]N random alloys with 0.05≤x≤0.15 are predicted to have Curie temperatures over 600 K. Experimentally, we have characterized and optimized the molecular beam epitaxy thin film growth process, and observed room temperature ferromagnetism with a coercive field, H[sub c], of 120 Oe. The measured magnetic susceptibility indicates that over 33% of the Cr is magnetically active at room temperature and 40% at low temperature. [ABSTRACT FROM AUTHOR]

The one-dimensional dopant profile of a silicon p–n junction was characterized using off-axis electron holography in a transmission electron microscope (TEM). Quantitative comparisons were made with simulated voltage profiles based on data obtained from secondary-ion mass spectroscopy. Close agreement was obtained over a range of sample thicknesses, and a spatial resolution of 5 nm and sensitivity of 0.1 V were established. By using a sample that had been wedge polished and briefly ion milled, depleted surface layers did not need to be taken into account, and beam-induced charging was removed by carbon coating one exposed surface of the TEM specimen. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report the development of a simple chemical route to growing Ge[sub 1-x]Sn[sub x] semiconductors using ultrahigh-vacuum chemical vapor deposition and the molecular precursor (Ph)SnD[sub 3] as the source of Sn atoms. Thin films were deposited on oxidized and oxide-free Si by reactions of (Ph)SnD[sub 3] with Ge[sub 2]H[sub 6] at 350 °C. The composition, microstructure, and bonding properties of the films were characterized by Rutherford backscattering, high-resolution analytical electron microscopy, and Raman spectroscopy. As-deposited Ge[sub 1-x]Sn[sub x] on oxidized Si displayed good crystallinity which improved significantly by annealing at 400 °C. High-resolution electron microscopy and diffraction indicated a diamond-cubic structure with lattice constants intermediate to those of Ge and α-Sn. As-deposited Ge[sub 1-x]Sn[sub x] on pure Si was monocrystalline and epitaxial. Nanoprobe analysis in plan view and cross section revealed that the as-deposited and annealed materials were homogeneous with good chemical purity. The Raman spectra showed bands corresponding to Ge-Ge and Sn-Ge vibrations with frequencies consistent with a random tetrahedral alloy. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Off-axis electron holography and micromagnetic simulations have been used to investigate magnetization reversal mechanisms and remanent states in exchange-biased submicron Co[sub 84]Fe[sub 16]/Fe[sub 54]Mn[sub 46] patterned elements. Domain structures within the elements were characterized despite the narrow thickness (∼3 nm) of the ferromagnetic layer relative to the total element thickness (∼42 nm). Individual elements were able to support different remanent states and their magnetic microstructure was sensitive to their size. The simulations confirmed that the coercivities of the elements and their domain structures were highly sensitive to the strength and orientation of the pinning field. A good fit to the experimental data was provided by using an interface exchange field that had a fixed amplitude and direction in the simulations, and small disagreements were attributed to structural imperfections. These differences emphasize the value of an experimental technique such as electron holography for probing local micromagnetic structure in individual nanostructured elements. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electron holography has been used to image electrostatic potential variations across an AlGaN/InGaN/AlGaN heterojunction diode. Features in the energy profile have been interpreted in terms of the expected built-in voltage across the p-n junction of the diode as well as contributions from the spontaneous and piezoelectric polarization fields within the material. Additional profile features indicate the presence of two-dimensional electron gas at the upper interface of the InGaN well, and evidence for hole accumulation close to the lower interface. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The induction of 90° magnetic domains in a Nd[sub 2]Fe[sub 14]B hard magnet has been mapped at high spatial resolution using off-axis electron holography. Line profiles from the reconstructed phase image established an upper limit for domain wall width of 10 nm. Thermal annealing resulted in domain wall movement, magnetization rotation, and evidence for pinning at a structural defect. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]