We have determined the magnetic structures of single-crystal thin-films of IrMn3 for the crystallographic phases of chemically-ordered L12, and for chemically-disordered face-centred-cubic, which is the phase typically chosen for information-storage devices. For the chemically-ordered L12 thin-film, we find the same triangular magnetic structure as reported for the bulk material. We determine the magnetic structure of the chemically-disordered face-centred-cubic alloy for the first time, which differs from theoretical predictions, with magnetic moments tilted away from the crystal diagonals towards the face-planes. We study the influence of these two antiferromagnetic structures on the exchange-bias properties of an epitaxial body-centred-cubic Fe layer showing that magnetization reversal mechanism and bias-field in the ferromagnetic layer is altered significantly. We report a change of reversal mechanism from in-plane nucleation of 90° domain-walls when coupled to the newly reported cubic structure towards a rotational process, including an out-of-plane magnetization component when coupled to the L12 triangular structure.

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Atomic layer deposition ͑ALD͒ is an attractive technique in fabrication of microelectronics presently and in the future, for its accurate thickness control in atomic scale, excellent conformality, and uniformity over large areas at low temperature. It has been adapted and used in deposition of ultrathin TaN x films as diffusion barriers for Cu metallization. In this study, composition, structure, and stability of ultra-thin ͑1.5-10 nm͒ atomic layer deposited films are characterized by a set of complementary analytical techniques. The results indicate that the N to Ta atomic concentration ratio in the ALD TaN x films is approximately 2, independent of the film thickness and annealing up to 750°C. Hydrogen, oxygen, and carbon are detected as impurities within the as-deposited films. The as-deposited ALD TaN x films have an fcc NaCl-type nanocrystalline structure even when the film thickness is 1.5 nm. Following thermal anneal at 600°C and higher, the films do not undergo a structural change except for an increase in grain size and a decrease in the lattice constant. X-ray photoelectron spectra results indicate that all the Ta atoms in the films are bonded ionically with the surrounding N atoms. An ex situ thermal treatment at 600°C for 1 h removes the O, which penetrated the layers, by a reduction reaction with the residual H and results in densification of the ALD films. Our analysis of the experimental results indicates that the excess of N atoms of the ALD TaN x films is mainly due to Ta vacancies in the fcc NaCl-type structure. The structural and compositional characteristics of the films explain why the films serve as good diffusion barriers to Cu metallization.

The bottom-up synthesis of nanoscale building blocks is a versatile approach for the formation of a vast array of materials with controlled structures and compositions. This approach is one of the main driving forces for the immense progress in materials science and nanotechnology witnessed over the past few decades. Despite the overwhelming advances in the bottom-up synthesis of nanoscale building blocks and the fine control of accessible compositions and structures, certain aspects are still lacking. In particular, the transformation of symmetric nanostructures to asymmetric nanostructures by highly controlled processes while preserving the modified structural orientation still poses a significant challenge. We present a one-step ex situ doping process for the transformation of undoped silicon nanowires (i-Si NWs) to p-type/n-type (p-n) parallel p-n junction configuration across NWs. The vertical p-n junctions were measured by scanning tunneling microscopy (STM) in concert with scanning tunneling spectroscopy (STS), termed STM/S, to obtain the spatial electronic properties of the junction formed across the NWs. Additionally, the parallel p-n junction configuration was characterized by off-axis electron holography in a transmission electron microscope to provide an independent verification of junction formation. The doping process was simulated to elucidate the doping mechanisms involved in the one-step p-i-n junction formation.

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