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Superconducting qubits have arisen as a leading technology platform for quantum computing, which is on the verge of revolutionizing the world's calculation capacities. Nonetheless, the fabrication of computationally reliable qubit circuits requires increasing the quantum coherence lifetimes, which are predominantly limited by the dissipations of two-level system defects present in the thin superconducting film and the adjacent dielectric regions. In this paper, we demonstrate the reduction of two-level system losses in three-dimensional superconducting radio frequency niobium resonators by atomic layer deposition of a 10 nm aluminum oxide Al2O3 thin films, followed by a high vacuum heat treatment at 650 °C for few hours. By probing the effect of several heat treatments on Al2O3-coated niobium samples by x-ray photoelectron spectroscopy plus scanning and conventional high resolution transmission electron microscopy coupled with electron energy loss spectroscopy and energy dispersive spectroscopy, we witness a dissolution of niobium native oxides and the modification of the Al2O3-Nb interface, which correlates with the enhancement of the quality factor at low fields of two 1.3 GHz niobium cavities coated with 10 nm of Al2O3. [ABSTRACT FROM AUTHOR]

We report different growth modes and corresponding magnetic properties of thin EuSe films grown by molecular beam epitaxy on BaF2, Pb1−xEuxSe, GaAs, and Bi2Se3 substrates. We show that EuSe grows predominantly in the (001) orientation on GaAs(111) and Bi2Se3, but along the (111) crystallographic direction on BaF2 (111) and Pb1−xEuxSe (111). High resolution transmission electron microscopy measurements reveal a sharp and highly crystalline interface for both (001) and (111) EuSe films. In agreement with previous studies, ordered magnetic phases include antiferromagnetic, ferrimagnetic, and ferromagnetic phases. In contrast to previous studies, we found a strong hysteresis of the antiferromagnetic–ferrimagnetic transition. The ability to grow epitaxial films of EuSe on Bi2Se3 and of Bi2Se3 on EuSe enables further investigation of interfacial exchange interactions between various phases of an insulating metamagnetic material and a topological insulator. [ABSTRACT FROM AUTHOR]

Recently, SnSe based thermoelectric materials attained much interest due to their environment friendly IV–VI semiconductor group. Herein, Al doped SnSe (Sn1−xAlxSe) specimens were prepared by combined ball milling and spark plasma sintering. High resolution transmission electron microscopy analysis of (Sn1−xAlxSe) nanostructure samples confirmed the existence of different crystal defects and dislocation induced by Al doping. Lower thermal conductivity (0.63 W/mK at 750 K) is observed for Sno.92Al0.08Se samples than pristine SnSe (1.14 W/mK at 750 K), which is mainly attributed to various crystal defects, such as lattice dislocation, stacking fault, grain boundary scattering, and excellent anharmonic bonding nature of SnSe. The maximum electrical conductivity is observed for the SAS-2 sample, which correlates well with the low activation energy of 0.20 eV. The minimal doping of Al (SAS-2) decoupled the strong interdependency of electrical and thermal transport properties, leading to a maximum ZT of 0.18 at 743 K. The Al doped SnSe (Sn1−xAlxSe) induced point defects in the sample, which provides a new strategy for waste heat recovery. [ABSTRACT FROM AUTHOR]

Ion implantation induced phase transformation and the crystal structure of a series of ion implanted β-Ga2O3 samples were studied using electron diffraction, high resolution transmission electron microscopy, and scanning transmission electron microscopy. In contrast to previous reports suggesting an ion implantation induced transformation to the orthorhombic κ-phase, we show that for 28Si+, 58Ni+, and stoichiometric 69Ga+/16O+-implantations, the monoclinic β-phase transforms to the cubic γ-phase. The γ-phase was confirmed for implantations over a range of fluences from 1014 to 1016 ions/cm2, indicating that the transformation is a general phenomenon for β-Ga2O3 due to strain accumulation and/or γ-Ga2O3 being energetically preferred over highly defective β-Ga2O3. [ABSTRACT FROM AUTHOR]

Gallium nitride (GaN) nanowires (NWs) have been fabricated by top-down etching from GaN heteroepitaxial films, which provides an accurate control of their position and dimensions. However, these NWs contain, similar to the initial GaN films, high density of structural defects such as threading dislocations (TDs). In this work, different strategies to reduce the density of defects along the NWs have been compared based on two different wet etching approaches followed by a rapid thermal annealing (RTA) at 750 °C. The addition of a 30 nm SiNx coating is also explored. The defects and strain/stress along the NWs have been studied by high resolution transmission electron microscopy, diffraction contrast imaging in two-beam conditions and 4D STEM, as well as strain maps calculated from scanning precession electron diffraction measurements. RTA reduced the density of TDs at the middle of GaN NWs with bare surfaces by approximately 25%. The reduction increased to approximately 70% by RTA of GaN NWs with surfaces coated by amorphous SiNx, which is attributed to enhancement of dislocation movements by stresses induced from differential thermal expansion of GaN and SiNx. These results suggest a process route that, if optimized and combined with reduction of NW diameter, could establish etching as an efficient fabrication method for high crystal quality GaN NWs. [ABSTRACT FROM AUTHOR]

The visualization of electron orbitals in real space is expected as a next-generation technique that has been evolved from high spatial resolution electron microscopy. Core excitation electron energy-loss spectra with a high signal-to-noise ratio were recorded in a scanning transmission electron microscope with high spatial resolution to directly observe the electron orbitals in real space. We experimentally demonstrate that anisotropic distributions of oxygen 2p orbitals in SrTiO3 were observed in real space and were dependent on the difference in the chemical bonds between Ti and O atoms. The results open the door to the visualization of electronic orbitals with electron microscopes. [ABSTRACT FROM AUTHOR]

Anharmonicity and impurities have a significant impact on the dynamic and optical properties of crystalline solids. In this report, we have performed temperature-dependent Raman spectroscopy in the range of 300–800 K for hydrothermally synthesized titanium dioxide (TiO2) nanorod composed microflowers doped with Cu. X-ray diffraction and high resolution transmission electron microscopy confirm the pure rutile phase of both pristine and Cu doped TiO2. The most intense Eg and A1g modes exhibit a frequency redshift, and the linewidth increases with temperature, which leads to Fano line shape type asymmetry. The anharmonicity induced phonon frequency shift as a function of temperature was well fitted using the Klemens model by combining three and four-phonon coupling processes. The Raman modes soften with the increasing concentration of Cu doping. The Cu dopant acts as an impurity, which manifests defect states to tune the bandgap and shorten the phonon lifetime and anharmonicity. Such an anharmonic effect can lead to applications in the sensing devices with suitable thermal and electrical conductivities. [ABSTRACT FROM AUTHOR]