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With their shielded 4f orbitals, rare-earth ions (REIs) offer optical and electron spin transitions with good coherence properties even when embedded in a host crystal matrix, highlighting their utility as promising quantum emitters and memories for quantum information processing. Among REIs, trivalent erbium (Er3+) uniquely has an optical transition in the telecom C-band, ideal for transmission over optical fibers, making it well suited for applications in quantum communication. The deployment of Er3+ emitters into a thin film TiO2 platform has been a promising step toward scalable integration; however, like many solid-state systems, the deterministic spatial placement of quantum emitters remains an open challenge. We investigate laser annealing as a means to locally tune the optical resonance of Er3+ emitters in TiO2 thin films on Si. Using both nanoscale x-ray diffraction measurements and cryogenic photoluminescence spectroscopy, we show that tightly focused below-gap laser annealing can induce anatase to rutile phase transitions in a nearly diffraction-limited area of the films and improve local crystallinity through grain growth. As a percentage of Er:TiO2 is converted to rutile, the Er3+ optical transition blueshifts by 13 nm. We explore the effects of changing laser annealing time and show that the amount of optically active Er:rutile increases linearly with laser power. We additionally demonstrate local phase conversion on microfabricated Si structures, which holds significance for quantum photonics. [ABSTRACT FROM AUTHOR]

Next-generation dark matter (DM) detectors searching for weakly interacting massive particles (WIMPs) will be sensitive to coherent scattering from solar neutrinos, demanding an efficient background-signal discrimination tool. Directional detectors improve sensitivity to WIMP DM despite the irreducible neutrino background. Wide-bandgap semiconductors offer a path to directional detection in a high-density target material. A detector of this type operates in a hybrid mode. The WIMP or neutrino-induced nuclear recoil is detected using real-time charge, phonon, or photon collection. The directional signal, however, is imprinted as a durable sub-micron damage track in the lattice structure. This directional signal can be read out by a variety of atomic physics techniques, from point defect quantum sensing to x-ray microscopy. In this Review, we present the detector principle as well as the status of the experimental techniques required for directional readout of nuclear recoil tracks. Specifically, we focus on diamond as a target material; it is both a leading platform for emerging quantum technologies and a promising component of next-generation semiconductor electronics. Based on the development and demonstration of directional readout in diamond over the next decade, a future WIMP detector will leverage or motivate advances in multiple disciplines toward precision dark matter and neutrino physics. [ABSTRACT FROM AUTHOR]

Functional properties of transition-metal oxides strongly depend on crystallographic defects; crystallographic lattice deviations can affect ionic diffusion and adsorbate binding energies. Scanning x-ray nanodiffraction enables imaging of local structural distortions across an extended spatial region of thin samples. Yet, localized lattice distortions remain challenging to detect and localize using nanodiffraction, due to their weak diffuse scattering. Here, we apply an unsupervised machine learning clustering algorithm to isolate the low-intensity diffuse scattering in as-grown and alkaline-treated thin epitaxially strained SrIrO3 films. We pinpoint the defect locations, find additional strain variation in the morphology of electrochemically cycled SrIrO3, and interpret the defect type by analyzing the diffraction profile through clustering. Our findings demonstrate the use of a machine learning clustering algorithm for identifying and characterizing hard-to-find crystallographic defects in thin films of electrocatalysts and highlight the potential to study electrochemical reactions at defect sites in operando experiments. [ABSTRACT FROM AUTHOR]

In-line high resolution X-ray diffraction has been used to analyze embedded silicon-germanium (eSiGe) epitaxially grown in the source/drain regions of complementary metal-oxide-semiconductor devices. Compared to blanket films, the diffraction from patterned devices exhibited distinct features corresponding to the eSiGe in the source/drain regions and Si under the gate and SiGe. The diffraction features modulated with structural changes, alloy composition, and subsequent thermal processing. Reciprocal space measurements taken around the (224) diffraction peak revealed both in-plane (h) and out-of-plane (l) lattice deformation, along with features corresponding to the regular spacing between the gates. [ABSTRACT FROM AUTHOR]

Ptychographic imaging is a powerful means of imaging beyond the resolution limits of typical x-ray optics. Recovering images from raw ptychographic data, however, requires the solution of an inverse problem, namely, phase retrieval. Phase retrieval algorithms are computationally expensive, which precludes real-time imaging. In this work, we propose PtychoNN, an approach to solve the ptychography data inversion problem based on a deep convolutional neural network. We demonstrate how the proposed method can be used to predict real-space structure and phase at each scan point solely from the corresponding far-field diffraction data. Our results demonstrate the practical application of machine learning to recover high fidelity amplitude and phase contrast images of a real sample hundreds of times faster than current ptychography reconstruction packages. Furthermore, by overcoming the constraints of iterative model-based methods, we can significantly relax sampling constraints on data acquisition while still producing an excellent image of the sample. Besides drastically accelerating acquisition and analysis, this capability has profound implications for the imaging of dose sensitive, dynamic, and extremely voluminous samples. [ABSTRACT FROM AUTHOR]

Phase competition in correlated oxides offers tantalizing opportunities as many intriguing physical phenomena occur near the phase transitions. Owing to a sharp metal-insulator transition (MIT) near room temperature, the correlated vanadium dioxide (VO2) exhibits a strong competition between insulating and metallic phases, which is important for practical applications. However, the phase boundary undergoes a strong modification when strain is involved, yielding complex phase transitions. Here, we report the emergence of nanoscale M2 phase domains in VO2 epitaxial films under anisotropic strain relaxation. The competing phases of the films are imaged by multilength-scale probes, detecting the structural and electrical properties in individual local domains. Competing evolution of the M1 and M2 phases indicates the critical role of lattice-strain on both the stability of the M2 Mott phase and the energetics of the MIT in VO2 films. This study demonstrates how strain engineering can be utilized to design phase states, which allow deliberate control of MIT behavior at the nanoscale in epitaxial VO2 films. [ABSTRACT FROM AUTHOR]

Polar instabilities are well known to be suppressed on scaling materials down to the nanoscale, when the electrostatic energy increase at surfaces exceeds lowering of the bulk polarization energy. Surprisingly, here we report an emergent low symmetry polar phase arising in nanoscale powders of CaTiO3, the original mineral named perovskite discovered in 1839 and considered nominally nonpolar at any finite temperature in the bulk. Using nonlinear optics and spectroscopy, X-ray diffraction, and microscopy studies, we discover a well-defined polar to non-polar transition at a TC = 350 K in these powders. The same polar phase is also seen as a surface layer in bulk CaTiO3 single crystals, forming striking domains with in-plane polarization orientations. Density functional theory reveals that oxygen octahedral distortions in the surface layer lead to the stabilization of the observed monoclinic polar phase. These results reveal new ways of overcoming the scaling limits to polarization in perovskites. [ABSTRACT FROM AUTHOR]

The local changes in copper oxidation state and the corresponding resistance changes in Pt/CuOx/Pt nanoscale heterostructures have been investigated using x-ray nanoprobe spectro-microscopy and current-voltage characterization. After gentle electroforming, during which the current-voltage behavior remains non-linear, the low resistance state was reached, and we observed regions of 160 nm width that show an increase in Cu K-alpha fluorescence intensity, indicative of partial reduction of the CuOx. Analysis of the current voltage curves showed that the dominant conduction mechanism is Schottky emission and that the resistance state is correlated with the Schottky barrier height. We propose that the reversible resistivity change in these Pt/CuOx/Pt heterostructures occurs through local electrochemical reduction leading to change of the Schottky barrier height at the interface between Pt and the reduced CuOx layers and to change of the CuOx resistivity within laterally confined portions of the CuOx layer. These experiments reveal important insights into the mechanism of resistance switching of Pt/CuOx/Pt performed in a current and voltage regime that does not create a metallic conduction path. [ABSTRACT FROM AUTHOR]

In order to achieve elemental and chemical sensitivity in scanning tunneling microscopy (STM), synchrotron x-rays have been applied to excite core-level electrons during tunneling. The x-ray photo-excitations result in tip currents that are superimposed onto conventional tunneling currents. While carrying important physical information, the varying x-ray induced currents can destabilize the feedback loop causing it to be unable to maintain a constant tunneling current, sometimes even causing the tip to retract fully or crash. In this paper, we report on an easy-to-implement filter circuit that can separate the x-ray induced currents from conventional tunneling currents, thereby allowing simultaneous measurements of topography and chemical contrasts. The filter and the schematic presented here can also be applied to other variants of light-assisted STM such as laser STM. [ABSTRACT FROM AUTHOR]

We report an elastic relaxation and increase in local strain variation correlated with ferroelectric domains within epitaxial BiFeO3 thin film nanostructures fabricated by combined electron-beam and focused ion-beam nanolithography. Nano-focused x-ray diffraction microscopy provided new insights into the relationship between film strain and ferroelectric domains in nanostructures, namely: (i) an out-of-plane (C-axis) elastic relaxation of as much as -1.8% Δc/c in a BFO film-based nanostructure relative to the planar film lattice constant; (ii) an out-of-plane rotation trending from the center towards all released edges of the nanostructure; and (iii) an increase of inter-domain strain variation within the nanostructure of approximately 10 times the inter-domain variation found within the planar film, correlated with ferroelectric domain boundaries as confirmed by piezoresponse-force microscopy. These results indicate that the release of in-plane BFO/SRO mismatch strain in a planar film is taken up by the local ferroelectric domain structure after patterning, resulting in greatly increased mechanical strain gradients within the structure. [ABSTRACT FROM AUTHOR]

We report experiments to measure material changes in tantalum oxide-based memristive devices. The high endurance and low power demonstrated in this material system suggests a unique mechanism for the switching, which we investigated using x-ray based spectromicroscopy and nanospectroscopy. Our study nondestructively identified a localized (<150nm diameter) Ta-rich phase surrounded by nano- or polycrystalline Ta2O5. [ABSTRACT FROM AUTHOR]

We report improved results for hard x-ray focusing using a multilayer Laue lens (MLL). We have measured a line focus of 16 nm width with an efficiency of 31% at a wavelength λ=0.064 nm (19.5 keV) using a partial MLL structure with an outermost zone width of 5 nm. The results are in good agreement with the theoretically predicted performance. [ABSTRACT FROM AUTHOR]

Silicon nanomembranes are suspended single-crystal sheets of silicon, tens of nanometers thick, with areas in the thousands of square micrometers. Challenges in fabrication arise from buckling due to strains of over 10-3 in the silicon-on-insulator starting material. In equilibrium, the distortion is distributed across the entire membrane, minimizing the elastic energy with a large radius of curvature. We show that flat nanomembranes can be created using an elastically metastable configuration driven by the silicon-water surface energy. Membranes as thin as 6 nm are fabricated with vertical deviations below 10 nm in a central 100 μm × 100 μm area. [ABSTRACT FROM AUTHOR]