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Abstract We introduced and applied a set of parameters to quantify surface modifications and pattern resolutions made by a Ga ion beam in a focused ion beam instrument using two material systems, Si and SrTiO3. A combination of top-view scanning electron microscopy and cross-sectional scanning transmission electron microscopy imaging and energy-dispersive X-ray spectroscopy was used to study the structure, composition and measure dimensions of the patterned lines. The total ion dose was identified as the key parameter governing the line characteristics, which can be controlled by the degree of overlap among adjacent spots, beam dwell time at each spot, and number of beam passes for given beam size and current. At higher ion doses (>1015 ions/cm2), the Ga ions remove part of the material in the exposed area creating “channels” surrounded with amorphized regions, whereas at lower ion doses only amorphization occurs, creating “ridges” on the wafer surface. To pattern lines with similar sizes, an order of magnitude different ion doses was required for Si and SrTiO3 indicating strong material dependence. Quantification revealed that lines as fine as 10 nm can be reproducibly patterned and characterized on the surfaces of materials. 

To increase the storage capacity of hard disk drives, Heat-Assisted Magnetic Recording (HAMR) takes advantage of laser heating to temporarily reduce the coercivity of recording media, enabling the writing of very small data bits on materials with high thermal stability. One key challenge in implementing HAMR is effective thermal management, which requires reliable determination of the thermal properties of HAMR materials over their range of operating temperature. This work reports the thermal properties of dielectric (amorphous silica, amorphous alumina, and AlN), metallic (gold and copper), and magnetic alloy (NiFe and CoFe) thin films used in HAMR heads from room temperature to 500 K measured with time-domain thermoreflectance. Our results show that the thermal conductivities of amorphous silica and alumina films increase with temperature, following the typical trends for amorphous materials. The polycrystalline AlN film exhibits weak thermal anisotropy, and its in-plane and through-plane thermal conductivities decrease with temperature. The measured thermal conductivities of AlN are significantly lower than that which would be present in single-crystal bulk material, and this is attributed to enhanced phonon-boundary scattering and phonon-defect scattering. The gold, copper, NiFe, and CoFe films show little temperature dependence in their thermal conductivities over the same temperature range. The measured thermal conductivities of gold and copper films are explained by the diffuse electron-boundary scattering using an empirical model. 

Exploration and advancements in ultrawide bandgap (UWBG) semiconductors are pivotal for next-generation high-power electronics and deep-ultraviolet (DUV) optoelectronics. Here, we used a thin heterostructure design to facilitate high conductivity due to the low electron mass and relatively weak electron-phonon coupling, while the atomically thin films ensured high transparency. We used a heterostructure comprising SrSnO₃/La:SrSnO₃/GdScO₃(110), and applied electrostatic gating, which allow us to effectively separate charge carriers in SrSnO₃from dopants and achieve phonon-limited transport behavior in strain-stabilized tetragonal SrSnO₃. This led to a modulation of carrier density from 10¹⁸to 10²⁰cm⁻³, with room temperature mobilities ranging from 40 to 140 cm²V⁻¹s⁻¹. The phonon-limited mobility, calculated from first principles, closely matched experimental results, suggesting that room temperature mobility could be further increased with higher electron density. In addition, the sample exhibited 85% optical transparency at a 300-nm wavelength. These findings highlight the potential of heterostructure design for transparent UWBG semiconductor applications, especially in DUV regime. 

The requirement for C₂H₂concentrations below 2 parts per million (ppm) in gas streams for C₂H₄polymerization necessitates its semihydrogenation to C₂H₄. We demonstrate selective chemical looping combustion of C₂H₂in C₂H₄-rich streams by Bi₂O₃as an alternative catalytic pathway to reduce C₂H₂concentration below 2 ppm. Bi₂O₃combusts C₂H₂with a first-order rate constant that is 3000 times greater than the rate constant for C₂H₄combustion. In successive redox cycles, the lattice O of Bi₂O₃can be fully replenished without discernible changes in local Bi coordination or C₂H₂combustion selectivity. Heterolytic activation of C–H bonds across Bi–O sites and the higher acidity of C₂H₂results in lower barriers for C₂H₂activation than C₂H₄, enabling selective catalytic hydrocarbon combustion leveraging differences in molecular deprotonation energies. 

Rich electron-matter interactions fundamentally enable electron probe studies of materials such as scanning transmission electron microscopy (STEM). Inelastic interactions often result in structural modifications of the material, ultimately limiting the quality of electron probe measurements. However, atomistic mechanisms of inelastic-scattering-driven transformations are difficult to characterize. Here, we report direct visualization of radiolysis-driven restructuring of rutile TiO₂under electron beam irradiation. Using annular dark field imaging and electron energy-loss spectroscopy signals, STEM probes revealed the progressive filling of atomically sharp nanometer-wide cracks with striking atomic resolution detail. STEM probes of varying beam energy and precisely controlled electron dose were found to constructively restructure rutile TiO₂according to a quantified radiolytic mechanism. Based on direct experimental observation, a “two-step rolling” model of mobile octahedral building blocks enabling radiolysis-driven atomic migration is introduced. Such controlled electron beam-induced radiolytic restructuring can be used to engineer novel nanostructures atom-by-atom. 

We report the molecular beam epitaxy of Bi1−xSbx thin films (0 ≤ x ≤ 1) on sapphire (0001) substrates using a thin (Bi,Sb)2Te3 buffer layer. The characterization of the films using reflection high energy diffraction, x-ray diffraction, atomic force microscopy, and scanning transmission electron microscopy reveals the epitaxial growth of films of reasonable structural quality. This is further confirmed via x-ray diffraction pole figures that determine the epitaxial registry between the thin film and the substrate. We further investigate the microscopic structure of thin films via Raman spectroscopy, demonstrating how the vibrational modes vary as the composition changes and discussing the implications for the crystal structure. We also characterize the samples using electrical transport measurements.