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  1. Abstract

    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.

     
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  2. The oxides of platinum group metals are promising for future electronics and spintronics due to the delicate interplay of spin-orbit coupling and electron correlation energies. However, their synthesis as thin films remains challenging due to their low vapour pressures and low oxidation potentials. Here we show how epitaxial strain can be used as a control knob to enhance metal oxidation. Using Ir as an example, we demonstrate the use of epitaxial strain in engineering its oxidation chemistry, enabling phase-pure Ir or IrO2 films despite using identical growth conditions. The observations are explained using a density-functional-theory-based modified formation enthalpy framework, which highlights the important role of metal-substrate epitaxial strain in governing the oxide formation enthalpy. We also validate the generality of this principle by demonstrating epitaxial strain effect on Ru oxidation. The IrO2 films studied in our work further revealed quantum oscillations, attesting to the excellent film quality. The epitaxial strain approach we present could enable growth of oxide films of hard-to-oxidize elements using strain engineering. 
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    Free, publicly-accessible full text available May 22, 2024
  3. Abstract Understanding the kinetics of interfacial reaction in the deposition of metal contacts on 2D materials is important for determining the level of contact tenability and the nature of the contact itself. Here, we find that some metals, when deposited onto layered black-arsenic films using e-beam evaporation, form a-few-nm thick distinct intermetallic layer and significantly change the nature of the metal contact. In the case of nickel, the intermetallic layer is Ni 11 As 8 , whereas in the cases of chromium and titanium they are CrAs and a-Ti 3 As, respectively, with their unique structural and electronic properties. We also find that temperature, which affects interatomic diffusion and interfacial reaction kinetics, can be used to control the thickness and crystallinity of the interfacial layer. In the field effect transistors with black-arsenic channel, due to the specifics of its formation, this interfacial layer introduces a second and more efficient edge-type charge transfer pathway from the metal into the black-arsenic. Such tunable interfacial metal contacts could provide new pathways for engineering highly efficient devices and device architectures. 
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