Tungsten oxide and its associated bronzes (compounds of tungsten oxide and an alkali metal) are well known for their interesting optical and electrical characteristics. We have modified the transport properties of thin WO3 films by electrolyte gating using both ionic liquids and polymer electrolytes. We are able to tune the resistivity of the gated film by more than five orders of magnitude, and a clear insulator-to-metal transition is observed. To clarify the doping mechanism, we have performed a series of incisive operando experiments, ruling out both a purely electronic effect (charge accumulation near the interface) and oxygen-related mechanisms. We propose instead that hydrogen intercalation is responsible for doping WO3 into a highly conductive ground state and provide evidence that it can be described as a dense polaronic gas.

Helium-ion beams (HIB) focused to subnanometer scales have emerged as powerful tools for high-resolution imaging as well as nano-scale lithography, ion milling or deposition. Quantifying irradiation effects is essential for reliable device fabrication but most of the depth profiling information is provided by computer simulations rather than experiment. Here, we use atomic force microscopy (AFM) combined with scanning near-field optical microscopy (SNOM) to provide three-dimensional (3D) dielectric characterization of high-temperature superconductor devices fabricated by HIB. By imaging the infrared dielectric response we find that amorphization caused by the nominally 0.5 nm HIB extends throughout the entire 26.5 nm thickness of the cuprate film and by ∼500 nm laterally. This unexpectedly widespread structural and electronic damage can be attributed to a Helium depth distribution substantially modified by internal device interfaces. Our study introduces AFM-SNOM as a quantitative nano-scale tomographic technique for non-invasive 3D characterization of irradiation damage in a wide variety of devices.In a pioneering recent work, superconductor-insulatorsuperconductor (SIS) Josephson Junctions (JJs) have been written by HIB in thin films of YBa 2 Cu 3 O 7 (YBCO) hightemperature superconducting (HTS) cuprates [1,2]. This is potentially quite exciting because a reproducible technology for fabricating high-quality and uniform arrays of in-plane SIS junctions remains the most desired goal in the field of HTS electronics. Such devices would allow manufacturing of sensitive magnetometers, voltage standards, and voltage-tunable THz radiation sources, and would provide a technology platform for high-speed computing [3,4,5,6]. SIS-JJ physics may also reveal the fingerprints of bosonic excitations involved in electron pairing, thus providing a clue about the as-yet unresolved mechanism of HTS in cuprates [7,8]. However, HTS-based JJ devices typically exhibit properties of normal-metal weak links, while true SIS behavior is observed only very rarely. The challenge arises from the very short (1 -2 nm) coherence length in HTS materials and the consequent sensitivity to point defects. Lithography by photons, electrons or heavier ions all exhibit excess damage or insufficient resolution for the required barrier sizes.To verify the great potential of HIB for nano-fabrication [9, 10, 11], one needs to study and evaluate irradiationinduced damage [12,13]. Compared to more commonly used heavy ions, Helium ions undergo lower energy loss per unit length, which leads to longer depth profiles and larger interaction volumes [10]. Since the defect density is largest near the stopping range of ions, HIB is expected to be less destructive for atomic layers closer to the surface [10,14]. However, the impact of the beam depends markedly on the softness of the materials, and back-scattering can occur from harder sub-surface layers [14]. This is relevant for nanoscale devices based on multi-layer structures, which are typical of most practical ...

We show that high-dose ion implantation can be used to introduce rare-earth dopants for the control of precessional dynamics in magnetic thin films. Tb and Gd ions have been implanted in Ni 81 Fe 19 through Ta masks at dosages from 1 ϫ 10 14 /cm 2 to 1 ϫ 10 15 /cm 2. Effects on dynamics are found to be similar to those contributed by cosputtered Tb and Gd dopants in Ni 81 Fe 19 ͑50 nm͒. Broadband ferromagnetic resonance measurements from 0 to 18 GHz show that adjustments in damping ␣ from 0.008 to 0.040 are fully intrinsic ͑Gilbert type͒ and roughly proportional to dose. The technique enables the creation of films with spatially modulated precessional characteristics.

La 2-x Sr x CuO 4 nanowire devices have been fabricated and characterized using electrical transport measurements. Nanowires with widths down to 80 nm are patterned using high-resolution electron beam lithography. However, the narrowest nanowires show incomplete superconducting transitions with some residual resistance at T = 4 K. Here, we report on the refinement of the fabrication process to achieve narrower nanowire devices with complete superconducting transitions, opening the path to the study of novel physics arising from dimension-limited superconductivity on the nanoscale.