Exploring the Surface Oxidation and Environmental Instability of 2H-/1T'-MoTe2 Using Field Emission-Based Scanning Probe Lithography.

An unconventional approach for the resistless nanopatterning 2H- and 1T'-MoTe2 by means of scanning probe lithography is presented. A Fowler-Nordheim tunneling current of low energetic electrons (E = 30-60 eV) emitted from the tip of an atomic force microscopy (AFM) cantilever is utilized to induce a nanoscale oxidation on a MoTe2 nanosheet surface under ambient conditions. Due to the water solubility of the generated oxide, a direct pattern transfer into the MoTe2 surface can be achieved by a simple immersion of the sample in deionized water. The tip-grown oxide is characterized using Auger electron and Raman spectroscopy, revealing it consists of amorphous MoO3 /MoOx as well as TeO2 /TeOx . With the presented technology in combination with subsequent AFM imaging it is possible to demonstrate a strong anisotropic sensitivity of 1T'-/(Td )-MoTe2 to aqueous environments. Finally the discussed approach is used to structure a nanoribbon field effect transistor out of a few-layer 2H-MoTe2 nanosheet.

Ferrimagnetic Large Single Domain Iron Oxide Nanoparticles for Hyperthermia Applications.

This paper describes the preparation and obtained magnetic properties of large single domain iron oxide nanoparticles. Such ferrimagnetic particles are particularly interesting for diagnostic and therapeutic applications in medicine or (bio)technology. The particles were prepared by a modified oxidation method of non-magnetic precursors following the green rust synthesis and characterized regarding their structural and magnetic properties. For increasing preparation temperatures (5 to 85 °C), an increasing particle size in the range of 30 to 60 nm is observed. Magnetic measurements confirm a single domain ferrimagnetic behavior with a mean saturation magnetization of ca. 90 Am2/kg and a size-dependent coercivity in the range of 6 to 15 kA/m. The samples show a specific absorption rate (SAR) of up to 600 W/g, which is promising for magnetic hyperthermia application. For particle preparation temperatures above 45 °C, a non-magnetic impurity phase occurs besides the magnetic iron oxides that results in a reduced net saturation magnetization.

Three-dimensional platinum nanoparticle-based bridges for ammonia gas sensing.

This study demonstrates the fabrication of self-aligning three-dimensional (3D) platinum bridges for ammonia gas sensing using gas-phase electrodeposition. This deposition scheme can guide charged nanoparticles to predetermined locations on a surface with sub-micrometer resolution. A shutter-free deposition is possible, preventing the use of additional steps for lift-off and improving material yield. This method uses a spark discharge-based platinum nanoparticle source in combination with sequentially biased surface electrodes and charged photoresist patterns on a glass substrate. In this way, the parallel growth of multiple sensing nodes, in this case 3D self-aligning nanoparticle-based bridges, is accomplished. An array containing 360 locally grown bridges made out of 5 nm platinum nanoparticles is fabricated. The high surface-to-volume ratio of the 3D bridge morphology enables fast response and room temperature operated sensing capabilities. The bridges are preconditioned for ~ 24 h in nitrogen gas before being used for performance testing, ensuring drift-free sensor performance. In this study, platinum bridges are demonstrated to detect ammonia (NH3) with concentrations between 1400 and 100 ppm. The sensing mechanism, response times, cross-sensitivity, selectivity, and sensor stability are discussed. The device showed a sensor response of ~ 4% at 100 ppm NH3 with a 70% response time of 8 min at room temperature.

Localized and Programmable Chemical Vapor Deposition Using an Electrically Charged and Guided Molecular Flux.

Chemical vapor deposition is a widely used material deposition technique. It commonly provides a uniform material flux to the substrate to cause uniform thin film growth. However, the ability to precisely adjust the local deposition rate would be highly preferable. This communication reports on a chemical vapor deposition method performed in a localized and programmable fashion by introducing an electrically charged and guided molecular flux. This allows for local adjustments of the deposition rate and three-dimensional shape by controlling the electric fields. Specifically, the precursor molecules are charged and then guided by arrays of electrodynamic funnels, which are created by a patterned dielectric layer, to predetermined deposition locations with a minimal spot size of 250 nm. Furthermore, nearest neighbor coupling is reported as a shaping method to cause the deposition of three-dimensional nanostructures. Additionally, the integration of individually addressable domain electrodes offers programmable charge dissipation to achieve an ON/OFF control. The described method is applicable to a wide variety of materials and precursors. Here, the localized and programmable deposition of three-dimensional copper oxide, chromium oxide, zinc oxide, and carbon nanowires is demonstrated.

Effect of annealing on the properties of indium-tin-oxynitride films as ohmic contacts for gan-based optoelectronic devices.

Indium-tin-oxynitride (ITON) films have been fabricated by rf sputtering from an indium-tin-oxide target in nitrogen plasma. The influence of postdeposition annealing up to 800 degrees C is analyzed by electrical, optical, and surface characterization of the films in comparison to indium-tin-oxide (ITO) films fabricated in argon plasma. High-temperature annealing resulted in ITO(N) films with similar carrier concentrations. However, the resistivity and optical transmittance of the ITON films were higher than those of the ITO films. Photoelectron spectroscopy revealed that nitrogen is incorporated into the ITON structure in an unbound state as well as through the formation of metal-nitrogen and oxynitride bonds that decorate oxygen vacancies. When the core level electron spectra of ITO and ITON films are compared, a correlation between carrier concentration and the incorporated nitrogen is found. Changes in ITON electrical properties are mainly induced by the release of nitrogen at temperatures above 550 degrees C. In this context, ohmic contact behavior was achieved for ITON on p-type GaN after annealing at 600 degrees C, while no ohmic contact could be realized using ITO.