Tin oxide (SnO2) nanowires of different diameters can be conveniently grown by combining the chemical influence of a single‐molecular precursor [Sn(OtBu)4] with vapor–liquid–solid growth. Upon illumination with UV light at a wavelength of 370 nm, the nanowires exhibit interesting photoconductance, which can be modulated by tuning the wire diameter, as demonstrated for samples possessing radial dimensions in the range 50–1000 nm (see image).

Iron oxide nanotubes of 50−150 nm outer diameter and 2−20 nm wall thickness are prepared in ordered arrays. Atomic layer deposition (ALD) of Fe2O3 from the precursor iron(III) tert-butoxide at 130−180 °C yields very smooth coverage of the pore walls of anodic alumina templates, with thickness growth of 0.26(±0.04) Å per cycle. The reduced Fe3O4 tubes are hard ferromagnets, and variations of the wall thickness d w have marked consequences on the magnetic response of the tube arrays. For 50 nm outer diameter, tubes of d w = 13 nm yield the largest coercive field (H c > 750 Oe), whereas lower coercivities are observed on both the thinner and thicker sides of this optimum.

Nanometer-sized zinc aluminate (ZnAl 2 O 4 ) particles were synthesized from heterometal alkoxides, [ZnAl 2 (OR) 8 ], possessing an ideal cation stoichiometry for the ZnAl 2 O 4 spinel. ZnAl 2 O 4 is formed at 400°C, which is the lowest temperature reported for the formation of monophasic ZnAl 2 O 4 . 27 Al magic-angle spinning nuclear magnetic resonance spectroscopy revealed that ZnAl 2 O 4 possesses an inverse structure at <900°C, while the normal spinel phase is observed at higher temperatures. The homogeneity of the in-depth composition and Zn:Al stoichiometry (1:2) was confirmed by electron spectroscopy for chemical analysis. Evaluation of the valence-band spectra of ZnAl 2 O 4 and ZnS suggested that the hybridization of O 2p and Zn 3d orbitals is responsible for lowering the bandgap in the latter. The average crystallite size showed an exponential relationship to the calcination temperature (X-ray diffractometry and transmission electron microscopy data). The optical spectra of different spinel powders (average particle sizes, 20 -250 nm) showed that the absorption edge exhibits a blue shift as particle size decreases.

Low power consumption and reliable selectivity are the two main requirements for gas sensors to be applicable in mobile devices. [1] These technological platforms, e.g. smart phones or wireless sensor platforms will facilitate personalized detection of environmental and health conditions, and hence becoming the basis of the future core technology of ubiquitous sensing. Even today, health control as well as environmental monitoring is relying on immobile and complex detection systems with very limited availability in space and time. Recent works have shown promising concepts to realize selfpowered gas sensors that are capable of detecting gases without the need of external power sources to Submitted to 2 activate the sensor-gas interaction or to actively generate a read out signal. [2,3] These sensors drastically reduce power consumption compared to conventional semiconductor gas sensors and additionally reduce the required space for integration. All these attempts so far were based on purely nano structured inorganic metal oxide sensor materials that provide a good sensitivity towards different gases due to their high surface-to-volume ratio. However, due to their non-selective sensing mechanism based on oxygen vacancy-gas interactions, these purely inorganic sensors cannot accomplish a meaningful gas selectivity. [4,5] High selectivities towards single gas species have been recently reported via modifying the inorganic surface of nanostructured semiconductors with a defined organic functionality. [6][7][8][9] Theoretical simulations based on ab-initio density functional theory (DFT) for a system composed of SnO2 NWs modified with a defined self assembled monolayer (SAM) elucidated the reason for the high selectivity of such gas sensor: the energetic position of the SAM-gas frontier orbitals with respect to the NW Fermi level have been identified to be the crucial factor to ensure an efficient charge transfer upon gas-SAM binding interactions and thus to sense or discriminate a certain gas species. [7] The high flexibility of organic surface modifications in terms of functional groups as well as their sterical and electronic structure possibly might enable the targeted design of various specific gas sensors. However, all organic surface modified sensor systems so far are based on compact conductometric or field effect transistor (FET) sensor concepts that still require a remarkable amount of energy to generate a sensor signal (e.g. by applying a source-drain current). Up to date, none of the semiconductor based gas sensor systems could accomplish both, the selfpowered/low powered sensor operation and highly selective gas detection within a single and compact device.In this work, we present a semiconductor based gas sensor concept that combines the two substantial requirements of mobile gas sensing in a singular sensor device: self-powered operation combined with high gas selectivity. Beyond the combination of self-powered sensing and high selectivity, also a very high sensitivity could also been demonst...

High-yield synthesis of germanium nanowires (NWs) and core−shell structures is achieved by the chemical vapor deposition (CVD) of dicyclopentadienyl germanium ([Ge(C5H5)2]). The one-dimensional (1D) nanostructures are formed on an iron substrate following a base-growth model in which an Fe−Ge epilayer functions as a catalytic bed. The wire growth is selective and no catalyst particles are observed at the tip of the NWs, which is contrary to the characteristic feature of a 1D growth based on the vapor−liquid−solid (VLS) mechanism. The diameter and length of the NWs were in the ranges 15−20 nm and 25−40 μm, respectively, as found by high-resolution electron microscopy. Both axial and radial dimensions of the NWs can be controlled by adjusting the precursor feedstock, deposition temperature, and size of alloy nuclei in the Fe−Ge epilayer. High precursor flux produced coaxial heterostructures where single-crystalline Ge cores are covered with an overlayer of nanocrystalline Ge. Single-crystal Ge nanowires exhibit a preferred growth direction [112̄] confirmed by X-ray and electron diffraction patterns. When compared to bulk Ge, the micro-Raman spectra of Ge NWs show a low field shift, probably due to the dimensional confinement. Patterned growth of Ge NWs was achieved by shadow-masking the Fe substrate with a carbon film, which prevents the formation of Fe−Ge nuclei, thereby inhibiting the nanowire growth.

A new Y-Fe alkoxide, [YFe(OPr i ) 6 (Pr i OH)] 2 , is used in the sol-gel process to obtain the orthoferrite, YFeO 3 . The Y/Fe stoichiometry (1:1) and Y-O(R)-Fe chemical links in the single molecular precursor kinetically control the formation of metastable YFeO 3 which is otherwise difficult to prepare due to the easy formation of the garnet composition, Y 3 Fe 5 O 12 . TG/DTA analysis showed the crystallization of YFeO 3 at 680 °C, which was confirmed by XRD data. The powders obtained were nanocrystalline (TEM) and the only crystalline compound present between 600 and 1300 °C was monophasic YFeO 3 . The absence of garnet and other ironcontaining residual phases observed in previous studies was confirmed by temperaturedependent Mo ¨ssbauer and magnetization measurements. The magnetization data support a weak ferromagnetic behavior and reveal low-and high-field regimes in M-T and M-H curves, corresponding to magnetocrystalline and antisymmetric-exchange anisotropy, respectively.

We present an experimental study of self-assembled polymeric nanoparticles in the process of Flash NanoPrecipitation using a Multi-Inlet Vortex Mixer (MIVM). β-carotene and polyethyleneimine (PEI) are used as a model drug and a macromolecule, respectively, and encapsulated in diblock copolymers. Flow patterns in the MIVM are microscopically visualized by mixing iron nitrate and potassium thiocyanate to precipitate Fe(SCN) x (3-x)+ . Effects of physical parameters including Reynolds number, supersaturation rate, interaction force, and drug loading rate, on size distribution of the nanoparticle suspensions are investigated. It is critical for the nanoprecipitation process to have a short mixing time, so that the solvent replacement starts homogeneously in the reactor. The properties of the nanoparticles depend on the competitive kinetics of polymer aggregation and organic solute nucleation and growth. We report the existence of a threshold Reynolds number over which nanoparticle sizes become independent of mixing. A similar value of the threshold Reynolds number is confirmed by independent measurements of particle size, flow-pattern visualization, and our previous numerical simulation along with experimental study of competitive reactions in the MIVM.

Tin oxide (SnO 2 ) nanowires grown by chemical vapor deposition were modified by Ar/O 2 plasma treatment through preferential etching of the lattice oxygen atoms, which produced nonstoichiometric surface compositions that imparted a manyfold higher sensitivity toward gas absorption on such surfaces. Microstructures of asgrown and plasma-treated SnO 2 nanowires confirmed the gradual change in the chemical composition and morphologies. Surficial disorder caused by the bombardment of argon and oxygen ions present in the plasma was visible as a disordered overlayer in high-resolution TEM micrographs, when compared to single crystalline as-grown SnO 2 nanowires. Gas-sensing experiments on modified SnO 2 nanostructures showed higher sensitivity for ethanol gas at lower operating temperatures and exhibited an improved transduction response toward changing gas atmospheres, attributed to the increased concentration of oxygen vacancies on the surface of SnO 2 nanowires. Modulation of surface chemistry was also supported by photoluminescence and X-ray photoemission spectroscopy studies.