Influence of precursor chemistry on CVD grown TiO2 coatings: differential cell growth and biocompatibility

Nanocrystalline titanium oxide (TiO2) coatings with different phases and surface topographies were deposited using chemical vapor deposition (CVD) of different homo- and heteroleptic titanium precursors of general formula [XTi(OiPr)3] (X = Cl (1), -NEt2 (2), -N(SiMe3)2 (3), -C5H5 (4), -OiPr (5) and -OtBu (6)) to elucidate the influence of molecular configuration on resulting material properties. The interdependence of precursor chemistry and materials features of the CVD deposits was verified by performing film growth under similar conditions using different precursor molecules (1-6). Studies on composition (XPS), structure (SEM, XRD) and bio-functional properties (cell tests) revealed that the decomposition process is markedly influenced by the auxiliary ligands, which led to incorporation of heteroelements (Si, Cl, N) in the films. Cell tests performed to evaluate the biocompatibility of the coatings towards the growth of bone cells showed a pronounced correlation between cell adhesion and surface morphology as well as the chemical composition. Growth of osteoblast cells was strongly enhanced on films obtained using [Ti(OiPr)4] and [CpTi(OiPr)3], whereas TiO2 coatings produced by [ClTi(OiPr)3] significantly inhibited the cell growth and their proliferation due to Cl contamination. Also, the nanomorphological features of the films were found to stimulate the cell adhesion and growth

Inducing imperfections in germanium nanowires

Nanowires with inhomogeneous heterostructures such as polytypes and periodic twin boundaries are interesting due to their potential use as components for optical, electrical, and thermophysical applications. Additionally, the incorporation of metal impurities in semiconductor nanowires could substantially alter their electronic and optical properties. In this highlight article, we review our recent progress and understanding in the deliberate induction of imperfections, in terms of both twin boundaries and additional impurities in germanium nanowires for new/enhanced functionalities. The role of catalysts and catalyst–nanowire interfaces for the growth of engineered nanowires via a three-phase paradigm is explored. Three-phase bottom-up growth is a feasible way to incorporate and engineer imperfections such as crystal defects and impurities in semiconductor nanowires via catalyst and/or interfacial manipulation. “Epitaxial defect transfer” process and catalyst–nanowire interfacial engineering are employed to induce twin defects parallel and perpendicular to the nanowire growth axis. By inducing and manipulating twin boundaries in the metal catalysts, twin formation and density are controlled in Ge nanowires. The formation of Ge polytypes is also observed in nanowires for the growth of highly dense lateral twin boundaries. Additionally, metal impurity in the form of Sn is injected and engineered via third-party metal catalysts resulting in above-equilibrium incorporation of Sn adatoms in Ge nanowires. Sn impurities are precipitated into Ge bi-layers during Ge nanowire growth, where the impurity Sn atoms become trapped with the deposition of successive layers, thus giving an extraordinary Sn content (>6 at.%) in Ge nanowires. A larger amount of Sn impingement (>9 at.%) is further encouraged by utilizing the eutectic solubility of Sn in Ge along with impurity trapping

Bulk sensitive photo emission spectroscopy of C1b compounds

This work reports about bulk-sensitive, high energy photoelectron spectroscopy from the valence band of CoTiSb excited by photons from 1.2 to 5 keV energy. The high energy photoelectron spectra were taken at the KMC-1 high energy beamline of BESSY II employing the recently developed Phoibos 225 HV analyser. The measurements show a good agreement to calculations of the electronic structure using the LDA scheme. It is shown that the high energy spectra reveal the bulk electronic structure better compared to low energy XPS spectra.Comment: J. Electron Spectrosc. Relat. Phenom. accepte

Nanoscale ferroelectric and piezoelectric properties of Sb2S3 nanowire arrays

We report the first observation of piezoelectricity and ferroelectricity in individual Sb2S3 nanowires embedded in anodic alumina templates. Switching spectroscopy-piezoresponse force microscopy (SS-PFM) measurements demonstrate that individual, c-axis-oriented Sb2S3 nanowires exhibit ferroelectric as well as piezoelectric switching behavior. Sb2S3 nanowires with nominal diameters of 200 and 100 nm showed d33(eff) values around 2 pm V–1, while the piezo coefficient obtained for 50 nm diameter nanowires was relatively low at around 0.8 pm V–1. A spontaneous polarization (Ps) of approximately 1.8 μC cm–2 was observed in the 200 and 100 nm Sb2S3 nanowires, which is a 100% enhancement when compared to bulk Sb2S3 and is probably due to the defect-free, single-crystalline nature of the nanowires synthesized. The 180° ferroelectric monodomains observed in Sb2S3 nanowires were due to uniform polarization alignment along the polar c-axis

Einsatz von Infrarotlichtquelle und WebKamera zur Analyse von Prozessen beim Experimentieren

Das Ergebnis eines Experiments kann oft auf unterschiedlichen Wegen zu Stande kommen und es ist häufig nicht möglich, Details des Experimentierprozesses auf der Grundlage der Ergebnisdarstellung zu rekonstruieren. Unsere Forschungsgruppe beschäftigt sich u.a. mit der Untersuchung physikalischer Kompetenz und ist insbesondere am Experimentierprozess und nicht nur am Ergebnis (Produkt) interessiert. Eine herkömmliche Videoaufzeichnung dieses Prozesses und die anschließende Analyse der Videodaten ist naheliegend. Aufgrund des inhaltlichen Schwerpunkts von Experimenten aus dem Themenbereich Atomphysik und Optik sind derartige Videodaten jedoch entweder schwer möglich oder unmöglich, da die meisten Experimente mit stark reduzierter Ausleuchtung des Experimentierbereichs durchgeführt werden. Wir stellen eine Möglichkeit vor, wie durch Kombination kostengünstiger Technik (Infrarotlichtquelle und WebKamera) für den Alltagsgebrauch Aufnahmen in abgedunkelten Räumen und für den mobilen Einsatz (z. B. in der Schule) möglich werden

Einsatz von Infrarotlichtquelle und WebKamera zur Analyse von Prozessen beim Experimentieren

Das Ergebnis eines Experiments kann oft auf unterschiedlichen Wegen zu Stande kommen und es ist häufig nicht möglich, Details des Experimentierprozesses auf der Grundlage der Ergebnisdarstellung zu rekonstruieren. Unsere Forschungsgruppe beschäftigt sich u.a. mit der Untersuchung physikalischer Kompetenz und ist insbesondere am Experimentierprozess und nicht nur am Ergebnis (Produkt) interessiert. Eine herkömmliche Videoaufzeichnung dieses Prozesses und die anschließende Analyse der Videodaten ist naheliegend. Aufgrund des inhaltlichen Schwerpunkts von Experimenten aus dem Themenbereich Atomphysik und Optik sind derartige Videodaten jedoch entweder schwer möglich oder unmöglich, da die meisten Experimente mit stark reduzierter Ausleuchtung des Experimentierbereichs durchgeführt werden. Wir stellen eine Möglichkeit vor, wie durch Kombination kostengünstiger Technik (Infrarotlichtquelle und WebKamera) für den Alltagsgebrauch Aufnahmen in abgedunkelten Räumen und für den mobilen Einsatz (z. B. in der Schule) möglich werden

Diameter-controlled solid-phase seeding of germanium nanowires: structural characterization and electrical transport properties

Despite the huge progress recently made in understanding the phenomena of metal-promoted growth of one-dimensional (1D) semiconductors, the controlled formation of small diameter semiconductor nanowires is still challenging. Liquid growth promoters, such as the low melting Au/Ge eutectic, allow control of the aspect ratio, diameter, and structure of 1D crystals via external parameters, such as precursor feedstock, temperature, and operating pressure. However, the incorporation of metal atoms during the growth process, size variations of the nanowires due to agglomeration of the nucleating metal seeds, and surface diffusion of Au via the vapor–liquid–solid route have been reported. Here, we detail the influence of solid growth seeds, such as NiGe2 formed from Ni nanoparticles, on the lateral dimensions of Ge nanowires grown using a supercritical fluid growth process. Beneficial control over the mean nanowire diameter, in the sub-20 nm regime, with a predominantly ⟨110⟩ growth direction and low structural defect concentration was obtained using Ni seeds. In addition, the effect of prealloying of Ni–Fe films for the growth of Ge nanowires was investigated, which leads to a bimodal nanowire distribution. Electrical characterization performed on single nanowire devices showed p-type behavior for Ge nanowires grown from Ni and Ni/Fe seeds. Determination of resistivities, majority carrier concentrations, and mobilities suggest significant doping of the Ge nanowires by Ni when grown via a supercritical fluid–solid–solid (SFSS) mechanism

Lead-supported germanium nanowire growth

The Pb-assisted growth of Ge nanowires (NWs) has been investigated under high and low pressure conditions via thermal decomposition of diphenylgermane. Highly crystalline Ge NWs were obtained and Pb was established as a viable growth promoter with the Pb particle being in the solid and liquid state

A new model for in vitro testing of vitreous substitute candidates

Purpose: To describe a new model for in vitro assessment of novel vitreous substitute candidates. Methods: The biological impact of three vitreous substitute candidates was explored in a retinal explant culture model; a polyalkylimide hydrogel (Bio-Alcamid®), a two component hydrogel of 20 wt.% poly (ethylene glycol) in phosphate buffered saline (PEG) and a cross-linked sodium hyaluronic acid hydrogel (Healaflow®). The gels where applied to explanted adult rat retinas and then kept in culture for 2, 5 and 10 days. Gel-exposed explants were compared with explants incubated under standard tissue culture conditions. Cryosections of the specimens were stained with hematoxylin and eosin, immunohistochemical markers (GFAP, Vimentin, Neurofilament 160, PKC, Rhodopsin) and TUNEL. Results: Explants kept under standard conditions as well as PEG-exposed explants displayed disruption of retinal layers with moderate pyknosis of all neurons. They also displayed moderate labeling of apoptotic cells. Bio-Alcamid®-exposed explants displayed severe thinning and disruption of retinal layers with massive cell death. Healaflow®-treated explants displayed normal retinal lamination with significantly better preservation of retinal neurons compared with control specimens, and almost no signs of apoptosis. Retinas exposed to Healaflow® and retinas kept under standard conditions showed variable labeling of GFAP with generally low expression and some areas of upregulation. PEG-exposed retinas showed increased GFAP labeling and Bio-Alcamid®-exposed retinas showed sparse labeling of GFAP. Conclusions Research into novel vitreous substitutes has important implications for both medical and surgical vitreoretinal disease. The in vitro model presented here provides a method of biocompatibility testing prior to more costly and cumbersome in vivo experiments. The explant culture system imposes reactions within the retina including disruption of layers, cell death and gliosis, and the progression of these reactions can be used for comparison of vitreous substitute candidates. Bio-Alcamid® had strong adverse effects on the retina which is consistent with results of prior in vivo trials. PEG gel elicits reactions similar to the control retinas whereas Healaflow® shows protection from culture-induced trauma indicating favorable biocompatibility.Swedish Research CouncilUniversity of Lund. Medical FacultyPrincess Margaret's Foundation for Blind ChildrenKnut and Alice Wallenberg FoundationGeneral Sir John Monash Foundation (Scholarship)In Vivo Therapeutics Corporatio

Visualization and thermodynamic encoding of single-molecule partition functions

Ensemble averaging of molecular states is fundamental for the experimental determination of thermodynamic quantities. A special case occurs for single-molecule investigations under equilibrium conditions, for which free energy, entropy and enthalpy at finite-temperatures are challenging to determine with ensemble-averaging alone. Here, we provide a method to access single-molecule thermodynamics, by confining an individual molecule to a nanoscopic pore of a two-dimensional metal-organic nanomesh, where we directly record finite-temperature time-averaged statistical weights using temperature-controlled scanning tunneling microscopy. The obtained patterns represent a real space equilibrium probability distribution. We associate this distribution with a partition function projection to assess spatially resolved thermodynamic quantities, by means of computational modeling. The presented molecular dynamics based Boltzmann weighting model is able to reproduce experimentally observed molecular states with high accuracy. By an in-silico customized energy landscape we demonstrate that distinct probability distributions can be encrypted at different temperatures. Such modulation provides means to encode and decode information into position-temperature space or to realize nanoscopic thermal probes.Comment: 20 Pages Main text, 5 Figures. 10 Pages Annexed tex