Maghemite (Fe2O3) iron oxide nanoparticles (IONPs) were synthesized, modified with covalent surface-bound CO-releasing molecules of a tri(carbonyl)-chlorido-phenylalaninato-ruthenium(II) complex (CORM), and coated with a dextran polymer. The time- and temperature-dependent CO release from this CORM-3 analogue was followed by a myoglobin assay. A new measurement method for the myoglobin assay was developed, based on confining "water-soluble" polymer-coated Dextran500k@CORM@IONP particles in hollow spheres of nontoxic and easily prepared calcium alginate. Dropping a mixture of Dextran500k@CORM@IONP and sodium alginate into a CaCl2 solution leads to stable hollow spheres of Ca(2+) cross-linked alginate which contain the Dextran500k@CORM@IONP particles. This "alginate-method" (i) protects CORM-3 analogues from rapid CO-displacement reactions with a protein, (ii) enables a spatial separation of the CORM from its surrounding myoglobin assay with the alginate acting as a CO-permeable membrane, and (iii) allows the use of substances with high absorptivity (such as iron oxide nanoparticles) in the myoglobin assay without interference in the optical path of the UV cell. Embedding the CORM@IONP nanoparticles in the alginate vessel represents a compartmentation of the reactive component and allows for close contact with, yet facile separation from, the surrounding myoglobin assay. The half-life of the CO release from Dextran500k@CORM@IONP particles surrounded by alginate was determined to be 890 ± 70 min at 20 °C. An acceleration of the CO release occurs at higher temperature with a half-life of 172 ± 27 min at 37 °C and 45 ± 7 min at 50 °C. The CO release can be triggered in an alternating current magnetic field (31.7 kA m(-1), 247 kHz, 39.9 mT) through local magnetic heating of the susceptible iron oxide nanoparticles. With magnetic heating at 20 °C in the bulk solution, the half-life of CO release from Dextran500k@CORM@IONP particles decreased to 155 ± 18 min without a noticeable temperature increase in the dispersion. At 37 and 50 °C, the half-life for the CO release triggered by local magnetic heating was 65 ± 5 min and 30 ± 3 min, respectively. Thus, at a physiological temperature of 37 °C, magnetic heating accelerates the CO release of the IONP-bound CORM by a factor of ∼ 2.6. The activation energy for CO release from a CORM-3 analogue was determined to be EA = 78 kJ/mol.
Plasma-enhanced atomic layer deposition (PE-ALD) of cobalt (Co) using cyclopentadienylcobalt dicarbonyl [CpCo(CO)2] combined with hydrogen, nitrogen, ammonia, and argon based plasma gases was investigated. The utilized ALD tool was clustered to an ultrahigh vacuum analytic system for direct surface analyses including X-ray photoelectron spectroscopy (XPS). The combination with a nondestructive surface analysis system enabled a sample transfer without vacuum break and thereby a direct qualification and quantification of the chemical surface composition under quasi in situ conditions. The authors studied the influence of process parameters (e.g., pulse times, plasma power, and substrate temperature) on film compositions and film properties. The occurrence and prevention of sputtering effects due to ion bombardment at high plasma powers were discussed. Beyond those results, precise information about the impact of different plasma gas compositions on the resulting film properties was obtained. Cobalt films grown using a hydrogen/nitrogen (H2/N2) plasma as a coreactant showed a stable film composition (CoNx) with a high Co content of 75 at. %. Using scanning electron microscopy and four point probe measurements, a moderate electrical resistivity of about 56 μΩ cm was calculated for a 20 nm film. The high sensitivity of in vacuo XPS measurements allowed investigations of interface reactions for a single PE-ALD pulse as well as investigations of the initial film growth mechanisms. The nucleation of CoNx films during PE-ALD using H2/N2 plasma as a coreactant was investigated on several substrate materials by XPS. After the very first cycle of the PE-ALD process, no Co could be detected on all the investigated substrates. XPS revealed that the plasma pulse was needed to provide active binding sites for the adsorption reaction of precursor molecules due to the formation of Si-Nx or Si-NxOy surfaces. Therefore, the plasma pulse plays an important role in the PE-ALD process of Co on silicon surfaces. The early cycles were characterized by the onset of Co—O bonds. The homogeneous film body on all substrates consisted of Co-nitride compounds.
A novel transistor with a graphene base embedded between two n-type silicon emitter and collector layers (graphene-base heterojunction transistor) is fabricated and characterized electrically. The base voltage controlled current of the device flows vertically from the emitter via graphene to the collector. Due to the extremely short transit time for electrons passing the ultimately thin graphene base, the device has a large potential for high-frequency RF applications. The transistor exhibits saturated output currents and a clear modulation of the collector current by means of the graphene base voltage. The vertical transfer current from the emitter via the graphene base to the collector is much lower than expected from device simulations. A comparison of the graphene-base transistor and a reference silicon n-p-n bipolar transistor is performed with respect to the main DC transistor characteristics. A common-emitter gain of larger than one has been achieved for the reference device while the graphene-base transistor so far exhibits a much lower gain.
This work describes the fabrication of anisotropically etched, faceted pyramidal structures in amorphous layers of silicon dioxide or glass. Anisotropic and crystal‐oriented etching of silicon is well known. Anisotropic etching behavior in completely amorphous layers of silicon dioxide in combination with purely isotropic hydrofluoric acid as etchant is an unexpected phenomenon. The work presents practical exploitations of this new process for self‐perfecting pyramidal structures. It can be used for textured silica or glass surfaces. The reason for the observed anisotropy, leading to enhanced lateral etch rates, is the presence of thin metal layers. The lateral etch rate under the metal significantly exceeds the vertical etch rate of the non‐metallized area by a factor of about 6–43 for liquid and 59 for vapor‐based processes. The ratio between lateral and vertical etch rate, thus the sidewall inclination, can be controlled by etchant concentration and selected metal. The described process allows for direct fabrication of shallow angle pyramids, which for example can enhance the coupling efficiency of light emitting diodes or solar cells, can be exploited for producing dedicated silicon dioxide atomic force microscopy tips with a radius in the 50 nm range, or can potentially be used for surface plasmonics.
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