Mn DOPING OF GaN LAYERS GROWN BY MOVPE

In this contribution we present a growth of Ga1-xMnxN layers by MOVPE. Mn doped GaN layers were grown with and without undoped GaN templates on (0001) sapphire substrates in a quartz horizontal reactor. For the deposition of Ga1-xMnxN layers (MCp)2Mn was used as a Mn – precursor. The flow of the Mn precursor was 0.2-3.2 μmol.min-1. The deposition of Ga1-xMnxN layers was carried out under the pressure of 200 mbar, the temperature 1050 °C and the V/III ratio of 1360. For the growth of high quality GaN:Mn layers it was necessary to grow these layers on a minimally partially coalesced layer of pure GaN. The direct deposition of GaN:Mn layer on the low temperature GaN buffer layer led to a three-dimensional growth during the whole deposition process. Another investigated parameter was the influence of nitrogen on the layer’s properties. A nearly constant ferromagnetic moment persisting up to room temperature was observed on the synthesized thin films

On the history and recent applications of hyperfree energy describing thermodynamics of mobile components in partly open ceramis systems

Nestechiometrické oxidy vytvářejí novou kapitolu v nově přizpůsobených materiálech. Založení a výstavba termodynamických funkcí souvisejících s pevnými (geologickými a metalurgickými ) materiály je sledována pomocí interakcí mezi českým profesorem F. Waldem a Rusy R.S. Kurnakov a D.S. Korzhinskiy v rané definici fází a charakterizaci částečně otevřených systémů. Vývoj termodynamických konceptů týkajících se popisu v pevném stavu je přezkoumán. Pro související definici mobilní komponenty byla definováma supervolná energie ve smysku přístupu P. Holby a aplikována na několik systémů. Novým termínem plutability je navržena jako míra citlivosti materiálu k volnému příjmu složek v důsledku různých prediktorů, jako je teplota, tlak a aktivita. Byly odvozeny Ehrenfestovy rovnice zahrnující se změny plutability.Nonstoichiometric oxides form a new chapter in tailored materials. Founding and construction of thermodynamic functions related to solid (geologic) materials is traced showing interactions between Czech Professor F. Wald and Russians R.S. Kurnakov and D.S. Korzhinskiy in the early definition of phases and characterization of partly open systems. Development of thermodynamic concepts regarding solid-state description is reviewed. For the associated definition of a mobile component the hyperfree energy was invented and recently applied on several systems. A novel term plutability is put forward as a measure of material susceptibility towards free component uptake as a result of varying predictors such as temperature, pressure and activity. Ehrenfest-like equations involving the changes of plutabilities were derived

Size and Shape-Dependent Solubility of CuO Nanostructures

In our theoretical study, the enhanced solubility of CuO nanoparticles in water saturated by air is predicted based on a simple thermodynamic model. CuO is considered in the form of nanoparticles with various shapes. The interfacial energy of a solid CuO/dilute aqueous solution interface was assessed by applying the average CuO surface energy and contact angle of a sessile drop of water. The equilibrium CuO solubility was calculated using Gibbs energy minimization technique. For the smallest spherical nanoparticles considered in this work (r = 2 nm), the solubility is significantly higher than the solubility of bulk material. In the case of cylindrical nanoparticles, the solubility increase is even more considerable. The CuO spherical nanoparticles solubility was also calculated using the Ostwald–Freundlich equation which is known to overestimate the solubility as discussed in this contribution

The Effect of Nanosizing on the Oxidation of Partially Oxidized Copper Nanoparticles

Copper nanoparticles are of great interest in various applications, such as catalysis, cooling fluids, conductive inks or for their antibacterial activity. In this paper, the thermal behavior of copper nanoparticles was studied using thermogravimetry, differential thermal analysis and differential scanning calorimetry. Original Cu samples as well as the products of oxidation were analysed by X-ray diffraction, scanning/transmission electron microscopy and energy dispersive spectroscopy. A step-by-step oxidation mechanism during the oxidation of Cu nano-powders was observed. The Cu-nano oxidation starts slightly above 150 °C when bulk copper does not yet react. The dominant oxidation product in the first step is Cu2O while CuO was identified as the final state of oxidation. Our results confirm an easier oxidation process of Cu-nano than Cu-micro particles, which must be attributed to kinetic not thermodynamic aspects of oxidation reactions

Synthesis and Applications of Graphene Oxide

Thanks to the unique properties of graphite oxides and graphene oxide (GO), this material has become one of the most promising materials that are widely studied. Graphene oxide is not only a precursor for the synthesis of thermally or chemically reduced graphene: researchers revealed a huge amount of unique optical, electronic, and chemical properties of graphene oxide for many different applications. In this review, we focus on the structure and characterization of GO, graphene derivatives prepared from GO and GO applications. We describe GO utilization in environmental applications, medical and biological applications, freestanding membranes, and various composite systems

Precise tuning of the charge transfer kinetics and catalytic properties of MoS2 materials via electrochemical methods

MoS2 has become particularly popular for its catalytic properties towards the hydrogen evolution reaction (HER). It has been shown that the metallic 1T phase of MoS2, obtained by chemical exfoliation after lithium intercalation, possesses enhanced catalytic activity over the semiconducting 2H phase due to the improved conductivity properties which facilitate charge-transfer kinetics. Here we demonstrate a simple electrochemical method to precisely tune the electron-transfer kinetics as well as the catalytic properties of both exfoliated and bulk MoS2-based films. A controlled reductive or oxidative electrochemical treatment can alter the surface properties of the film with consequently improved or hampered electrochemical and catalytic properties compared to the untreated film. Density functional theory calculations were used to explain the electrochemical activation of MoS2. The electrochemical tuning of electrocatalytic properties of MoS2 opens the doors to scalable and facile tailoring of MoS2-based electrochemical devices

Oxygen-free highly conductive graphene papers

Graphene papers have a potential to overcome the gap from nanoscale graphene to real macroscale applications of graphene. A unique process for preparation of highly conductive graphene thin paper by means of Ar+ ion irradiation of graphene oxide (GO) papers, with carbon/oxygen ratio reduced to 100:1, is presented. The composition of graphene paper in terms of carbon/oxygen ratio and in terms of types of individual oxygen-containing groups is monitored throughout the process. Angle-resolved high resolution X-ray photoelectron spectroscopy helps to investigate the depth profile of carbon and oxygen within reduced GO paper. C/O ratios over 100 on the surface and 40 in bulk material are observed. In order to bring insight to the processes of oxygen removal from GO paper by low energy Ar+ ion bombardment, the gases released during the irradiation are analyzed by mass spectroscopy. It is proven that Ar+ ion beam can be applied as a technique for fabrication of highly reduced graphene papers with high conductivities. Such highly conductive graphene papers have great potential to be used in application for construction of microelectronic and sensor devices