Electronic correlation effects and the Coulomb gap at finite temperature

We have investigated the effect of the long-range Coulomb interaction on the one-particle excitation spectrum of n-type Germanium, using tunneling spectroscopy on mechanically controllable break junctions. The tunnel conductance was measured as a function of energy and temperature. At low temperatures, the spectra reveal a minimum at zero bias voltage due to the Coulomb gap. In the temperature range above 1 K the Coulomb gap is filled by thermal excitations. This behavior is reflected in the temperature dependence of the variable-range hopping resitivity measured on the same samples: Up to a few degrees Kelvin the Efros-Shkovskii ln$R \propto T^{-1/2}$ law is obeyed, whereas at higher temperatures deviations from this law are observed, indicating a cross-over to Mott's ln$R \propto T^{-1/4}$ law. The mechanism of this cross-over is different from that considered previously in the literature.Comment: 3 pages, 3 figure

Tribological properties of hydraulic fluids modified by peat-based additives

The paper presents physicochemical investigations of the structure and properties of a nano-modifier synthesized from peat, the local raw material subjected to pyrolysis in air-free conditions. This nano-modifying additive is a combination of various forms of nanocarbon and polar and non-polar adsorbing materials such as silica (SiO[2]), calcium carbonate (CaCO[3]) and carbon (C). Different nanocarbon forms (nanotubes, fullerenes, nanodiamonds, nanofiber, nanodispersed carbon) used in different proportions with micro and macro peat components give multifunctional properties to the synthesized nano-modifier and the ability to positively change tribological properties of hydraulic fluids and oil lubricants. Test results of type TMT-600 show that its different percentage is required to modify tribological properties of the steel tribocouple under different loading conditions. At 0.5 wt.% content of this nano-modifier, stabilization of the friction ratio and an increase of seizure load are observed

About low field memory and negative magnetization in semiconductors and polymers

Ginzburg-Landau bulk magnetization of itinerant electrons can provide a negative effective field in the Weiss model by coupling to localized magnetic moments. The coupling enforces remnant magnetization, which can be negative or positive depending on the sample magnetic history. Stable magnetic susceptibility of coupled nonequilibrium subsystems with magnetization reversal is always positive. Gauss-scale fields could be expected for switching between negative and positive remnant moments in semiconductors with coupling at ambient temperatures. Negative magnetization in ultra-high conducting polymers is also discussed within the developed framework.Comment: 8 pages, no figure

Анализ наночастиц и наноматериалов методом рентгеновской фотоэлектронной спектроскопии

Objectives. The main aim of this review is to summarize the existing knowledge on the use of X-ray photoelectron spectroscopy (XPS) for the characterization of nanoparticles and nanomaterials.Results. XPS or electron spectroscopy for chemical analysis can provide information on the qualitative and quantitative composition, valence states of the elements of the samples under study, the chemical composition of the surface and interfaces that determine the properties of nanoparticles and nanostructured materials. The review describes the role of several different methods for the characterization of nanomaterials, highlights their advantages and limitations, and the possibilities of an effective combination. The main characteristics of XPS are described. Various examples of its use for the analysis of nanoparticles and nanomaterials are given in conjunction with additional methods to obtain complementary information about the object under study.Conclusions. XPS provides depth information comparable to the size of nanoparticles (up to 10 nm depth from the surface) and does not cause significant damage to the samples. Two disadvantages of XPS analysis are sample preparation requiring a dry solid form without contaminations and data interpretation. XPS provides information not only on the chemical identity, but also on the dielectric properties of nanomaterials, recording their charging/discharging behavior. Chemical information from the surface of nanoparticles analyzed by XPS can be used to estimate the thickness of nanoparticle coatings. XPS has a high selectivity, since the resolution of the method makes it possible to distinguish a characteristic set of lines in the photoelectron spectrum at kinetic energies determined by the photon energy and the corresponding binding energies in elements. The intensity of the lines depends on the concentration of the respective element. Obtaining a sufficiently complete picture of the properties of nanomaterials requires the use of a group of complementary instrumental methods of analysis.Цели. Основная цель данного обзора - обобщить существующие знания об использовании метода рентгеновской фотоэлектронной спектроскопии (РФЭС) для характеризации наночастиц и наноматериалов.Результаты. Метод РФЭС или электронной спектроскопии для химического анализа может предоставить информацию о качественном и количественном составе, валентных состояниях элементов исследуемых образцов, химическом составе поверхности и границ раздела, которые определяют свойства наночастиц и наноструктурных материалов. В обзоре описана роль нескольких различных методов для характеристики наноразмерных материалов, подчеркнуты их преимущества, ограничения и возможности эффективной комбинации. Описаны основные характеристики РФЭС. Приведены различные примеры ее использования для анализа наночастиц и наноматериалов в совокупности с дополнительными методами для получения комплементарной информации об изучаемом объекте.Выводы. РФЭС предоставляет информацию о глубине, сравнимой с размером наночастиц (до 10 нм глубины от поверхности), и не вызывает значительного повреждения образцов. Двумя недостатками анализа РФЭС являются подготовка образцов (требуется сухая твердая форма без загрязнения) и интерпретация данных. РФЭС предоставляет информацию не только о химической идентичности, но и о диэлектрических свойствах наноматериалов, регистрируя их поведение при зарядке/разрядке. Химическая информация с поверхности наночастиц, проанализированная с помощью РФЭС, может использоваться для оценки толщины покрытий наночастиц. РФЭС обладает высокой селективностью, поскольку разрешающая способность метода позволяет различить характерный набор линий в фотоэлектронном спектре при кинетических энергиях, определяемых энергией фотонов и соответствующими энергиями связи в элементах. Интенсивность линий зависит от концентрации соответствующего элемента. Получение достаточно полной картины свойств наноматериалов требует использования группы взаимодополняющих инструментальных методов анализа

High-Quality Graphene Using Boudouard Reaction

Following the game-changing high-pressure CO (HiPco) process that established the first facile route toward large-scale production of single-walled carbon nanotubes, CO synthesis of cm-sized graphene crystals of ultra-high purity grown during tens of minutes is proposed. The Boudouard reaction serves for the first time to produce individual monolayer structures on the surface of a metal catalyst, thereby providing a chemical vapor deposition technique free from molecular and atomic hydrogen as well as vacuum conditions. This approach facilitates inhibition of the graphene nucleation from the CO/CO2 mixture and maintains a high growth rate of graphene seeds reaching large-scale monocrystals. Unique features of the Boudouard reaction coupled with CO-driven catalyst engineering ensure not only suppression of the second layer growth but also provide a simple and reliable technique for surface cleaning. Aside from being a novel carbon source, carbon monoxide ensures peculiar modification of catalyst and in general opens avenues for breakthrough graphene-catalyst composite production

Hf–Zr anomalies in clinopyroxene from mantle xenoliths from France and Poland: implications for Lu–Hf dating of spinel peridotite lithospheric mantle

Clinopyroxenes in some fresh anhydrous spinel peridotite mantle xenoliths from the northern Massif Central (France) and Lower Silesia (Poland), analysed for a range of incompatible trace elements by laser ablation inductively coupled plasma mass spectrometry, show unusually strong negative anomalies in Hf and Zr relative to adjacent elements Sm and Nd, on primitive mantle-normalised diagrams. Similar Zr–Hf anomalies have only rarely been reported from clinopyroxene in spinel peridotite mantle xenoliths worldwide, and most are not as strong as the examples reported here. Low Hf contents give rise to a wide range of Lu/Hf ratios, which over geological time would result in highly radiogenic εHf values, decoupling them from εNd ratios. The high 176Lu/177Hf could in theory produce an isochronous relationship with 176Hf/177Hf over time; an errorchron is shown by clinopyroxene from mantle xenoliths from the northern Massif Central. However, in a review of the literature, we show that most mantle spinel peridotites do not show such high Lu/Hf ratios in their constituent clinopyroxenes, because they lack the distinctive Zr–Hf anomaly, and this limits the usefulness of the application of the Lu–Hf system of dating to garnet-free mantle rocks. Nevertheless, some mantle xenoliths from Poland or the Czech Republic may be amenable to Hf-isotope dating in the future