Unintentional boron incorporation in AlGaN layers grown by plasma-assisted MBE using highly efficient nitrogen RF plasma-sources

Plasma-assisted molecular beam epitaxy (PA-MBE) is now widely used for the growth of group III-nitrides. Many years ago it became clear that during PA-MBE there is unintentional doping of GaN with boron (B) due to decomposition of the pyrolytic boron nitride (PBN) cavity of the RF plasma source. In this paper we discuss the unintentional B incorporation for PA-MBE growth of GaN and AlxGa1−xN using a highly efficient RF plasma source. We have studied a wide range of MBE growth conditions for GaN and AlxGa1−xN with growth rates from 0.2 to 3 µm/h, RF powers from 200 to 500 W, different nitrogen flow rates from 1 to 25 sccm and growth times up to several days. The chemical concentrations of B and matrix elements of Al, Ga, N were studied as a functions of depth using secondary ion mass spectrometry (SIMS). We demonstrate that boron incorporation with this highly efficient RF plasma source is approximately 1×1018 to 3×1018 cm−3 for the AlxGa1−xN growth rates of 2 – 3 µm/h

Growth of free-standing bulk wurtzite AlxGa1−xN layers by molecular beam epitaxy using a highly efficient RF plasma source

The recent development of group III nitrides allows researchers world-wide to consider AlGaN based light emitting diodes as a possible new alternative deep ultra–violet light source for surface decontamination and water purification. In this paper we will describe our recent results on plasma-assisted molecular beam epitaxy (PA-MBE) growth of free-standing wurtzite AlxGa1−xN bulk crystals using the latest model of Riber's highly efficient nitrogen RF plasma source. We have achieved AlGaN growth rates up to 3 µm/h. Wurtzite AlxGa1−xN layers with thicknesses up to 100 μm were successfully grown by PA-MBE on 2-inch and 3-inch GaAs (111)B substrates. After growth the GaAs was subsequently removed using a chemical etch to achieve free-standing AlxGa1−xN wafers. Free-standing bulk AlxGa1−xN wafers with thicknesses in the range 30–100 μm may be used as substrates for further growth of AlxGa1−xN-based structures and devices. High Resolution Scanning Transmission Electron Microscopy (HR-STEM) and Convergent Beam Electron Diffraction (CBED) were employed for detailed structural analysis of AlGaN/GaAs (111)B interface and allowed us to determine the N-polarity of AlGaN layers grown on GaAs (111)B substrates. The novel, high efficiency RF plasma source allowed us to achieve free-standing AlxGa1−xN layers in a single day's growth, making this a commercially viable process

X-ray Diffraction Analysis of the Chromium-containing Electroerosion Powders of Micro - and Nanoparticles

Presents the results of a study of x-ray analysis of the powder obtained by electro erosion dispersing of waste nichrome H15N60 brand in kerosene lighting. The major phases in Nickel-chromium powder obtained by electroerosion dispersion method in kerosene lighting are Ni and Si2O

Molecular beam epitaxy as a growth technique for achieving free-standing zinc-blende GaN and wurtzite AlxGa1-xN

Currently there is a high level of interest in the development of ultraviolet (UV) light sources for solid state lighting, optical sensors, surface decontamination and water purification. III-V semiconductor UV LEDs are now successfully manufactured using the AlGaN material system; however, their efficiency is still low. The majority of UV LEDs require AlxGa1-xN layers with compositions in the mid-range between AlN and GaN. Because there is a significant difference in the lattice parameters of GaN and AlN, AlxGa1-xN substrates would be preferable to those of either GaN or AlN for many ultraviolet device applications. However, the growth of AlxGa1-xN bulk crystals by any standard bulk growth techniques has not been developed so far. There are very strong electric polarization fields inside the wurtzite (hexagonal) group III-nitride structures. The charge separation within quantum wells leads to a significant reduction in the efficiency of optoelectronic device structures. Therefore, the growth of non-polar and semi-polar group III-nitride structures has been the subject of considerable interest recently. A direct way to eliminate polarization effects is to use non-polar (001) zinc-blende (cubic) III-nitride layers. However, attempts to grow zinc-blende GaN bulk crystals by anystandard bulk growth techniques were not successful. Molecular beam epitaxy (MBE) is normally regarded as an epitaxial technique for the growth of very thin layers with monolayer control of their thickness. In this study we have used plasma-assisted molecular beam epitaxy (PA MBE) and have produced for the first time free-standing layers of zinc-blende GaN up to 100 μm in thickness and up to 3-inch in diameter. We have shown that our newly developed PA-MBE process for the growth of zinc-blende GaN layers can also be used to achieve free-standing wurtzite AlxGa1-xN wafers. Zinc-blende and wurtzite AlxGa1-xN polytypes can be grown on different orientations of GaAs substrates - (001) and (111)B respectively. We have subsequently removed the GaAs using a chemical etch in order to produce free-standing GaN and AlxGa1-xN wafers. At a thickness of ∼30 μm, free-standing GaN and AlxGa1-xN wafers can easily be handled without cracking. Therefore, free-standing GaN and AlxGa1-xN wafers with thicknesses in the 30–100 μm range may be used as substrates for further growth of GaN and AlxGa1 xN-based structures and devices. We have compared different RF nitrogen plasma sources for the growth of thick nitride AlxGa1-xN films including a standard HD25 source from Oxford Applied Research and a novel high efficiency source from Riber. We have investigated a wide range of the growth rates from 0.2 to 3 μm/h. The use of highly efficient nitrogen RF plasma sources makes PA-MBE a potentially viable commercial process, since free-standing films can be achieved in a single day. Our results have demonstrated that MBE may be competitive with the other group III-nitrides bulk growth techniques in several important areas including production of free-standing zinc-blende (cubic) (Al)GaN and of free-standing wurtzite (hexagonal) AlGaN

Molecular beam epitaxy of highly mismatched N-rich GaNSb and InNAs alloys

GaN materials alloyed with group V anions form the so-called highly mismatched alloys (HMAs). Recently, the authors succeeded in growing N-rich GaNAs and GaNBi alloys over a large composition range by plasma-assisted molecular beam epitaxy (PA-MBE). Here, they present first results on PA-MBE growth and properties of N-rich GaNSb and InNAs alloys and compare these with GaNAs and GaNBi alloys. The enhanced incorporation of As and Sb was achieved by growing the layers at extremely low growth temperatures. Although layers become amorphous for high As, Sb, and Bi content, optical absorption measurements show a progressive shift of the optical absorption edge to lower energy. The large band gap range and controllable conduction and valence band positions of these HMAs make them promising materials for efficient solar energy conversion devices

СЫВОРОТОЧНОЕ СОДЕРЖАНИЕ РАСТВОРИМЫХ МОЛЕКУЛ CD25 И CD95 У ОЖОГОВЫХ БОЛЬНЫХ

Background: Burn injury is accompanied by modulation of the many components of immunity, including the system regulation, which includes soluble forms of leukocyte differentiation molecules. Earlier in burn patients, we detected changes in serum levels of soluble differentiation molecules CD25 (sCD25) and CD95 (sCD25). Despite the existence of data on change of serum level of the soluble molecules CD25 and CD95 in the blood of patients with a burn trauma, there are no data on particular cell producers.Aims: To conduct the analysis of serum level of the molecules sCD25 and sCD95 in the blood of patients with acute burn trauma in comparison with peripheral blood cells composition to obtain data on the types of cells that produce the molecules sCD25 and sCD95.Materials and methods: Blood samples from 24 heavily burnt patients aged 16 to 77 years were studied. Determination of sCD25 and sCD95 molecules serum levels was performed by ELISA. Number of CD45+CD25+ lymphocytes, CD45+CD95+ cells, CD14+CD95+ monocytes, CD16b+CD95+ neutrophils, and RFMI (relative mean fluorescence intensity) was evaluated by flow cytometry.Results: In the first five days of the date of burn sCD25 and sCD95 serum levels tended to increase. sCD25 molecules contents in the blood of surviving and dead patients did not depend on the relative content of CD45+CD25+ lymphocytes, RFMI index, but correlated with the absolute level of lymphocytes and leukocytes. Serum levels of sCD95 molecules showed the dependence on the absolute neutrophil count and leukocytes in the survivors and on the absolute content of lymphocytes, neutrophils, and leukocytes in patients who died.Conclusions: The findings suggest that the lymphocytes in the early period of burn disease are the main cells-producers of sCD25 and affect the increase of its content in the blood serum not due to changes in the density of CD25 molecules expression on their membrane followed by increased shedding but by increasing the number of CD25 positive cells. The main cells-producers of sCD95 molecules for survivors in the early period of burn disease are likely to be the neutrophils and lymphocytes; in the dead patients, the main producers are neutrophils.Обоснование. Ожоговая травма сопровождается модуляцией многих звеньев иммунитета, в том числе системой регуляции, в состав которой входят растворимые формы лейкоцитарных дифференцировочных молекул. Ранее у ожоговых больных были обнаружены изменения в сывороточном содержании растворимых дифференцировочных молекул CD25 (sCD25) и CD95 (sCD25). Несмотря на наличие данных об изменении сывороточного содержания растворимых молекул CD25 и CD95 в крови пациентов с ожоговой травмой, отсутствуют данные о том, какими клетками они продуцируются.Цель исследования — провести анализ сывороточного уровня молекул sCD25 и sCD95 в крови пациентов в остром периоде ожоговой травмы в сопоставлении с популяционным составом клеток периферической крови с целью получения данных о типах клеток, продуцирующих молекулы sCD25 и sCD95.Методы. Исследованы образцы крови 24 тяжело обожженных пациентов в возрасте от 16 до 77 лет. Определение сывороточного содержания молекул sCD25 и sCD95 проводили иммуноферментным методом. Количество CD45+CD25+ лимфоцитов, CD45+CD95+ клеток, CD14+CD95+ моноцитов, CD16b+CD95+ нейтрофилов и RFMI (relative mean fluorescence intensity) оценивали с помощью проточной цитофлуорометрии.Результаты. В первые пять суток от момента ожога сывороточное содержание sCD25 и sCD95 имело тенденцию к повышению. Содержание молекул sCD25 как у выживших, так и погибших больных не зависело от относительного содержания CD45+CD25+ лимфоцитов, индекса RFMI, но коррелировало с абсолютным содержанием лимфоцитов и лейкоцитов. Сывороточный уровень молекул sCD95 обнаруживал зависимость от абсолютного содержания нейтрофилов и лейкоцитов у выживших больных и абсолютного содержания лимфоцитов, нейтрофилов и лейкоцитов — у погибших.Заключение. Полученные данные позволяют заключить, что лимфоциты в раннем периоде ожоговой болезни являются основными клетками-продуцентами sCD25 и влияют на повышение их содержания в сыворотке крови не за счет изменения плотности экспрессии на их мембране молекул CD25 с последующим усилением шеддинга, а путем увеличения количества СD25-положительных клеток. Основными клетками-продуцентами молекул sCD95 у выживших больных в раннем периоде ожоговой болезни, вероятно, являются нейтрофилы и лимфоциты, у погибших — нейтрофилы.

Влияние обработки почвы и минерального питания на динамику биологической активности и NPK при возделывании ярового ячменя

The use of scientifically based doses of fertilizers in the cultivation of crops does not lead to the removal of nutrients from the natural reserves of the organic and mineral soil by microflora. At the same time, the methods and terms for the introduction of mineral fertilizers must be linked with the technology of soil preparation and moisture supply. Nitrogen fertilizers, because of their rapid volati-lization, are recommended to be applied for pre-sowing cultivation with sealing in the surface layer, and phosphorous fertilizers, as inactive — along with the main soil treatment. In this connection, in studies of the significant influence of the methods of basic soil cultivation with and without application of nitrogen, its dynamics along layers are not revealed. Deep soil-free tillage allows significantly more accumulation and longer storage of moisture in the soil layers; In comparison with the classical plowing and dumping plowing and planing in a meter layer of soil, the additional moisture reserves before sowing the crop are respectively 300 and 230 m3 / ha, in the tubing phase — barley — 256 and 189 m3/ha, in the phase of milk ripeness — 270 And 128 m3/ha. Deficiency of moisture reduces the biological activity of the soil, in this regard, moisture-saving methods of basic soil cultivation are especially important in conditions of rain-fed farming, not only on the yield of agricultural crops, but also on the processes of humus formation. The total accumulation of amino acids in the half-meter layer in the variant with deep soil-free tillage before sowing barley was 424 μg amine / G of cloth, in the phase of tubing — ear — 400 μg amine / G canvas, in the phase of milk ripeness — 210 μg amine / G of canvas. The values obtained are higher in comparison with the control data and the variant with planar tillage at 7 and 18%, 48 and 32%, 10 and 36% respectively. Positive dynamics in terms of productive moisture and accumulation of amino acids in the variant with deep soil-free soil treatment, application of calculated phosphorus doses for main processing and nitrogen for pre-sowing cultivation, had an effect on a significant increase in grain relative to control at 0.4 t/ha, Processing — at 0.35 t/ha.Применение научно обоснованных доз удобрений при возделывании сельскохозяйственных культур не приводит к выносу питательных элементов из естественных запасов органической и минеральной части почвы микрофлорой. При этом способы и сроки внесения минеральных удобрений необходимо увязывать с технологией подготовки почвы и влагообеспеченностью. Азот-ные удобрения из-за их быстрого улетучивания рекомендуется вносить под предпосевную культива-цию с заделкой в поверхностный слой, а фосфорные, как малоподвижные — вместе с основной обработкой почвы. В связи с этим в исследованиях существенного влияния способов основной обработки почвы с внесением и без внесения азота на его динамику по слоям не выявлено. Глубокая безотвальная обработка почвы позволяет существенно больше накапливать и дольше сохранять влагу в почвенных слоях; в сравнении с классической лемешно-отвальной вспашкой и плоскорезной обработкой в метровом слое почвы дополнительные запасы влаги перед посевом культуры составля-ют соответственно 300 и 230 м3/га, в фазу трубкование — колошение ячменя — 256 и 189 м3/га, в фазу молочной спелости — 270 и 128 м3/га. Дефицит влаги снижает биологическую активность почвы, в связи с этим влагосберегающие способы основной обработки почвы имеют особенно большое значение в условиях неорошаемого земледелия не только на урожайность сельскохозяйст-венных культур, но и на процессы гумусообразования. Суммарное накопление аминокислот в полу-метровом слое в варианте с глубокой безотвальной обработкой почвы перед посевом ячменя состав-ляло 424 мкг амин. / г полотна, в фазу трубкование — колошение — 400 мкг амин. / г полотна, в фазу молочной спелости — 210 мкг амин. / г полотна. Полученные значения выше в сравнении с данными по контролю и варианту с плоскорезной обработкой почвы на 7 и 18%, 48 и 32%, 10 и 36% соответст-венно. Положительная динамика по продуктивной влаге и накоплению аминокислот в варианте с глубокой безотвальной обработкой почвы, внесением расчетных доз фосфора под основную обра-ботку и азота под предпосевную культивацию подействовала на существенную прибавку зерна по отношению к контролю на уровне 0,4 т/га, варианту с мелкой обработкой — на уровне 0,35 т/га

Оценка динамической составляющей работы ДВС

Briefly the technique of assessing the impact of transient modes for comprehensive indicators on the toxicity of diesel or fuel efficiency, with respect to the NRTC test cycle for off-road equipment.Кратко рассмотрена методика оценки влияния неустановившихся режимов работы на интегральные показатели дизеля по токсичности или топливной экономичности, применительно к ездовому циклу NRTC для внедорожной техники

Electroerosive Powder Obtained from Alloy VK8 Waste into Butanol

The results of studies of the properties of the powders obtained by electroerosive dispersing of the hard alloy wastes of mark VK8 in butanol. It is found that the powder particles obtained by electroerosive dispersing of waste carbide grade VK8 in butyl alcohol, consist of the following major elements: W, Co, Fe, C and O