Synthesis and Characterization of Large Stereoregular Organosiloxane Cycles

The large stereoregular phenyltrimethylsiloxysiloxane macrocycles of general formula [PhSi(OSiMe3)O]n (n=6 and 12) have been selectively obtained with high yields by trimethylsilylation of cage-like oligophenylmetallasiloxanes (OPMS) which we described earlier. The compounds 3 (n=6) and 4 (n=12) have been characterized by NMR-spectroscopy method and by single crystal X-ray analysis. This investigation showed unambiguously that the siloxane macrocycles keep their size and configuration (the same as in the initial OPMS) during the trimethylsilylation. Thus a synthetic route for obtaining large stereoregular siloxane macrocycles has been developed

2D/3D Metallic Nano-objects Self-Organized in an Organic Molecular Thin Film

We present the fabrication and investigation of the properties of nanocomposite structures consisting of two-dimensional (2D) and three-dimensional (3D) metallic nano-objects self-organized on the surface and inside of organic molecular thin-film copper tetrafluorophthalocyanine (CuPcF4). Metallic atoms, deposited under ultrahigh vacuum (UHV) conditions onto the organic ultrathin film, diffuse along the surface and self-assemble into a system of 2D metallic overlayers. At the same time, the majority of the metal atoms diffuse into the organic matrix and self-organize into 3D nanoparticles (NPs) in a well-defined manner. The evolution of the morphology and electronic properties of such structures as a function of nominal metal content is studied under UHV conditions using transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM), and photoelectron spectroscopy (PES) techniques. Using HR-TEM, we have observed the periodicity of atomic planes of individual silver NPs. The steady formation of agglomerates from individual single nanocrystallites with intercrystallite boundaries is observed as well. PES reveals generally weak chemical interactions between silver and the organic matrix and n-doping of CuPcF4 at the initial stages of silver deposition, which is associated with charge transfer from the 2D wetting layer on the basis of core-level spectra shift analysis. Copyright © 2020 American Chemical Society

Atomic and electronic structure of nanostructured few-layer graphene with self-aligned boundaries synthesized on SiC/Si(001) wafers

This work was partially supported by the Russian Academy of Sciences, Russian Foundation for Basic Research (grant № 17-02-01139, 17-02-01291), Beijing Institute of Technology Research Fund Program for Young Scholars, and Science Foundation Ireland

Transport properties of copper phthalocyanine based organic electronic devices

Ambipolar charge carrier transport in Copper phthalocyanine (CuPc) is studied experimentally in field-effect transistors and metal-insulator-semiconductor diodes at various temperatures. The electronic structure and the transport properties of CuPc attached to leads are calculated using density functional theory and scattering theory at the non-equilibrium Green's function level. We discuss, in particular, the electronic structure of CuPc molecules attached to gold chains in different geometries to mimic the different experimental setups. The combined experimental and theoretical analysis explains the dependence of the mobilityand the transmission coefficient on the charge carrier type (electrons or holes) and on the contact geometry. We demonstrate the correspondence between our experimental results on thick films and our theoretical studies of single molecule contacts. Preliminary results for fluorinated CuPc are discussed.Comment: 18 pages, 16 figures; to be published in Eur. Phys. J. Special Topic

Методы исследования дислокационной структуры полупроводниковых монокристаллов группы AIIIBV

The development pace of advanced electronics raises the demand for semiconductor single crystals and strengthens the requirements to their structural perfection. Dislocation density and distribution pattern are most important parameters of semiconductor single crystals which determine their performance as integrated circuit components. Therefore studies of the mechanisms of dislocation nucleation, slip and distribution are among the most important tasks which make researchers face the choice of suitable analytical methods. This work is an overview of advanced methods of studying and evaluating dislocation density in single crystals. Brief insight has been given on the main advantages and drawbacks of the methods overviewed and experimental data have been presented. The selective etching method (optical light microscopy) has become the most widely used one and in its conventional setup is quite efficient in the identification of scrap defects and in dislocation density evaluation by number of etch pits per vision area. Since the introduction of digital light microscopy and the related transfer from image analysis to pixel intensity matrices and measurement automation, it has become possible to implement quantitative characterization for the entire cross-section of single crystal wafers and analyze structural imperfection distribution pattern. X-ray diffraction is conventionally used for determination of crystallographic orientation but it also allows evaluating dislocation density by rocking curve broadening in double-crystal setup. Secondary electron scanning electron microscopy and atomic force microscopy allow differentiating etch patterns by origin and studying their geometry in detail. Transmission electron microscopy and induced current method allow obtaining micrographs of discrete dislocations but require labor-consuming preparation of experimental specimens. X-ray topography allows measuring bulky samples and also has high resolution but is hardly suitable for industry-wide application due to the high power consumption of measurements.Digital image processing broadens the applicability range of basic dislocation structure analytical methods in materials science and increases the authenticity of experimental results.Темпы развития современной электроники помимо повышения спроса на полупроводниковые монокристаллы приводят к возрастанию требований по их структурному совершенству. Плотность дислокаций и характер их распределения являются важнейшими характеристиками полупроводниковых монокристаллов, определяющими дальнейшую эффективность их применения в качестве элементов интегральных систем. В связи с этим изучение механизмом возникновения, скольжения и распределения дислокаций — одна из актуальных задач, которая ставит ученных перед выбором метода исследования. В данной работе приведен обзор современных методик исследования и подсчета плотности дислокаций в монокристаллах. Дан краткий анализ основных преимуществ и недостатков каждого метода, а также приведены экспериментальные результаты. Метод избирательного травления (световой оптической микроскопии) получил наибольшее распространения и в своем классическом варианте является очень эффективным при решении задач обнаружения дефектов, приводящих к браку, и оценки плотности дислокаций по числу ямок травления, пересчитанных на площадь поля зрения. С использованием цифровой световой микроскопии, за счет перехода от анализа изображений к матрице значений интенсивности отдельного пикселя и автоматизации процесса измерений, становится возможным количественный анализ по всему поперечному сечению монокристаллической пластины и анализ характера распределения структурных несовершенств. Метод рентгеновской дифракции традиционно используется для определения кристаллографической ориентации, но также позволяет оценить величину плотности дислокаций по уширению кривой качания в случае двухкристальной геометрии. Методы растровой электронной микроскопии во вторичных электронах и атомно-силовой микроскопии позволяют дифференцировать фигуры травления по природе их возникновения и детально изучить их геометрию.Просвечивающая электронная микроскопия и метод наведенных токов позволяют получать микрофотографию отдельных дислокаций, но требуют трудоемкой предварительной подготовки экспериментальных образцов. Рентгеновская топография дает возможность работать с массивными образцами и также обладает высокой разрешающей способностью, но в связи с высокой энергоемкостью процесса измерений слабо применима в условиях производства.Цифровая обработка изображений позволяет расширить спектр возможностей основных материаловедческих методов исследования дислокационной структуры и повысить объективность получаемых результатов

Исследование влияния вида обработки на прочность монокристаллических пластин нелегированного антимонида индия

The method of plane-transverse bending was used to measure the strength of thin single-crystal plates of undoped InSb with a crystallographic orientation of (100). It was found that the strength of the plates (thickness ≤ 800 μm) depends on their processing. Using a full processing cycle (grinding and chemical polishing) allows to increase the strength of InSb plates by 2 times (from 3.0 to 6.4 kg/mm2). It is shown that the dependence of strength on processing for wafers with (100) orientation is similar to this dependence for wafers (111), while the strength of wafers (111) is 2 times higher. The contact profilometry method was used to measure the roughness of thin plates, which also passed successive processing steps. It was found that during a full cycle of processing, the roughness of InSb plates decreases (Ra from 0.6 to 0.04 μm), leading to a general smoothing of the surface roughness. The strength and roughness of the (100) InSb and GaAs wafers are compared. It was found that the strength of GaAs cut wafers is 2 times higher than the strength of InSb cut wafers and slightly increases after a full cycle of their processing. It was shown that the roughness of GaAs and InSb plates after a full cycle of surface treatment is significantly reduced: 10 times for InSb due to overall surface leveling and 3 times for GaAs (Rz from 2.4 to 0.8 μm) due to a decrease in the peak component. Conducting a full cycle of processing InSb plates can increase their strength by removing broken layers by sequential operations and reducing the risk of mechanical damage.Методом плоско-поперечного изгиба проведены измерения прочности тонких монокристаллических пластин нелегированного InSb с кристаллографической ориентацией (100). Установлено, что прочность пластин (толщиной ≤ 800 мкм) зависит от их обработки. Использование полного цикла обработки (шлифовки и химической полировки) позволяет увеличить прочность пластин InSb в 2 раза (от 3,0 до 6,4 кг/мм2). Показано, что зависимость прочности от обработки для пластин с ориентацией (100) аналогична этой зависимости для пластин (111), при этом величина прочности пластин (111) в 2 раза выше. Методом контактной профилометрии измерена шероховатость тонких пластин, также прошедших последовательные этапы обработки. Установлено, что при проведении полного цикла обработки шероховатость пластин InSb уменьшается (Ra от 0,6 до 0,04 мкм), приводя к общему выравниванию шероховатости на поверхности. Проведено сравнение прочности и шероховатости пластин (100) InSb и GaAs. Установлено, что прочность резаных пластин GaAs в 2 раза выше прочности резаных пластин InSb и незначительно увеличивается после полного цикла их обработки. Показано, что шероховатость пластин GaAs и InSb после полного цикла обработки поверхности значительно уменьшается: в 10 раз для InSb за счет общего выравнивания поверхности и в 3 раза для GaAs (Rz от 2,4 до 0,8 мкм) за счет снижения пиковой составляющей. Проведение полного цикла обработки пластин InSb позволяет повысить их прочность, удаляя нарушенные слои последовательными операциями и снижая риск развития механических повреждений

A photochemical approach for a fast and self-limited covalent modification of surface supported graphene with photoactive dyes

Herein, we report a simple method for a covalent modification of surface supported graphene with photoactive dyes. Graphene was fabricated on cubic-SiC/Si(001) wafers due to their low cost and suitability for mass-production of continuous graphene fit for electronic applications on millimetre scale. Functionalisation of the graphene surface was carried out in solution via white light induced photochemical generation of phenazine radicals from phenazine diazonium salt. The resulting covalently bonded phenazine-graphene hybrid structure was characterised by scanning tunnelling microscopy (STM) and spectroscopy (STS), Raman spectroscopy and density functional theory (DFT) calculations. It was found that phenazine molecules form an overlayer, which exhibit a short range order with a rectangular unit cell on the graphene surface. DFT calculations based on STM results reveal that molecules are standing up in the overlayer with the maximum coverage of 0.25 molecules per graphene unit cell. Raman spectroscopy and STM results show that the growth is limited to one monolayer of standing molecules. STS reveals that the phenazine-graphene hybrid structure has a band gap of 0.8 eV

Large positive in-plane magnetoresistance induced by localized states at nanodomain boundaries in graphene

Graphene supports long spin lifetimes and long diffusion lengths at room temperature, making it highly promising for spintronics. However, making graphene magnetic remains a principal challenge despite the many proposed solutions. Among these, graphene with zig-zag edges and ripples are the most promising candidates, as zig-zag edges are predicted to host spin-polarized electronic states, and spin-orbit coupling can be induced by ripples. Here we investigate the magnetoresistance of graphene grown on technologically relevant SiC/Si(001) wafers, where inherent nanodomain boundaries sandwich zig-zag structures between adjacent ripples of large curvature. Localized states at the nanodomain boundaries result in an unprecedented positive in-plane magnetoresistance with a strong temperature dependence. Our work may offer a tantalizing way to add the spin degree of freedom to graphene

Arterial hypertension in Ryazan region: data of the third section of the EPOHA study

Aim. To study the nine-year dynamics of prevalence, risk factors, approaches to the treatment of arterial hypertension (AH) in the Ryazan region according to a representative sample survey, to assess the impact of risk factors and cardiovascular diseases on achieving blood pressure (BP) control.Material and methods. A representative sample of the population of the Ryazan region, created in 2002 by the method of step-by-step randomization, was reexamined in 2007 and 2016. The group of AH included people with blood pressure >140/90 mm Hg. with double measurement or normal blood pressure, receiving antihypertensive therapy. The role of risk factors (age, smoking, alcohol abuse, salt, obesity, burdened heredity, low physical activity) and cardiovascular diseases was analyzed.Results. In 2016, the prevalence of AH was 43,9%, the number of people receiving antihypertensive drugs — 89,5%, those who are treated effectively — 373%, which is higher than in 2007 (39,3%, 799% and 16,6%, respectively). Smoking (RR 1,23; 1,11-1,37, p=0,005), salt abuse (RR 1,11; 1,01-1,23, p=0,04) and obesity (RR 1,16; 1,06¬1,27 p=0,003) negatively effect on the effectiveness of AH treatment. Treatment of AH is more effective in the absence of cardiovascular diseases (35,0% vs. 26,8%), signs of chronic heart failure (24,9% vs. 34,9%) and intermittent claudication (8,3% vs. 31,7%), p <0,001.Conclusion. Over nine years, the standardized by age prevalence of AH has increased significantly, the number of individuals taking antihypertensive drugs and the treatment effectively, the structure of the drugs taken has changed positively. Smoking, obesity, salt abuse and the presence of diseases of the cardiovascular system adversely affect the effectiveness of therapy. Study participants: Yepikhina E. A., Biryukova Zh. A., Larina T. A., Ivushkina L. I., Kozakova Yu. V., Motsnaya O. A., Surova A. I., Skorobogatova S. Yu., Tolmacheva E. A., Golubeva I. V., Smagina E. V., Kiseleva E. A., Bulavchenkova O. N., Shvykova T. A., Bashmakova G. N., Soloveva N. N., Davydkina S.A., Gorbunova L. A., Khoteenkova N. V., Dukova E. V., Varlamova L. A., Vorobyova G. A., Korzhevskaya A. A., Tabolkina A. A., Nechaeva G. P., Vybornova E. Z., Kashapova L. M., Tarasova A. I., Ryazantseva L. L., Yakovleva N. S., Semenets A. A., Chikova N. A., Muravyova G.V., Chizhikova M. I

Crystal Structure of the Nd, Gd, and Dy Sandwich Complexes Involving 8-Membered Macrocyclic Phenylsiloxanolate Ligands

An X-ray structural investigation of the interaction products of anhydrous trivalent neodymium, gadolynium, and dysprosium chlorides with sodium phenylsiloxanolate was carried out. The synthesized compounds with the general formula Na6[PhSiO2]8M4(μ4-O)[O2SiPh]8 · 10EtOH · 8H2O (M = Nd, Gd, Dy) were found to be isomorphous isostructural sandwich complexes. The macrocyclic octaphenyloctasiloxanolate ligands in the complexes have anall-cis-configuration and are arranged in co-axial antiparallel pairs and coordinate the square planar groups of the four Nd3+, Gd3+, or Dy3+ ions stabilized by an additional central μ4-bridging O2− ligand. Six Na+ counterions form the outer coordination sphere of the complexes such that four of them coordinate the siloxane macrocycle O atoms in pairs in analogy with crown-ether complexes