Literatura académica sobre el tema "Monocrystals Synthesis"

Purpose. To synthesize diamond polycrystals in a thermodynamically stable region, and to grow up a single crystal shell under conditions of thermodynamic metastability. To investigate some physical properties and features of the internal structure for synthesized single crystals for the development of new models and hypotheses regarding the issue of diamond genesis. Methodology. Experimental studies using shock-wave effects on a metal alloy containing non-diamond carbon. Methods of infrared and ultraviolet spectroscopy, X-ray phase analysis, electron paramagnetic resonance, isotope analysis, differential thermal analysis, electron microscopy, and others are used. The synthesis of nanocrystalline diamond particles as nuclei for growing single crystals is carried out by the shock-wave method using profiled shock waves. Findings. A complex of physicochemical methods for studying the grown diamond monocrystals has been carried out. The reasons for the discrete growth of diamond and the retention of the central inclusion (a polycrystalline diamond of shock-wave origin) in the process of growth have been established and analyzed. It is shown that the discreteness of diamond formation is characteristic only for thermodynamically metastable conditions. The results of the experiments give grounds to make an assumption about the metastable growth, including of diamonds from primary deposits. Originality. The hypothesis has been developed concerning the origin of diamond nanoparticles in interstellar carbon clouds which refer exclusively to central polycrystalline inclusions in a monocrystal diamond shell. The hypothesis eliminates the scientific contradiction that arises in all cases when attempts are made to interpret the natural discreteness of diamond formation based on the regularities of the graphite-diamond state diagram. Possible causes of discrete diamond formation in nature and the scenario of the formation of diamond nanocrystals in an interstellar cloud of atomic carbon have been considered. Practical value. The value of the experimental research results refers to the development of a non-energy-intensive technology for the growing large diamond monocrystals at temperatures of 5001400 K, and pressures of 105107 Pa.

A peculiar tower-like ZnO nanostructure was synthesized using an economical and facile hydrothermal method, with zinc acetate [ZAc, Zn(CH3COO)2 · 2H2O] and hexamethylenetetramine (HMTA, C6H12N4) as the source materials. The as-synthesized tower-like ZnO was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The characterization results indicated that the tower-like ZnO nanostructures are high-quality monocrystals. The as-synthesized ZnO nanostructures may have application in sensing area due to its high specific surface areas. The growth mechanism, as well as the optical properties of the as-synthesized tower-like ZnO nanostructures was also studied.

This study presents the synthesis, structural characterization, and in vitro evaluation of anticancer activity of some newly benzo[f]quinoline derivatives. The synthesis is facile and efficient, involving two steps: quaternization of nitrogen heterocycle followed by a [3+2] dipolar cycloaddition reaction. The synthesized compounds were characterized by FTIR, NMR, and X-ray diffraction on monocrystals in the case of compounds 6c and 7c. An in vitro single-dose anticancer assay of eighteen benzo[f]quinoline compounds, quaternary salts, and cycloadducts was performed. The results showed that the most active compounds were quaternary salts 3d and 3f with aromatic R substituents. Quaternary salt 3d revealed non-selective activity against all types of cancer cells, while salt 3f exhibited highly selective activity against leukemia cells. Compound 3d also presented remarkable cytotoxic efficiency against four distinct types of cancer cells—namely, non-small cell lung cancer HOP-92, melanoma LOX IMVI, melanoma SK-MEL-5, and breast cancer MDA-MB-468. The study also includes SAR correlations.

Cobalt ferrite (CoFe2O4) nanoparticles were successfully synthesized by polymer matrix templated synthesis. Synthetic ion-exchange resins were used as hosts for the coprecipitation of cobalt ferrite where the nanopores of the resin acted as the constrained environment. The weight fraction of the particles within the resin was roughly 16%. X-ray diffraction analysis indicated that cobalt ferrite crystallites were about 1–7 nm in diameter. Magnetic properties measured using an alternating gradient magnetometer showed the particles (prepared using initial salt solution ratio of Fe3+:Co2+ of 1.5:1.0) were superparamagnetic with magnetization M (of the particle-resin system) in the range of 3.0 to 4.4 emu/g at 10 kOe of applied field. The least upper bound of the magnetic size was about 3 nm in diameter. Ratios of Fe3+ to Co2+ within the matrix of the resin before and after precipitation were investigated by x-ray fluorescence spectrometry and were found to be sensitive to the initial salt solution mixture. The ratio Fe3+:Co2+ of 1.5:1.0 was found to be a better mixture in terms of magnetization value. Spherical shape cobalt ferrite particles 2–8 nm in diameter were observed using transmission electron microscopy. The close agreement between the physical and crystallite size indicated that the particles are largely monocrystals.

Quaternary sulfides of the PbLnCuS3 type (Ln–La, Nd, Sm, Gd, Dy, Er) have been obtained either by melting the elements or through furnace charge, 2PbS+Cu2S+Ln2S3 in a graphite crucible placed in a sealed quartz ampoule at a temperature of 1200–1275 K. Monocrystals of PbSmCuS3 and PbGdCuS3 have been grown by mineralization method. The study of X-ray analysis showed that compounds of PbLnCuS3 type crystallize in the orthorhombic singony (а=8.268.20; b=8.848.80; с=7.967.9Å, space group Pmn21). In a series of PbLnCuS3 compounds, the phenomenon of morphotropy manifests itself, which flows from the exchange of the structural type (PbCuSbS3 KZrCuSe3  Eu2CuS2), i.e. when the radius of the cation Ln changes. Their standard thermodynamic functions have been calculated and the temperature dependences of the magnetic susceptibility have been measured

Microporous triclinic AlPO4-34, known as APO-Tric, serves as an excellent water adsorbent in thermal energy storage, especially for low temperature thermochemical energy storage. Increased water adsorption capacity of thermochemical material usually leads to higher thermal energy storage capacity, thus offering improved performance of the adsorbent. The main disadvantage of aluminophosphate-based TCM materials is their high cost due to the use of expensive organic templates acting as structure directing agents. Using ionic liquids as low cost solvents with associated structure directing role can increase the availability of these water adsorbents for TES applications. Here, a green synthesis of APO-Tric crystals at elevated and ambient pressure by using 1-ethyl-3-methyl imidazolium bromide ionic liquid is presented. Large 200 µm romboid shaped monocrystals were obtained at 200 °C after 6 days. The structure of APO-Tric and the presence of 1,3-dimetylimidazolium cation in the micropores were determined by single crystal XRD at room temperature and 150 K. Water sorption capacity of APO-Tric prepared by ionothermal synthesis at elevated pressure increased in comparison to the material obtained at hydrothermal synthesis most probably due to additional structural defects obtained after calcination. The reuse of exhausted ionic liquid was also confirmed, which adds to the reduction of toxicity and cost production of the aluminophosphate synthesis.

Double phosphates compounds may possess catalytic, magnetic, electrophysical, non-linear optical properties and are used as monocrystals or polycrystals, ceramics etc. The tailor-made synthesis of double phosphates of alkali and multivalent metals is the basis for the in-depth research and investigation of physical and chemical properties, composition and structure of the compounds to be used for the development of new materials for multi-purpose use. Episodic syntheses of compounds MI3MIІMIV(PO4)3, MI2MIIMIV(P2O7)2, MI2MII(PO3)4 and МІMІІ4(РО4)33 (where МI – Li, Na, K; МIІ – Mn, Co, Ni; MIV – Zr), were made from various starting materials by the sintering method. After all, the selection of compounds for the synthesis of compounds of this type is a rather difficult task, often impossible. A systematic approach to the selection of starting reagents, temperature regime, interaction time between components are factors that can be adjusted and operated to achieve the target. The work used the method of solid-phase synthesis, after working out the synthesis method on the “model” Na2NiZr(P2O7)2. The synthesis was carried out starting from Na2CO3, NiO, CoO, ZrO2, ammonium hydro- and dihydrogen phosphate. The synthesis of compounds was carried out based on preliminary derivatographic studies of the passage of processes according to the corresponding reaction schemes. Completeness of synthesis stages was monitored at all stages using physico-chemical research methods. The DTA method confirmed the possibility of solid-phase synthesis of complex phosphate compounds that contain several transition metals – MINi2MIV(PO4)3 (where МI – Li, Na, K; MIV – Ti, Zr, Sn). The optimal temperature conditions for obtaining a number of phosphate compounds based on various starting substances for their synthesis have been found. The synthesized compounds were investigated by X-ray diffraction, DTA and IR spectroscopy, and their complete chemical analysis was carried out. The influence of a number of factors on the conditions of production of phosphate compounds of the MINi2MIV(PO4)3 (where МI – Li, Na, K; MIV – Ti, Zr, Sn) has been found. It can be assumed that the ionic conductivity in the synthesized compounds is of the “NASICON” type, and therefore the synthesized substances can be used as functional materials with valuable electro-physical properties.

The Fe–C system, which is widely used to grow commercial high-pressure–high-temperature diamond monocrystals, is rather complicated due to the formation of carbides. The carbide Fe3C is a normal run product, but the pressure at which Fe7C3 carbide becomes stable is a subject of discussion. This paper demonstrates the synthesis of Fe7C3 carbide and its detailed study using single-crystal and powder X-ray diffraction, as well as electron probe micro-analysis and scanning electron microscopy. The experiments were performed using a multiple-anvil high-pressure apparatus of `split-sphere' (BARS) type at a pressure of 5.5 GPa and a temperature of 1623 K. Our results show that in the Fe–C system, in addition to diamond, a phase that corresponds to the Fe7C3 carbide was synthesized. This means that both carbides (Fe7C3 and Fe3C) are stable at 5.5 GPa. Two crystal phases are described, Fe14C6 and Fe28C12−x . Fe14C6 is based on the well known rhombic structure of Fe7C3, while Fe28C12−x has a different packing order of Fe6C polyhedrons. The results obtained in this study should be taken into account when synthesizing and growing diamond at high pressures and temperatures in metal–carbon systems with a high iron content, as well as when conducting experimental studies on the synthesis of diamond directly from carbide.

Made available in DSpace on 2014-10-09T12:37:29Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:03:27Z (GMT). No. of bitstreams: 1 02033.pdf: 7170847 bytes, checksum: 0f6482c59ed081703c64e988f898b301 (MD5)
Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP

Thesis (Ph.D.); Submitted to the University of California, Berkeley, Berkeley, California (US); 15 Dec 2004.
Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56814" Westerberg, Staffan Per Gustav. USDOE Director. Office of Science. Office of Basic Energy Sciences (US) 12/15/2004. Report is also available in paper and microfiche from NTIS.

Cette thèse présente l’étude des propriétés électroniques et de transitions de phases de deux dichalcogénures de métaux de transition en couches fines : WTe2 et MoTe2. L’intérêt de ces matériaux réside dans leurs phases métastables à température et pression ambiantes, 1T’ et Td, les classant dans les semi-métaux de Weyl. Grâce à un échange réalisé à IISER Pune en Inde, nous avons pu synthétiser des monocristaux de 2H-MoTe2, 1T’-MoTe2 et Td-WTe2 par transport chimique en phase vapeur (CVT). Ces cristaux d’une grande qualité ont pu être caractérisés par DRX, MEB-EDX et spectroscopie Raman. Nous avons ensuite exfolié ces derniers par la méthode de collage anodique propre à notre laboratoire pour les caractériser en couches minces, puis mettre en place des dispositifs de mesure de transport grâce à l’évaporation de contacts en Or. Dans le contexte de pluralité de phases stables et métastables des dichalcogénures de métaux de transition, l’étude des transitions entre ces phases est très intéressante. Nous présentons la transition en température 1T’-Td dans MoTe2 et observons l’impact de l’épaisseur sur la température de transition, pouvant ainsi établir un diagramme de phase. Également, nous prouvons l’absence de transition 2H-1T’ et de sa réversibilité dans une monocouche de MoTe2 induite purement par dopage électrostatique, revendiquée dans des travaux récents. Cette transition, de la phase semi-conductrice vers la phase semi-métallique, présente un fort potentiel d’application dans le domaine des nanotechnologies comme switch électronique. Nous mettons en évidence, grâce à une expérience de dopage par charge d’espace fort et de mesure par spectroscopie Raman, le rôle de la migration du Tellure et de la création de lacunes dans cette transition. Nous avons également mesuré les propriétés de transport (magnétorésistance et effet Hall) de différente épaisseur de couches de Td-WTe2. Grâce à l’ajustement des paramètres d’un modèle à deux porteurs, nous avons déterminé les densités de porteurs ainsi que leurs mobilités et avons relié nos résultats à la théorie des semi-métaux compensés responsable de la gigantesque magnétorésistance de ce matériau. Ces expériences mettent en évidence le comportement plus résistif des couches les plus fines accompagné d’anti-localisation faible à basse température, tandis que les couches les plus épaisses sont plus conductrices et présentent des oscillations quantiques Shubnikov-de Haas à fort champ magnétique
This work presents the study of phase transitions and electronic properties of two transition metal dichalcogenides: WTe2 and MoTe2. The relevance of those materials lies in its two metastable phases at ambient pressure and temperature, 1T’ and Td, classifying them as Weyl semi-metals. We had the chance to synthesize 2H-MoTe2, 1T’-MoTe2 and Td-WTe2 monocrystals by chemical vapour transport during an exchange at IISER Pune in India. High quality resulting crystals were characterized by XRD, SEM-EDX and Raman spectroscopy. Then we could exfoliate it by the anodic bonding method proper to our laboratory, characterize their 2D form and build electronic measurement devices by gold contact deposition. In the context of multiple transition metal dichalcogenides stable and metastable phases, the study of the transitions between those phases is very interesting. We first present 1T’ to Td temperature induced phase transition in MoTe2 and observe the impact of layer thickness on transition temperature and establish a phase diagram. Then, we prove the absence of 2H to 1T’ transition and its reversibility in a MoTe2 monolayer purely induced by electrostatic doping, claimed by recent works. This transition, from semi-conductive to semi-metallic phase is likely predicted for applications in nanotechnologies as an electronic switch. Through space charge doping and Raman spectroscopy experiment, we highlight the role of Tellurium migration and the creation of vacancies in this transition. We also measured Td-WTe2 transport properties (magnetoresistance and Hall effect) of various layer thicknesses. Through a two band model parameters adjustment, we could determine carriers densities and mobilities and relate them to compensated semi-metal theory responsible of Giant Magnetoresistance response of this material. Those experiments could highlight the more insulating behaviour of thinner layers and the presence of weak anti-localization at low temperature, whereas the thinner layers are more conductive and exhibits Shubnikov-de Haas quantum oscillations at high magnetic field

Le diamant presente des proprietes physiques intrinseques extremement attractives qui sont notamment appropriees pour des applications electroniques. Cependant, il convient de rester prudent car les caracteristiques globales des films (purete de la phase diamant, tailles des cristallites, epaisseur, morphologie, texture, contraintes internes etc. . . ) dependent fortement des conditions de croissance et conditionnent les proprietes des films. L'analyse quantitative de la texture (logiciel d'analyse de texture beartex) de films de diamant polycristallins deposes sur substrat de silicium par mpcvd a permis d'estimer l'influence des parametres d'elaboration (temperature du substrat, 650-880c, taux de methane, 0. 3%-2%), de l'epaisseur des films (jusqu'a 70 m) et du taux d'incorporation de bore (jusqu'a 5x10#2#0 b-cm#-#3) sur le developpement d'une orientation preferentielle au cours de la croissance. L'analyse du profil des raies de diffraction a permis d'etudier l'influence du dopage au bore sur la microstructure des films polycristallins. Les resultats issus des methodes des largeurs integrales, de fourier et de la variance indiquent une evolution (amelioration jusqu'a 10#1#9 b-cm#-#3 puis deterioration) de la qualite cistalline des films avec le dopage. Une etude structurale conjointement menee sur des films polycristallins et monocristallins deposes respectivement sur substrat de silicium et de diamant monocristallins montre que le parametre cristallin du diamant augmente avec le dopage au bore. La dilatation atteint 0. 2% pour un dopage de 8x10#2#0 b-cm#-#3 et devient significative au dela de la transition semiconducteur-metal.

The possibility of low-temperature synthesis of graphene on the surface of porous silicon (PS) is associated with the excess surface energies of nc-PS nanocrystallites ; the boundary interface nanocrystallties nc-PS / c-Si monocrystal matrix; the dangling bonds of silicon atoms of nanocrystallites skeleton nc-PS. This opens up new prospects for the development of methods for the low-temperature synthesis of graphene without metal catalysts for the decomposition of carbon precursors, including using the ALD method.