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Papers by Christo Nanev

Silver-Mercury Whiskers

De Gruyter eBooks, Dec 31, 1972

Physica status solidi, Jul 16, 1973

Uber eine Moglichkeit zur Ziichtung von Zinkeinkristallen hoher Perfektion Von CHR. NANEV (a) und... more Uber eine Moglichkeit zur Ziichtung von Zinkeinkristallen hoher Perfektion Von CHR. NANEV (a) und H. WADEWITZ (b) I n Erweiterung einer von Stranski, Kaischew und Mitarbeitern entwicketten Methode zur Ziichtung von Zinkeinkristallen im Innern einer Glasampulle geliagt es durch Aufdampfen einer Kohleschicht als Unterlage fur die aus der Schmelze, und weiter aus der Dampfphase, zu zuchtenden Kristalle, Einkristalle hoher Perfektion herzustellen. Durch Berg-Barrett-Aufnahmen wird nachgewiesen, daO die auf einer Kohleschicht gewachsenen Zinkeinkristalle gegenuber den direkt auf Glas gewachsenen keine Subkorngrenzen enthalten. The method of growing of zinc single crystals in a glass ampoule by freezing of molten drops and further growth from own vapours, previously described by Stranski, Kaischew and co-workers, is improved. The crystals are grown on thin vacuum deposited carbon films covering the glass which ensured the production of more perfect crystals. Contrary to the crystals obtained directly on glass support, the zinc single crystals on carbon film substrate did not contain Iow-angle boundaries as shown by Berg-Barrett X-ray topography.

On the Morphological Instability of Growing Crystals (I) Morphological Peculiarities of the Transition Shapes of Crystals in Diffusioncontrolled Regime of Growth

De Gruyter eBooks, Dec 31, 1988

The shape and size of the gross morphological defect which occurs (in the form of a depression) a... more The shape and size of the gross morphological defect which occurs (in the form of a depression) as a result of the diffusion inhomogeneity in the matter supply on the growing crystal face with supercritical dimensions are investigated. The transition shapes of similar skeletal crystal faces are determined by considering the configuration of the steps which are moving (and accumulating) from the edge toward the centre of the crystal face. The basic parameter which is evaluated, is the width of the macroscopically flat periphery which grows around the depression and its alteration when the crystal is enlarged. The theoretical analysis is carried out by presuming that no transportation of crystallizing material occurs parallel to the crystal face. The calculations are based on the different thicknesses of the Nernst diffusion layer, a magnitude which can be easily determined experimentally by some interferometric technique, over the various regions of the growing face. Es werden die Beschaffenheit und die Ausdehnung des groben morphologischen Defekts untersucht, welcher infolge der diffusions-bedingten Ubersattigungsinhomogenitat auf den Kristallflachen uberkritischer Grose (in der Form einer Vertiefung) entsteht. Die Ubergangsformen solcher skelettartigen Kristallflachen werden auf Grund der Stufenkonfigurationen bestimmt, welche bei der Bewegung (und Anhaufung) der auf den Kristallecken entstandenen und sich in Richtung Flachenmitte bewegenden Wachstumsstufen auftreten. Die Breite der um der Vertiefung wachsenden makroskopisch ebenen Peripherie und ihre Veranderung mit der Vergroserung des Kristalls ist der berechnete Grundparameter. Die theoretische Analyse wurde unter der Voraussetzung durchgefuhrt, das kein Transport des zu kristallisierenden Stoffes parallel der Kristallflache stattfindet. Die Berechnungen beruhen auf dem Unterschied in der Dicke der Nernst'schen Diffusionsschicht uber die verschiedenen Bereiche der wachsenden Kristallflache — eine experimentell (interferometrisch) leicht mesbare Grose.

How to Manage a Crystallization Process Aimed at Obtaining a Desired Combination of Number of Crystals and Their Distribution by Size: Learn Here

Crystal Research and Technology, Jan 18, 2021

Managing a crystallization process adequately, it is possible to obtain a crystalline product hav... more Managing a crystallization process adequately, it is possible to obtain a crystalline product having the desired crystal size distribution. Recommendations for selecting crystallization parameters that are needed to achieve this goal are given basing of a theoretical analysis in which special attention is paid to the growth of crystals from solutions with a preset concentration. Mathematical equations which enable calculation of the theoretical yield for the crystallization process have been elaborated. New formula giving the crystal nuclei number per unit volume as a function of both supersaturation and nucleation time has been devised based on the logistic kinetics of crystal nucleation proceeding under constant supersaturation. The quantitative relation between number density and mean size of crystals growing in batch crystallization is calculated. The calculation shows that the mean size of crystals reached at any time of their growth is inversely proportional to root third of the crystal number density.

Acta Physica Academiae Scientiarum Hungaricae, Oct 1, 1979

The method of direct synthesis of A 11 B VI thin layers on metal single crystal substrates enable... more The method of direct synthesis of A 11 B VI thin layers on metal single crystal substrates enables us to obtain the whole set of compounds of Zn and Cd with S, Se and Te. The morphology and the structure (texture and epitaxy) of the layers were investigated by means of TEM, SEM, X-ray and electron diffraction methods. The epitaxial layers have been synthesized at relatively low temperatures on the basal faces of the supporting single crystals.

Direct synthesis of epitaxial zinc sulphide layers on zinc single-crystal substrates

Thin Solid Films, Jun 1, 1976

Abstract Epitaxial thin zinc sulphide layers have been grown by direct synthesis on the basal fac... more Abstract Epitaxial thin zinc sulphide layers have been grown by direct synthesis on the basal face of zinc single crystals. Sulphur vapour reacted on the surface of the crystals, which were grown in sealed glass ampoules evacuated to 10−6 torr. The thicknesses of the layers investigated varied from several hundred to 1000–1500 A. The morphology, structure and epitaxy of the films were examined by electron microscope, electron and X-ray diffraction techniques. It was found that the film lattice had a sphalerite-type cubic structure, the perfection of the layer structure increasing with rise in both the substrate temperature and the sulphur vapour pressure. The layers were produced at substrate temperatures of 250°–400°C: polycrystalline ZnS films were obtained in the range 250°–300°C; at higher temperatures a definite texture gradually appeared and above 370°C, with a sulphur vapour pressure of 0.2–10 torr, the films became epitaxial. The following epitaxial relation was established: {111} ZnS ∥ {0001} Zn with ZnS ∥ 20 > Zn The zinc sulphide films reproduced the surface structure of the supporting zinc single crystals very well and could conveniently be used as electron microscope replicas.

Progress in Crystal Growth and Characterization of Materials, May 1, 2020

Balance between crystal bond energy and destructive surface energies Supersaturation dependence o... more Balance between crystal bond energy and destructive surface energies Supersaturation dependence of crystal nucleus size Protein crystal nucleation in pores Hydrophobicity assisted protein crystallization Kinetics of protein crystal nucleation comparison with small-molecule crystallization Logistic dependence of nuclei number density on nucleation time Crystal size distribution resulting from batch crystallization Biochemical aspects of protein crystal nucleation Bond selection mechanism (BSM) Electric field effects on the protein crystallization Monte Carlo simulations of crystal polymorph selection A B S T R A C T energies (tending to tear-up the crystal) is revisited first. Examples of EBDE application are following, such as studies of protein crystal nucleation in pores [2] (with emphasis put on closest-packed crystals) and hydrophobicity assisted protein crystallization [3]. Then, some kinetic rules, which govern both small-molecule and protein crystallization, are presented. Firstly, a logistic functional dependence of nuclei number density on nucleation time has been observed and explained theoretically. On this basis, some crystallization aspects (such as supersaturation dependence of crystal nuclei number density at fixed

Silver-Mercury Whiskers

De Gruyter eBooks, Dec 31, 1972

Recent experimental and theoretical studies on protein crystallization

Crystal Research and Technology, Sep 20, 2016

Crystals are required to determine three‐dimensional structures of proteins and other bio‐molecul... more Crystals are required to determine three‐dimensional structures of proteins and other bio‐molecules via X‐ray diffraction. This is the prime cause for the keen interest in protein crystallization. Recently published experimental and theoretical studies on protein crystal nucleation and growth are reviewed, and the prospects of protein‐based crystalline pharmaceuticals mass‐production are considered. A new insight into protein crystal nucleation is presented from a physical perspective. It refers to modeling nuclei number density as a definite (curved) surface where each point has two coordinates, supersaturation and time. In doing so, theoretical S‐shaped dependences of nuclei number densities on both supersaturation and time are found. These dependences are confirmed experimentally by plotting insulin crystal nucleation data. Growth of protein crystals of narrow size distribution is monitored to establish crystal polydispersity cause. Ostwald ripening is considered as a post‐growth stage of the crystallization process.

Journal of Crystal Growth, Oct 1, 2015

A non-linear differential equation expressing the new phase nucleation rate in the different step... more A non-linear differential equation expressing the new phase nucleation rate in the different steps of the process (non-stationary and stationary nucleation and in the plateau region) is derived from basic principles of the nucleation theory. It is shown that one and the same sigmoid (logistic) function describes both nucleation scenarios: the one according to the classical theory, and the other according to the modern two-stage mechanism of protein crystal formation. Comparison to experimental data on both insulin crystal nucleation kinetics and on bovine β-lactoglobulin crystallization indicates a good agreement with the sigmoidal prediction. Experimental data for electrochemical nucleation and glass crystallization obey the same sigmoid time dependence, and suggest universality of this nucleation kinetics law.

Journal of Crystal Growth, 1968

The process of formation of cavities on the surface of zinc single diffusion in the gas phase. Th... more The process of formation of cavities on the surface of zinc single diffusion in the gas phase. The critical size above which the crystals upon growth from the vapour in the presence of hydrogen formation of a cavity occurs was established experimentally. The is investigated. This effect is considered to be due, according to results obtained are in accord with the theoretical values calcuthe kinematic theory of the growth forms of crystals, to non-lated using Chemov's estimate. homogeneity in the supersaturation which occurs as a result of

Crystal Size Distribution Resulting from the Time Dependence of Crystal Nucleation

Crystal Research and Technology, Mar 13, 2018

Most of the experimental studies show that new‐phase nucleation runs over prolonged time periods ... more Most of the experimental studies show that new‐phase nucleation runs over prolonged time periods rather than instantaneously. After crystals nucleate, they start growing immediately. Therefore, the earlier a crystal nucleates, the larger it grows. This instigates a definite crystal size distribution (CSD). The resulting (from the initial crystal growth during the nucleation stage) CSD is calculated from the logistic time dependence of crystal number density. Having the shape of an ogee curve, CSD remains practically unchanged during the following crystal growth stage until the onset of Ostwald ripening. Only earlier born (and hence larger) crystals survive during the Ostwald ripening; the smallest crystals, which are the last born species, are dissolved. As far as the logistic dependence of crystal nuclei number density vs. nucleation time explains small molecule and protein crystallization, the calculated CSD should also describe crystallization of both small and large bio‐molecules.

Physica Status Solidi B-basic Solid State Physics, 1966

Inatitut fur Physikaliache Chemie a h BulgariscLn Akademie dpr Wiasenachaften, Sofia Elektronenmi... more Inatitut fur Physikaliache Chemie a h BulgariscLn Akademie dpr Wiasenachaften, Sofia Elektronenmikroskopische Untersuchung der Wachstumsmorphologie von Zink-und Kadmiumeinkristallen Von CIIR. NAKEV Es wird iiber eine nach dem Platin-Kohlc-Abdruckvcrfahrcn durchgefiihrte elektronenmikroskopisehe Untersuchung der Oberfliiehenmorphologie von Zink-und Kadmiumeinkristallen berichtet. Die Kristalle werden unter best.immten Bedingungen aus der Dampfphase geziichtet. Die Untersuchung zeigt, daB die Oberflaehenstruktur der Kristalle von den Wachstumsbedingungen abhiingt. Die Temperaturabhangigkeit der Gleichgewichtsform der Kristalle wird gekliirt und auf dieser Basis eine gute Ubereinstimmung der experimentellen Daten mit friiheren Ergebnissen iibcr die Gleichgewichtsformen VOD Zink [3] gefunden, die dureh direkte mikroskopische Beobachtung der Anfangswaehstumsformen erhalten wurdcn. The platinum-carbon replica technique is used to study the surface morphology of zinc and cadmium single-crystals grown under definite conditions from their vapours. It is shown that the surface relief depends on the growth conditions. Special attention is given to the temperature dependence of the equilibrium form of the crystals. I n this connection an explanation is given of the good agreement between the experimental data and the result,s obtained previously when the equilibrium form was determined by direct microscopic observations of the initial growth forms [3].

Growth of Zinc and Cadmium Whiskers from the Vapour Phase on a Single Crystal Substrate of the Same Material

Physica Status Solidi B-basic Solid State Physics, 1967

A determination is made of the crystallographic orientation of zinc and cadmium whiskers grown on... more A determination is made of the crystallographic orientation of zinc and cadmium whiskers grown on single crystal substrates of the same substances which have well‐formed faces, edges and tips. Zinc and cadmium whiskers grown in this way in the presence of hydrogen or argon are oriented as 〈1120〉, however zinc whiskers grown in vacuum have the orientation 〈1123〉. These are in fact the directions of the screw dislocations in the lattice. These and other results indicate that the whiskers grow preferentially via a screw dislocation mechanism. Some cases are observed in which zinc “whiskers” grow at large supersaturations without involving a surface diffusion mechanism as required by the classical theory of whisker growth. Possible causes for the appearance of whiskers on a single crystal substrate are discussed, as well as the factors which determine their orientation.

Untersuchung über die Gleichgewichtsformen von Zinkeinkristallen Von

Physica Status Solidi B-basic Solid State Physics, 1965

Es wird die experimentelle und theoretische Bestimmung der Gleichgewichtsformen von Zinkeinkrista... more Es wird die experimentelle und theoretische Bestimmung der Gleichgewichtsformen von Zinkeinkristallen in Abhängigkeit von der Übersättigung behandelt. Zur Untersuchung des Wachstums der Zinkeinkristalle aus ihrer eigenen Dampfphase wird eine Apparatur beschrieben, die es ermöglicht, störende Keimbildung bei größeren Übersättigungen zu vermeiden. Dadurch war es möglich, eine Übersättigungsschwelle – gemessen als eine Temperaturdifferenz ΔT1 = 7,5 ± 0,5 °C zwischen dem wachsenden Einkristall und dem verdampfenden Zinkvorrat – nachzuweisen, oberhalb derer die Flächen {1012} und {1120} in der Gleichgewichtsform nicht mehr auftreten. Dieses Versuchsergebnis wird vom Standpunkt der Kristallwachstumstheorie nach Stranski und Kaischew diskutiert. Man erhält unter der Annahme, daß die Bindungsenergie zwischen den Bausteinen des Kristallgitters eine Potenzfunktion des reziproken Atomabstandes ist, als Exponent n dieser Funktion. den Wert 7,5 ± 0,3. Mit diesem Wert wird die Temperaturdifferenz ΔT2 = 2,1 ± 0,3 °C berechnet, unterhalb welcher in der Gleichgewichtsform des Zinks noch zusätzlich die Flächen {1121} und {1122} erscheinen müssen.

International Journal of Molecular Sciences, Sep 14, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Kristall und Technik, 1975

ifber das Wachstum von Silberamalgamwhiskern Das Wachstum von nadelformigen Einkristallen aus Sil... more ifber das Wachstum von Silberamalgamwhiskern Das Wachstum von nadelformigen Einkristallen aus Silberamalgam (s. g. Whisker) wurde untersucht. Sie wurden geziichtet aus waBrigen Losungen auf einer Queclisilberoberfliiche durch eine Art von Innenelektrolyse. Die Whisker sind mit Quecksilber gefullte hexagonale Kapillarrohrchen. Es wurde eine potentiostatische Methode entwickelt, mit deren Hilfe die Ubersattigung bzw. die Uberspannung, unter welcher die Whisker wuchscn, bestimmt wurde. Dieselbe Methodc bictet weiterhin auch eine Moglichkeit zur Steuerung des Whiskerwachstumsprozesses.

Kristall und Technik, 1967

Iastitut far Physilmliseb Clmmio dt& Bulgarisohon Akadcmie derWiRscnschaften, Sofia Morphologie d... more Iastitut far Physilmliseb Clmmio dt& Bulgarisohon Akadcmie derWiRscnschaften, Sofia Morphologie des Hristallwachstums in Anwesenheit von Schrmbenversehungen H e m Prof. Dr. 1. Rexer zum 65. G e b u w g gewidmct Es wird fiber eine nach der KapiIlarmethode (KAISCHEW, BLIZNAKOV, SELUDKO; BOSTANOV, KOEEVA, BUDEVSKX; BUDEVSKI, BOSTANOV, VITANOV, STOJNOV, K O~E V A , KAISCHE W) durchgefiihrte Untemuchung der Waahstume-und Auflbungsmorphologie bei der Elektrokrisbllisation des Silbers berichtet und eine Impulamethode zur Bestimmung der Form und der AusbreitungsSsschwindigkeit von Spiralwachstumsfronten beachrieben. Duroh anodische (Auflosungs-) Impulse werden sowohl die Schrauben-und Stufsnverwtaungen ds auch die fremden Teilchen cntwickelt, die in den Tiilern zwiwhen den Spirslwechstumshiigeln eingeschlossen sitid. Eine Methode zur Bestimmung der Fortsetzungsrichtung von Schraubenvcrsetzungeri beim elcktrolytischen Kristallwachstum wurde entwickelt. Nach dieser Methode wurde in tfbereinstimmung mit der Theorie [ 1101 als hiiufigste Richtung dcr Schraubenversetzungen in Silberkristallen gefrinden.

Journal of Crystal Growth, Dec 1, 2017

The use of the classical nucleation-growth-separation principle (NGSP) was restricted hitherto to... more The use of the classical nucleation-growth-separation principle (NGSP) was restricted hitherto to nucleation kinetics studies only. A novel application of the NGSP is proposed. To reduce crystal polydispersity internal seeding of equally-sized crystals is suggested, the advantage being avoidance of crystal grinding, sieving and any introduction of impurities. In the present study, size distributions of grown insulin crystals are interpreted retrospectively to select the proper nucleation stage parameters. The conclusion is that when steering a crystallization process aimed at reducing crystal polydispersity, the shortest possible nucleation stage duration has to be chosen because it renders the closest size distribution of the nucleated crystal seeds. Causes of inherent propensity to increasing crystal polydispersity during prolonged growth are also explored. Step sources of increased activity, present in some crystals while absent in others, are pointed as the major polydispersity cause. Insulin crystal morphology is also considered since it determines the dissolution rate of a crystalline medicine.

De Gruyter eBooks, Dec 31, 1972

Silver-Mercury Whiskers

De Gruyter eBooks, Dec 31, 1972

Physica status solidi, Jul 16, 1973

Uber eine Moglichkeit zur Ziichtung von Zinkeinkristallen hoher Perfektion Von CHR. NANEV (a) und... more Uber eine Moglichkeit zur Ziichtung von Zinkeinkristallen hoher Perfektion Von CHR. NANEV (a) und H. WADEWITZ (b) I n Erweiterung einer von Stranski, Kaischew und Mitarbeitern entwicketten Methode zur Ziichtung von Zinkeinkristallen im Innern einer Glasampulle geliagt es durch Aufdampfen einer Kohleschicht als Unterlage fur die aus der Schmelze, und weiter aus der Dampfphase, zu zuchtenden Kristalle, Einkristalle hoher Perfektion herzustellen. Durch Berg-Barrett-Aufnahmen wird nachgewiesen, daO die auf einer Kohleschicht gewachsenen Zinkeinkristalle gegenuber den direkt auf Glas gewachsenen keine Subkorngrenzen enthalten. The method of growing of zinc single crystals in a glass ampoule by freezing of molten drops and further growth from own vapours, previously described by Stranski, Kaischew and co-workers, is improved. The crystals are grown on thin vacuum deposited carbon films covering the glass which ensured the production of more perfect crystals. Contrary to the crystals obtained directly on glass support, the zinc single crystals on carbon film substrate did not contain Iow-angle boundaries as shown by Berg-Barrett X-ray topography.

On the Morphological Instability of Growing Crystals (I) Morphological Peculiarities of the Transition Shapes of Crystals in Diffusioncontrolled Regime of Growth

De Gruyter eBooks, Dec 31, 1988

The shape and size of the gross morphological defect which occurs (in the form of a depression) a... more The shape and size of the gross morphological defect which occurs (in the form of a depression) as a result of the diffusion inhomogeneity in the matter supply on the growing crystal face with supercritical dimensions are investigated. The transition shapes of similar skeletal crystal faces are determined by considering the configuration of the steps which are moving (and accumulating) from the edge toward the centre of the crystal face. The basic parameter which is evaluated, is the width of the macroscopically flat periphery which grows around the depression and its alteration when the crystal is enlarged. The theoretical analysis is carried out by presuming that no transportation of crystallizing material occurs parallel to the crystal face. The calculations are based on the different thicknesses of the Nernst diffusion layer, a magnitude which can be easily determined experimentally by some interferometric technique, over the various regions of the growing face. Es werden die Beschaffenheit und die Ausdehnung des groben morphologischen Defekts untersucht, welcher infolge der diffusions-bedingten Ubersattigungsinhomogenitat auf den Kristallflachen uberkritischer Grose (in der Form einer Vertiefung) entsteht. Die Ubergangsformen solcher skelettartigen Kristallflachen werden auf Grund der Stufenkonfigurationen bestimmt, welche bei der Bewegung (und Anhaufung) der auf den Kristallecken entstandenen und sich in Richtung Flachenmitte bewegenden Wachstumsstufen auftreten. Die Breite der um der Vertiefung wachsenden makroskopisch ebenen Peripherie und ihre Veranderung mit der Vergroserung des Kristalls ist der berechnete Grundparameter. Die theoretische Analyse wurde unter der Voraussetzung durchgefuhrt, das kein Transport des zu kristallisierenden Stoffes parallel der Kristallflache stattfindet. Die Berechnungen beruhen auf dem Unterschied in der Dicke der Nernst'schen Diffusionsschicht uber die verschiedenen Bereiche der wachsenden Kristallflache — eine experimentell (interferometrisch) leicht mesbare Grose.

How to Manage a Crystallization Process Aimed at Obtaining a Desired Combination of Number of Crystals and Their Distribution by Size: Learn Here

Crystal Research and Technology, Jan 18, 2021

Managing a crystallization process adequately, it is possible to obtain a crystalline product hav... more Managing a crystallization process adequately, it is possible to obtain a crystalline product having the desired crystal size distribution. Recommendations for selecting crystallization parameters that are needed to achieve this goal are given basing of a theoretical analysis in which special attention is paid to the growth of crystals from solutions with a preset concentration. Mathematical equations which enable calculation of the theoretical yield for the crystallization process have been elaborated. New formula giving the crystal nuclei number per unit volume as a function of both supersaturation and nucleation time has been devised based on the logistic kinetics of crystal nucleation proceeding under constant supersaturation. The quantitative relation between number density and mean size of crystals growing in batch crystallization is calculated. The calculation shows that the mean size of crystals reached at any time of their growth is inversely proportional to root third of the crystal number density.

Acta Physica Academiae Scientiarum Hungaricae, Oct 1, 1979

The method of direct synthesis of A 11 B VI thin layers on metal single crystal substrates enable... more The method of direct synthesis of A 11 B VI thin layers on metal single crystal substrates enables us to obtain the whole set of compounds of Zn and Cd with S, Se and Te. The morphology and the structure (texture and epitaxy) of the layers were investigated by means of TEM, SEM, X-ray and electron diffraction methods. The epitaxial layers have been synthesized at relatively low temperatures on the basal faces of the supporting single crystals.

Direct synthesis of epitaxial zinc sulphide layers on zinc single-crystal substrates

Thin Solid Films, Jun 1, 1976

Abstract Epitaxial thin zinc sulphide layers have been grown by direct synthesis on the basal fac... more Abstract Epitaxial thin zinc sulphide layers have been grown by direct synthesis on the basal face of zinc single crystals. Sulphur vapour reacted on the surface of the crystals, which were grown in sealed glass ampoules evacuated to 10−6 torr. The thicknesses of the layers investigated varied from several hundred to 1000–1500 A. The morphology, structure and epitaxy of the films were examined by electron microscope, electron and X-ray diffraction techniques. It was found that the film lattice had a sphalerite-type cubic structure, the perfection of the layer structure increasing with rise in both the substrate temperature and the sulphur vapour pressure. The layers were produced at substrate temperatures of 250°–400°C: polycrystalline ZnS films were obtained in the range 250°–300°C; at higher temperatures a definite texture gradually appeared and above 370°C, with a sulphur vapour pressure of 0.2–10 torr, the films became epitaxial. The following epitaxial relation was established: {111} ZnS ∥ {0001} Zn with ZnS ∥ 20 > Zn The zinc sulphide films reproduced the surface structure of the supporting zinc single crystals very well and could conveniently be used as electron microscope replicas.

Progress in Crystal Growth and Characterization of Materials, May 1, 2020

Balance between crystal bond energy and destructive surface energies Supersaturation dependence o... more Balance between crystal bond energy and destructive surface energies Supersaturation dependence of crystal nucleus size Protein crystal nucleation in pores Hydrophobicity assisted protein crystallization Kinetics of protein crystal nucleation comparison with small-molecule crystallization Logistic dependence of nuclei number density on nucleation time Crystal size distribution resulting from batch crystallization Biochemical aspects of protein crystal nucleation Bond selection mechanism (BSM) Electric field effects on the protein crystallization Monte Carlo simulations of crystal polymorph selection A B S T R A C T energies (tending to tear-up the crystal) is revisited first. Examples of EBDE application are following, such as studies of protein crystal nucleation in pores [2] (with emphasis put on closest-packed crystals) and hydrophobicity assisted protein crystallization [3]. Then, some kinetic rules, which govern both small-molecule and protein crystallization, are presented. Firstly, a logistic functional dependence of nuclei number density on nucleation time has been observed and explained theoretically. On this basis, some crystallization aspects (such as supersaturation dependence of crystal nuclei number density at fixed

Silver-Mercury Whiskers

De Gruyter eBooks, Dec 31, 1972

Recent experimental and theoretical studies on protein crystallization

Crystal Research and Technology, Sep 20, 2016

Crystals are required to determine three‐dimensional structures of proteins and other bio‐molecul... more Crystals are required to determine three‐dimensional structures of proteins and other bio‐molecules via X‐ray diffraction. This is the prime cause for the keen interest in protein crystallization. Recently published experimental and theoretical studies on protein crystal nucleation and growth are reviewed, and the prospects of protein‐based crystalline pharmaceuticals mass‐production are considered. A new insight into protein crystal nucleation is presented from a physical perspective. It refers to modeling nuclei number density as a definite (curved) surface where each point has two coordinates, supersaturation and time. In doing so, theoretical S‐shaped dependences of nuclei number densities on both supersaturation and time are found. These dependences are confirmed experimentally by plotting insulin crystal nucleation data. Growth of protein crystals of narrow size distribution is monitored to establish crystal polydispersity cause. Ostwald ripening is considered as a post‐growth stage of the crystallization process.

Journal of Crystal Growth, Oct 1, 2015

A non-linear differential equation expressing the new phase nucleation rate in the different step... more A non-linear differential equation expressing the new phase nucleation rate in the different steps of the process (non-stationary and stationary nucleation and in the plateau region) is derived from basic principles of the nucleation theory. It is shown that one and the same sigmoid (logistic) function describes both nucleation scenarios: the one according to the classical theory, and the other according to the modern two-stage mechanism of protein crystal formation. Comparison to experimental data on both insulin crystal nucleation kinetics and on bovine β-lactoglobulin crystallization indicates a good agreement with the sigmoidal prediction. Experimental data for electrochemical nucleation and glass crystallization obey the same sigmoid time dependence, and suggest universality of this nucleation kinetics law.

Journal of Crystal Growth, 1968

The process of formation of cavities on the surface of zinc single diffusion in the gas phase. Th... more The process of formation of cavities on the surface of zinc single diffusion in the gas phase. The critical size above which the crystals upon growth from the vapour in the presence of hydrogen formation of a cavity occurs was established experimentally. The is investigated. This effect is considered to be due, according to results obtained are in accord with the theoretical values calcuthe kinematic theory of the growth forms of crystals, to non-lated using Chemov's estimate. homogeneity in the supersaturation which occurs as a result of

Crystal Size Distribution Resulting from the Time Dependence of Crystal Nucleation

Crystal Research and Technology, Mar 13, 2018

Most of the experimental studies show that new‐phase nucleation runs over prolonged time periods ... more Most of the experimental studies show that new‐phase nucleation runs over prolonged time periods rather than instantaneously. After crystals nucleate, they start growing immediately. Therefore, the earlier a crystal nucleates, the larger it grows. This instigates a definite crystal size distribution (CSD). The resulting (from the initial crystal growth during the nucleation stage) CSD is calculated from the logistic time dependence of crystal number density. Having the shape of an ogee curve, CSD remains practically unchanged during the following crystal growth stage until the onset of Ostwald ripening. Only earlier born (and hence larger) crystals survive during the Ostwald ripening; the smallest crystals, which are the last born species, are dissolved. As far as the logistic dependence of crystal nuclei number density vs. nucleation time explains small molecule and protein crystallization, the calculated CSD should also describe crystallization of both small and large bio‐molecules.

Physica Status Solidi B-basic Solid State Physics, 1966

Inatitut fur Physikaliache Chemie a h BulgariscLn Akademie dpr Wiasenachaften, Sofia Elektronenmi... more Inatitut fur Physikaliache Chemie a h BulgariscLn Akademie dpr Wiasenachaften, Sofia Elektronenmikroskopische Untersuchung der Wachstumsmorphologie von Zink-und Kadmiumeinkristallen Von CIIR. NAKEV Es wird iiber eine nach dem Platin-Kohlc-Abdruckvcrfahrcn durchgefiihrte elektronenmikroskopisehe Untersuchung der Oberfliiehenmorphologie von Zink-und Kadmiumeinkristallen berichtet. Die Kristalle werden unter best.immten Bedingungen aus der Dampfphase geziichtet. Die Untersuchung zeigt, daB die Oberflaehenstruktur der Kristalle von den Wachstumsbedingungen abhiingt. Die Temperaturabhangigkeit der Gleichgewichtsform der Kristalle wird gekliirt und auf dieser Basis eine gute Ubereinstimmung der experimentellen Daten mit friiheren Ergebnissen iibcr die Gleichgewichtsformen VOD Zink [3] gefunden, die dureh direkte mikroskopische Beobachtung der Anfangswaehstumsformen erhalten wurdcn. The platinum-carbon replica technique is used to study the surface morphology of zinc and cadmium single-crystals grown under definite conditions from their vapours. It is shown that the surface relief depends on the growth conditions. Special attention is given to the temperature dependence of the equilibrium form of the crystals. I n this connection an explanation is given of the good agreement between the experimental data and the result,s obtained previously when the equilibrium form was determined by direct microscopic observations of the initial growth forms [3].

Growth of Zinc and Cadmium Whiskers from the Vapour Phase on a Single Crystal Substrate of the Same Material

Physica Status Solidi B-basic Solid State Physics, 1967

A determination is made of the crystallographic orientation of zinc and cadmium whiskers grown on... more A determination is made of the crystallographic orientation of zinc and cadmium whiskers grown on single crystal substrates of the same substances which have well‐formed faces, edges and tips. Zinc and cadmium whiskers grown in this way in the presence of hydrogen or argon are oriented as 〈1120〉, however zinc whiskers grown in vacuum have the orientation 〈1123〉. These are in fact the directions of the screw dislocations in the lattice. These and other results indicate that the whiskers grow preferentially via a screw dislocation mechanism. Some cases are observed in which zinc “whiskers” grow at large supersaturations without involving a surface diffusion mechanism as required by the classical theory of whisker growth. Possible causes for the appearance of whiskers on a single crystal substrate are discussed, as well as the factors which determine their orientation.

Untersuchung über die Gleichgewichtsformen von Zinkeinkristallen Von

Physica Status Solidi B-basic Solid State Physics, 1965

Es wird die experimentelle und theoretische Bestimmung der Gleichgewichtsformen von Zinkeinkrista... more Es wird die experimentelle und theoretische Bestimmung der Gleichgewichtsformen von Zinkeinkristallen in Abhängigkeit von der Übersättigung behandelt. Zur Untersuchung des Wachstums der Zinkeinkristalle aus ihrer eigenen Dampfphase wird eine Apparatur beschrieben, die es ermöglicht, störende Keimbildung bei größeren Übersättigungen zu vermeiden. Dadurch war es möglich, eine Übersättigungsschwelle – gemessen als eine Temperaturdifferenz ΔT1 = 7,5 ± 0,5 °C zwischen dem wachsenden Einkristall und dem verdampfenden Zinkvorrat – nachzuweisen, oberhalb derer die Flächen {1012} und {1120} in der Gleichgewichtsform nicht mehr auftreten. Dieses Versuchsergebnis wird vom Standpunkt der Kristallwachstumstheorie nach Stranski und Kaischew diskutiert. Man erhält unter der Annahme, daß die Bindungsenergie zwischen den Bausteinen des Kristallgitters eine Potenzfunktion des reziproken Atomabstandes ist, als Exponent n dieser Funktion. den Wert 7,5 ± 0,3. Mit diesem Wert wird die Temperaturdifferenz ΔT2 = 2,1 ± 0,3 °C berechnet, unterhalb welcher in der Gleichgewichtsform des Zinks noch zusätzlich die Flächen {1121} und {1122} erscheinen müssen.

International Journal of Molecular Sciences, Sep 14, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Kristall und Technik, 1975

ifber das Wachstum von Silberamalgamwhiskern Das Wachstum von nadelformigen Einkristallen aus Sil... more ifber das Wachstum von Silberamalgamwhiskern Das Wachstum von nadelformigen Einkristallen aus Silberamalgam (s. g. Whisker) wurde untersucht. Sie wurden geziichtet aus waBrigen Losungen auf einer Queclisilberoberfliiche durch eine Art von Innenelektrolyse. Die Whisker sind mit Quecksilber gefullte hexagonale Kapillarrohrchen. Es wurde eine potentiostatische Methode entwickelt, mit deren Hilfe die Ubersattigung bzw. die Uberspannung, unter welcher die Whisker wuchscn, bestimmt wurde. Dieselbe Methodc bictet weiterhin auch eine Moglichkeit zur Steuerung des Whiskerwachstumsprozesses.

Kristall und Technik, 1967

Iastitut far Physilmliseb Clmmio dt& Bulgarisohon Akadcmie derWiRscnschaften, Sofia Morphologie d... more Iastitut far Physilmliseb Clmmio dt& Bulgarisohon Akadcmie derWiRscnschaften, Sofia Morphologie des Hristallwachstums in Anwesenheit von Schrmbenversehungen H e m Prof. Dr. 1. Rexer zum 65. G e b u w g gewidmct Es wird fiber eine nach der KapiIlarmethode (KAISCHEW, BLIZNAKOV, SELUDKO; BOSTANOV, KOEEVA, BUDEVSKX; BUDEVSKI, BOSTANOV, VITANOV, STOJNOV, K O~E V A , KAISCHE W) durchgefiihrte Untemuchung der Waahstume-und Auflbungsmorphologie bei der Elektrokrisbllisation des Silbers berichtet und eine Impulamethode zur Bestimmung der Form und der AusbreitungsSsschwindigkeit von Spiralwachstumsfronten beachrieben. Duroh anodische (Auflosungs-) Impulse werden sowohl die Schrauben-und Stufsnverwtaungen ds auch die fremden Teilchen cntwickelt, die in den Tiilern zwiwhen den Spirslwechstumshiigeln eingeschlossen sitid. Eine Methode zur Bestimmung der Fortsetzungsrichtung von Schraubenvcrsetzungeri beim elcktrolytischen Kristallwachstum wurde entwickelt. Nach dieser Methode wurde in tfbereinstimmung mit der Theorie [ 1101 als hiiufigste Richtung dcr Schraubenversetzungen in Silberkristallen gefrinden.

Journal of Crystal Growth, Dec 1, 2017

The use of the classical nucleation-growth-separation principle (NGSP) was restricted hitherto to... more The use of the classical nucleation-growth-separation principle (NGSP) was restricted hitherto to nucleation kinetics studies only. A novel application of the NGSP is proposed. To reduce crystal polydispersity internal seeding of equally-sized crystals is suggested, the advantage being avoidance of crystal grinding, sieving and any introduction of impurities. In the present study, size distributions of grown insulin crystals are interpreted retrospectively to select the proper nucleation stage parameters. The conclusion is that when steering a crystallization process aimed at reducing crystal polydispersity, the shortest possible nucleation stage duration has to be chosen because it renders the closest size distribution of the nucleated crystal seeds. Causes of inherent propensity to increasing crystal polydispersity during prolonged growth are also explored. Step sources of increased activity, present in some crystals while absent in others, are pointed as the major polydispersity cause. Insulin crystal morphology is also considered since it determines the dissolution rate of a crystalline medicine.

De Gruyter eBooks, Dec 31, 1972