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Thin SixCyNz:H coatings deposited with the RF PECVD method

Oleśko K., Szymanowski H., Gazicki-Lipman M., Balcerzak J., Sobczyk-Guzenda A.

Inżynieria Materiałowa

2018

Vol. 39, nr 4

140--147

Coatings of hydrogenated silicon nitride and silicon carbonitride find numerous applications stemming from their various useful properties which can be easily modified during the deposition process. In this work, the effect of discharge power on the physical properties of the coatings synthesized from organosilicone precursors is presented. Compared to explosively flammable silane, these precursors are safe and do not require costly safety measures installed in the equipment. The coatings investigated were deposited from hexamethyldisilazane (HMDSN) using radiofrequency plasma enhanced chemical vapour deposition in an atmosphere of such working gases as nitrogen, ammonia and hydrogen. HMDSN constitutes a valuable precursor since its saturated vapour pressure is relatively high (1.8 kPa at 25°C) and its molecule contains both silicon and nitrogen atoms. The coatings synthesized were broadly investigated with the help of such analytical techniques as variable angle spectroscopic ellipsometry (VASE), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The effect of the glow discharge power on the coatings chemical structure and, therefore, on the magnitude of their refractive index was studied. It has been demonstrated that the discharge power strongly affects quantitative proportions between Si–N, Si–NH–Si, Si–O chemical bonds in the resulting films which, in turn, determine their index of refraction.

Celem pracy było wytworzenie uwodornionych powłok węglikoazotku krzemu (SixNyCz:H) i zbadanie ich składu, struktury oraz właściwości optycznych. Materiały te są planowane jako składnik o wysokiej wartości współczynnika załamania światła (n) filtra optycznego z gradientem tego współczynnika. Składnikiem o małym współczynniku n będzie w tym układzie powłoka SiOxCy:H. Przejście od jednego materiału do drugiego będzie można uzyskać przez zmianę składu gazowej mieszaniny reakcyjnej z NH3/N2 na O2, przy zachowaniu stałego przepływu par prekursora krzemorganicznego. W pracy jako związek wyjściowy dla krzemu wykorzystano heksametylodisilazan (HMDSN). Do wytwarzania tego typu powłok metodą RF PECVD (Radio Frequency Plasma Enhanced Chemical Vapour Desposition) najczęściej jest stosowany silan (SiH4). Ze względu na to, że jest to gaz wybuchowy doskonałą alternatywę dla tego prekursora stanowią związki krzemoorganiczne. We wcześniejszych badaniach autorów nad powłokami SixNyCz otrzymanymi z HMDSN, w optymalnych warunkach nanoszenia warstw uzyskano współczynnik n na poziomie 1,9. Głównym powodem tak małej wartości n była pozostałość ugrupowań węglowych w strukturze powłoki pochodzących od zastosowanego związku wyjściowego. Z punktu widzenia przyszłych zastosowań tych powłok jest to stanowczo za mała wartość. Z tego powodu zostały podjęte próby zwiększenia wartości współczynnika n przez dodawanie do mieszaniny reakcyjnej wodoru.

Zastosowanie topologicznej analizy gęstości elektronowej do opisu oddziaływań niekowalencyjnych

Bankiewicz B., Rybarczyk-Pirek A., Małecka M., Domagała M., Palusiak M.

Wiadomości Chemiczne

2014

[Z] 68, 5-6

457--486

All atomic and molecular properties are governed by an electron density distribution. Thus, the methods that deal with an analysis of the electron density distribution should have a particular appeal for chemists and help to understand the electron structure of molecules. The Quantum Theory of Atoms in Molecules gives the unique opportunity to have an insight into a region (e.g., an atom) of a given system (e.g. a molecule), delivering partitioning scheme which is defined explicitly within the rigorous quantum theory, from one side, and is applicable for experimentally available set of observables, from the other side. In that way QTAIM delivers a chemist a theoretical tool to study a small part of a molecule only, instead of dealing with the total energy of a whole system. In consequence, QTAIM has become one of the most powerful utilities of modern chemistry, forming a bridge between advanced theoretical and experimental techniques. In particular the properties of the electron density function in the so-called bond critical point (BCP, the (3, -1) saddle point on electron density curvature) seem to be valuable information for chemists, since it was proven in many papers that the chemical bonding can be characterized and classified on the basis of electron density characteristics measured in BCPs . In this review we firstly give a brief introduction to the theory, explaining most basic terms and dependences. In the main part of the review we discuss application of QTAIM in the qualitative and quantitative analysis of several various noncovalent interactions, focusing readers attention on such aspects as classification of interactions and interaction energy assessment. Both theoretical and experimental approaches are taken into account. We also discuss extensions of QTAIM to the analysis of the so called source function – the method which additionally enlarge interpretative possibilities of its parent theory. Finally, we give some examples which perhaps escape a rigorous QTAIM definition of chemical bonding. We acquaint the potential reader with arguments being pro- and against the QTAIM-based deterministic model of a chemical bond.

Local electronic and charge state of iron in FeTe2

Stanek J., Fornal P.

Nukleonika

2004

Vol. 49,suppl.3

63-65

From 57Fe Mössbauer spectrum of FeTe2 taken in high external magnetic field (B = 4.6 T), the sign of electric field gradient was determined as negative, with an asymmetry parameter of 0.2. A comparison of these data with results of calculation of the electric field gradient within point charge model suggests the lattice character of electric field gradient with some contribution from covalency effects. The effective magnetic field acting on 57Fe is less than the applied, which points out the diamagnetic Fe+2 state of iron. This "electronic state" is in a contradiction to Fe+3 "charge state" concluded from 125Te experiments on 3d transition metal ditellurides as well as from 57Fe quadrupole splitting and isomer shift.