STRUCTURAL AND ELECTRONIC PROPERTIES OF CVD SILICON FILMS NEAR THE CRYSTALLIZATION TEMPERATURE

Nous avons examiné les propriétés structurales de films déposés par C.V.D. dans la gamme de température 600-750°C avec une attention particulière sur la répartition en volume des cristaux pour les films déposés autour de la température de cristallisation. Nous démontrons que le mécanisme général de cristallisation déterminant la structure est celui de dépôt de matériau amorphe suivi de cristallisation dans la phase solide pendant la durée du dépôt. Ce processus dans la phase solide apparaît par une nucléation prédominante à l'interface film-substrat. Les implications de ceci sur la morphologie et les propriétés physiques des films seront discutées.We have examined the structural properties of films grown by CVD in the range of temperatures 600-750°C. with particular emphasis on the volume repartition of crystals for films deposited around the crystallization temperature. We find that the general crystallization mechanism which determines the structure is one of deposition of an amorphous material followed by subsequent solid phase crystallization during the deposition time. This solid phase process occurs through a dominant nucleation at the film-substrate interface. The implications of this on the physical properties and morphology of these films will be discussed

Comparative study of the structure of a-CNx and a-CNx:H films using NEXAFS, XPS and FT-IR analysis

EMRS 2004, Symposium JAmorphous carbon nitride thin films have become a matter of great attention due to their remarkable electronic and mechanical properties. It has been shown that hydrogen and nitrogen incorporation deeply modifies the properties of carbon films. Therefore, the optimization of their properties requires a deep knowledge of various kind of chemical bonds composing in the film matrix. The topic of this presentation is to get more insight into the different local environment of the C and N atoms for hydrogenated and hydrogen-free amorphous carbon nitrides films. H-incorporation has been varied using different deposition technique from plasma-enhanced chemical vapor deposition (PECVD) leading to highly hydrogenated films up to 40 at.% to radio-frequency (RF) magnetron sputtering providing nearly hydrogen-free films. The study of the local structure is done using the combination of Fourier transform infrared (FT-IR), X-ray photo-emission spectroscopy (XPS) and high resolution near edge X-ray absorption fine structure (NEXAFS) analysis. FT-IR spectroscopy is widely used to probe the bonding configurations in the carbonaceous materials, especially the CN, CH and NH bonds in a-CNx:H. In addition, XPS and NEXAFS provide surface information on the environment around C and N atoms and on the chemical composition. NEXAFS gives a better description of the π* states inside the films, due to its remarkable energy resolution. The combination of both characterizations FT-IR and NEXAFS may leave the controversy about the interpretation of the XPS spectra, and allows a fine analysis of the evolution of the local structure as a function of nitrogen incorporation, according to the hydrogen concentration into the films. Fundamental differences can be revealed between hydrogenated and hydrogen-free carbon nitride: in the former, hydrogen promotes double bonds CNH, whereas in the latter nitrogen atoms prefer to substitute to carbon or interconnect aromatic rings through single bonds (>CN). A strong conjugation of imines (NCNH) for PECVD film and nitrile (NCN) groups for hydrogen-free films is evidenced

Influence on the sp3/sp2 character of the carbon on the insertion of nitrogen in RFMS carbon nitride films

RFMS carbon nitride films have been elaborated at several substrate temperatures between 150 °C and 450 °C, where they evolve from a highly resistive to highly conductive comportment. Their local structure has been determined from X-ray photoemission, Raman and infrared spectroscopic results. The films composition has been measured by nuclear reaction analysis and elastic recoil detection. We will correlate the strong modifications of the electronic properties of the films to their well characterized structural changes. We will show how the substrate temperature acts on the incorporation of nitrogen in carboneous RFMS films and which is the resulting consequence on the sp3/sp2 character of the carbon network

Stoichiometry and infrared absorption of amorphous a-C1-xNx : H carbon nitride films

Stoichiometry, bonding configurations and structural properties of plasma-deposited hydrogen-rich amorphous carbon nitride a C12xNx :H (0,x,0.20) films have been investigated using infrared and Raman vibrational spectroscopies, along with x-ray photoemission spectroscopy at the C and N K-edges. With increasing N incorporation in a-C12xNx :H, the total H content decreases slightly and CH vibrations are progressively replaced by NH vibrations. The dominant bonding configuration is CvN throughout the composition range, although CvN and CN saturate above 10 N at. %, and CwN configurations steadily increase throughout the stoichiometry range. A strong conjugation of imine (CvN) and nitrile (CwN) groups with aromatic rings is evidenced while the Raman signature of the sp2 C phase indicates an increase in the D to G peak intensity ratio, related to some ordering of the sp2 clustered phase

Effect of sequence built on photonic band gap properties of one-dimensional quasi-periodic photonic crystals: Application to Thue-Morse and Double-period structures

International audienceWe elaborated by Radio frequency magnetron sputtering two types of one-dimensional quasi-periodic photonic crystals, based on Si/SiO2 materials, according to the Thue Morse sequence and the Double-period one. We have investigated their optical properties, throughout the reflection transmission spectra, experimentally as well theoretically by using the transfer matrix method. The experimental spectra of these two structures are performed at normal incident light configuration, in the near infrared wavelengths range, and, are compared for the same number of layers, for a generation number N varying from 0 to 5, corresponding to a number of layers varying from 1 to 32, respectively. We experimentally put in evidence the appearance of photonic band gaps for N higher than 2, which are then well defined for N equal to 4, for the two structures. Furthermore, the results show that these two quasi-periodic structures exhibit sharp localized modes of light within the photonic band gaps, covering the optical telecommunication wavelengths 133 and 1.55 pm, with different number and position depending, on the built in distribution structures. The results also show a good agreement between the experimental and calculated spectra. (C) 2017 Elsevier Ltd. All rights reserved

Comparative study of the structure of a-CNx et a-CNx :H films using NEXAFS, XPS and FTIR analysis

Rapport CEA-

Optical filters using Cantor quasi-periodic one dimensional photonic crystal based on Si/SiO2

International audienceQuasi-periodic one-dimensional Cantor photonic crystals are elaborated by depositing alternating silicon and silica Si/SiO2 layers by radiofrequency magnetron sputtering technique with cold plasma. Transmittance and reflectance spectra of these quasi crystals exhibit a large photonic band gap in the infrared range at normal incidence which is well reproduced by a theoretical model based on the transfer matrix method. The obtained wide photonic band gap reveals the existence of permitted modes depending on the nature and characteristics of the built in system which can constitute optical windows. This effect can be a good alternative for the design of flexible filters used in many areas of applications such as telecommunication and optoelectronic devices. (C) 2016 Elsevier Ltd. All rights reserved