C. Popov

Optical, electrical and mechanical properties of nitrogen-rich carbon nitride films deposited by inductively coupled plasma chemical vapor deposition

An inductively coupled plasma utilizing chemical transport reactions has been used to deposit thin carbon nitride films with a high nitrogen content [N/(C+N) of approximately 0.5 or higher]. We report on the characterization of the application relevant properties of these films, especially the optical (refractive index, transmission), electrical (dielectric constant, resistivity) and mechanical characteristics (stress, hardness, wear resistance). The refractive index is in the order of 1.5–1.8 depending on the deposition conditions; furthermore, the films are highly transmitting for wavelengths above 600 nm. C–V curves indicate the insulating character of the CNx films which was confirmed by I–V measurements yielding resistivities up to 1011 Ω cm at room temperature. The layers possess marginal stress as measured by the bending method on silicon cantilevers. The hardness is in the range of 1 GPa, and a friction coefficient of 0.6 was determined by ball-on-disc tests against stainless steel balls. The investigations showed that these films may be suited especially for optical and electrical applications. Finally, we correlate the films characteristics with the composition and structure of the coatings.

Preparation of nitrogen-rich CNx films with inductively coupled plasma CVD and pulsed laser deposition

Abstract Nitrogen-rich amorphous carbon nitride films with N/(N+C)≥0.5 have been deposited with three different methods, namely: (i) inductively coupled plasma CVD utilizing chemical transport reactions (ICP–CTR); (ii) inductively coupled plasma CVD with gaseous precursors (ICP–GP) and (iii) pulsed laser deposition (PLD) with additional r.f. plasma discharge. By means of plasma diagnostic measurements it is shown that in each case high concentrations of active radical species (e.g. CN and N ) are necessary to obtain high nitrogen concentrations. On the other hand, these nitrogen-rich films turned out to be mainly sp2 bonded having rather low densities of 1.8–2.0 g cm−3 only, irrespective of the method. From a comparison of the three techniques, and of further literature data, conclusions are drawn regarding the conditions necessary to obtain high N/(N+C) ratios, and regarding the deposition of superhard, crystalline sp3 bonded carbon nitride modifications.

Investigation of the thermal stability of nitrogen-rich amorphous carbon nitride films

Abstract The thermal stability of nitrogen-rich amorphous carbon nitride films (N/C≥1) is investigated from room temperature up to 600°C. The films were deposited by three different methods, namely pulsed laser deposition (PLD), inductively coupled plasma chemical vapour deposition (ICP-CVD) with gaseous precursors, and ICP-CVD utilizing transport reactions. As-deposited and annealed films were characterized with respect to their thickness, composition and bonding structure by a variety of methods including wavelength dispersive X-ray analysis (WDX), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). Annealing at 200°C leads to desorption of surface contaminants while in the range between 200 and 400°C a significant densification is observed. Above 400°C a drastic loss of film material, especially nitrogen-rich groups, sets on, leading to the total destruction of the films at 600–700°C. These observations are compared with the annealing behaviour of films with lower nitrogen content.

Low-Pressure CVD of Carbon Nitride Using Triazine-Containing Precursors†

Carbon nitride (CxNy) layers with N/C ratios of 0.76–1.26 have been grown under low pressure from two organic chemical systems, namely 2,4-dichloro-6-bis(trimethylsilyl)imido-1,3,5-triazine [C3N3Cl2N(SiMe3)2] and tetramethylguanidine (C5H13N3) + 2,4,6-trichloro-1,3,5-triazine (C3Cl3N3). The films synthesized are transparent, well-adhered on silicon, homogeneous in morphology, and uniform in thickness. In addition, a technology has been developed for the deposition of carbon nitride powders with a N/C ratio of 1.3 as starting materials for further thermal treatment attempts in order to synthesize crystalline C3N4. At deposition temperatures between 400 and 800 °C and high supersaturation of reagents in the reactor, the powders obtained exhibit nuclei of crystalline phases.

Plasma chemical vapor deposition of thin carbon nitride films utilizing transport reactions

Abstract Inductively coupled plasma chemical vapor deposition (ICP-CVD) has been used for the preparation of thin carbon nitride films from a solid carbon source (at floating potential) and nitrogen. Atomic nitrogen obtained as a result of the r.f. plasma activation interacts with the carbon source to form volatile carbon–nitrogen species. The latter are transported to the substrate where carbon nitride films are deposited in excess of atomic nitrogen. The supposed process mechanism was verified by microscopic observations of the carbon source before and after the process and by in situ mass spectrometric studies of the gas phase. The main advantage of the process is the possibility to obtain carbon nitride films with rates between 2 and 10 nm/min at rather low r.f. powers. The basic deposition parameters varied were the r.f. power (up to 100 W) and the working pressure in the reactor (up to 100 Pa). The surface topography of the films was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM); the deposited layers were found to be very smooth and uniform. The N/C ratio in the films was close to 1 as detected by Auger electron spectroscopy (AES) and elastic recoil detection (ERD) analysis. Infrared absorption and X-ray photoelectron spectra showed the presence of different carbon–nitrogen bonds in the layers.

Nanoscience Advances in CBRN Agents Detection, Information and Energy Security

The present volume comprises the most important contributions to the NATO ASI “Nanoscience advances in CBRN agent detection, information and energy security” held on 29.5.–6.6.2014 in Sozopol, Bulgaria. This short introduction aims to give an overview of the topics of the ASI and to relate them to the presently actual state of the art, but also to future fields of research in nanosciences and nanotechnology. Another aim of this introduction is to hint the reader to the most important contributions of these proceedings. Although nanotechnological products can presently be found in a wide range of application fields, in the ASI the topics were restricted to a number of fields which are related to the future wellbeing and safety of planet earth. This may sound exaggerated but the future of our planet will indeed rely on the ability to detect dangerous agents (chemical, biological and radionuclear1⁄4CBRN) as well as to provide a clean environment, health, and energy and information safety. With other words: The topics of this ASI are at the leading edge to solve many of the currently most important questions to be tackled by science and technology.

Ultrananocrystalline Diamond-Based High-Velocity SAW Device Fabricated by Electron Beam Lithography

Surface acoustic wave (SAW) devices have been used extensively for a variety of applications such as telecommunications, electronic devices, and sensors. The emerging need for high-bit data processing at gigahertz frequencies and the requirement of high-sensitivity sensors demand the development of high-efficiency SAW devices. With the objective of exploiting the high acoustic velocity of diamond, we report on an optimally developed nanodiamond thin film with crystal size of 3-5 nm, embedded in an amorphous carbon matrix with grain boundaries of 1-1.5 nm, that is integrated with aluminum nitride (AlN) to extend the operating frequency of SAW transducers. We utilize this attractive property of diamond through facile synthesis of a bilayer structure consisting of sputtered AlN deposited on an ultrananocrystalline diamond (UNCD) film. We report the realization of a high-frequency SAW resonator, using a device architecture based on an UNCD layer. The UNCD films were synthesized using a microwave plasma-enhanced chemical vapor deposition (MWPECVD) technique and were used to enhance the SAW velocity in the AlN thin film, thus opening the way for the application of CMOS compatible high-frequency SAW devices. The deposition and characterization of UNCD thin films are presented and highlighted for the realization of the SAW resonators. The high velocity associated with the UNCD/AlN bilayered approach together with the high lateral resolution of the interdigital transducers obtained with electron beam lithography is essential for the realization of high-frequency SAW devices. The fabricated devices demonstrate resonance frequencies of 11.3 and 6.2 GHz corresponding to spatial periods of 800 and 1600 nm, respectively, yielding a SAW velocity of 9040 and 10 064 m/s, respectively.

Super-high-frequency SAW transducer utilizing AIN/ultrananocrystalline diamond architectures

SAW devices have been used in a variety of applications including high-volume telecommunications, electronic devices, and advanced sensors. Recently, high-bit-rate data processing in the gigahertz frequency range and ultrahigh-sensitivity sensors have called for the development of advanced SAW transducers. Because of its high acoustic velocity, ultrananocrystalline diamond (UNCD) with a crystal size of 3 to 5 nm, embedded in an amorphous carbon matrix with grain boundaries of 1 to 1.5 nm, is integrated with AlN to extend the operating frequency of SAW devices. We utilize this attractive property of UNCD through the facile synthesis of bilayer architectures consisting of sputtered AlN deposited on UNCD film. The UNCD films were synthesized using microwave plasma-enhanced chemical vapor deposition. The SAW devices were fabricated by electron beam lithography and lift off processes. The fabricated SAW nanodevices exhibit resonance frequencies up to 15.4 GHz. Multiple SAW transducers were fabricated with spatial periods ranging from 580 nm to 3.2 μm.

Strong attachment of circadian pacemaker neurons on modified ultrananocrystalline diamond surfaces

Diamond is a promising material for a number of bio-applications, including the fabrication of platforms for attachment and investigation of neurons and of neuroprostheses, such as retinal implants. In the current work ultrananocrystalline diamond (UNCD) films were deposited by microwave plasma chemical vapor deposition, modified by UV/O3 treatment or NH3 plasma, and comprehensively characterized with respect to their bulk and surface properties, such as crystallinity, topography, composition and chemical bonding nature. The interactions of insect circadian pacemaker neurons with UNCD surfaces with H-, O- and NH2-terminations were investigated with respect to cell density and viability. The fast and strong attachment achieved without application of adhesion proteins allowed for advantageous modification of dispersion protocols for the preparation of primary cell cultures. Centrifugation steps, which are employed for pelletizing dispersed cells to separate them from dispersing enzymes, easily damage neurons. Now centrifugation can be avoided since dispersed neurons quickly and strongly attach to the UNCD surfaces. Enzyme solutions can be easily washed off without losing many of the dispersed cells. No adverse effects on the cell viability and physiological responses were observed as revealed by calcium imaging. Furthermore, the enhanced attachment of the neurons, especially on the modified UNCD surfaces, was especially advantageous for the immunocytochemical procedures with the cell cultures. The cell losses during washing steps were significantly reduced by one order of magnitude in comparison to controls. In addition, the integration of a titanium grid structure under the UNCD films allowed for individual assignment of physiologically characterized neurons to immunocytochemically stained cells. Thus, employing UNCD surfaces free of foreign proteins improves cell culture protocols and immunocytochemistry with cultured cells. The fast and strong attachment of neurons was attributed to a favorable combination of topography, surface chemistry and wettability.

The effect of d.c. substrate bias on the properties of nitrogen-rich CNx films

The influence of d.c. substrate bias on the properties of nitrogen-rich CNx films deposited by inductively coupled plasma chemical vapor deposition (ICP-CVD) utilizing transport reactions has been investigated. The film forming species are CN and/or (CN)2 generated by the interaction of the atomic nitrogen from the ICP with a solid pure carbon mesh; they are deposited on the substrate in the presence of nitrogen species from the plasma. A study of the surface topography of the coatings by atomic force microscopy (AFM) shows that the average roughness slightly increases from below 1 nm without bias to 1.6 nm at −300 V. The deposition rate decreases by a factor of 1.3–1.5 (depending on the working pressure) with increasing the bias up to −300 V, mainly as a result of desorption of CN species from the substrate enhanced by the ion bombardment. The CNx films deposited with bias exhibit nitrogen atomic fraction N/(C+N) in the range of 50–60%, as revealed by surface and bulk techniques. The chemical bonding structure of the layers investigated by Fourier transform infrared (FTIR) spectroscopy showed only a marginal influence of the d.c. substrate bias. The increase of the refractive index n from 1.6 to 1.8 is probably due to slight densification of the films deposited with substrate biasing as a result of reduction of voids.