M. Lejeune

Correlation between plasma parameters, microstructure and optical properties of sputtering magnetron CNx films

Abstract Analysis of carbon nitride films (CN x ) deposited by radio frequency (RF) magnetron sputtering on crystalline silicon, under different target self-bias, is reported. Plasma characterisation was performed using mass spectroscopy (MS) and the properties of films were determined in their as deposited state using elastic recoil detection analysis (ERDA), nuclear reaction analysis (NRA), X-ray photoelectron spectroscopy (XPS), infrared absorption, transmission spectroscopy and photothermal deflection spectroscopy (PDS) experiments. A good correlation is observed between the variation of N/C ratio and the growth rate. The resulting changes in the microstructure can be analyzed in terms of surface processes, nitrogen incorporation within the films and the Csp 2 content.

Stress and structural relaxation in amorphous hydrogenated carbon films

The correlation between the residual stress and the atomic-bond structure has been investigated in detail in hydrogenated amorphous films (a-C:H). The relaxation process was studied in relation with the Raman characteristics evolution and the induced metric distortions during growth. The analysis of the Raman data shows that the metric distortions alone cannot explain the stress relaxation in the deposited films. The creation of some topological defects, such as odd rings, is required to explain both the Raman features behavior and the structural relaxation in the a-C:H samples.

Structure and optical properties of carbon nitride films deposited by magnetron sputtering

Abstract Carbon nitride (CN x ) thin films were deposited using RF magnetron sputtering technique of a graphite target in a pure N 2 atmosphere at different RF power. Film composition was analysed using X-ray photoelectron spectroscopy measurements correlated with infrared absorption, Raman spectroscopy, optical transmission and photothermal deflection spectroscopy experiments. The observed variation of the optical properties are attributed to the changes in the atomic bonding structures, which were induced by ion bombardment, increasing both the sp 2 carbon content and their relative disorder.

Optical investigations and Raman scattering characterisation of carbon bonding in hard amorphous hydrogenated carbon films

Abstract Hydrogenated amorphous carbon films were prepared by plasma enhanced chemical vapour deposition (PECVD) of methane–argon (5%) gas mixtures at low pressure, in a dual electron cyclotron resonance (ECR)-rf glow discharge. Optical transmission spectroscopy, Raman spectroscopy, elastic recoil detection analysis (ERDA) and infra-red (IR) absorption spectra were combined to examine the relationship between the local microstructure (CH and CC bonds) and the optical properties at different negative bias voltage. The amount of bonded H, obtained by IR spectra, is higher in series deposited at low bias voltage, in qualitative agreement with the ERDA results. In all cases, most of the incorporated H is bonded to sp3C sites, with a predominance of CH3 methyl groups. These results are also consistent with the Raman spectroscopy measurements. The positions, widths, and relative intensities of the two characteristic features, the D and G peaks are found to vary systematically with deposition conditions and film properties. The series prepared at high bias voltage shows a higher disorder (D) over the graphitic (G) band ratio, which also indicates a structure with a high disorder form of Csp2 sites.

Influence of disorder on localization and density of states in amorphous carbon nitride thin films systems rich in π-bonded carbon atoms

We discuss in this paper the evolution of both the density of states (DOS) located between the band-tail states and the DOS around the Fermi level N(EF) in amorphous carbon nitride films (a-CNx) as a function of the total nitrogen partial pressure ratio in the Ar/N2 plasma mixture. The films were deposited by three different deposition techniques and their microstructure was characterized using a combination of infrared and Raman spectroscopy and optical transmission experiments, completed with electrical conductivity measurements, as a function of temperature. The observed changes in the optoelectronic properties are attributed to the modification in the atomic bonding structures, which were induced by N incorporation, accompanied by an increase in the sp2 carbon bonding configurations and their relative disorder. The electrical conductivity variation was interpreted in terms of local effects on the nature and energy distribution of π and π∗ states.

Effect of target self-bias on carbon nitride thin films deposited by RF magnetron sputtering

Abstract Analysis of carbon nitride films (CNx) deposited by RF magnetron sputtering on crystalline silicon, under different target self-bias, is reported. The properties of films were determined in their as-deposited state using X-ray photoelectron spectroscopy (XPS), IR absorption, transmission spectroscopy and residual stress measurements. The presence of various types of C–N bonds, as well as of hydrogen and oxygen, is revealed. A good correlation is observed between the variation of N/C ratio, the optical gap E04 and the internal stress as a function of the target bias. The optical gap E04 decrease is discussed in terms of N/C ratio evolution, the sp2 bond content and the local distortions of the sp2 bonds.

Growth and bonding structure of hard hydrogenated amorphous carbon thin films deposited from an electron cyclotron resonance plasma

Analysis of hard hydrogenated amorphous carbon films (a-C:H) deposited from an electron cyclotron resonance radio frequency discharge of methane–argon (5%) mixture at low pressure is reported. The properties of films were determined in their as deposited state using elastic recoil detection analysis, infrared absorption, Raman spectroscopy, transmission spectroscopy, photothermal deflexion spectroscopy, and residual stress measurements. The microstructural changes (i.e., hydrogen content and C-sp3/C-sp2 ratio) have been explained qualitatively in terms of a balance between implantation and relaxation processes. A good correlation is observed between the variation of Raman features and the optical gap as a function of the self-bias substrate. The residual stress versus bias plot shows behavior similar to that already obtained for tetrahedral amorphous carbon films and the optimum energy, which corresponds to films of maximum C–C sp3, is similar to those obtained in the literature.

Wavelength Dependent Remote Power Supply for Shape Memory Alloy

The use of shape memory alloy (SMA) actuators in smart structures is increasing significantly especially in the field of Micro-Electro-Mechanical Systems (MEMS) due to their unique properties. In this work wavelength dependent remote power supply for SMA is presented to avoid electrical cables from the working area of the structure and to demonstrate the selective addressing of a high number of micro-actuators placed in a small space. Low power (∼100 mW) continuous mode laser diodes are used as remote power supply sources. A thermal numerical model is presented to visualize the temperature evolution in a Nitinol sample (3 mm × 1 mm × 100 μm) irradiated by 785 nm laser source. A series of experiments are performed to validate the modelling results, to estimate the response time under different loadings (15 g and 20 g) and to demonstrate the wavelength dependent deformation in SMA samples for selective addressing which is realized by depositing thin layers having specific optical filtering properties directly over the SMA sample and using laser diode sources with different wavelengths (785 nm and 658 nm).

Optical behavior of reactive sputtered carbon nitride films during annealing

The effect of annealing temperature (TA) on amorphous carbon nitride (a-CNx) thin films, deposited using radio-frequency (rf) magnetron sputtering technique of a graphite target in a pure nitrogen (N2) atmosphere at different rf power, is investigated. Film composition was analyzed using Fourier transform infrared absorption (FTIR), Raman spectroscopy, optical transmission, and photothermal deflection spectroscopy (PDS) experiments. The refractive index and the mass density were determined using optical transmission spectroscopy and elastic recoil detection analysis measurements. The microstructure analysis revealed the porous character of films, which decreases slowly with increasing annealing temperature (TA). The results of Raman spectroscopy, FTIR, and PDS experiments demonstrate that the films below 400°C mainly consist of aromatic cluster component and polymeric component. With increasing TA, the progressive graphitization of the material is accompanied by a high disorder form of Csp2 sites.

On the induced microstructure changes of the amorphous carbon nitride films during annealing

The analysis of the stress release and structural changes caused by postdeposition thermal annealing of amorphous carbon nitride thin films (a‐CNx) has been carried out. The a‐CNx films were deposited on Si (100) using reactive radio frequency (rf) magnetron sputtering of a high-purity graphite target in a pure nitrogen plasma under various different rf powers. Combined Fourier transform infrared (FTIR), Raman spectroscopy, transmission spectroscopy, photothermal deflexion spectroscopy, and residual stress measurements were used to fully characterize the films. Annealing of the samples in vacuum at temperature up to 600°C produces changes in their structural properties and the intrinsic stress. These changes are found to be strongly dependent on both the deposition conditions and microstructure changes occurring within the films during heating. FTIR spectra showed the existence of N–C sp3, NC sp2, and CN triple bonds in the deposited films. The analysis of the spectra versus annealing temperature (TA) r...