A. Zeinert

Nanocrystalline silicon thin films prepared by radiofrequency magnetron sputtering

Abstract The effects of the hydrogen dilution and pressure on the structural and electrical properties of hydrogenated nanocrystalline silicon (nc-Si:H) films deposited at 250°C by radiofrequency (RF) magnetron sputtering method have been studied in a large range of total pressure (1–15 Pa) and H 2 dilution percentage (30–100%) in the gas phase mixture (Ar+ x % H 2 ). A combination of Raman spectroscopy, infrared (IR) absorption, X-ray diffraction, DC electrical conductivity and intrinsic stress measurements has been used to characterize the films. Only SiH 2 and (SiH 2 ) n bonds essentially in grain boundaries, corresponding to well-defined doublets in the bending (844–877 cm −1 ) and the stretching (2083–2100 cm −1 ) vibrational modes regions, have been detected. The best properties in terms of structure (crystalline volume fraction) and electrical conductivity of the nc-Si films are obtained for H 2 percentage of 70%, where the crystalline volume fraction f c is approximately 80% for 5 Pa and increases up to 92% with increasing pressure up to 15 Pa. An increase of approximately three orders of magnitude in the room temperature DC electrical conductivity is also obtained for these deposition conditions. The intrinsic stress is very low and not significantly affected by the changes in the crystalline volume fraction.

Spins and microstructure of hydrogenated amorphous carbon: A multiple frequency electron paramagnetic resonance study

Polymer-like and diamond-like hydrogenated amorphous carbon films, characterized by high spin concentrations of 1020 cm−3, have been studied by multiple frequency electron paramagnetic resonance (EPR) spectroscopy at 9, 35, and 94 GHz. Whereas the low-frequency measurements show only one single symmetric EPR line, the high-frequency measurements reveal the anisotropic nature of the g tensor. They show the presence of two different paramagnetic centers with anisotropic g tensors of g∥(1)=2.005, g⊥(1)≈2.003, and g∥(2)=2.010, g⊥(2)≈2.003. We attribute both to localized π states on nanosized sp2 graphitic clusters. The g∥ values of the g tensors, which are correlated to the size of the graphite like carbon clusters, indicate two different cluster sizes with values below 50 A.

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.

Effect of annealing on the structural and electrical properties of d.c. multipolar plasma deposited a-C:H films

Abstract The changes upon annealing in CH and CC bonding in relation to the structural and electronic properties have been investigated in two different series of a-C:H samples prepared in a direct current (d.c.) multipolar plasma system from pure methane at quite different substrate bias (−40 and −600 V). Using a combination of infrared absorption, elastic recoil detection analysis, high resolution transmission electron microscopy and electrical resistance measurements, we fully characterize the samples in their as-deposited state as well as after successive annealing cycles at increasing temperatures up to 700°C. The results show clearly that the two types of series exhibit quite different microstructures and hydrogen incorporation in their as-deposited state. The low bias (−40 V) series exhibits a highly disordered structure, while the high bias (−600 V) one already contains well ordered regions. They also have a completely different behavior upon annealing up to high temperature. A microstructure conversion such as from hydrogenated as well as non-hydrogenated sp 3 C sites to sp 2 C ones occurs in the temperature range 400–500°C in all cases. However, a more efficient graphitization is observed in the high bias series (−600 V) for annealing temperatures as high as 700°C. Quite surprising results are obtained for the low bias series (−40 V): contrarily to what is usually observed for this type of sample, this series is found to be more thermally stable for high annealing temperature (>400°C) than the high bias one (−600 V). These results are discussed and explained in terms of the relaxation process in the local microstructure.

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...

Contactless and selective energy transfer to a bistable micro-actuator using laser heated shape memory alloy

Contactless energy transfer (CET) methods offer great flexibility in the design of complex micro-systems. This paper reports a laser based contactless and selective energy transfer method. A compliant bistable micro-actuator (curved beam of size 25 mm × 1.5 mm × 0.508 mm) is actuated between its two stable positions using the laser heated shape memory alloy (SMA) active elements (size: 3 mm × 1 mm × 0.1 mm). The switching time of the actuator turns out to be 0.5 s for d0 equal to 700 μm and a laser power of 90 mW (d0 is half of the total stroke length). The paper also demonstrates the selective energy transfer technique to the SMA active elements by depositing silver based optical filters directly onto the SMA active elements. A successful demonstration is presented for four wavelengths, 532, 660, 785, and 980 nm, using different values of d0 for the bistable micro-actuator. Finally, a long-term test is performed to highlight the thermo-mechanical effect on the selective addressing capability of the optical filters.

Optical Characterization of Porous Sputtered Silver Thin Films

The optical properties of various porous silver films, grown with a commercial DC sputter coater, were investigated and compared for different plasma parameters. Effective Drude models were successfully used for those films whose spectra did not show particular resonance peaks. For the other films, neither an effective Drude model nor effective medium models (Maxwell Garnett, Bruggeman, and Looyenga) can describe the optical properties. It turns out that a more general approach like the Bergman representation describes the optical data of these films accurately adopting porosity values consistent with physical measurements.

Comparative study of microstructure in a-CxN1–x films deposited by radiofrequency magnetron sputtering

Abstract In this work, optical properties and the microstructure of non-hydrogenated amorphous carbon nitride (a-CxN1–x) have been investigated on films deposited by a reactive r.f. magnetron sputtering source with a graphite target. The r.f. power applied to the target varies between 15 and 350 W, leading to a negative target voltage range approximately −94 to −795 V. A combination of Raman spectroscopy measurements and infrared (IR) absorption experiments, which give information about the local microstructure and optical transmission measurements in the UV-Visible and near IR and photothermal deflection spectroscopy from which we determined the refractive index n and the optical gap E04 are applied to fully characterise the films in their as-deposited state. The variation of the ID/IG ratio indicates that the microstructure of the samples shows a critical change in the local bonding of the C atoms, for deposition parameters corresponding to a target voltage of −400 V and a nitrogen pressure approximately 4–5 Pa. Photoluminescence spectra show a maximum at approximately 650 nm and the photoluminescence efficiency presents a maximum as a function of the r.f. power in the same range as the maximum of the ID/IG ratio.