M. A. El Khakani

Grain size effect on the semiconductor-metal phase transition characteristics of magnetron-sputtered VO2 thin films

Single-phase vanadium dioxide (VO2) thin films have been grown on Si3N4∕Si substrates by means of a well-controlled magnetron sputtering process. The deposited VO2 films were found to exhibit a semiconductor-to-metal transition (SMT) at ∼69°C with a resistivity change as high as 3.2 decades. A direct and clear-cut correlation is established between the SMT characteristics (both amplitude and abruptness of the transition) of the VO2 films and their crystallite size.

Hardness and Young's modulus of amorphous a -SiC thin films determined by nanoindentation and bulge tests

Due to its interesting mechanical properties, silicon carbide is an excellent material for many applications. In this paper, we report on the mechanical properties of amorphous hydrogenated or hydrogen-free silicon carbide thin films deposited by using different deposition techniques, namely plasma enhanced chemical vapor deposition (PECVD), laser ablation deposition (LAD), and triode sputtering deposition (TSD). a -Si x C 1− x : H PECVD, a -SiC LAD, and a -SiC TSD thin films and corresponding free-standing membranes were mechanically investigated by using nanoindentation and bulge techniques, respectively. Hardness ( H ), Youngs modulus ( E ), and Poissons ratio ( v ) of the studied silicon carbide thin films were determined. It is shown that for hydrogenated a -Si x C 1− x : H PECVD films, both hardness and Youngs modulus are dependent on the film composition. The nearly stoichiometric a -SiC: H films present higher H and E values than the Si-rich a -Si x C 1−x : H films. For hydrogen-free a -SiC films, the hardness and Youngs modulus were as high as about 30 GPa and 240 GPa, respectively. Hydrogen-free a -SiC films present both hardness and Youngs modulus values higher by about 50% than those of hydrogenated a -SiC: H PECVD films. By using the FTIR absorption spectroscopy, we estimated the Si-C bond densities ( N SiC ) from the Si-C stretching absorption band (centered around 780 cm −1 ), and were thus able to correlate the observed mechanical behavior of a -SiC films to their microstructure. We indeed point out a constant-plus-linear variation of the hardness and Youngs modulus upon the Si-C bond density, over the N SiC investigated range [(4–18) × 10 22 bond · cm −3 ], regardless of the film composition or the deposition technique.

Effect of rapid thermal annealing on both the stress and the bonding states of a-SiC:H films

The stress evolution of plasma enhanced chemical vapor deposition a‐SiC:H films was studied by increasing the annealing temperature from 300 to 850 °C. A large stress range from −1 GPa compressive to 1 GPa tensile was investigated. Infrared absorption, x‐ray photoelectron spectroscopy, and elastic recoil detection analysis techniques were used to follow the Si‐C, Si‐H, and C‐H absorption band evolutions, the Si2p and C1s chemical bondings, and the a‐SiC:H film hydrogen content variations with the annealing temperatures, respectively. It is pointed out that the compressive stress relaxation is due to the hydrogenated bond (Si—H and C—H) dissociation, whereas the tensile stress is caused by additional Si—C bond formation. At high annealing temperatures, a total hydrogen content decrease is clearly observed. This total hydrogen loss is interpreted in terms of hydrogen molecule formation and outerdiffusion. The results are discussed and a quantitative model correlating the intrinsic stress variation to the Si...

Properties of TiC thin films grown by pulsed laser deposition

Abstract Titanium carbide thin films have been deposited on both (100) silicon and fused silica substrates by pulsed laser ablating a polycrystalline TiC target. At a KrF excimer laser intensity of about 8×10 8 W/cm 2 , the pulsed laser deposition (PLD) of TiC films was investigated at substrate deposition temperatures ranging from 25 to 600°C. The structure, surface composition, electrical resistivity, stress, work function and morphology of the PLD TiC films were characterized as a function of the deposition temperature. While all the deposited TiC films are polycrystalline with a preferred (111) orientation, both the magnitude of their compressive stress and their resistivity were found to decrease gradually as a function of the deposition temperature, from −7 to ∼−3 GPa and from 140 to 80 μΩ cm, respectively. The X-ray photoelectron spectroscopy (XPS) analysis revealed that oxygen (at an average level of ∼10 at.%) is incorporated into the TiC films where it substitutes for C. The surface composition of the films is found to be stoichiometric with an average Ti/(C+O) ratio of 0.98±0.06. The deposited TiC films exhibited low work functions in the (3.74–3.94) eV range. Their surface morphology is characterized by a very smooth surface on which some particulates are present. The density of these particulates (of which typical lateral dimension is about 1 μm and height is about 100 nm) is of the order of 2 per 100 μm 2 . The properties of these PLD TiC films are discussed in view of their use as electron injecting electrode materials for organic electroluminescent devices.

A study of the effect of composition on the microstructural evolution of a–Si x C 1 − x : H PECVD films: IR absorption and XPS characterizations

Amorphous silicon carbide films (a–Si x C 1 − x :H) deposited by the argon- or helium-diluted PECVD technique were studied as a function of their composition. Microstructural investigations were mainly achieved by means of FTIR and XPS techniques. Nuclear techniques were used to obtain precise information on the film hydrogen content. The Si–H IR-absorption band was deconvoluted in different monohydride and dihydride silicon environments. The existence of SiH 2 bonds in the Si-rich composition was evidenced. From the analysis of the C–H and Si–H absorption bands it is shown that hydrogen atoms are preferentially bonded to carbon atoms. The deconvolution of the Si 2 p core level peak suggests that above a composition of x ∊ 0.5, the noncarburized (Si, Si, H) local environment contribution increases to the detriment of the hydrocarburized (Si, C, H) environments. From the evolution of the C 1 s peak, it can be deduced that there is a change in the carbon atom bonding states when the film composition is varied. These results are correlated and discussed in terms of the local bonding environments and their evolution with film composition.

Effect of laser intensity on the microstructural and mechanical properties of pulsed laser deposited diamond-like-carbon thin films

Diamond-like-carbon (DLC) thin films have been deposited at room temperature on Si substrates by ablation of a graphite target using a KrF excimer laser at intensities ranging from 0.9×108 W/cm2 to 6.0×109 W/cm2. The microstructure of the films was studied by x-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The macroscopic properties were evaluated by measurement of their optical constants using in-situ laser reflectometry and their hardness using the continuous stiffness measurement technique. Analysis of the XPS C 1s core level spectra of the DLC films shows that their sp3 hybridized carbon atom content increases with laser intensity up to a maximum value of about 60% obtained at 7.0×108 W/cm2. At higher laser intensities, the sp3 content appears to stabilize at about 53%. Such an evolution of the sp3 content can be understood in terms of the subsurface carbon ions implantation model which has been proposed for ion beam deposited films. On the other hand, Raman analysis indicates that an i...

Iridium thin films deposited by radio-frequency magnetron sputtering

Deposition of metallic iridium thin films has been achieved by sputtering an Ir target with argon. The deposition of the Ir films was investigated at argon gas pressures in the (10–40) mTorr range with various rf power densities. The stress, resistivity, and structure of the Ir films were systematically determined as a function of both the Ar pressure and the rf power density. While all the deposited Ir films are polycrystalline with a preferred (111) orientation, not only their stress but also their resistivity were found to be particularly sensitive to the Ar gas pressure. As for many sputtered metal thin films, the stress of Ir films, deposited at a power density of 5 W/cm2, drastically changes from highly compressive (−2 GPa) to highly tensile (+1.2 GPa) in a relatively narrow range of Ar pressure (10.5–25.5 mTorr). Likewise, the room-temperature resistivity of Ir sputtered films changes by a factor of about 5 when the Ar pressure is increased from 22.8 to 36.0 mTorr. Deposition conditions yielding Ir...

Terahertz conductivity of the metal-insulator transition in a nanogranular VO2 film

Terahertz time-domain spectroscopy is used to measure the complex terahertz conductivity of a nanogranular vanadium dioxide (VO2) thin film as a function of temperature through the metal-insulator transition. The Drude–Smith model provides a good fit to the observed terahertz conductivity, revealing a metallic state that forms via switching of individual nanograins and strong carrier confinement within the nanograins due to scattering off grain boundaries. Furthermore, the directly applied Drude–Smith model provides a more accurate description of the measured terahertz conductivity in this material than either Bruggeman or Maxwell–Garnett effective medium theories.

High-k titanium silicate dielectric thin films grown by pulsed-laser deposition

We report the pulsed-laser deposition of high-k titanium silicate thin films. The titanium silicate films were deposited by laser ablating a (Ti, Si) target in an oxygen pressure of 70 mTorr. The deposited films were found to exhibit nanocrystalline structure with a grain size of about 3.5 nm as deduced from x-ray diffraction measurements. Fourier transform infrared spectroscopy confirmed the existence of Ti–O–Si bonds in the films. The binding energies of [Ti 2p3/2 (458.6 eV), Si 2p (102.3 eV), O 1s (531.8 eV)] as measured by means of x-ray photoelectron spectroscopy provided evidence of titanium silicate. On the other hand, the average dielectric constant of the pulse laser deposited titanium silicate thin films were found to be about 11 in the frequency range of 100 kHz to 13 MHz.

Pulsed laser deposition of highly conductive iridium oxide thin films

Highly conductive IrO2 thin films have been deposited on Si (100) substrates by means of pulsed laser ablation of iridium metal target in an oxygen ambient pressure of 200 mTorr. IrO2 films grown at substrate temperatures in the 400–550 °C range are polycrystalline with a preponderant (101) IrO2 reflection and exhibit a dense granular morphology. Their room‐temperature resistivities are very comparable to that of bulk single‐crystal IrO2. IrO2 thin films with a resistivity of (39±4) μΩ cm are obtained at a substrate temperature as low as 400 °C. The dependence of IrO2 films properties on the nature and/or the preparation of their underlying substrates is pointed out.