Ph. Houdy

Nanoindentation investigation of Ti/TiN multilayers films

The hardness of Ti/TiN nanolaminated films is investigated in this study. Monolithic Ti and TiN films and Ti/TiN multilayers were deposited on silicon substrates by radio-frequency sputtering. The period thickness of multilayers was decreased from 20 to 2.5 nm. Grazing x-ray reflectometry showed that the modulation of composition of Ti/TiN multilayers exists for all the period thickness considered. From nanoindentation measurements, we determined the hardness and Young’s modulus of multilayers. Hardness increased with decreasing period thickness to go beyond the rule-of-mixture value for samples with period thickness of Λ⩽5 nm. The maximum hardness, 1.6 times higher than the value obtained by the rule of mixture, is obtained for Λ=2.5 nm. Our results are compared to a dislocation-based model previously introduced by Lehoczky.

Magnetic and structural properties of rf‐sputtered Co/Fe and Co/Cr multilayers

Multilayers alternating cobalt with different spacers such as iron and chromium at nanometric scale have been deposited by rf diode sputtering. The structures have been characterized in situ by kinetic ellipsometry and ex situ by grazing x‐ray reflection, x‐ray diffraction, Auger profile analysis, and transmission electron microscopy. Nuclear magnetic resonance (NMR) and high‐field SQUID magnetometry have been used to determine the magnetic properties. In Co/Fe multilayers the structure strongly depends on the cobalt thickness tCo. For tCo below 2 nm, the cobalt layers exhibit a bcc crystalline structure, and the crystalline coherence extends over many periods. For tCo above 2 nm, for Co a mixed fcc‐hcp phase has been observed. In this case the crystalline coherence is destroyed from one iron layer to the other. The NMR frequency (198 MHz), and the magnetic moment (1.58 μB/atom) of bcc cobalt have been evaluated. A similar behavior is observed in Co/Cr multilayers, the bcc phase disappearing around tCo=1....

Tb/Fe multilayers : a study by conversion electron Mössbauer spectrometry and polar Kerr effect

Abstract Sputtered Tb/Fe multilayers (ρ Tb =0.2–1.9 nm, ρ Fe = 0.2–3.3 nm) have been characterized both by CEMS and the Kerr effect. Saturated Kerr angles υ K vary linearly with the hyperfine field at the iron site, indicating the υ K comes mainly from the iron magnetic moment. All the structural and magnetic results can be interpreted in a (ρ Tb ,ρ Fe ) diagram.

Structural and magnetic properties of diode radio‐frequency sputtered Cr/Co multilayers

Structural properties of diode radio‐frequency (rf)‐sputtered Cr/Co multilayers have been investigated using in situ kinetic ellipsometry, grazing x‐ray reflection, x‐ray diffraction, and nuclear magnetic resonance. Results have been correlated with magnetic characterizations obtained by SQUID susceptometry. Interdiffusion along ≂10 A occurs at the ‘‘Cr on Co’’ interface. The Co on Cr interface appears sharper. X‐ray diffraction and nuclear magnetic resonance show that Co layers grow with bcc structure when the Co layer thickness dCo is lower than ≂15 A. In this case, the films are strongly textured with the Cr bcc (100) direction perpendicular to the plane of the substrate. A better structural coherence is observed for the thinner layers. When dCo is thicker than ≂15 A, a mixture of hcp and fcc Co phases appears by x‐ray diffraction and nuclear magnetic resonance. The good structural quality of the films is confirmed by the occurrence of satellite peaks in the x‐ray diffraction patterns. The Co magnetic ...

Two-dimensional defects in InSe

Two‐dimensional precipitates associated with stacking faults in layer semiconductors have previously been put forward to explain transport properties of these crystals, especially their remarkable electrical anisotropy. High‐field cyclotron resonance behavior, among others, can be accounted for by two‐dimensional accumulation layers in the vicinity of these defects. Direct evidence for the existence of these defects has been obtained by electron microscopy and x‐ray microprobe analysis in indium selenide. Planar faults act like sinks for impurity atoms. This accounts for the unique behavior of layer compounds which exhibit intrinsic behavior (low apparent carrier concentration—high mobilities) even with high (100 ppm) initial doping levels. Optical, transport, and magnetotransport properties at low temperature can be explained along this model. As regards the applications of indium selenide to the photovoltaic conversion of solar energy, the existence of these defects explains most features of this semiconductor in this respect: (i) Its comparatively low effective diffusion length parallel to the c axis. (ii) p‐ to n‐type switching under thermal annealing which allows fabrication of p‐n junctions. (iii) Low apparent carrier density which precludes abrupt profiles for p‐n structures.

Structural and magneto‐optical properties of Tb/Fe and (Tb/Fe)/Si3N4 multilayers

Tb/Fe and (Tb/Fe)/Si3N4 multilayer films with layers in the nanometric range have been prepared using a reactive diode rf sputtering system. Their structural and magneto‐optical properties have been investigated to determine the stack parameters, the crystallization states, the direction of easy magnetization, and the Kerr angle values. The multilayer structure can be observed even when terbium layers are about 0.2 nm thick. Iron crystallization appears to depend on the terbium layer thickness. For Tb layer thicknesses greater than 0.37 nm, iron is amorphous when thinner than 3 nm. It spontaneously crystallizes when the layer becomes thicker. When Tb layer thickness is smaller than 0.37 nm, Fe crystallization is always detected: It occurs in the whole stack through the incomplete Tb layers. Kerr rotation measurements show a magnetic anisotropy depending on the Tb/Fe thickness ratio. Indeed, the direction of easy magnetization was found to be in the plane of the samples for ratio values of about 0.23 and 1...

Structural and magnetic phase diagram of Tb/Fe multilayers determined by conversion electron Mössbauer spectrometry

Abstract Tb/Fe multilayers have been prepared by rf-pulverization on Si〈111〉 substrates. Conversion electron Mossbauer spectrometry was used to obtain information on the structure and the spin texture of the multilayers. A structural and magnetic diagram is proposed in the e Tb = 0.2−1.9 nm, e Fe = 0.2−3.3 nm thickness range. In the amorphous samples, the magnetic hyperfine field varies continously with the iron thickness and exhibits a maximum for e Fe ≅ 1.0 nm.

Direct experimental evidence of a body-centered-cubic Co phase in radio-frequency-sputtered Co/Fe multilayers

Radio‐frequency‐sputtered Co/Fe multilayers with layer thicknesses varying in the 8–100 A range were studied by extended x‐ray absorption fine structure (EXAFS), x‐ray absorption near edge spectroscopy (XANES), and nuclear magnetic resonance (NMR) techniques. While the Fe environment is body‐centered‐cubic (bcc) in all the samples, the Co environment depends drastically on the Co layer thickness. Under ≂20 A, investigation at the Co K edge by XANES provides a bcc fingerprint in both polarization directions. The XANES profile becomes typical of a full hcp stacking only for Co layer thicknesses larger than 98 A. This behavior is confirmed by EXAFS spectra at the Co K edge and NMR analysis. For Co layer thickness between 6 and 18 A, eight first neighbors at 2.48 A and six second neighbors at 2.83 A are detected which match the bcc phase. Resonance peak at a very low frequency is also observed (198 MHz). The second shell radius appears at 2.78 A only for larger Co layer thicknesses. This effect goes along wit...

Magnetic and magneto-optical properties of Tb/Fe multilayers

Abstract We report on magnetic and magneto-optical properties of [Tb/Fe] n multilayers. The dependence on Tb and Fe thicknesses and on the stacking parameter n have been studied. For a thick sample ( n =40), we confirm that the ferrimagnetic or compensation temperatures and the magneto-optical effects are close to those deduced previously for Tb x -Fe 1- x metallic alloys having the same nominal composition. Thinner samples ( n n is evidenced and discussed. Magnetization reversal dynamics are studied and analyzed from magnetic after-effect measurements and microscopic domain imaging. Typical values of Barkhausen volumes are deduced.

Anisotropic differential magnetoresistance of Cu/Co(100) multilayers

We report on structural and magnetic properties of diode rf‐sputtered fcc Cu/Co(100) multilayers. All the samples exhibit a pseudo‐epitaxial structure with interface roughness of the order of 6 A. As the Cu layer thickness is varied, we observe oscillations of magnetoresistance corresponding to oscillations of the interlayer coupling. The maximum of magnetoresistance is found for tCu=18.5 A (up to ΔR/R≊6%). We furthermore measure a very high differential magnetoresistance (ΔR/RΔH=1.4 kOe−1). A combination of antiferromagnetic coupling and quadratic in‐plane anisotropy is responsible for this large value of magnetoresistivity.