The electrodeposition of thin films of the element cobalt on silicon wafers opens the possibility of producing magnetic structures on top of a technological substrate using an efficient and inexpensive method. In this paper, we present an extensive study of the electrodeposition of Co on Si͑100͒ n-type substrates. Co thin films with metallic appearance and uniform thickness were obtained at deposition rates of 0.6 ͑2.8͒ nm/s for the 26 ͑104͒ mM Co electrolyte. A strong dependence of the surface roughness on the nucleation mechanism, i.e., instantaneous or progressive, was observed for layer thicknesses below 300 nm. Simultaneous magneto-optical Kerr effect and magnetoresistance measurements showed that magnetic behavior depends on the nucleation mechanism as well. Coercivity decays with increasing thickness, t, following a power law of the type t Ϫn , with n ϭ 1.6 ͑2.1͒ for the 26 ͑104͒ mM electrolyte, which reflects a strong dependence of the magnetic behavior on surface effects. A large variation of the in-plane coercive fields was observed for the 104 mM electrolyte, which varied from 730 to 13 Oe as film thickness increased from 26 to 260 nm.The electroplating technique is especially interesting due to its low cost, high throughput, and high quality of the deposits, being extensively used in the magnetic recording industry to deposit relatively thick Permalloy layers, for example. In this work, electrodeposition is used to prepare Co thin films on n-type Si substrates. The semiconducting substrates used conduct sufficiently well to allow electrodeposition without the need for a seed layer, leading to the integration of a convenient method for fabricating thin magnetic films and magnetic sensors with silicon technology.Different groups have already demonstrated the feasibility of direct electrodeposition of metallic layers on Si. 1-13 In particular, we draw attention to the fact that not much work has been done on the electrodeposition of Co layers on Si͑100͒. Continuous Co layers on Si with uniform thicknesses were obtained by Pasa and Schwarzacher. 6 The authors also describe the influence of hydrogen evolution as a function of deposition potential and cobalt sulfate concentration. More recently, Cerisier et al. 9 have reported on the structure and magnetic properties of Co films electrodeposited on Si͑100͒.In this paper we investigate in detail the deposition rate, current efficiency, as well as the evolution of surface roughness of Co thin films prepared under instantaneous and progressive nucleation mechanisms. Additionally, the simultaneous measurement of the surface magnetic hysteresis and magnetoresistance allowed us to obtain the dependence of the coercive field as a function of the thickness of the samples and concentration of the electrolytes. ExperimentalThe substrates used in our experiments were single side polished, technical grade ͑100͒-oriented Si wafers n-doped for a resistivity of 1-10 ⍀ cm. Electrical contact to each substrate was made through a GaAl back contact. An adhesive tape was used ...

Systematic measurements of giant magneto-impedance (GMI) and its relaxation (magneto-impedance aftereffect) have been carried out in a series of Co-rich amorphous ribbons ranging in magnetostriction values from −3.5 to +3.5 ppm. The value of GMI is a maximum for the alloy with the lowest value of magnetostriction, corresponding to a maximum of the transverse permeability. The impedance relaxation between two fixed times depends on the magnetostriction constant (λs) of the samples, and the observed trend is consistent with the theories which predict a direct relationship of the conventional permeability aftereffect (MAE) with the square of λs. Furthermore, the variation of the impedance aftereffect with the driving current resembles the behavior of MAE, and a connection between both effects can be established.

Thin films with the composition of the constantan alloy (a solid solution with 35 to 50 wt. % of Ni in Cu) have a high-thermoelectric power, which allows the fabrication of very sensitive heat-flux sensors based on planar technology. In this article, the thermoelectric properties of CuxNi100−x thin films electrodeposited on silicon were studied as a function of the composition, temperature, and thickness. The electrodeposition of thin layers on silicon is an important step for the integration of thermal sensors with semiconductor technology. The CuxNi100−x alloys were electrodeposited potentiostatically at room temperature, from a citrate electrolyte containing both copper and nickel sulfates. The layer composition was controlled by the applied potential in the range from pure copper (at −0.4 V/SCE) up to a solid solution of about 25 wt. % Cu in Ni (at −1.2 V/SCE). Extremely high values of thermoelectric power were measured for very thin layers of Cu40Ni60 on Si, showing a strong influence of the substrate. By considering the system as a thermoelectric bilayer and extracting the contribution of the semiconductor, thermopower values for the Cu40Ni60 alloys comparable to the expected ones for constantan wires were obtained.

No abstract

Cycloidal sector mass analyzers have, in principle, perfect focusing due to perpendicularly oriented uniform electric and magnetic fields, making them ideal candidates for incorporation of spatially coded apertures. We have previously demonstrated a proof-of-concept cycloidal-coded aperture miniature mass spectrometer (C-CAMMS) instrument and achieved a greater than 10-fold increase in throughput without sacrificing resolution, compared with a single slit instrument. However, artifacts were observed in the reconstructed mass spectrum due to nonuniformity in the electric field and misalignment of the detector and the ion source with the mass analyzer focal plane. In this work, we modified the mass analyzer design of the previous C-CAMMS instrument to improve electric field uniformity, improve the alignment of the ion source and the mass analyzer with the detector, and increase the depth-of-focus to further facilitate alignment. A comparison of reconstructed spectra of a mixture of dry air and toluene at different electric fields was performed using the improved C-CAMMS prototype. A reduction in reconstruction artifacts compared to our proof-of-concept C-CAMMS instrument highlights the improved performance enabled by the design changes.

Among the many methods developed for the synthesis of titanium dioxide, cathodic electrosynthesis has not received much attention because the resulting amorphous oxy‐hydroxide matrix demands a further thermal annealing step to be transformed into crystalline titania. However, the possibility of filling deep recessed templates by the control of the solid–liquid interface makes it a potentially suitable technique for the fabrication of porous scaffolds for photovoltaics and photocatalysis. Furthermore, a careful control of the crystallization process enables the growth of larger grains with lower density of grain boundaries, which act as electron traps that slow down electronic transport and promote charge recombination. In this report, well crystallized titania deposits were obtained by thermal annealing of amorphous deposits fabricated by cathodically assisted electrosynthesis on indium‐tin oxide (ITO)substrates. The combined use of Raman spectroscopy and X‐ray diffraction showed that the crystallization process is more intricate than previously assumed. It is shown that the amorphous matrix evolves into a rutile‐free mixture of brookite and anatase at temperatures as low as 200 °C that persists up to 800 °C, when pure anatase dominates. The amount of brookite in the brookite–anatase mixture reaches a maximum at 400 °C. This very simple method for obtaining a brookite–anatase mixture and the ability to tune their proportions by thermal annealing is a promising alternative whose potential for solar cells and photocatalysis deserves a careful evaluation. Copyright © 2011 John Wiley & Sons, Ltd.

A slow relaxation of the high-frequency impedance is observed in a Co 68.25 Fe 4.5 Si 12.25 B 15 amorphous wire after nucleation of a new domain pattern in a previously saturated sample. The observed impedance decay follows quasilogarithmic kinetics, and it is probably associated with the low-field ac magnetic permeability aftereffect of the circular domain walls. The impedance drop achieves relative amplitudes up to 1%, 16 s after the removal of the saturating external field. The effect is studied under typical magnetoimpedance experimental conditions, varying both the ac current amplitude and frequency. Although completely undesirable for many technical applications, the unique kinetic features of the impedance aftereffect may be explored to study circular magnetization processes under extreme domain-wall velocities. ͓S0163-1829͑97͒50410-3͔Although amorphous magnetic materials have been known for more than thirty years, their basic and applied interest has been constantly renewed, owing to the discovery of new and attractive properties. Recently, the observation of large field-induced changes in the high-frequency impedance of soft magnetic amorphous wires 1-3 and ribbons 4,5 opened enormous perspectives in the use of amorphous materials as cheap and sensitive magnetic-field sensors. When a highfrequency ( f Ͼ100 kHz͒ and low-intensity (iϽ15 mA͒ electrical current flows through a soft magnetic material, its impedance suffers a strong variation if an external magnetic field is applied to the sample. This effect, known as giant magnetoimpedance ͑GMI͒, can be qualitatively understood in terms of field-induced changes in the magnetic penetrationwhere is the electrical resistivity, is the transversal permeability ͑in the case of wires, it is the circular permeabil-ity͒, and f is the field ͑current͒ frequency. In a naive view, the application of a longitudinal dc magnetic field causes a strong variation in the transversal permeability, which is directly related to the imaginary component of the impedance ͑the reactance X͒, 3 causing a strong change in the penetration depth, and therefore influencing also the real part of the impedance ͑the resistance R͒. 3 Although rooted in classical electrodynamics, there are several aspects of GMI that remain to be understood, in particular, the role of induced anisotropies and the effect of different magnetization mechanisms in the observed phenomena. [2][3][4][5] On the other hand, it is well known that after a sudden rearrangement of the magnetic domain structure in amorphous ferromagnetic materials, a relaxing behavior of the low-field permeability is observed at any temperature ͑up to T c ͒, being characterized by quasilogarithmic relaxation kinetics. 7,8 This relaxation, also known as magnetic permeability aftereffect ͑MAE͒, or simply disaccommodation, has been explained in terms of directional ordering mechanisms of specific atoms, or atom pairs, interacting with the local magnetization vector. 7,8 The time relaxation of the magnetic permeability is thought to be an intrins...

We use evaporated C60 as the emitter in a vertical transistor structure with Au base and Si collector. The proportion of emitted electrons that overcome the barrier is measured as at least 0.99. Our metal-base transistor is easy to fabricate as it does not involve wafer bonding or require perfect semiconductor-on-metal growth.