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 ...

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A decadência da tiragem de jornais impressos no Brasil, que acompanhava uma tendência internacional, transformou-se em um fenômeno único observado no país. A retomada do sucesso editorial deste meio com a adoção de novas características que dirigem conteúdo e forma às camadas populares. Em Santa Catarina, foram examinados jornais numa amostra representativa de todo o estado, através da Análise de Conteúdo de acordo com as definições de Krippendorff (1990). O que se pode observar é o estabelecimento de um novo padrão de jornalismo de interior catarinense, com o conteúdo próprio do que hoje se classifica como Jornalismo Popular de Qualidade – a preferência pelo local e pelo serviço à  comunidade a que se destina, abandonando antigos traços deste segmento, como o sensacionalismo.

The electrochemical etching of (100) n-type Si was investigated in dilute HF solutions containing copper. Two anodic current regimes were observed: one, as expected, dependent on the HF concentration and the other one on the Cu concentration. The enhancement of the anodic current in the Cu concentration dependent regime is related to an increase of the chemical etching of silicon associated to reactions involving OH (or H20) species. The etching of Si, influenced by the metal, occurs concomitantly to the reduction of Cu ions. Rutherford backscattering from Cu deposits obtained in the anodic regime revealed the existence of oxygen at the Cu/Si.The interaction of silicon surfaces with fluoride ions is an important method for surface modification.1'2 One example is the anodic dissolution of both p-and n-type silicon in fluoride-containing aqueous media. Under the appropriate conditions this dissolution leads to the electropolishing of silicon or to the formation of a porous silicon layer.Concerning the reaction mechanism for anodic etching of silicon in fluoride-containing electrolytes there are some details which remain unresolved, It is unclear if the etching of silicon occurs through direct rupture of the Si-Si back bonds at the Si-H surface or through the formation of intermediate species such as Si-F or Si-OH.2 There are strong evidences suggesting that the reaction proceeds through the formation of Si-OH followed by reaction of the Si-Si back bonds with HF. Bitzer et al.3 observed Si-OH species at the surface of silicon at the peak of a dark current transient and Watanabe et aL4 detected a stretching vibration corresponding to Si-OH species on HF treated (100) Si surface followed by immersion into water. Jakob and Chabal5 suggested possible reactions involving OH (or H20) and Si-H groups and the subsequent attack by HF. As the surface remains hydrogen-terminated during the etching process, it is expected that the reaction involving the HF attack is relatively fast as compared to the insertion of the OH groups into Si-H bondsY In this article, the approach is to show an enhancement of the anodic current of n-type silicon electrodes mediated by the presence of copper in dilute HF solutions. The results are correlated to an etching mechanism involving OH groups.The anodic electrodeposition experiments were performed in a conventional three-electrode cell using a potentiostat (EG&G Model 362) to control the potential retative to a saturated calomel reference electrode (5CE). The electrochemical cell was made of polyvinyl chloride (PVC, hydrofluoric acid-resistant) and the counterelectrode consisted of a Pt foil. The working electrodes were ntype (100) Si single crystals with a resistivity of 10 cm. Prior to the experiment, the Si substrates were etched with an aqueous solution containing 5% hydrofluoric acid. An ohmic back contact was then fabricated with a Ga-Al eutectic alloy. All the samples were fixed on a stain'ess steel oU with a conductive paste. The resulting structure was electrically isolated from the el...