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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...

In this work we investigated the surface morphology of electrodeposited polyaniline (PANI) and sulfonated polyaniline (SPAN) films grown directly on Si or on Au/glass substrates respectively, by applying constant or square wave potentials. Atomic force micrographs of samples with thicknesses in the range of 20 to 800 nm showed compact and granular surfaces with roughness varying between 3 and 30 nm. To investigate the evolution of roughness in a more quantitative way scaling analysis was applied, revealing characteristics of a self-affine fractal surface with exponents showing a dependence on the material (PANI or SPAN) and on the applied potential (constant or square wave).

Two anodic current regimes are observed during electrochemical etching of (100) n-type Si in dilute CuSO4/HF; one is dependent on the HF concentration and the other on the Cu2+ concentration. Assuming a dissolution mechanism of Si based on the reaction of OH (or H2O) species followed by HF attack, the presence of copper accelerates this mechanism and consequently increases the anodic current. -(MARTINS, L. F. O.; SELIGMAN, L.; SANTOS FILHO, S. G.; D'AJELLO, P. C. T.; HASENACK, C. M.; PASA, A. A.; J. Electrochem. Soc. 144 (1997) 5, L106-L108; Dep. Fis., Univ. Fed.