The ellipsometry of anisotropic manganese dioxide films electrodeposited at anodic potentials

Abstract

A eletrodepositação galvanostática de filmes de dióxido de manganês com espessuras en tre 0 e 1000 nm foi investigada por elipsometria in situ. Os resultados obtidos podem ser ajustados em termos de uma anisotropia uni ax ial do filme para o intervalo completo de espessuras. Os índices ópticos e as espessuras foram calculados. As propriedades anisotrópicas podem ser relacionadas a uma orientação preferencial do depósito.The galvanostatic electrodeposition of man ga nese di ox ide films in the thick ness range from 0 to 1000 nm was in ves ti gated by in situ ellipsometry. The re sults ob tained can be fit into the whole thick ness range in terms of the uni ax ial ani so tropy of the film. The op ti cal in di ces and thick nesses were cal cu lated. The anisotropic prop er ties may be re lated to a pref er en tial orien ta tion of the de pos its. Key words: ellipsometry, man ga nese ox ide, ani so tropy In tro duc tionThe man ga nese ox ides are nu mer ous and many of their struc tures are poorly known 1 . Mn0 2 has been widely studied and many phys i cal and chem i cal prop er ties such as elec tri cal con duc tiv ity, po ros ity, man ga nese con tent, surface area, elec trode po ten tial, pore size, and par ti cle shape and size, have been mea sured and dis cussed in terms of the dry cell per for mance 2 . The ac tiv ity of the man ga nese ox ide lay ers de pends strongly on the de po si tion con di tions 3,4 . The op ti cal char ac ter iza tion of Mn0 2 is very valu able for the cor re la tion of in situ charge stor age ca pac ity and structural changes as a func tion of the ap plied po ten tial. However, ellipsometric stud ies are lim ited to a few ar ti cles 5,6 . Re cently, an od i cally de pos ited Mn0 2 films were in ves tigated by ellipsometry 7 . Op ti cal re sults could not be explained as the growth of iso tro pic or anisotropic lay ers in the case of thick films and the re ported data were in terpreted as sum ing a de pend ence of the ex tinc tion co ef fi cient on the thick ness 6,7 .In the pres ent pa per, we re port an in situ ellipsometric in ves ti ga tion of an odic man ga nese ox ide films grown galvanostatically. The re sults ob tained give ev i dence of the uni ax ial ani so tropy of the films, which may be re lated to a pref er en tial ori en ta tion of the de pos its.Ar ti cle

An Ellipsometric Study of Manganese Oxide Films

“…23,24 The results obtained can be reasonably fitted into the whole thickness range in terms of the uniaxial anisotropy of the films. The anisotropic properties were related to preferential orientation of the deposits.…”

“…21,22 More recently, we have obtained a good fit of the optical data for the galvanostatic growth of MnO 2 films in a wide thickness range using a single-film model with optical anisotropy of the oxide. 23,24 The optical properties obtained for the anisotropic films were found to be dependent on the current density employed for the growth. shows the ellipsometric results for a film grown at E f ϭ 0.75 V ͑in this case ⌿ and ⌬ values were collected for both signs of ellipticipy͒ as well as the simulations for the best fit using the single-layer model up to a thickness of ca.…”

“…23 Pulses of 1 s (⌬t ϭ 1 s) were applied from an initial potential E in ϭ 0.65 V ͑vs. Hg/Hg 2 SO 4 /Na 2 SO 4 1 M͒ to different final potential values (E f ), where the anodic deposition of MnO 2 from Mn 2ϩ takes place.…”

“…Hg/Hg 2 SO 4 /Na 2 SO 4 1 M͒ to different final potential values (E f ), where the anodic deposition of MnO 2 from Mn 2ϩ takes place. 23 E f was changed in the potential range from 0.68 to 0.90 V. The number of pulses (N) was varied between 2 and 100. The platinum substrate was cleaned in a 1:1 H 2 SO 4 ϩ HNO 3 mixture and then polished to a mirror surface with 0.05 m alumina.…”

“…The ⌿-⌬ plots were analyzed according to different models. 23,24 The Simplex Method 26,27 was used to minimize the error as previously described. 28,29 The anodic growth of manganese oxide films was followed ellipsometrically during the application of the potentiostatic pulses in the deposition solution.…”