Mju Ferreira

Optical characterisation of anatase: a comparative study of the bulk crystal and the polycrystalline thin film

The optical parameters of crystalline anatase and polycrystalline anatase films prepared by reactive magnetron sputtering were examined by spectroscopic ellipsometry and optical transmittance spectroscopy, respectively. Some films were doped with aluminium or chromium. In general, the values of the optical bandgap for the films are consistently blue-shifted as compared with the crystal. The blue shift is also found for some films doped with Al and Cr. The width of the absorption bands is considerably narrower in the films than in the crystal. These effects are interpreted as resulting from the spatial confinement of electrons and holes in the TiO2 microcrystallites. The average crystallite size determined from the shift of the optical gap was found to be in the range ∼5–8 nm, in excellent agreement with the data obtained from small-angle X-ray diffractometry.

Thin film deposition by magnetron sputtering and determination of some physical parameters

Abstract We have deposited semiconductor thin films by means of a home-made magnetron sputtering apparatus. Some physical parameters of the films have been determined, namely the thickness, the optical properties, the electrical resistivity and the crystalline structure.

Construction and performance of a magnetron sputtering apparatus

A magnetron sputtering device has been designed, built and tested in the physics laboratory of the University of Minho and is currently being used to deposit high quality metal films onto polymer substrates. The design includes twin sputtering heads to allow for two layer film production without removing the substrate from the vacuum chamber. In house development and construction of most parts and the use of readily available parts in some cases, permitted the construction of low cost equipment in a very short time. The equipment has proven to be very reliable in use, and details are given of its performance in terms of cycle time and electrical characteristics. The films produced have been characterized in terms of adhesion, thickness, reflectivity and crystal structure and the results of those analyses are presented. Further experiments with this equipment will include tests with reactive sputtering and the deposition of films for surface hardening. This future work is outlined in the presentation.

Triterpenoids as antiproliferative agents in classical and atypical multidrug resistant cancer cells

Resistance of cancer cells to multiple classes of structurally and mechanistically unrelated antitumor drugs can be defined as multidrug resistance (MDR), and it is one of the major causes of chemotherapy failure. The most significant mechanism of MDR, referred as typical or classical, results from altered cell membrane transport due to overexpression of transporter proteins that act as efflux pumps, such as P-glycoprotein (Pgp/MDR1). Conversely, MDR cells without overexpression of transporter proteins are referred as atypical MDR cells and their resistance has been associated with altered DNA topoisomerase II. Topoisomerases are nuclear enzymes crucial to DNA replication, transcription, and recombination. According to some authors, atypical MDR may result from altered expression of some metabolizing enzymes [1]. Therefore, a promising approach to overcome MDR is the development of compounds that are selectively cytotoxic to resistant cancer cells.

Antimalarial activity of triterpenoids with the cucurbitane skeleton

Malaria, caused by protozoan parasites of the genus Plasmodium, is a devastating infectious disease in developing countries. One of the biggest problems that have hindered the control of malaria is the emergence and spread of drug resistant Plasmodium strains, particularly Plasmodium falciparum. In order to overcome this problem, new therapeutic agents based on new mechanisms of action or with new structures are urgently needed. Plants have been an important source of medicines against malaria. Quinine and artemisinin, two of the most important antimalarials currently in use, were derived from plants [1,2].