<p>This paper presents reliable synthesis of germanium nanowires by the vapor-liquid-solid method using copper as an alternative catalyst to gold, the most commonly used metal. The morphological study showed long range single-crystalline germanium nanowires with diamond structure and diameters ranging from 20 nm to 80 nm and lengths in tenths of a micrometer, which was much larger than the cross-section. In an investigation of electronic properties, devices built from a thin film of nanowires were studied and the semiconductor behavior of the samples confirmed, with variable range hopping identified as the main transport mechanism. Additionally, metal-nanowire contact behavior - ohmic or with Schottky barrier - was found to depend on the metal used in the device. Therefore, the possibility of controlling current-voltage behavior combined with the good crystalline quality of the nanowires renders these nanostructures an attractive option for future electronic and optoelectronic applications.</p>

Neste trabalho, apresentamos um experimento simples para o estudo e análise dos possíveis danos que uma máquina rotativa, desbalanceada, pode causar em um sistema quando esta encontra-se com freqüência de rotação próxima ou igual a freqüência de ressonância do sistema. Embora o modelo apresentado seja simples, poderá servir de base para compreender a importância do estudo em vibração neste ramo da engenharia.

In this work, we reported an experiment useful to the study and analysis of the damages caused by an unbalanced machine in a given system when the machine presents a vibration frequency near the characteristic resonance frequency of the system. Besides the simplicity of the model it will be useful in order to ilustrate the importance of the study of vibrations in enginnering.

Tratar fenômenos ondulatórios como o de batimentos e ressonância em cursos introdutórios de Física pode, às vezes, apresentar-se como um processo complicado, dada a dificuldade de visualização dos fenômenos citados. Neste trabalho, apresentamos uma forma bastante simples e acessível para proporcionar a visualização destes fenômenos usando um oscilocópio e um circuito amplificador muito simples.

It can be a hard task to introduce the beating and resonance effects in physics courses due to the difficulties for the visualization of these effects. In this work, we present a simple way which can help the visualization of these effects, using an oscilloscope and an easy-to-built electronic amplifier.

A systematic investigation of the properties of the InAs/GaAs self-assembled quantum dots (SAQDs) system subjected to a post-growth annealing using capacitance-voltage, Raman scattering and photoluminescence measurements is presented. The application of both electrical and optical methods allowed us to obtain reliable information on the microscopic structural evolution of this system. The single layer and the multilayer quantum dots were found to respond differently to the annealing process, due to the differences in strain that occur in both systems. The diffusion activated by strain provoked the appearance of an InGaAs alloy layer in substitution to the quantum dots layers; this change occurred at the annealing temperature T = 600 ºC in the multilayer system. A single dot layer, however, was observed even after the annealing at T = 700 ºC. Moreover, the low temperature annealing was found to improve the homogeneity of the multilayer system and to decrease the electrical interlayer coupling.