Contact-induced spin polarization in carbon nanotubes

Motivated by the possibility of combining spintronics with molecular structures, we investigate the conditions for the appearance of spin-polarization in low-dimensional tubular systems by contacting them to a magnetic substrate. We derive a set of general expressions describing the charge transfer between the tube and the substrate and the relative energy costs. The mean-field solution of the general expressions provides an insightful formula for the induced spin-polarization. Using a tight-binding model for the electronic structure we are able to estimate the magnitude and the stability of the induced moment. This indicates that a significant magnetic moment in carbon nanotubes can be observed.Comment: To appear in Phys. Rev. B (2003

Thermal resistanse and nonuniform distribution of electroluminescence and temperature in high-power AlGaInN light-emitting diodes

The paper studies current spreading, light emission, and heat transfer in high-power flip-chip light-emitting diodes (LEDs) and their effect on the chip thermal resistance by experimental and theoretical approaches. The thermal resistance was measured using two methods: by monitoring the transient response of the LED operation voltage to the temperature variation with the Transient Tester T3Ster and by temperature mapping with the use of an infrared thermal-imaging microscope. The near field of the electroluminescence intensity was recorded with an optical microscope and a CCD camera. Three-dimensional numerical simulation of the current spreading and heat transfer in the LED chip was carried out using the SimuLED package in order to interpret the obtained experimental results