Direct generation of charge carriers in c-Si solar cells due to embedded nanoparticles

It is known that silicon is an indirect band gap material, reducing its efficiency in photovoltaic applications. Using surface plasmons in metallic nanoparticles embedded in a solar cell has recently been proposed as a way to increase the efficiency of thin film silicon solar cells. The dipole mode that dominates the plasmons in small particles produces an electric field having Fourier components with all wave numbers. In this work, we show that such a field creates electron-hole-pairs without phonon assistance, and discuss the importance of this effect compared to radiation from the particle and losses due to heating.Comment: 1 figur

Slow Relaxation and Equilibrium Dynamics in a 2 D Coulomb Glass: Demonstration of Stretched Exponential Energy Correlations

We have simulated energy relaxation and equilibrium dynamics in Coulomb Glasses using the random energy lattice model. We show that in a temperature range where the Coulomb Gap is already well developed, (T=0.03-0.1) the system still relaxes to an equilibrium behavior within the simulation time scale. For all temperatures T, the relaxation is slower than exponential. Analyzing the energy correlations of the system at equilibrium, we find a stretched exponential behavior. We define a time \tau_\gamma from these stretched exponential correlations, and show that this time corresponds well with the time required to reach equilibrium. From our data it is not possible to determine whether \tau_\gamma diverges at any finite temperature, indicating a glass transition, or whether this divergence happens at zero temperature. While the time dependence of the system energy can be well fitted by a random walker in a harmonic potential for high temperatures (T=10), this simple model fails to describe the long time scales observed at lower temperatures. Instead we present an interpretation of the configuration space as a structure with fractal properties, and the time evolution as a random walk on this fractal-like structure

Nonlinear acoustic and microwave absorption in disordered semiconductors

Nonlinear hopping absorption of ultrasound and electromagnetic waves in amorphous and doped semiconductors is considered. It is shown that even at low amplitudes of the electric (or acoustic) field the nonlinear corrections to the relaxational absorption appear anomalously large. The physical reason for such behavior is that the nonlinear contribution is dominated by a small group of close impurity pairs having one electron per pair. Since the group is small, it is strongly influenced by the field. An external magnetic field strongly influences the absorption by changing the overlap between the pair components' wave functions. It is important that the influence is substantially different for the linear and nonlinear contributions. This property provides an additional tool to extract nonlinear effects.Comment: correction : misspelled name in references correcte

Nonlinear acoustic and microwave absorption in glasses

A theory of weakly-nonlinear low-temperature relaxational absorption of acoustic and electromagnetic waves in dielectric and metallic glasses is developed. Basing upon the model of two-level tunneling systems we show that the nonlinear contribution to the absorption can be anomalously large. This is the case at low enough frequencies, where freqeuency times the minimal relaxation time for the two-level system are much less than one. In dielectric glasses, the lowest-order nonlinear contribution is proportional to the wave's intensity. It is negative and exhibits anomalous frequency and temperature dependencies. In metallic glasses, the nonlinear contribution is also negative, and it is proportional to the square root of the wave's intensity and to the frequency. Numerical estimates show that the predicted nonlinear contribution can be measured experimentally

Patients’ quest for recognition and continuity in health care: time for a new research agenda?

User involvement is important in democratization of health care and is assumed to contribute to better and more relevant research. Despite increased requirements for user involvement in research, more studies are still needed. This study aimed at exploring what research agenda people with varied health problems consider as important, based on their own experience. The study had a phenomenological approach with a qualitative design. The sample consisted of 23 informants; nine had been critically ill and 14 were suffering from chronic muscle pain. Data were collected in five focus group interviews and one individual interview. A phenomenological approach was used in analyzing the data. Written consent was obtained from all the participants, and ethical considerations were taken throughout the entire research process. Despite various experiences among the participants, a quest to be taken seriously over time by healthcare professionals emerged as a strong meaning structure in both groups. Based on these experiences, continuity across lifetime changes turned out to be an important research topic for future research. User involvement should be appreciated in all parts of the research process. A crucial prerequisite is that the users get the opportunity to bring their own experiences into the process.acceptedVersio