Search results for "AAS"
showing 10 items of 1173 documents
Optical characterization of individual GaAs quantum dots grown with height control technique
2013
We show that the epitaxial growth of height-controlled GaAs quantum dots, leading to the reduction of the inhomogeneous emission bandwidth, produces individual nanostructures of peculiar morphology. Besides the height controlled quantum dots, we observe nanodisks formation. Exploiting time resolved and spatially resolved photoluminescence we establish the decoupling between quantum dots and nanodisks and demonstrate the high optical properties of the individual quantum dots, despite the processing steps needed for height control. © 2013 AIP Publishing LLC.
Blue lasing at room temperature in high quality factor GaN/AlInN microdisks with InGaN quantum wells
2007
The authors report on the achievement of optically pumped III-V nitride blue microdisk lasers operating at room temperature. Controlled wet chemical etching of an AlInN interlayer lattice matched to GaN allows forming inverted cone pedestals. Whispering gallery modes are observed in the photoluminescence spectra of InGaN/GaN quantum wells embedded in the GaN microdisks. Typical quality factors of several thousands are found (Q>4000). Laser action at similar to 420 nm is achieved under pulsed excitation at room temperature for a peak power density of 400 kW/cm(2). The lasing emission linewidth is down to 0.033 nm.
Landau Fermi Liquid Theory and Beyond
2014
In this chapter we consider the Landau theory of the Fermi liquid that has a long history and remarkable results in describing a numerous properties of the electron liquid in ordinary metals and Fermi liquids of the \(^3\)He type. The theory is based on the assumption that elementary excitations determine the physics at low temperatures, resembling that of weakly interacting Fermi gas. These excitations behave as quasiparticles with a certain effective mass. The effective mass \(M^*\) exhibits a simple universal behavior, for it is independent of the temperature, pressure, and magnetic field strength and is a parameter of the theory. Microscopically deriving the equation determining the eff…
The Statistical Description of de Haas—van Alphen Oscillations in Silicon Nanosandwich
2020
Here, we present room temperature de Haas—van Alphen oscillations measured in silicon nanosandwich in a weak magnetic field. Our results demonstrate a decrease of the oscillation magnitude with increasing magnetic field strength. This behavior is drastically different from the results reported earlier and it is attributed to the low-dimensionality of the studied structure, which enables room temperature observation of the de Haas—van Alphen effect in moderate magnetic fields up to 1000 Oe. We employ the classic Lifshitz-Kosevich formalism based on the dependence of the carrier effective mass on the applied magnetic field, to statistically describe this effect. We note that the statistical a…
Chiral Instabilities and the Onset of Chiral Turbulence in QED Plasmas
2020
We present a first principles study of chiral plasma instabilities and the onset of chiral turbulence in QED plasmas far from equilibrium. By performing classical-statistical lattice simulations of the microscopic theory, we show that the generation of strong helical magnetic fields from a helicity imbalance in the fermion sector proceeds via three distinct phases. During the initial linear instability regime the helicity imbalance of the fermion sector causes an exponential growth(damping) of magnetic field modes with right(left) handed polarization, for which we extract the characteristic growth (damping) rates. Secondary growth of unstable modes accelerates the helicity transfer from fer…
Electric conduction in semiconductors: a pedagogical model based on the Monte Carlo method
2008
We present a pedagogic approach aimed at modelling electric conduction in semiconductors in order to describe and explain some macroscopic properties, such as the characteristic behaviour of resistance as a function of temperature. A simple model of the band structure is adopted for the generation of electron–hole pairs as well as for the carrier transport in moderate electric fields. The semiconductor behaviour is described by substituting the traditional statistical approach (requiring a deep mathematical background) with microscopic models, based on the Monte Carlo method, in which simple rules applied to microscopic particles and quasi-particles determine the macroscopic properties. We …
Kalmbergin kartasto R IVa : List 3
1856
Toiminnanohjausjärjestelmä pilvessä vai yrityksen sisällä : ei-toiminnallisten ominaisuuksien vertailu
2018
ERP-järjestelmät ovat yrityksen menestyksen kannalta tärkeä osa, etenkin isoissa yrityksissä. Niiden tarkoituksena on käsitellä, kerätä, analysoida ja tuottaa dataa yrityksen tarpeisiin. ERP-järjestelmien ongelmana on korkeat lisenssikustannukset ja niiden tarvitsema kallis infrastruktuuri. Pilviteknologian kehitys on tuonut mahdollisuuden myös pienille- ja keskisuurille yrityksille hankkia ERP-järjestelmä. Pilvipohjaiset ERP-järjestelmät ovat kustannustehokkaita, joustavia ja helposti skaalautuvia, joten ne soveltuvat erityisen hyvin pienille yrityksille. Tässä kandidaatintutkielmassa, joka on tehty kirjallisuuskatsauksena, on tarkoitus tehdä vertailua perinteisen ERP-järjestelmien ja pilv…
Mikroaaltoplasmageneraattorin happi- ja typpiplasmojen valoemissio näkyvän valon aallonpituusalueella
2016
Työssä analysoidaan matalan lämpötilan happi- ja typpiplasmojen emissiospektrejä näkyvän valon alueella. Työn teoreettisessa osiossa käydään läpi plasman määritelmä, törmäysreaktioiden vaikutusala, tuottotaajuuskertoimet, yksittäisen atomin sekä kaksiatomisen molekyylin viritystilat ja näistä johtuvat mahdolliset emissiopurkaustyypit. Kokeellisessa osassa esitellään mittauslaitteisto ja käydään läpi 2,45\,GHz mikroaaltoplasmageneraattorin operointiparametrien vaikutus valontuottoon. Tarkastellut operointiparametrit ovat magneettikentän voimakkuus, neutraalin kaasun paine ja plasmaa lämmittävän mikroaaltolähettimen teho. Happiplasman emissiospektri eroaa typpiplasman emissiospektristä. Happi…