Simple and efficient scanning tunneling luminescence detection at low-temperature

We have designed and built an optical system to collect light that is generated in the tunneling region of a low-temperature scanning tunneling microscope. The optical system consists of an in situ lens placed approximately 1.5 cm from the tunneling region and an ex situ optical lens system to analyze the emitted light, for instance, by directing the light into a spectrometer. As a demonstration, we measured tip induced photoluminescence spectra of a gold surface. Furthermore, we demonstrate that we can simultaneously record scanning tunneling microscope induced luminescence and topography of the surface both with atomic resolution

InAs quantum dot morphology after capping with In, N, Sb alloyed thin films

Using a thin capping layer to engineer the structural and optical properties of InAs/GaAs quantum dots (QDs) has become common practice in the last decade. Traditionally, the main parameter considered has been the strain in the QD/capping layer system. With the advent of more exotic alloys, it has become clear that other mechanisms significantly alter the QD size and shape as well. Larger bond strengths, surfactants, and phase separation are known to act on QD properties but are far from being fully understood. In this study, we investigate at the atomic scale the influence of these effects on the morphology of capped QDs with cross-sectional scanning tunneling microscopy. A broad range of capping materials (InGaAs, GaAsSb, GaAsN, InGaAsN, and GaAsSbN) are compared. The QD morphology is related to photoluminescence characteristics

Erratum: Height control of self-assembled quantum dots by strain engineering during capping [Appl. Phys. Lett. 105, 143104 (2014)]

Two of the histograms in Fig. 3 have been accidentally swapped. 1 The third histogram (blue bars) represents the height distribution for quantum dots (QDs) capped with In x Ga (1- x )As, where x¿=¿0.05. The corresponding average height is 3.1¿±¿0.4¿nm. The second histogram (green bars) represents the height distribution for QD capped with In x Ga (1- x )As, where x¿=¿0.10. The average height for this distribution is 4.0¿±¿0.5¿nm

Kinetic Monte Carlo simulations and cross-sectional scanning tunneling microscopy as tools to investigate the heteroepitaxial capping of self-assembled quantum dots

In the last decade, an ever increasing understanding of heteroepitaxial growth has paved the way for the fabrication of a multitude of self-assembled nanostructures. Nowadays, nanostructures such as quantum rings,1 quantum wires,2 quantum dashes,3 quantum rods,4 and quantum dots (QDs)5 can be grown with relative ease. Among these, QDs have, due to their 0-dimensional nature, received the most attention and are applied or suggested in QD lasers,6,7 single-photon emitters,8 single-electron transistors,9 and spin manipulation.10,11 As the electronic properties of QDs strongly depend on their size, shape, and chemical composition, a detailed knowledge of the growth process and the resulting QD morphology is needed in order to understand the involved physics and tune their properties. A large variety of imaging techniques are available to study the morphology, the dimensions, and the chemical composition of self-assembled QDs, e.g., scanning/ transmission electron microscopy,12 x-ray diffraction,13 atomic force microscopy,14,15 atom probe tomography,16,17 and cross-sectional scanning tunneling microscopy (X-STM).18 However, all the existing imaging techniques can only provide snapshots of the QDs after the growth is completed. At the moment, only a few techniques, e.g., reflection highenergy electron diffraction (RHEED),19 in situ accumulated stress measurements,20 and spectroscopic ellipsometry,21 can give real-time information during the growth and thereby help monitoring the growth. But, if such techniques provide valuable information about the growth surface, the averaging nature of the techniques makes them of little use when studying atomic-scale processes such as intermixing or segregation. In this respect, kinetic Monte Carlo (KMC) simulations of the heteroepitaxial growth process can be of great value and provide further insight on the growth dynamics. However, such KMC simulations are computationally challenging22,23 and still need validation by an experimental imaging technique. In this paper, we presentKMCresults using recent developments in computational methods.24 The KMC simulations are compared to atomically precise QD morphologies extracted from experimental X-STM images. These two techniques are used in conjunction to study strain engineering of the capping layer25,26 as a method to control the height of quantum dots, an important parameter determining the QDs emission wavelength. We show that KMC simulations not only are in good agreement with the X-STM study, but also provide valuable details of the growth process that hitherto could not be obtained