The wave function of a hole bound to an individual Mn acceptor in GaAs is spatially mapped by scanning tunneling microscopy at room temperature and an anisotropic, crosslike shape is observed. The spatial structure is compared with that from an envelope-function, effective mass model and from a tight-binding model. This demonstrates that anisotropy arising from the cubic symmetry of the GaAs crystal produces the crosslike shape for the hole wave function. Thus the coupling between Mn dopants in GaMnAs mediated by such holes will be highly anisotropic.

We demonstrate experimentally the electrical ballistic electron spin injection from a ferromagnetic metal / tunnel barrier contact into a semiconductor III-V heterostructure. We introduce the Oblique Hanle Effect technique for reliable optical measurement of the degree of injected spin polarization. In a CoFe / Al 2 O 3 / GaAs / (Al,Ga)As heterostructure we observed injected spin polarization in excess of 8 % at 80K.

Localized surface plasmon resonances possess very interesting properties for a wide variety of sensing applications. In many of the existing applications, only the intensity of the reflected or transmitted signals is taken into account, while the phase information is ignored. At the center frequency of a (localized) surface plasmon resonance, the electron cloud makes the transition between in- and out-of-phase oscillation with respect to the incident wave. Here we show that this information can experimentally be extracted by performing phase-sensitive measurements, which result in linewidths that are almost 1 order of magnitude smaller than those for intensity based measurements. As this phase change is an intrinsic property of a plasmon resonance, this opens up many possibilities for boosting the figure-of-merit (FOM) of refractive index sensing by taking into account the phase of the plasmon resonance. We experimentally investigated this for two model systems: randomly distributed gold nanodisks and gold nanorings on top of a continuous gold layer and a dielectric spacer and observed FOM values up to 8.3 and 16.5 for the respective nanoparticles.

Nanometer-scale pores are capable of detecting the size and concentration of nanometer-sized analytes at low concentrations upon analyzing their translocation through the pore, in small volumes and over a short time without labeling. Here, we present a simple, widely applicable, robust, and precise method to measure the zeta-potential of different nano-objects using nanopores. Zeta-potential i.e., a quantity that represents electrical charge in nanocolloids, is an important property in manufacturing of pharmaceuticals, inks, foams, cosmetics, and food. Its use is also imperative in understanding basic properties of complex dispersions including blood, living organisms, and their interaction with the environment. The characterization methods for zeta-potential are limited. Using the nanopore technique, the zeta-potential and the charge of nanoparticles can be measured independently of other parameters, such as particle size. This simple method is based on measuring the duration of the translocation of analytes through a nanopore as a function of applied voltage. A simple analytical model has been developed to extract the zeta-potential. This method is able to detect and differentiate nanometer-sized objects of similar size; it also enables the direct and precise quantitative measurement of their zeta-potential. We have applied this method to a wide range of different nanometer-sized particles and compared the results with values measured by commercially available tools. Furthermore, potential capability of this method in detection and characterization of virions is shown by measuring the low zeta-potential of HIV and EBV viruses.

We demonstrate an electrically injected electron spin polarization in GaAs of 80% at 4.6 K by interband tunneling from the valence band of (Ga,Mn)As into an (Al,Ga)As light-emitting diode. The polarization is analyzed by the oblique Hanle effect and vanishes at 120 K, the Curie temperature of the (Ga,Mn)As injector. The temperature and the bias dependence of the polarization are explained in terms of the properties of the (Ga,Mn)As/GaAs diode.

The plasmonic properties of individual subwavelength-sized silver nanocubes are mapped with nanometric spatial resolution by means of electron energy-loss spectroscopy in a scanning transmission electron microscope. Three main features with different energies and spatial behavior (two peaked at the corners, one on the edges) are identified and related to previous measurements on ensemble or individual nanoparticles. The highly subwavelength mapping of the energy position and intensity of the excitations shows that the surface plasmon modes, localized at specific areas of the particles, for example, the corners or the edges, are modified by their size, the presence of a substrate, and the very local environment. Helped by discrete dipole approximation numerical simulations, we discuss how local modifications of the environment affect the global modes of the particles. In particular, we show both experimentally and theoretically that absorption resonances at different corners of the same nanocube are largely independent of each other in energy and intensity. Our findings provide a better understanding of the spatial coherence of the surface plasmons in nanoparticles but also give useful insights about their roles in the nanoparticle sensing properties.

We investigate the electrical injection of spin-polarized electrons into a semiconductor ͓Al͑GaAs͔͒ heterostructure from ferromagnetic FeCo metal through an AlO x tunnel barrier. We have developed the optical oblique Hanle effect approach for the quantitative analysis of electrical spin injection into semiconductors. This technique is based on the manipulation of the electron spins within a semiconductor when spin polarized electrons have been injected. This allows us to clearly separate the effects caused by spin injection from others, that are magneto-optical, Zeeman, etc. Simultaneously, the oblique Hanle effect approach provides additional information on the spin dynamics in the semiconductor. In the FeCo/AlO x /Al(GaAs) heterostructures we observe spin injection of 21% and 16% at 80 and 300 K, respectively. The importance of electron thermalization effects and the impact of the doping level of the semiconductor for practical investigation of spin injection by optical means are demonstrated.

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