The optical response from metal nanoparticles and nanostructures is dominated by surface plasmon generation and is critically dependent on the local structure and geometry. Electron energy-loss spectroscopy (EELS), combined with recent developments in spectrum imaging and data processing, has been used to observe the energy and distribution of surface plasmons excited by fast electrons. The energy of the plasmon responses is consistent with the optical response and with calculations. For gold and silver rods and ellipsoids, longitudinal, transverse and distinct cluster modes were readily identified and mapped. The spatial resolution of the presented maps is one order of magnitude better than that achievable with scanning near-field optical microscopy (SNOM)-based techniques.

https://iopscience.iop.org/article/10.1088/0957-4484/18/16/165505/pdf

Mapping surface plasmons at the nanometre scale with an electron beam

The recent experimental progress in spin-polarized scanning tunnelling microscopy (SP-STM)—a magnetically sensitive imaging technique with ultra-high resolution—is reviewed. The basics of spin-polarized electron tunnelling are introduced as they have been investigated in planar tunnel junctions for different electrode materials, i.e. superconductors, optically excited GaAs, and ferromagnets. It is shown that ferromagnets and antiferromagnets are suitable tip materials for the realization of SP-STM. Possible tip designs and modes of operations are discussed for both classes of materials. The results of recent spatially resolved measurements as performed with different magnetic probe tips and using different modes of operation are reviewed and discussed in terms of applicability to surfaces, thin films, and nanoparticles. The limits of spatial resolution, and the impact of an external magnetic field on the imaging process are debated.

https://iopscience.iop.org/article/10.1088/0034-4885/66/4/203/pdf

Spin-polarized scanning tunnelling microscopy

The combination of scanning tunneling microscopy (STM) with optical excitation adds new information to STM. A review is presented covering the work done on light-induced effects in STM during the past 15 years. Effects discussed include thermal effects, nonlinear effects, field enhancement at the STM tip, various effects on semiconductor surfaces, excitation of surface plasmons, detection of photoelectrons, spin-polarized tunneling, as well as light-induced nanomodifications, local optical spectroscopy, the use of ultrashort laser pulses for time-resolved STM, and the combination of STM and scanning near-field optical microscopy.

Photoassisted scanning tunneling microscopy

J. M. Ziman London: Cambridge University Press. 1964. Pp. 360. Price 45s. This book is essentially an account of the consequences of the lattice periodicity in solids. Much of the ground was well tilled in the author's treatise Electrons and Phonons (Oxford: The Clarendon Press, 1962) but, as a textbook, the new work covers a larger area while being less rigorous.

http://iopscience.iop.org/article/10.1088/0031-9112/16/7/012/pdf

Principles of the Theory of Solids

Nano-scale properties of defects in compound semiconductor surfaces

We report the direct imaging of electrically active Si dopants near the GaAs(110) surface with a scanning tunneling microscope at a temperature of 4.2 K. In the filled state images, we observe patterns of rings which are centered around the individual doping atoms. We believe these ring patterns are induced by the individual impurities, which, due to their charge, disturb the local potential and cause oscillations in the charge density, also called Friedel oscillations. In the empty state images no Friedel oscillations can be observed.

Direct observation of Friedel oscillations around incorporated SiGa dopants in GaAs by low-temperature scanning tunneling microscopy.

Zn- and Cd-induced features at the GaAs(110) and InP(110) surfaces studied by low-temperature scanning tunneling microscopy

STM-induced photon emission spectroscopy of granular gold surfaces in air

Advances toward spin‐sensitive scanning tunneling microscopy are reported here, using optically created spin polarized electrons in GaAs. As a first step, tunneling spectroscopy has been performed on GaAs samples with light excitation. Dependence of photoinduced effects on excitation power, tip–sample distance, and doping density are presented. Similar measurements were conducted for a cleaved GaAs tip, showing short circuit currents of several hundred pA upon laser illumination. Results support the feasibility of using such tips as a spin‐sensitive local probe.

Progress toward spin‐sensitive scanning tunneling microscopy using optical orientation in GaAs

Semiconductor tips are used as local photodetectors in a scanning tunneling microscope. We demonstrate that this configuration is sensitive to small light intensity variations, as supported by a simple model. The principle is applied to the detection of Faraday ellipticity of a Pt/Co multilayer sample. The outlook of this new technique in magneto-optical imaging is briefly discussed. >

M. C. M. M. van der Wielen

Papers

Direct observation of Friedel oscillations around incorporated SiGa dopants in GaAs by low-temperature scanning tunneling microscopy.

Zn- and Cd-induced features at the GaAs(110) and InP(110) surfaces studied by low-temperature scanning tunneling microscopy

STM-induced photon emission spectroscopy of granular gold surfaces in air

Progress toward spin‐sensitive scanning tunneling microscopy using optical orientation in GaAs

Magneto-optical Faraday effect probed in a scanning tunneling microscope