Third Day Poster Session, 17 June 2010 - NanoTR-VI

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P and
Poster Session, Thursday, June 17
Theme F686 - N1123
Photon Scanning Tunneling Microscopy System for Observing Optical Excitations at Nanoscale
Tunnel Junctions
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Tansu ErsoyP P, Mehmet Selman TamerP
UOuzhan GürlüUP P*
1
Pstanbul Technical University, Department of Physics, Maslak, 34469, stanbul, Turkey
Abstract-We are developing an optical system which is capable of collecting the photons emitted from the tunnel junction of a scanning
tunneling microscope. These systems allow mapping the photon emission from a surface with sub nanometer spatial resolution. Electronic and
optical properties of nanostructures like quantum dots or quantum wires will be studied by this system.
Images with atomic resolution of semiconductor and metal
surfaces can be obtained using scanning tunneling microscopy
(STM) [1]. Moreover optical and electronic properties of these
surfaces can be examined by STM at nanoscale [2]. The
tunneling current between the tip and the surface can excite
optical transitions on the surface [3]. This is called
electroluminescence due to inelastic tunneling. STM-light
emission experiment is a recently emerging and very useful
technique for investigating optical properties of surfaces with
nanometer resolution [4].
Nanostructures have different characteristics from bulk
materials. As the size of the materials approach to nanoscale,
quantum effects appear, which is very important for device
applications [5]. If a semiconductor crystal becomes very
small, motion of the charge carriers is restricted. This
phenomenon is known as quantum confinement. This results
in sharp electronic states in these structures. In order to
understand quantum effects there are numerous studies for
developing nanostructures and methods for investigating their
electronic and optical properties [4,5,6].
Metals also behave unconventionally physical properties at
nano scale. For instance Ag films coated on glass or mica has
a rough structure due to which the surface plasmon polaritons
are confined. These effects the optical properties of the films
greatly like giving the film unexpected color. Using the
photon scanning microscope one can study the local electrooptical
properties [7] of these films and their interaction with
adsorbates.
most efficient way [10] and they have to be spectroscopically.
analyzed. Thus, electroluminescence spectroscopy at
nanoscale can be performed.
Figure 2. In inelastic tunneling, electrons that tunnel from the tip to
the surface lose some of their energy. Photons are generated in this
process. Energy lost due to excitations can be observed by
conductivity measurements. They appear as peaks in the second
derivative of the tunneling current with respect to sample bias [9].
Figure 3. A simple representation of photon STM setup.
First we are planning to investigate optical properties of
metal surfaces like vacuum evaporated rough Au or Ag films
on glass. Later on we will investigate core/shell quantum dots
like CdSe/ZnS. Optical behavior of QDs on gold surfaces will
be observed by STM induced light emission technique.
Depending on structures and positions of QDs on gold surface
we are expecting variations in their optical behaviors.
Moreover, we will investigate the results of the interactions of
QDs with various surfaces and with their environments.
*Corresponding author: HTgurlu@itu.edu.trTH
Figure.1. (a) STM image of sputter coated Ag film on glass.
(500 nm x 500 nm at Vs = 2.0 V and I = 5.0 nA.). (b) Photon
map of the surface due to inelastic tunneling [7].
In this work, we are designing a setup which is suitable for
STM light emission experiments. When inelastic electron
tunneling occurs at nanoscale tunnel junctions, photon
emission is possible [8] (Figure.2). Our aim is to develop the
experimental setup which will allow investigating the systems
that cause photon emission from these tunnel junctions.
The main problem in these experiments is low photon
efficiency in most of the physical systems to be investigated.
Therefore the generated photons have to be collected in the
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6th Nanoscience and Nanotechnology Conference, zmir, 2010 623