download - Gaia Science

attolight
Attolight AG
EPFL Innovation Square
PSE D
1015
Description
Lausanne
Switzerland
t
The
+41
core
21 626
piece
0100
of Attolight's instrument is a
custom designed scanning electron microscope
www.attolight.com
(SEM). SEM is a widely used scanning probe
technology since it has the ability to image the
surface features of a sample with very high
spatial resolutions going below one nanometer
(10 -9 m) today. An SEM consists of an electron
source and electron optics that focuses the
electron beam to a nanometer sized spot. The
image (or map) is constructed by scanning the
electron beam over the sample point by point
(see Fig. 1). The impinging electron beam on
the sample surface creates secondary electrons
and photons that are emitted. At each scanned
point on the sample, the intensity of the secondary
electron (SE) signal is recorded and a
pixel is shown on the screen with a grey scale
level proportional to the SE signal intensity.
incoming
electron beam
TECHNOLOGY BRIEF
Attolight uses a proprietary technology to create
ultrashort electron pulses instead of a continuous
electron beam (see Fig. 2). The SEM
and electron source have to be custom designed
to reach high spatial resolutions and
short pulses. Our new tool will deliver a few
nanometers spatial resolution and pulses
shorter than 10 picoseconds (1 picosecond =
10 -12 s) at a repetition rate of typical 80 MHz
(repetition rate can be changed easily). The
photoelectric effect is used to create such short
electron pulses: short UV laser pulses are sent
on a thin metal film which creates short electron
pulses. The design and manufacturing of
the electron source is a core competence of
Attolight. A lot of care has to be taken in designing
the electron source and the electron
optics in order to keep the pulses short and
well focused and still intense enough to carry
out measurements.
electrons
incoming
electron beam
Sample
light
Fig. 2 Attolight technology
electrons
Sample
light
Fig. 1 Principle of standard SEM
Time resolved spectroscopy
This is our “home” application in the R&D market.
Initially, the tool was built for this application.
We exploit a phenomena called cathodoluminescence
(CL): some semiconductors emit
light when they are bombarded with an electron
beam containing electrons carrying a certain
energy. This light is called CL and contains
a lot of information on optical properties of the
material under test. CL is often used to analyse
semiconductor based nanostructures since the
spatial resolution is very high. CL is a excitation
spectroscopy technique with very high spatial
resolution.
Our idea was not just to look at a continuous
CL signal but also at the lifetime of the signal
in the picosecond regime. To achieve this we
adapted an ultrafast light detector (STREAK
camera) to our instrument. We call this tool
pTRCL (picosecond time-resolved CL).
© 2011 Attolight AG - All rights reserved.