Electron flashes for the nanoworld -- a new source of ultrashort electron pulses

January 30, 2007
Electron flashes for the nanoworld
Schematic of the experiment with metal needle (gray) and surface groove (yellow structure). In the experiments, the needle is illuminated with a 0.007 ps short light pulse and raster scanned across the nanostructure. The locally varying electron yield is monitored. Bottom: Electron image of the nano groove. The colored part of the image displays the local electron generation rate (bright: high yield), which allows for a determination of the profile and the local electromagnetic field strength of the nano groove. Credit: MBI

Researchers at the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) in Berlin, Germany, have developed a novel source of extremely short electron pulses.

The electron source is based on an ultra-sharp metallic needle illuminated with short light pulses from a laser. “With these electron pulses, it is possible to directly observe fast processes in the nanoworld”, Claus Ropers explains, who performed the work in collaboration with Daniel Solli, Claus-Peter Schulz, Christoph Lienau and Thomas Elsaesser.

The researchers report their findings in the present issue of Physical Review Letters (Volume 98, 043907 (2007)).

Nanostructures play a key role in physics, chemistry and materials sciences, and they are at the foundation of modern microelectronics and communication technology. These structures with dimensions of few nanometers exhibit physical and chemical properties which can be tailored in a wide range.

In order to determine the dimensions and other structural characteristics of nanostructures, researchers often employ powerful electron microscopes. Such instruments only deliver static images of the time averaged state of the sample investigated. The function of nanosystems is, however, often closely related to dynamical processes occuring on time scales of less than one picosecond (1 ps, one millionth of a millionth of a second). Therefore, intense research efforts worldwide are devoted to develop methods capable of imaging such processes, for example as a series of snapshots. Besides ultrashort pulses of light, x-ray and electron pulses are particularly suited for this purpose, as they can provide direct information on rapid structural changes.

The team at the MBI has now demonstrated a new technique to generate ultrashort and localized electron pulses. A metallic needle of only 40 nm diameter is illuminated with laser light pulses of only 0.007 ps duration. The intensity of the incident light is enhanced at the needle tip to an extent that it leads to strong emission of electrons. These charged particles can be used to investigate a sample close to the needle. The particluar excitation conditions result in an extremely short duration of the electron pulses of less than 0.02 ps which determines the temporal resolution of this new “electron camera”.

The potential of this “point-like” electron source for the imaging of nanostructures has been demonstrated in experiments, where the illuminated needle is raster-scanned in close proximity across a 50 nm wide nano-groove in a gold surface. Along the cross-section of the metal groove, the electron yield varies due to the varying generation conditions. This allows for a direct determination of the profile and the electromagnetic field distribution at the groove with nanometer precision. In the same way, microelectronic devices on the nano scale and their properties can be investigated.

Currently, the electron pulses are used in first time-resolved experiments on nanostructures to image ultrafast processes. Beyond the application of the source in the raster scanning scenario, the researchers suggest a broad applicability for electron diffraction experiments with highest temporal resolution on solids, surfaces or molecular systems.

Source: Forschungsverbund Berlin

Explore further: Biochemical sensor implanted at initial biopsy could allow doctors to better monitor, adjust cancer treatments

Related Stories

Atom probe assisted dating of oldest piece of earth

April 21, 2014

(Phys.org) —It's a scientific axiom: big claims require extra-solid evidence. So there were skeptics in 2001 when University of Wisconsin-Madison geoscience professor John Valley dated an ancient crystal found in Australia ...

Scientists line up unruly gas molecules for X-rays

December 20, 2013

(Phys.org) —It's hard to study individual molecules in a gas because they tumble around chaotically and never sit still. Researchers at SLAC overcame this challenge by using a laser to point them in the same general direction, ...

Recommended for you

Fusion reactors 'economically viable' say experts

October 2, 2015

Fusion reactors could become an economically viable means of generating electricity within a few decades, and policy makers should start planning to build them as a replacement for conventional nuclear power stations, according ...

Iron-gallium alloy shows promise as a power-generation device

September 29, 2015

An alloy first made nearly two decades ago by the U. S. Navy could provide an efficient new way to produce electricity. The material, dubbed Galfenol, consists of iron doped with the metal gallium. In new experiments, researchers ...

Invisibility cloak might enhance efficiency of solar cells

September 30, 2015

Success of the energy turnaround will depend decisively on the extended use of renewable energy sources. However, their efficiency partly is much smaller than that of conventional energy sources. The efficiency of commercially ...

Extending a battery's lifetime with heat

October 1, 2015

Don't go sticking your electronic devices in a toaster oven just yet, but for a longer-lasting battery, you might someday heat them up when not in use. Over time, the electrodes inside a rechargeable battery cell can grow ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.