Since the early 2010s, ultrafast probing of materials in atomic-level resolution has been enabled by a Terahertz scanning tunneling microscope (THz-STM). But these devices cannot detect the energy dissipation that occurs during events such as when photons are emitted through the recombination process of the electron-hole pair in a light-emitting diode (LED).
However, a new technology has allowed tracking of just such energy dynamics with THZ-STM, opening new avenues of investigation for nanoscale science and technology.
Researchers in Japan have developed a microscopy technique that combines the ability to manipulate the motion of electrons over a femtosecond timescale and detect a photon at sub-nanometer resolution.
The new method provides scientists with a new platform to conduct experiments involving the sensing and control of quantum systems, which opens new doors for nanoscale science and for the development of nanotechnologies.
The team, which consists of scientists at Yokohama National University and RIKEN, published a description of their technique in the journal ACS Photonics on 27 January.
The Scanning Tunneling Microscope (STM) was developed in 1981 as an instrument that produces images of surfaces at the atomic level. The technique relies on the phenomenon of quantum tunneling, in which a particle “tunnels” through an otherwise impermeable barrier.
The surface being examined by the microscope is sensitive to the tip of a very fine and sharp conduction. When the tip approaches the surface, a voltage is applied across the tip and the surface allows electrons to tunnel through the vacuum between them. In turn the current created by this tunneling provides information about the object which can then be translated into a visual image.
STM took a major leap forward in early 2010 with the THG-STM technology, which uses an ultrafast electric-field pulse at the scanning probe tip of an STM to manipulate electrons under a picosond (a second. Trillion).
This is great for ultrafast probing of materials in atomic-level resolution, but cannot detect the energy dissipation that occurs during quantitative conversion.
This includes, for example, electron-photon conversion, which occurs when the electron, or an injection of holes, hits an LED, the LED loosens exactly one photon inside the semiconductor material. It would be very useful to combine the ultrafast atomic-level resolution of STM with being able to track such dynamics of energy propagation.
A technique that can actually track such dynamics, called scanning tunneling luminescence spectroscopy (STL), measures photons converted by electrons and has been developed parallel to THz-STM. STL provides abundant information on the photon energy, intensity, polarization, and efficiency of its emission triggered by electron tunneling.
“But THz-STM and STL have never been added to a single set up that co-led the study,” said Jun Takeda of Yokohama National University. “So we put the two techniques together.”
A lens was placed in this way to focus the THz pulses at the tip of the STM. The photons generated from these pulses were then collected using a second lens and directed to the photon detector, allowing the desired investigation of the energy dynamics of quantum conversions that occur during the STM ultrafast probe of the material at the atomic level is.
This revealed an ultrafast excitation of plasmas (surface electrons) at extremely high voltages.
Ikufumi Katyama said, “This may provide a whole new platform for the use and exploration of light-matter interactions in plasmonic nanocavity”. But it will incorporate these surface electrons.
The nanocavity method can examine the energy dynamics generated by electron tunneling in semiconductors, and also synchronous reversals in other molecular systems – quartiles of each other, or the amount of time typically taken for molecular dynamics, physical motion.
To be different atoms or molecules. This allows greater sensing and control of quantum systems, providing novel insights and advances in nanoscale technology and science.