Final Report Summary - USPLADYN (Ultrafast Surface Plasmon Dynamics)
Most of the planned technical developments on the Scanning Tunneling Microscope (STM) were accomplished during the year 2008. This included the stabilization of the scanner, the electric shielding of the scanner head the conversion of the signal processing chain and the corresponding software from analogue to digital. In addition, I implemented some essential modifications on the control electronics of the microscope that allowed for special scanning modes (Task B2 in the Work Plan). These activities were carried out in the Max Planck Institute for Quantum Optics (MPQ), Garching, Germany. The transport of the equipment to the Host Institution in Budapest, Hungary took place in March 2009 (Task B1). Numerous experiments were carried out with the STM microscope in this phase, including:
- Recording the tunneling current vs. bias voltage characteristics using both tungsten and gold tips
- Simultaneous recording of topography-, thermal- and plasmon-images with laser excitation
- Optical power dependence of the tunneling current.
The results showed localization effects of the surface plasmon polaritons. This means, the magnitude of the local electric field becomes larger between close surface structures that are just a few nanometres apart (e.g. at grain boundaries) and it can overcome the static electric field of the STM tip. The electric field of the optical light waves are rectified due to the nonlinearity of the tunnel junction. The superposition of the static and the rectified current components results in a current that can be negative in the presence (and only in the presence) of optical excitation. We studied this phenomenon as a function of laser pulse energy which shed light into the strongly nonlinear dependence of the tunneling current. I have published the first results in January 2009 in the Physics of Quantum Electronics (PQE) conference (Snowbird, USA) and in an extended form in the Photon 10 conference in 2010 (Southampton, UK). A comprehensive summary of the results along with a detailed analysis have been disseminated in Physical Review B in 2011.
In addition to the experiments, I fostered close contacts to my former Host Institution, the Nanoscale Physics Research Laboratory in the University of Birmingham, in order to leverage from their expertise in the field of Scanning Tunneling Microscopy. I personally visited the Laboratory in September 2008 for technical consultation and experimental training.
The developments of the pulsed femtosecond laser source (described in Task A in the Work Plan) were successfully accomplished. This work package included the dispersion optimization of the resonator of the long-cavity Titanium-Saphire oscillator in order to achieve shortest possible pulses and the improvement of the temporal stability of the optical pulse train. The results of this development were published in Optics Express.
In 2009 I requested the suspension of the project (effective from 1st April 2009) as I received an opportunity to take part in a research project outside Hungary. This suspension has been accepted by the REA and prolonged until 1st April 2011. During the active phase of the project I have trained a PhD student for the operation of the STM microscope who continued the conduction of the planned experiments and developments in my absence. This included the setup and the test of a new solid-state picosecond laser source according to Task B. As a result, the generation of surface plasmons has been successfully demonstrated with the new light source.
I had to request the early termination of the USPLADYN project effective from 31th March 2011. The reason for the request was that I have received an alternative job offer which I accepted. In consequence, I had to quit my position in the Host Institution in Budapest, thus the realization of the project objectives became unviable.
- Recording the tunneling current vs. bias voltage characteristics using both tungsten and gold tips
- Simultaneous recording of topography-, thermal- and plasmon-images with laser excitation
- Optical power dependence of the tunneling current.
The results showed localization effects of the surface plasmon polaritons. This means, the magnitude of the local electric field becomes larger between close surface structures that are just a few nanometres apart (e.g. at grain boundaries) and it can overcome the static electric field of the STM tip. The electric field of the optical light waves are rectified due to the nonlinearity of the tunnel junction. The superposition of the static and the rectified current components results in a current that can be negative in the presence (and only in the presence) of optical excitation. We studied this phenomenon as a function of laser pulse energy which shed light into the strongly nonlinear dependence of the tunneling current. I have published the first results in January 2009 in the Physics of Quantum Electronics (PQE) conference (Snowbird, USA) and in an extended form in the Photon 10 conference in 2010 (Southampton, UK). A comprehensive summary of the results along with a detailed analysis have been disseminated in Physical Review B in 2011.
In addition to the experiments, I fostered close contacts to my former Host Institution, the Nanoscale Physics Research Laboratory in the University of Birmingham, in order to leverage from their expertise in the field of Scanning Tunneling Microscopy. I personally visited the Laboratory in September 2008 for technical consultation and experimental training.
The developments of the pulsed femtosecond laser source (described in Task A in the Work Plan) were successfully accomplished. This work package included the dispersion optimization of the resonator of the long-cavity Titanium-Saphire oscillator in order to achieve shortest possible pulses and the improvement of the temporal stability of the optical pulse train. The results of this development were published in Optics Express.
In 2009 I requested the suspension of the project (effective from 1st April 2009) as I received an opportunity to take part in a research project outside Hungary. This suspension has been accepted by the REA and prolonged until 1st April 2011. During the active phase of the project I have trained a PhD student for the operation of the STM microscope who continued the conduction of the planned experiments and developments in my absence. This included the setup and the test of a new solid-state picosecond laser source according to Task B. As a result, the generation of surface plasmons has been successfully demonstrated with the new light source.
I had to request the early termination of the USPLADYN project effective from 31th March 2011. The reason for the request was that I have received an alternative job offer which I accepted. In consequence, I had to quit my position in the Host Institution in Budapest, thus the realization of the project objectives became unviable.