NEW MICROSCOPIES LABORATORY
LABORATORIO DE NUEVAS MICROSCOPÍAS
Prof. Arturo M.
Baró
Prof.Jaime
Colchero; Prof. Julio Gómez Herrero; Prof. José María Gómez Rodríguez,; Prof.
Javier Méndez Pérez-Camarero.
Phd Students: Iván Brihuega,
Óscar Custance, Adriana Gil Gil, Cristina Gómez Navarro; Fernando Moreno Herrero; Nicoleta Nicoara;
Pedro José de Pablo Gómez.
SFM image of a DNA molecule connected to a
gold electrode. The molecule after being cut using an SFM
Research Lines
1. Scanning force microscopy
(SFM):
Electrical tranport in
molecules.
Carbon
nanotubes belongs to the fullerens’ family. These
cylinder-like molecules can be seen as folded graphene planes with a minimum
diameter of 1 nm. By using a Scanning Force Microscope we have measured the
electrical current transport as a function of the voltage drop along
the nanotube length. These characteristics have allowed us to obtain the
resistance of the nanotube. In addition, we have been able to distinguish
between contact resistance and intrinsic resistance of the nanotube. In the
latest case, we have established a relation between the experimental
resistivity obtained from our experiments and the defects along the nanotube.
Finally, a number of predictions indicate that the current vs. voltage
characteristic of a nanotube may change along the nanotube length from
semiconductor to metal type and vice versa. These kind of phenomena have been
also detected in our experiments.
DNA is the most relevant molecule in biology since life is based on it.
However, little is known about the electrical transport properties of the DNA
molecules. These properties are important, first from a biology point of view,
because is known that electron transport plays an important role in the
mechanism of damage and repair under external radiation. Second, because if the
DNA is a conductor or can be modified to be a conductor, then it can be used to
fabricate nanodevices. A number of works have been published suggesting that
DNA can support electrical transport. In our group we have shown the regular
DNA is not a conductor and therefore in order to be used in electrical circuits
is should be modified.
Proteins and DNA
interactions
SFM
studies of DNA-protein complexes have been done in the direction to localize
protein-binding sites in gene promoters. SFM appears as a powerful and
complementary tool to the standard biochemical techniques. SFM can compete with
biochemical techniques in terms of simplicity, cost and speed.
Biopolymers structure characterization
The Paired Helical
Filaments (PHF) are an aberrant structure present in Alzheimer patients. They
are mainly made of a protein called tau, and the exact arrange of this protein
in the polymer is not yet understood.
We have used the SFM to characterize the structure of this type of polymers.
Fundamental studies on SFM.
We have developed and studied a number of scanning
modes for SFM: Jumping Mode, Dynamic modes, 3D modes, Electrostatic and
Magnetic Force Microscopy. In order to obtain a better understanding of SFM we
have carefully studied the tip-sample interaction.
2. Scanning Tunneling Microscopy
(STM):
STM instrumentation.
We have fully designed and built the first variable
temperature ultra-high-vacuum scanning tunneling microscope available in Spain.
This variable temperature STM, connected to a continuous flow liquid He
ultra-high-vacuum cryostat, allows imaging at sample temperatures in the range
of 40K to 400K.
Variable temperature STM (40-400K) Ultra-high-vacuum system
(5x10-11 Torr)
Diffusion at the atomic
scale of metal adsorbates on semiconductor surfaces.
The detailed knowledge at the atomic scale
of adsorption and diffusion mechanisms of single adatoms on highly
reconstructed semiconductor surfaces is of fundamental importance in a great
deal of current and future technological processes. In particular, recent works
have unveiled the potentiality for next generation devices of self-organization
of nanoclusters on Si(111)-(7x7) surfaces. Although the
identification of stable adsorption sites and diffusion pathways and energy
barriers is crucial for the understanding of the formation of such
nanoclusters, there is still a lack of both theoretical and experimental
information. In our group we have performed a variable temperature scanning
tunneling microscopy study of the surface diffusion of
single Pb and Sn adatoms on Si(111)-(7x7) surfaces working in a temperature
range between 40K and 400 K. A careful analysis of Pb/Si(111)-(7x7) has been
carried out, yielding valuable information on the atomistic mechanisms and
energetics of this prototype system.
Si(111)-7x7 at room temperature
Si(111)7x7 at low temperature (40K)
Phase transitions on low
dimensional metal-semiconductor systems.
Structural and electronic phase transitions on
metal-semiconductor surfaces are subjects of fundamental interest. By means of
variable temperature UHV scanning tunneling microscopy and spectroscopy,
several phase transitions have been analyzed on Pb/Si(111), Sn/Si(111) and
Pb/Si(001) systems.
Adsorption and growth properties of organic molecules
on surfaces.
The adsorption and growth of PTCDA molecules on inorganic substrates is
under current investigation by means of UHV STM and STS and SFM in air. This
fundamental research is included in the DIODE European Union Network for the future design of organic-inorganic devices.
40 K
RT
Pb/Si(111)-(Ö 3xÖ3) Û (3x3) phase transition