Marcin Marczak
Johnson & Johnson Pharmaceutical Research & Development
Division of Janssen Pharmaceutica n.v.
Turnhoutseweg 30
B-2340 Beerse
Belgium
Tel: +32 16607138
Email: mmarczak@its.jnj.com
“Alignment and Characterization of Semiconduting Nanowires”
This seminar will describe the research conducted during my PhD at IEMN. The aim
was to align and characterize semiconducting nanowires for applications in
nanodevices. Work was divided into three main parts.
The first one deals with the results of Raman scattering of well-separated silicon
nanowires (SiNWs) obtained by thermal decomposition on gold-catalytic sites by CVD
method and deposited on Au surface. The Raman spectra analysis indicates the
presence of two silicon phases: crystalline (cSi) - 520 cm-1 and amorphous (aSi) - 470
cm-1, forming a core (cSi) - shell (aSi) structure. The Raman spectra have been
acquired from three points along cone shaped nanowires: base, center and tip. Based
on the Stokes/anti-Stokes intensity ratios, the position and full width at half maximum of
the Raman peaks, the temperatures of the TcSi < TaSi have been determined. It suggests
that the nanowire cSi core is in a good thermal contact with the metallic substrate,
allowing heat evacuation of the SiNW core, for which the thermal conductivity is known
to be low. Moreover the carrier concentration of the boron-doped SiNWs was estimated
at 1019 cm-3 from the Fano-like asymmetry of the peak at 520 cm-1.
In the second one, a new approach to SiNW manipulation is presented. At the
beginning the travelling wave dielectrophoresis (twDEP) micro liquid pump design and
its work principle is presented. Our device is used to simultaneously pump a weakly
ionic SiNW suspension and to trap and to rotate SiNWs. The rotation is out-of-plane
with respect to the electrodes. To maximize liquid pumping the cross-over frequency of
the RC replacement circuit representing the liquid conductivity and the insulating layer
covering the electrodes was determined by impedance spectroscopy. The observed
propagation and rotation of nanowires is explained by means of a frequency dependent
competition between trapping and drag forces.
In the last part two different approaches have been tested for obtaining a suspended
nanowire structures. The first one is based on static dielectrophoresis and the second
one on the direct alignment during the growth process. These systems were intended
for : (1) nanoelectromechanical systems ; (2) nanowire field effect transistor structures
coupled with Raman spectrometer (to observe a change in the asymmetry of the Fanolike 520 cm-1 peak in function of a gate voltage).