TY - JOUR
T1 - Artifacts identification in apertureless near-field optical microscopy
AU - Gucciardi, P. G.
AU - Bachelier, G.
AU - Allegrini, M.
AU - Ahn, J.
AU - Hong, M.
AU - Chang, S.
AU - Jhe, W.
AU - Hong, S. C.
AU - Baek, S. H.
N1 - Funding Information:
Partial financial support from the CNR-CNRS bilateral project “Diffusione Raman e Brillouin risonante e localizzazione spaziale di stati elettronici,” and from the Italy-Korea bilateral project E1 “Apertureless near-field scanning optical microscopy of single quantum systems and single molecules” is greatly acknowledged. This work was also supported in part by Korea Research Foundation Grant funded by Korea Government (MOEHRD, Basic Research Promotion Fund) (KRF-2005-070-C00054) (S.-C.H and S.-H.B) and in part by the Seoul R&D Program (S.-C.H). Nanotec is acknowledged for free software WSXM (www.nanotec.es).
PY - 2007
Y1 - 2007
N2 - The aim of this paper is to provide criteria for optical artifacts recognition in reflection-mode apertureless scanning near-field optical microscopy, implementing demodulation techniques at higher harmonics. We show that optical images acquired at different harmonics, although totally uncorrelated from the topography, can be entirely due to far-field artifacts. Such observations are interpreted by developing the dipole-dipole model for the detection scheme at higher harmonics. The model, confirmed by the experiment, predicts a lack of correlation between the topography and optical images even for structures a few tens of nanometers high, due to the rectification effect introduced by the lock-in amplifier used for signal demodulation. Analytical formulas deduced for the far-field background permit to simulate and identify all the different fictitious patterns to be expected from metallic nanowires or nanoparticles of a given shape. In particular, the background dependence on the tip-oscillation amplitude is put forward as the cause of the error-signal artifacts, suggesting, at the same time, specific fine-tuning configurations for background-free imaging. Finally a careful analysis of the phase signal is carried out. In particular, our model correctly interprets the steplike dependence observed experimentally of the background phase signal versus the tip-sample distance, and suggests to look for smooth variations of the phase signal for unambiguous near-field imaging assessment.
AB - The aim of this paper is to provide criteria for optical artifacts recognition in reflection-mode apertureless scanning near-field optical microscopy, implementing demodulation techniques at higher harmonics. We show that optical images acquired at different harmonics, although totally uncorrelated from the topography, can be entirely due to far-field artifacts. Such observations are interpreted by developing the dipole-dipole model for the detection scheme at higher harmonics. The model, confirmed by the experiment, predicts a lack of correlation between the topography and optical images even for structures a few tens of nanometers high, due to the rectification effect introduced by the lock-in amplifier used for signal demodulation. Analytical formulas deduced for the far-field background permit to simulate and identify all the different fictitious patterns to be expected from metallic nanowires or nanoparticles of a given shape. In particular, the background dependence on the tip-oscillation amplitude is put forward as the cause of the error-signal artifacts, suggesting, at the same time, specific fine-tuning configurations for background-free imaging. Finally a careful analysis of the phase signal is carried out. In particular, our model correctly interprets the steplike dependence observed experimentally of the background phase signal versus the tip-sample distance, and suggests to look for smooth variations of the phase signal for unambiguous near-field imaging assessment.
UR - http://www.scopus.com/inward/record.url?scp=34047096826&partnerID=8YFLogxK
U2 - 10.1063/1.2696066
DO - 10.1063/1.2696066
M3 - Article
AN - SCOPUS:34047096826
VL - 101
JO - Journal of Applied Physics
JF - Journal of Applied Physics
SN - 0021-8979
IS - 6
M1 - 064303
ER -