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Effect of tip geometry on contrast and spatial resolution of the near-field microwave microscope

Summary: Effect of tip geometry on contrast and spatial resolution of the near-field
microwave microscope
Atif Imtiaz and Steven M. Anlagea
Center for Superconductivity Research, Department of Physics, University of Maryland, College Park,
Maryland 20742-4111
Received 20 December 2005; accepted 20 June 2006; published online 16 August 2006
The near-field scanning microwave microscope NSMM can quantitatively image materials
properties at length scales far shorter than the free space wavelength . Here we report a study of
the effect of tip geometry on the NSMM signals. This particular NSMM utilizes scanning tunneling
microscopy STM for distance-following control. We systematically examined many commercially
available STM tips and found them to have a conical structure on the macroscopic scale, with an
embedded sphere of radius rsphere at the apex of the tip. The rsphere values used in the study ranged
from 0.1 to 12.6 m. Tips with larger rsphere show good signal contrast as measured by the
frequency shift f signal between tunneling height and 2 m away from the sample with
NSMM. For example, the tips with rsphere=8 m give signal contrast of 1000 kHz compared to
85 kHz with a tip of rsphere=0.55 m. However, large rsphere tips distort the topographic features
acquired through STM. A theoretical model is used to understand the tip-to-sample interaction. The
model quantitatively explains the measured change in quality factor Q as a function of height over
bulk copper and silicon samples. 2006 American Institute of Physics. DOI: 10.1063/1.2234801


Source: Anlage, Steven - Center for Superconductivity Research & Department of Physics, University of Maryland at College Park


Collections: Materials Science