Single-Molecule AFM Cantilever for THz Force Detection

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Abstract/Contents

Abstract: Increasing the resonance frequency of an Atomic Force Microscope (AFM) cantilever is necessary to effectively probe short-range chemical forces. Current AFM cantilevers have frequencies of about 100−200 kHz, limiting the minimum force-gradient that can be measured to the order of 10 pN/nm. This study demonstrates the ability of Inelastic Tunneling Spectroscopy (IETS) to probe THz vibrational modes of a single CO molecule attached to the tip of a low-temperature Scanning Tunneling Microscope (STM). Using molecular manipulation, a CO molecule is transferred to the end of the STM tip and lock-in techniques are used to measure 𝑑2𝐼/𝑑𝑉2 tunneling spectra. Shifts in the frequency of specific vibrational modes of the CO molecule are analyzed as a function of the tip-to-sample distance. This shows that a single molecule can be used as an AFM cantilever for force spectroscopy with the ability to measure small force-gradients to the order of 10−6 pN/nm. IETS with a CO terminated STM tip is also performed over adsorbed CO molecules on a Cu(111) surface revealing a novel vibrational mode due to coupling between the two CO molecules. In future, the small force-gradients detected by STM-IETS can be used to resolve single atoms within a molecule to reveal additional molecular structure.

Type of resource	text
Date created	2010

Author	Mahmood, Fahad
Primary advisor	Manoharan, Harindran C. (Harindran Chelvasekaran) "Hari"
Advisor	Moler, Kathryn
Department	Stanford University, Department of Physics

Subject	Atomic Force Microscope (AFM)
Subject	Inelastic Tunneling Spectroscopy (IETS)
Genre	Thesis

Location	https://purl.stanford.edu/cy977mf7313

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License: This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

Preferred Citation: Mahmood, Fahad (2010). Single-molecule AFM cantilever for THz force detection. Stanford Digital Repository. Available at http://purl.stanford.edu/cy977mf7313.

Undergraduate Theses, Department of Physics

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