Site-Selective Chemistry Induced by Probe Microscopy Techniques

Working on the nanometer scale requires the ability to synthesize, manipulate, and organize matter in a controllable manner as well as to predict and understand the properties of the resulting structure. One means of synthesizing material at the nanoscale is to actually create it molecule by molecule. In this regard, novel approaches are needed to understand surface reactions at a molecular scale. Scanning probe techniques offer the prospect of manipulating atoms and molecules on surfaces. In this regard, the project herein described involves using an atomic force microscopy (AFM) tip, derivatized at the end with a catalytic nanocrystal/powder, to initiate and catalyze localized nanometer-scale chemical reactions on a surface, one molecule at a time. In effect, this work takes advantage of the ultralow dimension of the functionalized tip to catalyze reactions on a single molecule level.

 

(a). Selective Borohydride Reduction Using Functionalized Atomic Force Microscopy Tips

A powder of a selective reducing agent, sodium triacetoxyborohydride (Na(OAc)₃BH), was attached to an AFM tip and used to selectively reduce a monolayer of imines to their corresponding secondary amines within a well-defined region. Reaction completion was confirmed using surface mid-IR results and the chloranil test. Ref.: Langmuir, v.18, 5055 (2002).

(b). Current-less Photoreactivity Catalyzed by Functionalized AFM Tips

Spatially confined photocatalytic oxidation of a synthetic textile azo dye (Procion Red MX-5B) was carried out using TiO₂-functionalized AFM probes on a homogeneous surface of a synthetic textile dye deposited on a glass substrate. Reaction process was confirmed through optical microscopy and AFM images and analyses as well as through surface FT-mid-IR spectroscopy studies. Ref.: Chem. Commun., (36), 4598 (2005).