Contents 1. Introduction 4367 2. Elimination Lithography 4369 2.1. STM Modification under Ambient Conditions 4370 2.2. STM Modification in UHV 4372 2.3. Modification with AFM (Mechanical and Electrical) 4374 2.4. Scanning Probe Lithography with SECM 4380 2.5. Scanning Probe Lithography with NSOM 4380 3. Addition Lithography 4384 3.1. Historical Precedent for Addition Lithography 4384 3.2. Fundamentals of DPN 4384 3.3. Variation of the Ink and Substrate 4388 3.4. DPN Structures as Templates 4391 3.5. Mechanistic Aspects underlying DPN 4393 4. Substitution Lithography 4397 4.1. Substitution Initiated by Removal of SAM under Elevated Bias 4398 4.2. Substitution Initiated by Removal of SAM via Mechanical Desorption 4401 4.3. Substitution Followed by ex-Situ Addition to Patterns 4404 4.4. Substitution via Tip-Induced Terminal Group Modification 4406 5. Conclusions and Outlook 4413 6. Acknowledgments 4414 7. Glossary 4414 8. References 4415

Nanometer-sized metal particles (e.g., gold and silver) are certain to be important fundamental building blocks of future nanoscale electronic and optical devices. However, there are numerous challenges and questions which must be addressed before nanoparticle technologies can be implemented successfully. For example, basic capping ligand chemistrysnanoparticle electronic function relationships must be addressed in greater detail. New methods for assembling nanoparticles together into higher-order arrays with more complex electronic functions are also required. This review highlights our recent progress toward characterizing electron transport in gold nanoparticles as a function of capping ligand charge state. These studies have shown that single electron tunneling energies can be manipulated predictably via pH-induced charge changes of surfacebound thiol capping ligands. We also show that rigid phenylacetylene molecules are useful bridges for assembling gold and silver nanoparticles into arrays of two, three, and four particles with psuedo D ∞h , D 3h , and T d symmetries. These nanoparticle "molecules" interact electromagnetically in a manner qualitatively consistent with dipole coupling models.

The phenomenon of negative differential resistance (NDR) is potentially very useful in molecular electronics device schemes. Here, it is shown that NDR can be observed in self-assembled monolayers composed of electroactive thiols on gold. Furthermore, these monolayers can be patterned using a scanning probe lithography technique described earlier to form a basis for potential molecular electronic device construction.

Complex mesostructures showing gradient‐type surface coverage with ω‐substituted alkanthiols can be generated by STM replacement lithography. Variations of the replacement bias, lithographic scan rate, or raster line spacing create the gradient. The Figure (see also front cover) shows an L‐shaped gradient structure where Au(111) is separately thiol‐covered in the corner, and highly covered on both ends.

The negative differential resistance (NDR) peak current observed in redox active self-assembled monolayer-based molecular junctions has been attenuated by controlling the composition of the molecular junction. Two approaches studied here include capping the electroactive ferrocenyl groups with beta-cyclodextrin and functionalizing the scanning tunneling microscope tip used to probe the self-assembled monolayer (SAM) with n-alkanethiols of different lengths. These are the first examples of systematic modification of the magnitude of the NDR response in a molecule-based system.