First controlled vertical manipulation of a single H atom with AFM tip
Due to the continuous improvement of scanning probe microscopy techniques, the long thought inaccessible goal of inducing and visualizing chemical reactions at the atomic scale is now routinely achievable by many groups around the world. In the framework of so-called mechanochemistry,
[1] mechanical force induced reactions have been studied using NCAFM.
[2] Recent works reported force induced atomic-scale switching,
[3] quantitative force measurements to induce the diffusion of single atoms
[4] and molecules,
[5] as well as studying molecular conformers
[6] and tautomerization.
[7] A few earlier studies also showed examples of mechanically induced vertical manipulation of single atoms. [8, 9] However, direct observation of mechanically induced covalent bonding of two different atoms using NC-AFM remain scarce.
Researchers report the first controlled vertical manipulation of a single H atom using the tip of an AFM sensor and its application in characterizing and engineering silicon DB-based structures of relevance to nanoelectronic devices.
They showed that following a tip induced desorption, a hydrogen atom can be deposited on the surface or transfered to the tip apex resulting in a H-functionalized tip. The physisorbed single hydrogen atom on the chemically inert H-Si surface could be stably imaged in STM and AFM modes. The H-functionalized tip was used to
(i) characterize silicon dangling bonds and
(ii) to mechanically induce the covalent bonding of single hydrogen and silicon atoms. We showed the potential of this mechanically induced reaction to precisely modify multiple DB structures such as coupled DBs and artificial molecular states.
In 2001, the Drexler-Smalley debate on molecular nanotechnology was a public dispute between K. Eric Drexler, the originator of the conceptual basis of molecular nanotechnology, and Richard Smalley, a recipient of the 1996 Nobel prize in Chemistry for the discovery of the nanomaterial buckminsterfullerene.
Just a reminder that Richard Smalley's two objections to the concept of molecular assembler, which he called the "fat fingers problem" and the "sticky fingers problem" were full of crap back then and are even more full of crap now. Also a reminder that molecular nanotechnology concepts are feasible and should be aggressively funded and pursued. Smalley clearly made up a bunch of arguments to squash the molecular nanotechnology field and ensure that billions of dollars went to his areas of carbon nanotubes.
Alberta, Canada researchers report the mechanically induced formation of a silicon-hydrogen covalent bond and its application in engineering nanoelectronic devices. They show that using the tip of a noncontact atomic force microscope (NC-AFM), a single hydrogen atom could be vertically manipulated. When applying a localized electronic excitation, a single hydrogen atom is desorbed from the hydrogen-passivated surface and can be transferred to the tip apex, as evidenced from a unique signature in frequency shift curves. In the absence of tunnel electrons and electric field in the scanning probe microscope junction at 0 V, the hydrogen atom at the tip apex is brought very close to a silicon dangling bond, inducing the mechanical formation of a silicon-hydrogen covalent bond and the passivation of the dangling bond. The functionalized tip was used to characterize silicon dangling bonds on the hydrogen-silicon surface, which was shown to enhance the scanning tunneling microscope contrast, and allowed NC-AFM imaging with atomic and chemical bond contrasts. Through examples, we show the importance of this atomic-scale mechanical manipulation technique in the engineering of the emerging technology of on-surface dangling bond based nanoelectronic devices.
