Imaging Molecular Orbitals by Scanning Tunneling Microscopy on a Passivated Semiconductor

Abstract

Decoupling the electronic properties of a molecule from a substrate is of crucial importance for the development of single-molecule electronics. This is achieved here by adsorbing pentacene molecules at low temperature on a hydrogenated Si(100) surface (12 K). The low temperature (5 K) scanning tunneling microscope (STM) topography of the single pentacene molecule at the energy of the highest occupied molecular orbital (HOMO) tunnel resonance clearly resembles the native HOMO of the free molecule. The negligible electronic coupling between the molecule and the substrate is confirmed by theoretical STM topography and diffusion barrier energy calculations.

Characterization of PTCDA nanocrystals on Ge(001):H-(2×1) surfaces

“…For example, in case of metal surfaces such a scenario is realized by means of few monolayers of insulator, like NaCl [5][6][7][8][9][10][11][12][13], for semiconductor surfaces it might be either few monolayers of insulator, like KBr on InSb [14,15], or a single layer of atomic hydrogen, e.g. Si:H and Ge:H surfaces [16][17][18][19][20]. The buffer layer dramatically enhances mobility of adsorbed molecular species and eventually may ease their selfassembly and formation of molecular nanocrystals [9][10][11]20,21].…”

Direct imaging of molecular orbitals of metal phthalocyanines on metal surfaces with an O2-functionalized tip of a scanning tunneling microscope

“…In this respect, researchers seek to image molecular structures with higher resolution, allowing direct observation of detailed molecular orbitals, thus, providing a deeper understanding of the moleculesubstrate interaction and reactions at a sub-molecular or even atomic scale. This could be accomplished by decoupling molecules from the substrate, for example, using an ultrathin insulating film [12,13], a molecular layer between molecules and a metal substrate [14,15], physisorbed molecules [16], or a semiconductor substrate [17]. An alternative way to get high-resolution images of molecules is to functionalize the scanning 524 tunneling microscope (STM) tip by attaching a molecule at its apex [18][19][20][21][22].…”

Electronic properties of then-doped hydrogenated silicon (100) surface and dehydrogenated structures at 5 K

“…For this purpose, the Si͑100͒:H surface appears as a good candidate because of its ability to electronically decouple adsorbed molecules from the silicon substrate. 1,2 Moreover, this surface can be considered as a flexible medium as it can be structured-at will-by locally desorbing hydrogen atoms and thus creating lines, 3,4 spirals, 5 or more complex patterns 6 of silicon dangling bonds. However, despite being investigated at room temperature, 7-9 the electronic properties of the various observed structures on the Si͑100͒:H surface such as single silicon dangling bonds or bare silicon dimers are still badly understood.…”