Chemically modified STM tips for atomic-resolution imaging of ultrathin NaCl films

Abstract

Cl-functionalized scanning tunneling microscopy (STM) tips are fabricated by modifying a tungsten STM tip in situ on islands of ultrathin NaCl(100) films on Au(111) surfaces. The functionalized tips are used to achieve clear atomicresolution imaging of NaCl(100) islands. In comparison with bare metal tips, the chemically modified tips yield drastically enhanced spatial resolution as well as contrast reversal in STM topographs, implying that Na atoms, rather than Cl atoms, are imaged as protrusions. STM simulations based on a Green's function formalism reveal that the experimentally observed contrast reversal in the STM topographs is due to the highly localized character of the Cl-p z states at the tip apex. An additional remarkable characteristic of the modified tips is that in dI/dV maps, a Na atom appears as a ring with a diameter that depends crucially on the tip-sample distance.The chemical termination of the tip apex in scanning tunneling microscopy (STM) experiments determines the interaction between the wave functions of the tip and those of the sample and hence the achievable resolution in STM images. For example, it has been demonstrated that a molecule-terminated STM tip yields high-resolution molecular-orbital imaging because of the p-orbital character of the tip apex, which is far superior to images achieved with a bare metal tip [1,2]. Atomic-resolution imaging is of utmost importance for the manipulation and investigation of surface point defects and adatoms as well as for the determination of the atomic structures of molecules and nanoparticles [3][4][5][6].Ultrathin insulating films grown on conductive substrates effectively reduce the electronic coupling between deposited nanoparticles and their metallic support and are therefore ideally suited for localprobe-based investigations. The intrinsic electronic properties of atoms [7], molecules [8,9], and clusters [10], as well as the charge [11,12] and spin [13][14][15] manipulations of single atoms have been investigated Nano Research

Electron Orbital Contribution in Distance‐Dependent STM Experiments

“…Figures 3-5 correspond to probing the tip electronic structure by the surface atomic orbitals. Similar STM experiments revealing the tip atom's subatomic structure with decreasing tunneling gap have recently been reported for several tip-sample systems [89][90][91][92]. Figure 6(a) shows the STM image of the Cu(014)-O surface measured with a polycrystalline tungsten tip [30].…”

“…However, the tip functionalization procedures are generally not capable of producing stable apexes with well-defined structure. These tips could produce substantial noise [58] and asymmetric subatomic features [89] at small tunneling gaps. Besides, STM images measured with the molecule-terminated tips can strongly depend on the precise orientation of the molecule at the apex and the bias voltage [102,103] that can complicate the interpretation of the atomically resolved STM data.…”

Spatial metrology of dopants in silicon with exact lattice site precision

“…Recent studies 27,[44][45][46][47] explored the role of the higher orbitals in tip state based on Chen's proposal. We have also coupled the same derivative rule with our TB wave function.…”

Combining scanning tunneling microscope (STM) imaging and local manipulation to probe the high dose oxidation structure of the Si(111)-7×7 surface

“…The STM can induce molecular manipulation via local injection of electrons directly into single atoms and molecules. This manipulation may induce weakening (diffusion, switching) or breaking (desorption, dissociation, and transformation) of bonds, probing the chemistry and energetics of the surface [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20].…”