Akademik Veri Yönetim Sistemi
PHYSICA B-CONDENSED MATTER, cilt.557, ss.126-131, 2019 (SCI-Expanded)
Applying bias voltage generates the electric field between the sample and the probe tip of the scanning tunneling microscopy (STM). At the tunneling distance, individual fullerene molecule on a metal surface can be induced to diffuse into the region beneath the tip or desorb by the field strength. Finite Element Method Magnetics (FEMM) simulations were performed to investigate the electric field effect on a C-60 molecule on a finite metal surface with a metallic STM tip. The field gradient has been simulated to study the effect of tip-apex size, 10, 30 and 50 nm and bias voltage, from + 1.7 V to + 4.8 at the calculated tunneling distance. This model appropriately defines the field strength just over the fullerene molecule as 6.8 x 109 V/m at + 4.4 V and then exponentially decays with increasing radial distance from the tip about 69% in a range of 5 nm. Similar trends are obtained in between the molecule and surface gap but the field strength is enhanced by 2.5 times higher than the field over the C-60 molecule with an effective range of 1 nm. The effective range of the field is enhanced by the bias voltage and the tip radii. For both the tip-molecule and molecule-sample gap, the E-field strengths show a linear increase with varying the bias voltage up to a maximum similar to 17 x 10(9) V/m which is less than the threshold strength to yield a field evaporation of the surface adatoms. Independent from bias voltage polarity, the molecule can be diffused preferentially towards the tip-apex up to + 3.0 V without thermal decomposition. Above + 5.0 V voltage pulse, the desorption of the molecule is possible in the presence of the E-field. The van der Waals force with a range of 12-15 angstrom does not provide sufficient energy to induce either diffusion or desorption of the molecule.