Kelvin probe force microscopy of C₆₀ on metal substrates: towards molecular resolution

Abstract

Surface workfunction changes upon C60 adsorption onto different metal single crystals are investigated by Kelvin probe force microscopy (KPFM). Literature values for similar metal/organic systems, showing a broad variation for both the measured metal workfunction and workfunction change, are compared to the acquired KPFM values. Good agreement is found between nanoscopic KPFM results and macroscopic photoelectron spectroscopy or Kelvin probe literature data. The model of a linear dependence between the metal substrate workfunction and the C60-induced workfunction change is confirmed. Former numerical simulations predicted a lateral quantitative KPFM resolution in the range of 10 nm, in this work results are published that show the achievement of this resolution with Cr coated, sharp tips. Furthermore, numerical simulations are presented that show the possibility of molecular contrast for KPFM.

Open loop Kelvin probe force microscopy with single and multi-frequency excitation

“…Since then, Kelvin probe force microscopy (KPFM) has undergone significant advances in both sensitivity [4][5][6][7] and resolution [8][9][10], with a broad spectrum of configurations now available. KPFM has been applied to study a variety of materials, including organic, biological, and energy conversion and storage-related materials.…”

Tuning of electronic properties of fullerene-oligothiophene layers

“…45 Despite the difficulties described above, a vast number of authors have successfully applied the Kelvin probe method in the studies of electrical properties of metal/organic semiconductor systems. 43,[45][46][47][48] This approach was used to describe the nature of interfacial interactions occurring between fullerene C 60 layer and chosen metals (Au, Mg, Cu and Ag). 43 It turned out to be helpful also in the explanation of the work function optical switching at the surface of fullerene-porphyrin conjugates.…”

Relating the Functional Properties of an Organic Semiconductor to Molecular Structure by nc‐AFM

“…As such, care must be taken to account for the full geometry of the capacitive system involved, that is, where the biases are applied, the sample geometry and dielectric properties, and the position of the tip and cantilever beam relative to the applied biases, in order to make quantitative comparisons between measurements from different instruments. [21,22] While great effort has been made to model the effect of tip geometry on resolution limits and accuracy of CPD measurements and KPFM, [23][24][25][26] previous interpretation for molecular and insulating thin films assumes metallic-like behavior. [26,27] As the dielectric properties of a thick insulating sample will clearly influence the quantitative interpretation of the CPD values here, a more complete theoretical framework for the interpretation of such data is needed.…”

“…[21,22] While great effort has been made to model the effect of tip geometry on resolution limits and accuracy of CPD measurements and KPFM, [23][24][25][26] previous interpretation for molecular and insulating thin films assumes metallic-like behavior. [26,27] As the dielectric properties of a thick insulating sample will clearly influence the quantitative interpretation of the CPD values here, a more complete theoretical framework for the interpretation of such data is needed. Due to the complex geometry of our apparatus, these effects are not considered, and as such only the direction and relative magnitudes of CPD shifts are considered.…”