Organic devices & potential mapping 3D simulations and experiments Dimitri Charrier, M. Kemerink and R.A.J. Janssen TU/e

Agenda 1.Scanning Kelvin Probe Microscope - why & basics 2.SKPM - Problems 3.Parameter free modeling 4.Conclusions

1.Introduction = organic device = I, , E, V

SiO 2 tip Au Scanning Kelvin probe microscope Interleave mode -Atomic Force Microscope in tapping mode -Surface potential at Lift Height Z L V V

Principle: Force microscope F = force between tip and sample V = tip-sample voltage difference C = capacity between tip and sample V dc = tip voltage V ac = amplitude voltage V cpd = contact potential difference Then V cpd = V dc For F  =0

2.Experimental results SiO2 Au V = 10 V true surface potential Room temperature experiments 3D problem

What is wrong? K.P. Puntambekar, P.V. Pesavento, and C.D. Frisbie Appl. Phys. Lett. 83, 5539 (2003) “the linear drop along the contacts […] “  V exp < 10 V

What is the real potential? Limited resolutions due to Capacitive coupling between the tip and the surface Capacitive coupling between the tip and the surface DRAIN (8 V)SOURCE

Analytical resolution? IT CAN WORK ONLY FOR SYMETRICAL PROBLEMS: APEX + CONE APEX CONTRIBUTION IN 2 DIMENSIONS CONE CONTRIBUTION IN 2 DIMENSIONS C. Argento and R.H. French, J. Appl. Phys. 80 (1996) 6081

3.Steps of modeling Software used: COMSOL (Finite Element Method software) + MatLab Olympus tip: Pt coat 3D Drawing in COMSOL 2D simulations done in 2001 by T.S. Gross et al, Ultramicroscopy 87 (2001) 147

Steps of modeling MeshingZoom on meshing of the tip surface tip Memory limit with 2 GB of RAM = tetrahedrons Discretization problem: finite amount of tetrahedrons

Vertical resolution of modeling For obtaining good lateral resolution, first check the vertical resolution Scattering due to meshing limitation For each tip position we calculate the tip-sample force for few tip voltages, then we deduce the surface potential

Modeling TRICK tip sourcedrain MOVE THE SURFACE POTENTIAL AND NOT THE TIP OTHERWISE channel remeshing = scattering

Modeling results - match perfectly Calculation time for ONE curve = 5 min X 3 voltages x 30 points  8 hours

Further results Modeling results Rescaling: V x (V sd ) = . V x (V sd /  )

Further results Experimental results SiO2 Au

4.CONCLUSION We developed a FREE-PARAMETER-FREE SKPM simulation tool, taking into account the lift height influence Experimental data ≠ real potential due to the capacitive coupling Experimental response of SKPM is understood But: so far we cannot ‘invert the system response’

The clean-room people Erik-Jan Geluk, Tjibbe de Vries, and Barry Smalbrugge Thanks to TU/e The M2N group René Janssen, Martijn Kemerink, Klara Maturova, Alexandre Nardes, Yingxin Liang, Ron Willems, Simon Mathijssen, … Technical University of Eindhoven