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DTSTART:20260329T030000
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DTSTAMP:20260629T131552Z
UID:1785744000@ist.ac.at
DTSTART:20260803T100000
DTEND:20260803T110000
DESCRIPTION:Speaker: Felix Pertl\nhosted by Georgios Katsaros\nAbstract: Co
 ntact electrification (CE) is a simple yet elusive phenomenon that occurs 
 when two materials come into contact and separate\, leaving behind net ele
 ctrical charge. Despite its ubiquity\, the microscopic origin of CE remain
 s unclear. In this thesis\, we investigate CE from three complementary per
 spectives: developing a quantitative method to measure charge at the nanos
 cale\, exploring the dynamic behavior of charge on insulating surfaces\, a
 nd uncovering the role of mechanical history in forming a triboelectric se
 ries.In the first part\, we establish a rigorous framework for converting 
 qualitative Kelvin probe force microscopy (KPFM) voltage maps into quantit
 ative charge density distributions. Using finite element method (FEM) simu
 lations\, we determine the point-spread function of the KPFM tip–sample 
 geometry and demonstrate that the true surface charge can be reconstructed
  by numerical deconvolution. This procedure enables the recovery of both t
 he magnitude and sign of charge density with high fidelity\, resolving nan
 oscale features that are otherwise obscured. Applying the method to contac
 t-charged SiO$_2$ surfaces\, we show that existing analytical approximatio
 ns\, such as parallel plate or spherical models\, can miscalculate charge 
 magnitude by orders of magnitude. Our hybrid FEM/KPFM approach therefore p
 rovides a fast and general method to convert qualitative KPFM signals into
  quantitative charge data\, enabling nanoscale charge mapping under realis
 tic experimental conditions.In the second part\, we study the temporal sta
 bility of CE-induced charges and identify the key material factors that de
 termine whether KPFM can capture meaningful charge patterns. Through time-
 resolved experiments combining a custom-built transfer system with both mi
 croscopic and macroscopic measurements\, we demonstrate that only the best
  insulators\, such as SiO$_2$\, preserve CE charge long enough for station
 ary imaging. For less conductive polymers\, such as PDMS\, charge decays w
 ithin the duration of a single KPFM scan due to bulk conduction. Using a s
 imple capacitor-based model\, we reproduce the observed decay dynamics and
  confirm that the transferred charge decays characteristic to the sample's
  bulk conductivity. Further\, we always observe homogeneous charge transfe
 r.In the third part\, we address the question: can we form a triboelectric
  series with identical materials? Using controlled repetitive contact expe
 riments\, we show that nominally identical materials can progressively ord
 er themselves into a triboelectric series\, where surfaces with more conta
 ct history charge negatively relative to fresher ones. By constructing a m
 inimal model based on this contact bias''\, we replicate the evolution fro
 m random to ordered charging observed in experiments. Supporting surface a
 nalyses\, including atomic force microscopy\, reveal that repeated contact
  induces nanoscale morphological changes\, suggesting a mechanism tightly 
 coupled to mechanical strain. These results highlight the crucial role of 
 surface history and nanoscale mechanics in dictating charge transfer\, mot
 ivating further exploration of mechanisms such as mechanochemical bond cle
 avage and flexoelectric polarization.
LOCATION:Sunstone Bldg / Ground floor / Big Seminar Room B (I23.EG.102) and
  Zoom\, ISTA
ORGANIZER:
SUMMARY:Felix Pertl: Thesis Defense: Experimental probing of nanoscale char
 ge features and surface morphology changes during tribocharging
URL:https://talks-calendar.ista.ac.at/events/6537
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