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SUMMARY:Microscopic characterization of organic thin films for appliaction
 s in organic electronics - Gregor Witte\, Department of Physics\, Philipps
 -University Marburg\, Germany
DTSTART:20110602T150000Z
DTEND:20110602T160000Z
UID:TALK30121@talks.cam.ac.uk
CONTACT:Stephen Walley
DESCRIPTION:Driven by the recent success of using organic semiconductors a
 s active materials for organic electronic applications\, detailed microsco
 pic studies on structural and electronic properties of such soft materials
  have become a focus of scientific interest. Of particular interest are ol
 igoacenes because of their ability to form crystalline phases which reveal
  remarkable high carrier mobilities and hence constitute well defined mode
 l systems. In view of the interrelation between intermolecular packing and
  electronic properties of such materials there is a fundamental interest i
 n a precise control of the molecular packing and orientation in highly ord
 ered thin films which is also of vital interest for an optimization of thi
 n film devices such as organic field effect transistors (OFETs) where high
  charge carrier mobility is required. \nIn this talk I will discuss growth
  phenomena and structural properties of various organic semiconductor film
 s prepared by molecular beam deposition under vacuum conditions onto diffe
 rent substrates surfaces. By combining various spectroscopic and diffracti
 on techniques with microscopy\, the evolution of their resulting structure
  can be traced as a function of film thickness. It is found that the resul
 ting molecular orientation and film morphology depend critically on the ro
 ughness and chemical termination of the substrate whereas growth rate and 
 substrate temperature mainly affect the grain size. Films that were grown 
 on differently pre-structured substrate surfaces indicate that the film mo
 rphology can be controlled to some extend (template effect) whereas the cr
 ystalline structure is usually not affected. Moreover\, for many metal sub
 strates a pronounced island growth occurs after completion of the first we
 tting layer or upon post deposition dewetting and result in non-contiguous
  films. Such dewetting phenomena can be effectively suppressed by first co
 ating the substrate with self-assembled monolayers (SAMs). Possible drivin
 g forces for the appearance of the various film structures and strategies 
 for a rational control of the microstructure of such organic films are dis
 cussed. Finally I will demonstrate that the concept of specific surface mo
 difications can also be applied to the electrodes in bottom contact OFETs 
 and leads to largely improved device characteristics.
LOCATION:Mott Seminar Room\, Cavendish Laboratory\, Department of Physics
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