Today’s Technology: Liquid Crystal Alignment by Rubbed Polymer Films

1. in-plane out-of-plane Cylindrical Mirror Analyzer in-plane o o -45 +45 Before After y y more x x A remaining puzzle: Liquid crystals also align on ion beam irradiated polymers - but the opposite way! Sample b f e out-of-plane a c f Pretilt z AEY = Surface Rubbing c Metal Grid Before After z X-rays Flux Monitor y f y E Rubbing 2 to 6 nm Pretilt b x Direction x e x x z e z z’ z C C C C C e O g C N f y Ion Beam Irradiation TEY = Bulk y’ z ’ g Chaudhari et al. Jpn. J. Appl. Phys. 37, L55 (1998) x’ f Polystyrene Ion Beam Molecular tilt g C x ’ out-of-plane z Pretilt Angle in-plane x rubbed Poly- imide z f Rubbing Direction y ’ Polyimide O N C o o -45 +45 y y Pretilt N e F x x Ion beam 284 286 288 290 292 o NEXAFS solves LC Alignment Mechanism on Polymer Surfaces IB Poly- imide (Variable) Surface Sensitivity Elemental Composition Polyimide - e Auger Yield (AEY) probes top 2 nm Liquid crystal orientation Rotating 285 295 a 285 295 rubbing wheel Photon Energy (eV) Photon Energy (eV) z Ion Beam p p y Surface layer Plate movement ~ 1nm x -x x Orientation Chemical Bonding Polymer surface orientation Radius of gyration less ~ 10nm destroyed Polyimide chains and monomer Total Yield (TEY) probes top 10 nm The rubbed polymer surface can be viewed as an oriented liquid crystal and the alignment mimics the parallel alignment of two liquid crystals Polarization dependence of NEXAFS spectra reveals molecular orientation Rubbing orients polymer groups preferentially - can be viewed as pulling on polymer chains NEXAFS Provides Key to Ion Beam Alignment Puzzle Substituting Polymer by A-Carbon Summary The breakthrough suggested by NEXAFS: Do away with the polymer altogether, start with a-Carbon and irradiate it with ion beam • Work solves old scientific puzzle • Scientific understanding redirects technology • and leads to new materials and processes for • manufacturing of liquid crystal displays • Chaudhari et al., Nature 411, 56 (2001) It works! Ion beam treatment introduces preferential orientation of a-Carbon and liquid crystals align beautifully • Understanding of alignment origin and discovery • of a-carbon surface layer leads to development • of new materials and processes • Stöhr et al., Science 292, 2299 (2001) Chemical bonds in amorphous carbon surface layer on polyimide are preferentially oriented The same in-plane but opposite out-of-plane molecular asymmetry found by NEXAFS for rubbed and ion beam treated polyimide explains different liquid crystal orientations on two surfaces Ion beam treatment converts polymer surface into a thin layer of amorphous carbon Molecular orientation in a-Carbon arises from preferential bond breaking by directional ion beam From NEXAFS Spectroscopy to New Flat Panel Displays: A Story of Basic Science with Technological Impact J. Stöhr1,2, M. Samant 2, J. Lüning1, Y. Momoi 3, S. Odahara 3, P. Chaudhari 4, and S.A. Lien 4 1 Stanford Synchrotron Radiation Laboratory, Stanford University, Stanford CA 94309 2 IBM Research Division, Almaden Research Center, 650 Harry Road, San Jose CA 95120 4 IBM Display Business Unit, Yamato, Japan 4 IBM Research Division, T.J. Watson Research Center, Today’s Technology: Liquid Crystal Alignment by Rubbed Polymer Films NEXAFS Spectroscopy Flat Panel Displays A $20 billion world-wide business In-plane Alignment and Pretilt of Liquid Crystals Unique properties of NEXAFS Spectroscopy render it “technique of choice” for surface analysis Pretilt eliminates multidomain boundary lines Twisted liquid crystalsmodulate light transmission The Established Rubbing Technology Liquid Crystal Display Production • Rubbing process: • is ineffective and costly • introduces debris and streaks • produces electrostatic discharging • allows only single domains – limited viewing angles • process is environmentally unfriendly Finding a replacement process has been the holy grail of the flat panel industry. This is the story of how it was accomplished. Liquid Crystals are magically aligned by rubbed polymer films