Page 1 of 8
`
`Tianma Exhibit 1013
`
`Page 1 of 8
`
`Tianma Exhibit 1013
`
`

`
`APPLIED PHYSICS LETTE
`
`. W
`
`. ,.. wt-"r"
`
`"
`
`Vol. 73, No. 23, 7 December 1998
`
`E‘ EN: APPLAB
`
`ISSN: 0003-6951
`
`Ultrafast phase dynamics of coherent carriers in Ga‘
`
`Self—consistent Green’s function approach to the analysis of
`dielectrically apertured vertical-cavity surface—emitting lasers
`
`Efficient contour generation and tracking of a moving object with a
`rhodium-doped BaTiO3 crystal working in the near infrared
`
`lein, L. F. Register, K. Hess,
`D.G. Deppe, Q. Deng
`Pierre Mathey, Pierre Jullien,
`Daniel Rytz
`
`Optical engineering with Fibonacci dielectric multilayers
`
`Enrique Macia
`
`OPTICS
`
`3321
`
`3324
`
`3327
`
`3330
`3333
`
`3336
`
`An application of the apertureless scanning near-field optical
`microscopy: imaging a GaA|As laser diode in operation
`
`Direct fabrication of polyimide waveguide grating by synchrotron
`radiation
`
`A phase jump phenomenon in interferometry
`
`Measurement of temperature gradient in diode-laser-pumped
`high-power solid-state laser by low-coherence reflectometry
`
`Electroabsorption spectroscopy study of an azopolymer film
`fabricated by electrostatic adsorption
`
`Effect of well number on organic multiple-quantum-well
`electroluminescent device characteristics
`
`Lasing from lnGaAs/GaAs quantum dots with extended wavelength
`and well-defined harmonic-oscillator energy levels
`
`Optical fiber temperature sensor using a gain-switched Fabry—Perot
`semiconductor laser self-seeded from a linearly chirped fiber Bragg
`grating
`
`ACOUSTICS
`3357
`
`Observation of vibrational modes of irregular drums
`
`R. Bachelot, G. Wurtz, P. Floyer
`
`Junya Kobayashi, Tohru Maruno,
`Tetsuyoshi lshii,
`Toshiaki Tamamura,
`Toshiyuki Horiuchi
`
`Weidong Zhou, Lilong Cal
`
`8. L: Huang, W. L. Wu, P. L. Huang
`
`Ke Yang,
`Srinivasan Balasubramanian,
`Xiaogong Wang, Jayant Kumar,
`Sukant Tripathy
`
`Jingsong Huang, Kaixia Yang,
`Zhiyuan Xie, Baijun Chen,
`Hongjin Jiang, Shiyong Liu
`G. Park, 0. B. Shchekin,
`D. L. Huffaker, D. G. Deppe
`
`Shenping Li, K. T. Chan
`
`Olivier Haeberlé, Bernard Sapoval,
`Kristen Menou, Holger Vach
`
`CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
`3360
`
`Platinum nanodot formation by atomic point contact with a scanning
`tunneling microscope platinum tip
`
`D. H. Huang, T. Nakayama, M. Aono
`
`3363
`
`lon induced disordering and dissolution of Ni3A| precipitates
`
`Activation fields in ferroelectric thin film capacitors: Area
`dependence
`
`Room-temperature diffusivity of self-interstitials and vacancies in
`ion-implanted Si probed by in situ measurements
`
`A method for liquid crystal alignment using in situ ultraviolet
`exposure during imidization of polyimide
`
`Meta|—insulator transition in SrRuO3 induced by ion irradiation
`
`J. C. Ewen, G. Schmitz,
`F. Harbsmeier, M. Uhrmacher,
`F. Haider
`
`T. K. Song, S. Aggarwal, Y. Gallais,
`B. Nagaraj, R. Flamesh,
`J. T. Evans, Jr.
`
`Salvatore Coffa, Sebania Libertino
`
`Jae-Hoon Kim, Bharal R. Acharya,
`Satyendra Kumar, Ki Flyong Ha
`. Z. Sefrioui, D. Arias,
`M. A. Navacerrada, M. Varela,
`G. Loos, M. Lucia, J. Santamaria,
`F. Sanchez-Quesada,
`M. A. Lopez de la Torre
`
`(Continued)
`
`© 1998 American Institute of Physics
`
`Page 2 of 8
`
`

`
`Appl. Phys. Lett., Vol. 73, No.23, 7 December 1998
`
`Hydrogen desorption and adsorption measurements on graphite
`nanofibers
`
`Transient thermochromism_during ArF excimer laser ablation of
`poIy(3-dodecylthiophene) films
`Scale dependence of submicron polycrystals due to configurational
`entropy
`'
`Thermal diffusivity measurements of sub-micron organic dye thin
`films using a high temperature superconductor bolometer
`
`SEMICONDUCTORS
`
`3390
`
`Photoluminescence of localized excitons in pulsed-laser-deposited
`GaN
`
`Silica capping for Al0_3Gao_7As/GaAs and lno_2Ga0_8AslGaAs quantum
`well intermixing
`»
`
`Dependence of the silicon nanowire diameter on ambient pressure
`
`Spectroscopic characterization of the evolution of self-assembled
`CdSe quantum dots
`
`Ohmic contacts formed by electrodeposition and physical vapor
`deposition on p-GaN
`Improved optical response of superlattice graded lnAlAs/lnGaAs
`p—i-n photodetectors
`’
`
`Improved carrier collection in intermixed lnGaAs/GaAs quantum
`wells
`
`Highly packed lnGaAs quantum dots on GaAs(311)B
`
`Investigation of broadband p-type quantum-well infrared
`photodetectors
`Direct detection and imaging of low-energy electrons with
`delta-doped charge-coupled devices
`
`Observation of wire width fluctuations in the optical spectra of
`GaAs-—AlGaAs V-groove quantum wires
`
`‘Current-induced persistent capacitance in Au/n-ln Ga
`Schottky contacts
`0'03
`
`A
`0'92 S051
`
`P
`
`0'49
`
`Piezoelectric effects on the optical properties of GaN/Al Ga,
`multiple quantum wells
`X
`
`“X
`
`N
`
`Charge-ring model for the charge-induced confinement enhancement
`in stacked quantum-dot transistors
`
`A Photoconductivity mechanism of quantum well infrared
`photodetectors under localized photoexcitation
`
`C. C. Ahn, Y. Ye, B. V. Ratnakumar,
`C. Witham, R. C. Bowman, Jr.,
`B. Fultz
`
`Katsunori Tsunoda, Keiko Kakinuma,
`Hirofumi Yajima, Tadahiro Ishii
`
`Qiang Yang, Wei Yang
`
`Steven M. Savoy, Cyndi A. Wells,
`John T. McDevitt,
`Timothy A. Rhodes
`
`M. Cazzanelli, D. Cole,-
`J. F. Donegan, J. G. Lunney,
`P. G. Middleton, K. P. O’Donneil,
`C. Vinegoni, L. Pavesi
`
`G. Li, S. J. Chua, S. J. Xu,
`X. C. Wang, A. Saher Helmy,
`Mao-Long Ke, J. H. Marsh
`
`H. Z. Zhang, D. P. Yu, Y. Ding,
`Z. G. Bai, Q. L. Hang, S. Q. Feng
`
`J. C. Kim, H. Rho, L. M. Smith,
`Howard E. Jackson, S. Lee,
`M. Dobrowolska, J. L. Merz,
`J. K. Furdyna
`
`‘ J. M. DeLucca, H. S. Venugopalan,
`S. E. Mohney, R. F. Karlicek, Jr.
`
`C. Lenox, H. Nie, G. Kinsey,
`P. Yuan, A. L. Holmes, Jr.,
`B. G. Streetman, J. C. Campbell
`
`L. V. Dao, M. B. Johnston, M. Gal,
`L. Fu, H. H. Tan, C. Jagadish
`Kouichi Akahane,
`Takahiro Kawamura, Kenji Okino,
`Hiromichi Koyama, Shen Lan,
`Yoshitaka Okada, Mitsuo Kawabe,
`Masahiro Tosa
`
`J. Chu, Sheng S. Li, A. Singh
`
`Shouleh Nikzad, Qiuming Yu,
`Aimée L. Smith, Todd J.’ Jones,
`T. A. Tombrello, 8. Tom Elliott
`
`W. R. Tribe, M. J. Steer,
`A. N. Forshaw, K. L. Schumacher,
`D. J. Mowbray, D. M. Whittaker,
`M. S. Skolnick, J. S. Roberts, G. Hill
`
`Ho Ki Kwon, Y. Kim, H. Lim
`
`H. S. Kim, J. Y. Lin, H. X. Jiang,
`W. W. Chow, A. Botchkarev,
`H. Morkog
`A. M. Fiudin, L. J. Guo,
`L.
`I. Glazman, S. Y. Chou
`M. Ershov
`
`Free-carrier_generation in amorphous semiconductors by intense
`subgap excitation,
`
`Keiji Tanaka
`
`Correlation between the surface defect distribution and minorit
`carrier transport properties in GaN
`
`y
`
`P. M. Bridger, Z. Z. Bandié,
`E. C. Piquette, T. C. McGil|
`
`(Continued)
`
`Page 3 of 8
`
`

`
`Appl. Phys. Lett., Vol. 73, No. 23, 7 December 1998
`
`Examination of deuterium transport through device structures
`3441
`3444 Mechanism of generation of f—f radiation in semiconductor
`heterostructures
`
`P. J. Chen, Fl. M. Wallace
`
`G. G. Zegrya, V. F. Masterov
`
`SUPERCONDUCTORS
`3447
`‘Spatially resolved microwave field distribution in YBaCuO disk
`resonators visualized by laser scanning
`.
`3450 Dependence on the microwave field of the surface resistance for
`YBa2Cu307_,; films fabricated on copper substrates
`
`MAGNETISM
`
`3453 CoPt/Ag nanocomposites for high density recording media
`
`3456 Magnetic homogeneity of colossal-magnetoresistance thin films
`determined by alternating current magnetic susceptibility
`
`Spin-dependent band structure, Fermi surface, and carrier lifetime of
`permalloy
`
`Giant magnetoresistance near the magnetostructural transition in
`Gd5(3i1.aGe2.2)
`
`PAPERS IN OTHER FIELDS
`
`3465
`
`Single-walled carbon nanotube probes for high-resolution
`nanostructure imaging
`
`3468
`
`CUMULATIVE AUTHOR INDEX
`
`T. Kaiser, M. A. Hein, G. Muller,
`M. Perpeet
`
`Jian—Fei Liu, Kiyomitsu Asano,
`’ Eizi Ezura, Shigemi lnagaki,
`Shigeru lsagawa, Hiroshi Nakanishi,
`Masao Fukutomi, Kazunori Komori,
`Masakazu Saito
`
`S. Stavroyiannis, I. Panagiotopoulos,
`D. Niarchos, J. A. Christodoulides,
`Y. Zhang, G. C. Hadjipanayis
`
`F. M. Araujo-Moreira, M. Flajeswari,
`A. Goyal, K. Ghosh,
`V. Smolyaninova, T. Venkatesan,
`C. J. Lobb, R. L. Greene
`’
`
`D. Y. Petrovykh, K. N. Altmann,
`H. Héchst, M. Laubscher, S. Maat,
`G. J. Mankey, F. J. Himpsel
`
`L. Morellon, J. Stankiewicz,
`B. Garcia-Landa,.P. A. Algarabel,
`M. Fl. lbarra
`
`g
`Stanislaus S. Wong,
`Adam T. Woolley, Teri Wang Odom,
`Jin-Lin Huang, Philip Kim,
`Dimitri V. Vezenov,
`Charles M. Lieber
`
`A publication of the American Institute of Physics, 500 Sunnysiden Blvd., Woodbury, NY 11797-2999
`
`Page 4 of 8
`
`

`
`APPL ED
`PHYSICS
`LETTERS
`
`CODEN: APPLAB
`ISSN: 0003-6951
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`Editor
`
`.
`
`Nghi Q. Lam
`Argonne National Laboratory
`Argonne, IL
`
`Walter Potz
`David Long Price
`Lynn E. Rehn
`Jules Routbort
`Linda Young
`
`Consulting Editor
`Gilbert J. Perlow
`Associate Editors
`Charles W. Allen
`Samuel D. Bader
`Alan R. Krauss
`David S. Kupperman
`F. Paul Mooring
`Editorial Board
`Term ending 31 December 1998
`Dieter M. Gruen (Argonne Nat’! Lab., Argonne, lL)
`Patricia M. Mooney (IBM Corp., Yorktown Heights, NY)
`James S. Williams (Australian Nat’| Univ., Canberra,
`Australia)
`'
`Term ending 31 December 1999
`David B. Geohegan (Oak Ridge Nat’l Lab., Oak Ridge,TN)
`Andreas Mandelis (Univ. of Toronto, Toronto, Canada)
`Teh Y. Tan (Duke Univ., Durham, NC) '
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`Term ending 31 December 2000
`Robert Hull (Univ. of Virginia, Charlottesville, VA)
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`Page 5 of 8
`
`

`
`‘ APPLIED PHYSICS LETTERS
`
`VOLUME 73, NUMBER 23
`
`7 DECEMBER 1998
`
`A method for liquid crystal alignment using in situ, ultraviolet
`exposure during imidization of polyimide
`
`Jae—Hoon Kim, Bharat Ft. Acharya, and Satyendra Kumara)
`Departmem‘ of Physics, Kent State University, Kent, Ohio 44242
`
`Ki Ryong Ha
`Department of Chemical Engineering, Keimyimg University, Taegu 704-701, Korea
`
`(Received 24 August 1998; accepted for publication 5 October 1998)
`
`Homogeneous alignment of liquid crystals can be achieved by a technique using polyimide films
`and in situ exposure to linearly polarized ultraviolet (LPUV) light during imidization. The alignment
`layers prepared by this method exhibit higher thermal stability while requiring shorter processing
`time than the conventional UV alignment method which employs UV exposure after the imidization
`of polyimide is complete. Multidomain cells can be easily fabricated with the use of a photomask
`and multistep in situ LPUV exposure during hard bake. © 1998 American Institute of Physics.
`[S0003-6951(98)02949-0]
`
`of the alignment layers prepared by the conventional UV
`method for PI films. This method can be applied to any UV
`sensitive polymer film to produce an alignment layer.
`The materials used in this study are the PI SE6lO (Nis-
`san Chemical Co.) and the nematic LC E48 (British Drug
`House). PI films were prepared by heat curing of precursor
`polyamic acid (PAA) solutions which was synthesized from
`the reaction between tetracarboxylic dianhydride and di-
`amines. Glass substrates were spin coated with a solution of
`PAA (unimidized P1) in _N-methyl-2-pyrrolidinone at 3000
`rpm for 30 s. The films were then soft baked at 100 °C for 10
`min to evaporate the solvent. The PAA film was then imi-
`dized by hard baking at 250 °C for 1 h. In the conventional
`method, the spin coated PI film followed by thermal imidiza-'
`tion is exposed to LPUV at room temperature.5‘6 In our
`study, we exposed LPUV for 30 min during thermal imidiza-
`tion (or hard bake) at 250°C. To distinguish it from the
`conventional method, we are calling it an in situ UV expo-
`sure method.
`
`Figure I shows schematically the experimental setup. A
`collimated beam UV light from a Xe lamp was polarized
`
`2 1
`
`l 1
`
`FIG. -1. Schematic dia
`gram of experimental setup; (1) UV source, (2) UV
`polanzer, (3) UV transparent window, (4) PAA layer
`(5) glass substrate,
`“"9 (5) hot Stage. The sample hot stage is mounted such that it can be
`rotated for Oblique ex
`posure to generate finite pretilt.
`
`© 1998 American institute of-Phi/Sics
`
`The preparation of highly oriented liquid crystals (LCS)
`is of great importance for the basic understanding of interfa-
`cial phenomena and for the operation of electro-optical de-
`vices. Substrates with obliquely evaporated SiO layers,
`Langmuir—Blodgett films, rubbed polymer films, and lin-
`early photopolymerized films possess anisotropic surface po-
`tential and have been successfully used to align liquid
`crystals.“4
`Mechanical rubbing of polyimide (Pl) layers is the most
`common alignment method used in mass production of liq-
`uid crystal displays (LCDs) because of its simplicity and
`high thermal stability of the resultant alignment. The disad-
`vantages of the rubbing method are the generation of dust
`particles, electrostatic charge, and physical damage which
`are detrimental to the fabrication of thin film transistor based
`devices.
`
`To eliminate these problems, nonrubbed (noncontact)
`photoalignment processes have been developed in recent
`years.
`It
`has
`been
`demonstrated
`that
`poly(vinyl)4-
`methoxycinnamate (PVMC) and poly(vinyl)cinnamate films,
`when anisotropically cross linked using linearly polarized
`ultraviolet (LPUV) light, can be very effective as alignment
`layers.” However, their performance deteriorates with time.
`Recently, the alignment of LCs by P1 films exposed to the
`LPUV light has been reported.5’9 The photoalignment
`method allows for an easy control of the alignment direction
`and anchoring strength so that multidomain devices, with
`improved viewing angle characteristics, can be readily pro-
`duced. However, under this method the LPUV exposure is
`carried out after the imidization of the film is complete. The
`PI alignment layers prepared by this method possess poor
`thermal and chemical stability. Evidently, many researchers
`are attempting to develop new noncontact alignment meth-
`ods for producing a stable alignment layer.
`In this letter, we report the development of a noncontact
`UV alignment method for LCs. The alignment layers pm-
`pared by this method have much higher thermal stability than
`
`“Electronic mail: satyen@xray-kent.edu
`
`0003-6951/98/73(23)/3372/3/$15.00
`
`Page 6 of 8
`
`

`
`Appl. Phys. Lett., Vol. 73, No. 23, 7 December 1998
`
`Kim et al.
`
`3373
`
`..,.+..,....-
`
`0.006r~
`0.004
`
`0.002
`
`0.000
`
`-0.002 L
`
`0.0006
`
`0.0003
`
`0.0000
`
`-0.0003
`
`ABSORBANCE
`
`-0.0006 -
`_;_i_1ijiI.;|.:ml.~..|....l.-.._J.iu:liii:
`1900
`1800
`1700
`1600
`1500
`1400
`1300
`1200
`1100
`
`WAVENUMBER (cm'1)
`
`FIG. 2. The polarized FTIR spectra obtained by subtracting the spectra
`taken with IR polarization parallel to the rubbingtlirection or the direction
`of polarization of LPUV from the spectrum taken with IR polarization per-
`pendicular to the respective direction for (a) rubbed PI film and (b) PI film
`prepared by the in Sim method. Peaks (1), (2), and (3) are attributed to the
`v(C=O), 1/(L4-Cal-I4), and V(imide C—N—C), respectively.
`
`using an Oriel UV sheet polarizer. The intensity of the po-
`larized UV light was approximately 6 mW/cmz at the film’s
`surface. The PI/PAA coated substrate was placed perpen-
`dicular to the polarized UV beam with the polymer side to-
`ward the lamp.
`PI/PAA films spun onto CaF2 were used for the mea-
`surement of Fourier transform infrared (FTIR) spectra using
`Magna 550 FTIR (Nicolet) spectrometer. From the Collected
`FTIR spectrum, the CaF2 spectrum was subtracted to obtain
`the contribution of the sample. A single diamond IR polar-
`izer from Harrick Co. was used for this study. To reduce the
`noise level, over 300 scans were obtained at a resolution of 4
`cm”.
`
`Figure 2 shows the difference of the polarized IR spec-
`trum obtained by subtracting the spectrum taken with polar-
`ization parallel and perpendicular to the rubbing direction
`and the polarization vector of LPUV. The peaks at 1722,
`1503,
`and I377 cm” are attributed to the 1J(C=O),
`u(l,4-CGH4), and 1/(imide C—N—C), respectively. Although
`the transition moment of C=O bonds is perpendicular to the
`main chain direction,
`those of C6H4 and CNC functional
`groups are parallel to the main chain direction. In the rubbed
`sample, the absorbance is positive at 1503 and 1377 cm”,
`and negative at 1722 cm_l. It indicates that rubbed PI chains
`are oriented along the rubbing direction. In contrast to the
`rubbed sample,
`the difference absorption spectra of the
`sample prepared by in siru method is quite the opposite;
`negative values at 1503 and 1377 cm_1, and positive value at
`1722 cm”. The reverse sign of each of the components in p
`the two samples suggests that the orientation of the unreacted
`PI molecules is perpendicular to the polarization direction of
`LPUV. The change in PI’s molecular orientation after LPUV
`exposure appears to be primarily due to a preferential degra-
`dation of the PI molecules along the direction of polarization
`of LPUV. Reorientation of the molecular chain due to the
`imide bond breaking may also play a role.
`
`FIG. 3. Polarizing microscopy texture of a homogeneously aligned cell
`prepared by conventional UV method: (a) before and (b) after thermal an-
`nealing at 100°C for 12 h. The loss of alignment in (b) shows thermal
`instability of this alignment method.
`
`The LC texture in a cell prepared with the alignment
`layer using the conventional method is initially uniform as
`shown in Fig. 3(a). However after thermal annealing at
`100 °C for 12 h, it shows schlieren texture indicating that the
`alignment is lost [Fig. 3(b)]. The optical texture of the cell
`prepared by the in Sim method is also uniform over the
`whole area as shown in Fig, 4(a). After thermal annealing
`under similar conditions, no degradation of alignment is ob-
`served [Fig. 4(b)]. At elevated temperature (150 °C for 12 h),
`some loss of alignment is observed as shown in Fig. 4(c).
`Clearly, the in situ method yields much more stable‘ align-
`ment layers than the conventional method. It is expected that
`this method can be further developed to provide even higher
`thermal stability.
`We believe that there are several factors responsible for
`the enhancement in thermal stability for the in situ method.
`In the conventional method, the LPUV dissociates bonds in
`polymer chains after polymerization (imidization) had been
`completed. As a result, smaller chain (segments) are left in
`the direction of polarization while the orthogonal direction is
`populated by longer chains.8 The smaller segments are not
`able to relax and perhaps reorient as the UV exposure is
`conducted at room temperature. Consequently, there is sig-
`niflcant strain energy stored in these films which is released
`at higher temperatures during thermal annealing. This relax-
`ation process renders the polymer chain orientation more
`random which in turn loses the ability to align liquid crystal
`molecules. On the other hand,
`in the in situ method,
`the
`
`Page 7 of 8
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`
`Appl. Phys. Lett., Vol. 73, No. 23, 7 December 1998
`
`(a)
`
`FIG. 4. Polarizing microscopy texture for a homogeneously aligned nematic cell prepared by them situ UV exposure method: (a) before and (b) after thermal
`annealing at 100 °C for 12 h, and (c) after thermal annealing at 150 "C for 12 h. Evidently, the alignment is more stable compared to that of the conventional
`method shown in Fig. 3.
`
`depolymerization by LPUV and polymerization by thermal
`reaction occur simultaneously. Therefore,
`the imidization
`rate is anisotropic. Moreover, since we expose LPUV at high
`temperature in the in ritu method, the mobility of polymer
`chains is higher. Small polymer chains that reorient and be-
`come perpendicular to the direction of polarization are likely
`to undergo imidization and thus increase the number and
`length of the chains in that direction. Thus,
`the resulting
`alignment films are not only free of strain energy and hence
`more stable, they are more effective than the conventionally
`prepared films. It
`is believed that
`this method holds the
`promise of producing even more stable alignment layers,
`when all parameters, such as temperatures of soft and hard
`bake, intensity of UV, duration, and the time of UV expo-
`sure, have been optimized.
`Since, in the in situ method, LPUV exposure takes place
`during imidization of PI, the number of steps in preparing an
`alignment layer and the processing time are significantly re-
`duced compared to the conventional process. Moreover, mul-
`tidomain cells can be easily fabricated with multistep LPUV
`exposure using a photomask during the hard bake. In our
`study, the whole area of the substrate was exposed to nor-
`mally incident LPUV for the first 20 min of hard baking.
`
`(IUUVZ.
`
`FIG. 5. Appearance of a homogeneously aligned multidomain cell between ‘
`crossed polarizers.’The polarization direction of first exposed LPUV’coin-
`cidcs with the axis of one of the crossed polarizers. The polarization direc-
`tion was at 45° to the polarizer axes. Dark (bright) region marked as I (11)
`represents one (two) LPUV exposure(s).
`
`,
`
`During the next 20 min of hard baking, one half of the sub-
`strate was covered by a photomask and the second half was
`exposed normally to LPUV with polarization direction ro-
`tated by 45° with respect to the first exposure. Figure 5
`shows the microscopic texture of the sample. In one region
`(marked as I) which is exposed to LPUV only once,
`the
`polarization direction of the LPUV exposure coincides with
`the axis of one of the cross polarizers and minimum trans-
`mittance is obtained, as expected. The other region (marked
`as H), with two LPUV exposures with polarization direction
`rotated through 45 ° during the second exposure, appears
`bright. The minimum transmission for this region is obtained
`by rotating the LC cell through 45° showing that the LC
`alignment direction has changed by 45°- and is perpendicular
`to the polarization direction of the second LPUV exposure.
`In conclusion, we have demonstrated a novel method for
`LC alignment using LPUV exposure during the imidization
`of polyimide. The preliminary results show that samples pre-
`pared by this method have better thermal stability and re-
`quire less processing time. Research to generate pretilt angle
`using the in situ method is now underway. We note that this
`method may also be applicable to other photopolymer films
`during evaporation of the solvent and to solutions of a cross-
`linkable resin and a curing agent.
`
`This work was supported in part by NSF Science and
`Technology Center ALCOM Grant No. DMR—89-20147.
`
`:1 Cognard,Mo1. Cryst. Liq. Cryst. Suppl. Ser. 1 (1982).
`A. Dyadyusha, T. ,Marnsii, Y. Resnikov, A. Khizhnyak, and V. Reshet-
`“Yak, Pis’ma Zh. Eksp. Teor. Fiz. 56, 18 (1992) [Pis’ma Zh. Eksp. T6015
`Fiz. 56, 17 (l992)].
`3M. Schadt, K. Schmitt, V. Kozinkov) gmd V_ Chjgrjnov’ Jpn. J, Appl.
`4Phys., Part 1 31, 2155 (l992).
`E- Guyon and W. Urbach, None/m's.rive Elecrro-optic Displays, edited by
`$112.14I:me1z and F. K. von Willsen (Plenum, New York, 1976). PP-
`:M' Hasegawa and Y. Taira, J. Photopolym. Sci. Technol. 8, 241 (1995)-
`.l..L. West, X. Wang, Y. Li. and J. R. Kelly, Society of Information
`7D1splay Digest XXVI, 703 (1995).
`‘
`J. Chen, D. L. Johnson, P. J. Bos, X. Wang and J. L. West, Phys. Rev. E
`54, 1599 (1996).
`°’
`81--H Kim. Y. Shi, S.—D. Lee, and s. Kumar, Appl. Phys. Lett. 71, 3162
`(1998);P11ys. Rev. 1-: 57,5644 (1998).
`9
`._
`.
`_
`ggglggfhlkawai 13- Tahefl. and J. L. West, Appl. Phys. Lett. 72, 2403
`
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