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Showing papers by "Younan Xia published in 1995"


Journal ArticleDOI
01 Aug 1995-Nature
TL;DR: In this article, a low-viscosity polymer precursor is placed in contact with the network of channels formed when a substrate and a patterned elastomeric master are placed in intimate contact.
Abstract: THE formation of patterned structures on micrometre-length scales is essential for the fabrication of many electronic, optical and mechanical devices1. Patterning technologies are well established for semiconductors and metals, but are relatively undeveloped for organic polymers (with the notable exception of the specialized polymers used in photolithography1). Polymeric replicas of some structures have been formed by filling them with monomers which are subsequently polymerized2a¤-5. But these procedures have important limitations, in that the usually involve the destruction of the template structure, or the resulting structures are not sufficiently regular for most applications. Here we describe a general moulding procedure which does not suffer from these limitations. For the mould we use the continuous network of channels formed when a substrate and a patterned elastomeric master are placed in intimate contact. A low-viscosity polymer precursor is placed in contact with the network, which then fills spontaneously by capillary action. After cross-linking the precursor, the master is removed (and can be reused), leaving a patterned polymer layer; depending on the choice of substrate, patterned free-standing films can be similarly produced.

958 citations


Journal ArticleDOI
TL;DR: In this article, the authors showed that PANI-HCSA has a more expanded coillike conformation in m-cresol, p-Cresol and 2-chlorophenol than in chloroform, NMP, DMF and benzyl alcohol.
Abstract: Spectroscopic results indicate that camphorsulfonic acid-doped polyaniline (PANI-HCSA) has a more expanded coillike conformation in m-cresol, p-cresol, 2-chlorophenol, 2-fluorophenol and 3-ethylphenol than in chloroform, NMP, DMF and benzyl alcohol. With the UV/Vis/near IR spectroscopic method, one can easily choose an appropriate solvent to process PANI-HCSA into a highly conductive form

566 citations


Journal ArticleDOI
TL;DR: In this paper, the use of microcontact printing for patterning self-assembled monolayers (SAMs) of alkylsiloxanes on the surface of silicon dioxide is described.
Abstract: This paper describes the use of microcontact printing ({mu}CP) for patterning self-assembled monolayers (SAMs) of alkylsiloxanes on the surface of silicon dioxide. {mu}CP is a convenient technique for generating patterned SAMs of alkanethiolates on gold, but it has not been applied to Si/SiO{sub 2} and glass. The SAMs of alkyltrichlorosilanes on the hydroxyl-terminated surfaces are less ordered than those of alkanethiolates on gold, and they form more slowly. Here we demonstrate that {mu}CP can, nonetheless, be used to produce patterned SAMs of alkylsiloxanes on Si/SiO{sub 2}. We believe this technique will prove valuable for many other applications: for example, studies of protein absorption and cell attachment where high edge resolution is not critical. 17 refs., 2 figs., 1 tab.

276 citations


Journal ArticleDOI
TL;DR: In this paper, a technique that generates patterned self-assembled monolayers of alkanethiolates (SAI{s) is described. But the technique is not suitable for the fabrication of structures with feature sizes of 1 millimeter and larger.
Abstract: Nl icrocontact pr int ing t r rCPtr is a technique that generates patterned self-assembled monolayers lSAtr{s t2 of' alkanethiolates t typically, hexadecanethiolate ) on the surfaces of goid,1 silver,l l and copper,l and of alkylsiloxanes on hydroxyl-terminated surf'aces.r' Patterned SAI{s of alkanethiolates serve as nanomc.ter-thick resists in certain etching solutions: the one we i.rave. used most extensively when gold is the underiving substrate has been aqueous KCN so lu t ion (p l l ' . 1 t . ICN ] . . ,0 .1 M) saturated with 0z.6 Llsing this etchant. t l-re patterns in the SAMs can be transf'erred faithfuih' into the thin fi lms of gold; the resulting patterns of gold can be used subsequently as secondarv masks for the etching (isotropic or anisotropic ) of' underlving la.vers of sil icon dioxide and si l icon; ' or i ls funct ional e lements ( for example, for microerlectrodese and diffraction gratingsi0). Microcontact printing is renrarkablv convenient fbr the fabrication of structures rvith feature sizes of 1 zrm and larger: it can be r-rsed. rvith more diff iculty and less reliabil itv. to fabricate f 'eatures with sizes down to 100

213 citations



Journal ArticleDOI
TL;DR: In this paper, an ultraviolet nonlinear optical crystal called Strontium boratoberyllate Sr2Be2B2O7 (SBBO) has been discovered, which has very good mechanical properties and it is also not deliquescent.
Abstract: Potassium fluoroboratoberyllate KBe2BO3F2 (KBBF) has been revealed theoretically and experimentally as a novel ultraviolet nonlinear optical crystal, but it is found to be very difficult to grow in a large size, because of the weak binding interaction between the (Be2BO3)∞ units, which leads to an apparent layer habit in the growth. By using a molecular engineering approach, oxygen bridges when brought in to strengthen the binding between the infinite units are found to be useful to overcome the above shortcoming of KBBF, and in the light of it another new ultraviolet nonlinear optical crystal—strontium boratoberyllate Sr2Be2B2O7 (SBBO) has been discovered. The linear optical properties of SBBO are similar to KBBF’s, but its nonlinear optical properties are better than that of the latter. d22(SBBO)≂d22(β‐BaB2O4), which is two times higher than d11 of KBBF. SBBO has very good mechanical properties, and it is also not deliquescent. So SBBO is expected to have great potential for the application in ultraviol...

209 citations


Journal ArticleDOI
TL;DR: In this paper, the authors describe a procedure that uses the controlled reactive spreading of a liquid on a solid surf-ace to reduce the size of features produced by microcontact printing (rCP).
Abstract: This paper describes a procedure that uses the controlled reactive spreadingl 2 of a liquid on a solid surf'ace to reduce the size of features produced by microcontact printing (rCP).r It suggests a strategy for generating small f-eatures ( 100-500 nrnt in patterns on surfaces that relies on a physical process occuming on a surf-ace-lateral reactive spreading of a liquid-rather than on exposure to short-wavelength radiation or electrons. 4CP prints the patterned self-assembled monolayer' (SAM)r on the surface of gold, using an elastomeric stamp whose surface has itself been patterned in an appropriate relief structure. The stamp is wetted with an alkanethiol (typically hexadecanethiol, CH3(CH2)rsSH) and brought into contact with the gold in air for 10-20 s. I t is a very convenient technique for fornring patterned SAMs with features having dintensions of -2 lm or larger. The photolithography required to make the ntasters used to mold the e lastomer ic s tamps is s t ra ight lbrward ar th is sca le .5 and the edge resolution that can be obtained presentl)' using this method (about 50 nm)2 does not limit the resolutton of the overall pattern. It is more difficult to make t'eatures smaller than 2 ltmby pCP, primarily because fabricating the required stamps requires more complex photolithography. Features as small as 200 nm have, however, been made using masters prepared (with difficulty) by X-ray lithography.5-7 We are developing procedures that extend the capabilities of 4CP into the submicrometer range and that do not require highresolut ion photol i thography.8'e In part icular. we wish to f ind methods that start with an elastomeric stamp having features with dimensions of -2 pm or larger (that is, in the range that is easily prepared by routine photolithographic methods) and

167 citations


Journal ArticleDOI
01 Aug 1995-Langmuir
TL;DR: In this article, self-assembled monolayers (SAMs) of alkylsiloxanes were patterned by microcontact printing (μCP) on a number of substrates: N/Al 2 O 2, Si/SiO 2, TiN/TiO 2, glasses, indium tin oxide (ITO), and plasma modified polyimide.
Abstract: Self-assembled monolayers (SAMs) of alkylsiloxanes were patterned by microcontact printing (μCP) on a number of substrates : N/Al 2 O 2 , Si/SiO 2 , TiN/TiO 2 , glasses, indium tin oxide (ITO), and plasma-modified polyimide. The patterned SAMs on these surfaces define and direct the selective chemical vapor deposition (CVD) of copper using (hexafluoroacetylacetonato)(vinyltrimethylsilane)copper(I) (Cu I (hfac)(vtms)) as the source gas. This paper presents several examples of microstructures of copper fabricated by selective, SAM-directed CVD, including fabrication of thin-film interconnects (with feature sizes of 0.5-100 μm), and selective filling of trenches and vias (models of microstructures having high aspect ratios) with feature sizes below 1 μm.

162 citations




Journal ArticleDOI
TL;DR: In this article, light emitting electroluminescenters have been studied in which the conjugated light emitting polymer is separated on both sides from the device electrodes by a film of nonconducting polyaniline.
Abstract: : Light emitting electroluminescent devices have been studied in which the conjugated light emitting polymer is separated on both sides from the device electrodes by a film of non-conducting polyaniline. The devices operate under an AC applied potential. Aluminum, copper, or gold serve as the metal electrodes. Flexible, completely organic polymer dispersed liquid crystal light valves have been fabricated from transparent plastic substrates on which a conducting film of polypyrrole has been deposited. A new concept, 'microcontact printing', is being investigated for patterning the polypyrrole.