Showing papers by "Alex K.-Y. Jen published in 2006"
TL;DR: It is concluded that QD-LEDs could be made more efficient by further optimization of the organic semiconductors by using multiple spin-on HTLs.
Abstract: We report multilayer nanocrystal quantum dot light-emitting diodes (QD-LEDs) fabricated by spin-coating a monolayer of colloidal CdSe/CdS nanocrystals on top of thermally polymerized solvent-resistant hole-transport layers (HTLs). We obtain high-quality QD layers of controlled thickness (down to submonolayer) simply by spin-coating QD solutions directly onto the HTL. The resulting QD-LEDs exhibit narrow ( approximately 30 nm, fwhm) electroluminescence from the QDs with virtually no emission from the organic matrix at any voltage. Using multiple spin-on HTLs improves the external quantum efficiency of the QD-LEDs to approximately 0.8% at a brightness of 100 cd/m(2) (with a maximum brightness over 1,000 cd/m(2)). We conclude that QD-LEDs could be made more efficient by further optimization of the organic semiconductors.
508 citations
TL;DR: This work demonstrated intensity modulation of light with light in a silicon–polymer waveguide device, based on the all-optical Kerr effect—the ultrafast effect used in four-wave mixing, and showed experimentally that the mechanism of this modulation is ultrafast through spectral measurements.
Abstract: Although gigahertz-scale free-carrier modulators have been demonstrated in silicon, intensity modulators operating at terahertz speeds have not been reported because of silicon's weak ultrafast nonlinearity. We have demonstrated intensity modulation of light with light in a silicon–polymer waveguide device, based on the all-optical Kerr effect—the ultrafast effect used in four-wave mixing. Direct measurements of time-domain intensity modulation are made at speeds of 10 GHz. We showed experimentally that the mechanism of this modulation is ultrafast through spectral measurements, and that intensity modulation at frequencies in excess of 1 THz can be obtained. By integrating optical polymers through evanescent coupling to silicon waveguides, we greatly increase the effective nonlinearity of the waveguide, allowing operation at continuous-wave power levels compatible with telecommunication systems. These devices are a first step in the development of large-scale integrated ultrafast optical logic in silicon, and are two orders of magnitude faster than previously reported silicon devices.
282 citations
TL;DR: In this article, the authors have demonstrated intensity modulation of light with light in a silicon-polymer integrated waveguide device, based on the all-optical Kerr effect -the same ultrafast effect used in four-wave mixing.
Abstract: Although Gigahertz-scale free-carrier modulators have been previously demonstrated in silicon, intensity modulators operating at Terahertz speeds have not been reported because of silicon's weak ultrafast optical nonlinearity. We have demonstrated intensity modulation of light with light in a silicon-polymer integrated waveguide device, based on the all-optical Kerr effect - the same ultrafast effect used in four-wave mixing. Direct measurements of time-domain intensity modulation are made at speeds of 10 GHz. We showed experimentally that the ultrafast mechanism of this modulation functions at the optical frequency through spectral measurements, and that intensity modulation at frequencies in excess of 1 THz can be obtained in this device. By integrating optical polymers through evanescent coupling to high-mode-confinement silicon waveguides, we greatly increase the effective nonlinearity of the waveguide for cross-phase modulation. The combination of high mode confinement, multiple integrated optical components, and high nonlinearities produces all-optical ultrafast devices operating at continuous-wave power levels compatible with telecommunication systems. Although far from commercial radio frequency optical modulator standards in terms of extinction, these devices are a first step in development of large-scale integrated ultrafast optical logic in silicon, and are two orders of magnitude faster than previously reported silicon devices.
209 citations
130 citations
TL;DR: In this paper, the bandpass-modulation characteristics of a ring resonator-based traveling-wave modulator using an electrooptic polymer AJL8/APC were reported.
Abstract: The authors report the bandpass-modulation characteristics of a ring resonator-based traveling-wave modulator using an electrooptic polymer AJL8/APC. The use of the traveling-wave electrode makes it possible to achieve an efficient modulation around 28 GHz, which is the free spectral range of the resonator, with a 3-dB bandwidth of 7 GHz. The modulation sensitivity is evaluated by defining an equivalent half-wave voltage of ring modulators. It is shown that the modulator has a potential in the microwave and millimeter-wave photonics applications
117 citations
TL;DR: In this article, the tricyanopyrroline (TCP) electron acceptor was used to synthesize a new class of highly efficient nonlinear optical (NLO) chromophores.
Abstract: We have synthesized a new class of highly efficient nonlinear optical (NLO) chromophores based on the novel tricyanopyrroline (TCP) electron acceptor. Molecular linear and nonlinear optical properties of the prototypical chromophores were measured and calculated to understand structure−property relationships. One such chromophore showed molecular first hyperpolarizability (β) of (8700 ± 702) × 10-30 esu at excitation wavelengths of 1.9 μm, and another showed macroscopic electro-optic (EO) coefficients (r33) of 51 pm/V at 1.55 μm with 20 wt % chromophore loading when poled with 65 V/μm in amorphous polycarbonate film. Synthetic strategies for extending the utility of the acceptor and chromophores are discussed.
111 citations
TL;DR: In this paper, the authors used Diels-Alder (DA) click chemistry to post-functionalize NLO chromophores onto polymers, and showed that high chromophore loading levels (up to 35 wt %) and large r33 values ( up to 110 pm V) could be achieved in in situ generated side-chain dendronized NLO polymers with non-reacted chromophors as guest dopants.
Abstract: Poled electro-optic (EO) polymers have enabled many advances in the exploration of high-speed and broadband information technologies. Polymer based EO devices have been demonstrated to have large bandwidths (over 110 GHz), low driving voltages, and sustain their performance in a flexible form or under extreme environmental conditions. For optical circuits, EO polymers can be easily integrated with striplineor ring-structured waveguides made of sol–gels, low-loss fluorinated polymers, silicon slots, conducting oxides, and photonic crystals. Recently, EO polymers have also been utilized for the generation/detection of a gap-free pulsed THz system with a bandwidth up to ca. 12 THz. Large numbers of discrete photonic components need to be inserted into integrated systems of telecommunication and silicon microphotonics, especially where an extreme amount of data is required to travel in a very small space. Therein lies the great challenge for polymer-based EO technologies: to have thermally stable EO coefficients (r33) of around 500 pm V at wavelengths of 1.31 or 1.55 lm. Currently, the most commonly used materials for polymeric EO devices are based on poled polymers with r33 values around 50–80 pm V at wavelengths of 1.31 or 1.55 lm. In these materials, dipolar nonlinear optical (NLO) chromophores have been doped or incorporated at a level of ca. 20– 25 wt % to reach their maximum r33 values. [5–10] Beyond such a moderate loading of chromophores, strong intermolecular electrostatic interactions severely limit the poling-induced polar order and cause phase-separation problems between chromophores and polymers. To further improve EO activity, research efforts have focused on developing shape-engineered chromophores with high molecular optical nonlinearities (lb), where lb is a product of first hyperpolarizability and the dipole moment of the NLO chromophore, and increasing order within the matrices by controlling the nanoscale architecture of macromolecules. In our recent study we have demonstrated, using Diels–Alder (DA) “click chemistry” to post-functionalize NLO chromophores onto polymers, that high chromophore loading levels (up to 35 wt %) and large r33 values (up to 110 pm V) could be achieved in in situ generated side-chain dendronized NLO polymers with non-reacted chromophores as guest dopants. This opens a new avenue to explore optimal host–guest combinations and to develop an efficient way to control lattice hardening in these hybrid polymers. The ultimate goal is to simultaneously achieve very large EO activity, good thermal stability, high optical transparency, and excellent mechanical properties within the same material via molecular design and facile processing. In this paper, we report a novel method to disperse a highly efficient secondary chromophore into in situ crosslinked NLO polymer networks, leading to both enhanced EO activity (> 260 pm V at 1.31 lm) and alignment stability at 85 °C. In photorefractive (PR) polymers and liquid-crystal (LC) systems, binary chromophore mixtures have been shown to elevate the loading density of small dipolar dyes without causing phase separation. We have extended this further by incorporating highly polarizable NLO chromophores into these binary systems. In addition, DA click chemistry has also been employed to improve the physical properties of these materials. This combined effort demonstrates that binary mixtures of large-bl chromophores can be loaded into side-chain NLO matrices and efficiently poled to give EO activities higher than the summed value of two added chromophores. These systems can also be mildly cured to ensure a thermally stable EO response. The EO polymers studied in this work exist as a three-component host–guest system (Fig. 1). The host polymer is a copolymer, poly[(methyl methacrylate)-co-(9-anthracenyl methyl methacrylate)] (PMMA-AMA), with around 10 mol % of the anthracenyl moiety. To this host, AJC146 was added together with compound 1a, 1b, or 1c as binary guest chromoC O M M U N IC A TI O N S
103 citations
TL;DR: A facile synthetic route has been developed to convert an electron-rich, sterically hindered dialkylaminodienone into a conjugated dial Kylaminotetraene-type nonlinear optical chromophores, which possess an all-trans conformation and can be functionalized with fluoro-dendron to provide proper shape modification for poling.
90 citations
TL;DR: In this article, a bilayer hole-injection/transport structure was prepared by thermally crosslinking two separate hole-transport layers (HTL) and the resulting films possess excellent optical quality and solvent resistance.
Abstract: A bilayer hole-injection/transport structure was prepared by thermally crosslinking two separate hole-transport layers (HTL). The resulting films possess excellent optical quality and solvent resistance. Cascade hole-injection and effective electron-blocking/exciton confinement can be achieved for light-emitting diodes (LEDs) using blue phosphorescent emitters, such asbis(4′,6′-difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate. The first HTL was based on tetraphenyldiamine (TPD) has its highest occupied molecular orbit (HOMO) level lies at −5.3eV, and the second HTL with 4,4′,4″-tri(N-carbazolyl)triphenylamine has its HOMO level lies at −5.7eV. The preliminary results from blue LEDs using these cascade HTLs showed much improved device performance than those only use a single layer hole-transporting polymer.
88 citations
TL;DR: In this paper, an organically modified sol-gel cladding layer was used for electro-optic polymers to achieve a Pockel coefficient enhancement of up to a factor of 2.5.
Abstract: Ultraefficient poling of electro-optic polymers is reported using an organically modified sol-gel cladding layer. This poling technique has resulted in a Pockel’s coefficient enhancement of up to a factor of 2.5, going from 26pm∕V when poled without a sol-gel cladding to 65pm∕V when optimally poled with a sol-gel cladding. The poling process directly applies to a previously reported hybrid electro-optic polymer/sol-gel waveguide modulator and may have applications in other poled polymer based devices.
61 citations
TL;DR: In this paper, a hybrid electro-optic (EO) polymer-sol-gel modulator with low half-wave voltage (Vπ) and low insertion loss is presented.
Abstract: The authors report on hybrid electro-optic (EO) polymer–sol-gel modulators with low half-wave voltage (Vπ) and low insertion loss. Larger EO coefficient r33 results from the high poling field achieved when EO polymer is sandwiched between sol-gel cladding layers. The reduced interelectrode distance (d) resulting from the elimination of the sol-gel core layer in the active region further reduces Vπ. Straight channel phase modulators operate with Vπ=4.2V at 1550nm using a reduced d of 11.5μm, which corresponds to an r33 of 78pm∕V, among the highest r33 reported. The authors also examine a Mach-Zehnder modulator with Vπ=3.9V using a conventional d of 15μm.
TL;DR: Structurally robust unimolecular columnar stacks of HATNA with tunable length have been fabricated through a combination of supramolecular self-assembly and post-polymerization approach, which can be utilized to transfer the self-assembled nanostructures to the surface to create desired functional patterns.
Abstract: The one-dimensional (1-D) self-assembly property of an n-type hexaazatrinaphthylene (HATNA) discotic pi-conjugated molecule was studied. Structurally robust unimolecular columnar stacks of HATNA with tunable length have been fabricated through a combination of supramolecular self-assembly and post-polymerization approach. Moreover, microcontact printing can be utilized to transfer the self-assembled nanostructures to the surface to create desired functional patterns.
TL;DR: In this paper, two novel multifunctional copolymers consisting of a temperature-responsive poly(N-isopropylacrylamide) (PNIPAA) segment and a fluorescent fluorene-containing acrylic polymer segment with pH responsiveness and/or DNA-sensing ability were reported.
Abstract: We report two novel multifunctional copolymers consisting of a temperature-responsive poly(N-isopropylacrylamide) (PNIPAA) segment and a fluorescent fluorene-containing acrylic polymer segment with pH responsiveness and/or DNA-sensing ability. The functional acrylic monomer with a fluorene dimer side group substituted with amino units was synthesized first. Then, it was copolymerized with N-isopropyl-acrylamide to result in a new water-soluble, fluorescent PNIPAA copolymer (P1). The fluorescent properties of P1 under neutral and acidic conditions did not change with the temperature. However, significant variation was observed under basic conditions. The protonation of the amino moiety at a low pH improved the solubility and prevented aggregation for fluorescence quenching, but not under the basic conditions. Although aggregation of the fluorene units was significant at room temperature under basic conditions, the aggregation was resolved at a temperature above the lower critical solution temperature. These findings indicated the pH- and temperature-responsive characteristics of P1. Moreover, after the amino groups were quaternized, the obtained polymer could be used as a biosensor because the fluorescence intensity was quenched with the addition of DNA. This study demonstrates that multifunctional materials with pH- and temperature-sensing characteristics and biological molecules could be realized by the incorporation of a functional fluorene-containing moiety with PNIPAA.
TL;DR: In this article, high-speed polymer modulators were fabricated using low-Vpi AJL8 chromophore in amorphous polycarbonate, and highly calibrated frequency response measurements were obtained using convenient coplanar-microstrip transitions.
Abstract: High-speed polymer modulators were fabricated using low-Vpi AJL8 chromophore in amorphous polycarbonate, and highly calibrated frequency response measurements were obtained using convenient coplanar-microstrip transitions. These Mach-Zehnder modulators show good frequency response to 50 GHz, with a loss and velocity mismatch-limited Vpi at 50 GHz <12 V. The measurements establish AJL8 as an excellent candidate for future military analog optical links
TL;DR: A detailed quantum-chemical investigation of donor-acceptor substituted dipolar nonlinear optical chromophores incorporating the 4-(dimethylamino)phenyl donor end group and a variety of strong heterocyclic acceptor end groups, including tricyanofurans andtricyanopyrroles.
Abstract: We report a detailed quantum-chemical investigation of donor-acceptor substituted dipolar nonlinear optical chromophores incorporating the 4-(dimethylamino)phenyl donor end group and a variety of strong heterocyclic acceptor end groups, including tricyanofurans and tricyanopyrroles. In particular, we study the variation of the molecular second-order polarizability (β) with the acceptor end group and when inserting auxiliary donors (thiophene) and acceptors (thiazole) into the π bridge. Both finite-field calculations (in the context of local contributions) and sum-over-states calculations were carried out in order to probe the relationship between β and the chemical structure of the various chromophores. The trends obtained with these two methods are fully consistent. The large β values (up to 700×10−30esu) as well as the observed tunability of the optical absorption maximum (λmax) make the chromophores investigated here interesting candidates for use in electro-optic applications at telecommunications wav...
TL;DR: In this article, the authors have experimentally verified that the light emission from conjugated polymers can be enhanced through the use of surface plasmon coupling layers and showed that the recombination rate can be increased due to the surface Plasmon polaritons.
Abstract: The authors have experimentally verified that the light emission from conjugated polymers can be enhanced through the use of surface plasmon coupling layers. Carrier dynamics of such plasmon-enhanced organic light emitters were studied and a recombination rate increase due to surface plasmon polaritons was experimentally observed. Internal quantum efficiency data from the polyfluorenes studied follow the trend supported by the time resolved photoluminescence measurements.
01 Sep 2006
TL;DR: In this paper, the authors developed a tunable Fabry-Perot filter using an electro-optic hybrid organic-inorganic incorporated in highly reflective distributed Bragg reflector (DBR) mirrors.
Abstract: We report on the development of a tunable Fabry-Perot filter using an electro-optic hybrid organic-inorganic incorporated in highly reflective distributed Bragg reflector (DBR) mirrors. Large tunability (≫0.7 nm/V) and high finesse (≫ 200) have been obtained.
TL;DR: In this paper, a thermally stable modulator using a novel Diels-Alder crosslinkable electrooptic (EO) polymer was fabricated using a smartly controlled process to overcome the EO coefficient-thermal stability tradeoff.
Abstract: A thermally stable modulator using a novel Diels-Alder crosslinkable electrooptic (EO) polymer was fabricated. This new material system presents a smartly controlled process to overcome the EO coefficient-thermal stability tradeoff of conventional thermosetting EO polymers and obtains poling efficiency and thermal stability simultaneously. The modulator showed long-term stability at 85/spl deg/C, which shows potential for industrial applications.
TL;DR: Strong hydrogen bonding and pi-pi stacking between 1-pyrylphosphonic acid molecules were exploited to create self-assembled two-dimensional supramolecular structures that possess good mechanical properties and were easily transferred onto a SiO2/Si substrate that was patterned with Au electrodes without breaking their crystalline structures.
Abstract: Strong hydrogen bonding and π−π stacking between 1-pyrylphosphonic acid (PYPA) molecules were exploited to create self-assembled two-dimensional supramolecular structures. Polycrystalline films of these laminate crystalline PYPA bilayers were easily deposited onto the solid supports through a simple spin-coating technique. Atomic force microscopy (AFM), scanning tunneling microscopy (STM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV−vis absorption, and fluorescence spectroscopy reveal that processing parameters, such as solvent, concentration, and surface of the substrate, are critical factors in determining the final morphology of the stacked film. Robust laminate structures could be obtained only when short alkyl chain protic solvents (methanol or ethanol) and a nonhydrophobic substrate surface were used. Polycrystalline films were formed through the nucleation and growth of PYPA molecules into laminate structures at the air/solvent interface before they land on the subst...
TL;DR: In this article, nonlinear optical chromophore coupled hybrid sol-gel materials have been synthesized and incorporated in Fabry-Perot etalon devices (EDs) using highly reflective distributed Bragg reflector mirrors.
Abstract: Nonlinear optical chromophore coupled hybrid sol-gel materials have been synthesized and incorporated in Fabry-Perot etalon devices (ED’s) using highly reflective distributed Bragg reflector mirrors. Etalon structures with indium tin oxide electrodes outside the ED cavity have been applied to reduce absorptive loss. Large tunability (∼0.75nm∕V), high finesse (∼235), and wide tunable range (>50nm) have been obtained. A transmitted light intensity isolation ratio of ∼35dB at ∼1550nm has been achieved at a low drive voltage of 10V. The electro-optic effect and inverse piezoelectric effect are discussed. The results indicate that such hybrid sol-gel ED’s are promising candidates for tunable filters in wavelength division multiplexing communication systems.
TL;DR: In this article, an efficient UV-blue polymer light-emitting diodes based on a fluorene-based nonconjugated polymer, poly[2,7-(9,9-dihexylfluorene)-alt-4,4′-phenylether] (PFPE), are fabricated.
Abstract: Efficient UV-blue polymer light-emitting diodes based on a fluorene-based nonconjugated polymer, poly[2,7-(9,9-dihexylfluorene)-alt-4,4′-phenylether] (PFPE), are fabricated. The device with PFPE as emitting layer shows a very narrow ultraviolet-blue electroluminescence emission with a peak at 397nm and a maximal external quantum efficiency of 1.07%. By blending PFPE into poly(N-vinylcarbazole) (PVK), the device performance can be further improved. A maximum external quantum efficiency of 1.81%, with a maximum irradiance power density of 1223μW∕cm2, was reached by using a blend of PVK and PFPE in the weight ratio of 95:5 as emitting layer.
TL;DR: High-efficiency polymer light-emitting diodes were fabricated by inserting a layer of nonionic neutral surfactant between the electroluminescent (EL) layer and the high-work-function aluminum cathode via spin coating and it was found that both the poly(ethylene glycol)- and poly(propylene glycol-based surfactants as well as their copolymers can all demonstrate similar performance enhancement.
Abstract: High-efficiency polymer light-emitting diodes were fabricated by inserting a layer of nonionic neutral surfactant between the electroluminescent (EL) layer and the high-work-function aluminum cathode via spin coating. It was found that both the poly(ethylene glycol)- and poly(propylene glycol)-based surfactants as well as their copolymers can all demonstrate similar performance enhancement. Device performances comparable to or even better than those of the control devices using calcium as the cathode have been achieved for both poly(p-phenylene)-based and polyfluorene-based conjugated polymers with orange-red, green, and blue emission colors. It is possible that when both surfactant and aluminum are used as the cathode, the abundant hole injection through a hole-transporting layer and hole pile-up at the inner side of the EL/surfactant interface might cause an effective electric field to induce the realignment of the dipole moment of those polar surfactant molecules, thus lowering the barrier for electron...
TL;DR: In this paper, a Fabry-Perot etalon using an electro-optic (EO) polymer material as the nonlinear medium is presented, and two electrodes used to apply voltage across the EO polymer include an indium tin oxide electrode outside the etalon cavity and a low-absorption indium oxide electrode inside the cavity.
Abstract: The authors present a Fabry-Perot etalon using an electro-optic (EO) polymer material as the nonlinear medium The two electrodes used to apply voltage across the EO polymer include an indium tin oxide electrode outside the etalon cavity and a low-absorption indium oxide electrode inside the etalon cavity High finesse (∼234) and a low insertion loss (∼4dB) have been obtained An isolation ratio of 10dB and ∼10% modulation depth at 200kHz with 5V applied voltage have been achieved These results indicate that EO polymer etalons are promising as spatial light modulators for information technology
TL;DR: In this paper, the effects of dye donor group esterification in guest−host systems and by dye−polymer covalent attachment on near-infrared absorption behavior were examined.
Abstract: The mono-azo dyes Disperse Red 1 and Disperse Red 19 have been studied for several years as chromophores in polymers for nonlinear optical properties. These materials are examined here for the effects of dye donor group esterification in guest−host systems and by dye−polymer covalent attachment on near-infrared absorption behavior. The dye−polymer systems DR1−acrylate, DR1−poly-4-vinylphenol, and DR19−aliphatic epoxy are characterized by UV−vis absorption spectroscopy and photothermal deflection spectroscopy as guest−host systems with and without esterification of the DR1 and DR19 ethanol −OH substituents in guest−host systems, and as covalently attached dye copolymers, as a function of dye concentration up to 1700 μmol per gram of polymer. Esterification is shown to be an effective route to reducing near-IR loss in DR1/acrylate guest−host materials at high concentrations and in DR19/epoxy guest−host materials at most concentrations. Dye−polymer covalent attachment is shown to be highly effective for mini...
TL;DR: In this paper, photobleaching is used for the fabrication of polymer waveguide microring resonators for the first time, which can be used to make polymer thin films that are not compatible with other fabrication techniques, and therefore can be a useful complement to traditional fabrication methods.
Abstract: Photobleaching is demonstrated to be a viable method for the fabrication of polymer waveguide microring resonators for the first time. Resonators made with this simple, one-step fabrication technique have shown extinction ratio and insertion loss better than 15 and 9 dB, respectively. This method does not involve solvents or chemicals and can be used to make microring resonators in polymer thin films that are not compatible with other fabrication techniques, and therefore, can be a useful complement to traditional fabrication methods
01 Jan 2006
TL;DR: In this paper, the authors review the recent progress on interface engineering between polymer and electrodes to optimize charge injection, transport, and recombination in PLEDs, as well as on material engineering to tune the emission color, electron affinity, and charge mobility.
Abstract: Polymer light‐emitting diodes (PLEDs) have great potential to compete with LCD displays that are currently used for computer and television screens. The efficiency and stability of PLEDs still need to be improved in order to fully realize the advantages of low cost and ease of fabrication provided by organic materials. Our effort in improving the PLED's performance have been focused on two parallel approaches: 1) Modify the interface between polymer and the charge‐injection electrodes for more efficient device structures; 2) Enhance the efficiency of PLEDs through the development of new conjugated materials with balanced charge‐transporting properties. In this paper, we review our recent progress on the interface engineering between polymer and electrodes to optimize charge‐injection, ‐transport, and ‐recombination in PLEDs, as well as on the material engineering to tune the emission color, electron affinity, and charge mobility.
TL;DR: A simple approach to form arrays of covalently bonded single gold nanoparticles (AuNPs) is demonstrated, taking advantage of the interplay of electrostatic interactions and covalent bonding in conjunction with the positional constraint on the template.
Abstract: A simple approach to form arrays of covalently bonded single gold nanoparticles (AuNPs) is demonstrated. Asymmetric molecular assemblies composed of two layers of rigid aromatic molecules with different structures, arranged in hexagonal arrays on a template produced by edge-spreading lithography, are used to guide the assembly of AuNPs. Arrays of single AuNPs are achieved by taking advantage of the interplay of electrostatic interactions and covalent bonding in conjunction with the positional constraint on the template. Schiff base chemistry is highlighted in the surface chemical reaction to selectively modify nanoscale surface features with high yield.
09 Feb 2006
TL;DR: In this paper, a broadband E-field sensor based on an electro-optic polymer micro-ring resonator directly coupled to the core of optical fiber is proposed and demonstrated.
Abstract: A novel broadband E-field sensor based on electro-optic polymer micro-ring resonator directly coupled to the core of optical fiber is proposed and demonstrated. A flat is made on the side of the optical fiber by polishing and an electro-optic polymer waveguide in the shape of a ring is placed on the polished flat. One side of the ring is directly above the core of the fiber and light is evanescently coupled between the fiber and the micro-ring. External electric fields change the index of refraction of the ring resonator and therefore its resonant wavelengths. The sensor is all dielectric without metal layers to distort the measured E-field. The resonance structure allows the sensor to potentially have much higher sensitivity than other electro-optic sensors based on interferometry or polarization modulation. Since electro-optic polymers have higher electro-optic coefficients, lower dielectric constants and faster electro-optic responses than inorganic crystals, higher sensitivity, lower invasiveness and higher bandwidth of E-field sensing can be expected. The sensor with EO polymer micro-ring directly coupled to side-polished fiber eliminates unreliable and possibly lossy fiber to waveguide butt coupling as well as the high propagation loss which comes from the long straight EO polymer waveguides. Unlike devices based on waveguide technology, a supporting substrate is not necessary in this device. This leads to sensors of small size and low disturbance to the measured electric field. In the proof-of-concept experiment, a sensitivity of 100 mV/m has been achieved at frequencies up to 550 MHz (limited by the measurement system) using
AJLS103 electro-optic polymer.
TL;DR: The use of high-sensitivity, off-normal transmission IR spectroscopy with s-polarized light to probe the chemical identity and orientation of quaterphenyldithiol molecular assemblies on GaAs as a function of ammonium hydroxide (NH4OH) concentration is demonstrated.
Abstract: We demonstrate the use of high-sensitivity, off-normal transmission IR spectroscopy with s-polarized light to probe the chemical identity and orientation of quaterphenyldithiol (QPDT) molecular assemblies on GaAs as a function of ammonium hydroxide (NH4OH) concentration. NH4OH is added to the assembly solution to convert the thioacetyl groups on the QPDT precursor to thiolates. When assembled at high NH4OH concentrations, the acetyl groups are completely removed, and QPDT is disordered on GaAs. Assembly at low NH4OH concentrations, however, results in QPDT assemblies that are preferentially upright. The molecular orientation is further quantified with near-edge X-ray absorption fine structure spectroscopy.
TL;DR: In this paper, a conjugated molecule, C 60 -mercaptophenylanthrylacetylene (C 60 -MPAA), has been self-assembled on a gold surface to form a highly ordered monolayer.