Effect of SAM layer on bias-stability of inkjet printed TIPS pentacene thin-film transistor

We have studied the effect of self-assembled monolayer (SAM) on the performance and bias-induced changes in bottom contact, inkjet printed organic thin-film transistors (OTFTs) with 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene). The device was fabricated using the photo-definable photoacryl (PA) and silver (Ag) as gate insulator and source/drain metal electrodes, respectively. The SAM was formed by immersing the patterned Ag electrodes in pentafluorothiophenol (PFBT) solution or by spin coating of phenethyltrichlorosilane (PTS) on the substrate, and TIPS pentacene was inkjet printed at 90 °C. The OTFT with SAMs exhibited the field-effect mobility of 0.18 cm²/Vs and showed the stretched exponential decay with time constant of 1.13 × 10⁷ s and exponential exponent of 0.28.     

Improved device performance in nonpolar a ‐plane GaN LEDs using a Ni/Al/Ni/Au n‐type ohmic contact

The authors report upon the increased light‐output power (P_out) via a reduction in the forward voltage (V_f) for nonpolar a ‐plane GaN LEDs using Ni/Al/Ni/Au n‐type ohmic contacts. The specific contact resistivity of the Ni/Al/Ni/Au contact is found to be as low as 5.6 × 10^–5 whereas that of a typical Ti/Al/Ni/Au contact is 6.8 × 10^–4 Ω cm², after annealing at 700 °C. The X‐ray photoelectron spectroscopy results show that the upward surface band bending is less pronounced for the Ni/Al contact compared to the Ti/Al contact, leading to a decrease in the effective Schottky barrier height (SBH). The V_f of the nonpolar LEDs decreases by 10% and P_out increases by 15% when the Ni/Al/Ni/Au scheme is used instead of the typical Ti/Al/Ni/Au metal scheme. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Surface‐enhanced Raman scattering‐based approach for DNA detection at low concentrations via polyvinyl alcohol‐protected silver grasslike patterns

A simple method is demonstrated to detect DNA at low concentrations on the basis of surface‐enhanced Raman scattering (SERS) via polyvinyl alcohol‐protected silver grasslike patterns (PVA‐Ag GPs) grown on the surface of the common Al substrate. By the SERS measurements of sodium citrate and thymine, the PVA‐Ag GPs are shown to be an excellent SERS substrate with good activity, stability and reproducibility. With the use of the tested molecule of thymine, the enhancement factor of the PVA‐Ag GPs is up to ~1.4 × 10⁸. The PVA‐Ag GPs are also shown to be an excellent SERS substrate with good biocompatibility for DNA detection, and the detection limit is down to ~10⁻⁵ mg/g. Meanwhile, the assignations of the Raman bands and the adsorption behaviors of the DNA molecules are also analyzed. In this work, the geometry optimization and the wavenumber analysis of adenine–Ag and guanine–Ag complexes for the ground states are performed using density functional theory, B3LYP functional and the LanL2DZ basis set. The transition energies and the oscillator strengths of adenine–Ag and guanine–Ag for the lowest six singlet excited states were calculated by using the time‐dependent density functional theory method with the same functional and basis set. The results show that the charge transfer in the adenine–Ag and guanine–Ag complexes should be the chemical factor for the SERS of the DNA molecules. Lastly, this method may be employed in large‐scale preparation of substrates that have been widely applied in the Raman analysis of DNA because the fabrication process is simple and inexpensive. Copyright © 2011 John Wiley & Sons, Ltd.     

Immobilization of galactose oxidase on self‐assembled monolayers of thiols on Au and Ag surfaces

Galactose oxidase (GalOD) was immobilized on self‐assembled monolayers of thiols on silver and gold surfaces using trans‐stilbene (4,4′‐diisothiocyanate)‐2,2′disulphonic acid (DIDS) as the bridging compound. DIDS is the symmetrical bifunctional reagent that reacted with the amine moiety of the thiol and with primary amino groups of enzyme. The Raman measurement revealed that onto cysteamine‐modified silver and gold electrodes, bands corresponding to the galactose oxidase (about 694, 1076, 1274 cm^—1 on Au and 762, 1058, 1274 cm^–1 on Ag ) appeared and clearly demonstrated its immobilization onto Au and Ag surfaces. Simultaneously, we have also observed changes in the ratio of trans–gauche conformers of adsorbed cysteamine molecules. Layers revealing high content of trans conformer are transformed into layers composed mainly of cysteamine molecule in gauche conformation after galactose oxidase adsorption. These observations deliver a strong support for enzyme immobilization on cysteamine‐modified gold and silver surfaces. The surface plasmon resonance experiment gave a surface coverage of ~8.4 × 10⁷ g/cm² for gold electrode modified cysteamine using DIDS chemistry and 1.1 × 10⁷ g/cm² for the cysteamine only modified gold substrate and demonstrated that galactose oxidase layers immobilized with DIDS coupling reagent are quite stable and cannot be easily removed from the surface by treatment with a buffer solution. The surface plasmon resonance results indicated that in this method, a multilayer of galactose oxidase have been immobilized. Our new method of covalent attachment of enzymes seems to be quite promising as a new way of manufacturing biosensors. Copyright © 2012 John Wiley & Sons, Ltd.     

Particle‐Arrayed Silver Mesocubes Synthesized via Reducing Silver Oxide Mesocrystals for Surface‐Enhanced Raman Spectroscopy

In this study, we demonstrate an easy particle‐mediated protocol using the specific structure of mesocrystal Ag₂O sacrificial templates to synthesize highly rough‐cubic Ag mesocages. To the best of our knowledge, the mesocrystal particles are reported for the first time as sacrificial templates for synthesizing metal particles. The obtained Ag mesocages show high surface‐enhanced Raman scattering (SERS) sensitivity because of the highly rough topography formed by arrays of uniform individual Ag nanoparticles. Abundant “hot spots” with greatly enhanced local electromagnetic field are promoted densely on the mesocage surface by the plenty of deep and narrow gaps and the hollow structure. The single‐particle SERS signal generated by the Ag mesocage has an enhancement factor of approximately 10⁹, which is approximately four times higher than the Ag mesocage synthesized using single‐crystal Ag₂O particle as a template. Meanwhile, this signal displays a linear dependence on the detected analyte concentration, sensitively down to 1.0 × 10^?12 m .     

Measurement of the third‐order nonlinear optical susceptibility χ(3) for the 1002‐cm–1 mode of benzenethiol using coherent anti‐Stokes Raman scattering with continuous‐wave diode lasers

The components of the third‐order nonlinear optical susceptibility χ⁽³⁾ for the 1002‐cm^–1 mode of neat benzenethiol have been measured using coherent anti‐Stokes Raman scattering with continuous‐wave diode pump and Stokes lasers at 785.0 and 852.0 nm, respectively. Values of 2.8 ± 0.3 × 10^–12, 2.0 ± 0.2 × 10^–12, and 0.8 ± 0.1 × 10^–12 cm·g^–1·s² were measured for the xxxx, xxyy, and xyyx components of |3χ⁽³⁾|, respectively. We have calculated these quantities using a microscopic model, reproducing the same qualitative trend. The Raman cross‐section σ_RS for the 1002‐cm^–1 mode of neat benzenethiol has been determined to be 3.1 ± 0.6 × 10^–29 cm² per molecule. The polarization of the anti‐Stokes Raman scattering was found to be parallel to that of the pump laser, which implies negligible depolarization. The Raman linewidth (full‐width at half‐maximum) Γ was determined to be 2.4 ± 0.3 cm^–1 using normal Stokes Raman scattering. The measured values of σ_RS and Γ yield a value of 2.1 ± 0.4 × 10^–12 cm·g^–1·s² for the resonant component of 3χ⁽³⁾. A value of 1.9 ± 0.9 × 10^–12 cm·g^–1·s² has been deduced for the nonresonant component of 3χ⁽³⁾. Copyright © 2011 John Wiley & Sons, Ltd.     

A facile high‐performance SERS substrate based on broadband near‐perfect optical absorption

Plasmonic systems based on metal nanoparticles on a metal film with high optical absorption have generated great interests for surface‐enhanced Raman scattering (SERS). In this study, we prepare a broadband‐visible light absorber consisting Au nanotriangles on the surface of a continuous optically opaque gold film separated with a dielectric SiO₂ layer, which is a typical metal‐insulator‐metal (MIM) system, and demonstrate it as an efficient SERS substrate. The MIM nanostructure, prepared using nanosphere lithography with a very large area, shows a broadband with absorption exceeding 90% in the wavelength regime of 630–920 nm. We observe an average SERS enhancement factor (EF) as large as 4.9 × 10⁶ with a 22‐fold increase compared to a single layer of Au nanotriangles directly on a quartz substrate. A maximum SERS EF can be achieved by optimizing the thicknesses of the dielectric layer to control the optical absorption. Owing to the simple, productive, and inexpensive fabrication technique, our MIM nanostructure could be a potential candidate for SERS applications. Copyright © 2015 John Wiley & Sons, Ltd.     

Identification of two Ag‐2,2′:6′,2″‐terpyridine surface species on Ag nanoparticle surfaces by excitation wavelength dependence of SERS spectra and factor analysis: evidence for chemical mechanism contribution to SERS of Ag(0)–tpy

Measurement and interpretation of the excitation wavelength dependence of surface‐enhanced Raman scattering (SERS) spectra of molecules chemisorbed on plasmonic, e.g. Ag nanoparticle (NP) surfaces, are of principal importance for revealing the charge transfer (CT) mechanism contribution to the overall SERS enhancement. SERS spectra, their excitation wavelength dependence in the 445–780‐nm range and factor analysis (FA) were used for the identification of two Ag‐2,2′:6′,2″‐terpyridine (tpy) surface species, denoted Ag⁺–tpy and Ag(0)–tpy, on Ag NPs in systems with unmodified and/or purposefully modified Ag NPs originating from hydroxylamine hydrochloride‐reduced hydrosols. Ag⁺–tpy is a spectral analogue of [Ag(tpy)]⁺ complex cation, and its SERS shows virtually no excitation wavelength dependence. By contrast, SERS of Ag(0)–tpy surface complex generated upon chloride‐induced compact aggregate formation and/or in strongly reducing ambient shows a pronounced excitation wavelength dependence attributed to a CT resonance (the chemical mechanism) contribution to the overall SERS enhancement. Both the resonance (λ_exc = 532 nm) and off‐resonance (λ_exc = 780 nm) pure‐component spectra of Ag(0)–tpy obtained by FA are largely similar to surface‐enhanced resonance Raman scattering (λ_exc = 532 nm in resonance with singlet metal to ligand CT (¹ MLCT) transition) and SERS (λ_exc = 780 nm) spectra of [Fe(tpy)₂]²⁺ complex dication. Copyright © 2014 John Wiley & Sons, Ltd.     

Drop‐cast and dye‐sensitized ZnO nanorod‐based visible‐light photodetectors

We report the facile fabrication of metal–semiconductor–metal (MSM) photodetectors with dye‐sensitized ZnO nanorods (NRs) operating at wavelengths of ～405–638 nm by a simple drop casting method. The ZnO NRs were synthesized by the hydrothermal synthesis method at 75 °C. The droplet of ethanol solution containing ZnO NRs was dropped between two metal electrodes and dried at 65 °C, which allows the ZnO NRs to be adhered and contacted to both metal electrodes. When a violet light of 405 nm was illuminated into the MSM ZnO NRs‐based photodetector, the photocurrent gain was obtained as ～3.9 × 10³ at the applied bias voltage of 5 V. By increasing the bias voltage from 10 V to 15 V, the device exhibited good recovery performance with a largely reduced reset time from 85.68 s to 2.47 s and an increased on–off ratio from 17.9 to 77.4. To extend the photodetection range towards the long visible spectral region, the ZnO NRs were sensitized by the N719 dye and then drop‐cast. The dye‐sensitized ZnO NRs‐based photodetector also exhibited good photocurrent switching under 638 nm of light illumination. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of ultra-thin and flexible Au–Ag–Au transparent conducting electrode

The performance of ultra-thin Au–Ag–Au tri-layer film deposited thermally over a flexible substrate is investigated using structural, optical, mechanical and electrical-transport measurements. The optimum total thickness of the tri-layer for high transparency and conductivity is determined to be around 8 nm using a theoretical model. The Au–Ag–Au tri-layer shows maximum transmittance (≅ 62%) at wavelength 500 nm. XRD pattern shows peak corresponding to (111) plane of Au and/or Ag. Sheet resistance (≅ 10.42 Ω/□) measured at 300 K using four probe technique is stable up to 150 °C. Hall effect measurements show high conductivity (1.34 × 10⁵ (Ω cm)⁻¹), carrier concentration (2.48 × 10²³/cm³), and mobility (3.4 cm²/Vs). Scotch tape test confirms good adhesion of the film onto PET substrate. Bending-twisting tests using an indigenous apparatus indicate high resistance-stability even after 50,000 cycles. These results imply the viability of Au–Ag–Au tri-layer film as a transparent conducting electrode worth exploring for optoelectronic applications.     

Design of Enhanced Catalysts by Coupling of Noble Metals (Au,Ag) with Semiconductor SnO2 for Catalytic Reduction of 4‐Nitrophenol

The reduction of 4‐nitrophenol (Nip) into 4‐aminophenol (Amp) by NaBH₄, which is catalyzed by both binary and ternary yolk–shell noble‐metal/SnO₂ heterostructures, is reported. The binary heterostructures contain individual Au or Ag nanoparticles (NPs) and the ternary heterostructures contain both Au and Ag NPs. The Au@SnO₂ yolk–shell NPs are synthesized via a silica seeds‐mediated hydrothermal method. Subsequently, the Au@SnO₂@Ag and Au@SnO₂@Au yolk–shell–shell (YSS) NPs are synthesized, whereby SnO₂ is located between the Au and Ag NPs. The morphology, composition, and optical properties of the as‐prepared samples are analyzed. For the binary heterostructures, the rate of the reduction reaction increases with decreasing particle size. The catalytic results demonstrate the synergistic effect of Au and Ag in the ternary metal–semiconductor heterostructures, which is beneficial to the catalytic reduction of Nip into Amp. Both the binary and ternary heterostructures exhibit significantly better catalytic performances than the corresponding bare Au and Ag NPs. It is envisaged that the current synthesized strategy will promote further interest in the field of bimetal NP‐based catalysis.     

Significantly reduced leakage currents in organic thin film transistors with Mn‐doped Bi2Ti2O7 high‐k gate dielectrics

We report the fabrication of organic thin‐film transistors (OTFTs) with high‐k gate dielectrics of Mn‐doped Bi₂Ti₂O₇ (BTO) films. 3% Mn‐doped BTO films deposited on polymer substrates by pulsed laser deposition at room temperature exhibit low leakage currents of 2.1 × 10^–8 A/cm² at an applied electric field of 0.3 MV/cm, while undoped BTO films show much higher leakage currents of 4.3 × 10^–4 A/cm². Mn doping effectively reduces the number of oxygen vacancies in the films and improves the electrical properties. Low operation voltage and significantly reduced leakage currents are demonstrated in pentacene‐based OTFTs with the Mn‐doped BTO gate dielectrics. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Possibility of non‐adiabatic level crossing by DFT study of tautomerism and potential energy surfaces in of 3‐hydroxy‐5‐(pyrimidin‐2‐yl)‐2H‐pyrrol‐2‐one and its tautomer

3‐Hydroxy‐5‐(pyrimidin‐2‐yl)‐2H‐pyrrol‐2‐one (HYPO, T1) and 2‐hydroxy‐5‐(pyrimidine‐2‐yl)‐3H‐pyrrole‐3‐one (HYPO, T2) have designed in this research to study potential energy curves for their dynamic motions and possibility of crossing between levels. Study of tautomerism shows that T1 tautomer is more stable than T2 (about 5.83 kJ/mol). Dynamic study of possible motions show rate constants (highest possible) equal to 8.82 M/s for tautomerism, 1.70 × 10⁹ M/s for relative rotation of ring (rr) and 3.67 × 10⁶ M/s for rotation of OH bond (br). Moreover, variations of orbital populations, NBO charges, hybridations, and acceptor–donor interactions in IRC steps have been investigated to study the possibility of non‐adiabatic crossing between tautomerism and ring rotation potential energy curves. The data showed that in spite of the fact that these two potentials share three common points, these two potential curves cannot have non‐adiabatic crossing because of different symmetries and a large difference between their barrier energies. Copyright © 2010 John Wiley & Sons, Ltd.     

Ag‐nanoparticle‐modified single Ag nanowire for detection of melamine by surface‐enhanced Raman spectroscopy

Silver nanowires synthesized by a solvothermal method were used as templates for fabricating silver‐nanoparticle‐decorated silver (AgNP/Ag) nanowires. The number density and particle size of Ag nanoparticles can be controlled by varying the concentration of Ag precursor. Single AgNP/Ag nanowire exhibited strong surface‐enhanced Raman scattering effect. Detection of melamine molecules at concentrations as low as 1.0 × 10⁻⁸ M was used as an example to show the possible applications of such AgNP/Ag nanowires. Their application in rapid detection of melamine in milk solution was further demonstrated. It was shown that melamine in milk solution at a low concentration of 5.0 × 10⁻⁸ M can be easily detected with little sample pretreatment. The results demonstrate the potential of single AgNP/Ag nanowire as a surface‐enhanced Raman scattering substrate for convenient and sensitive detection of trace amounts of melamine in a complex mixture. Copyright © 2012 John Wiley & Sons, Ltd.     

Fabrication of periodical Ag–Au compound nanostructure films with controllable Ag nanoparticle aggregate patterns: a study on surface‐enhanced Raman scattering

The Ag–Au compound nanostructure films with controllable patterns of Ag nanoparticle (NP) aggregates were fabricated. A strategy of two‐step synthesis was employed toward the target products. Firstly, the precursor Au NP (17 nm) films were synthesized as templates. Secondly, the Ag NPs (45 nm) were deposited on the precursor films. Three types of Ag NP aggregates were obtained including discrete Ag NPs (discrete type), necklace‐like Ag NP aggregates (necklace type), and huddle‐like Ag NP aggregates (huddle type). The surface‐enhanced Raman scattering (SERS) property was studied on these nanostructures by using the probing molecule of rhodamine 6G under the excitation laser of 514.5 nm. Interestingly, the different types of samples showed different enhancement abilities. A statistical method was employed to assess the enhancement. The relative enhancement factor for each Ag NP was estimated quantitatively under the ratio of 1 : 25 : 18 for the discrete‐type, necklace‐type, and huddle‐type samples at the given concentration of 10⁻⁸ mol/l. This research shows that the enhancement ability of each Ag NP is dependent on the aggregate morphology. Moreover, the different enhancement abilities displayed different limit detection concentrations up to 10⁻⁸, 10⁻¹¹, and 10⁻⁹ mol/l, separately. The understanding of the relationship between the defined nanostructures and the SERS enhancement is very meaningful for the design of new SERS substrates with better performance. Copyright © 2015 John Wiley & Sons, Ltd.     

Silver-Mediated Growth of Chiral Ag/Au-Cysteine Hybrid Nanospheres with Giant Chiroptical Response

The chiral Ag/Au-cysteine hybrid nanospheres (HNSs) have been prepared by using cysteine (Cys) as an inductive agent via wet chemistry methods. Unlike the case of the dipole approximation, the circular dichroism spectra can be divided into two components: 1) one region associated with the interband absorption enhanced optical activity of structural arrangement of Cys molecules at 200–320 nm; 2) another region corresponding to a ligand-to-metal charge transfer mixed with ligand-to-metal-metal charge transfer excitation due to the synergetic interplay of the electrostatic interaction between Cys side chains and the Au(I)⋅⋅⋅Au(I) aurophilic attraction in the Au(I)-Cys complexes, located at 350–400 nm. The chiroptical response increases dramatically with increasing the concentration of Au from 0.1 to 1.56 × 10⁻³ m , and subsequently decreases with further increasing the concentration of Au from 3.12 to 12.5 × 10⁻³ m , which is similar to the sergeants and soldiers effect of chiral polymer materials. Furthermore, the circinate-like morphology of the alloyed nanospheres is strongly dependent on the presence of Ag and the chiral bimetal HNSs present excellent enantioselective recognition for amino acids in catalytic electrochemical reactions due to the specific activity and chiral active spots.     

X‐ray fluorescence analysis of Co,Ni, Pd,Ag, and Au in the scrapped printed‐circuit‐board ash

A method for the quantitative analysis of Co, Ni, Pd, Ag, and Au in the scrapped printed‐circuit‐board ash by X‐ray fluorescence (XRF) spectrometry using loose powder was developed. The printed‐circuit‐board samples were converted to ash pyrolytically in porcelain crucibles by sequential heating using a gas burner and electric furnace, and then were ground with a ball mill. The calibrating standards were prepared by adding the appropriate amounts of NiO powder and aqueous standard solutions containing Co, Pd, Ag, and Au to the base mixtures of Al₂O₃ (5.0 mass%), SiO₂ (49 mass%), CaCO₃ (11 mass%), Fe₂O₃ (3.3 mass%), and CuO (30 mass%) as a matrix. Then, 10 g of the resulting mixtures were dried and homogenized for 90 min with a V‐type mixing machine. Specimens for XRF analysis were prepared from the so‐called loose‐powder method in which powder samples were compacted into a hole (12.0‐mm diameter and 5.0‐mm height) in an acrylic plate and covered with a 6‐µm thickness of polypropylene film. Matrix effects were corrected using the intensity value of Compton scattering for PdKα, AgKα, and AuLβ₂, and that of background scattering at 35.8° (2θ) for CoKα and NiKα. The detection limits corresponding to three times the standard deviation of the blank intensity were 2.5–45 µg g^?1. The proposed method was validated against the pressed‐powder‐pellet method by comparing the calibration curves. Moreover, the concentrations of Co, Ni, Pd, and Ag determined using the proposed XRF method were approximately the same as those resulting from an atomic‐absorption‐spectrometric analysis. Copyright © 2013 John Wiley & Sons, Ltd.     

Ultra‐thin (002)‐oriented Al‐doped zinc oxide transparent electrode grown on oxygen‐controlled homo‐seed layer

Highly (002)‐oriented Al‐doped zinc oxide (AZO) thin films with the thickness of less than 200 nm have been deposited on an oxygen‐controlled homo‐seed layer at 200 °C by DC magnetron sputtering. With the homo‐seed layer being employed, the full‐width at half maximum (FWHM) of the (002) diffraction peak for the AZO ultra‐thin films decreased from 0.33° to 0.22°, and, the corresponding average grain size increased from 26.8 nm to 43.0 nm. The XRD rocking curves revealed that the AZO ultra‐thin film grown on the seed layer deposited in atmosphere of O₂/Ar of 0.09 exhibited the most excellent structural order. The AZO ultra‐thin film with homo‐seed layer reached a resistivity of 4.2 × 10^–4 Ω cm, carrier concentration of 5.2 × 10²⁰ cm^–3 and mobility of 28.8 cm² V^–1 s^–1. The average transmittance of the AZO ultra‐thin film with homo‐seed layer reached 85.4% in the range of 380–780 nm including the substrate. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

p‐type conduction in stacking‐fault‐free m ‐plane GaN

Transport measurements of p‐type m ‐plane GaN films grown on low extended‐defect density, free‐standing m ‐plane (10 0) GaN substrates are presented. No significant anisotropy in in‐plane mobility was found for hole concentrations between 2.45 × 10¹⁷ and 8.7 × 10¹⁸ cm^–3. Since faulted, heteroepitaxial m ‐plane films showed significant anisotropy in electron and hole mobility a microstructural feature with anisotropic distribution (basal plane stacking faults) is discussed as a possible source of anisotropic scattering in non‐polar and semi‐polar films. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of the structural order of all‐trans‐β‐carotene on the Raman scattering cross section at low concentrations

Using the technique of liquid‐core optical fiber (LCOF), we measured the Raman scattering cross sections (RSCSs) of the carbon–carbon (C C) stretching vibrational modes of all‐trans‐β‐carotene in carbon disulfide (CS₂) at concentrations ranging from 10⁻⁶ to 10⁻¹¹ M . It was found that the RSCSs of all‐trans‐β‐carotene were extremely high with decreasing concentration, and the absolute RSCS of C stretching modes of all‐trans‐β‐carotene reached the value of 2.6 × 10⁻²⁰ cm² molecule⁻¹ Sr⁻¹ at 8 × 10⁻¹¹ M , which is larger than at 8 × 10⁻⁶ Mby 4 orders of magnitude. A theoretical interpretation of the anomalous experimental results is given, which introduces a qualitative nonlinear model of coherent weakly damped electron‐lattice vibrations in structural order of all‐trans‐β‐carotene. Copyright © 2010 John Wiley & Sons, Ltd.