Photoswitch based on bacteriorhodopsin Langmuir–Blodgett films

Langmuir–Blodgett (LB) films of bacteriorhodopsin (bR) without addition of lipids were deposited on indium tin oxide (ITO) conductive electrodes. A sandwich photocell with a juction structure of ITO/bR/electrolyte/ITO has been constructed in which the bR LB film was put into contact directly with an aqueous electrolyte immobilized in an agar gel. Under visible light irradiation a transient photocurrent due to a change in light intensity can be observedl showing the property of vision-imitative material. It can be used as a multiple optical switch, since it gives positive and negative transient photocurrnts during application and removal of light irradiation respectively and has a photoresponse repeatedly in the same direction when the light intensity increases or decreases stepwise. A photoalarm consisting of the bR photocell and an amplifier was set up by utilizing the switching function of the bR LB film.     

Micro‐Raman Scattering Imaging of Langmuir–Blodgett Surface Relief Gratings

Surface relief gratings (SRGs) recorded on Langmuir–Blodgett (LB) films of an azobenzene homopolymer were visualized using micro‐Raman imaging. Raman scattering (RS) was achieved using the 780 nm laser line while pre‐resonance Raman scattering (pre‐RRS) and resonance Raman scattering were achieved using the 633 and 514.5 nm laser lines, respectively. Pre‐surface‐enhanced resonance Raman scattering (pre‐SERRS) and surface‐enhanced resonance Raman scattering (SERRS) were collected for the LB films covered with a 6 nm thick silver island film. The SRG could be chemically identified by the spatial variation in the Raman signal scattered by the film due to a concentration gradient. The pre‐SERRS provided signals of the same intensity along and across the grooves, indicating that the molecular architecture at the SRG surface is the same at the peaks as in the valleys.     

The photovoltage signals of bacteriorhodopsin in Langmuir–Blodgett films with different molecular orientations

The photoresponse of bacteriorhodopsin (bR) has been studied in Langmuir–Blodgett (LB) films bR was deposited by vertical dipping as x- or z-type monolayers and as z-type multi layers between stearic acid LB films. The electrodes used were a transparent vacuum-deposited ITO on a quartz substrate and an InGa metal alloy. The signals were observed from samples containing a single bR layer or five bR layers both at room humidity and in water-saturated conditions. The photoelectric signals of x- and z-type monolayers had opposite polarities and both had two exponential kinetics on a microsecond time scale with time constants of about 10 and 70 μs. The amplitude of the fast negative component of the signal of a bR monolayer was 0.4 mV, in the opposite direction to that in which protons were pumped. The amplitude due to five layers was five times as high as that due to a monolayer. The ratio between the amplitudes of the fast negative component and the slow positive part of the signal, in the proton-pumping direction, was 1:3. The photoresponse signal saturated with a light intensity of about 1.7 mJ cm^?2, which is equivalent to a photon density of 0.5 Å^?2. The activation energy of the bR photovoltage was 75 ± 5 kJ mol^?1 in the temperature range between 17 and 35°C.     

Langmuir–Blodgett films of a benzothiazolium dye containing a crown ether ring

The structure of Langmuir–Blodget (LB) films built up from a novel benzothiazolium steryl dye containing a 1, 10-dithia-18-crown-6 ether group has been investigated using ellipsometry and polarised absorption spectroscopy. The Y-type deposition results in a uniaxial film with a thickness of 2.18 ± 0.08 nm per monolayer and an index of refraction of 1.57 ± 0.03. the chromophore parts of the moelcule exhibit an in-Plane orientation. The influence of mercury vapouron the LB films has been investigated using the technique of surface plasmon resonance.     

The kinetics of charges in dry bacteriorhodopsin Langmuir–Blodgett films—an analysis and comparison of electrical and optical signals

The decay of the M intermediate and the recovery kinetics of bacteriorhodopsin (bR) were detected optically in dry and wet bR Langmuir–Blodgett (LB) films and electrically in dry films. From the electrical signals the kinetics of the proton motion was distinguished from the cell function and it was found to be equal to that determined optically for the M intermediate decay. The rate-determining step for the recovery rate of bR was found to be the M state.     

Preparation and characterisation of Langmuir–Blodgett films of 4‐(4‐(N‐octadecyl‐N‐methylamino) phenylazo)benzoic acid

Langmuir films of the title compound have been spread on an aqueous subphase at various values of pH at 10, 15 and 20°C. Increasing pH and increasing temperature favour stable films, but at the higher subphase pH and temperature values the pressure–area isotherms exhibit a transition to aggregated forms. Tilt angles between the alkyl chains and the normal to the subphase increase with increasing subphase pH and temperature. The area per molecule for films deposited at 15 °C decreased steadily with time at a fixed surface pressure, except at the highest pH, indicating poor stability. Langmuir–Blodgett films deposited at a surface pressure of 30 mN m⁻¹ and a subphase temperature of 15 °C were of Y‐type and showed transfer ratios above unity for the lower subphase pH values. UV/visible spectra of the LB films showed features characteristic of the formation of H aggregates for deposition at the higher subphase pH values. Over long periods of time the spectra for high pH showed evidence of increasing aggregation. Small‐angle X‐ray diffraction confirmed molecular tilts larger than those deduced in the floating monolayer. Reflection–absorption infrared spectroscopy of the LB films showed differences from the bulk also indicative of significant tilt, as did surface‐enhanced Raman spectroscopy. The LB films showed weak second‐harmonic generation from 1064 nm radiation consistent with a polar film structure parallel to the substrate. Copyright © 1999 John Wiley & Sons, Ltd.     

Organic Thin‐Film Transistors Based on Tolyl‐Substituted Oligothiophenes

Thin films based on the tolyl‐substituted oligothiophenes 5,5′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′‐terthiophene ( 1 ), 5,5′′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′:5′′,2′′′‐quaterthiophene ( 2 ) and 5,5′′′′‐bis(4‐methylphenyl)‐2,2′:5′,2′′:5′′,2′′′:5′′′,2′′′′‐quinqethiophene ( 3 ) exhibit hole‐transport behavior in a thin‐film transistor (TFT) configuration, with reasonable mobilities and high current on/off (I_on/I_off) ratios. Powder X‐ray diffraction (PXRD) reveals that these films, grown by vacuum deposition onto the thermally grown silicon oxide surface of a TFT, are highly crystalline, a characteristic that can be attributed to the general tendency of phenyl groups to promote crystallinity. Atomic force microscopy (AFM) reveals that the films grow layer by layer to form large domains, with some basal domain areas approaching 1000 μm². The PXRD and AFM data are consistent with an “end‐on” orientation of the molecules on the oxide substrate. Variable‐temperature current–voltage (I–V) measurements identified the activation regime for hole transport and revealed shallow level traps in thin films of 1 and 2 , and both shallow and deep level traps in thin films of 3 . The activation energies for thin films of 1 , 2 , and 3 were similar, with values of E_a = 121, 100, and 109 meV, respectively. The corresponding trap densities were N_trap/N_v = 0.012, 0.023, and 0.094, where N_trap is the number of trap states and N_v is the number of conduction states. The hole mobilities for the three compounds were similar (μ ? 0.03 cm² V^–1 s^–1), and the I_on/I_off ratios were comparable with the highest values reported for organic TFTs, with films of 2 approaching I_on/I_off = 10⁹ at room temperature.     

Langmuir–Blodgett films of indandione-l,3 pyridinium betaine. II: Molecular structure and properties of monolayers; simulation and optical absorption data

The molecular structure and optical properties of a monolayer at the air/water interface of novel amphiphilic derivatives of indandione-1,3 pyridinium betaine (IPB) with different lengths of the aliphatic tail, namely C_1lIPB and C₁₇IPB, have been studied using optical absorption techniques and computer simulation approaches. The compression π-A isotherm of the C₁₇IPB monolayer and computer simulation of its molecular structure show that there may exist two energetically stable molecular configurations, one with antiparallel orientation of the dipole moments of the C₁₇IP ‘heads’ in the low-pressure region at π = 5–32 mN m^?1 and the second (after a distinct phase transition at π = 33 mN m^?1) with parallel orientation of the dipoles, with different tilt angles and areas per molecule. For C₁₁IPB only the first structural phase is observable. The compression-induced changes in spectral characteristics of the two structural phases go in diametrically opposite directions. In the low-pressure phase compression induces a red shift and an increase in intensity of the S₁ absorption band, while in the high pressure phase a blue shift and a decrease in the intensity of this band are observed. These spectral changes correlate reproducibly with the compression π-A isotherms. Measurements of absorption dichroism confirm the change in the tilt angle at the phase transition pressure. The compression-induced spectral changes have been substantiated by the results of quantum chemical calculations.     

Aligning Single‐Walled Carbon Nanotubes By Means Of Langmuir–Blodgett Film Deposition: Optical,Morphological, and Photo‐electrochemical Studies

An alkoxy‐substituted poly(phenylene thiophene) is used in order to suspend single‐walled carbon nanotubes in an organic solvent. The suspension is spread on the air–water interface of a Langmuir trough and the floating film is characterized by means of Brewster angle microscopy and UV‐visible reflection spectroscopy and the compression isotherm is recorded. The polymer/carbon‐nanotube blend is transferred onto different substrates using the Langmuir–Blodgett technique. AFM measurements indicate the formation of globular structures for the samples transferred at low surface‐pressure values and a tubular morphology for high‐pressure‐deposited samples. AFM analysis is repeated on a sample exposed to soft X‐rays for about 5 h and a highly organized structure of bundles of carbon nanotubes rises up. Samples with different numbers of layers are transferred onto ITO substrates by means of the Langmuir–Blodgett method and are tested as photocathodes in a photo‐electrochemical cell. A V_oc of 0.18 V, an I_sc of 85.8 mA, FF of 40.0%, and η of (6.23 × 10^?3)% are obtained.     

Langmuir–Blodgett films of indandione-1,3 pyridinium betaine. III: Linear dichroism and non-linear optical properties

Linear dichroism and second-harmonic generation (SHG) have been measured in Langmuir-Blodgett (LB) multilayers of Z-type structure of amphiphilic indandione-1,3 pyridinium betaine (IPB) with an aliphatic tail containing 17 carbon atoms (C17IPB). The dichroic ratio A_s/A_p of electronic absorption of s- and p-polarised light and the SHG intensity show that the ‘heads’ of C17IPB molecules are predominantly oriented along the deposition direction of monolayers on a quartz substrate. Orientation parameters and mean statistical azimuthal and tilt angles are evaluated as a function of the number of monolayers. The SHG efficiency has been measured in C17IPB monolayers on a water surface as a function of surface pressure. The effective hyperpolarisability β of the IPB molecule has been determined experimentally in a chloroform solution by the hyper-Rayleigh-scattering method. The obtained value of β = (138 ± 16) × 10⁻³⁰ esu is in good agreement with theoretical estimates.     

Langmuir–Blodgett films of indandione-1,3 pyridinium betaine. I: Preparation,electronic structure,optical properties

The synthesis of a new polar amphiphilic derivative of indandione-1,3 pyridinium betaine (IPB) with different lengths of the aliphatic tail, containing 11 (C11IPB) and 17 (C17IPB) carbon atoms respectively, is described. The electronic structure (charge distribution, energy spectra, dipole moments in ground and excited states) of the IPB molecule has been calculated in the framework of the MO CNDO methods. Studies of compression π-A isotherms of these compounds show that C17IPB forms two stable phases of monolayer on the water surface, one in the 10–30 mN m^?1 and the other in the 35–50 nM m^?1 surface pressure region. The corresponding areas A₀ per molecule are 37 and 33 Ų respectively. Techniques for the preparation of Langmuir-Blodgett (LB) multilayers of C17IPB in the high-pressure region (π = 40 mN m^?1) on glass, quartz or sapphire substrates are described. C17IPB forms LB multilayer films of Z-type configuration with oriented dipole moments. Ellipsometric data, luminescence spectra and results of preliminary studies of second-harmonic generation in these LB films are presented.     

Design of Novel Dielectric Surface Modifications for Perylene Thin‐Film Transistors

Dielectric surface modifications (DSMs) can improve the performance of organic thin‐film transistors (OTFTs) significantly. In order to gain a deeper understanding of this performance enhancement and to facilitate high‐mobility transistors, perylene based devices utilizing novel dielectric surface modifications have been produced. Novel DSMs, based on derivates of tridecyltrichlorosilane (TTS) with different functional end‐groups as well as polymeric dielectrics have been applied to tailor the adhesion energy of perylene. The resulting samples were characterized by electronic transport measurements, scanning probe microscopy, and X‐ray diffraction (XRD). Measurements of the surface free energy of the modified dielectric enabled the calculation of the adhesion energy of perylene upon these novel DSMs by the equation‐of‐state approach. These calculations demonstrate the successful tailoring of the adhesion energy. With these novel DSMs, perylene thin‐films with a superior film quality were produced, which enabled high‐performance perylene‐based OTFTs with high charge‐carrier mobility.     

Thiophene–Benzothiadiazole Co‐Oligomers: Synthesis,Optoelectronic Properties,Electrical Characterization,and Thin‐Film Patterning

Newly synthesized thiophene (T) and benzothiadiazole (B) co‐oligomers of different size, alternation motifs, and alkyl substitution types are reported. Combined spectroscopic data, electrochemical analysis, and theoretical calculations show that the insertion of a single electron‐deficient B unit into the aromatic backbone strongly affects the LUMO energy level. The insertion of additional B units has only a minor effect on the electronic properties. Cast films of oligomers with two alternated B rings (B–T–B inner core) display crystalline order. Bottom‐contact FETs based on films cast on bare SiO₂ show hole‐charge mobilities of 1 × 10^?3–5 × 10^?3 cm² V^?1s^?1 and I_on/I_off ratios of 10⁵–10⁶. Solution‐cast films of cyclohexyl‐substituted compounds are amorphous and do not show FET behavior. However, the lack of order observed in these films can be overcome by nanorubbing and unconventional wet lithography, which allow for fine control of structural order in thin deposits.     

Review of Polymer‐Based Nanodielectric Exploration and Film Scale‐Up for Advanced Capacitors

The uprising demands for electrical power and electrification requires advanced dielectric functionalities including high capacitance density, high energy density, high current handling capability, high voltage, high temperature, high thermal conductivity, light weight, and environmental reliability. Nanodielectric engineering emerges and attracts extensive efforts from many countries as a result. Unlike prior reviews focusing on lab scale nanocomposite study, this review focuses on recent innovations in polymer‐based nanodielectric design on a large scale and their film scale‐up efforts for advanced capacitors. The unconventional polymer‐nanofiller engineering and their process in the last two decades are discussed. The nanofunctionalized polymers on a molecular level for high dielectric constants and high dielectric strength are briefly described. The challenge associated with film scale‐up and retention of nanodielectric properties are then pointed out to be crucial toward a transfer of dielectric and capacitor technology. Several important attempts at scaling up dielectric films and capacitors recently supported by the US government and industry are reviewed. An alternative strategic approach to achieving high performance polymer films is introduced by leveraging 2D surface coating on commercially mature large‐scale polymer films. Future pathways for high quality scalable dielectric films exhibiting desirable dielectric properties and feasibility for capacitor manufacturing are suggested.     

From Fragility to Flexibility: Construction of Hydrogel Bridges toward a Flexible Multifunctional Free‐Standing CaCO3 Film

Free‐standing CaCO₃ materials are an important member in biological systems because of their existence in many natural organisms such as nacre, shell, and crustacean cuticle. However, toughness of those artificial mineral films is sacrificed once their inorganic content is up to 90%, thus free‐standing characteristics have seldom been achieved for CaCO₃ films, let alone their real applications. Herein a fast and simple method for constructing hydrogel “bridges” for CaCO₃ microparticles is presented, developing highly flexible free‐standing CaCO₃ films with only 5% organic content. Such integrated films have underwater superoleophobicity and self‐cleaning function, which guarantee their repeated application in oil/water separation. Furthermore, heavy metal ions can be efficiently removed by simple filtration with the films. Because of the self‐similar structure, the films are able to resist mechanical abrasion without losing the anti‐wetting property and separation efficiency. The free‐standing CaCO₃ films are put forward for the first time to practical application, demonstrating the strategy can bring a brilliant prospect to artificial biomineral materials.     

Study of Martensitic Phase Transformation in a NiTiCu Thin‐Film Shape‐Memory Alloy Using Photoelectron Emission Microscopy

Thermally induced martensitic phase transformation in a polycrystalline NiTiCu thin‐film shape‐memory alloy is probed using photoelectron emission microscopy (PEEM). In situ PEEM images reveal distinct changes in microstructure and photoemission intensity at the phase‐transition temperatures. In particular, images of the low‐temperature, martensite phase are brighter than that of the high‐temperature, austenite phase, because of the lower work function of the martensite. UV photoelectron spectroscopy shows that the effective work‐function changes by about 0.16 eV during thermal cycling. In situ PEEM images also show that the network of trenches observed on the room‐temperature film disappears suddenly during heating and reappears suddenly during subsequent cooling. These trenches are also characterized using atomic force microscopy at selected temperatures. The implications of these observations with respect to the spatial distribution of phases during thermal cycling in this thin‐film shape‐memory alloy are discussed.     

Role of Side‐Chain Branching on Thin‐Film Structure and Electronic Properties of Polythiophenes

Side‐chain engineering is increasingly being utilized as a technique to impact the structural order and enhance the electronic properties of semiconducting polymers. However, the correlations drawn between structural changes and the resulting charge transport properties are typically indirect and qualitative in nature. In the present work, a combination of grazing incidence X‐ray diffraction and crystallographic refinement calculations is used to determine the precise molecular packing structure of two thiophene‐based semiconducting polymers to study the impact of side‐chain modifications. The optimized structures provide high‐quality fits to the experimental data and demonstrate that in addition to a large difference in interchain spacing between the two materials, there exists a significant disparity in backbone orientation as well. The calculated structures are utilized in density functional theory calculations to determine the band structure of the two materials and are shown to exhibit a dramatic disparity in interchain dispersion which accounts for the large observed difference in charge carrier mobility. The techniques presented here are meant to be general and are therefore applicable to many other highly diffracting semicrystalline polymers.     

III‐Vs at scale: a PV manufacturing cost analysis of the thin film vapor–liquid–solid growth mode

The authors present a manufacturing cost analysis for producing thin‐film indium phosphide modules by combining a novel thin‐film vapor–liquid–solid (TF‐VLS) growth process with a standard monolithic module platform. The example cell structure is ITO/n‐TiO₂/p‐InP/Mo. For a benchmark scenario of 12% efficient modules, the module cost is estimated to be $0.66/W(DC) and the module cost is calculated to be around $0.36/W(DC) at a long‐term potential efficiency of 24%. The manufacturing cost for the TF‐VLS growth portion is estimated to be ~$23/m², a significant reduction compared with traditional metalorganic chemical vapor deposition. The analysis here suggests the TF‐VLS growth mode could enable lower‐cost, high‐efficiency III‐V photovoltaics compared with manufacturing methods used today and open up possibilities for other optoelectronic applications as well. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of Arylene Diimide Thin Film Growth Conditions on n‐Channel OFET Performance

A series of eight perylene diimide (PDI)‐ and naphthalene diimide (NDI)‐based organic semiconductors was used to fabricate organic field‐effect transistors (OFETs) on bare SiO₂ substrates, with the substrate temperature during film deposition (T_d) varied from 70–130 °C. For the N,N′‐n‐octyl materials that form highly ordered films, the mobility (µ) and current on‐off ratio (I_on/I_off) increase slightly from 70 to 90 °C, and remain relatively constant between 90 and 130 °C. I_on/I_off and µ of dibromo‐PDI‐based OFETs decrease with increasing T_d, while films of N,N′‐1H,1H‐perfluorobutyl dicyanoperylenediimide (PDI‐FCN₂) exhibit dramatic I_on/I_off and µ enhancements with increasing T_d. Increased OFET mobility can be correlated with higher levels of molecular ordering and minimization of film morphology surface irregularities. Additionally, the effects of SiO₂ surface modification with trimethylsilyl and octadecyltrichlorosilyl monolayers, as well as with polystyrene, are investigated for N,N′‐n‐octyl dicyanoperylenediimide (PDI‐8CN₂) and PDI‐FCN₂ films deposited at T_d = 130 °C. The SiO₂ surface treatments have modest effects on PDI‐8CN₂ OFET mobilities, but modulate the mobility and morphology of PDI‐FCN₂ films substantially. Most importantly, the surface treatments result in substantially increased V_th and decreased I_off values for the dicyanoperylenediimide films relative to those grown on SiO₂, resulting in V_th > 0.0 V and I_on/I_off ratios as high as 10⁸. Enhancements in current modulation for these high‐mobility, air‐stable, and solution‐processable n‐type semiconductors, should prove useful in noise‐margin enhancement and further improvements in organic electronics.