Optimal deposition condition of chlorophyll a Langmuir–Blodgett film

The optimal deposition condition of chlorophyll a (Chl a) Langmuir–Blodgett (LB) film were investigated based on π–a isotherms, absorption spectrum and scanning tunneling microscopy (STM) observation. The π–a isotherms of Chl a LB film at various air temperatures and subphase pHs were obtained. Optimum temperature and pH for dense packing of Chl a LB layers are 25 °C and 7.0, respectively. The formation of J- and H-aggregations of the ordered chlorophyll a molecules was confirmed by absorption spectrum measurements. The well-ordered structure of Chl a LB layer was observed by STM. Thus, the densely packed Chl a LB layer could be fabricated by the proposed optimal deposition condition.     

Functionalized surfaces of polylactide modified by Langmuir–Blodgett films of amphiphilic block copolymers

To modify the surface of poly(L-lactide) (PLA) supports, we have investigated the feasibility to deposit on the PLA surface Langmuir–Blodgett films of amphiphilic block copolymers based on poly(L-lactide). AB and ABA block copolymers were prepared with PLA as the A block and either poly(ethylene oxide), -methoxy--hydroxy poly(ethylene oxide), -carboxy--hydroxy poly(ethylene oxide) or poly(L-aspartic acid) as the B blocks. Films with phase-separated hydrophilic and hydrophobic blocks in a bilayer brush structure were prepared by compression of the copolymer Langmuir films on the water/air interface. The interfacial behavior of the monolayers and the effect of the copolymer composition on the phase separation was followed by measurements of the surface-pressure/area isotherms using a Langmuir trough and by contact angle measurement of deposited Langmuir–Blodgett (LB) films. The phase separation of the hydrophilic and PLA blocks is more effective in diblock AB copolymers compared with triblock ABA copolymers. The presence of ionic groups in the hydrophilic chains facilitates penetration of hydrophilic segments into the water subphase. Dynamic contact angle measurements were used to study the stability of the LB-films transferred on the PLA support and the changes in the surface properties upon incubation of surfaces in water.     

Electrical properties of a calix[4]acid/amine Langmuir–Blodgett thin film

In this work the DC and AC characteristics for metal-LB film-metal structures deposited by a standard Langmuir–Blodgett film deposition technique are investigated. The conduction mechanism has been studied for a thin film structure in which a calix[4]arene substituted with carboxylic acid groups has been deposited alternately with a calix[4]arene molecule substituted with amine groups. This LB film structure shows a typical insulating behaviour for low voltage values and the Schottky effect becomes dominant when the voltage increases. The conductivity at low voltage values was found to be 1.34 × 10⁻¹³ S cm⁻¹. The height of the potential barrier was determined to be 1.65 eV for this alternate layer LB film system.     

Role of metal ions of Langmuir–Blodgett film in hydrophobic to hydrophilic transition of HF-treated Si surface

Hydrophobic to hydrophilic transition of HF-treated Si surface strongly depends upon the metal ions, which are present in the headgroups of the deposited Langmuir–Blodgett (LB) film. Structure of LB films studied by X-ray reflectivity technique and chemical analysis of LB film–substrate interfaces studied by X-ray photoelectron spectroscopy combinedly suggest that the partial transition or partial oxidation of the HF-treated Si surface takes place under the subphase water but further transition or oxidation is possible only in the presence of metal ions. Electrovalent and covalent natures of the metal ions tune this transition or oxidation. Ni ions, for which bonding with headgroups are electrovalent in nature, are favorable for such transition/oxidation and as a result, complete transition/oxidation takes place when nickel arachidate LB film is deposited. On the other hand, Cd ions, for which bonding with headgroups show covalent nature, is not favorable for such transition and can not oxidize the underlying H-passivated Si substrate totally when cadmium arachidate LB film is deposited on such HF-treated Si surface. This ion-specific hydrophobic to hydrophilic transition is visualized by X-ray reflectivity, contact angle and X-ray photoelectron spectroscopy measurements.     

Electrical characterisation of stearic acid/calix[4]amine Langmuir–Blodgett thin film

Within this work we deposited 16 monolayers of stearic acid alternated with 15 monolayers of calix[4]amine to form a non-centrosymmetric Langmuir–Blodgett (LB) thin film onto an aluminized (50 nm coated) glass microscopic slide. Dielectric constant and dielectric loss for the film were determined using C-f and tan (δ-f) measurements. The value of the pyroelectric figure of merit was determined as 1.73 μC m⁻² K⁻¹. To elucidate the conduction mechanism of stearic acid/calix[4]amine LB film, DC current–voltage measurements between −4 and +4 V were carried out. The I(V) behaviour shows a symmetrical and highly non-linear behaviour. Analysis of this behaviour of the stearic acid/calix[4]amine LB film showed a conductivity value of 1.12 × 10⁻¹³ S m⁻¹ for ohmic region. The exponential part of I(V) dependence obeyed the Schottky conduction mechanism with a barrier height of 1.67 eV. This LB film structure shows a typical insulating behaviour for low voltage values and the Schottky effect becomes dominant when the voltage increases. The frequency dependence of conductivity shows a power law relationship between conductance and frequency.     

Preparation and conductivity of dithiolene complex Langmuir–Blodgett films

The d.c. electrical property of the dithiolene complex, or bis(4-diethyannodithiobenzil)nickel (BDN) and stearyl alcohol (SA) mixed Langmuir–Blodgett films was investigated. The conductivity of the LB films as a function of the thickness of the films and the ratio of BDN:SA as well as the current versus voltage (I–V) characteristics have been measured. The conductivity of the LB films is about 3.5 x 10^-10 S cm^-1 which is less than the bulk conductivity of BDN, and the conductivity of the LB films is strongly influenced by BDN concentration. The I–V property of Al-LB films is governed by the thickness of oxide layers at the LB films with Al electrodes after Auger depth profiling analysis.     

A heterostructured SnO2–TiO2 thin film prepared by Langmuir–Blodgett technique

SnO₂–TiO₂ heterostructure films were prepared through Langmuir–Blodgett (LB) route. LB films of octadecyl amine (ODA)–titanyl oxalate multilayer deposited on Si (100) and decomposed at 600 °C showed rutile and anatase phases of ultrathin TiO₂ film. Subsequently, multilayer LB film of ODA–stannate deposited on the pre deposited TiO₂ film after decomposition at 600 °C resulted in thin SnO₂ films on the TiO₂ thin film. The phase analysis of the SnO₂–TiO₂ film showed cassiterite phase of SnO₂ as well as the rutile/anatase mixture of TiO₂ indicating a SnO₂–TiO₂ heterostructured film. Surface morphology of the pure TiO₂ film and SnO₂–TiO₂ film were analyzed by using AFM. Electrical characterization by AC impedance analysis suggested SnO₂–TiO₂ heterostructure formation. DC current voltage measurement showed increase in photocurrent indicating visible light absorption and efficient charge separation under the sunlight type radiation.     

In-vitro forming of calcium phosphate layer on sol–gel hydroxyapatite-coated metal substrates

In-vitro deposition of calcium phosphate layer (CPL) on metallic substrate requires special surface preparation in order to provide an interfacial bond. In this work 316 stainless steel surface is modified through deposition of a thin film (0.5 m) of sol–gel hydroxyapatite (SG-HA). This well-bonded film acts as an intermediary and nucleation surface of the CPL film. The SG-HA films were annealed at 375 °C (samples coded 375-ACS) and 400 °C (400-ACS) to achieve different crystallinity of the films, and thus to affect and study the CPL nucleation process. The CPL growth was investigated in terms of deposition kinetics and microstructural development. A deposition rate of dense CPL of about 0.43 m/day was achieved on the crystallized film of 400-ACS, and 0.22 m/day of porous CPL on amorphous 375-ACS. A compositional variation of Ca/P ratio across the CPL film thickness (400-ACS) was observed. Lower Ca/P ratio of 1.2 was detected near the substrate-CPL interface and about 1.5 near the solution-CPL interface. Infrared analysis showed the CPL to be of apatitic calcium-deficient structure. Kinetic model explaining the advancement of the CPL upon the in-vitro immersion is proposed.     

Spectroscopic properties of Langmuir–Blodgett films containing a potential-sensitive dye

This paper reports the incorporation of a potential-sensitive fluorescent dye, Di-8-ANEPPS, in Langmuir–Blodgett (LB) films mixed with amphiphiles of different nature. We used dihexadecylphosphate (DHP) and octadecyltrimethylammonium bromide (OTMA) as lipid matrices. Surface pressure versus molecular area isotherms reveal the presence of small interactions between the components in the mixture, resulting in the formation of microcrystallites and aggregates in the LB films. The optical characteristics of the mono- and multilayers were evaluated by UV–VIS absorbance and fluorescence emission spectroscopy and they were controlled for different mixing ratio and number of LB layers.     

Electrical conductivity properties of boron containing Langmuir–Blodgett thin films

Electrical characterisations of Mesitylene-2-boronic acid (MBA), Phenylboronic acid (PBA) and 1-Naphthylboronic acid (NBA) are investigated using C-f and I–V measurements. All materials are used to fabricate Langmuir–Blodgett (LB) thin film by vertical dipping method. Metal/LB film/Metal sandwich structure is prepared to investigate electrical properties of boron containing LB films. For evaluation of electrical measurements, the theoretical thickness is determined using ChemDraw software and experimental thickness value is calculated from surface plasmon resonance (SPR) curves. Dielectric measurements are used to determine the dielectric constant (ε) and to compare refractive index value which is determined from SPR results. The values of ε are determined as 2.79, 2.70, 2.82 for MBA, PBA and NBA respectively. The refractive indexes of three materials are calculated to be around 1.6. I–V results are used to study the conduction mechanism of these LB films. The low voltage region shows an ohmic characteristic for each LB film and conductivity values are calculated as 0.55 × 10^?11 S m^?1, 0.42 × 10^?11 S m^?1 and 3.62 × 10^?11 S m^?1 for MBA, PBA and NBA respectively. In the high voltage region of I–V curves that show Schottky type conduction mechanisms with the barrier heights estimated for each LB film as 0.77, 0.79 and 0.76 eV respectively.     

The kinetics of Langmuir–Blodgett ZnO nano-film deposition for sensing electrodes

The kinetics of the monolayer formation of zinc oxide nanoparticles on water subphase was studied at different sample concentrations and barrier speeds. The recorded isotherms indicate that stearic acid can act as a suitable microenvironment for the deposition of zinc oxide when the spreading solution contains ~ 50% sample. The AFM image of the double layer shows that the film is nearly homogeneous with average thickness ~ 15 nm. The sensing ability of the nano-films was studied by cyclic voltammetry using ITO substrates, coated with zinc oxide nanoparticles as working electrode. It gave different reduction peaks for different pH electrolytes.     

Changes on the nanostructure of cementitius calcium silicate hydrates (C–S–H) induced by aqueous carbonation

The nanostructure of the main binding phase of the hydrated cements, the calcium silicate hydrates (C–S–H), and their structural changes due to aqueous carbonation have been characterized using TEM, nitrogen physisorption, and SAXS. Synthetic C–S–H has been used for this purpose. Two different morphologies were identified, similar to the high density and low density C–S–H types. When submitting the sample to a CO₂ flux, the low density phase was completely carbonated. The carbonation by-products, calcium carbonate, and silica gel were also identified and characterized. The precipitation of the silica gel increased the specific surface area from 95 to 132 m²/g, and its structure, formed by particles of ~5 nm typical radius, was observed by small angle X-ray scattering. In addition, the resistance of the high density C–S–H to carbonation is reported, and the passivating effect of the precipitated calcium carbonate is also discussed. Finally, the results have been compared with carbonation features observed in Portland cement carbonated experimentally at downhole conditions.     

Growth of CdS nanoparticles in Y- and Z-type Langmuir–Blodgett thin film using 1,3-bis-(p-iminobenzoic acid)indane

Cadmium sulphide (CdS) nanoparticles were formed in 1,3-bis-(p-iminobenzoic acid)indane by exposing Cd²⁺ doped Y- and Z-type multilayered Langmuir–Blodgett (LB) films to H₂S gas. The growth of CdS nanoparticles were monitored by UV–visible spectroscopy measurements. It was observed that CdS nanoparticles in both Y- and Z-type LB films cause a blue-shift in absorption spectra. The surface morphology of LB films were characterized with atomic force microscopy DC electrical measurements were carried out for these LB films grown in a metal/LB film/metal sandwich structures with and without CdS nanoparticles. By analyzing I–V curves and assuming Schottky conduction mechanism the barrier height was found to be as 1.25 and 1.17?eV for Y-type unexposed and exposed samples; 1.18 and 1.25?eV for Z-type unexposed and exposed samples, respectively.     

Enhanced performance of polymer solar cells with a monolayer of assembled gold nanoparticle films fabricated by Langmuir–Blodgett technique

We reported the enhanced performance of polymer solar cells with the blend of poly (2-methoxy-5(2′-ethylhexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) as active layer by incorporation of an assembled gold nanoparticle (Au NP) monolayer. The dense Au NP monolayer has been fabricated by Langmuir–Blodgett (LB) assembly and positioned between the transparent electrode ITO and the anode-modification PEDOT:PSS [poly (3,4-ethylenedioxythiophene):poly(styrene sulfonate)] layer, resulting in the device architecture of ITO/Au/PEDOT:PSS/MEH-PPV:PCBM/Al. We attribute the performance improvement to the localized surface plasmon resonance (LSPR) effect of Au NP films, which could lead to the increased absorption of the active layer. The parameters (nanoparticle size and interparticle distance) that govern this SPR effect have been optimized by selecting various sizes of Au NPs and controlling the LB assembly conditions. We observed ～10–20% enhancement in power conversion efficiency for all the devices with the Au NP monolayer.     

Apatite-forming ability of Ti–15Zr–4Nb–4Ta alloy induced by calcium solution treatment

Ti–15Zr–4Nb–4Ta alloy free from cytotoxic elements shows high mechanical strength and high corrosion resistance. However, simple NaOH and heat treatments cannot induce its ability to form apatite in the body environment. In the present study, this alloy was found to exhibit high apatite-forming ability when it was treated with NaOH and CaCl₂ solutions, and then subjected to heat and hot water treatments to form calcium titanate, rutile, and anatase on its surface. Its high apatite-forming ability was maintained even in 95% relative humidity at 80°C after 1 week. The surface layer of the treated alloy had scratch resistance high enough for handling hard surgical devices. Thus, the treated alloy is believed to be useful for orthopedic and dental implants.     

Block copolymer assisted self-assembly of nanoparticles into Langmuir–Blodgett films: Effect of polymer concentration

We propose to use the self-assembly ability of a block copolymer to obtain CdSe quantum dots (QDs) structures of different morphology. The methodology proposed consist in transferring mixed Langmuir monolayers of QDs and the polymer poly (styrene-co-maleic anhydride) partial 2 buthoxy ethyl ester cumene terminated, PS-MA-BEE onto mica by the Langmuir–Blodgett (LB) methodology. The morphology of the LB films was analyzed by AFM and TEM measurements. Our results show that it is possible to modulate the self-assembly process by modifying the composition of the mixed Langmuir monolayer precursor of the LB film. The different morphologies are interpreted according to two different dewetting mechanisms, growth of holes and spinodal-like dewetting. The growth of holes dewetting process is driven by gravitatory effects and was observed for LB films obtained by transferring Langmuir monolayer of the smallest elasticity values in which the polymer is in brush conformation. The spinodal dewetting mechanism prevailed when the Langmuir monolayer presents the highest elasticity values.     

Physical–chemical and biological behavior of an amorphous calcium phosphate thin film produced by RF-magnetron sputtering

This work evaluates the thermal reactivity and the biological reactivity of an amorphous calcium phosphate thin film produced by radio frequency (RF) magnetron sputtering onto titanium substrates. The analyses showed that the sputtering conditions used in this work led to the deposition of an amorphous calcium phosphate. The thermal treatment of this amorphous coating in the presence of H₂O and CO₂ promoted the formation of a carbonated HA crystalline coating with the entrance of CO₃^2 ? ions into the hydroxyl HA lattice. When immersed in culture medium, the amorphous and carbonated coatings exhibited a remarkable instability. The presence of proteins increased the dissolution process, which was confirmed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses. Moreover, the carbonated HA coating induced precipitation independently of the presence of proteins under dynamic conditions. Despite this surface instability, this reactive calcium phosphate significantly improved the cellular behavior. The cell proliferation was higher on the Ticp than on the calcium phosphate coatings, but the two coatings increased cellular spreading and stress fiber formation. In this sense, the presence of reactive calcium phosphate coatings can stimulate cellular behavior.     

One-step synthesis of poly(2-hexadecyloxyaniline)/selenium nanocomposite Langmuir–Blogett film by in situ redox reaction

Poly(2-hexadecyloxyaniline)/selenium (Se) nanocomposite monolayer was successfully prepared by spreading 2-hexadecyloxyaniline (2-C₁₆OAn) on selenious acid aqueous solution without additional oxidant and reductant. The formation of Se nanoparticles and the polymerization of 2-C₁₆OAn in the monolayer occurred simultaneously. The results showed that the limiting area per repeat unit on selenious acid subphase was larger than that on pure water, which indicated the formation of poly(2-hexadecyloxyaniline)/Se nanocomposite monolayer at air/water interface. The amorphous spherical Se nanoparticles and triangular single-crystal ones in the Langmuir–Blogett (LB) films were formed at 20 ± 1 °C and 35 ± 1 °C, respectively. Poly(2-hexadecyloxyaniline)/Se nanocomposite LB films with excellent quality could be obtained on different substrates, indicating that the transfer ratio of monolayer was close to unity. Furthermore, poly(2-hexadecyloxyaniline)/Se nanocomposite LB films possessed high conductivity with the current of 10⁻⁵ A cm⁻¹.     

Formation of Highly Conducting Optically Transparent Films with Multigraphene Structure via Carbonization of Polyimide Langmuir–Blodgett Films

Technical Physics Letters - Multigraphene films have been for the first time obtained on the surface of quartz glass via carbonization of polyimide Langmuir–Blodgett films. The Raman spectra...