Polar Polymeric Langmuir−Blodgett Films for Optical Applications

Abstract

A side-chain liquid crystalline copolymer containing ether−nitrobiphenyl groups was investigated as a nonlinear optical material. Ultrathin films have shown second harmonic generation and therefore have a variety of interesting applications. Waveguides composed of multilayers of the copolymer have been fabricated, and propagation losses as low as 2.3 dB/cm in a lowest order TE mode at 800 nm wavelength have been measured. The second harmonic coefficient is d 33 = 42.0 ± 1.7 pm/V at the 1064 nm fundamental wavelength and is consistent with an oriented gas model. From spectroscopic ellipsometry measurements the film refractive index is 2.24 ± 0.15 and the extinction coefficient ≤0.05 in the visible range of wavelengths. The monolayer and multilayer repeat structures were also studied by X-ray reflectivity and diffraction. The optical thickness and the oscillations in the reflectivity were in reasonable accord with a repeat length of about 3.6 nm.

Application of Dielectric Relaxation Spectroscopy to Ultrathin Langmuir−Blodgett Films

“…The multilayer samples had a head-to-tail polar structure with a net dipole (Figure ). X-ray diffraction indicated a noncentrosymmetric structure. − The layer thickness calculated from X-ray diffraction measurements is in agreement with the measurement from X-ray reflectivity …”

“…X-ray diffraction indicated a noncentrosymmetric structure. [21][22][23] The layer thickness calculated from X-ray diffraction measurements is in agreement with the measurement from X-ray reflectivity. 22 The dielectric measurement was done using a capacitance bridge, and the data were obtained as capacitance and loss (in picofarad, pF), which were converted to ′ and ′′ by the following equations M is the area (in m 2 ), R is the sample thickness (in m), and 0 is the vacuum permittivity 10 where the sample geometry was unknown; a comparison was made by comparing the geometry-independent dissipation factor.…”

“…Materials . All the synthesis and characterization of the materials were reported in previous publications. − All the variations of the structure that were used in this study are shown in Figure . The annotation for copolymer will be referred to as “Cop”, followed by the spacer length, copolymer composition, and the chromophore type.…”

Langmuir−Blodgett Films of Regioregular Poly(3-hexylthiophene) as Field-Effect Transistors

“…Langmuir−Blodgett (LB) techniques offer a unique approach to prepare ordered ultrathin films with well-defined architecture, − thus providing a promising and versatile method for constructing molecular devices. − Conjugated polymers have drawn intense research interest as active materials for such devices, due to their unusual electrical and optical properties, reasonable chemical stability, and easy processability. − The application of the LB technique to conjugated polymers has produced a variety of electrical and optical ultrathin film devices, such as light emitting diodes (LED), − thin film conductors, − memory devices, ferroelectric thin films, − nonlinear optical devices, − sensors − and field-effect transistors (FET). , …”

Langmuir monolayer properties of 4-methylbenzenethiol capped gold nanoparticles

“…However this view has been revised in recent years. A wide range of polymers [21,22] and even materials as diverse as fullerenes [23] have been shown to form stable Langmuir monolayers, and by careful selection of the stabilizing ligand, this is also true for gold nanoparticles.…”