Graham H. Cross

The metrics of surface adsorbed small molecules on the Young's fringe dual-slab waveguide interferometer

A method for analysing thin films using a dual-waveguide interferometric technique is described. Alternate dual polarization addressing of the interferometer sensor using a ferroelectric liquid crystal polarization switch allowed the opto-geometrical properties (density and thickness) of adsorbed layers at a solid?liquid interface to be determined. Differences in the waveguide mode dispersion between the transverse electric and transverse magnetic modes allowed unique combinations of layer thickness and refractive index to be determined at all stages of the layer formation process. The technique has been verified by comparing the analysis of the surface adsorption of surfactants with data obtained using neutron scattering techniques, observing their behaviour on trimethylsilane coated silicon oxynitride surfaces. The data obtained were found to be in excellent agreement with analogous neutron scattering experiments and the precision of the measurements taken to be of the order of 40?pm with respect to adsorbed layer thicknesses. The study was extended to a series of surfactants whose layer morphology could be correlated with their hydrophilicity/lipophilicity balance. Those in the series with longer alkyl chains were observed to form thinner, denser layers at the hydrophobic solid/aqueous liquid interface and the degree of order attained at sub-critical micelle concentrations to be correlated with molecular fluidity.The technique is expected to find utility with those interested in thin film analysis. An important and growing area of application is within the life sciences, especially in the field of protein structure and function.

An assessment of second harmonic generation by donor acceptor molecules containing stilbenyl or diarylazo bridges between ferrocenyl donor and nitro acceptor groups

Abstract The compounds [Fe(η 5 -C 5 H 5 )(η 5 -C 5 H 4- -Ar) (Ar = 4,4′-C 6 H 4 N 2 C 6 H 4 NO 2 ( 1 ), 4, 4−C 6 H 4 N 2 C 6 H 3 (2′-Me)NO 2 ( 2 ), 4,4′-C 6 H 3 (3−Me)N 2 C 6 H 3 (2′-Me)NO 2 ( 3 ) and trans -4,4′-C 6 H 4 (CHCH)C 6 H 4 NO 2 ( 4 ) have been synthesized and their second order non-linear optical properties assessed by use of the Kurtz powder test for second hartnonic generation on irradiation at 1907 nm. The stilbenyl compound, 4 , gave a signal of similar intensity to that of a urea standard but the others gave no detectable signal.

Young’s fringes from vertically integrated slab waveguides: Applications to humidity sensing

Using a multiple layer optical waveguide system consisting of two vertically slab waveguides, classical Young’s fringes may be obtained in the far-field diffraction plane. In agreement with the simple theory of diffraction interference the spacing of the far-field fringes is easily observed on mm to cm dimensions without further transformation of the output light. The simple methods of fabrication and means of optical coupling should provide a readily adaptable method for examining the principles of interferometry in an integrated optical format. The structure acts to transform polarized incident plane wave input light into separate slab modes of the device which emerge as two closely spaced and coherent sources at the output. The elements required for a classical Young’s fringe demonstration are therefore all embodied in this approach. The basic concept can be applied to an optical method for sensing. In one example of this we demonstrate measurement of the phase difference induced between the upper and lower propagating modes in structures due to water vapor diffusion into the layers which are formed from hydrophilic polymers. The Young’s fringe patterns exhibit a spatial intensity distribution which is sensitive to water vapor introduced over the surface of the structure. Differences in the effective index between the modes of the two waveguides during the diffusion of the vapor causes phase shifts which result in redistribution in the fringe pattern. The anticipated limit of detection of these devices is lower than 1 ppm for water vapor.

Real time, high resolution studies of protein adsorption and structure at the solid?liquid interface using dual polarization interferometry

A novel method for the analysis of thin biological films, called dual polarization interferometry?(DPI), is described. This high resolution (<1??), laboratory-based technique allows the thickness and refractive index (density) of biological molecules adsorbing or reacting at the solid?liquid interface to be measured in real time (up to 10 measurements per second). Results from the adsorption of bovine serum albumin (BSA) on to a silicon oxynitride chip surface are presented to demonstrate how time dependent molecular behaviour can be examined using DPI. Mechanistic and structural information relating to the adsorption process is obtained as a function of the solution pH.

Molecular materials for non-linear optics. Second harmonic generation and the crystal and molecular structure of the 4-nitrophenylimine of ferrocenecarboxaldehyde

Abstract Ferrocenyl derivatives of the form [(η-C 5 H 5 )Fe(η-C 5 H 4 )CHN-( p -C 6 H 4 X)], where XNO 2 , F, Br, were tested for second harmonic generation (s.h.g.). Only when XNO 2 was such activity observed. This was not large, however, at 1/3 times that of the urea standard. X-ray analysis confirms that the material is non-centrosymmetric, crystallizing in the space group P 2 1 2 1 2 1 . This dictates that despite being acentric the crystal arrangement essentially ensures a cancelling of the dipolar nature of the molecule. The residual s.h.g. must arise from intermolecular effects . This is only the second structural report of such a metallocene derivative to display s.h.g. The possible influence of the molecular shape of 1 and of related compounds is also discussed.

Preparation of diphenylsilylene polymers containing main-chain acetylene and (hetero)aromatic groups : χ(2) non-linear optical and other properties

Abstract Polymers having the structure ???CCSi(Ph 2 )CCZ??? (Z = 1,4-benzene, 4,4′-biphenyl, 9,10-anthracene, 2,7-fluorene, 6,6′-bipyridine, 2,5 and 2,6-pyridine, 2,5-thiophene, 2,6- p -dimethylaminonitrobenzene, 2,6- p -nitroaniline, 2,6- p -nitrophenol, 2,6- p -cyanophenol, p -tetrafluorobenzene and 2,7-fluoren-9-one) were prepared by reaction of diethynyldiphenylsilane with the appropriate (hetero)aromatic dibromide or diiodide in the presence of [(PPh 3 ) 2 PdCl 2 ], CuI and PPh 3 , the solvent being either triethylamine or triethylamine with toluene. Depending on the Z group and the solvent system, the weight-average molecular weight as determined by SEC ranged from 2600 for 2,6-pyridine to 34,000 for 1,4-benzene. The UV/visible spectra show absorption maxima in the region 250–400 nm. The polymer with 2,6- p -dimethylaminonitrobenzene groups was χ (2) active, the value of r 33 being 0.8 pm V −1 following fixed electrode poling at 17.5 V μm −1 . The polymers did not melt below the decomposition temperature, and all transitions shown in the DSC thermogram to 300°C were found to be absent on repeat scans. Thermogravimetric and thermal dynamic analysis of the polymer where Z = 1,4-benzene showed decomposition commencing at 290°C and continuing up to ca . 750°C. The residue was composed of α-SiC and amorphous carbon. Treatment of the same polymer with BH 3 /SMe 2 gave rise to an insoluble polymer containing boron. The polymer where Z = 6,6′-bipyridine reacted with copper(II) trifluoromethanesulfonate to give a copper(II) -containing polymer, hydrazine reduction of which afforded the corresponding Cu I -containing polymer.

Design and characterization of organic and organometallic molecules for second order nonlinear optics

Publisher Summary This chapter focuses on how to design, characterize, and optimize the first hyperpolarizability β of organic and organometallic molecules for nonlinear optics (NLO) applications. The chapter also presents NLO effects and examines the relation between molecular and macroscopic NLO properties. The theoretical methods which have been employed to calculate these properties are discussed. The chapter presents a description of methods for the experimental determination of molecular second-order (SO) NLO parameters with emphasis on the recently widely used hyper-Rayleigh scattering (HRS) technique. The different types of compounds which have been synthesized and characterized for SO NLO are discussed for organic and organometallic molecules, respectively, up to the recent developments in this field. A number of criteria which these compounds have to meet for applications and some materials aspects are also considered in the chapter.

Optical waveguide humidity sensor with symmetric multilayer configuration

Abstract A polymer waveguide sensor with a symmetric multilayer configuration is fabricated and integrated, and its application in sensing low humidity concentration has been demonstrated. The sensor measured the induced optical phase changes when the water molecules diffuse into the polymer waveguide. Sensitivity of several parts per million humidity concentration is achieved. The sensor also supplies the absolute sign of the movement of the produced interference fringes, which offers an easy indication of the index changes (increase or decrease) in the sensing layer. This study demonstrates a very promising prospect to make a compact, disposable optical-sensing device with low cost for humidity sensing application.

THE MAGNETIC AND SECOND-ORDER NONLINEAR OPTICAL PROPERTIES OF SOME PARAMAGNETIC SALTS CONTAINING METALLOCARBABORANE ANIONS

Abstract A series of air-stable salts containing the paramagnetic metallocarboranes [MCb2]− (M = Fe, Ni; Cb2− = 7,8-C2B9H112−) has been prepared and their magnetic properties investigated. The paramagnetic salts [FeIIITp2][FeIIICb2] Tp = HB(C3H3N2)3, [FeIIIC6H4(O)C(Me) = N(CH2)2NHCH22][FeIIICb2], [C5H5NMe][FeIIICb2], [4-MeC5H4NMe][FeIIICb2], [4-PhC5H4NMe][FeIIICb2], [C9H7NMe][FeIIICb2], [FeIIITp2][TCNQ] and [FeIIICp2][FeIIICb2] have been isolated. Magnetic susceptibility measurements show that these salts exhibit typical paramagnetic behaviour with no evidence of cooperative magnetic interactions over the temperature range 6–300 K. The salts [E-Fc-CH = CH-p-C5H4NMe][MIIICb2] (M = Fe, Ni, Co) were also synthesised and their second-order nonlinear optical properties assessed using the Kurtz powder test. Only the cobalt-containing complex gave detectable, though weak, second harmonic generation of 0.01 times urea at 1.907 μm. The salt [C5H5NMe][FeIIICb2] exhibits SHG with an efficiency of 0.5 times urea at 1.907 μm and 0.1 at 1.064 μm. Mass spectrometric and 13C1H NMR studies of the products formed by the degradation of [Co(Cb)2]− by base in the presence of Co2+ ions has provided no evidence for the formation of higher oligomers than the previously reported [Co(Cb)2(C2B8H10)]2− and [CoCb(C2B8H10)2Co]3−. The structures of [FeIIICp2*][NiIIICb2] (Cp* = η5-C5Me5) and [4-MeC5H4NMe][FeIIICb2] have been determined by single crystal X-ray diffraction studies.

Synthesis and nonlinear optical properties of a range of 1-ferrocenyl(2-(4-alkyl)pyridiniumyl)ethylene iodides

Abstract The preparation of a range of compounds of general formula FcCHCHC 5 H 4 N + X, where X=C n H 2 n +1 ( n =1–5, 10 or 18) and O − , was achieved via condensation of the relevant picolinium iodide with ferrocene carboxaldehyde. The spectroscopic properties of these materials were shown to be very similar, however the SHG, measured by the Kurtz powder technique, showed that increasing the alkyl chain above three carbons resulted in a dramatic loss of SHG efficiency. The O − compound also yielded very little SHG.