John K. Pike

Single layers of inorganic extended lattices formed at Langmuir-Blodgett templates

Abstract Zirconium octadecylphosphonate monolayer and multilayered films have been prepared and characterized by Brewster angle microscopy (BAM), attenuated total reflection-Fourier transform IR spectroscopy, ellipsometry, X-ray diffraction and X-ray photoelectron spectroscopy (XPS). BAM data reveal the rigid nature of a Langmuir monolayer of octadecylphosphonic acid compressed on a Zr 4+ ion subphase; therefore a deposition procedure combining Langmuir-Blodgett (LB) and self-assembly techniques has been developed. First, an octadecylphosphonic acid organic template is prepared by the LB technique and then Zr 4+ ions are self-assembled onto the template from solution. Finally, a capping layer of octadecylphosphonic acid is transferred to the zirconated template to complete the bilayer assembly. The asymmetric methylene stretch frequency υ a (CH 2 ) appears at 2918 cm −1 and possesses a full width at half-maximum of 20 cm −1 for the template layer, a bilayer and a multilayered film. The position and width of the ν a (CH 2 ) band indicates that close-packed well-ordered films are formed. Ellipsometry demonstrates a layer-by-layer deposition in multilayered films, while X-ray diffraction proves that the films are indeed layered, possessing a d spacing of 52 A. XPS analysis of the template layer shows a Zr:P ratio of 1:1 within 10% error, while the bilayer and multilayered films possess a Zr:P ratio of 1:2 consistent with the stoichiometry of the bulk zirconium phosphonates.

X-ray photoelectron spectroscopy, attenuated total reflectance Fourier transform IR spectroscopy and transmission electron diffraction studies of oriented cadmium iodide prepared in a Langmuir-Blodgett template

Abstract Oriented CdI 2 has been prepared in a deposited Langmuir-Blodgett (LB) film by the reaction of gaseous HI with a 20-layer LB film of cadmium arachidate. Attenuated total reflectance Fourier transform IR spectroscopy shows that the conversion goes to completion, while X-ray photoelectron spectroscopy analysis of the HI-exposed cadmium arachidate film reveals a Cd:I ratio consistent with the CdI 2 stoichiometry. Electron diffraction shows that the CdI 2 is oriented exclusively with its [001] axis normal to the LB film basal plane and for domains ranging up to several microns has a preferred alignment about the [001] axis. The results suggest that the organic template plays a role in orienting the CdI 2 within the LB plane and that some degree of lattice matching exists between the LB template and the (001) face of CdI 2 . The oriented synthesis described here is in contrast with previous attempts at template-directed syntheses using deposited LB films which have resulted in the mediation of particle size only and not particle orientation. The difference here may be that CdI 2 has a layered structure in the bulk, crystalline phase which complements the LB film structure.

Molecular self-assembly at a pre-formed Langmuir-Blodgett template

Abstract The use of a Langmuir-Blodgett monolayer as a template for subsequent self-assembly of organic molecules from solution has been investigated. The template is formed by transferring a monolayer of octadecylphosphonic acid to a hydrophobic substrate and then binding Zr4+ ions to the surface from solution. The asymmetric methylene (va(CH2)) band of the template layer appears at 2918 cm−1 and possesses a full width at half-maximum of 20 cm−1 indicating that an all-trans close-packed template is formed. X-ray photoelectron spectroscopy (XPS) analysis of the template layer shows a 1:1 ratio of Zr:P. Octadecylphosphonic acid, 1,10-decadediyldiphosphonic acid (DDPA) and quaterthiophenediphosphonic acid (QDP) have been self-assembled to the template and characterized by attenuated total reflection-Fourier transform IR, XPS and UV-visible techniques. Octadecylphosphonic acid self-assembles to the zirconium template and produces a well-ordered close-packed film as followed by IR analysis. Multilayers of DDPA have been assembled to the template layer; however, the increase in the integrated area of the va(CH2) band is not linear with the number of DDPA layers assembled. A rigid diphosphonic acid molecule such as QDP has also been assembled one layer at a time to the template. A plot of UV-visible absorbance vs. the number of layers of QDP shows a linear increase in absorbance after each QDP deposition step.

Langmuir-Blodgett films as single-layer analogs of known organic/inorganic solid-state materials

Abstract Langmuir-Blodgett films of manganese octadecylphosphonate (Mn(O 3 PC 18 H 37 )·H 2 O) are prepared by depositing octadecylphosphonate monolayers from a MnCl 2 ·4H 2 O containing subphase at a pH range of 5.2–5.5. The LB films possess crystalline order that is analogous to the bulk manganese organophosphonates. Pressure versus area isotherms suggest that the Mn 2+ ions cross-link the phosphonate groups at the air/water interface. Two sharp IR bands at 978 cm −1 and 1088 cm −1 can be assigned to the symmetric and asymmetric PO 3 2− stretching modes, respectively, and a H 2 O bending mode at 1608 cm −1 is also observed. XPS analysis demonstrates that the Mn to P ratio is 1 to 1 which is consistent with the bulk manganese phosphonates. X-ray diffraction yields a layer spacing of 48.5 A. The in-plane structure is determined by transmission electron diffraction (TED). The combined diffraction data yield lattice parameters for the LB film based on an orthorhombic space group of a a = 5.7 A, b = 48.5 A and c = 4.9 A. The in-plane order is analogous to that of the known bulk manganese organophosphonates. The shape and g-value of the EPR signals for the bulk manganese phenylphosphonate and the LB film are identical. Temperature dependent magnetic susceptibility of the LB film demonstrates short-range antiferromagnetic order with the coherence length of the interaction increasing as the temperature is lowered.