During the past decade, enormous progress has been made in growing ultrathin organic films and multilayer structures with a wide range of exciting optoelectronic properties. This progress has been made possible by several important advances in our understanding of organic films and their modes of growth. Perhaps the single most important advance has been the use of ultrahigh vacuum (UHV) as a means to achieve, for the first time, monolayer control over the growth of organic thin films with extremely high chemical purity and structural precision.1-3 Such monolayer control has been possible for many years using well-known techniques such as Langmuir-Blodgett film deposition,4 and more recently, self-assembled monolayers from solution have also been achieved.5 However, ultrahighvacuum growth, sometimes referred to as organic molecular beam deposition (OMBD) or organic molecular beam epitaxy (OMBE), has the advantage of providing both layer thickness control and an atomically clean environment and substrate. When combined with the ability to perform in situ highresolution structural diagnostics of the films as they are being deposited, techniques such as OMBD have provided an entirely new prospect for understanding many of the fundamental structural and optoelectronic properties of ultrathin organic film systems. Since such systems are both of intrinsic as well as practical interest, substantial effort worldwide has been invested in attempting to grow and investigate the properties of such thin-film systems. This paper is a review of recent progress made in organic thin films grown in ultrahigh vacuum or using other vapor-phase deposition methods. We will describe the most important work which has been published in this field since the emergence of OMBD in the mid-1980s. Both the nature of thin-film growth and structural ordering will be discussed, as well as some of the more interesting consequences to the physical properties of such organic thin-film systems will be considered both from a theoretical as well as an experimental viewpoint. Indeed, it will 1793 Chem. Rev. 1997, 97, 1793−1896

Ultrathin Organic Films Grown by Organic Molecular Beam Deposition and Related Techniques.

Thin films of surfactant-templated mesoporous materials1,2 could find applications in membrane-based separations, selective catalysis and sensors. Above the critical micelle concentration of a bulk silica–surfactant solution, films of mesophases with hexagonally packed one-dimensional channels can be formed at solid–liquid and liquid–vapour interfaces3,4,5. But this process is slow and the supported films3,5 are granular and with the pore channels oriented parallel to the substrate surface, so that transport across the films is not facilitated by the pores. Ogawa6,7 has reported a rapid spin-coating procedure for making transparent mesoporous films, but their formation mechanism, microstructure and pore accessibility have not been elucidated. Here we report a sol–gel-based dip-coating method for the rapid synthesis of continuous mesoporous thin films on a solid substrate. The influence of the substrate generates film mesostructures that have no bulk counterparts, such as composites with incipient liquid-crystalline order of the surfactant–silica phase. We are also able to form mesoporous films of the cubic phase, in which the pores are connected in a three-dimensional network that guarantees their accessibility from the film surface. We demonstrate and quantify this accessibility using a surface-acoustic-wave nitrogen-adsorption technique. We use fluorescence depolarization to monitor the evolution of the mesophase in situ, and see a progression through a sequence of lamellar to cubic to hexagonal structures that has not previously been reported.

Continuous formation of supported cubic and hexagonal mesoporous films by sol–gel dip-coating

Organic semiconductor lasers.

Diffraction characteristics of general dielectric planar (slab) gratings and surface-relief (corrugated) gratings are reviewed. Applications to laser-beam deflection, guidance, modulation, coupling, filtering, wavefront reconstruction, and distributed feedback in the fields of acoustooptics, integrated optics, holography, and spectral analysis are discussed. An exact formulation of the grating diffraction problem without approximations (rigorous coupled-wave theory developed by the authors) is presented. The method of solution is in terms of state variables and this is presented in detail. Then, using a series of fundamental assumptions, this rigorous theory is shown to reduce to the various existing approximate theories in the appropriate limits. The effects of these fundamental assumptions in the approximate theories are quantified and discussed.

Analysis and applications of optical diffraction by gratings

A pulsed tunable dye laser with a bandwidth of less than 0.004 A, repetitively pumped by a nitrogen laser, is described. An intracavity beam expanding telescope together with a diffraction grating in Littrow mount and a tilted Fabry-Perot etalon provide convenient, very reproducible wavelength tuning and good stability. Output peak powers in the kilowatt range at 5–100 nsec pulse width and repetition rates up to 100 pps can be generated from the near-ultraviolet throughout the visible spectrum.

Repetitively Pulsed Tunable Dye Laser for High Resolution Spectroscopy

Efficient spectral narrowing, and tunability over a wide spectral range, has been demonstrated in solid and liquid organic dye lasers using diffraction gratings as cavity reflectors.

B. B. McFarland

Papers

Continuously tunable, narrow‐band organic dye lasers