Thin-film replicas

The PL spectrum and onset of the absorption spectrum of poly(2,5-dioctyloxy-para-phenylene vinylene) (DOO-PPV) are shown in Figure 7-8b. The PL spectrum exhibits several phonon replica at 1.8, 1.98, and 2.15 eV. The PL spectrum is not corrected for the system spectral response or self-absorption. These corrections would affect the relative intensities of the peaks, but not their positions. The highest energy peak is taken as the zero-phonon (0-0) transition and the two lower peaks correspond to one- and two-phonon transitions (1-0 and 2-0, respectively). The 2-0 transition is significantly broader than the 0-0 transition. This could be explained by the existence of several unresolved phonon modes which couple to electronic transitions. In this section we concentrate on films and dilute solutions of DOO-PPV, though similar measurements have been carried out on MEH-PPV [23]. Fresh DOO-PPV thin films were cast from chloroform solutions of 5% molar concentration onto quartz substrates the films were kept under constant vacuum. 

A most useful technique for examining surface structure is that of replication. One method is to deposit the sample on a freshly cleaved mica surface on to which carbon (and, if desired, a heavy metal) is vacuum-evaporated. The resulting thin film, with the specimen particles still embedded, is floated off the mica on to a water surface. The particles are dissolved out with a suitable solvent and the resulting replica is mounted on a copper grid. 

Three different techniques, namely FFEM [20, 22], Cryo-Direct Imaging (Cryo-DI) [104] and freeze-fracture direct imaging (FFDI) [105], can be used to visualise the structure of micro emulsions. In FFEM the samples are prepared in a protected fashion in a sandwich. They are then rapidly frozen, fractured, shadowed with metal, and replicated with a thin carbon film. The replica of the fractured surface, the morphology of which is controlled by the sample s microstructure, is then studied by a TEM. In contrast to FFEM, in Cryo-DI thin films of the sample are rapidly frozen but immediately, without replication, trans-... 

Soft lithography The pattern-transfer element is formed by pouring a liquid polymer onto a master made from silicon. This replica can be used as a stamp to transfer chemical ink, such as a solution of alkanethiol, to a surface. Spin-coating Thin film formation by deposition of a solution onto a solid, which is then rotated at a speed of several thousand revolutions per minute. 

Electron microscope inspection of a film replica of a polished surface of each of the bars as well as direct transmission electron micrographs of thin sections of each bar, reveals that these channels are evenly distributed throughout the bars. The channels are generally tetragonal or triangular in shape and have a diameter (calculated as the diameter of a circle having the same area as the pore cross section) of about 0.1-0.5 p.m. The pores are of such uniformity of size that practically no pores smaller than 0.1 pm or larger than 1 pm are found in the bars. The invention claimed is ... 

Fig. 2.20 Examples of electron micrographs of polymers, (a) A defocussed bright-field image of a thin film of isotactic polystyrene annealed and crystallised at about 170 °C (b) An image of a fracture surface replica from a sample of linear polyethylene crystallised from the melt at 4.95 kbar. ((a) Adapted by permission of Masaki Tsuji and (b) adapted from Principles of Polymer Morphology by D. C. Bassett. Cambridge University Press 1981.)...

This chapter will review the generation of free-standing thin films and fibers with a coarse-grained simulation method on a high coordination lattice,performed in a manner that allows accurate reverse-mapping of individual replicas to a fully atomistic representation in continuous space.4 After describing some of the properties of these films and fibers, we will present some new information about the limits on the stability of the models of these nanofibers. 

Because of the low penetrating power of electrons, specimens for examination in transmission have to be very thin, depending on the circumstances tens or hundreds of nanometres in thickness. Surface features on thick specimens can be examined by making a thin replica. A standard technique is to evaporate a thin film of carbon on to the surface of interest, to shadow it by depositing an even thinner layer of platinum at a different angle, and then to remove the deposited replica, for example, by dissolution of the original specimen. 

In the model studies discussed thus far, thin films were formed from solutions or melts, thus limiting preparation artifacts. Important model studies have also been conducted by methods more commonly employed to study the morphology of commercial materials. Two types of studies have been conducted on samples prepared by (1) production of microtomed and stained sections (Section 4.4) and (2) formation of replicas (Section 4.6) of acid etched (Section 4.5) materials. Both methods have been developed to the point where clear images of lamellar structures can be obtained. Bassett and coworkers have been responsible for developing the second method, and have reviewed its use for... 

Figure 6.18 Electron micrographs of replicas of hedrites formed in the same melt-crystallized thin film of poly(4-methylpentene-1). (a) An edge-on view of a hedrite. Note the distinctly lamellar character and the sheaflike arrangement of the lamellae, (b) A flat-on view of a hedrite. Note the degenerate overall square outline of the object, whose lamellar texture is evident (33).

Figure 10.19 (a) Replica of an etched surface of isotactic polystyrene crystallised at 215°C in the form of a thin film. Replication involved an extraction procedure whereby a thin film of crystalline material remained adhering to the carbon replica, (b) Electron diffraction pattern from the replica... 

Diffractive elements are very lightweight, as they are typically formed in thin films of a few micrometer thickness only (this is valid even for the so-called volume structures where a thickness of only a few wavelengths usually suflftces.) They can be completely flat even if they perform functions of conventional elements with curved surfaces. On the other hand, a DOE can be fabricated on any arbitrary shape of the substrate. Their fabrication is cheap in comparison to conventional optics (typically a master element is fabricated and its replicas are created by some mass production methods). 

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