Cis-Trans Photoisomerization of Perinaphthothioindigo for Use as a Photo-Imaging Sensor Using Fluorescence under He-Ne Laser Excitation

Abstract

A new technique is described for measuring the adhesion between a sharply curved metal point (platinum, tungsten, titanium, nickel or gold, with a radius of curvature typically 300 nm) and a flat surface (platinum, tungsten, cobalt, silicon or graphite). Adhesion forces as small as 100nN can be measured with a sensitivity (limited by friction and vibration) of 20 nN, and the electrical resistance of the contact region is measured as a function of positive and negative load. Any plastic deformation of the metal point, as well as its cleanliness, is monitored by current and voltage measurements on electrons drawn by field emission from the point before and after contact.For platinum and tungsten surfaces placed in contact with near-zero loads, high values of adhesion (up to 55 pN) were measured provided that both surfaces were sufficiently clean; there is evidence that one area of 'single-asperity' contact is obtained, Ductile extension was occasionally observed, but the experimental curves of resistance against load were otherwise reversible for both positive and negative loads, and unaffected by the magnitude of any previously applied positive load. Measurements of adhesion, resistance and change in resistance as a function of load may be divided into two categories according to whether separation took place at the interface or within the bulk of one of the samples. Generally the results are not consistent with the elastic theory of Johnson er al or with the model of Gane et al. Differences in the behaviour of contacts between the other materials are described. Further analysis may enable the method to be used for measuring values of work of adhesion (change in surface energy) for interfaces between stiff solids.

Probes for Nanoscopy: Photoswitchable Fluorophores

“…% 10 9 s À1 ), leaving no chance for the molecule to emit light in the short time it remains in S 1 before isomerizing. As a result, relatively few photochromic compounds display emission in (at least) one of the isomers [17,[22][23][24][25].…”

Synthesis and optical properties of photochromic perinaphthothioindigo

“…Furthermore, their fluorescence may be excited in the red, where inexpensive diode lasers are available. The photoswitching of bis(perinaphtho)thioindigo has been previously suggested for optical data storage and imaging [3,4].…”

“…Thus, even with monochromatic light incident on the sample at the maximum absorption of either form, only photostationary states containing a mixture of the two isomers could be prepared. Perinaphthothioindigo dyes have been reported by several groups [3][4][5][6][7][8][9][10]; the absorption spectra and properties differ among the dyes. Little information is available in the literature regarding synthesis of the perinaphthothioindigos: typically reference is made to a paper by HarleyMason and Mann [11], which does not provide specific details on this synthesis.…”

“…(B) The perinaphthothioindigo studied here, PNT, cis form. (C) The perinaphthothioindigo studied in Refs [3,4,6]. referred to as NTI.…”

Rewritable Near-Field Optical Recording on Photochromic Perinaphthothioindigo Thin Films: Readout by Fluorescence

“…These spots could be erased. In the present study we chose photochromic perinaphthothioindigo (NTI) [19][20][21][22][23] as the recording medium and tried to detect recorded spots by…”