Jessie A. DeAro

Single-molecule detection fluorescence of surface-bound species in vacuum

Abstract We have performed single-molecule fluorescence detection of DiIC 12 molecules adsorbed on a solid substrate where the surrounding pressure is controlled. The triplet lifetimes are significantly longer (4–100 ms) and far more easily observed at moderate vacuum pressures than in air (typically

Mesoscale optical properties of conjugated polymers probed by near-field scanning optical microscopy

Abstract Near-field scanning optical microscopy (NSOM) has been used to study the mesoscale optical properties of oriented and non-oriented free-standing thin films of poly( p -phenylene vinylene) (PPV). We report a strong correlation between film morphology and the optical properties on a 100 nm scale. The non-oriented PPV thin film exhibits mesoscale domains of local molecular orientation as well as areas which are characterized by a low photoluminescence efficiency. Upon stretch orientation, PPV thin films show average polymer chain orientation parallel to the stretch axis as well as distinct areas of perpendicular molecular orientation correlated to film topography.

Near‐field scanning optical microscopy in reflection: A study of far‐field collection geometry effects

We have designed and demonstrated two simple and versatile reflection mode near‐field scanning optical microscopes (NSOMs). In one scanner far‐field collection is coaxial with the NSOM tip, and in the other scanner, the far‐field collection is at a 45° angle to the NSOM tip. We quantitatively compare images obtained with the two scanners. While off‐axis collection offers a significantly higher signal‐to‐noise ratio, it also introduces tip shadowing in samples with topographic features larger than approximately 40 nm. The additional contrast from the shadowing further complicates image interpretation and must be considered when performing NSOM in reflection with off‐axis collection. In addition, we discuss some general issues that should be considered when designing a reflection NSOM.

Near-field photoconductivity of stretch-oriented poly(para-phenylene vinylene)

Near-field scanning optical microscopy (NSOM) with photoconductivity contrast is used to map the transport properties of stretch-oriented poly(p-phenylene vinylene) thin films on a 150 nm length scale. Near-field photoconductivity is highly sensitive to film morphology and contrast is observed even in films with uniform photoluminescence. Regions of relatively higher photocurrent signals are correlated to regions with higher molecular order which have contrast approaching 15%. In addition, the photocurrent signal decreases sharply as the near-field tip approaches the surface of the film while at the same time the photoluminescence signal increases. The sharp decrease is attributed to the perturbation of the applied electric field within the polymer film by the metal on the NSOM tip.

Probing nanoscale photo-oxidation in organic films using spatial hole burning near-field scanning optical microscopy

Spatial hole burning near-field scanning optical microscopy (SHB–NSOM) is used to locally photopattern three species of organic thin films, poly(2-methoxy, 5-(2′-ethyl hexyloxy)–p-phenylene vinylene) (MEH–PPV), tris-8-hydroxyquinoline aluminum (Alq3) and dye-functionalized polyelectrolyte self-assembled layers, on a 100 nm length scale. In SHB–NSOM the film is illuminated with light from a stationary NSOM tip to induce photo-oxidation. The reduction in the fluorescence yield resulting from this exposure is then mapped using fluorescence NSOM (FL–NSOM). We have examined the localized photo-oxidation as a function of time, position, and environment free from the limits of far-field spatial averaging. In all of the thin film materials studied we find that the long-time diameter of the dark spot is much larger than the tip diameter and is a signature of energy migration. Characteristic lengths of the energy migration are extracted from this data by a simple diffusion model and are found to be of the order of ...

Nanoscale Optical Microscopy of Conjugated Polymer Films

Near-field scanning optical microscopy (NSOM) has been used to probe the photoluminescence, linear dichroism and photoconductivity of free-standing poly(p-phenylene vinylene) (PPV) films with spatial resolution better than 100 nm. We observe a strong correlation between each of these properties and film morphology in both non-oriented and stretch-oriented films. The non-oriented PPV thin films exhibit mesoscale non-uniform photoluminescence correlated to polymer clusters. Upon stretch-orientation, PPV thin films show average polymer chain orientation parallel to the stretch axis as well as distinct areas of perpendicular molecular orientation correlated to film topography.

Near-field scanning optical microscopy of cleaved vertical-cavity surface-emitting lasers

Near-field scanning optical microscopy (NSOM) and near-field optical spectroscopy (NFOS) techniques have been applied to cleaved vertical-cavity surface-emitting lasers (VCSELs). Collection mode NSOM of the cleaved VCSEL operating above the threshold current indicates emission outside the active layer. Using the spatially resolved spectroscopy afforded by NFOS, it was possible to map changes in the electroluminescence spectrum with spatial resolution of the order of 100 nm . The emission spectra acquired with the tip positioned over the p-DBR layers show evidence for p-DBR luminescence. The p-DBR luminescence indicates the presence of minority carriers in this region of the device which have been postulated as a cause of dark line defects (DLDs) which play an important role in device degradation.

Near-field scanning optical microscopy of nanostructures

Abstract The applications of near-field scanning optical microscopy (NSOM) to various nano-structured materials are reviewed. The review begins with a description of experimental aspects of NSOM and the various contrast mechanisms available with the technique. Applications of NSOM to a variety of different materials are then addressed including: NSOM of semiconductor heterostructures, NSOM of polymers and molecular crystals, and NSOM of Langmuir-Blodgett films and layered organic self-assemblies.