We report the creation of nano-structures via Dip Pen Nanolithography by locally exploiting the mechanical response of
polymer thin films to an acidic environment. Protonation of cross linked poly(4-vinylpyridine) (P4VP) leads to a
swelling of the polymer. We studied this process by using an AFM tip coated with a pH 4 buffer. Protons migrate
through a water meniscus between tip and sample into the polymer matrix and interact with the nitrogen of the pyridyl
group forming a pyridinium cation. The increase in film thickness, which is due to Coulomb repulsion between the
charged centers, was investigated using Atomic Force Microscopy. The smallest structures achieved had a width of about
40 nm. Different control experiments support our claim that the protonation is the reason for the swelling and therefore
the formation of the structures. Kelvin probe force microscopy measurements suggest the presence of counter ions which
compensate the positively charged pyridinium ions. We investigated the influence of the water meniscus on the structure
formation by varying the relative humidity in the range from 5% to 60% for different dwell times. The diffusion of
protons and counter ions is humidity-dependent and requires a water meniscus.
We have experimentally demonstrated the fabrication and the functioning of a rapidly prototyped optical
cylindrical microcavity waveguide based biosensor. The device works on the principle of determination of the change to
the light intensity of the input coupled light to the waveguide due to the interaction and binding of proteins to the
cylindrical waveguide structure. The variation to the coupled light intensity is dependant on the nature of the protein i.e.
its surface charge and the density of the proteins. This technique has been used to identify a specific protein biomarker
associated with the identification of vulnerable coronary plaque -Myeloperoxidase (MPO). Detection sensitivity in the
order of pg/ml has been demonstrated. The detection speed is in the order of seconds from the time of injection of the
protein onto the sensor surface. The optical signature that is obtained to identify a protein is entirely dependant on the
nature of adsorption of the protein on to the cylindrical cavity surfaces. This technique is a demonstration of detection of
nanoscale proteins using a label free optical biosensor technique with unprecedented sensitivity.
This paper describes recent results obtained with the Ultrasonic/Shear-Force Microscope (SUNM), an analytical tool suitable for investigating the quite different dynamic displayed by fluid-like films when subjected to mesoscopic confinement and while in intimate contact with two sliding solid boundaries. The SUNM uses two sensory modules to concurrently but independently monitor the effects that fluid-mediated interactions exert on two sliding bodies: the microscope's sharp probe (attached to a piezoelectric sensor) and the analyzed sample (attached to an ultrasonic transducer). This dual capability allows correlating the fluid-like film's viscoelastic properties with changes in the probe's resonance frequency and the generation of sound. A detailed monitoring of sliding friction by ultrasonic means and with nanometer resolution is unprecedented, which opens potential uses of the versatile microscope as a surface and subsurface material characterization tool. As a surface metrology
tool, the SUNM presents a potential impact in diverse areas ranging from fundamental studies of nanotribology, confinement-driven solid to liquid phase transformation of polymer films, characterization of industrial lubricants, and the study of elastic properties of bio-membranes. As a sub-surface metrology tool, the SUNM can be used in the investigation of the elastic properties of low- and high-k dielectric materials, piezoelectric and ferroelectric films, as well as quality control in the construction of micro- and nano-fluidics devices.
This paper presents a new method that exploits the interference and polarization properties of light to monitor, in real time, the rapid thermal elongation of near-field optical probes. The typically flat (nanometer in size) morphology of the probe apex serves as one mirror of a Fabry-Perot type cavity; a flat semitransparent metal coated surface constitutes the other mirror. The optical-interferometry set-up permits distance acquisition with a high frequency bandwidth (compared to other methods based on electronic feedback) while control of the light polarization allows an increase of the signal to noise ratio of the measurements.
In measurements of sample temporal response with a near-field scanning optical microscope, or NSOM, one must account for the temporal response of the probe. The coupling of thermal and temporal effects in an NSOM fitted with a coated tapered fiber probe is considered. Study of the perturbation of cw infrared light by a pulse of visible light simultaneously sent through an illumination mode NSOM allows one to separate the relatively slow thermal response of the probe from the appreciably faster response of a silicon sample imaged with the probe. Temporal and thermal contrast in NSOM imaging are discussed in terms of the results.
KEYWORDS: Infrared detectors, Semiconductors, Infrared imaging, Visible radiation, Silicon, Near field scanning optical microscopy, Infrared radiation, Semiconducting wafers, Signal detection, Near field optics
We demonstrate the ability of near-field scanning optical microscopy (NSOM) technique to detect inhomogeneities of the dynamics of excess carriers in oxidized silicon wafers. NSOM is used to improve the spatial resolution of a standard IR-scattering optical technique, which is carried out in a noncontact fashion. Continuous wave infrared light is used as a detector of the time dependent carrier population produced by a pulsed visible laser. We will show high resolution images of carrier lifetime, and discuss some aspects of the NSOM measurement that differentiate it from its far field counterpart.