An aluminum-coated tapered fiber probe, as used in near-field scanning optical microscopy ͑NSOM͒, is heated by the light coupled into it. This can destroy the probe or may modify the sample, which can be problematic or used as a tool. To study these thermal effects, we couple modulated visible light of various power through probes. Simultaneously coupled infrared light senses the thermal effects. We report their magnitude, their spatial and temporal scales, and real-time probe damage observations. A model describes the experimental data, the mechanisms for induced IR variation, and their relative importance.

An ultrasonic transducer is incorporated into a near-field scanning optical microscope ͑NSOM͒ to augment its versatility to characterize the properties of layers adsorbed to a sample's surface. Working under typical NSOM operation conditions, the ultrasonic transducer-attached underneath the sample-demonstrates sufficient sensitivity to monitor the waves generated by the tapered NSOM probe that oscillates in the proximity of, and parallel to, the sample's top surface. This capability makes the newly integrated ultrasonic/shear-force microscope a valuable diagnostic tool in the study of sliding friction and surface phenomena in general. Here, it is used to concurrently and independently monitor the effects that probe-sample interactions exert on the probe ͑that is attached to a piezoelectric tuning fork͒ and on the sample ͑that is attached to the ultrasonic transducer͒. The signal from the tuning fork ͑TF͒ constitutes the so called "shear-force" signal, widely used in NSOM as a feedback to control the probe's vertical position but whose working mechanism is not yet well understood. Tests involving repeated vertical z motion of the probe towards and away from the sample's surface reveal that the TF and ultrasonic ͑US͒ signals have distinct z dependence. Additionally, where the TF signal showed abrupt changes during the approach, the US changed accordingly. A shift in the probe's resonance frequency that depends on the probe-sample distance is also observed through both the TF and the US responses. Within the sensitivity of the apparatus, ultrasonic signals were detected only at probe-sample distances where the probe's resonance frequency had shifted significantly. These measured signals are consistent with a probe entering and leaving a viscoelastic fluid-like film above the sample. The film acts as the medium where waves are generated and coupled to the ultrasonic sensor located beneath the sample. To our knowledge, this is the first reported use of ultrasonic detection for detailed monitoring of the distance dependence of probe-sample interactions, and provides direct evidence of sound as an energy dissipation channel in wear-free friction. This newly integrated ultrasonic/shear-force microscope, which can be implemented with any functionalized proximal probe ͑including aperture and apertureless NSOM͒, can become a valuable metrology tool in surface science and technology.

Full understanding of the physics underlying the striking changes in viscoelasticity, relaxation time, and phase transitions that mesoscopic fluid-like films undergo at solid-liquid interfaces, or under confinement between two sliding solid boundaries, constitutes one of the major challenges in condensed matter physics. Their role in the imaging process of solid substrates by scanning probe microscopy (SPM) is also currently controversial. Aiming at improving the reliability and versatility of instrumentation dedicated to characterize mesoscopic films, a noninvasive whispering-gallery acoustic sensing (WGAS) technique is introduced; its application as feedback control in SPM is also demonstrated. To illustrate its working principle and potential merits, WGAS has been integrated into a SPM that uses a sharp tip attached to an electrically driven 32-kHz piezoelectric tuning fork (TF), the latter also tighten to the operating microscope's frame. Such TF-based SPMs typically monitor the TF's state of motion by electrical means, hence subjected to the effects caused by the inherent capacitance of the device (i.e., electrical resonance differing from the probe's mechanical resonance). Instead, the novelty of WGAS resides in exploiting the already existent microscope's frame as an acoustic cavity (its few centimeter-sized perimeter closely matching the operating acoustic wavelength) where standing-waves (generated by the nanometer-sized oscillations of the TF's tines) are sensitively detected by an acoustic transducer (the latter judiciously placed around the microscope's frame perimeter for attaining maximum detection). This way, WGAS is able to remote monitoring, via acoustic means, the nanometer-sized amplitude motion of the TF's tines. (This remote-detection method resembles the ability to hear faint, but still clear, levels of sound at the galleries of a cathedral, despite the extraordinary distance location of the sound source.) In applications aiming at characterizing the dynamics of fluid-like mesoscopic films trapped under shear between the TF probe and the solid substrate, WGAS capitalizes on the well-known fact that the TF's motion is sensitively affected by the shear-forces (the substrate and its adsorbed mesocopic film playing a role) exert on its tip, which occurs when the latter is placed in close proximity to a solid substrate. Thus, WGAS uses a TF as an efficient transducer sandwiched between (i) the probe (that interact with the substrate and mesoscopic film), and (ii) the acoustic cavity (where an assessment of the probe mechanical motion is obtained). In short, WGAS has capability for monitoring probe-sample shear-force interactions via remote acoustic sensing means. In another application, WGAS can also be used as feedback control of the probe's vertical position in SPM. In effect, it is observed that when the microscope's probe stylus approaches a sample, a monotonic change of the WGAS acoustic signal occurs in the last ~20 nm before the probe touches the solid sample's surface, which allows implem...

The applicability of near‐field scanning optical microscopy (NSOM) for optical characterization of semiconductors is discussed. The NSOM technique and some of its properties relevant to real‐time in‐situ measurements are reviewed. Several optical characterization methods widely used in the far‐field, including reflectance, reflectance‐difference spectroscopy, Raman spectroscopy, ellipsometry, and carrier lifetime, are evaluated for their use with NSOM. Experimental data are included for some of these methods. It is concluded that several, but not all, of the standard optical characterization methods can be coupled with NSOM to provide higher spatial resolution. The applicability of NSOM as a real‐time in‐situ probe shares some of the problems of other proximal probe methods, but offers enough new capabilities to warrant its application.

Dip-pen nanolithography (DPN) has attracted increased attention for its ability to generate nanometer-scale patterns on solid surface using an “ink”-coated atomic force microscope (AFM) tip. In contrast to this conventional anchoring-molecules procedure, nanopatterns can also be created by triggering the structural response of the proper substrate. In one approach, the delivery of acidic buffer from the tip into a poly(4-vinylpyridine) (P4VP) thin film (while the tip is being laterally moved, in a raster fashion, along a preprogrammed pattern) leads to the polymer swelling in response to the local protonation. This practice, however, has suffered from a lack of consistency due to the potentially many factors influencing the pattern formation. Herein we report that a more reliable strategy for well controlling the protonation process results when applying an electric field between the AFM tip and the sample. We demonstrate the improved capabilities of the electric-field-assisted DPN method towards reproducibly and reliably fabricating nanostructures by taking advantage of the responsive characteristics (i.e. swelling) of P4VP. Our work includes a systematic study of pattern fabrication under different patterning parameters (mainly the applied bias and contact force) and, very important, provides evidence of the reversible characteristic of the pattern formation process.