Jay K. Trautman

Near-Field Optics: Microscopy, Spectroscopy, and Surface Modification Beyond the Diffraction Limit

The near-field optical interaction between a sharp probe and a sample of interest can be exploited to image, spectroscopically probe, or modify surfaces at a resolution (down to ∼12 nm) inaccessible by traditional far-field techniques. Many of the attractive features of conventional optics are retained, including noninvasiveness, reliability, and low cost. In addition, most optical contrast mechanisms can be extended to the near-field regime, resulting in a technique of considerable versatility. This versatility is demonstrated by several examples, such as the imaging of nanometric-scale features in mammalian tissue sections and the creation of ultrasmall, magneto-optic domains having implications for highdensity data storage. Although the technique may find uses in many diverse fields, two of the most exciting possibilities are localized optical spectroscopy of semiconductors and the fluorescence imaging of living cells.

Breaking the Diffraction Barrier: Optical Microscopy on a Nanometric Scale

In near-field scanning optical microscopy, a light source or detector with dimensions less than the wavelength (λ) is placed in close proximity (λ/50) to a sample to generate images with resolution better than the diffraction limit. A near-field probe has been developed that yields a resolution of ∼12 nm (∼λ/43) and signals ∼104- to 106-fold larger than those reported previously. In addition, image contrast is demonstrated to be highly polarization dependent. With these probes, near-field microscopy appears poised to fulfill its promise by combining the power of optical characterization methods with nanometric spatial resolution.

Near‐field magneto‐optics and high density data storage

Near‐field scanning optical microscopy (NSOM) has been used to image and record domains in thin‐film magneto‐optic (MO) materials. In the imaging mode, resolution of 30–50 nm has been consistently obtained, whereas in the recording mode, domains down to ∼60 nm have been written reproducibly. Data densities of ∼45 Gbits/in.2 have been achieved, well in excess of current magnetic or MO technologies. A brief analysis of speed and other issues indicates that the technique may represent a viable alternative to these and other methods for anticipated high density data storage needs.

Imaging and Time-Resolved Spectroscopy of Single Molecules at an Interface

Far-field microscopy was used to noninvasively measure the room-temperature optical properties of single dye molecules located on a polymer-air interface. Shifts in the fluorescence spectrum, due to perturbation by the locally varying molecular environment, and the orientation of the transition dipole moment were correlated to variation in the excited-state lifetime. The lifetime dependence on spectral shift is argued to result from the frequency dependence of the spontaneous emission rate; the lifetime dependence on dipole orientation was found to be a consequence of the electromagnetic boundary conditions on the fluorescent radiation at the polymer-air interface.

Polarization contrast in near-field scanning optical microscopy

Recent advances in probe design have led to enhanced resolution (currently as significant as ~ 12 nm) in optical microscopes based on near-field imaging. We demonstrate that the polarization of emitted and detected light in such microscopes can be manipulated sensitively to generate contrast. We show that the contrast on certain patterns is consistent with a simple interpretation of the requisite boundary conditions, whereas in other cases a more complicated interaction between the probe and the sample is involved. Finally application of the technique to near-filed magneto-optic imaging is demonstrated.

Optical spectroscopy of a GaAs/AlGaAs quantum wire structure using near‐field scanning optical microscopy

We report the first spectroscopic study using a low temperature near‐field scanning optical microscope. We have studied an array of GaAs/AlGaAs cleaved edge overgrowth quantum wires. The three luminescence peaks originate from different structures in the sample: The (001)‐oriented multiple quantum wells, the (110)‐oriented single quantum well, and the quantum wires. The linewidth of the quantum wire emission is related to roughness in the (110)‐oriented single quantum well. Quenching of the multiple quantum wells and single quantum well emission near the quantum wires is attributed to diffusion of photoexcited carriers into the wires.

Design and implementation of a low temperature near‐field scanning optical microscope

The design and implementation of a low temperature (T≥1.5 K), near‐field scanning optical microscope are described herein. This microscope, which is based on the recently developed tapered fiber probe, is optimized for luminescence imaging and spectroscopy of mesoscopic semiconductor systems.

Image contrast in near-field optics

The resolution of optical microscopy can be extended beyond the diffraction limit by placing a source or detector of visible light having dimensions much smaller than the wavelength, λ, in the near‐field of the sample (<λ/10). This technique, near‐field scanning optical microscopy, is sensitive to a variety of important sample properties including optical density, refractive index, luminescence, and birefringence. Although image contrast based on certain sample characteristics is similar to that observed in traditional optical microscopy, strong coupling between the probe and sample often produces contrast unique to the near‐field.

High density near‐field optical recording (invited) (abstract)

Near‐field scanning optical microscopy (NSOM) has been used to image and record domains in thin‐film magneto‐optic (MO) materials (e.g., a Co/Pt multilayer). In this technique, a subwavelength‐sized source or detector of visible light is placed in close proximity to a sample and raster scanned to read or write data on a scale inaccessible to traditional lens based systems. The technique, therefore, represents a hybridization of conventional magnetic and MO storage technologies. In the imaging mode, resolution of 30–50 nm has been consistently obtained, whereas in the recording mode, domains down to −60 nm have been written reproducibly. Data densities of −45 Gbits/in.2 have been achieved, well in excess of current magnetic and MO methods. A brief analysis of speed and other issues indicates that the technique may represent a viable alternative to these and other methods for anticipated high density data storage needs.