Aaron Lewis, Ph.D. - US grants

A near field scanning optical microscope (NSOM) will be designed and constructed which will have at least 500A spatial resolution (using visible light) and spectral selectivity. It will be based on the near field collimation of radiation and on recent demonstration of techniques to transmit visible light through apertures as small as 1/16 the wavelength. Contrast and resolution tests will be completed on patterns generated with the electron beam lithographic capabilities at the National Research and Resource Facility for Submicron Structures at Cornell. Various modes of illumination and detection will be investigated to maximize the contrast and signal to noise in this new form of super-resolution light microscopy. The working scanning optical microscope that will be constructed will have a spatial resolution comparable to that of a scanning electron microscope but will be inherently non-destructive since it does not use ionizing radiation and does not require the sample to be placed in a vacuum. It will have enormous potential in biology and medicine since it will be able to view living systems at a resolution between 80A (the limit of chemical labeling methods) and 2500A (the limit of fluorescence microscopy). Such an instrument will permit non-destructive measurements for integrated circuit metrology.

The need to concentrate optical radiation to dimensions less than a wavelength will increase as lightwave technology develops. This will arise out of the desire to have an increasing conentration of devices per unit wavelength squared as well as the necessity to guide optical radiation among the devices. The present effort is directed toward this end. Beginning with a micropipette, a fiber having exceedingly small dimensions is drawn.

The Hopfield neural network has two important aspects. The first is a thresholding amplification scheme. In the simplest situation this can be an electronic amplifier whose output does not go beyond a certain level even if the input to the amplifier is increased. The second aspect characteristic of the network is that of being able to interconnect the outputs of all amplifiers with the inputs of all amplifiers through paths which have specified but selectable resistances to the flow of electrons. The research addresses this latter problem. Photo-sensitive material will be used to program these interconnections to enable the network to be changed at will and show the full flexibility of the Hopfield network.

In preliminary experiments a novel method for focusing and amplifying electromagnetic radiation has been discovered. This method is cheap, reproducible and readily available and is capable of effectively focusing a wide spectrum of radiation from visible light to x-rays and even acoustic waves. The method involves heating a glass capillary and applying tension to produce a variety of capillary geometries with outer diameters at the tip that can be <50nm. There are apertures at these tips which are, for the smallest pipettes, considerably less than 50nm. Such capillaries are not novel; they have been used for approximately a decade by biologists to inject substances into cells. The novelty of these capillaries is to focus and amplify light beyond the diffraction limit and to produce sub-micron intense x-ray spots.