Boston College Nano-Optical Antenna Compresses Light into Nanoscopic Dimensions for Easy Nanolithography

In U.S. Patent 7,634,162,   Boston College (Chestnut Hill, MA) inventors Krzysztof J. Kempa, Michael J Naughton, Zhifeng Ren,  and Jakub A. Rybczynski disclose apparatus and methods for nanolithography using nanoscale optics. Their discovery provides an inexpensive and effective solution for nanolithography that may both successfully and easily be used to create sub-micron structures

Submicron-scale structures may be obtained using standard photolithography systems with a de-magnifying lens. A de-magnifying lens for use in a standard photolithography system includes a film having a top surface, a bottom surface and a plurality of cylindrical channels containing a dielectric material; and an array of carbon nanotubes penetrating the film through cylindrical channels, wherein an image on the top surface of the film is converted into a de-magnified image on the bottom surface of the film by the carbon nanotubes.

Nano-optics is the study of optical interactions with matter on a subwavelength scale. Nano-optics has numerous applications in optical technologies such as nanolithography, optical data storage, photochemistry on a nanometer scale, solar cells, materials imaging and surface modification with subwavelength lateral resolution, local linear and nonlinear spectroscopy of biological and solid-state structures, quantum computing, quantum communication and optical networking.

Nanolithography is a method for the creation of nanoscale structures. Usually one creates a pattern of a desired nanostructure in a template material, and then uses this template to fabricate the nanostructure. Nanolithography can employ a computer controlled electron beam and an electron sensitive template material. Several other nanolithography techniques employ nanotools, like the scanning probe microscope (SPM) or atomic force microscope (ATM) to create the templates. However, these techniques are extremely expensive and slow.

The Boston College nanolithography de-magnifying lens has a metallic film with a top surface, a bottom surface and cylindrical channels containing a dielectric material; and an array of nanorods penetrating the metallic film through the cylindrical channels, the array of nanorods having a protruding portion that extends beyond a surface of the metallic film and an embedded portion that is within the metallic film.

A de-magnifying lens for use in a standard photolithography system is comprised of: a film having a top surface, a bottom surface and a plurality of cylindrical channels containing a dielectric material; and an array of carbon nanotubes penetrating and converging through the film through the plurality of cylindrical channels, wherein an image on the top surface of the film is converted into a de-magnified image on the bottom surface of the film by the carbon nanotubes, wherein each carbon nanotube connects a light-receiving pixel on the top surface of the film with a light-emitting pixel on the bottom surface of the film, and wherein the light-receiving pixels on the top surface of the film are indirectly mapped to the light-emitting pixels on the bottom surface of the film by scrambled wiring through a nano-coaxial transmission line.

The portion that extends beyond the top surface of the film and the bottom surface of the film act as nano-optical antennas for receiving, transmitting, and re-emitting an optical signal.  The de-magnifying lens forms the nano-optical antenna on the top surface of the film  and compresses the optical signal into nanoscopic dimensions. The film acts as a nano-coaxial transmission line and converts energy trapped in currents along the nano-optical antenna on the top surface of the film into a manageable signal and allows for propagation of the optical signal with a wavelength exceeding a perpendicular dimension of the carbon nanotube through the nano-coaxial transmission line. Light from an optical signal is collected by the receiving pixel on the top surface of the film which excites the nano-optical antenna on the top surface of the film to transmit the light through the nano-coaxial transmission line to the nano-optical antenna on the bottom surface of the film and re-emit the light into the light-emitting pixel. The light-receiving pixels on the top surface of the film are directly mapped to the light-emitting pixels on the bottom surface of the film by direct wiring through the nano-coaxial transmission lines.

Boston College Researchers Extend Range of Near-Field Scanning Optical Microscopy with Nanoscale Magnifiers

Nanoscale optical probes using carbon nanotubes that facilitate sub-wavelength, sub-diffraction limit, and spatial resolution for near-field scanning optical microscopes are disclosed in U.S. Patent 7,623,746.  Boston College researchers developed a nanoscale optical probe for use with a near-field scanning optical microscope that includes an inner conductor with a top end, a bottom end, and a body; a dielectric material which surrounds the inner conductor; and an outer conductor which surrounds the dielectric material.  The inner conductor is longer at a tip surface of the probe than the dielectric material and the outer conductor. The nanoscale optical probe can achieve resolutions of less than about 10 nanometers (nm) in a transverse direction. In the art for nanoscale optical probes, the Boston College probe extends the range of measurements possible compared with conventional near-field scanning optical microscopy techniques.

Professor Michael J. Naughton, Krzysztof J. Kempa and Zhifeng Ren created a magnifying element for use with a near-field scanning optical microscope.  The magnifying probe is made of a film with a top surface, a bottom surface and cylindrical channels and an array of nanoscale optical probes penetrating the film through cylindrical channels.   Each nanoscale optical probe has an inner nanowire with a top end, a bottom end, and a body; a dielectric material which surrounds the inner nanowire; and an outer metal material which surrounds the dielectric material. Because the width of the inner conductor may be significantly smaller than the wavelength of visible light, which is in the range of about 300 nm to about 700 nm, the nanoscale optical probe may be used to image objects with spatial resolution well under this range.

The inventors developed a method of fabricating a nanoscale optical probe which involves growing a carbon nanotube (CNT) on the optical fiber; depositing a dielectric material over the carbon nanotube; and depositing an outer metal material over the dielectric material. They also fabricated a nanoscale optical probe by electrodepositing a catalytic transition metal on an AFM-type tip; growing a carbon nanotube (CNT) on the optical fiber; depositing a dielectric material over the carbon nanotube; and depositing an outer metal material over the dielectric material.

Plasma enhanced chemical vapor deposition (PECVD) is used grow the carbon nanotube. A dielectric photovoltaic material having both electrical conductivity and transparency (for example silicon- and non-silicon-based materials) is deposited over the carbon nanotube via (for example, via PECVD, sputtering, or evaporation). Typically, the dielectric material is coated to yield a thickness of about 10 nm to about 200 nm. An outer metal (for example, aluminum) is then deposited (via CVD, sputtering or evaporation) over the dielectric material, forming a nanoscale optical probe having a coplanar waveguide configuration. If desired, the outer metal may be removed from the bottom surface of the probe (via focused ion beam or wet etch), thus exposing the photovoltaic material and the carbon nanotube, yielding a nano-optical antenna at the substrate surface of the probe. 

Near-field scanning optical microscopy (NSOM) is a type of microscopy where a sub-wavelength light source, usually a fiber tip with an aperture smaller than 100 nm, is used as a scanning probe over a sample. Near-field scanning optical microscopy is one in a family of scanned probe techniques that includes scanning tunneling microscopy and atomic force microscopy (AFM) where an image is obtained by raster scanning a probe across a surface collecting data at an array of points during the scan. In order to achieve an optical resolution better than the diffraction limit, the scanning probe has to be brought within the near-field region (that part of the radiated field nearest to the antenna, where the radiation pattern depends on the distance from the antenna). NSOM is based upon the detection of non-propagating evanescent waves in the near-field region. The probe is scanned over a surface of the sample at a height above the surface of a few nanometers and allows optical imaging with spatial resolution beyond the diffraction limit.

The scanning probe can either detect in the near-field directly, by means of the sub-wavelength size aperture (collection mode), or by using the probe as a waveguide with a sub-wavelength scattering source and detecting the evanescent waves as they propagate into the far-field (transmission mode). The achievable optical resolution of NSOM is mainly determined by the aperture size of the scanning probe and the probe-surface gap. NSOM may, in theory, be combined with any spectroscopic technique to gather spectra from small regions of a sample. Infrared (IR), Raman, visible, and V, as well as NSOM fluorescence, photoluminescence, photoconductance, and magnetooptical (MOKE) spectroscopies have been investigated.