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Category Archives: nanotechnology

Optical tip for Near-Field Scanning Optical Microscope; Optonet Inc.; U.S. Pat. No. 8,201,268

27 Jul

U.S. Patent No. 8,201,268, issued on June 12, 2012 to OptoNet Inc. of Evanston, IL, discloses a sub-wavelength optical tip for a near-field scanning optical microscope (NSOM).

 

Due to the diffraction limit, resolution in conventional optical microscopy is limited so that features have to be larger than about one-half wavelength to be resolved.  In contrast, near-field scanning optical microscopy is able to image smaller features since its resolution is not diffraction-limited.  An NSOM scans a small optical tip (e.g., at the end of an optical waveguide) that serves as a light source in close proximity to the surface being imaged, and utilizes the evanescent field in the near-field region to detect the surface features.  The ’268 patent discloses an optical tip that has values of the refractive indices of the core and cladding of the waveguide which result in high energy throughput for near-field scanning operations and faster scanning speeds, with low localized heating at the probe.

According to its website, OptoNet “develops advanced, innovative photonic chips and modules based on proprietary approaches to monolithic integration of InP photonic devices” and “Si packaging platform design for avionic applications,” and its customers include the Navy and Air Force.  OptoNet has ties with Northwestern University’s Nano-Photonics and Quantum Electronics group.  For example, the inventors of the ’268 patent include Northwestern’s Professor S.T. Ho and Yingyan Huang, a former Ph.D. candidate, now President of OptoNet.

The company received a Small Business Innovative Research (SBIR) “Phase I” grant in 2008 of $100,000 from the National Science Foundation for developing an NSOM probe “utilizing an innovative high-refractive-index nanoscale waveguide (nanoWG) as the probing tip,” which sounds like the invention disclosed by the ’268 patent.  More recently, the company received a 2011 SBIR Phase I grant of $150,000 from the Department of Energy for developing a “proof-of-concept prototype,” with future work planned to develop ”a full series of ultra-high-power NSOM probe modules” that are plug-compatible with current NSOM probes.

According to the USPTO database, OptoNet owns four U.S. patents, three of which have been received in 2012.

 
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Posted by on July 27, 2012 in detector, fiber optics, imaging, nanotechnology, spectroscopy

 

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Process for making silicon nanowires; Bandgap Engineering Inc.; U.S. Pat. No. 8,143,143

30 May

U.S. Patent No. 8,143,143, issued on March 27, 2012 to Bandgap Engineering Inc. of Waltham, MA, discloses a process for fabricating silicon nanowires.

According to the ’143 patent, silicon nanowires have been previously grown “from the bottom up” using various deposition techniques performed under vacuum conditions, and formed by removing material from bulk silicon “from the top down” using various plasma etching techniques performed under vacuum conditions.  However, the costs and limited scalability of these techniques has hindered their use.  Existing solution-based processes to etch silicon wafers in a direction normal to the surface have had limited success in achieving diameters that are less than 100 nanometer, which the ’143 patent describes as being of value “to a variety of electronic, optoelectronic, electrochemical and electromechanical applications” since “it is within the sub-100 nm range that silicon begins to demonstrate novel properties distinguishable from the properties of bulk silicon.” 

The ’143 patent discloses a solution-based etching process that deposits sub-100 nm nanoparticles and a silver film onto the silicon wafer, which is then exposed to an etchant aqueous solution of HF and an oxidizing agent.  The silicon wafer is etched in the regions between the nanoparticles, leaving an array of sub-100 nm silicon nanowires standing up on the silicon wafer.  For example, the electron microscope micrographs above show a field of silicon nanowires that have diameters ranging from 12-70 nanometers.  The ’146 patent mentions various uses of this material, including as an interfacial layer between bulk silicon and another material, and novel LED and transistor applications.  Of particular interest to Bandgap Engineering are photovoltaic applications, which utilize the quantum confinement in the silicon nanowires to form intermediate band photovoltaic (IBPV) materials for solar cells, and as anodes in lithium ion batteries.

 According to its website, “Bandgap’s nanowire-enhanced solar cell designs combine low-cost processing with crystalline silicon to yield high-efficiency products” which are made possible by their “highly tunable silicon nanowires.”  They tout that their high-efficiency photovoltaics can reduce reflection of incident light and can “dramatically increase the optical absorption of silicon.”  The company is also developing their silicon nanowires for “high-capacity Li-ion battery anodes.”

According to the USPTO database, the ’146 patent is Bandgap Engineering’s second U.S. patent, the first being issued in July 2011 (U.S. Pat. No. 7,973,995) for an optoelectronic device having a nanowire array and a host material intermingled with the nanowire array and containing light-scattering or absorption/luminescence centers.

 
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Posted by on May 30, 2012 in materials, nanotechnology, photovoltaics

 

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