MRI: Development of a New Paradigm for Apertureless Near-fieldScanning Optical Microscope

Gang-yu Liu, University of California, Davis, DMR 0723118

We have completed a new design and construction of a dual optical path near field scanning optical microscope (NSOM). The schematic diagram of the optical path and a photo of the scanner are shown in Figure 1 on the left. This NSOM enables researchers to visualize materials with nanometer resolution in topographic images, in addition, the NSOM signal taken at the same time of the topography provides spectroscopy information of the materials underneath. This availability of the visible (405 and 530 nm) and IR (980 nm) light broadens the materials that can be probed using this set up. The use of 980 nm enables the investigation of rare earth based nanomaterials which have great potential in bioimaging and photovoltaic applications.

Figure 1: Schematic and picture of the current configuration of the combined Asylum AFM and inverted microscope for near-field scanning optical microscopy (NSOM) and optical characterization of rare-earth doped nanocrystals.

The final goal of microscopy technology development is to visualize the object with molecular or nanometer resolution as well as to know the functionality of the materials. The NSOM technique has long been recognized as a potential solution towards this goal. The broader applications have long been hampered by the lack of sensitivity and high difficulties in operating NSOM. The proposed approach offers a simple to operate and high sensitivity configuration to NSOM technology development. With the completion of the construction, we anticipate revealing information about materials be forthcoming, as exampled by the results on the right..

Figure 2. NOSM imaging of NaYF4:Yb,Er nanocrystal arrays generated by particle lithography. Optical image of the upconversion luminescence collected upon the excitation with the 980 nm laser and an AFM image and its corresponding line scan of the same region. The size of the nanocrystal may be extracted from the cursor profiles under the images.

MRI: Development of a New Paradigm for Apertureless Near-fieldScanning Optical Microscope

Gang-yu Liu, University of California, Davis, DMR 0723118

Broad Impact:

The funded work is disseminated by a variety of venues. During the projectyear 2007-2008 Liu’s postdoc, Dr. Valentin Leulevych, was invited to present talks in ACS meeting. The NSOM imaging of metal nanoarrays was presented by Liu’s student, Weifeng Lin at 2009 CPIMA Forum at IBM Research Center. In 2009, Liu’s postdoc, Dr. TJ Mullen, presented the NSOM imaging of rare earth nanostructures at ACS National Meeting and was well received. So far, 10 students and postdocs have participated construction and utilization of this NOSM. Since it is not completed, we anticipate much more usage in the final grant year.

NSOM has hosted various outreach activities including (a) summer students from local high school, typically, under-represented minorities; (b) a “must see” point during visits by prospective students at department of chemistry and NEAT ORU; (c) incubating international collaborations with China under UC’s 10+10 Aliance program, for which Liu is in charge of coordination at UC Davis. China has the largest rare earth resources, more than 80% of the world total reserve. The strong interests from Chinese researchers to collaborate on rare earth nanomaterials is mainly due to the availability of this NOSM with 980 nm excitation. To our knowledge, this is the only apertureless NSOM with this capability.

MRI: Development of a New Paradigm for Apertureless Near-fieldScanning Optical Microscope

Gang-yu Liu, University of California, Davis, DMR 0723118