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Publications
The ability to image the optical near-fields of nanoscale structures, map their morphology, and concurrently obtain spectroscopic information, all with high spatiotemporal resolution, is a highly sought-after technique in nanophotonics. As a step toward this goal, we demonstrate the mapping of electromagnetic forces between a...
Liquid crystals can organize dispersed particles into useful and exotic structures. In the case of lyotropic cholesteric polypeptide liquid crystals, polypeptide-coated particles are appealing because the surface chemistry matches that of the polymeric mesogen, which permits a tighter focus on factors such as extended particle...
We present a theoretical and experimental analysis of the cantilever motions detected in photoinduced force microscopy (PiFM) using the sideband coupling detection scheme. In sideband coupling, the cantilever dynamics are probed at a combination frequency of a fundamental mechanical eigenmode and the modulation frequency of...
New results on the nanoscale mechanics of shale and the nano-mechanics and nano-chemistry of asphalt binder (bitumen) will be presented in the context of the history and promise of atomic force microscopy.
We report on stimulated Raman spectroscopy and nanoscopy of molecules, excited without resonant electronic enhancement gain, and recorded using near field photon induced forces. Photon-induced interaction forces between the sharp metal coated silicon tip of an Atomic Force Microscope (AFM) and a sample resulting from...
The intense local field induced near metallic nanostructures provides strong enhancements for surface-enhanced spectroscopies, a major focus of plasmonics research over the past decade. Here we consider that plasmonic nanoparticles can also induce remarkably large electromagnetic field gradients near their surfaces. Sizeable field gradients can...
Correlating spatial chemical information with the morphology of closely packed nanostructures remains a challenge for the scientific community. For example, supramolecular self-assembly, which provides a powerful and low-cost way to create nanoscale patterns and engineered nanostructures, is not easily interrogated in real space via existing...
Collagen is the major structural protein of bone, dentine and the extracellular matrix and can template the nucleation and growth of numerous mineral phases. Collagen meso-scale architecture on surfaces, which is critical for its function, is controlled by the relative magnitude of collagen-substrate (C-S) and...
FIGURE 1. Spectral photoinduced force microscopy (PiFM) images of a polystyrene-poly(methyl methacrylate) (PS-PMMA) block copolymer sample with a pitch of 40nm. Left: Image at 1492cm_-1_. Center: Image at 1732cm_-1_. Right: Topography of sample. PiFM at 1492 and 1732c_-1_ images the PS and PMMA polymer components...
A new method is presented for visualizing the electric field distributions associated with propagating surface-plasmon-polariton (SPP) modes directly in the near-field. The method is based on detecting the photo-induced gradient force exerted by the evanescent field onto a sharp and polarizable tip. Using a photo-induced...
The enormous advances made in nanotechnology have also intensified the need for tools that can characterize newly synthesized nanoaterials with high sensitivity and with high spatial resolution. Many existing tools with nanoscopic resolution or better, including scanning electron microscopy (SEM), atomic force microscopy (AFM), and...
Photo-induced force microscopy produces images with spectroscopic contrast at nanometer scale resolution. In this presentation, the basic principles of the photo-induced force microscope are described and application examples of this technique are highlighted.
We perform time-resolved pump-probe microscopy measurements by recording the local force between a sharp tip and the photo-excited sample as a readout mechanism for the material’s nonlinear polarization. We show that the photo-induced force is sensitive to the same excited state dynamics as measured in...
A theoretical and experimental analysis of the dominant forces measured in photoinduced force microscopy is presented. It is shown that when operated in the noncontact and soft-contact modes, the microscope is sensitive to the optically induced gradient force (Fg) and the scattering force (Fsc). The...
Actin filaments play essential roles in many kinds of cellular functions by interacting with hundreds of actin binding proteins. Here we probe the interaction between actin filament and a binding protein, α-actinin, using an atomic force microscopy (AFM) and dynamic force spectroscopy (DFS). The distribution...
The current challenge in the field of fluorescent nanoparticles (NPs) for bioimaging is to achieve extreme brightness and external control of their emission using biodegradable materials. Here we propose a new concept of fluorescent polymer NPs, doped with ionic liquid-like salts of a cationic dye...