RESUMEN
Rapid nanoscale imaging of the bulk heterojunction layer in organic solar cells is essential to the continued development of high-performance devices. Unfortunately, commonly used imaging techniques such as tunneling electron microscopy (TEM) and atomic force microscopy (AFM) suffer from significant drawbacks. For instance, assuming domain identity from phase contrast or topographical features can lead to inaccurate morphological conclusions. Here we demonstrate a technique known as photo-induced force microscopy (PiFM) for imaging organic solar cell bulk heterojunctions with nanoscale chemical specificity. PiFM is a relatively recent scanning probe microscopy technique that combines an AFM tip with a tunable infrared laser to induce a dipole for chemical imaging. Coupling the nanometer resolution of AFM with the chemical specificity of a tuned IR laser, we are able to spatially map the donor and acceptor domains in a model all-polymer bulk heterojunction with resolution approaching 10 nm. Domain size from PiFM images is compared to bulk-averaged results from resonant soft X-ray scattering, indicating excellent quantitative agreement. Further, we demonstrate that in our all-polymer system, the AFM topography, AFM phase, and PiFM show poor correlation, highlighting the need to move beyond standard AFM for morphology characterization of bulk heterojunctions.
RESUMEN
Developing a sensor that identifies and quantifies trace amounts of analyte molecules is crucially important for widespread applications, especially in the areas of chemical and biological detection. By non-invasively identifying the vibrational signatures of the target molecules, surface-enhanced Raman scattering (SERS) has been widely employed as a tool for molecular detection. Here, we report on the reproducible fabrication of wafer-scale dense SERS arrays and single-nanogap level near-field imaging of these dense arrays under ambient conditions. Plasmonic nanogaps densely populated the spaces among globular Ag nanoparticles with an areal density of 120 particles per µm2 upon application of a nanolithography-free simple process consisting of the Ar plasma treatment of a polyethylene terephthalate substrate and subsequent Ag sputter deposition. The compact nanogaps produced a high SERS enhancement factor of 3.3 × 107 and homogeneous (coefficient of variation of 8.1%) SERS response. The local near fields at these nanogaps were visualized using photo-induced force microscopy that simultaneously enabled near-field excitation and near-field force detection under ambient conditions. A high spatial resolution of 3.1 nm was achieved. Taken together, the generation of a large-area SERS array with dense plasmonic nanogaps and the subsequent single-nanogap level characterization of the local near field have profound implications in the nanoplasmonic imaging and sensing applications.
RESUMEN
A new approach for generating high-speed multispectral confocal images has been developed. The central concept is that spectra can be acquired for each pixel in a confocal spatial scan by using a fast spectrometer based on optical fiber delay lines. This approach merges fast spectroscopy with standard spatial scanning to create datacubes in real time. The spectrometer is based on a serial array of reflecting spectral elements, delay lines between these elements, and a single element detector. The spatial, spectral, and temporal resolution of the instrument is described and illustrated by multispectral images of laser-induced autofluorescence in biological tissues.