Nanometer-Scale Infrared Spectroscopy of Heterogeneous Polymer Nanostructures Fabricated by Tip-Based Nanofabrication

Abstract

There is a significant need for chemical identification and chemical imaging of nanofabricated structures and devices, especially for multiple materials integrated at the nanometer scale. Here we present nanofabrication, chemical identification, and nanometer-scale chemical imaging of polymer nanostructures with better than 100 nm spatial resolution. Polymer nanostructures of polyethylene, polystyrene, and poly(3-dodecylthiophene-2,5-diyl) were fabricated by tip-based nanofabrication. Nanometer-scale infrared measurements using atomic force microscopy infrared spectroscopy (AFM-IR) obtained quantitative chemical spectra of these nanostructures. We show chemical imaging of intersecting patterns of nanometer-scale polymer lines of different chemical compositions. The results indicate that for closely packed heterogeneous nanostructures, the spatial resolution of AFM-IR is not limited by nanometer-scale thermal diffusion, but is instead limited by the cantilever sensitivity and the signal-to-noise ratio of the AFM-IR system.

Nanoscale Chemical-Mechanical Characterization of Nanoelectronic Low-kDielectric/Cu Interconnects

“…[13][14][15][16][17][18][19][20] Of these, the atomic force microscope (AFM) IR technique, which is based on photothermally induced resonance (PTIR), 21,22 has recently garnered significant interest due to a demonstrated spatial resolution of 25-100 nm, and a close correlation to micron-scale Fourier transform infrared (FTIR) spectroscopy. 13,14 This combination has resulted in the utilization of AFM-IR in a number of biological, [23][24][25] polymeric, [26][27][28] and semiconductor [29][30][31] applications. However, AFM-IR and related techniques have yet to be routinely combined with other AFM based techniques to achieve the ultimate goal of nanoscale structure-property characterization.…”

Infrared Imaging and Spectroscopy Beyond the Diffraction Limit

“…PTIR characterization has been applied to investigate a wide array of samples including bacteria (28,29,(103)(104)(105)(106), cells (107)(108)(109)(110), lipids (111), proteins (112), polymers (30,(113)(114)(115)(116)(117)(118)(119)(120)(121), drugs (122,123), quantum dots (124), plasmonic nanostructures (97,(125)(126)(127), metal-organic frameworks (128), and organo-trihalide perovskites (129). PTIR setups require a pulsed, spectrally narrow, wavelength-tunable laser source; an AFM tip operating in contact mode; and far-field optics to focus light under the tip.…”

“…In fact, mismatches in phonon energy and density of states across different materials can cause phonon scattering instead of transmission, resulting 15 in interfacial thermal resistance (154,155). Even if not completely understood, these effects favor high lateral resolution in PTIR, which is typically 100 nm or better (30,104,107,114,116). Recently, the PTIR spectra range was extended to the visible range, enabling the acquisition of correlated vibrational (chemical) and electronic property maps and spectra with a wavelengthindependent resolution as high as ≈20 nm (130).…”

Nanoscale infrared absorption imaging permits non-destructive intracellular photosensitizer localization for subcellular uptake analysis

“…16 This restriction on resolution prevents IR imaging of many important cell features, a limitation that has driven IR biological studies into the near field. 17 One such emerging method is IR nanospectroscopic absorption imaging 11 , which enables chemically specific spectroscopic mapping and label-free chemical identification of materials at the nanoscale 18 .…”

“…However, the nanoimaging method is not diffraction limited and can achieve similar results, but with a much higher resolution, limited only by the AFM tip apex dimensions and not thermal effects. 18 In Figure 4c, by observation of the red channel intensity ranges for the sapphire background (dotted line), membrane (grey line) and cytoplasm and nucleus (black line), a simple image analysis method is suggested for localizing TBOGNPs within cells. Significant channel intensity for this wavelength ratio is only evident in from the cytoplasm red channel, a result which is confirmed by fluorescence microscopy in Figure 4a.…”