Dual-pulse photoactivated atomic force microscopy

Abstract

Photoactivated atomic force microscopy (pAFM), which integrates light excitation and mechanical detection of the deflections of a cantilever tip, has become a widely used tool for probing nanoscale structures. Raising the illuminating laser power is an obvious way to boost the signal-to-noise ratio of pAFM, but strong laser power can damage both the sample and cantilever tip. Here, we demonstrate a dual-pulse pAFM (DP-pAFM) that avoids this problem by using two laser pulses with a time delay. The first laser heats the light absorber and alters the local Grüneisen parameter value, and the second laser boosts the mechanical vibration within the thermal relaxation time. Using this technique, we successfully mapped the optical structures of small-molecule semiconductor films. Of particular interest, DP-pAFM clearly visualized nanoscale cracks in organic semiconductor films, which create crucial problems for small-molecule semiconductors. DP-pAFM opens a promising new optical avenue for studying complex nanoscale phenomena in various research fields.

Time-Domain Photothermal AFM Spectroscopy via Femtosecond Pulse Shaping

“…Although nonlinear signals are possible and measurable in higher-order experiments, such as transient absorption and 2D white light spectroscopy, these nonlinear signals are 3 orders of magnitude less than the linear signals. In addition, we do not observe the nonlinear thermal expansion effect, which would result in a slope of the FID but is not present in the FTPT data.…”

Shear‐Force Photoacoustic Microscopy: Toward Super‐Resolution Near‐Field Imaging

“…Unlike general optical imaging requires an exogenous fluorescent agent or staining for contrast imaging, it is possible to detect nanoscale surface defects, chemical mapping, and DNA or cell nucleus imaging of a sample by using the unique intrinsic light absorption properties of the sample. [16,17,22,[40][41][42] To obtain the near fields, we first used an uncoated, tapered fiber with an aperture size of 100 nm. Typically, the metal-coated tapered fibers were used to maximize light confinement in the near field, whereas the uncoated fiber was used to avoid unwanted PA signals from the coating (Figure S6, Supporting Information).…”

“…[ 12–15 ] Therefore, OR‐PAM has paved the way for the provision of information based on light absorption properties in a broad range of applications, spanning biological imaging, such as microvascular networks and cellular structures, to industrial imaging, such as metal surface defect detection. [ 16–23 ]…”

“…[12][13][14][15] Therefore, OR-PAM has paved the way for the provision of information based on light absorption properties in a broad range of applications, spanning biological imaging, such as microvascular networks and cellular structures, to industrial imaging, such as metal surface defect detection. [16][17][18][19][20][21][22][23] OR-PAM requires an optical objective to achieve high spatial resolution. [12,24,25] Therefore, additional optical alignment and optics are required to use the objective.…”

Tapered fiber-based shear force scanning photoacoustic microscopy

“…OR-PAM provides high optical contrast by using the light absorption characteristics of an object and high lateral resolution by using densely focused light beam using an objective lens 2,9,10 . As a result, OR-PAM has been employed in a variety of applications, ranging from medical imaging to industrial imaging [11][12][13][14][15][16][17][18][19][20] .…”