| AVS 60th International Symposium and Exhibition | |
| Nanometer-scale Science and Technology | Wednesday Sessions |
| Session NS+AS+BI+SP-WeM |
| Session: | Nanoscale Imaging and Microscopy |
| Presenter: | K. Kimura, Kyoto University, Japan |
| Authors: | K. Kimura, Kyoto University, Japan K. Kobayashi, Kyoto University, Japan H. Yamada, Kyoto University, Japan |
| Correspondent: | Click to Email |
Imaging of deeply buried subsurface features in soft matrices such as parasites in red blood cells [1], carbon nanoparticles in living cells [2], and buried electronic circuit in industrial products [3] have been demonstrated by heterodyne force microscopy [4] (HFM). Subsurface imaging using ultrasonic AFM (UAFM), which is a technique to evaluate contact stiffness with high sensitivity, has also been demonstrated in some papers. However, UAFM has been mainly applied for imaging subsurface features in hard matrices such as Si and metals, whose resolved maximum depth was typically less than 200 nm [5]. In this study, we visualized Au nanoparticles buried in a polymer matrix under 960 nm from the surface by using HFM and UAFM, which has never been achieved [6].
A dispersion of Au particles (50-nm-diameter) was dropped on a polyimide sheet (125-micro-meter-thick). After drying, a top-coat (photo polymer) was spin-coated on it and annealed at 150°C. Top-coat thickness was estimated from the film coated on a Si wafer. We used a modified commercial AFM instrument (JEOL: JSPM 4200). The sample was directly glued on a piezoelectric plate, which was fixed on a tube scanner. Another piezoelectric plate for HFM was attached on a cantilever holder. The contact resonance frequency used for imaging was determined by measuring the thermal noise spectrum of the cantilever contacted on the sample. The schematic diagrams of HFM and UAFM are shown in Figs. 1 and 2 in the supplemental file.
We performed subsurface imaging for the samples with the top-coat thickness of up to 1 micro-meter. We found that the maximum depth of the subsurface features resolved by HFM and UAFM depends on the spring constant (k) of the cantilever. Figure 3 in the supplemental file shows subsurface images of Au particles buried under a top-coat of 900-nm-thick obtained by UAFM using a Si cantilever (k: 1.3 N/m), which we found the most suitable for subsurface imaging on the polymer matrix. We suppose that subsurface features in a soft matrix at least buried under 1 micro-meter from the surface affect surface viscoelasticity, which are detected by AFM techniques when a cantilever of suitable stiffness is used.
This work was supported by the Murata Science Foundation and Grant-in-Aids from the Japan Society for the Promotion of Science (JSPS).
[1] G. S. Shekhawat et al., Science 310 (2005) 89.
[2] L. Tetard et al., Nature Nanotech. 3 (2008) 501.
[3] S. Hu et al., J. Appl. Phys. 109 (2011) 084324.
[4] M. T. Cuberes et al., J. Phys. D 33 (2000) 2347.
[5] Z. Parlak et al., J. Appl. Phys. 103 (2008) 114910.
[6] K. Kimura et al., Ultramicroscopy (2013) in press (10.1016/j.ultramic.2013.04.003).