Reconstruction of atomic force microscopy image by using nanofabricated tip characterizer toward the actual sample surface topography

Transcription

1 Supplemental Material Reconstruction of atomic force microscopy image by using nanofabricated tip characterizer toward the actual sample surface topography Mingsheng Xu 1,*, Daisuke Fujita 2,3,*, and Keiko Onishi 2 1 International Center for Young Scientists, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki , Japan 2 Advanced Nano Characterization Center, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki , Japan 3 International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki , Japan Fax: (+81) * Corresponding Author XU.Mingsheng@nims.go.jp (Dr. M. S. Xu), FUJITA.Daisuke@nims.go.jp (Prof./Dr. D. Fujita) 1

2 We performed tip estimation and image reconstruction by using three commercial softwares (P1, P2 and P3). Figure S1 and S2 are the results obtained with P1; Figure S3 is attained with P2; and Figure S4-S6 are with P3. The results obviously suggest that those image reconstruction programs based on blind tip estimation are not reliable. Figure S1. Tip shape estimated by using P1 to measure nanofabricated Si tip characterizer as shown in Figure S7a; (a) Top-view of estimated tip shape; (b) 3D view of estimated tip shape. From the 3D view image (b), we can see that the estimated tip shape exhibits obviously difference from the SEM observation in Figure S1(e). We changed tip estimation parameters such as pixel sizes of X and Y and noise threshold in accordance with the instructions of the tip estimation method, however, the resultant tip shapes were similar to the result here. 2

3 Figure S2. Reconstruction of the AFM image (size: 2.0 µm 2.0 µm) of nanofabricated Si tip characterizer by applying the estimated tip shape in Figure S6 to the image reconstruction program (P1). The tip characterizer features vertical-side-walls and 250 nm line-width of the rectangular ridges; (a) Original AFM image (before reconstruction); (b) Reconstructed image; (c) Typical cross-sectional line profiles before and after reconstruction. We used more than 10 sets of the parameters for tip estimation and applied the estimated tip shapes to the software. Unfortunately, either no obvious change of the vertical-side-walls was produced or the features marked with blue ellipses in (c) were present. 3

4 Figure S3. Tip estimation by using commercial program (P2) to various tip characterizers; (a) Anodic porous alumina tip characterizer, (Left: AFM image, Right: estimated tip shape); (b) Sharp protrusion on Si, (Left: AFM image, Right: estimated tip shape); (c) nanofabricated Si tip characterizer, (Left: AFM image, Right: estimated tip shape). Diameter means the diameter of the estimated tip at the position of 10 nm from tip apex. We can see that the estimated tip shapes are very strange and similar to the tip characterizers (Surely, not reconstructed image of the tip characterizer). Also, the tip analysis processing of P2 can only display 3D image of estimated tip shape. Although our version of the AFM image processing software does not have image reconstruction function (We are told to pay more for that), we believe that it is most unlikely to accurately restore AFM images by using such estimated tip shapes. 4

5 Figure S4. Tip estimation and image reconstruction of anodic porous alumina tip characterizer by using P3; (a) AFM image acquired by using a supersharp AFM tip; (b) Topview and (c) 3D-view of estimated tip shape. Although the resultant radii are in line with tip supplier, the cone angles are too larger; (d) Reconstructed image of the tip characterizer. After reconstruction, we see that the spikes became smaller to some degree. It seems that the blind reconstruction of P3 software worked well with anodic porous alumina, however, as seen in Figure S10 and S11, strange results were got by using P3. 5

6 Figure S5. Tip estimation and image reconstruction of nanofabricated Si tip characterizer by using P3; (a) AFM image acquired by using the same supersharp AFM tip as in Fig. S9; (b) top-view of estimated tip shape; (c) reconstructed image of the tip characterizer. The resultant tip shape is very strange and eroded little the sample as seen in (c); (d) and (e) Estimated tip crosssectional X and Y directions, respectively. Commercial software P3 did not work well with nanofabricated Si tip characterizer. 6

7 Figure S6. Estimating tip shape by using anodic porous alumina and reconstructing AFM image of nanofabricated Si tip characterizer by using P3; (a) Anodic porous alumina (AFM image of tip characterizer); (b) Estimated tip shape; (c) Original AFM image of nanofabricate Si tip characterizer; (d) Reconstructed image of the nanofabricated Si tip characterizer by using the tip shape in (b). We used different sets of tip estimation parameters, however, the reconstructed image were similar to the present one and is not accurate at all. Figs. S9-S11 suggest that the program (P3) is truly based on blind tip estimation, which means one cannot apply a tip shape estimated with tip characterizers to reconstruct other AFM image but the AFM image of tip characterizers. The program may only reconstruct special sample surfaces as shown in Fig. S9. 7

8 Our image reconstruction as below. (a) (b) θ (c) (d) (e) Figure S7. SEM images of AFM tips; (a) Used carbon nanotube (CNT) tip, θ is the inclined angle of CNT probe again the z-axis of the tip that is bonded, which is believed to be different from each CNT probe; (b) Used conventional AFM tip; (c) Used super sharp AFM tip; (d) New super sharp tip; (e) Top view of a used super sharp AFM tip. 8

9 (a) (b) (c) (d) Figure S8. Reconstruction of the AFM image of anodic porous alumina film acquired by CNT tip; (a) Two-dimensional view of the obtained AFM image (1000 nm 1000 nm); (b) Image reconstructed from the AFM image in panel (a); (c) Three-dimensional view of the AFM image with pixels; (d) Three-dimensional view of the reconstructed image. The original AFM image shows obvious artifacts. 9

10 (a) (b) (c) (d) Figure S9. Reconstruction of the AFM image of anodic porous alumina film acquired by conventional AFM tip; (a) Two-dimensional view of the obtained AFM image (1000 nm 1000 nm); (b) Image reconstructed from the AFM image in panel (a); (c) Three-dimensional view of the AFM image with pixel; (d) Three-dimensional view of the reconstructed image. The original AFM image shows obvious artifacts. 10

11 (a) (b) (c) (d) Figure S10. Reconstruction of the AFM image of anodic porous alumina film acquired by ultrasharp tip; (a) Two-dimensional view of the AFM image (1000 nm 1000 nm); (b) Image reconstructed from the AFM image in panel (a); (c) Three-dimensional view of the AFM image with pixels; (d) Three-dimensional view of the reconstructed image. No obvious difference is observed between the original AFM image and the reconstructed image. 11

12 Figure S11. Tip estimation by using a standard nanosphere. This work is in progress. 12