Surface roughness measurement on microchannels by atomic force microscopy using a bent tapered fiber probe

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Surface roughness measurement on microchannels by atomic force microscopy using

a bent tapered fiber probe

Sy-Hann Chen, Heh-Nan Lin, and Chii-Ron Yang

Citation: Review of Scientific Instruments 71, 3953 (2000); doi: 10.1063/1.1288234 View online: http://dx.doi.org/10.1063/1.1288234

View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/71/10?ver=pdfcov

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Surface roughness measurement on microchannels by atomic force

microscopy using a bent tapered fiber probe

Sy-Hann Chen

Department of Electrophysics, National Chiao Tung University, Hsinchu 300, Taiwan,

and Precision Instrument Development Center, National Science Council, Hsinchu 300, Taiwan, Republic of China

Heh-Nan Lina)

Department of Materials Science and Engineering, National Tsing Hua University, Hsinchu 300, Taiwan, Republic of China

Chii-Ron Yang

Precision Instrument Development Center, National Science Council, Hsinchu 300, Taiwan, Republic of China

共Received 9 May 2000; accepted for publication 11 June 2000兲

We demonstrate a high-resolution and nondestructive surface roughness measurement on microchannels by atomic force microscopy with the use of a bent tapered optical fiber probe. The probe was fabricated by a combination of laser heating-pulling and electric arc bending. Microchannels with a width of 41.5␮m and a height of 31.9␮m were fabricated on polycarbonate by excimer laser ablation and the resultant roughness was measured to be 4.8 nm. © 2000

American Institute of Physics. 关S0034-6748共00兲00210-0兴

The advances in microfabrication technology have real-ized microfluidic systems for biological diagnosis and chemical analysis.1–5 To perfect their performance, efforts on quantitative analysis of fluid flow6–8 inside the micro-channels in such systems have also been carried out. In ad-dition to other parameters, the surface roughness is known to play a role and a precise measurement of the roughness is therefore desirable. As the roughness is usually in the nm range, it is difficult to apply conventional techniques such as stylus profilometry, optical profilometry, or scanning elec-tron microscopy for such purposes.

Atomic force microscopy共AFM兲,9on the other hand, is the ideal technique for nanoscale roughness measurement. The tip heights of commercially available AFM probes, how-ever, are in the range of a few microns and thus inadequate for the investigation of microchannels. On the contrary, it is well known that bent tapered optical fiber probes can be produced with controllable bend angles and lengths, and uti-lized directly in AFM with comparable resolution and with-out instrument modification.10,11In this note, we make use of a bent tapered fiber probe with a bent length of around 750

␮m and the desired measurement can thus be realized. The bent probe was fabricated by a combination of laser heating-pulling12 and electric arc bending.11 A commercial

CO2 laser fiber pulser共P-2000, Sutter Instrument兲 was used

to produce a straight fiber probe from a 125␮m telecommu-nication single mode optical fiber 共SMV130, Prime Optical Fiber Corporation, Taiwan兲. Figure 1共a兲 shows the end part of a long and thin straight fiber probe with a tip diameter of around 100 nm as determined from scanning electron micro-scope measurement. The straight probe was then bent by a homemade electric arc instrument. After the bent probe was produced, a 5 nm Pt/Pd film was coated on the back of the probe by ion sputtering 共E1010, Hitachi, Japan兲 to increase the reflectivity necessary for normal force detection. The probe was then glued to a Si substrate for suitable placement in an AFM cantilever holder and the result is shown in Fig. 1共b兲. The cantilever length, i.e., the length measured from the bent point to the edge of the substrate, and the bent

a兲_{Author to whom correspondence should be addressed; electronic mail:} [email protected]

FIG. 1. Photographs of共a兲 the straight fiber probe and 共b兲 the bent probe with a bend angle of 70°.

REVIEW OF SCIENTIFIC INSTRUMENTS VOLUME 71, NUMBER 10 OCTOBER 2000

NOTES

BRIEF contributions in any field of instrumentation or technique within the scope of the journal should be submitted for this section. Contributions should in general not exceed 500 words.

3953

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length, i.e., the length from the bent point to the tip end, were around 1100 and 750␮m, respectively.

Microchannels were generated on a polycarbonate sub-strate with the use of an excimer laser micromachining sta-tion 共Series 7000, Exitech, England兲 operated at a wave-length of 248 nm. The fabrication detail can be found elsewhere.13 A photograph of the sample is shown in Fig. 2共a兲 with the bright stripes corresponding to the irradiated and ablated regions. The channels had a width and a depth of approximately 41.5 共W value兲 and 31.9 ␮m 共H value兲, re-spectively, as determined by an optical surface profiler共New View 5000, Zygo, USA兲 and the result is shown in Fig. 2共b兲. Tapping mode AFM was first tested on the sample, but the resolution was not high enough if a large probe vibration

amplitude was set as the feedback. For a small feedback amplitude, the sample surface was unfortunately easily dam-aged. On the contrary, high-resolution images could be ob-tained without sample damage by using a small force in con-tact mode operation. Surface images of 10⫻10 ␮m2 at an unirradiated region and a microchannel are presented in Figs. 2共c兲 and 2共d兲, respectively. The root-mean-square roughness values before and after laser exposure are approximately 0.8 and 4.8 nm, respectively. Also Fig. 2共d兲 provides a detailed picture of surface roughening. Application of the present technique could potentially make a valuable contribution to a precise understanding and control of the fluid flow in micro-fluidic systems.

1

Micro Total Analysis Systems ’98, edited by D. J. Harrison and A. van den

Berg共Kluwer, Dordrecht, 1998兲.

2_{P. C. Simpson, D. Roach, A. T. Woolley, T. Thorsen, R. Johnston, G. F.} Sensabaugh, and R. A. Mathies, Proc. Natl. Acad. Sci. USA 95, 2256

共1998兲.

3

B. H. Weigl and P. Yager, Science 283, 346共1999兲.

4_{R. S. Kane, S. Takayama, E. Ostuni, D. E. Ingber, and G. M. Whitesides,} Biomaterials 20, 2363共1999兲.

5_{M. Koch, C. G. J. Schabmueller, A. G. R. Evans, and A. Brunnschweiler,} Sens. Actuators A 74, 207共1999兲.

6_{K. Hosokawa, T. Fujii, and I. Endo, Anal. Chem. 71, 4781}_共1999兲. 7_{A. E. Kamholz, B. H. Weigl, B. A. Finlayson, and P. Yager, Anal. Chem.}

71, 5340共1999兲.

8_{I. Papautsky, J. Brazzle, T. Ameel, and A. B. Frazier, Sens. Actuators A} 73, 101共1999兲.

9_{S. N. Magonov and M.-H. Whangbo, Surface Analysis with STM and}

AFM共VCH, Weinheim, 1996兲.

10_{K. Lieberman, A. Lewis, G. Fish, S. Shalom, T. M. Jovin, A. Schaper, and} S. R. Cohen, Appl. Phys. Lett. 65, 648共1994兲.

11

H.-N. Lin, U. Lewlomphaisarl, S. H. Chen, L. J. Lee, and D. P. Tsai, Rev. Sci. Instrum. 69, 3843共1998兲.

12_{G. A. Valaskovic, M. Holton, and G. H. Morrison, Appl. Opt. 34, 1215}

共1995兲.

13

C. R. Yang, B. C. S. Chou, H. Y. Chou, F. H. H. Lin, W. K. Kuo, R. K. S. Luo, J. W. Chang, and Z. J. Wei, Proc. SPIE 3511, 342共1998兲. FIG. 2.共a兲 Photograph of microchannels 共bright stripes兲 on a polycarbonate

substrate made by excimer laser micromachining.共b兲 Surface profile of the microchannels with a width W and a depth H of 41.5 and 31.9␮m, respec-tively.共c兲 10⫻10␮m2_{contact mode AFM images on an unexposed region} and共d兲 on a microchannel. The root-mean-square roughness values before and after laser ablation are 0.8 and 4.8 nm, respectively.

3954 Rev. Sci. Instrum., Vol. 71, No. 10, October 2000 Chen, Lin, and Yang