Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1998-12-29
2001-08-07
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S559290
Reexamination Certificate
active
06271513
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical microscope. In particular, it relates to a shear force feedback system, a large area scanning-tip near field optical microscope using said system, and a scanning method for said microscope.
2. Description of Prior Art
The art of the near field optical microscopy transcends the restrictions of optical diffraction. It allows the observation of optical properties as small as several hundred angstroms on the surface of the sample, permitting its use in the fields of the sub-micron technology and the biology. However, while using this method, it is necessary to maintain a distance between the probe and the surface of the sample of less than several hundred angstroms. Thus, near-field optical microscopy requires a feedback control to keep this distance. At present, the feedback control mechanism is either optical or non-optical. In prior arts, there are many mechanisms using optical techniques such as “Near-Field Optics: Microscopy, Spectroscopy, and Surface Modification Beyond the Diffraction Limit, ” written by E. Betzig and J. K. Trautman, Science 257, 189(1992), and “Combined shear force and near-field scanning optical microscopy,” disclosed by E. Betzig, P. L. Finn and J. S. Weiner, Appl. Phys. Lett. 60, 2484 (1992), and “Minimum detectable displacement in near-field scanning optical microscopy,” of F. F Froehlich and T. D. Milster, Appl. Phys. Lett. 65, 2254(1994). There are also many mechanisms using non-optical technique such as “Piezoelectric tip-sample distance control for near field optical microscopes,” disclosed by K. Karrai and R. D. Grober, Appl. Phys. Lett. 66, 1842(1995), and “A non-optical tip-sample distance control method for near-field scanning optical microscopy using impedance changes in an electromechanical system,” disclosed by J. W. P. Hsu, M. Lee and B. S. Deaver, Rev. Sci. Instrum. 66, 3177 (1995). Optical methods have the benefit of simple and stable utility and are widely used by researchers.
FIG. 1
shows a prior art of a near-field optical microscope using an optical mechanism, which is described below:
At first, a piezoelectric material
10
actuates a fiber probe
12
to vibrate in a direction parallel to the surface (i.e., x direction).
Then the light beam is focused on the tapered region of the tip end of the fiber probe by the lens
14
, a part of the light beam reflected by the tip end being focused by the lens
16
.
The light focused by the lens
16
is then detected by the photo-detector
18
. The intensity of the light brings the information regarding to the vibration amplitude of the tip position.
The phase-locked amplifier is used to measure the small signal of the amplitudes or the phases of the vibration. Finally, the varieties of the amplitudes or the phases serve as the feedback signal of the distance between the fiber probe and the surface of the sample.
The optical method given above has been disclosed in “Direct measurements of the true vibrational amplitudes in shear force microscopy,” C. C. Wei, P. K. Wei and W. S. Fann, Appl. Phys. Lett. 67, 3835 (1995).
FIG. 2
shows a part of the light beam being reflected and passing through the lens
24
to the photo-detector
26
while a light beam is focused on the tip of the probe
22
in the transversal direction (x direction). The light beam (P
dc
(x)) reflected to the photo-detector
26
changes in intensity as the probe
22
moves. The relationship between the variation (P
ac
(x)) and the small displacement(&Dgr;x) is given below:
P
ac
(x)=|P
dc
(x+&Dgr;x)−P
dc
(x)|≈|P′
dc
(x)|&Dgr;X (1)
The distribution of a conventional laser light focus beam is a Gaussian distribution, i.e., exp
exp
(
-
x
2
d
2
)
,
so
P
ac
(
x
)
=
&LeftBracketingBar;
2
x
&RightBracketingBar;
d
2
Δ
x
P
dc
(
x
)
(
2
)
The measurement of the amplitude (P
ac
(x)) has a maximum value at the position
x
=
d
2
,
so
Max
(
P
ac
)
=
2
Δ
x
d
P
ac
(
x
=
d
2
)
(
3
)
This value is inversely proportional to the size of the focus spot and the position of the maximum value is at
x
=
d
2
,
so a preferred amplitude signal can be obtained if the size of the focus spot is small.
The optical feedback control method is necessary to put the fiber probe near the focus spot of the light beam, and the size of the focus spot should be as small as possible to obtain a higher value signal. This system provides only a small moving range for the probe on the parallel plane (x-y plane) when the probe scans the surface of the sample. Thus, in a conventional near-field optical microscope, the probe is not moved while scanning the sample's surface. Instead, a piezoelectric crystal is used to move the scanning sample along the parallel plane of the surface. This system is so called the scanning sample system.
However, when the sample needs to be fixed or is too heavy or big, it is impossible to use the sample in this system since the piezoelectric crystal can not move it. In this situation, it is necessary to use a scanning tip system in which the system moves along the x-y plane while controlling the distance between the fiber probe and the surface of the sample.
SUMMARY OF THE INVENTION
Thus the object of the present invention is to provide a large area scanning tip system, and a near field microscope using the system and a scanning method of the microscope.
An aspect of the present invention is that there is a wide dynamic scanning area for the fiber probe moving along the parallel surface. The structure of the present invention can be used in a scanning tip system for both fixed and unfixed samples.
Additionally, since the fiber probe is very light and the piezoelectric crystal need only move the fiber probe while the probe is scanning the sample (as opposed to moving the sample itself), the system of the present invention can improve the scanning speed.
In the present invention, it is not necessary to collimate the incident light beam and fiber probe in the parallel position because the light beam is uniformly distributed in the large area of the parallel plane. Thus, it is easy to use and requires fewer components.
REFERENCES:
patent: 5838000 (1998-11-01), Mertesdorf et al.
C. Wei, et al. “Direct Measurements of the True Vibrational Amplitudes in Shear Force Microscopy.”Applied Physics Letter67. p. 3836. 1995.
P. Wei, et al. “Tip-Sample Distance Regulation for Near-Field Scanning Optical Microscopy Using the Bending Angle of the Tapered Fiber Probe.”Journal of Applied Physics.vol. 84, No. 9. p. 4655. Nov., 1998.
P. Wei, et al. “Large Scanning Area Near Field Optical Microscopy.”Review of Scientific Instruments.vol. 69, No. 10. p. 3614. Oct., 1998.
Eric Betzig and Jay K. Trautman; “Near-Field Optics: Microscopy, Spectroscopy, and Surface Modification Beyond the Diffraction Limit;” Science; vol. 257; pp. 189-195; Jul. 10, 1992.
E. Betzig, et al.; “Combined Shear Force and Near-Field Scanning Optical Microscopy;” Appl. Phys. Lett. 60 (20); pp. 2484-2486; May 18, 1992.
Fred F. Froehlich and Tom D. Milster; “Minimum Detectable Displacement in Near-Field Scanning Optical Microscopy;” Appl. Phys. Lett. 65 (18), pp. 2254-2256; Oct. 31, 1994.
Khaled Karraj and Robert D. Grober; “Piezoelectric tip-sample distance control for near field optical microscopes;” Appl. Phys. Lett., vol. 66, No. 14, pp. 1842-1844; Apr. 3, 1995.
J.W.P. Hsu, et al.; “A nonoptical tip-sample distance control method for near-field scanning optical microscopy using impedance changes in an electromechanical system;” Rev. Sci. Instrum; vol. 66, No. 5; pp. 3179-3181; May, 1995.
M.N. Armenise; “Fabrication Techniques of Lithium Niobate Waveguides;” Lee Proceedings, vol. 135, Pt. J, No. 2; pp. 85-91; Apr., 1988.
Chih-Chun Wei, et al.; “Direct Measurements of the True Vibrational Amplitudes in Shear Force Microscopy;” Appl. Phys. Lett. 67 (26); pp. 3835-3837; Dec. 25, 1995.
Y.T. Yang, et al.; “Vibrati
Fann Wunshain
Wei Pei-Kuan
Knobbe Martens Olson & Bear LLP
Le Que T.
Luu Thanh X.
National Science Council
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