CN101113887A - Surface plasma resonance measurement mechanism and method thereof - Google Patents
Surface plasma resonance measurement mechanism and method thereof Download PDFInfo
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Abstract
The measurement method or device of the invention is realized by the principle of surface plasma resonance; the invention can measure the tiny gap, displacement or relative position between two objects. The measurement method of the invention first provides a horizontal magnetic (TM) wave beam, and uses the mentioned beam to generate the surface plasma resonance phenomenon in one of the two mentioned objects. Then measures the signal size of the reflection light or the transmission light of the referred beam, and by adopting the characteristics of sensitive when the width of the referred tiny gap is less than or equal to two times of the penetration depth of the surface plasma wave, the surface plasma resonance phenomena has sensitive response to the referred tiny gap, the displacement or the change of the relative position to get the referred tiny gap, the displacement or the relative position from the change of the signal size. In this way, the invention can measure gap width, displacement, relative position or surface flatness which is two times less than the penetration depth or below the 10nm.
Description
Technical Field
The invention relates to a device and a method for measuring the width, displacement or relative position of a tiny gap by applying the surface plasmon resonance principle, in particular to a device and a method for measuring the surface plasmon resonance of a nanoscale gap, displacement or relative position.
Background
For a long time, in optical measurement methods in the scientific field, the measurement technique of optical interferometry is mainly used, and displacement change (displacement shift) of a relative object can be calculated by analyzing slight changes of interference fringes, and the higher the precision of the instrument is, the more minute the displacement change can be detected. But the method for measuring the gap width (gap width) of the nanometer level is difficult to achieve breakthrough development all the time. The reason for this is that the technique of measuring a minute gap by optical interferometry is limited by the difficulty of not having an interference pattern when the gap width is one-half wavelength or less, and therefore, it is difficult to measure a gap having a width of less than 300nm, not to mention a gap on the order of nanometers of less than 100nm or 10nm, in a measuring method by ordinary visible light.
The research group of the national institute of technology and technology of Massachusetts has utilized the so-called "sharpened-Talbot effect" to measure the nanogap, indicating that the sensitivity of the method can reach below 1 nm; however, the measurable range is about 30 μm to 1 μm. Based on this, in order to overcome the problem that the optical method for measuring the gap width of the object can not break through the interference limit of one-half wavelength, the present invention proposes to use the "surface plasmon resonance" method to measure the width, displacement change and relative position of the nanoscale gap between two objects.
The so-called "surface plasmon resonance" phenomenon is a collective oscillation behavior of metal surface electrons, which is characterized in that after Transverse Magnetic (TM) mode light parallel to an incident surface is coupled through a prism or other objects, a metal film (generally gold or silver) is coated on the other surface of the prism, so that a surface plasmon wave is generated on the metal surface, when the incident light wave vector is equal to the surface plasmon wave vector of a dielectric material at the metal film interface, a resonance phenomenon is generated, and at this time, the incident light transfers energy to the interface where the surface plasmon resonance phenomenon occurs, so that the reflected light intensity (or reflectivity) is rapidly reduced, as shown in fig. 1. The surface plasmon resonance phenomenon occurs characterized by: when the incident light satisfies the surface plasmon resonance condition, the resonance angle B occurs at a specific angle (about 44 degrees in this example) greater than the critical angle a for total reflection, and most of the incident light energy is absorbed, even almost completely absorbed, so that the reflected light intensity (or reflectance) at the resonance angle B is the lowest and can be reduced to zero theoretically.
When the incident light wave vector is equal to the surface plasmon wave vector as shown in the following formula (1) and the surface plasmon wave vector as shown in the following formula (2), the wave vectors match, and a surface plasmon resonance phenomenon occurs, so that the incident light energy is transferred to the surface plasmon wave. In fact, the surface plasmon resonance phenomenon can be generated only if a specific condition (e.g., a specific incident angle or a specific wavelength) is satisfied. Wherein the incident light wave vector can be expressed as
k x ＝k o n p sinθ (1)
Wherein k is x Representing the component of incident light parallel to the wave vector at the interface of the metal and the prism, k 0 Is the wave vector k in vacuum 0 = ω/c =2 π/λ, ω is angular frequency, c is speed of light, λ is wavelength of incident light, θ is angle of incidence of light, n is p Is the refractive index of the prism. And the surface plasmon wave vector k sp Is shown as
Wherein epsilon m And e d Are respectively the metal dielectric coefficient and the dielectric coefficient of the object to be measured, and
n d is the refractive index of the object to be measured.
When the incident light and the surface plasma wave satisfy the wave vector k x ＝k sp When the surface plasmon resonance phenomenon is formed, if any parameter in the formula (2) is slightly changed (such as refractive index change), the original resonance condition is no longer satisfied, and the energy coupling between the incident light and the surface plasmon wave is changed again. As a result, the surface plasmon resonance phenomenon can be used to measure small physical or chemical property changes on the object to be measured.
Basically, there are three ways of coupling incident light to generate surface plasmon resonance, respectivelyGrating coupling, optical waveguide coupling and prism coupling. The prism coupling method is often combined with an attenuated total internal reflection (ATR) method to measure the reflectivity, and has become the most popular surface plasmon resonance measuring device because of the simplest and most convenient use. The prism coupling has both KR and Otto configurations, depending on the structural configuration of the basic assembly. The KR configuration is mainly formed by coating a metal film on the bottom surface of a prism, and the Otto configuration is formed by placing a prism on a flat plate coated with a metal film on the surface. However, regardless of its configuration or its optical coupling, so long as it satisfies the incident light wave vector k x Wave vector k with interface dielectric material sp The same condition can form surface plasma resonance effect, and can be used for various measurement applications.
Currently, the measurement of the surface plasmon resonance phenomenon is basically divided into four modes, namely angle detection (angular interaction), wavelength detection (wavelength interaction), intensity detection (intensity interaction) and phase interaction.
The "angle detection" changes the incident angle of the incident light, so that the horizontal wave vector increases with increasing angle. When the horizontal wave vector of the light is equal to the surface plasmon resonance wave vector at a specific incident angle, the reflected light intensity has a minimum value, which is the resonance angle of the surface plasmon wave. Then, if the refractive index of the adjacent medium on the interface changes, or the refractive index, weight or density of the object to be measured attached to the interface changes, the surface plasmon wave vector changes, and the resonance angle changes and drifts. The change of the physical or chemical properties of the object to be measured at or on the interface can be known by measuring the angle drift.
The wavelength detection is performed by changing different wavelengths of incident light with a fixed incident angle, and when the wavelength of incident light is adjusted to a specific wavelength, the surface plasmon resonance condition is satisfied, and the intensity of reflected light is reduced to a minimum value, and the specific wavelength is the surface plasmon resonance wavelength. Then, if the refractive index of the adjacent medium on the interface changes, or the refractive index, weight or density of the object to be measured attached to the interface changes, the wave vector of the surface plasmon will change, and the resonant wavelength will shift. The change of the physical or chemical properties of the object to be measured at or on the interface can be known by measuring the wavelength shift.
"intensity detection" is the change of the reflected light intensity caused by the change of the surface plasmon resonance condition when the physical or chemical properties of the interface slightly change; in this case, the change in the physical or chemical properties of the interface can be known by measuring the change in the intensity of the reflected light. Generally, in order to enable higher sensitivity, a fixed angle of incidence is selected to be measured at the position of the maximum value of the slope of the reflected light intensity curve.
The "phase detection" is to determine the physical or chemical property change at the interface by measuring the corresponding drastic change of the optical wave phase of the reflected light in addition to the change of the intensity of the reflected light when the surface plasmon resonance phenomenon occurs. When at resonance angle, this phase angle changes most dramatically, which is referred to as phase jump. In phase detection, the light incident angle is usually fixed near the resonance angle to obtain the highest sensitivity.
Because the principle of surface plasmon resonance is simple and the device is not complicated, the academic or industrial field has long applied the technology to the detection of gas or biochemistry. For example, in 1982, the official (1982) of Nylon and Liedberg firstly utilizes KR structure to apply to gas and biochemical detection technology, thereby laying the research foundation of various microsensors. In 1992, iorgenson and Yee used optical fiber as surface plasmon resonance sensor, and deposited silver metal film on traditional optical fiber to form surface plasmon resonance sensing structure, and detected the change of material characteristics on metal surface by wavelength detection method. In 1992, an integrated optical waveguide sensing structure using an optical interference system was used to convert a chemically changed signal into an optical signal and then read out the phase change generated by the optical interference to detect the properties of a chemical solution.
U.S. Pat. No. 6,208,422 discloses an Otto configuration surface plasmon sensing apparatus 20, as shown in fig. 2 (a). The basic structure is to place metal film plates 201, 202 capable of generating surface plasmon waves on a movable stage 203, under which a piezoelectric element 204 is attached, and spaced from a surface 206 of a prism 205 by a gap. During measurement, two incident light beams 209 and 209' are used to match a measurement light source 200, and two photodetectors 207 and 208 receive reflected light signals on the surface 206 to generate two light intensity signals 220 and 222, wherein the light intensity signal 222 passes through an amplifier 221. Then, the two light quantity signals 220, 222 are sent to a data processing unit 225, and a driving control signal 224 is generated. The driving control signal 224 controls a driver 223 to drive the up-and-down movement of the piezoelectric element 204. Thereby, the distance between the prism 205 and the metal film plate 201 can be controlled. However, the Otto-type surface plasmon sensing apparatus 20 has a complicated structure, and requires two incident light beams 209 and 209' and two photodetectors 207 and 208. Not only is the operation inconvenient, but also the stability is influenced due to the complex structure.
In addition, japanese patent No. JP6265336 discloses a precise distance control device 21 of the Otto configuration surface plasmon resonance effect, as shown in fig. 2 (b). The fine distance control device 21 is composed of a prism 210, a neutral density filter 211, a cylindrical lens 212, a photodiode array 213, a condenser lens 214, an aperture 215, a beam expander 216, a polarizer 217, a monochromatic laser light source 218, a dielectric film 219, a stage 230, a piezoelectric crystal 231, and a stage 232. The principle of operation is that the light beam generated by the monochromatic laser source 218 sequentially passes through the polarizer 217, the beam expander 216, the aperture 215 and the condenser lens 214 to the prism 210 to generate surface plasmon resonance. Then, a reflected light beam is generated to sequentially pass through the neutral density filter 211 and the cylindrical lens 212, and then is received and detected by the photodiode array 213, which mainly aims at measuring a resonance angle; the generated surface plasmon resonance is transmitted to the piezoelectric crystal 231 through the dielectric film 219 and the stage 230 (which is made of a conductive material). Then, the piezoelectric crystal 231 and the photodiode array 213 control the horizontal direction of the platform 232 through a data processing unit (not shown), so as to precisely control the distance between the two objects. However, the japanese patent is still limited to the application of surface plasmon resonance of Otto configuration, and does not describe the correlation of the resonance angle with the corresponding change in gap size, and cannot be used for measuring the gap width or displacement distance of two objects merely to control the distance of the two objects from the vicinity of the resonance angle position.
Disclosure of Invention
The invention aims to provide a device and a method for measuring geometrical numerical values such as width, displacement or relative position of a micro gap by applying a surface plasmon resonance principle, which can overcome the defect that an optical interference method cannot generate interference fringes in the range of less than one half wavelength of incident light, and are particularly suitable for measuring the nano-scale micro gap, displacement or relative position.
The invention uses optical Fresnel reflection theorem to calculate the corresponding relation of reflection coefficients between different multilayer interfaces and writes a change formula of the reflectivity (detailed description is in an implementation method). Then, a complete three-dimensional simulation program is developed based on the KR structure configuration and the change formula of the reflectivity, so as to obtain the change relation between the simulated incidence angle and the reflectivity. The invention utilizes the phenomenon that the change of the resonance curve of the incident angle and the reflectivity is very sensitive when the gap between two objects is less than or equal to 2 times of the penetration distance of the surface plasma wave, and takes the phenomenon as the measuring method of the nanometer micro gap, the displacement or the relative position, and develops the measuring device thereof.
Depth of penetration of surface plasmon waveEta, which is the intensity of the electric field of the mesoscopic surface plasmon wave decays to the intensity at the interface -1 And (e is a natural index) whose value varies with the wavelength of incident light, the refractive index of metal, the refractive index of medium, and the state of its interface (e.g. interface cleanliness), but has some error from the theoretical value. Theoretical value equationThe formula (3) is as follows:
where λ is the wavelength of the incident light, ε m And e d Are respectively the metal dielectric coefficient and the dielectric coefficient of the object to be measured, and
n d is the refractive index of the object to be measured.
The measuring device is developed by first calculating the relative relationship between the reflectivity variation and the gap size through the computer simulation, or directly establishing the corresponding relationship data between the reflectivity variation and the small gap in a measuring manner, so as to establish a data lookup Table (Look-Up Table, LUT), for example. When measuring the width of the small gap of an object to be measured, the data in the data lookup table can be compared with the values displayed in the light detection unit and the output unit to obtain the measured width of the small gap, and the relative displacement or the relative position of the two objects can be obtained by calculating the data difference value of the two different gap widths.
In order to achieve the above objects, the present invention discloses an optical measuring device using surface plasmon resonance, which comprises an illumination assembly, an optical coupling unit, an optical detection unit, an output unit and an opposite object.
The 'illumination assembly' is used to provide an incident beam containing TM waves, the light source of the incident beam can be laser, tungsten lamp, mercury lamp, light emitting diode, or synchrotron radiation light; the wavelength can be in the range of infrared light, visible light or ultraviolet light frequency band; the mode of generating TM-containing wave can be modulated by optical lens or polarizing polarizer. If the noise of the incident beam is reduced or the percentage of TM waves is adjusted, optical components such as lenses, filters, polarizers, etc. can be placed in the incident light path, which is still considered part of the illumination assembly.
The 'optical coupling unit' provides the incident beam energy to couple to the surface plasma wave, and generates the surface plasma resonance phenomenon when the specific conditions of the incident light wave vector and the surface plasma wave vector are equal. Therefore, the optical coupling unit is basically a prism with a metal film plated on the bottom surface, wherein the metal can be a single layer of gold, silver or other composite metal, or can be a plurality of layers of gold, silver or other composite metal or composite material; the total thickness of the metal film is not limited, as long as the metal film can excite surface plasma waves and can penetrate into the adjacent gap to be measured. The prism is not limited in refractive index, and the shape thereof can be a right-angle prism, a triangular prism, a hemispherical lens, a semi-cylindrical lens, etc. The metal film plating mode can be used for directly plating the bottom surface of the prism and attaching the slide glass containing the plated metal film to the prism by using matching liquid with the refractive index close to that of the prism. The optical coupling method may be any known coupling method such as grating coupling or optical waveguide coupling, in addition to the prism coupling method.
A "photo detection unit" is provided to convert the reflected light signal into an electrical signal, the basic elements of which are photo sensing diodes, photo multipliers, photo amplifiers, charge Coupled Device (CCD) sensors, complementary Metal Oxide Semiconductor (CMOS) sensors, or other photoelectric conversion devices. If, in order to reduce the accompanying noise of the reflected light entering the light detection unit, optical components such as lenses, filters, polarizers, etc. may be placed at the entrance thereof and still be considered as part of the light detection unit.
The "output unit" is used to transmit the electrical signal sent by the optical detection unit to a display element (such as an oscilloscope, a screen, and a printer), a storage element (such as a memory, a magnetic disk, a hard disk, and a memory card), or a control element (for precise distance control) by means of storage or conversion; the output signal can be obtained by comparing the data simulation result or the data lookup table to obtain the distance size of the tiny gap or displacement.
An "opposing object" is an object that is separated from the surface of the optical coupling unit plated with the metal film by a small gap (i.e. the gap to be measured in the front-end optical coupling unit), wherein the surface of the opposing object can be a single dielectric material or a film coated with other materials (such as oxide, nitride, halide, or other metals and compounds thereof), and the opposing object can be only a local area of a larger object surface. The relative object can be transparent, semi-transparent or opaque material, and if it is transparent material, the light sensing element can be mounted at the transmission position, and the variation of surface plasma resonance phenomenon can be calculated by utilizing the variation of transmitted light signal, so as to obtain the size of the micro gap. The filling material state of the micro-gap to be measured can be vacuum, gas (air, gas with any concentration), liquid (aqueous solution, alcohol solution or other liquid), jelly (resin, adhesive, etc.), or elastic solid medium (rubber, micro-reed, etc.), which does not affect the generation of plasma wave on the upper surface of the optical coupling element.
For the steps of the surface plasmon resonance measurement method of the present invention, after an incident light source is selected, an incident beam containing TM waves needs to be modulated, and when the incident beam is guided to the incident light coupling unit, surface plasmon waves are excited on the surface of the metal thin film; after the adjustment is made to meet the specific resonance condition, the surface plasmon resonance phenomenon starts to occur. Then, different modes of measuring the reflected light signal or the penetrating light signal can be selected, when the micro gap is smaller than or equal to the penetration depth of the surface plasma wave of the light beam by 2 times distance (because the electric field intensity of the surface plasma wave changes obviously along with the gap width distance within 2 times penetration depth), the surface plasma resonance condition changes sensitively according to the size of the micro gap, and the distance size of the micro gap can be obtained and the relative position can be calculated by measuring the variation of the signal, comparing the data simulation result or comparing the data lookup table previously implemented.
The measuring device can also measure the micro displacement by using the same principle, the specific measuring steps are completely the same as the method for measuring the gap, and finally the distance of the displacement is obtained by comparing the difference value of the gap before and after the relative displacement. By the characteristic that the surface plasma resonance is sensitive to the micro-displacement change, a high-resolution micro-displacement measuring method can be obtained.
Three incident light optical coupling modes, such as grating coupling, optical waveguide coupling and prism coupling, can be applied to the surface plasma resonance device and the surface plasma resonance method.
In addition, after capturing the image signal of the reflected light or the transmitted light by the CCD or CMOS sensor, the relative value is converted by the image value analyzing method, and the minute gap width, the displacement distance, or the relative position between the two objects can be measured as described above. Moreover, the image captured by the CCD or CMOS sensor can generate contrast change of the brightness of the surface plasma resonance image due to the difference of the relative gaps of the tiny local areas between the two objects, so that the flatness or shape change of the surface of the relative object can be known.
The invention can measure the clearance below 100nm even 10nm, and has wide application field, for example, the invention can be applied to a service control system of a near-field optical disk read-write head, can sense and control the distance between the read-write head and the optical disk at the near-field distance, and provides the accuracy and the reliability of reading and writing; or applied to a sub-nanometer photoetching system, and the proximity distance between the mask and the silicon chip is detected to improve the reliability of the system; or sensing control of the liquid crystal layer gap in a new generation LCD, or a surface profile plotter, etc., can be applied to the present invention. In addition, with the development of various nanotechnologies, various miniature products are continuously developed, and the present invention can be applied to a sensing unit for sensing the size of a gap and the change of displacement or controlling a precise distance of various product technologies, and the present invention has huge future application range.
In addition, due to the development of technology, many documents have disclosed increasing the resolution or sensitivity of the surface plasmon resonance measurement by using methods such as "common-path superextrapolation" or "phase compensation backtracking". In addition, methods for detecting the surface plasmon resonance effect by measuring the variation of the transmitted light signal transmitted through the metal film have also been proposed. However, whatever the complexity of the device or other auxiliary methods, the present invention still covers the device method that uses the characteristic that the resonance condition after the coupling of the incident light wave vector and the surface plasma wave vector is matched and the interface state is slightly changed and drastically changed to obtain the nanoscale gap width, displacement and relative position between two objects.
Drawings
FIG. 1 is a conventional surface plasmon resonance plot;
FIG. 2 (a) is a schematic diagram of a conventional gap measurement using the Otto configuration;
FIG. 2 (b) is a schematic diagram of a conventional gap distance control using the Otto configuration;
FIG. 3 (a) is a graph of the reflectivity of a conventional KR configuration 3-layer structure using a program simulation in the present invention;
FIG. 3 (b) is a graph of the reflectivity of a simulated KR configuration 3 layer structure in close proximity to a relative object in accordance with the present invention;
FIG. 4 illustrates a surface plasmon resonance measurement apparatus according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of the main components of a surface plasmon resonance measurement apparatus according to an embodiment of the present invention; and
FIG. 6 is a graph showing the reflectivity curve corresponding to different gap widths of the surface plasmon resonance in accordance with an embodiment of the present invention.
Detailed Description
The corresponding relation of reflection coefficients among different multilayer interfaces is calculated according to the optical Fresnel reflection theorem, and a change formula of the reflection rate can be written as follows:
r nm ＝(ε m k zn -ε n k zm )/(ε m k zn +ε n k zm ) (6)
in the above formulas, the subscript 0 represents the prism layer, 1 is the metal layer, 2 is the gap layer, 3 is the object to be measured, R is the reflectivity, R is 0123 Reflection coefficient, r, representing the effect of merging four layers 123 Reflection coefficient, r, for merging three-layer effects nm Is the reflection coefficient of any two adjacent nm layers, epsilon m Is the dielectric coefficient of the m-th layer, d m Thickness of m-th layer, k zm Is the z component, k, of the m-th layer wave vector inc Is the vector of the incident light wave, k x The x-component of the incident light wave vector.
The invention develops a complete three-dimensional simulation program based on KR structure configuration and by formulas (4) to (7), and the simulation result is shown in figure 3 (a). Fig. 3 (a) shows the reflectance versus incident angle for a conventional KR configuration tri-layer structure (prism/metal/air). The curve changes as shown in fig. 1, as the incident angle increases, the reflectivity enters the total reflection region, the reflectivity is the highest, and then the incident light energy is coupled to the surface plasmon wave, the reflectivity rapidly drops to the lowest point, the incident angle is called the resonance angle, and after the point, the resonance condition gradually disappears, and the reflectivity increases again.
Referring to fig. 3 (b), the same three-dimensional simulation procedure is used to simulate the change of reflectivity when the KR-configured three-layer structure is gradually approached by an opposite object (i.e. the opposite object is gradually approached by the prism). We have found that when the gap between the two is gradually reduced to a distance 2 times the penetration depth of the surface plasmon wave (about one-half of the wavelength of the incident light), the position of the resonance angle of the reflectance curve shifts to a large angle as the gap becomes smaller. The invention utilizes the phenomenon that the change of a resonance curve is very sensitive when the clearance between the prism and an object to be measured is less than or equal to the distance of 2 times of the penetration depth of the surface plasma wave, and the phenomenon is taken as a measuring method of the nano-scale tiny clearance, displacement or relative position, and develops a measuring device thereof.
Fig. 4 illustrates a surface plasmon resonance measuring apparatus 40 to which the present invention is applied. The main components of the measuring device 40 include an illumination assembly 51, a light coupling unit 400, a light detection unit 408 and an output unit 418. In this embodiment, the optical coupling element 400 is a prism, and the prism 400 is separated from an opposite object (not shown in FIG. 4, which will be described in detail in FIG. 5) by a gap, and the surface plasma measurement apparatus 40 is used to measure the gap size, and thereby measure the relative displacement and relative position. The output unit 418 is a display device, a storage device, or a control device.
In this embodiment, the illumination assembly 51 includes a light source 41, a chopper 42 (chopper), a half wave retarding element 43, a polarizing beam splitter 44 (polarizing beam splitters/PBS), a polarizing plate 47, and a beam splitter 48 (beam splitters/BS). The light source 41 is a linearly polarized helium-neon laser source with a wavelength of 632.8nm, and the generated light beam is converted into a pulsed laser by the continuous wave laser through the chopper 42, and then converted into a TM mode light beam through the half-wave retardation element 43 and the polarization beam splitter 44.
The TM mode beam is split into two beams by the beam splitter 48, one of which is used as a reference beam and the other of which is incident on the prism 400 for calculating the change in reflectivity. Then, the width of the gap between the prism 400 and the opposite object is adjusted by a translation device 404. The angle of the inscription on the rotating device 402 may provide for recording different resonance angle positions when surface plasmon resonance occurs. The rotating device 402 and the translating device 404 are operated by a controller 416 driving the motors. The two beams are measured and displayed in the output unit 418 (in this embodiment, the output unit 418 is an oscilloscope) by the light detection unit 408 and the other light detection unit 406, respectively, and then the related reflectivity data is inputted into the computer 420 for analysis.
In this embodiment, other components such as the light chopper 42, the polarization plate 47, the beam splitter 48, the lenses 410, 412 and 414, the mirrors 45 and 46, the rotating device 402, the computer 420 and the reference beam are added for the purpose of increasing the convenience and accuracy of the measurement, and may be appropriately changed or replaced as appropriate, and the relevant changes do not affect the integrity and utility of the present invention.
Referring to fig. 5, the structure of the prism 400 and associated mating components is illustrated in detail. The surface of the prism 400 facing a carrier 54 is coated with a metal film 52 (in this embodiment, a gold thin layer with a thickness of 40 nm), and a gap 53 is formed between the metal film 52 and the carrier 54. The TM mode beam 55 is generated by the illumination assembly 51 and enters the prism 400 to form surface plasmon resonance in the metal film 52, and the signal of the reflected light 56 is detected by the light detection unit 408. The carrier 54 may be made of glass, and the reflected light 56 is more uniform mainly by its flat surface. The carrier 54 can be mounted on the translation device 404 to move relative to the prism 400 to adjust the gap. The micro gap 53, besides being an air gap, can also operate in a vacuum environment or contain other gases, liquids or elastic media solids, and still be applied with the present invention.
When the carrier plate 54 is equivalent to the above-mentioned opposite object, and the gap 53 is less than or equal to 2 times the penetration depth of the TM mode light beam 55 (about one-half wavelength distance of the light beam 55), if the carrier plate 54 gradually approaches the prism 400, the intensity of the reflected light detected by the light detecting unit 408 will change, and the result is shown in fig. 6. The curves 61 to 66 are curves indicating that the minute gap is formed by data measured by the large taper. Curve 61 shows the phenomenon that the distance between the metal film 52 on the surface of the prism 400 and the carrier 54 (opposite to the object) is greater than one-second wavelength of the TM mode beam 55, and the position of the resonance angle is equivalent to that of the conventional KR three-layer structure, and the reflectivity is about only 0.12 at about 45 degrees. The gaps 53 corresponding to curves 62 to 66 then gradually decrease, with the resonance angle shifting towards a large angle and the reflectivity gradually increasing. For example, at curve 66 the resonance angle shifts to about 49 degrees, while at 45 degrees the reflectance increases to about 0.65. As the slight gap 53 continues to decrease, the resonance angle will continue to increase and eventually disappear completely (no dip in the curve).
When a small relative displacement is generated between the carrier plate 54 (relative object) and the prism 400, the small gap 53 will be changed to change the light intensity of the reflected light 56 detected by the light detection unit 408, and the width measured at two different gap positions is calculated by using the same principle, so as to calculate the difference, thereby obtaining the relative small displacement of the carrier plate 54 (relative object).
As described above, the measurement method using the surface plasmon resonance principle has several basic application methods, such as an angle detection method, a wavelength detection method, an intensity detection method, a phase detection method, or any combination thereof. Although the present invention is described in detail with reference to the accompanying drawings, it should be understood that the present invention is not limited to the above embodiments, but is capable of other embodiments. Therefore, it is still part of the present invention to utilize the different measurement signal types described above.
Compared with the conventional surface plasmon resonance apparatus as shown in fig. 2 (a), the present invention can measure a minute gap, displacement or relative position without a complicated structure by using only a single light source, a single photodetector. In addition, the conventional technique of fig. 2 (b) uses Otto configuration to generate surface plasmon resonance, and is not used to measure the gap between two objects, but it is different from the present invention that uses KR configuration surface plasmon resonance to find the gap and relative displacement between two objects.
The technical contents and technical features of the present invention have been disclosed as above, however, one skilled in the art may make various substitutions and modifications based on the teaching and disclosure of the present invention without departing from the spirit of the present invention. Accordingly, the scope of the present invention should not be limited by the disclosure of the embodiments, but should include various alternatives and modifications without departing from the invention and intended to be covered by the appended claims.
Claims (33)
1. A surface plasmon resonance measurement apparatus, comprising:
an illumination assembly for providing a beam of light containing Transverse Magnetic (TM) mode components;
the optical coupling unit comprises a metal film surface for the incident excitation of the light beam to generate surface plasma resonance wave;
a relative object, which is separated from the surface of the metal film of the optical coupling unit by a gap, and the width of the relative object is less than or equal to 2 times of the penetration depth of the surface plasma resonance wave;
the light detection unit is used for detecting a reflected light signal or a penetrating light signal of the light beam on the surface of the metal film and converting the reflected light signal or the penetrating light signal into an electric signal; and
and the output unit converts the electric signal into an output signal so as to obtain a geometric numerical value between the optical coupling unit and the opposite object.
2. The surface plasmon resonance apparatus of claim 1 wherein said geometric value is the width of said gap.
3. The surface plasmon resonance apparatus of claim 1 wherein said geometric value is the relative displacement of said optical coupling unit and said opposing object.
4. The surface plasmon resonance apparatus of claim 1, wherein said geometric value is the relative position of said optical coupling unit and said opposing object.
5. The surface plasmon resonance apparatus of claim 1 wherein said geometric value is the surface flatness of said opposing objects.
6. The surface plasmon resonance measurement apparatus of claim 1 wherein said gap is less than or equal to one-half the wavelength of said light beam.
7. The surface plasmon resonance measurement apparatus of claim 1 wherein the light source of the light beam produced by the illumination assembly is a laser, a tungsten lamp, a mercury lamp, a light emitting diode, or synchrotron radiation.
8. A surface plasmon resonance apparatus according to claim 1, wherein the light beam has a wavelength in the visible, infrared or ultraviolet range.
9. The surface plasmon resonance apparatus of claim 1, wherein said illumination assembly provides said beam with TM mode components modulated using an optical lens or a polarizing polarizer.
10. The surface plasmon resonance measuring apparatus of claim 1, wherein the optical coupling unit generates the surface plasmon resonance effect by prism coupling, grating coupling, or optical waveguide coupling.
11. The surface plasmon resonance measuring apparatus of claim 1, wherein the material of the metal thin film is a single layer of gold, silver, or a composite metal.
12. The surface plasmon resonance measurement apparatus of claim 1 wherein the material of the metal film is a plurality of layers of gold, silver, or a composite metal or composite material.
13. The surface plasmon resonance measurement apparatus of claim 1 wherein the light detection unit is a light sensing diode, a photomultiplier tube, a light amplifying diode, a CMOS sensor or a CCD sensor.
14. The surface plasmon resonance measuring apparatus of claim 1, wherein the output unit is a display device, a storage device, or a control device; and the output signal can be obtained by comparing data simulation results, looking up an experimental numerical control table or an image numerical analysis method.
15. A surface plasmon resonance measuring apparatus according to claim 1 wherein the surface of the opposing object is a single dielectric material or is coated with a layer of material.
16. A surface plasmon resonance apparatus according to claim 1, wherein the opposing object is a localized region of the surface of a larger object.
17. The surface plasmon resonance measuring apparatus of claim 1, wherein the opposing body is composed of a light-transmitting, semi-light-transmitting or light-non-transmitting material.
18. The surface plasmon resonance apparatus of claim 1 wherein the gap is filled with a vacuum, gas, liquid or elastic solid medium.
19. The surface plasmon resonance measurement apparatus of claim 1 wherein the gap is filled with air, an aqueous solution, an alcohol solution, a resin, an adhesive, a gel, rubber or a micro-reed.
20. The surface plasmon resonance apparatus of claim 1 wherein the geometric value is obtained by using the surface plasmon resonance effect by angle detection, wavelength detection, intensity detection, phase detection, or a combination thereof.
21. The surface plasmon resonance measuring apparatus of claim 10, wherein the prism using the prism coupling method is a right-angle prism, a triangular prism, a hemispherical prism or a semi-cylindrical prism.
22. The surface plasmon resonance measurement apparatus of claim 1 wherein the optical coupling unit is comprised of the metal film plated directly onto the prism, grating, or optical waveguide.
23. The surface plasmon resonance measuring apparatus of claim 1, wherein the optical coupling unit is composed of a slide coated with the metal thin film attached to a prism, a grating, or an optical waveguide by using a refractive index matching fluid.
24. The surface plasmon resonance measuring apparatus of claim 1, wherein the opposing object is a transparent or semi-transparent material, and the geometric value is obtained by using the variation of the transmitted light signal of the light beam on the surface of the metal thin film.
25. A surface plasmon resonance measurement method for measuring a geometric value between two objects includes the following steps:
providing a light beam containing TM mode components;
generating surface plasmon resonance waves on a surface of one of the two objects using the light beam; and measuring a reflected or transmitted light signal of the light beam; and when the gap between the two objects is less than or equal to 2 times of the penetration depth of the surface plasma resonance wave, the surface plasma resonance effect reacts sensitively to the change of the gap distance, and the geometric numerical value is obtained by the variation of the reflected light or the penetration light signal.
26. The surface plasmon resonance measurement method of claim 25 wherein the geometric value is the width of the gap.
27. The method of claim 25, wherein the geometric value is a surface flatness of the surface of one of the two objects.
28. The surface plasmon resonance measurement method of claim 25 wherein the geometric value is the relative displacement or relative position of the two objects.
29. The surface plasmon resonance measurement method of claim 25, wherein the gap is less than or equal to one-half the wavelength of the light beam.
30. The surface plasmon resonance measurement method of claim 25, wherein the surface plasmon resonance is generated using a prism coupling method, a grating coupling method, or an optical waveguide coupling method.
31. The surface plasmon resonance method of claim 25, wherein the reflected light or transmitted light signal of the light beam is converted into an electrical signal, and the electrical signal is compared with a data simulation result or an experimental value comparison table is looked up, or an image numerical analysis method is used to obtain the geometric value.
32. The surface plasmon resonance measurement method of claim 25, wherein the geometry is obtained using the surface plasmon resonance effect by angle detection, wavelength detection, intensity detection, phase detection, or a combination thereof.
33. The surface plasmon resonance measurement method of claim 25, wherein one of the two objects is a prism comprising a metal film surface, and surface plasmons are generated on the metal film surface.
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