WO2003056567A2 - Procede de production d'un embout de sonde, utilise en particulier en microscopie optique a champ proche et presentant une ouverture specifique - Google Patents

Procede de production d'un embout de sonde, utilise en particulier en microscopie optique a champ proche et presentant une ouverture specifique Download PDF

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Publication number
WO2003056567A2
WO2003056567A2 PCT/EP2002/014747 EP0214747W WO03056567A2 WO 2003056567 A2 WO2003056567 A2 WO 2003056567A2 EP 0214747 W EP0214747 W EP 0214747W WO 03056567 A2 WO03056567 A2 WO 03056567A2
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WO
WIPO (PCT)
Prior art keywords
layer
optically
intermediate layer
optically transparent
transparent
Prior art date
Application number
PCT/EP2002/014747
Other languages
German (de)
English (en)
Other versions
WO2003056567A3 (fr
Inventor
Khaled Karrai
Florian Bickel
Original Assignee
Ludwig-Maximilians- Universität München
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ludwig-Maximilians- Universität München filed Critical Ludwig-Maximilians- Universität München
Priority to AU2002361214A priority Critical patent/AU2002361214A1/en
Publication of WO2003056567A2 publication Critical patent/WO2003056567A2/fr
Publication of WO2003056567A3 publication Critical patent/WO2003056567A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01Q—SCANNING-PROBE TECHNIQUES OR APPARATUS; APPLICATIONS OF SCANNING-PROBE TECHNIQUES, e.g. SCANNING PROBE MICROSCOPY [SPM]
    • G01Q60/00—Particular types of SPM [Scanning Probe Microscopy] or microscopes; Essential components thereof
    • G01Q60/18—SNOM [Scanning Near-Field Optical Microscopy] or apparatus therefor, e.g. SNOM probes
    • G01Q60/22—Probes, their manufacture, or their related instrumentation, e.g. holders

Definitions

  • the invention relates to a method for producing a probe tip for optical examinations, in particular for optical near-field microscopy, with a desired aperture.
  • probe is to be understood in the broadest sense, that is to include both the case that this probe is intended to collect light that is reflected, transmitted or somehow emitted by a sample, and also the case that the sample is to be irradiated with light by means of this probe, and the case that the irradiation and collection is to be carried out.
  • two main process steps can be distinguished in the manufacture of probe tips from light-conducting fibers, preferably glass fibers, namely, on the one hand, the forming of a, preferably conical, tapered tip at one end of the fiber and on the other hand the production of an optical aperture by applying an optically non-transparent coating to this tip, which has a central hole at the apex of the tip.
  • light-conducting fibers preferably glass fibers
  • a glass fiber is first locally heated, in particular melted, with a CO 2 laser beam and at the same time pulled apart in the longitudinal direction of the fiber. This creates a double cone, which is torn apart at the thinnest point after switching off the laser by means of an additional tensile force. In this way, two glass fiber tips are obtained, each with an essentially flat end surface 912b in the area of the apex 912a of the cone 912 (see FIG. 4).
  • the cone 912 is then coated with metal in a vapor deposition system, for example with an adhesion promoter layer 918 made of NiCr and the actual non-transparent layer 920 made of aluminum.
  • the cone 912 is rotated about its axis of symmetry A or an axis running essentially parallel to this axis of symmetry. Tilting the axis of rotation relative to the direction of vaporization ensures that the flat end surface 912b on the apex 912a of the tip 912 is always in the "vaporization shadow" of the tip 912 and is not vaporized. In this way, an essentially round aperture 916 in the metal casing 918/920 is obtained in the area of the apex 912a of the tip 912.
  • the method described above allows the method parameters when producing the cone (intensity of the laser,
  • the glass fiber core is deformed on pulling over a relatively large distance, which results in a deterioration in the optical transmission of the glass fiber.
  • the method allows only the individual manufacture of tips, particularly due to the drawing step. Series production of large quantities is not possible.
  • the method known from US 4,469,554 has the advantage that the glass fiber is deformed only in the area of the cone, which has a favorable effect on the transmission properties of the probe tip, and that it can also be easily expanded to large quantities.
  • a disadvantage, however, is that the size of the aperture created in the area of the apex of the probe tip does not depend on process parameters can be controlled.
  • the etching-related surface roughness of the tips partially interferes with the vapor deposition process.
  • a self-illuminating probe tip is known from US Pat. No. 6,396,050 B1 and JP 2000-292 339 A.
  • a probe tip is known from EP 1 01 6 868 A1, in which the light exit end of a glass fiber is surrounded by a metallization.
  • This optically transparent intermediate layer can be applied to the glass fiber cone by any known thin-layer application method, the thickness of the deposited optically transparent intermediate layer being determined either by the composition of the Starting material or the deposition parameters, for example the deposition time, can be influenced in a targeted manner. It is thus possible in a simple manner to set the size of the optical aperture of the probe tip to the value desired in each case.
  • the optically transparent layer can for example be made of a dielectric material.
  • dielectric refers to the behavior of the respective material in the wavelength range relevant for the optical examinations and to the temperature at which these optical examinations are carried out. In particular, regardless of whether this material shows a different behavior in a different wavelength range, for example a metallic behavior
  • ITO indium tin oxide
  • correspondingly doped semiconductors and the like examples of materials which change their behavior depending on the wavelength and temperature.
  • the optically transparent intermediate layer is advantageously formed from an optically broadband permeable material.
  • MgF 2 is suitable as an optically transparent material for use in the near infrared and visible spectral range. Since, as described above using the example of the prior art, the optically non-transparent layer is usually applied to the probe tip anyway in a vapor deposition system, it is recommended in a development of the invention that the optically transparent intermediate layer is also a vapor-deposited layer.
  • MgF 2 has the advantage that it can be thermally evaporated at moderate temperatures, and this with a well controllable evaporation rate of about 1 nm / sec. Of course, other materials can also be used, for example SiO 2 .
  • the following thin-film processes are also suitable as processes for coating the glass fiber tips: Sputtering and other plasma-assisted deposition processes (e.g. PECVD; plasma enhanced chemical vapor deposition), molecular beam epitaxy (MBE; molecular beam expitaxy), electrolytic deposition, wetting with liquid coating materials, self-organized deposition processes (e.g. SAM; self-assembled monolayer deposition), Langmuir-BIodget- Methods of applying monatomic layers, and the like.
  • plasma-assisted deposition processes e.g. PECVD; plasma enhanced chemical vapor deposition
  • MBE molecular beam epitaxy
  • electrolytic deposition wetting with liquid coating materials
  • self-organized deposition processes e.g. SAM; self-assembled monolayer deposition
  • Langmuir-BIodget- Methods of applying monatomic layers and the like.
  • Applying the optically transparent intermediate layer by means of vapor deposition in turn has the advantage that, like in the application of the optically non-transparent layer, the probe tip can shade itself, so that the apex of the tip is not coated. But even if the apex of the tip is covered with optically transparent material, the opening width of the probe tip can be controlled in a simple manner, again via the thickness of the optically transparent intermediate layer. Examples of thin-film application methods that do not allow the tip to be shaded by itself are sputtering or immersion of the glass fiber cone in a liquid and curable material.
  • At least one further intermediate layer is provided between the peripheral surface of the light-conducting fiber and the optically transparent intermediate layer, which is preferably formed from an originally liquid, but curable material. After wetting the peripheral surface of the probe tip, the surface tension of the liquid smoothes the surface roughness of the probe tip.
  • the further intermediate layer can be formed, for example, from a polymer material, for example a UV-curable adhesive.
  • the use of such adhesives has the advantage that the refractive index that these materials have after curing is usually adapted to the refractive indices of conventional glasses, as are also used for glass fibers.
  • the additional intermediate layer can be applied, for example, by simply immersing the tips in the liquid material and then pulling them out again and then holding the apex upward, if desired.
  • the purpose of the latter measure is to avoid accumulation of polymer material in the area of the apex of the probe tip. Holding the apex upwards can be dispensed with if it is ensured that the surface tension of the liquid outweighs gravity in the dimensions under consideration.
  • special curing methods can be used, which can include, for example, at least one pre-curing step and at least one post-curing step.
  • the width of the opening of the probe tip can be influenced by the properties of the liquid polymer material, the number of "dives" and the like parameters.
  • the optically non-transparent layer it is proposed according to the invention to use a material which is essentially non-absorbent.
  • the optically non-transparent layer can comprise at least one metal layer.
  • the optically non-transparent layer can comprise a layer of aluminum, preferably at least 200 nm thick.
  • aluminum has very good mirror properties in the near infrared and visible spectral range, ie a low absorption capacity and a low penetration depth.
  • it draws aluminum is relatively easy to process. In particular, it can be quickly evaporated at low pressure to avoid the formation of alumina.
  • silver or rhodium can also be used to form the optically non-transparent layer.
  • the optically non-transparent layer can also be coated with a protective layer, for example a protective layer made of a polymer material, in order to avoid oxidation.
  • the optically non-transparent layer can also comprise a layer of NiCr, preferably a few nanometers thick.
  • NiCr serves as an adhesion promoter between the optically transparent intermediate layer and the aluminum metallization.
  • Fig. 4 is a probe tip manufactured according to the prior art.
  • a probe tip according to the invention is generally designated 10.
  • the center piece of this probe tip 10 forms a
  • the glass fiber cone 12 can, for example, with the processes known from US 4,469,554 can be produced by etching.
  • the exposed part of the glass fiber is then cleaned thoroughly with acetone and then with methanol or isopropanol.
  • the glass fibers prepared in this way are used for the following
  • Holders equipped with glass fibers are then again combined on a carrier.
  • the etching process takes place in a vibration-damped construction in order to prevent any relative movement between the glass fiber ends immersed in the etching liquid and the etching liquid or the stop layer.
  • the carrier receiving the plurality of glass fibers can be provided with a motor control which allows the tips to be automatically or remotely immersed in the etching liquid and withdrawn therefrom.
  • 40% hydrofluoric acid can be used as the etching solution.
  • the stop layer can be formed by the volatile solvent isooctane.
  • the fibers are immersed in the etching liquid for approx. 5 mm and remain there for about 80 minutes. After this time, the process is safely completed and the finished fiber cones are removed from the chamber. In a final cleaning step, the cones are boiled with the help of boiling, deionized water and heated acetone and Process residues are removed from isopropanol. Afterwards, the glass fibers should be introduced into the vacuum chamber of a vapor deposition system as soon as possible, since they could otherwise be contaminated by dust and particles in the room air, which could result in holes in the deposited coating during the subsequent vapor deposition.
  • the glass fiber carrier is attached to a motor, preferably a stepper motor, which rotates the glass fibers during the vapor deposition.
  • the axis of rotation is essentially parallel to the axis of symmetry.
  • a of the glass fiber cone 1 2 runs, tilted slightly with respect to the vapor deposition direction, in such a way that the apex 12a of the glass fiber cone points away from the vapor deposition source.
  • the end face 1 2b is always in the shadow of the glass fiber cone 1 2.
  • the end face 1 2 b remains uncoated.
  • stepper motor allows specific motor positions to be approached in a simple manner. This makes it possible, for example, to coat only certain peripheral sections of the glass fiber by not rotating the glass fiber continuously in one direction, but instead defining fixed reversal points at which the direction of rotation of the glass fiber is reversed. It would also be possible to implement a rotational speed that differs in some areas, as a result of which asymmetrical tips could be generated in the areas of slower rotation due to the increased material application.
  • an optically transparent layer 14 which can be formed, for example, from magnesium fluoride (MgF 2 ), is applied directly to the peripheral surface 1 2c of the glass fiber cone 1 2 in the evaporation system.
  • MgF 2 has the advantage that it has a very high broadband permeability for in the near infrared and visible spectral range has electromagnetic radiation.
  • it can be thermally evaporated from tungsten boats at relatively low current densities.
  • evaporation rates in the order of magnitude of about 1 nm / sec can be achieved without further ado, so that the layer thickness d of the vapor-deposited optically transparent layer and thus the diameter D of the optical aperture 16 of the probe tip 10 can be controlled in a simple manner by means of the vapor deposition time.
  • a metal layer is deposited on the outer circumferential surface of the optically transparent layer 14, for example first a thin adhesion promoter layer 18 made of a nickel-chromium alloy (NiCr) of a few nanometers thick and then the actual optically non-transparent layer 20 made of aluminum with a Thickness of at least 200 nm.
  • the aluminum layer 20 should be applied in the evaporation system in the shortest possible time and at the lowest possible residual pressures in order to suppress the formation of aluminum oxide.
  • the metal layer aluminum has on the one hand the advantage of being easy to process and on the other hand the advantage of low absorption and a low penetration depth for light.
  • the layer 20, for example if it is made of silver, can also be coated with an oxidation protection layer, which is not shown in FIG. 1, however.
  • an oxidation protection layer is not necessary due to the auto-passivation of aluminum.
  • the glass fiber cone 12 has a relatively strong surface roughness after the etching step.
  • the edges of the clearly recognizable crater structure represent nuclei for the deposition of the dielectric, for example MgF 2.
  • a smoothing layer 122 made of an initially liquid but curable material to the outer peripheral surface 1 12c of the glass fiber cone 1 12 during the manufacture of the probe tip 1 10.
  • Suitable materials for this smoothing layer are, for example, commercially available UV-curable polymer adhesives, for example the product NOA 61 from Thorlabs.
  • the glass fiber cone 1 12 can for example be immersed in the polymer liquid and immediately pulled out again.
  • the surface tension of the liquid after wetting the outer peripheral surface 1 12c of the glass fiber cone 1 12 ensures that the desired smoothing effect is achieved.
  • Figure b shows a glass fiber cone covered with a smoothing layer.
  • the probe tips 1 10 can be held upwards with the apex 1 12a after being pulled out of the polymer liquid. This last-mentioned process step can be dispensed with if the surface tension of the liquid clearly outweighs gravity.
  • the glass fiber cone 1 12 smoothed in this way can be further processed in a vapor deposition system to apply the optically transparent layer 1 14, the adhesion promoter layer 1 18 and the aluminum layer 120, as has been explained above using the example of the embodiment according to FIG. 1 , to the description of which reference is hereby made. It should be pointed out that the invention is not restricted to the special type of manufacture of the probe tips described here. Rather, the idea of deliberately enlarging the optical aperture through an optically transparent material can also be applied to other situations.
  • a "light-guiding fiber” is a "circumferential surface tapering towards the free end of the fiber", be it now made of glass or a suitable plastic or the like.

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  • Physics & Mathematics (AREA)
  • Health & Medical Sciences (AREA)
  • General Health & Medical Sciences (AREA)
  • General Physics & Mathematics (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Radiology & Medical Imaging (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Microscoopes, Condenser (AREA)

Abstract

L'invention concerne un procédé de production d'un embout de sonde (10) conçu pour des analyses optiques, en particulier dans le domaine de la microscopie optique à champ proche, et présentant une ouverture spécifique. Ce procédé consiste à appliquer, au niveau d'une fibre optique (12) comprenant une surface périphérique (12c) s'amincissant en direction de l'extrémité libre de la fibre, au moins une couche intermédiaire (14) optiquement transparente, entre ladite surface périphérique (12c) et une couche (18/20) optiquement non transparente surmontant cette surface périphérique (12c), l'épaisseur de la couche intermédiaire étant sélectionnée en fonction de l'ouverture souhaitée. Ainsi, les embouts de sonde (10) peuvent être produits au cours d'un procédé simple et évolutif.
PCT/EP2002/014747 2001-12-24 2002-12-23 Procede de production d'un embout de sonde, utilise en particulier en microscopie optique a champ proche et presentant une ouverture specifique WO2003056567A2 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002361214A AU2002361214A1 (en) 2001-12-24 2002-12-23 Method for the production of a probe tip, particularly for near-field optical microscopy, having a desired aperture

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE10164093 2001-12-24
DE10164093.5 2001-12-24

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WO2003056567A2 true WO2003056567A2 (fr) 2003-07-10
WO2003056567A3 WO2003056567A3 (fr) 2004-03-04

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4725727A (en) * 1984-12-28 1988-02-16 International Business Machines Corporation Waveguide for an optical near-field microscope
EP0487233A2 (fr) * 1990-11-19 1992-05-27 AT&T Corp. Microscope de balayage optique de champ proche et ses applications

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4725727A (en) * 1984-12-28 1988-02-16 International Business Machines Corporation Waveguide for an optical near-field microscope
EP0487233A2 (fr) * 1990-11-19 1992-05-27 AT&T Corp. Microscope de balayage optique de champ proche et ses applications

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
GENOLET G ET AL: "MICROMACHINED PHOTOPLASTIC PROBE FOR SCANNING NEAR-FIELD OPTICAL MICROSCOPY" REVIEW OF SCIENTIFIC INSTRUMENTS, AMERICAN INSTITUTE OF PHYSICS. NEW YORK, US, Bd. 72, Nr. 10, Oktober 2001 (2001-10), Seiten 3877-3879, XP001115999 ISSN: 0034-6748 *
MURANISHI M ET AL: "CONTROL OF APERTURE SIZE OF OPTICAL PROBES FOR SCANNING NEAR-FIELD OPTICAL MICROSCOPY USING FOCUSED ION BEAM TECHNOLOGY" JAPANESE JOURNAL OF APPLIED PHYSICS, PUBLICATION OFFICE JAPANESE JOURNAL OF APPLIED PHYSICS. TOKYO, JP, Bd. 36, Nr. 7B, PART 2, 15. Juli 1997 (1997-07-15), Seiten L942-L944, XP000742415 ISSN: 0021-4922 *
YUNG DOUG SUH ET AL: "IMPROVED PROBES FOR SCANNING NEAR-FIELD OPTICAL MICROSCOPY" ADVANCED MATERIALS, VCH VERLAGSGESELLSCHAFT, WEINHEIM, DE, Bd. 12, Nr. 15, 2. August 2000 (2000-08-02), Seiten 1139-1142, XP000963577 ISSN: 0935-9648 *

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AU2002361214A1 (en) 2003-07-15
AU2002361214A8 (en) 2003-07-15

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