DE19822871C2 - Method for producing a near-field probe for optical near-field microscopy - Google Patents

Description

In optical near-field microscopy (SNOM = scanning near field microscopy) becomes a surface with a probe scanned.

This probe serves as a light source. In most cases will turn on simultaneously with the optical signal recorded topographic signal, which additional, contains valuable information about the sample examined. To correctly interpret these results, they must both partial results are to be covered. This must so far in most cases Image editing happen because of the way it is made the topographic and optical tip probes are not are congruent.

In this proposal for the invention a probe for the combined force and near-field optical scanning microscopy already described during the measurement topographic and optical signal spatially to cover to be brought.

STATE OF THE ART

The most widely used near-field optical probes consist of glass fibers drawn to a point, with Aluminum are steamed [1]. The vaporization takes place that an aperture remains free at the front end through which the light can come out. To get this aperture, the fiber is drawn so that the foremost end is flat tears off [2]. Since the steaming takes place diagonally from behind, the aluminum layer forms a protruding bead the aperture. The location of the topographical image relative the simultaneously recorded optical image is determined due to the relative position of the center of the aperture to the am most protruding part of the bead. This relative  The position of each other is usually unknown and can can only be estimated.

This problem also exists with other types of probes such as e.g. B. with extended and steamed micropipettes [3].

With some designs of apertureless probes it may be that topographic and optical tip random to match. So far, apertureless probes have does not reach the technical level that it is represent a realistic alternative to aperture probes.

• 1. Betzig, E., et al., Breaking the Diffraction Barrier: Optical microscopy on a nanometer scale. Science, 1991. 251: p. 1468-1470.
• 2. Betzig, R.E. and J.K. Trautman, Near field scanning optical microscope having tapered waveguide. US 5,272,330, 1993.
• 3. Lewis, A., et al., Near field scanning optical microscopy. US 4,917,462, 1990.
• 4. Hecht, B., Forbidden light scanning near-field optical microscopy, Faculty of Humanities. 1996: Basel. p. 146.

DE 41 06 548 A1 describes a method for a wire as Transmitter or receiver made of electrically conductive material, but not an optical fiber.

EP 763742 A1 describes a rounded probe tip generated by etching.

DE 691 14 209 T2 describes a method for pulling Glass fibers from solid glass blanks.

The object of the invention is a reliably reproducible Process for the production of near-field optical probes with same aperture.  

The task is accomplished through a process according to the characteristics of claim 1 solved.

The glass fibers are pulled so that they are in front have a rounded end.

Then the probes are slanted from behind with metal (e.g. aluminum) vaporized. The size of the aperture can vary the evaporation angle can be set. The first place the probe can be made of glass or a thin one translucent metal coating exist.

Optical glass fibers serve as a starting point for telecommunications with a core diameter of 9 µm and an outer diameter of 125 µm.

The tips are cleaned with a P-2000 pipette puller Sutter Instrument pulled.

The device is microprocessor controlled. Various Parameters can be entered via a keyboard and on a Display can be checked. With this puller the Fiber clamped between two jaws. Through this Baking is a pull with constant force on the fiber transfer. With a CO2 laser, a spot on the fiber heated. The strength of the warming is preset. The The fiber begins to melt. Because of the constant force they are pulled apart while doing so in the heated area thinner. The train speed increases up to one value specified by the set parameter "Vel". A favorable value is 20. At this point the Laser switched off. After a by the parameter "Del" given time span (advantageously Del0126) the Train completed with a predetermined increased force.  

This force is determined by the value for "Pull" (Advantageous 150)

This last step determines the round tip shape.

If the tensile test is successful, the device gives a value for the parameter "Heat on" between 0.14 and 0.17.

The shape of the tip can be determined in a SEM to be controlled.

These tips are coated with aluminum. This is done in such a way that an aperture is formed. For example, a thermal evaporation system from Hochvakuum Dresden is used. Aluminum is divided into three tungsten boats S, for example, as vapor deposition material. The fibers FS are mounted vertically above the boat (see Fig. 2). The holder H for the fibers can rotate about its own axis. The fibers FS are steamed in three steps. The diameter of the aperture can be specified by the choice of the angle.

Fig. 1 shows the near-field probe according to the invention as well as a near-field probe according to the prior art.

Left: Conventional design (SEM image from [4]).

Right: new design (the probe was only incompletely coated to match the shape of the fiberglass core to illustrate)

Claims (3)

1. Method for producing a near-field probe for optical near-field microscopy,

• - in which a translucent glass fiber is heated and pulled
• and after the probe tip has been produced, the outside of the glass fiber is coated from its rear end with an opaque layer which leaves an aperture at the probe tip suitable for near-field optical microscopy,

characterized by

• - that the glass fiber is clamped between two clamping jaws, which exert a constant, predetermined force on the glass fiber,
• that the glass fiber between the two jaws is heated with a heat source of preset power, the glass fiber starting to flow and thereby becoming thinner in the heated area,
• - That the flow rate is measured and the heat source is switched off when the flow rate has reached a predetermined value
• - And that a predetermined period of time after switching off the heat source increases the tensile force to a second predetermined value and thereby the glass fiber is torn in two
• - The temperature of the glass fiber material present at the end of the time period in the area of the crack and thus its viscosity at this point in time ensures the formation of a rounded, non-flat end of the glass fiber.

2. The method according to claim 1, characterized in that a CO ₂ laser is used as the heat source. 3. Near field probe, characterized in that it uses a method according to claim 1 or 2 is made.