JP2000275160A - Method for observing sample by scanning proximity field optical microscope and ultra-flat sapphire substrate for scanning proximity field optical microscope - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable an improved AFM(atomic force microscope) image and a luminous image to be observed for II-VI, III to V, and IV-group semiconductors and quantum structure bodies with optical characteristic especially at red, blue, and ultraviolet regions by using an ultra-flat sapphire substrate as a sample substrate. SOLUTION: A sample is observed by a scanning proximity field optical microscope with an ultraviolet fiber probe 1 by using an ultra-flat sapphire substrate 2 where for example a general sapphire substrate is annealed at 1,000-1,400 deg.C for flattening in units of atomic layers. Since the ultra-flat sapphire substrate 2 can be made flatter than the sample, the influence to a sample emission image due to a substrate itself can be suppressed extremely and resolution can be improved. Also, the sapphire substrate 2 has a high transmittance from an ultraviolet region to a near-infrared region, so that the amount of absorption of ultraviolet emission from the sample can be reduced extremely and the AFM image and emission image of the sample using the ultraviolet fiber probe 1 can be obtained with further high resolution. Further, it has a hydrophobicity so that it is suited for observing a hydrophobic sample such as polysilane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for observing a sample using a scanning near-field optical microscope and an ultra-flat sapphire substrate for a scanning near-field optical microscope. More specifically, the invention of this application provides a novel scanning near-field optical microscope capable of observing a sample having optical characteristics such as band gap from red to blue to ultraviolet with excellent resolution. The present invention relates to an ultra-flat sapphire substrate for a scanning near-field optical microscope.

[0002]

2. Description of the Related Art In recent years, low-dimensional semiconductors such as quantum wires and quantum wells have been produced with the improvement of semiconductor fine processing technology. With the realization of such a confinement system, its unique properties have been observed. ing. On the other hand, also in the field of chemistry, low-dimensional semiconductors are created by synthetic methods.

Conventionally, in order to obtain information on the morphology of a polymer, a method using a viscosity index of a solution or a parameter obtained by light scattering measurement, and microscopic information obtained from nuclear magnetic resonance (= NMR) are statistically analyzed. For example, a method of predicting a molecular form by using such a method has been used. However, in each method, what was observed was the average value of the molecules, and only indirect information could be obtained.

For this reason, a scanning microscope such as an atomic force microscope (= AFM) capable of directly observing individual forms and information of molecules has been used. For example, in a measurement using an atomic force microscope, the form of an organic polymer such as a double helical structure of DNA can be directly confirmed, and a measurement of a single molecule is also performed. However, since only the height information can be obtained with an atomic force microscope, it is not possible to determine whether the obtained image is from the sample to be measured or from scratches or dust on the substrate by using the image and other predictions. There is no other way but to estimate from the correlation with the image and the change of the image when the condition is changed, and there is a problem that the reliability is low.

[0005] Therefore, in order to observe and identify a sample more reliably, a scanning near-field optical microscope capable of obtaining information unique to the sample such as an emission spectrum simultaneously with an AFM image has been developed. This scanning near-field optical microscope can scatter and detect light in a minute area, obtain a spatial resolution exceeding the diffraction limit of light, measure the microstructure and optical spectrum of the sample, and identify the image obtained. Will also be easier.

[0006]

However, in a conventional scanning near-field optical microscope, a sample having optical characteristics such as a large band gap in the ultraviolet region, for example, polysilane, polygermane, polystane, etc., is observed as follows. There were serious problems. That is, since a sample having a large band gap in the ultraviolet region has its absorption and emission in the ultraviolet region, it is necessary to use a scanning near-field optical microscope capable of measuring in the ultraviolet region. However, a scanning near-field optical microscope for ultraviolet light requires a fiber probe having a property of not absorbing ultraviolet light. However, since it is generally difficult to manufacture such a fiber probe for ultraviolet light, its practical use has progressed very little. Was not.

Therefore, in order to solve the problem of the fiber probe against ultraviolet light, ultraviolet fiber probes having high transmission efficiency for ultraviolet light have already been developed (Japanese Patent Application Laid-Open Nos. 10-082791 and 10-082).
792, JP-A-10-153604, JP-A-11-02
3587). With the use of the ultraviolet fiber probe, a scanning near-field optical microscope for ultraviolet has been realized, and observation of polysilane and the like in the ultraviolet region has become possible.

However, observation by a scanning near-field optical microscope using the ultraviolet fiber probe has a practical problem that an AFM image and an emission image in the ultraviolet region cannot be obtained with sufficient resolution. There is a great demand for high-resolution observation by a scanning near-field optical microscope for ultraviolet for spectroscopic analysis of individual particles such as quantum dots and quantum wires, and evaluation of semiconductors. For example, in a polymer semiconductor, theoretical calculations have already been made that the presence of links on the main chain greatly affects the linear and nonlinear optical characteristics, so the structure of the polymer semiconductor is obtained and the optical spectrum from each point is obtained. Accurate measurement of the length is very important for observing the effects of structural defects and segment length on the optical properties, and is not limited to understanding the physical properties of quantum wires. From the viewpoint of the relationship between the shape of a giant single molecule of several μm and the optical spectrum, there are many voices requesting early realization as contributing to further advancement and development of science and technology.

The invention of this application has been made in view of the circumstances described above, and solves the problems of the conventional scanning near-field optical microscope for ultraviolet light, and makes it possible to raise the sample having absorption and emission in the ultraviolet region. It is an object of the present invention to provide a new method for observing a sample using a scanning near-field optical microscope and an ultra-flat sapphire substrate for a scanning near-field optical microscope, which can be observed with excellent resolution.

[0010]

SUMMARY OF THE INVENTION The present invention is directed to a method for observing a sample with a scanning near-field optical microscope equipped with an ultraviolet fiber probe. A method for observing a sample using a scanning near-field optical microscope (claim 1), characterized by using a sapphire substrate, and an ultra-flat surface for a scanning near-field optical microscope used in the method for observing a sample using the scanning near-field optical microscope. A sapphire substrate (claim 2) is also provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The invention of this application is based on a research conducted by the inventors to further improve the resolution in sample observation by a scanning near-field optical microscope equipped with an ultraviolet fiber probe. It was made as a result of various trials and errors, such as trying to modify other components and the sample itself, and achieved its purpose by applying an ultra-flat sapphire substrate as a sample substrate. This makes it possible to obtain a resolution improving effect.

The ultra-flat sapphire substrate used in the present invention is already known in the field of atomic force microscopy, and is manufactured by annealing a general sapphire substrate in air at 1000 ° C. to 1400 ° C. It is an ultra-flat substrate that has been planarized by layers (M. Yoshimoto et al., "Atomic-scale formation of u
ltrasmooth surfaces on sapphire substrates for hig
h-quality thin-film fabrication ", Appl.Phys.Lett.67
(18), (Oct. 1995)). However, in the field of the scanning near-field optical microscope to which the present invention belongs, there is no known ultra-flat sapphire substrate, and the use of the ultra-flat sapphire substrate for the scanning near-field optical microscope is a trial and error process by the inventor of the present invention. This is a completely new concept that has never been found before, and can achieve the following remarkable effects.

[0013] First, since the ultra-flat sapphire substrate can be made flatter than the sample, the influence of the substrate itself on the sample emission image can be suppressed as much as possible, and the resolution of the scanning near-field optical microscope can be reduced. Will be improved. In addition, since this ultra-flat sapphire substrate has a high transmittance to ultraviolet light, the absorption amount of ultraviolet light emitted from the sample is extremely small, and the AFM image and the emission image of the sample can be obtained with a scanning near-field optical microscope equipped with an ultraviolet fiber probe. It will be possible to obtain with higher resolution.

Furthermore, in order to observe a sample having hydrophobicity such as polysilane, the substrate on which the sample is to be placed must also have hydrophobicity. However, this ultra-flat sapphire substrate has ultra-flatness and high transmittance to ultraviolet light. It has not only the property but also the hydrophobic property, and it turned out that it is very suitable for observation of a hydrophobic sample. As described above, according to the present invention, it is possible to observe a sample having optical characteristics such as absorption and emission bands in the ultraviolet region and a sample also having hydrophobicity with high resolution simply by using the ultra-flat sapphire substrate. Become like

Further, the ultra-flat sapphire substrate has high transmittance not only in the ultraviolet region but also in the ultraviolet region to the near-infrared region, and the ultraviolet fiber probe also has a high transmission efficiency for light in the same range. According to the present invention, a sample having optical characteristics not only in the ultraviolet region but also in the near infrared region, particularly in the red and blue regions, can be observed with high resolution. In particular, excellent AFM images and emission images can be obtained for 2-6, 3-5, and Group 4 semiconductors and quantum structures.

The scanning near-field optical microscope can be roughly classified into, for example, those for observing scattering and those for observing light emission.
Illumination mode for irradiating excitation light from the probe, collection mode for receiving signals with the probe,
Both can be divided into three modes: illumination & collection mode in which the probe is used. As a method of keeping the distance from the sample constant when scanning over the sample with the probe, for example, a method of applying feedback based on the detection intensity of light such as evanescent light, STM and ATM
A method of performing measurement in combination with FM is known.
The method of the present invention can be applied to any of the scanning near-field optical microscopes described above.

The embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a conceptual diagram showing the configuration of a main part of an example of a scanning near-field optical microscope to which the sample observation method of the present invention is applied. The scanning near-field optical microscope illustrated in FIG. 1 in this embodiment is of an illumination mode using feedback by shear force, which is a kind of AFM, and includes an ultraviolet fiber probe (1) as a fiber probe. The shear force is a method of measuring the distance between the sample and the probe by vibrating the probe and measuring the magnitude of the amplitude that changes due to the interaction between the sample and the probe.

The ultraviolet fiber probe (1) is
For example, as illustrated in FIG. _TwoDoped silica
(A), pure silica (B), low fluorine doped silica
(C) Double-core fiber is compounded and selected.
Triple taper and Al for light shielding
(D) is deposited by about 200 nm. Figure
Θ in 2₁And θ_TwoIs the first taper and the second taper
The sharp angle θ of the first taper₁Smaller
To improve the light shielding properties and resolution near the tip,
Two taper acute angle θ_TwoBy increasing the metal
Reduce the length of the core covered with
I have.

Other configurations are the same as those of a general illumination mode scanning near-field optical microscope.
(3) Ar laser as excitation light source, (4) laser diode, (5) photodiode, (6) lock-in amplifier, (7) computer, (8) photon counter, (9) A photomultiplier tube, (10) is a bandpass filter, and (11a) and (11b) are hemispherical silica lenses.

In the scanning near-field optical microscope having such a structure, an ultra-flat sapphire substrate (1) is used as a sample substrate.
Using polydi-n-hexylsilane (hereinafter, PDHS)
And n-decyl ((s) 2-methylbutyl)
AFM of each silane (hereinafter referred to as chiral-PS)
The image and the emission image were actually observed. The ultra-flat sapphire substrate (1) can change the step height by changing the direction of the crystal axis and the heating temperature.
In this embodiment, the steps are polished on both sides with a height of about 3 nm.

On the other hand, a PDHS sample and a chiral-PS sample used were prepared as follows. First, PD
HS, Chiral-PS is dissolved in toluene and the concentration is 10-
A 100 µmg / ml PDHS solution and a chiral-PS solution are prepared, and the solution is dropped on an ultra-flat sapphire substrate (1), air-dried at room temperature and in air for several minutes, and then dried again in vacuum for several minutes. Letting P
DHS samples and chiral-PS samples were prepared. As a solvent, toluene for electronics industry from which non-volatile components were removed so as not to hinder the measurement was used.

When observing polysilane, it is necessary to disperse the polysilane on the substrate at an appropriate concentration. If the concentration of polysilane on the substrate is high, the polysilane becomes a large lump and it is difficult to observe individual structures.If the concentration is low, polysilane does not exist within the measurement range and polysilane is observed. There is a risk that many measurements are required. Most preferably, the dispersion of polysilane is such that the entire substrate is uniform and a very small number of polysilanes are present within the measurement range.

However, since it is difficult to actually form such a dispersed state, instead, a method of intentionally forming a concentration distribution on a substrate and changing a measurement location from a measurement result to a desired concentration has been devised. Was. In order to use this method, it is necessary to create a gentle concentration distribution on the substrate, and for this purpose, the solution dropped on the substrate is slowly air-dried slowly in the air to disperse the solution with a gentle concentration distribution. I let it.

Further, even if the solution seems to have completely evaporated by natural drying, the toluene may actually remain as a film on the substrate. For this reason, vacuum drying is performed after natural drying to remove the toluene film. If vacuum drying is not used, probe with a shear force for remaining toluene film.
The control of the distance between the samples becomes unstable.

If vacuum drying is performed immediately after the dropping of the solution without natural drying, the polysilane will not only concentrate at a specific place but also agglomerate. Therefore, it becomes difficult to control the distance by the shear force.
Therefore, it is preferable to perform vacuum drying after natural drying.

Furthermore, since polysilane is decomposed by ultraviolet light, it is preferable that ultraviolet light such as a fluorescent lamp be irradiated as little as possible during drying. In consideration of the above points, in this example, a PDHS sample and a chiral-PS sample having a gentle concentration distribution by natural drying and vacuum drying were prepared as described above. FIG. 3 conceptually illustrates the density distribution of the prepared sample, and shows that the density decreases from a dark color to a light color.

The observation of the AFM image and the emission image of each sample prepared as described above was performed as follows. First, each sample is placed on an ultra-flat sapphire substrate (1), and the sample is excited by an Ar laser (3) through an ultraviolet fiber probe (1). This Ar laser (3)
Is 351n when observing the emission image of PDHS.
m, the wavelength 30 when observing the emission image of chiral-PS.
It was set to 0 nm. In addition, ultraviolet fiber probe (1)
A fiber coupler (not shown) is used at a wavelength of 351 nm for coupling the fiber and a fiber (not shown), and a quartz ball lens (not shown) is used at a wavelength of 300 nm because the objective lens is not transmitted. Was.

Next, light emitted from the sample is condensed by a pair of hemispherical silica lenses (11a) and (11b) provided on the back side of the ultra-flat sapphire substrate (2), and is condensed using a photomultiplier tube (9). To detect. When measuring the emission image of the sample, photon counting is performed by a photon counter (8), and the value is taken into a computer (7) together with height information obtained by shear force. In this emission image measurement, a bandpass filter (10) is provided between the hemispherical silica lens (11b) and the photomultiplier tube (9) to separate the excitation light from the signal. Is 380n in the emission image measurement of PDHS
m center, 330n in emission image measurement of chiral-PS
An m-centered one was used. Further, in the measurement of the scattering image of the ultra-flat sapphire substrate (1), it was taken into the computer (7) via the lock-in amplifier (6).

Here, each of the images thus observed will be described. Note that each observation image was observed at a position distant to some extent from the most aggregated portion in the concentration distribution as exemplified in FIG. The AFM image and the emission image of PDHS can be observed with higher resolution than those obtained when a superflat sapphire substrate is not used as in the related art, and the transplanner structure of PDHS can be recognized to some extent.

From the AFM image and the emission image of chiral-PS, a rigid rod-like molecular form could be confirmed with high resolution. In addition, when the polysilane was stirred in hot toluene to loosen the polysilane to obtain a sample having as little entanglement as possible, in this sample, a finer structure could be confirmed, and the AFM image and the emission image became more correlated images, thus forming a thread-like shape. Rigid rod-shaped polysilane was observed.

In particular, a remarkable improvement in vertical resolution has been observed, and accurate observation of a structure in the height direction, which has not been obtained conventionally, can be realized. In order to further improve the resolution, the measurement is preferably performed at a low temperature so that the polysilane does not fade. Of course, the present invention is not limited to the above-described example, and it goes without saying that various aspects are possible in detail.

[0033]

As described in detail above, the method for observing a sample by the scanning near-field optical microscope and the ultra-flat sapphire substrate for the scanning near-field optical microscope according to the present invention provide optical characteristics such as band gap from the ultraviolet region to the near infrared region. Can be observed with high resolution, especially in the red range,
Observation of excellent AFM images and emission images, which could not be obtained conventionally, is realized for 2-6, 3-5, Group 4 semiconductors and quantum structures having optical characteristics in the blue and ultraviolet regions. it can.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a main part configuration showing an example of a scanning near-field optical microscope to which a sample observation method of the present invention is applied.

FIG. 2 is a conceptual diagram illustrating an ultraviolet fiber probe in the scanning near-field optical microscope of FIG. 1;

FIG. 3 is a conceptual diagram illustrating the concentration distribution of a sample formed on an ultra-flat sapphire substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ultraviolet fiber probe 2 Ultra flat sapphire substrate 3 Ar laser 4 Laser diode 5 Photodiode 6 Lock-in amplifier 7 Computer 8 Photon counter 9 Photomultiplier tube 10 Bandpass filter 11a, 11b Hemispherical silica glass

Continuing on the front page (72) Inventor Mamoru Yoshimoto 4-2-5-1012 Sagamiono, Sagamihara-shi, Kanagawa (72) Inventor Ken Ishikawa 6-14-2 Otsuka, Bunkyo-ku, Tokyo F-term (reference) 2H052 AA07 AA09 AC05 AC12 AC15 AC26 AC34 AE03 AF06 AF11

Claims (2)

[Claims] 1. A method for observing a sample with a scanning near-field optical microscope equipped with an ultraviolet fiber probe,
A sample observation method using a scanning near-field optical microscope, wherein an ultra-flat sapphire substrate is used as a sample substrate. 2. An ultra-flat sapphire substrate for a scanning near-field optical microscope used in the method for observing a sample with the scanning near-field optical microscope according to claim 1.