JP5413716B2 - Electron emission apparatus and electron emission method - Google Patents

Description

The present invention relates to a novel electron emission device.
The present invention also relates to a novel electron emission method using the electron emission device.

  Recent progress in ultra-fine processing technology is remarkable, and unexplored technologies have been realized one after another. Ultrafine processing is a general term for technologies for processing dimensions of μm or less, and aims to realize and utilize atomic size processing (see Non-Patent Document 1). In fact, the ultra-fine processing technology has greatly contributed to the realization of high-definition and large-display displays and the realization of high functionality and low prices by increasing the density of devices. In particular, the increase in the density of integrated circuits (ICs) is remarkable, and in addition, the trend toward high-mix and low-volume production of ICs has become stronger. Due to this tendency, photolithography (light exposure), which is the mainstream of IC manufacturing, has begun to be regarded as a problem. This problem is particularly noticeable in MEMS (Micro Electro Mechanical Systems).

  MEMS is a small device or structure that uses semiconductor process technology by photolithography. Mechanical element parts, sensors, actuators, and electronic circuits are integrated on a single silicon substrate, glass substrate, organic material, etc. (See Non-Patent Document 2). MEMS is used in various types of sensors, digital micromirror devices (DMD), medical fields, etc., including automobile acceleration sensors, and is expected to be applied in various fields. For this reason, the above-mentioned multi-product / small-volume production is also conspicuous.

  Photolithography, which has become the mainstream in IC manufacturing and MEMS manufacturing, is a pattern transfer technology using light. In addition to being able to generate fine patterns, it is the mainstream of IC manufacturing because it can be mass-produced in a shorter time and at a lower cost than machining because it is a batch process.

  However, as described above, a wide variety of ICs have been demanded, and the increase in cost for producing the original plate has become a great burden. Therefore, a new processing technique replacing photolithography has been demanded. One of them is electron beam lithography.

  Electron beam lithography is a technique in which an electron beam is emitted by applying a voltage to an electron source (emitter), and a photosensitive agent is exposed by the emitted electron beam (see Non-Patent Document 3). Electron beam lithography has the advantage of not requiring an original. Since the size of the electron beam used for exposure is as ultra-fine as about 0.2 nm, a finer resolution than photolithography can be obtained and the controllability of the stage is excellent (see Non-Patent Document 1).

  However, existing electron beam lithography has major drawbacks. That is the processing time (see Non-Patent Document 3). In the electron beam lithography, only the portion irradiated with the electron beam is exposed, so that it is necessary to scan the entire substrate to be processed. Therefore, it takes much time compared to photolithography in which one section is exposed at a time.

  In order to overcome this drawback, improvements in the beam shape and the substrate scanning method have been made and put into practical use (see Non-Patent Document 1). In addition, parallel emitters have been proposed as a new method. In this method, a plurality of emitters are arranged and scanning / drawing is performed simultaneously or while switching. In addition, means for dividing one electron beam into a plurality of devices has been devised (see Non-Patent Documents 1 and 3). If this method is used, the processing time can be greatly reduced.

  In addition, P. Hommelhoff et al. Have reported research on electron emission devices (see Non-Patent Document 4). They irradiate a Ti: sapphire pulsed laser perpendicular to the tungsten emitter.

Tatsuo Mayo Basics of Ultra Fine Processing 2nd edition Nikkan Kogyo Shimbun (2001) Seiko Instruments Inc. Website http://www.sii.co.jp/ Hiroshi Yokoyama, Hiroyuki Akinaga Electron Lithography Textbook Ohmsha (2007) P. Hommelhoff, Y. van Sortais, A. Aghajani-Talesh, and M. A. Kasevich, “Field Emission Tip as a Nanometer Source of Free Electron Femtosecond Pulses”, Physical review letters, 96, 077401 (2006).

  As described above, in order to overcome the disadvantage that electron beam lithography takes much longer than photolithography, parallel emitters have been proposed as a new method. However, problems remain in paralleling the emitters. Since the voltage applied to the emitter is very high, it is difficult to reduce the size of the switching device that controls the voltage application to each emitter because of insulation and wiring, and there is a limit to narrowing the emitter array interval. Arise. As a result, it becomes difficult to arrange high-density emitters.

Also, as described above, research on electron emission devices has been reported by P. Hommelhoff et al. They irradiate a Ti: sapphire pulsed laser perpendicular to the tungsten emitter. We have succeeded in lowering the applied voltage by inducing an electric field at the tip of the emitter by irradiating the emitter with a large laser called a femtosecond pulse laser. However, the method used by P. Hommelhoff et al. Has a problem that a femtosecond pulse laser with a peak intensity of 30 GW / cm ² and an extremely high output is required.

  Therefore, development of a novel electron emission device and an electron emission method that solve such a problem is desired.

The present invention has been made in view of such problems, and an object thereof is to provide a novel electron emission device.
Another object of the present invention is to provide a novel electron emission method using the electron emission device.

  In order to solve the above-mentioned problems and achieve the object of the present invention, an electron emission device of the present invention irradiates a laser beam to an emitter, an extraction electrode to which a voltage is applied between the emitters, and a tip of the emitter. It has the laser irradiation apparatus which performs.

Here, although not limited, the emitter is preferably made of gold, silver, copper, aluminum, or platinum. Although not limited, it is preferable that the emitter tip diameter is in the range of 1 to 400 nm. Although not limited, the distance between the emitter tip and the extraction electrode is preferably within a range of 10 nm to 5 mm. Moreover, although not necessarily limited, it is preferable that the applied voltage exists in the range of 1mV-1000V. Although not limited, it is preferable that the intensity peak value of the pulse laser or the intensity of the continuous wave laser be in the range of 1 W / cm ^{2 to} 10 GW / cm ² .

  The electron emission method of the present invention is characterized in that a voltage is applied between the emitter and the extraction electrode under reduced pressure, and laser light is irradiated to the tip of the emitter.

Here, although not limited, the emitter is preferably made of gold, silver, copper, aluminum, or platinum. Although not limited, it is preferable that the emitter tip diameter is in the range of 1 to 400 nm. Although not limited, the distance between the emitter tip and the extraction electrode is preferably within a range of 10 nm to 5 mm. Moreover, although not necessarily limited, it is preferable that the applied voltage exists in the range of 1mV-1000V. Although not limited, it is preferable that the intensity peak value of the pulse laser or the intensity of the continuous wave laser be in the range of 1 W / cm ^{2 to} 10 GW / cm ² .

  The present invention has the following effects.

  The electron emission device of the present invention includes a emitter, an extraction electrode to which a voltage is applied between the emitter, and a laser irradiation device for irradiating laser light to the tip of the emitter, and thus provides a novel electron emission device can do.

  The electron emission method of the present invention can provide a novel electron emission method because a voltage is applied between the emitter and the extraction electrode under reduced pressure and the tip of the emitter is irradiated with laser light.

It is an electron micrograph (applied voltage: AC 2V) of an electropolished tungsten wire. It is a figure which shows the direction of gold | metal | money sputter | spatter. FIG. 3 is an electron micrograph of a tungsten wire on which gold is sputtered from the direction of FIG. 2. It is a figure which shows an experimental apparatus. It is a figure which shows the experimental result of an electron beam emission, and an approximated curve, (a) IV characteristic, (b) FN plot. It is a figure which shows the field emission using the electric field enhancement effect by plasmon resonance. It is a potential diagram for electrons at the tip of a metal emitter. It is a figure which shows the experimental apparatus for the optical control field emission experiment using plasmon resonance. It is a figure which shows the definition of angle (theta) showing a polarization direction. It is a figure which shows the experimental value in the case of (theta) = 90 degrees (s polarization | polarized-light), (a) I-V characteristic, (b) FN plot. It is a figure which shows the experimental value in the case of (theta) = 0 degree (p polarization | polarized-light), (a) I-V characteristic, (b) FN plot. It is a figure which shows the experimental value in the case of no laser irradiation, (a) I-V characteristic, (b) FN plot. It is a figure which shows the comparison of the I = V characteristic in the case of p polarized light irradiation, s polarized light irradiation, and a laser absence. (a) Comparison of applied voltages required to obtain 5 pA and (b) 0.1 pA emission (laser power 10 mW). It is a figure which shows the comparison of the emission current with respect to incident light output in the case of applied voltage (a) 650V and (b) 700V.

  Hereinafter, embodiments for carrying out the invention according to an electron emission device and an electron emission method will be described.

The electron emission device includes an emitter, an extraction electrode to which a voltage is applied between the emitters, and a laser irradiation device that irradiates laser light onto the tip of the emitter.
The electron emission method is a method in which a voltage is applied between the emitter and the extraction electrode under reduced pressure, and laser light is applied to the tip of the emitter.

  As the emitter, it is possible to use a sharp metal single piece or a sharp base material formed with a metal thin film.

  Gold, silver, copper, aluminum, platinum, or the like can be used as the pointed metal simple substance.

  As the sharp base material, tungsten, silicon, silicon oxide, silicon nitride, quartz glass, lithium niobate, aluminum oxide, or the like can be used.

  As the metal thin film, gold, silver, copper, aluminum, platinum or the like can be adopted.

  The thickness of the metal thin film is preferably in the range of 10 to 400 nm. When the thickness of the metal thin film is within this range, there is an advantage that plasmon resonance can be efficiently excited.

  The emitter tip diameter is preferably in the range of 1 to 400 nm. When the emitter tip diameter is 1 nm or more, there is an advantage that plasmon resonance having sufficient intensity at the tip can be excited. When the emitter tip diameter is 400 nm or less, there is an advantage that the electric field can be enhanced by plasmon resonance at the tip.

  As the extraction electrode, gold, silver, copper, aluminum, platinum, silicon, chromium, nickel, or the like can be used.

  The distance between the emitter tip and the extraction electrode is preferably in the range of 10 nm to 5 mm. When the distance between the emitter tip and the extraction electrode is 10 nm or more, there is an advantage that leakage current due to direct tunneling to the extraction electrode can be prevented. When the distance between the emitter tip and the extraction electrode is 5 mm or less, there is an advantage that electron beam emission can be performed at a voltage of 1 kV or less.

  The applied voltage is preferably in the range of 1 mV to 1000 V. When the applied voltage is 1 mV or more, there is an advantage that sufficient electric field strength can be obtained when the emitter and the extraction electrode are arranged at a distance of about 10 nm. When the applied voltage is 1000 V or less, there is an advantage that discharge can be performed with an inexpensive power supply device.

The degree of vacuum in the vacuum chamber is preferably in the range of 1 × 10 ⁻³ Torr or less. When the degree of vacuum is 1 × 10 ⁻³ Torr or less, there is an advantage that an electron beam can be easily emitted by increasing the mean free path of electrons.

  The wavelength of the laser is preferably in the range of 157 to 900 nm. When the laser wavelength is 157 nm or more, there is an advantage that an isolated plasmon of platinum can be excited. When the wavelength of the laser is 900 nm or less, there is an advantage that gold isolated plasmons having the longest plasmon resonance wavelength among metals can be excited.

  The laser output is preferably in the range of 0.001 to 500 mW. If the laser output is 0.001 mW or more, there is an advantage that sufficient plasmon resonance can be excited. When the laser output is 500 mW or less, there is an advantage that the laser device is classified into class 3 or less.

The intensity peak value of the pulse laser or the intensity of the continuous wave laser is preferably in the range of 1 W / cm ^{2 to} 10 GW / cm ² . When the intensity peak value of the pulse laser or the intensity of the continuous wave laser is 1 W / cm ² or more, there is an advantage that sufficient plasmon resonance can be excited. When the intensity peak value of the pulse laser or the intensity of the continuous wave laser is 10 GW / cm ² or less, there is an advantage that the influence of the change in the energy of electrons due to multiphoton absorption is small or can be ignored.

  The laser spot size is preferably in the range of 20 μm or less. When the spot size is 20 μm or less, there is an advantage that much of the energy of the incident laser contributes to plasmon resonance excitation.

  The polarization direction of the laser is preferably in the range of 0 to 90 °. When the polarization direction of the laser is 0 ° or more, there is an advantage that plasmon resonance can be excited by irradiation from the emitter base side. When the laser polarization direction is 90 ° or less, there is an advantage that plasmons can be excited in the emitter axis direction by irradiation from the side surface of the emitter.

  Applications of the electron emission apparatus or the electron emission method include electron beam lithography, X-ray source, terahertz light source, infrared light source and the like.

  Specific experimental examples of the electron emission apparatus and the electron emission method will be described.

  The production and evaluation of a field emission electron source will be described. In the present invention, a very important element is an electron source (emitter). In order to generate field emission, it is necessary to increase the electric field between the electrodes. Therefore, a sharp metal is used for the emitter. This is because an electric field is concentrated around such a fine protrusion, so that a high electric field can be generated more easily than a flat plate. The structure factor of the acicular emitter depends on the radius of curvature of the emitter tip. Therefore, the smaller the radius of curvature, the larger the electric field between the extraction electrodes can be applied with a lower applied voltage than the parallel plate electrodes.

  Furthermore, the tunnel effect depends on the thickness of the potential barrier and tunnels from the thinnest place of the barrier. In field emission, it is the electric field that determines the thickness of the barrier, and the higher the electric field, the thinner the barrier. Therefore, it can be seen that when the electric field is increased by sharpening the emitter, electron tunneling occurs only in the tip radius region of the emitter. From this, sharpening of the emitter leads to a reduction in the electron emission area in addition to an increase in electric field. The reduction of the emission area leads to an improvement in drawing resolution in electron beam lithography. Therefore, the electron source needs to be as sharp as possible.

  A method for manufacturing the electron source will be described. One method of processing and polishing metal is electrolytic polishing [8]. In the electrolytic polishing, the object to be polished is immersed in an electrolytic solution as an anode and a voltage is applied. And it is a technology to smooth the anode surface by the anodic dissolution action at that time, and this method can be processed into a clean surface, does not cause deterioration of the work piece, difficult to machine shape and size It is characterized by the fact that other metals can be processed [9]. Therefore, in the present invention, it is used as an emitter manufacturing means.

  In the electrolytic polishing apparatus, a commercial AC power supply was used, and the applied voltage was adjusted using a slide transformer manufactured by Tokyo Rikosha. A tungsten wire having a diameter of 0.15 mm was prepared as a material for the emitter base material, and a 10% by mass potassium hydroxide aqueous solution was used as the electrolyte. An iron washer was used as the counter electrode.

  As a procedure, first, a tungsten wire cut to an appropriate length is sandwiched between clips and passed through a washer fixed at the solution interface. Next, an arbitrary voltage is applied using a slide transformer. When it is confirmed that a spark has been generated from the tungsten wire and it has been cut, the voltage application is quickly stopped and the tungsten wire is pulled up from the solution. Finally, the polished tungsten wire is immersed in pure water to remove the solution. FIG. 1 shows an SEM image of a tungsten wire polished at 2V.

  The production and evaluation of an electron source for plasmon resonance will be described. In order to use plasmon resonance, it is necessary to make the resonance wavelength of the emitter coincide with the wavelength of irradiation light. The resonant wavelength of the emitter depends on the shape of the tip of the emitter and the material of the base material / metal thin film. In the present invention, in addition to the reference, a sharpened tungsten wire formed with a gold thin film is used as an emitter because the excitation light source is relatively easily available because the resonance wavelength is visible light [4, 5].

  Gold was sputtered onto a sharpened tungsten base material produced by the method described above. An apparatus (SC-701H) manufactured by Sanyu Electronics Co., Ltd. was used for sputtering. Sputtering was performed from the direction shown in FIG. Sputtering was performed only once toward the tip of the base material.

  A SEM image of the sputtered emitter is shown in FIG. The tip diameter was about 200 to 300 nm. In addition, although it vapor-deposited by the same method, about the gold | metal | money vapor-deposited in the front-end | tip and tungsten was exposed, the film thickness of gold was indirectly measured from this peeling part. As a result, it was found that a gold thin film of about 50 nm adhered.

  A field emission detection experiment will be described. First, the experimental apparatus will be described. In conducting a field emission light control experiment, it is necessary to first verify that field emission occurs in an experimental apparatus used in the present invention. As a basic experiment in the present invention, field emission was detected using a sharpened tungsten base material prepared in the manner described above and sputtered with a thin gold film of about 50 nm.

  Fig. 4 shows the experimental apparatus used. In consideration of the surface roughness, the extraction electrode 4 was prepared with a counter electrode plate in which a gold thin film was sputtered on a cover glass.

The gap between the emitter 3 and the counter electrode plate can be adjusted by the Z-axis stage 5. Insulating property is ensured by sandwiching the glass plate 7 and the fluororesin sheet 6 between the z-axis stage 5 and the counter electrode plate. The ADCMT microammeter (8340A) is used in combination for power supply and emission current measurement. This device can adjust the applied voltage from DC 0V to DC 1000V, and the detection current resolution is from 10 fA to 20 mA. The vacuum chamber 2 can reach a vacuum degree of about 2.0 × 10 ⁻⁶ Torr by baking.

The experimental method will be described. First, the inside of the vacuum chamber is evacuated until the degree of vacuum is about 2.0 × 10 ⁻⁶ Torr. Next, the gap between the emitter and the counter electrode plate is reduced by an automatic stage. At this time, the work is performed while checking whether the emitter is in contact with the CCD so that the emitter does not contact the counter electrode plate. The gap was 1 mm. Next, the applied voltage is increased in 10 V increments in an arbitrary range, and the current value at each voltage is recorded. The current value is 15 points for each voltage, and the averaged value is used as the detection value. Next, IV characteristics are created using the voltage and the detected current. Next, a Fowler-Nordheim plot (FN plot) is created in the same manner.

  The experimental results will be described. The current I generated by field emission is considered to vary exponentially with the applied voltage V. Therefore, it can also be expressed as follows.

  From this equation, it can be said that when performing a field emission detection experiment, it can be determined whether or not the detected current increases or decreases exponentially with respect to the applied voltage. Furthermore, it can be seen that the current generated by the field emission can be determined when it becomes a straight line in the FN plot.

  Fig. 5 shows the IV characteristics and F-N plots obtained from the experiment. Looking at the IV characteristics in the figure, it can be seen that the current increases exponentially with increasing voltage. In addition, the F-N plot shows that it is along a straight line that descends to the right.

  A discussion on the experimental results will be described. In the experimental results, an exponential increase in current and a linear approximation of the FN plot were confirmed. From these facts, the current detected in this experiment is a Fowler-Nordheim type tunnel current, which is considered to be generated by field emission.

  An optically controlled field emission experiment using plasmon resonance will be described. Here, as shown in FIG. 6, an experiment is performed in which plasmon resonance is excited using laser light to generate electric field enhancement, thereby inducing field emission.

  Since field emission requires a high electric field, the applied voltage is usually increased or the gap between the emitter and the extraction electrode is reduced. Since light is a kind of electromagnetic wave, the electric field is enhanced when it is irradiated with very strong light, and the thickness of the potential barrier in the gap can be reduced without increasing the applied voltage as shown in FIG. From this, it can be expected that the threshold of the applied voltage required for field emission is lowered, and this is confirmed by P. Hommelhoff et al. [2]. However, their research has the disadvantages that the power of the laser used to enhance the electric field is too large and the cost is very high, and that it is difficult to differentiate between field emission and photoemission due to the large laser power. . Electrons that have jumped out by photoelectron emission come out at a higher level than that by field emission, so that the energy of the electrons also increases. In electron beam lithography, the energy distribution of the electron beam affects the scattering in the photosensitizer and is also a factor in drawing resolution [1]. For this reason, it is not desirable that electrons having different energies are mixed as described above when optically controlled field emission is applied to electron beam lithography.

  On the other hand, plasmon resonance has the characteristic of significantly enhancing the electric field [6,7]. Therefore, it is confirmed that field emission assistance can be achieved by plasmon resonance even in a low-power laser that is easily available in the present invention and is less affected by photoelectron emission. And it is proved that the research is more applicable than the research of P.Hommelhoff et al.

  The experimental apparatus will be described. The apparatus used here is shown in FIG. The apparatus itself uses the same thing as FIG. Further, gold is sputtered on the surface of the emitter 3 to a thickness of about 50 nm as described above. For the excitation light, the second harmonic (532 nm) of a YAG (Yttrium Aluminum Garnet) laser is used in consideration of references and the like [6, 7]. The laser used is a continuous wave with a maximum output of 10 mW (SUWTECH LDC-1500 manufactured by Nippon Laser Corporation). However, the laser output is measured using a laser power meter (LaserCheck manufactured by Edmond) on the plane in front of the lens 14, and the laser output on this plane is used as an experimental condition thereafter. The laser spot size is reduced to about 17 μm by passing a lens 14 having a focal length of 25.6 mm. The direction of polarization of the laser with respect to the emitter tip is defined using θ shown in FIG.

The experimental method will be described. First, in a state where the vacuum chamber is open, the optical axis of the laser and the tip of the emitter are aligned while checking with a CCD. After aligning the optical axis, close the vacuum chamber. Next, the inside of the vacuum chamber is brought into a state where the degree of vacuum is about 2.0 × 10 ⁻⁶ Torr. Next, the gap between the emitter and the counter electrode plate is reduced by an automatic stage. The gap was 1 mm. Next, the laser polarization direction θ and the laser output P are changed, and the emission current under each condition is recorded by the same means as described above. Next, the current value when the laser is not irradiated is measured in the same manner. Next, using the voltage and detection current under each condition, each IV characteristic and FN plot are created.

  The experimental results will be described. First, experimental results are shown in FIGS. Fig. 10 shows an experiment under the polarization direction condition of θ = 90 ° (S-polarized light) and Fig. 11 shows the polarization direction of θ = 0 ° (P-polarized light). It is. In each polarization direction, the experiment was conducted with three laser output conditions: P = 1 mW, 5 mW, and 10 mW. FIG. 12 shows IV characteristics and F-N plots when the laser is not irradiated. The approximate expression in the IV characteristics in each figure is fitted using the above-described expression, and constants A and B in each condition are shown in Table 1.

 It can be confirmed that the current increases exponentially in any of the I-V characteristics, and that the F-N plot is along a straight line. From this, it can be said that in the experiment under all conditions, the detected current is a current generated by field emission.

  Next, FIG. 13 shows the variation in the low current value region between the approximate expression for each polarization direction and the approximate expression for non-irradiation at P = 5 mW and 10 mW. FIG. 13 shows that the current value increases most when the laser is irradiated with P-polarized light at the same applied voltage. Next, it is S-polarized light and no laser irradiation. In the case of P-polarized light, the current value increases by about 80% at the maximum compared to the case of S-polarized light.

  Furthermore, the applied voltages required to detect the currents of 5 pA and 0.1 pA were obtained using the respective polarization direction conditions at P = 10 mW and the approximate expression in the IV characteristics without laser irradiation. The results are shown in FIG. As shown in FIG. 14, the applied voltage is the lowest under the condition where the laser beam is incident with P-polarized light at any current value, which is a maximum decrease of about 14% compared to the case of no laser irradiation. Even under the S-polarized condition, it was confirmed that the required applied voltage was reduced by about 7% at maximum compared to the case without laser irradiation. In this way, the decrease in the applied voltage required for an arbitrary current value can be confirmed equally even in a remote region. Therefore, it is considered that the applied voltage is reduced by irradiating the laser in any emission current region in this experimental result.

  Finally, FIG. 15 shows emission current-laser output characteristics when applied voltages are 650 V and 700 V. FIG. From the figure, it can be seen that the increase in current with respect to laser output is saturated per mW for both P-polarized light and S-polarized light. This value is significantly smaller than that required for multiphoton absorption and thermionic emission [3].

From the above results, the following points can be said with respect to the current obtained in this experiment.
(1) The value of the field emission current increases by irradiating the laser.
(2) Depends on the laser polarization direction.
(3) Although there is a difference in value, the threshold value of the applied voltage decreases due to laser irradiation.
(4) The increase in current saturates at about 1 mW with respect to the laser output.

  Consider the experimental results. First, the dependence of experimental values on laser power will be described. From the experimental results, it was found that the increase in the experimental value with respect to the laser output disappeared after 1 mW. However, it can be imagined that there was some influence on the emitter from the laser because the current increased due to the laser irradiation.

  If this effect is due to photoemission, P.Hommelhoff et al. May suggest that the current value increases linearly with the laser output [2]. However, as shown in FIG. 15, no linearity of current with respect to the laser output is observed.

If the laser output is converted into heat when it hits the emitter and the electrons are emitted by that heat, this phenomenon can be attributed to the Schottky effect of thermionic emission [3]. However, thermionic emission is also dependent on the laser output or energy. Therefore, thermionic emission is not considered to be a factor from FIG.
From the above, it can be said that the current value increased only by field emission, not photoelectron emission or thermal electron emission.

The dependence between the experimental value and the laser polarization direction will be described. It was found that there is a dependency between the experimental value and the polarization direction of the laser. Therefore, in this experiment, it is presumed that the emitter was excited by plasmon resonance or photoemission, and the current was increased [2,10]. However, as described above, it has been confirmed that photoemission is not a factor.
From the above, it is considered that the increase in the detected current in this experiment is due to the electric field enhancement by plasmon resonance.

Explain the results of comparison with previous studies. The degree of threshold decrease confirmed in this experiment was significantly lower than in the previous study [2]. However, there are the following advantages compared to previous studies.
(1) The peak intensity of the femtosecond pulse laser used by P. Hommelhoff et al. Is 30 GW / cm ² , whereas the intensity of the second harmonic of the YAG continuous wave laser used in the present invention is 4.4 KW / cm ² The output is extremely low, and this is also an advantage. The intensity of the second harmonic of the YAG continuous wave laser used in the present invention was calculated as follows. That is, the calculation was performed assuming that the laser beam was 10 mW, the beam spot was a circle having a diameter of 17 μm, and the intensity was uniformly distributed in a circular cross section.
(2) It was possible to consider by eliminating factors other than field emission such as photoelectron emission and thermal electron emission. Therefore, the decrease in threshold in this experiment is purely due to plasmon resonance.

From the above, the conclusions of this experiment can be summarized as follows.
(1) The current increase phenomenon obtained in this experiment is caused by field emission with electric field enhancement assistance by plasmon resonance.
(2) By using plasmon resonance to assist field emission, the threshold of applied voltage can be reduced by up to 14%.

  It is to be noted that the present invention is not limited to the embodiment for carrying out the above-described invention, and various other configurations can be adopted without departing from the gist of the present invention.

[References]
[1] Hiroshi Yokoyama and Hiroyuki Akinaga Electron lithography textbook Ohmsha (2007)
[2] P. Hommelhoff, Y. van Sortais, A. Aghajani-Talesh, and MA Kasevich, “Field Emission Tip as a Nanometer Source of Free Electron Femtosecond Pulses”, Physical review letters, 96, 077401 (2006).
[3] Junichi Miyairi and Yoshio Hashimoto Easy electronic properties Morikita Publishing Co., Ltd. (2006)
[4] Muneyuki Date, Hidetoshi Fukuyama, Kosaku Yamada, Tsuneya Ando Graduate School of Physical Properties 1 Kodansha Scientific (1996)
[5] The Institute of Electrical Engineers, Plasma Engineering Ohmsha (1997)
[6] Takayuki Okamoto Optics, 33, 152 (2004)
[7] YC Martin, HF Hamann, and H. Kumar Wickramasinghe, “Strength of the electric field in apertureless near-field optical microscopy”, J. Appl. Phys, 89, 10, 15 (2001)
[8] Nakano Science Co., Ltd. Website http://www.nakano-acl.co.jp/index.html
[9] KM Corporation Website http://www.denkai-kenma.com/company.html
[10] S. Tsujino, P. Beaud, E. Krik, T. Vogel, H. Sehr, J. Gobrecht, and A. Wrulich, “Ultrafast electron emission from metallic nanotip arrays induced by near infrared femtosecond laser pulses”, Appl Phys. Lett. 92, 193501 (2008).

DESCRIPTION OF SYMBOLS 1 ... CCD camera, 2 ... Vacuum chamber, 3 ... Emitter, 4 ... Lead-out electrode, 5 ... Z axis stage, 6 ... Fluororesin sheet, 7 ... Glass plate, 8 ... Connector, 9 ... Current-voltage conversion, 10 Display, 12 Plannsmon resonance, 13 Laser, 14 Lens, 15 Electron beam, 16 Babinet Soleil compensator, 17 Polarizer, 18 Polarization direction

Claims (12)

An emitter,
An extraction electrode to which a voltage is applied between the emitter and
Have a laser irradiation apparatus for irradiating a laser beam on the tip of the emitter,
The emitter is made of gold, silver, copper, aluminum or platinum,
An electron-emitting device that irradiates the laser light from the base side of the emitter or from the side surface of the emitter . The electron emitter according to claim 1, wherein the emitter tip diameter is in a range of 1 to 400 nm. The electron emission device according to claim 2 , wherein the distance between the emitter tip and the extraction electrode is in the range of 10 nm to 5 mm. The electron emission device according to claim 3 , wherein the applied voltage is in a range of 1 mV to 1000 V. The electron emission device according to claim 4 , wherein the intensity peak value of the pulse laser or the intensity of the continuous wave laser is in the range of 1 W / cm ^{2 to} 10 GW / cm ² . The emitter tip diameter is in the range of 1 to 400 nm,
The distance between the emitter tip and the extraction electrode is in the range of 10 nm to 5 mm,
The applied voltage is in the range of 1mV to 1000V,
The electron emission apparatus according to claim 1, wherein the intensity peak value of the pulse laser or the intensity of the continuous wave laser is in the range of 1 W / cm ^{2 to} 10 GW / cm ² . Under reduced pressure,
Apply a voltage between the emitter and the extraction electrode,
Irradiate the tip of the emitter with laser light ,
The emitter is made of gold, silver, copper, aluminum or platinum,
An electron emission method in which the laser beam is irradiated from the base side of the emitter or from the side surface of the emitter . The electron emission method according to claim 7 , wherein an emitter tip diameter is in a range of 1 to 400 nm. The electron emission method according to claim 8, wherein a distance between the emitter tip and the extraction electrode is in a range of 10 nm to 5 mm. The electron emission method according to claim 9 , wherein the applied voltage is in a range of 1 mV to 1000 V. The electron emission method according to claim 10 , wherein the intensity peak value of the pulse laser or the intensity of the continuous wave laser is in the range of 1 W / cm ^{2 to} 10 GW / cm ² . The emitter tip diameter is in the range of 1 to 400 nm,
The distance between the emitter tip and the extraction electrode is in the range of 10 nm to 5 mm,
The applied voltage is in the range of 1mV to 1000V,
The electron emission method according to claim 7 , wherein the intensity peak value of the pulse laser or the intensity of the continuous wave laser is in the range of 1 W / cm ^{2 to} 10 GW / cm ² .

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