JP4900791B2 - CNT manufacturing apparatus, CNT manufacturing method, and CNT manufacturing program - Google Patents

Description

  The present invention relates to a CNT manufacturing apparatus, a CNT manufacturing method, and a CNT manufacturing program. More specifically, the CNT growth rate can be observed in situ regardless of the CNT growth height, and The present invention relates to a CNT manufacturing apparatus, a CNT manufacturing method, and a CNT manufacturing program that can be easily changed to an optimal growth condition at which the CNT growth rate becomes an optimal value.

  Carbon nanotubes (CNT) have a three-dimensional structure in which graphene sheets corresponding to one layer of graphite (sheets in which carbon atoms are arranged in a hexagonal network) are rolled into a cylindrical shape. The CNT includes a single-walled CNT made of one cylindrical graphene sheet and a multi-walled CNT in which a plurality of cylindrical graphene sheets are concentrically overlapped. In addition, the tip of the synthesized unprocessed CNT usually has a structure closed with a hemispherical graphite layer called “cap”.

  CNTs have a diameter on the order of nm and a length on the order of μm to cm, have an extremely large aspect ratio, and have a feature that the radius of curvature of the tip is as small as several nm to several tens of nm. CNT is mechanically tough, has excellent chemical and thermal stability, and is characterized by being both a metal and a semiconductor depending on the helical structure of the cylindrical portion. Therefore, CNT is an electronic wiring material for a light emitting device, a heat dissipation material, a fiber material, an electron emission source (surface light source), a transistor material, an electron emission source for an electron microscope (point light source), a probe for SPM, etc. Application to is expected.

To synthesize CNT,
(1) An arc method in which arc discharge is performed between carbon rods mixed with a catalyst in a gas atmosphere such as Ar or hydrogen, and CNT is deposited on the outer wall or cathode of the chamber,
(2) A laser evaporation method in which a strong pulsed light such as a YAG laser is applied to the surface of the graphite mixed with the catalyst, the generated carbon smoke is heated in an electric furnace, and CNTs adhere to the side walls of the reaction tube.
(3) a chemical vapor deposition (CVD) method in which a carbon compound (for example, methane, acetylene, benzene, ethanol, etc.) is thermally decomposed on catalytic metal fine particles,
Etc. are known.

  The CNTs obtained by the synthesis methods (1) and (2) are both in a state of being intertwined in a completely random direction. Moreover, it may contain a large amount of carbon nanocapsules, amorphous particles, and the like. On the other hand, in order to maximize the ultimate anisotropy of CNTs, it is desirable to orient a large number of CNTs on the substrate surface. In addition, when applying CNTs to electronic wiring materials, heat dissipation materials, fiber materials, etc., in order to obtain high current density, high thermal conductivity, high strength, etc., it is desirable to generate CNTs at a high density on the substrate surface. The CVD method (3) is suitable for this purpose.

When catalyst particles are supported on the substrate surface and high density CNTs are generated substantially perpendicular to the substrate surface, the growth rate of the CNTs depends on a plurality of growth conditions such as temperature, pressure, and gas flow rate. Conventionally, when investigating the relationship between these growth conditions and the growth rate of CNTs,
(A) Perform growth experiment of CNT by changing the growth conditions,
(B) After completion of the experiment, the substrate is taken out from the manufacturing apparatus, and the growth height of the CNT is measured with an electron microscope, etc.
(C) The method of calculating the growth rate from the measured growth height has been used.
However, in such a method, it is necessary to perform an experiment every time the condition is changed. Therefore, in order to determine the conditions for obtaining a higher CNT growth rate, it is necessary to perform many experiments.
In addition, since the growth of CNT progresses as the carbon source diffuses to the catalyst particles, the growth rate of CNT changes depending on the growth height of CNT, the environment around the catalyst particles, and the like. However, the growth rate obtained by the conventional method is only an average value under a certain condition, and a change with time of the growth rate cannot be known.

In order to solve this problem, various proposals have conventionally been made regarding methods for measuring in situ the growth height of CNTs.
As for the in-situ measurement methods reported so far, specifically,
(1) Optical interferometry (Non-Patent Documents 1 and 2) that measures the growth height of CNTs in situ using the process difference between the light reflected from the substrate surface and the light reflected from the CNT surface;
(2) An optical absorption method in which light is applied to a substrate on which CNTs are grown, the light absorption rate is obtained from the intensity of the light transmitted through the substrate, and the growth height of the CNTs is measured in situ using the light absorption rate (non-patented) Reference 3),
(3) A single slit laser diffraction method in which a slit is formed in a substrate, CNT is grown perpendicularly to the inner peripheral surface of the slit, and laser light is diffracted by this slit to measure the growth height of the CNT in situ ( Non-patent document 4),
Etc. are known.

Nano Lett. 3 (2003) 863-865 Carbon 41 (2003) 583-585 Chem. Phys. Lett. 403 (2005) 320-323 Nano Lett. 4 (2004) 1613-1620

In the optical interferometry, the interference amplitude decreases as the CNT film thickness increases. Moreover, when the film thickness of CNT becomes thicker, it becomes impossible to measure due to light impermeability. Therefore, the measurement limit of the optical interferometry is about several μm.
In the optical absorption method, the light absorption rate depends not only on the growth height of CNTs but also on the density of CNTs grown on the substrate surface. Further, when the film thickness of the CNT becomes a certain value or more, the light absorption rate is saturated. Therefore, the light absorption method can be applied only to uniformly grown CNTs, and the measurement limit is about 10 μm.
In the single slit laser diffraction method, the maximum measurable film thickness is limited by the slit width. Further, the growth amount of CNT is also affected by the slit shape.
In addition, these methods are not direct observations of the growth amount of CNT, but are indirect film thickness measurement methods for detecting the effects on light and laser. for that reason,
(1) As the amount of growth increases, measurement errors are likely to occur.
(2) The measurement method does not cover the film thickness range necessary for performing conditions.
(3) The special shape of the sample affects the growth rate change.
There are problems such as.
Furthermore, there has never been proposed an example in which a method for measuring CNT growth in situ, changing CNT growth conditions during growth, and growing CNT under optimum conditions has never been proposed.

The problem to be solved by the present invention is to provide a CNT manufacturing apparatus, a CNT manufacturing method, and a CNT manufacturing program capable of in-situ observation of the CNT growth rate regardless of the CNT growth height. It is in.
The problem to be solved by the present invention is to provide a CNT manufacturing apparatus, a CNT manufacturing method, and a CNT manufacturing program that can be easily changed to an optimal growth condition where the growth rate of the CNT becomes an optimal value.
Furthermore, other problems to be solved by the present invention include a CNT manufacturing apparatus, a CNT manufacturing method, a measurement error is small, a measurable film thickness range is wide, and a special sample shape is not required for measurement, and It is to provide a program for manufacturing CNTs.

In order to solve the above problems, the CNT manufacturing apparatus according to the present invention is:
CNT growth means for supplying a carbon source into a container on which the substrate is placed and growing CNTs on the substrate;
An observation means for measuring the growth height of the CNT in situ,
The observation means includes
An optical microscope for capturing an image of a side surface of the substrate;
A digital camera for storing the image as digital data;
It has.
The control means may further include an image processing device that processes the digital data and calculates the growth height.
The CNT manufacturing apparatus
Control means for calculating a growth rate of the CNT from the growth height and changing the growth condition of the CNT to an optimum growth condition based on the growth rate may be further provided.

The method for producing CNTs according to the present invention is as follows:
A first step of growing the CNT while measuring the growth height of the CNT in situ using the CNT manufacturing apparatus according to the present invention;
A second step of temporarily changing the growth conditions of the CNT after a predetermined time has elapsed;
A third step of measuring the growth height under the temporarily changed growth conditions;
A fourth step of obtaining a growth rate from the growth height and determining an optimum growth condition at which the growth rate is an optimum value;
And a fifth step of changing the growth condition to the optimum growth condition.

Furthermore, the CNT manufacturing program according to the present invention includes:
Computer
A first means for storing in a memory the growth conditions of the CNTs manufactured in the CNT manufacturing apparatus, and the growth height and measurement time of the CNTs under the growth conditions;
A second means for calculating the growth rate of the CNT from the growth height and the measurement time, and storing it in the memory;
A third means for instructing the CNT manufacturing apparatus to change the growth condition temporarily after a predetermined time has elapsed;
A fourth means for calculating the growth rate under the temporarily changed growth condition and storing it in the memory;
Fifth means for determining an optimum growth condition in which the growth rate calculated in the fourth means is an optimum value;
A sixth means for instructing the CNT manufacturing apparatus to change the growth condition to the optimum growth condition;
It is made to function as.

  When an image of the side surface of the substrate is captured using an optical microscope and a digital camera, the growth height of the CNT can be measured with high accuracy regardless of the growth amount of the CNT. In addition, when a predetermined time has elapsed after starting the growth of CNTs, if the growth conditions are temporarily changed while observing the growth height of the CNTs on the spot by observation means, The change in height can be measured accurately. Therefore, it is possible to know the CNT growth rate that changes from moment to moment while growing the CNTs, and to facilitate feedback of the optimum growth conditions to the CNT manufacturing apparatus.

Hereinafter, an embodiment of the present invention will be described in detail.
In FIG. 1, the schematic block diagram of the CNT manufacturing apparatus which concerns on one embodiment of this invention is shown.
The CNT manufacturing apparatus according to the present invention includes a CVD apparatus (CNT growth means), an observation apparatus (observation means), and a programmable controller (control means).

The CVD apparatus is for supplying a carbon source into a container on which a substrate is placed to grow CNTs on the substrate.
Since the CNT grown on the substrate is directly observed with an optical microscope, a material that transmits light (for example, a quartz glass tube or the like) is used for a container that accommodates the substrate. The substrate is fixed at a position away from the stage using a material having high heat resistance (for example, Ta wire). The substrate may be placed directly on the stage, but if the substrate is fixed at a position away from the stage, it becomes easier to observe the side surface of the substrate. Furthermore, a light irradiation means (not shown) is provided above the substrate so as to irradiate light on the upper surface of the substrate. The light irradiating means is not necessarily required. However, when light is irradiated onto the substrate, observation at a high magnification where the amount of light is particularly insufficient is facilitated. Examples of the light source include a halogen lamp, a xenon lamp, and an infrared lamp.

In addition, although not shown in the CVD apparatus,
(1) a heater for maintaining the inside of the container at a predetermined temperature;
(2) Exhaust and valve device for maintaining the inside of the container at a predetermined pressure,
(3) A carbon source supply device for supplying a carbon source into the container,
(4) A reducing gas supply device for supplying a reducing gas into the container,
(5) An oxidant gas supply device for supplying an oxidant gas into the container,
(5) A carrier gas supply device for supplying various gases into the container,
Etc. are provided.
In order to facilitate the observation of the substrate with an optical microscope, the reflection is made of a material that reflects light (for example, heat-resistant ceramics such as alumina, Si substrate, etc.) on the back surface (opposite side of the optical microscope). A plate may be provided.

The observation apparatus includes an optical microscope, a digital camera, an image processing apparatus, and a monitor.
The optical microscope is for capturing an image of the side surface of the substrate. As the optical microscope, a microscope having a very long focal length and capable of observation at a high magnification (for example, 1000 times) is used.
The digital camera is for storing an image of a side surface of a substrate captured by an optical microscope as digital data using a solid-state imaging device and an electromagnetic recording medium. The digital camera may be capable of capturing only a still image, or may be capable of capturing a moving image. In the example shown in FIG. 1, a CCD camera is used as a digital camera.
The image processing apparatus is for processing the digital data stored by the digital camera and calculating the growth height of the CNT. As the image processing apparatus, a real-time image processing apparatus capable of processing an image at an extremely short time interval is preferable. The method for calculating the growth height of CNTs using an image processing apparatus is not particularly limited, but the area (S) of the CNTs included in the image is obtained from the density difference between the substrate, the CNTs and the background, and this is used as the image. The growth height (S / L) is preferable by dividing by the lateral width (L) of the CNTs contained in. This method has the advantage that the average value of the CNT growth height can be accurately calculated. Note that when an image is displayed on a monitor built in the digital camera or an external monitor as shown in FIG. 1 and the operator reads the growth height directly from the image, the image processing apparatus is omitted. be able to.
The monitor is for displaying an image taken with a digital camera. Although a monitor is not always necessary, there is an advantage that an operator can visually recognize the CNT growth process. When the CNT growth is in a stable period, the operator can read the CNT growth height directly from the monitor with a ruler and manually operate the CVD apparatus.

The programmable controller calculates the CNT growth rate from the CNT growth height calculated by the image processing apparatus, and changes the CNT growth condition to the optimum growth condition based on the calculated growth rate. In the stable period of CNT growth, control by a programmable controller is not necessarily required, and an operator can also manually control the CVD apparatus. However, when a programmable controller is used, there is an advantage that precise condition control can be performed even in an unstable period such as the initial stage of film formation.
Specifically, the programmable controller is
(1) Growth condition changing means for instructing the CVD apparatus (CNT growth means) to change the growth conditions of the CNT temporarily during the growth of CNTs,
(2) Growth rate calculation means for measuring the growth height of CNT under temporarily changed CNT growth conditions, and calculating the growth rate of CNT using the measured growth height;
(3) Optimal condition determining means for determining an optimal growth condition in which the growth rate of the CNT is an optimal value;
(4) Change means for instructing the CVD apparatus (CNT growth means) to change the growth condition to the optimum growth condition,
The thing provided with is preferable.

Specifically, the growth conditions that affect the growth rate of CNT include CNT growth temperature, vessel internal pressure, carbon source flow rate, reducing gas flow rate, oxidant gas flow rate, carrier gas flow rate, and the gas flow rate ratio of these gases. and so on. The general influence of each growth condition on the growth rate of CNT is as follows.
(1) CNT growth temperature: If the CNT growth temperature is too low, the growth rate of CNTs decreases. Similarly, if the CNT growth temperature is too high, the CNT growth rate decreases.
(2) In-container pressure: If the in-container pressure is too low, the carbon source concentration in the container decreases, so the CNT growth rate decreases. On the other hand, if the pressure in the container is too high, the growth rate of CNT tends to be saturated.
(3) Carbon source flow rate: The growth rate of CNT increases as the carbon source flow rate increases. On the other hand, when the carbon source flow rate becomes excessive, the amount of amorphous carbon generated increases, and therefore the growth rate of CNTs decreases.
(4) Reducing gas flow rate: As the reducing gas flow rate increases, the oxidation of the catalyst supported on the substrate surface is suppressed, so the growth rate of CNTs increases. On the other hand, when the reducing gas flow rate becomes excessive, the carbon source concentration in the container decreases, and therefore the growth rate of CNTs decreases.
(5) Oxidant gas flow rate: As the oxidant gas flow rate increases, the by-product amorphous carbon is removed, so that the growth rate of CNT increases. On the other hand, when the oxidant gas flow rate becomes excessive, the catalyst is deactivated or the CNTs themselves are oxidized.
(6) Carrier gas flow rate: The carrier gas is for efficiently supplying a carbon source gas, a reducing gas, or an oxidant gas to the catalyst, and an inert gas such as Ar or He is used. If the carrier gas flow rate is too low, the circulation and supply of various gases in the vicinity of the catalyst may deteriorate, and the growth rate may decrease. On the other hand, if the carrier gas flow rate is too high, the carbon source concentration decreases and the growth rate also decreases.
(7) Gas flow ratio: There is an appropriate value at which the growth rate is maximized in the mixing ratio of various gases described above.

Next, the manufacturing method of CNT concerning the present invention is explained.
The CNT manufacturing method according to the present invention includes a first step, a second step, a third step, a fourth step, and a fifth step.
The first step is a step of growing CNTs while measuring the growth height of the CNTs in situ using the CNT manufacturing apparatus according to the present invention. As described above, first, an image of the side surface of the substrate is captured by an optical microscope, and the image is stored as digital data using a digital camera. The stored image is displayed on the monitor, and the growth height is read directly from the monitor. Alternatively, when an image processing apparatus is provided, the digital data is processed by the image processing apparatus, and the growth height of the CNT is calculated. In this case, the measurement interval of the growth height is not particularly limited, and can be arbitrarily selected according to the purpose.

The second step is a step of temporarily changing the CNT growth conditions after a predetermined time has elapsed.
The time interval for temporarily changing the CNT growth condition can be arbitrarily selected. In this case, the time interval may be constant throughout the CNT growth process, or the time interval may be changed according to the CNT growth stage.
The temporary change of the CNT growth conditions may be performed manually by an operator, or may be automatically controlled using a control device. When the growth conditions are changed using the control device, there is an advantage that precise condition control can be performed even in an unstable period such as the initial stage of film formation.

When temporarily changing the growth conditions of CNTs, first, priorities are given to the plurality of growth conditions described above. The method of assigning priorities is not particularly limited and can be arbitrarily selected according to the purpose. In general, it is preferable to give higher priority to growth conditions that have a larger influence on the growth rate. The priority order may be always the same throughout the CNT growth process, or the priority order may differ depending on the CNT growth stage.
Next, the growth condition having the first priority is temporarily changed. The growth conditions may be changed stepwise or continuously. In this case, the change width when changing stepwise or the change speed when changing continuously can be arbitrarily selected according to the purpose.
The growth condition with the priority order of 2 or lower is changed when the growth rate of the CNT does not reach a predetermined value (optimum value) even if the growth condition with the priority order higher than that is changed. . When changing the growth condition whose priority is 2nd or lower, the higher growth condition is usually fixed to the condition closest to the optimum value, but is not limited to this.

The third step is a step of measuring the CNT growth height under temporarily changed CNT growth conditions.
The growth height of the CNTs may be read directly from the monitor screen by the operator, or data output from the image processing apparatus may be read by the control device. The growth height may be calculated from the area and width of the CNT region in the image as described above, or the average value may be calculated by directly reading the height of several CNTs on a monitor.

The fourth step is a step of obtaining a growth rate from the measured growth height and determining an optimum growth condition at which the growth rate becomes an optimum value.
The calculation of the growth rate may be performed by the operator or may be performed by the control device.
The “optimum value” of the growth rate of CNTs can be arbitrarily defined according to the purpose.
As the definition of the optimum value, specifically,
(1) Regardless of the growth conditions, a constant growth rate is always the optimum value.
(2) The maximum growth rate at the time of temporary change of conditions is the optimum value,
(3) Depending on the growth stage of CNTs, different growth rates are set to optimum values (for example, when the initial growth stage is maintained at a constant growth speed and the latter growth stage is maintained at the maximum growth speed),
and so on.
When the growth rate becomes the optimum value by changing only the growth condition with the first priority, the growth condition at this time is determined as the optimum growth condition. On the other hand, if the growth rate does not become the optimum value only by changing the growth condition with the first priority, the growth conditions with the second priority or lower are sequentially changed and the growth rate becomes the optimum value. The growth conditions at this time are determined as the optimum growth conditions.

The fifth step is a step of changing the growth conditions of the CNT manufacturing apparatus to the optimum growth conditions determined in the fourth step.
The change of the growth condition to the optimum growth condition may be performed manually by an operator or may be automatically controlled by a control device.
After the growth condition is changed to the optimum growth condition, the growth of CNT is continued under the condition. The steps (second to fifth steps) from the temporary change of the growth conditions to the optimum growth conditions described above may be performed only once throughout the CNT manufacturing process, or may be repeated a plurality of times. .

Next, the CNT manufacturing program according to the present invention will be described.
The CNT manufacturing program according to the present invention includes a computer,
A first means for storing in a memory a growth condition of CNT produced in a CNT production apparatus, and a growth height and measurement time of the CNT under the growth condition;
A second means for calculating the growth rate of the CNT from the growth height of the CNT and the measurement time, and storing it in the memory;
A third means for instructing the CNT manufacturing apparatus to temporarily change the growth conditions of the CNTs after a predetermined time has elapsed;
A fourth means for calculating the growth rate of the CNT under the temporarily changed CNT growth condition and storing it in the memory;
A fifth means for determining an optimum growth condition in which the growth rate of the CNT calculated in the fourth means is an optimum value;
A sixth means for instructing the CNT manufacturing apparatus to change the growth condition to the optimum growth condition;
It is intended to function as. FIG. 2 shows an example of the flowchart.

First, in step 1 (hereinafter referred to as “S1”), the CNT growth height under the current growth conditions of the CNT manufactured in the CNT manufacturing apparatus and the measurement time of the growth height are measured, and the memory Remember me. In this case, the current CNT growth conditions are also stored in the memory at the same time. The measurement interval of the growth height and the measurement time can be arbitrarily selected according to the purpose.
Next, in S2, the current growth rate is calculated. The growth rate is calculated by using the current growth height (H _N ) and measurement time (t _N ), and the growth height (H _Nn ) and measurement time (t _Nn ) measured before that. It can be calculated by equation (a).
Growth rate = (H _N −H _Nn ) / (t _N −t _Nn ) (a)
In the formula (a), n represents the calculation rate of the growth rate. n can be arbitrarily selected according to the purpose. For example, the growth height can be measured at 1 second intervals, and the growth rate can be calculated at 30 second intervals. In general, when n is small, the value variation increases, but the time lag decreases. On the other hand, when n is large, the value is stabilized, but a time lag occurs.

  Next, in S3, it is determined whether or not the growth conditions are temporarily changed. If the growth conditions are not temporarily changed (S3: NO), the process proceeds to S4, where it is determined whether a predetermined time has elapsed. If the predetermined time has not elapsed (S4: NO), the process returns to S1, and the steps S1 to S4 are repeated until the predetermined time elapses. That is, the growth of CNTs is continued while the current growth conditions are maintained.

On the other hand, when the predetermined time has elapsed (S4: YES), the process proceeds to S5. In S5, it is determined whether or not the growth condition to be temporarily changed can be selected. Immediately after the predetermined time has elapsed, it is possible to select all growth conditions (S5: YES), so the process proceeds to S6, where the growth condition (for example, growth temperature) with the highest priority is selected. To do. Next, in S7, the selected growth condition is temporarily increased or decreased at a predetermined change width (for example, every 5 ° C.) or a change speed (for example, 1 ° C./min) for the CNT manufacturing apparatus. Instruct.
Next, returning to S1, the growth height and measurement time under the temporarily changed growth conditions are measured, and in S2, the growth rate is calculated from the growth height and measurement time and stored in the memory. Next, it progresses to S3 and it is judged whether the growth conditions are changed temporarily. At this time, since the growth conditions are temporarily changed (S3: YES), the process proceeds to S8.

  In S8, it is determined whether or not the growth rate calculated in S2 is an optimum value. If the growth rate is the optimum value (S8: YES), in S9, the growth condition corresponding to the optimum value is selected as the optimum growth condition (determination of the growth condition) and stored in the memory. In addition, the CNT manufacturing apparatus is instructed to change the growth condition to the optimum growth condition. Further, in S10, the temporary change of the growth condition is canceled, and the process returns to S1. And each step of S1-S4 is repeated until predetermined time passes again.

  On the other hand, if the growth rate is not the optimum value in S8 (S8: NO), the process proceeds to S11, where it is determined whether or not the growth rate has approached the optimum value compared with the growth rate under the immediately preceding growth condition. To be judged. When the growth rate approaches the optimum value (S11: YES), there is a possibility that the optimum value is reached only by increasing / decreasing the currently selected growth condition. Therefore, in this case, the process proceeds to S7, and the selected growth condition is increased or decreased again at a predetermined change width or change speed. Then, the steps S1 to S3, S8, S11, and S7 are repeated until the growth rate reaches the optimum value.

Even when the growth condition with the first priority is increased or decreased, when the growth rate does not reach the optimum value (S8: NO) and the growth rate does not approach the optimum value any more (S11: NO), Proceeding to S12, the condition (second best value) closest to the optimum value is selected and stored in the memory. In addition, the CNT manufacturing apparatus is instructed to change the growth condition to the next best value.
Next, in S5, it is determined again whether or not the growth condition can be selected. At this point, the first growth condition has only been increased / decreased, and it is possible to select a growth condition with the second priority or higher (S5: YES). Select the growth condition that is second.
Similarly, until the growth rate reaches the optimum value (S8: YES), or until there are no selectable growth conditions (S5: NO), S7, S1 to S3, S8, S11 to S12, and S5. Repeat each step.

When the growth rate does not reach the optimum value (S8: NO) but there are no selectable growth conditions (S11: NO, S5: NO), the process proceeds to S13. In S13, it is determined whether or not the growth rate has approached the optimum value as compared to before the change by a temporary change operation of a series of growth conditions. Depending on the definition of the “optimum value” of the growth rate, it may be difficult to keep the growth conditions at the optimum value throughout the growth process. For example, this is a case where the growth rate is controlled to be always constant. When the growth rate approaches the optimal value compared to before the change due to a temporary change of the growth condition (S13: YES), the growth rate cannot be made the optimal value by changing the growth condition, but the optimal value is reached. It may be possible to get closer. In this case, the process proceeds to S14 where the growth condition change is canceled. Further, returning to S1, the above-described steps are repeated until the growth condition does not approach the optimum value due to the temporary change of the growth condition.
On the other hand, when the temporary change of the growth condition acts only in the direction of moving the growth rate away from the optimum value (S13: NO), the temporary change of the growth condition is terminated.

Next, the operation of the CNT manufacturing apparatus, the CNT manufacturing method, and the CNT manufacturing program according to the present invention will be described.
Conventionally, the CNT growth height is measured by changing the growth conditions such as temperature, pressure, gas flow rate, etc., and performing CNT growth experiments, measuring the CNT growth height later with an electron microscope, etc., and calculating the growth rate. Was.
However, the growth rate obtained by such a method is only an average value of the whole CNT growth process. Therefore, in order to know the change over time of the growth rate under a specific condition, it is necessary to perform a plurality of experiments with only the growth time changed as shown in FIG. Further, when a CNT growth experiment is performed while changing the growth conditions, as shown in FIG. 3B, it may be difficult to distinguish between the influence of variation for each experiment and the influence of the growth condition. For this reason, it is necessary to perform a number of experiments in order to capture an accurate change in the growth rate accompanying a change in growth conditions. In addition, in order to find the optimum value of a plurality of growth conditions, it is necessary to repeat many more experiments.
Furthermore, when the conditions for obtaining the maximum value of the growth rate change every moment, even if the growth conditions are optimized at the time of starting the growth of the CNTs, a deviation from the optimum conditions occurs over time, and the growth rate of the CNTs is increased. Decreases rapidly.

  In order to solve this problem, it is conceivable to observe the growth height of CNTs in situ. However, all of the conventionally known in-situ observation methods are indirect film thickness measurement methods, and therefore measurement errors are likely to occur. In addition, there are problems such that the film thickness range that can be measured is limited and the special shape of the sample affects the growth rate.

On the other hand, when an image of the side surface of the substrate is captured using an optical microscope and a digital camera, as shown in FIG. 4A, a change with time in the growth height of the CNT can be measured in one experiment. it can. Moreover, since the cross section of the substrate is directly captured, the measurable film thickness range is virtually unlimited. In addition, the sample is not affected by the density of CNTs and does not require a specially shaped sample. Therefore, the growth height of CNT can be measured with high accuracy regardless of the growth amount of CNT. Further, when an image is processed using an image processing apparatus, the growth height of CNTs can be measured with higher accuracy.
Further, as shown in FIG. 4B, when a predetermined time has elapsed since the start of CNT growth, the growth condition is temporarily changed while observing the growth height of the CNT in situ by the observation means. In addition, it is possible to accurately measure a change in CNT growth height accompanying a change in growth conditions. Therefore, it is possible to know the CNT growth rate that changes from moment to moment while growing the CNTs, and to facilitate feedback of the optimum growth conditions to the CNT manufacturing apparatus.

Example 1
[1. experimental method]
A CNT growth experiment was conducted using the CNT manufacturing apparatus shown in FIG. As the substrate, a Si substrate carrying Fe—Ti—O catalyst particles was used. The growth conditions were as follows: hydrogen flow rate: 45 sccm, acetylene flow rate: 10 sccm, temperature: 710 ° C., pressure: 266 Pa. At that time, the state of CNT growth was observed with an optical microscope and a CCD camera. From the obtained image, the height of CNT growth (film thickness) was measured in situ using an image processing apparatus, and the growth rate was calculated as needed.

[2. result]
FIG. 5 shows a cross-sectional photograph of the substrate taken with a CCD camera. From FIG. 5, it can be seen that the growth height of the CNTs increases with time. “Growth time: 0 min” refers to the time when the temperature in the container reaches a predetermined temperature. The reason why the growth of CNT is slightly observed even at “growth time: 0 min” is because the growth of CNT starts in the middle of the temperature rise.
FIG. 6 shows changes with time in the CNT film thickness and growth rate. By using an optical microscope and a CCD camera, it was possible to measure the CNT film thickness in units of 1 μm and the growth rate in units of 1 μm / min.
When the film thickness of the CNT becomes thicker than the measurement field of view, the film thickness change is reduced by a method such as reducing the magnification of the optical microscope or tracking the change from the image of only the tip of the CNT. It was possible to measure.

(Example 2)
[1. experimental method]
In the process of growing CNTs, the CNTs were grown under the same conditions as in Example 1 except that the temperature, pressure, or C ₂ H ₂ / H ₂ flow rate ratio was temporarily changed. The (film thickness) was observed in situ.

[2. result]
FIG. 7 shows a change in growth rate when the temperature is periodically changed in the range of 690 ° C. to 740 ° C. FIG. 7 shows that the influence of temperature on the growth rate is large. The position of the temperature peak slightly deviates from the position of the growth rate peak, and it has been found that there is an optimum temperature for maximizing the growth rate. As the growth time elapses (that is, the amount of CNT growth increases), the influence of temperature on the growth rate gradually decreases.
FIG. 8 shows changes in the growth rate when the pressure is changed stepwise in the range of 150 to 800 Pa. FIG. 8 shows that the influence of pressure on the growth rate is large. In particular, at the initial stage of film formation, the growth rate could be changed greatly by changing the pressure. On the other hand, the influence of pressure on the growth rate gradually decreased with the passage of the growth time (that is, the increase in the amount of CNT growth).
FIG. 9 shows changes in the growth rate when the C ₂ H ₂ / H ₂ flow rate ratio is changed stepwise within the range of 0.1 to 0.75. FIG. 9 shows that the influence of the C ₂ H ₂ / H ₂ flow rate ratio on the growth rate is large. By increasing the C ₂ H ₂ / H ₂ flow ratio during CNT growth, the growth rate could be significantly increased.

(Example 3, Comparative Example 1)
[1. experimental method]
The CNTs were grown under the same conditions as in Example 1 except that the temperature was increased by 5 ° C. after 7 minutes, 12 minutes, 18 minutes, and 24 minutes after starting CNT growth at a temperature of 710 ° C. The growth height of the CNTs was observed in situ (Example 3).
For comparison, CNTs were grown under the same conditions as in Example 3 except that the temperature was kept constant at 710 ° C., and the growth height of the CNTs was observed in situ (Comparative Example 1).

[2. result]
FIG. 10 shows changes with time in the CNT film thickness and growth rate. From FIG. 10, it can be seen that a decrease in growth rate can be mitigated by raising the growth temperature during the growth of CNTs. When grown at a constant growth temperature (Comparative Example 1), the CNT film thickness after 30 minutes was 250 μm. On the other hand, when the growth temperature was adjusted (Example 3), the CNT film thickness after 30 minutes had reached 300 μm, and longer CNTs could be produced with the same growth time.

Example 4
[1. experimental method]
While detecting a change in growth rate during the growth of CNT, only the C ₂ H ₂ gas flow rate was automatically adjusted by a program to try to keep the growth rate constant. The growth conditions other than the C ₂ H ₂ gas flow rate were the same as in Example 1.
[2. result]
FIG. 11 shows changes over time in the growth rate and the C ₂ H ₂ / H ₂ flow rate ratio. From FIG. 11, it was found that the growth rate can be kept substantially constant by increasing the C ₂ H ₂ / H ₂ flow rate ratio (that is, the C ₂ H ₂ gas flow rate) as the growth time elapses.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention.
For example, in a system where the density of CNTs grown on the substrate surface tends to be uniform, the weight change of the growing substrate using a high-precision electronic balance instead of the in-situ observation method using an optical microscope and a digital camera And the CNT growth height may be calculated from the change in weight.

  A CNT manufacturing apparatus, a CNT manufacturing method, and a CNT manufacturing program according to the present invention include an electron emission source (point light source) used in an electron microscope and the like, a semiconductor wiring material, a heat dissipation material, a fiber material, and a scanning tunnel microscope. It can be used as a CNT manufacturing apparatus, a manufacturing method, and a CNT manufacturing program used for a probe used in a scanning probe microscope such as an atomic force microscope, a magnetic force microscope, and a scanning near-field optical microscope. it can.

It is a schematic block diagram of the CNT manufacturing apparatus which concerns on this invention. It is an example of the flowchart of the program for CNT manufacture which concerns on this invention. It is a schematic diagram which shows the evaluation method of the conventional CNT growth rate. It is a schematic diagram which shows the evaluation method of the CNT growth rate using this invention. CNTs are grown on the substrate surface using the CNT manufacturing apparatus according to the present invention, and after a predetermined time has elapsed (FIG. 5 (a): 0 minutes, FIG. 5 (b): 10 minutes, FIG. 5 (c) 20 minutes, FIG. 5 (d): 30 minutes) is a photograph of the side surface of the substrate taken with an optical microscope and a CCD camera. It is a figure which shows the time-dependent change of the CNT film thickness and growth rate at the time of keeping growth conditions constant. It is a figure which shows the time-dependent change of the growth rate at the time of changing growth temperature periodically. It is a figure which shows the time-dependent change of the growth rate at the time of changing a pressure in steps. The C ₂ H ₂ / H ₂ flow rate ratio is a graph showing the time course of the growth rate in the case of changing stepwise. It is a figure which shows the time-dependent change of the CNT film thickness and growth rate when the growth temperature is adjusted in the growth process of CNT and when the temperature is kept constant. It is a diagram showing the time course of the growth rate in the case of automatically controlling the C ₂ H ₂ / H ₂ flow ratio.

Claims (9)

CNT growth means for supplying a carbon source into a container on which the substrate is placed and growing CNTs on the substrate;
An observation means for measuring the growth height of the CNT in situ,
The observation means includes
An optical microscope for capturing an image of a side surface of the substrate;
A digital camera for storing the image as digital data;
A CNT manufacturing apparatus comprising:   The CNT manufacturing apparatus according to claim 1, wherein the observation unit further includes an image processing device that processes the digital data to calculate the growth height. The CNT manufacturing apparatus according to claim 1, further comprising a control unit that calculates a growth rate of the CNT from the growth height and changes the growth condition of the CNT to an optimum growth condition based on the growth rate. The control means includes
Growth condition changing means for instructing the CNT growth means to temporarily change the growth conditions during the growth of the CNT;
A growth rate calculating means for measuring the growth height under the temporarily changed growth conditions and calculating the growth rate using the growth height;
An optimum condition determining means for determining the optimum growth condition at which the growth rate is an optimum value;
The CNT manufacturing apparatus according to claim 3, further comprising a changing unit that instructs the CNT growing unit to change the growth condition to the optimum growth condition.   5. The CNT manufacturing apparatus according to claim 3, wherein the growth condition is a CNT growth temperature, a container internal pressure, a carbon source flow rate, a reducing gas flow rate, a carrier gas flow rate, an oxidant gas flow rate, or a gas flow rate ratio. A first step of growing the CNT while measuring the growth height of the CNT in situ using the CNT manufacturing apparatus according to any one of claims 1 to 5,
A second step of temporarily changing the growth conditions of the CNT after a predetermined time has elapsed;
A third step of measuring the growth height under the temporarily changed growth conditions;
A fourth step of obtaining a growth rate from the growth height and determining an optimum growth condition at which the growth rate is an optimum value;
And a fifth step of changing the growth condition to the optimum growth condition.   The CNT manufacturing method according to claim 6, wherein the growth condition is a CNT growth temperature, a container internal pressure, a carbon source flow rate, a reducing gas flow rate, a carrier gas flow rate, an oxidant gas flow rate, or a gas flow rate ratio.   The method for producing CNTs according to claim 6 or 7, wherein the steps from the second step to the fifth step are repeated a plurality of times. Computer
A first means for storing in a memory the growth conditions of the CNTs manufactured in the CNT manufacturing apparatus, and the growth height and measurement time of the CNTs under the growth conditions;
A second means for calculating the growth rate of the CNT from the growth height and the measurement time, and storing it in the memory;
A third means for instructing the CNT manufacturing apparatus to change the growth condition temporarily after a predetermined time has elapsed;
A fourth means for calculating the growth rate under the temporarily changed growth condition and storing it in the memory;
Fifth means for determining an optimum growth condition in which the growth rate calculated in the fourth means is an optimum value;
A sixth means for instructing the CNT manufacturing apparatus to change the growth condition to the optimum growth condition;
CNT manufacturing program to function as

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