JP2011215119A - Evaluation method of aggregate structure of multilayer carbon nanotube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate the whole aggregate structure of a multilayer CNT.SOLUTION: The evaluation method includes a step of making X-rays enter the aggregate structure of the multilayer CNT at a predetermined incidence angle, a step of scanning and changing, around the aggregate structure, the detection position of diffracted X-rays emitted from the aggregate structure, and measuring the diffracted X-ray intensity at each detection position, a step of scanning and changing the X-ray incident position of the aggregate structure in the height direction and measuring the intensity of transmitted X-rays at each scanning position, a step of calculating the peak area from the measuring data of the diffracted X-ray intensity and calculating the attenuation from the measuring data of the transmitted X-ray intensity, and a step of analyzing the orientation of the aggregate structure based on the peak area and attenuation.

Description

  The present invention relates to an evaluation method for an aggregate structure of multi-walled carbon nanotubes (hereinafter referred to as multi-walled CNTs) composed of two or more layers of a cylindrical graphene sheet.

  Multi-walled CNTs are formed by coaxial cylindrical tubes of two or more cylindrical graphene sheets. The graphene sheet is a six-membered ring network (hexagonal network) made of carbon, and as is well known, multi-walled CNTs having such a structure are excellent in electron emission ability and durability, and have a large screen field emission. It is a substance that is expected to be useful as an electron-emitting material for displays and the like, and because multilayer CNTs have high corrosion resistance, they are also expected to be used in various applications such as those that require corrosion resistance such as catalyst electrode layers of fuel cells. .

  As a manufacturing method for growing multilayer CNTs on a substrate, there is a substrate method in the CVD method. In this substrate method, a catalyst film is formed on a substrate and heat-treated to make the catalyst film a catalyst structure composed of a plurality of catalyst fine particles, and a gas containing carbon is allowed to act on the catalyst fine particles on the catalyst structure. Multi-walled CNTs are grown starting from fine particles.

  When multi-walled CNTs are manufactured using the above catalyst structure, the cross-sectional structure of each multi-walled CNT is intricately entangled, a randomly oriented structure, or a set of curved multi-walled CNTs drawn in a spiral or wavy shape It consists of a structure.

  Such an aggregate structure is considered to be caused by the fact that individual multi-walled CNTs have non-uniform tube diameters, and the whole has a curved shape.

  In recent years, it is not an assembly of curved multi-walled CNTs that draws such spirals and waves, but has a uniform diameter and overall linearity, and its orientation and dense structure are applied as they are, or There has been a demand for an aggregate structure with little entanglement that can be easily used by loosening multi-walled CNTs.

  Accordingly, the present inventors have conducted extensive research to develop a multi-walled CNT aggregate in which the tube diameter is generally uniform and linear, and the multi-walled CNTs are less entangled. Japanese Patent Application Laid-Open No. 2008-120658 It has become possible to develop a multilayered CNT aggregate structure as disclosed.

  In contrast to the aggregate structure of multi-walled CNTs related to such development, evaluation of the diameter uniformity, curvilinearity, linearity, etc. of each multi-walled CNT constituting the multi-walled CNTs is only an evaluation in a minute section, The structure could not be evaluated.

JP 2008-120658 A

  A problem to be solved by the present invention is to provide an evaluation method for an entire aggregate structure, not an evaluation in a minute section, for an aggregate structure composed of a plurality of multi-walled CNTs grown by the action of catalyst fine particles on a substrate. .

  The present invention is a method for evaluating an aggregate structure of a plurality of multi-walled CNTs grown by the action of catalyst fine particles on a substrate, the step of making X-rays incident on an arbitrary side of the aggregate structure, and another aspect of the aggregate structure Measuring X-ray intensity emitted from the collective structure at a plurality of surrounding detection positions, and calculating a peak area of the X-ray intensity from the X-ray intensity at each of the detection positions. And

  Preferably, scanning the X-rays in the height direction of the collective structure, measuring the X-ray intensity emitted from the collective structure at each scanning position, and calculating the X-ray intensity attenuation from the measured X-ray intensity And analyzing the orientation of the multilayer CNT in the aggregate structure from the calculated peak area and the attenuation calculated in the step.

  Preferably, the method includes a step of calculating a half-value width from an X-ray intensity peak value within the calculated peak area corresponding to the c-plane interval of the multi-layer CNT, and the multi-layer CNT from the correspondence of the half-value width to the c-plane interval Evaluate the linearity of

  The aggregate structure is not limited to a circular shape in plan view. For example, if the X-ray passage area in the planar view direction in the aggregate structure until incident X-rays enter and exit as diffracted X-rays is substantially constant, An arc shape or the like may be used.

According to the present invention, it is possible to evaluate the structure of the entire multilayer CNT aggregate structure.

FIG. 1 is a diagram for explaining the X-ray diffraction phenomenon. FIG. 2 is a diagram for explaining the X-ray diffraction phenomenon for multilayer CNTs. FIG. 3 is a diagram showing a planar configuration of an evaluation apparatus used for carrying out an evaluation method for a multilayer CNT aggregate structure according to an embodiment of the present invention. FIG. 4 is a diagram showing a side configuration of FIG. FIG. 5 is a diagram for explaining the Bragg condition on the c-plane of the multilayer CNT. FIG. 6 is a diagram showing transmitted X-rays and diffracted X-rays when incident X-rays are irradiated while rotating the multilayer CNT aggregate structure. FIG. 7 is a diagram showing the intensity waveform of the emitted X-ray with respect to the detection position of the emitted X-ray from the multilayer CNT aggregate structure. FIG. 8 is a diagram illustrating a state in which incident X-rays are scanned in the height direction with respect to the multilayer CNT aggregate structure. FIG. 9 is a diagram showing an intensity waveform of the outgoing X-ray with respect to the incident height of the incident X-ray shown in FIG. FIG. 10 is a view showing an SEM photograph of a multilayer CNT aggregate structure (samples 1, 2, and 3). FIG. 11 is a diagram showing the diffracted X-ray intensity at each X-ray detection position for each sample 1, 2, and 3 in FIG. FIG. 12 is a diagram showing the half-value width corresponding to the c-plane spacing of each of samples 1, 2, and 3 in FIG. FIG. 13 is a diagram showing the diffracted X-ray intensities at the X-ray detection positions at a plurality of points in the height direction of the samples 1, 2, and 3 in FIG. FIG. 14 is a diagram showing the half-value width corresponding to the c-plane interval at a plurality of points in the height direction of each of the samples 1, 2, and 3 in FIG.

  Hereinafter, an evaluation method for an aggregate structure of multilayer CNTs according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the present embodiment, since the X-ray diffraction phenomenon is used for the evaluation of the aggregate structure, first, the X-ray diffraction phenomenon will be described with reference to FIG. X-rays are electromagnetic waves having a wavelength of 0.001 nm to several tens of nm. X-rays are generally generated by accelerating thermionic electrons emitted from a filament in an X-ray tube at a high voltage and colliding with a metal target. In the embodiment, for example, Cu is used as the metal target.

  In this case, the X-ray wavelength is 1.5418 mm. In FIG. 1, 1a, 1b, and 1c show the arrangement line of the atom 2 which comprises Cu. If the distance between the lines 1a, 1b, and 1c is d and the incident angle of the incident X-ray 3 is θ, the optical path difference (A−O−A ′) of the diffracted X-ray 4 with respect to the incident X-ray 3 is 2d. × sin θ. If the optical path difference is an integer multiple n of the X-ray wavelength λ, the Bragg condition is satisfied, and the X-rays scattered by the atoms 2 strengthen each other and become diffracted X-rays 4. This is expressed by an equation: 2d × sin θ = nλ.

  As described above, when the incident X-rays are emitted, if the optical path difference between the incident X-rays and the emitted X-rays satisfies the Bragg condition, the intensity of the diffracted X-rays 4 increases.

  Then, regarding such a Bragg condition, an X-ray diffraction phenomenon with respect to the multilayer CNT 7 will be described with reference to FIG. The multilayer CNT 7 shown in FIG. 2 is schematically shown in its cross-sectional configuration. In this multi-layer CNT7, a plurality of graphene sheets 7a, 7b,... Are coaxially tubular, the graphene sheet surface is a c-plane, and the c-plane interval of the graphene sheets corresponds to the interval d in the Bragg condition. The details of the graphene sheet are well known and will not be described.

  X-rays 5 are incident on the tangent 9 on the graphene sheet surface at a predetermined incident angle (θ ± δφ), and the incident X-rays 5 are incident on the tangent 9 on the graphene sheet surface at a predetermined emission angle (θ Diffracted by ± δφ) and emitted as diffracted X-rays 8. In such diffraction, the volume element capable of satisfying the Bragg condition and causing X-ray diffraction is given by a crystal within a slight angle (± δφ).

  With reference to FIG. 3 to FIG. 5, the configuration of the evaluation apparatus used to implement the multilayer CNT aggregate structure evaluation method according to the embodiment of the present invention will be described. FIG. 3 shows a planar configuration of the X-ray generator and multilayer CNT aggregate structure in the evaluation apparatus, and FIG. 4 shows a side configuration of the X-ray generator and multilayer CNT aggregate structure. FIG. 5 shows incident X-rays and diffracted X-rays with respect to the multilayer CNT in the multilayer CNT aggregate structure. The X-ray generator is an X-ray generator in which the metal target is, for example, Cu.

  A slit 10-12 is arranged on the X-ray incident side with respect to the aggregate structure 14 of the multilayer CNT 19, and a slit 13 is arranged on the X-ray emission side. Of the incident side slits 10-12, the slits 10 and 11 are X-ray width limiting slits arranged to face each other at a predetermined interval, and the slit 12 is a scattering limiting slit arranged between both the slits 10 and 11. . These slits 10-12 limit the incident X-ray 15 to the radial line width L1 and the height direction line width to L2 or less. The line width L1 is equal to or less than the diameter D of the aggregate structure 14, and the line width L2 is equal to or less than the height H of the aggregate structure 14 from the substrate 17. However, the line widths L1 and L2 do not limit the present invention with respect to the structural evaluation of the multilayer CNT.

The multilayer CNT aggregate structure 14 is formed by densely gathering a plurality of multilayer CNTs 19, and the outer shape of the side surface in a plan view is a circular shape. However, the multilayer CNT aggregate structure 14 is not limited to a circular shape in plan view. That is, the multi-walled CNT aggregate structure 14 is not particularly limited in its planar view shape as long as the X-ray passage area in the planar view direction in the aggregate structure until incident X-rays enter and exit as diffracted X-rays is substantially constant. .

  The multilayer CNT 19 is grown on the substrate 17 by the action of catalyst fine particles. The substrate 17 on which the multilayered CNT aggregate structure 14 is arranged is driven to rotate in the direction of arrow A in the figure on the turntable 18. It should be noted that rotating the multilayer CNT aggregate structure 14 is intended to average the evaluation of the multilayer CNT, and it is not necessarily essential to rotate the multilayer CNT aggregate structure.

  In the above, the incident X-ray 15 is controlled to the line widths L1 and L2 by the slit 10-12, and then enters the multilayer CNT aggregate structure 14 from one side surface 14a, and exits from the other side surface 14b as a diffracted X-ray 16 at a diffraction angle 2θχ. To do.

  X-ray detection is performed so that X-rays 15 incident on the multilayer CNT aggregate structure 14 can be transmitted through the aggregate structure 14 as transmitted X-rays 20 or diffracted as diffracted X-rays 16 to measure the intensity of the emitted X-rays. A vessel 21 is arranged. The X-ray detector 21 can scan around the center of the multilayer CNT aggregate structure 14 in the direction of arrow B in the figure, and each scanning position is a detection position. When the incident X-ray 15 is not diffracted and is emitted as transmitted X-ray 20 (see FIG. 6), the detection position of the X-ray detector 21 in the emission direction is P0, and the incident X-ray 15 is diffracted and diffracted. When the X-ray 16 (see FIGS. 3 to 6) is emitted, the detection position of the X-ray detector 21 in the emission direction is represented by P1.

  The behavior of the X-rays 15 incident on the entire multilayer CNT aggregate structure 14 formed by the aggregation of a large number of multilayer CNTs 19 and the behavior of the X-rays 15 incident on the single multilayer CNTs 19 are considered to be equivalent. In FIG. 15 is shown as being diffracted and emitted as a diffracted X-ray 16 from the entire assembly structure 14, and in FIG. 5, the incident X-ray 15 is diffracted and emitted as a diffracted X-ray 16 from a single multilayer CNT 19. Indicated. In this case, the multilayer CNT 19 shown in FIG. 5 is an individual multilayer CNT constituting the aggregate structure 14, and the incident X-ray 15 is obtained by, for example, graphene sheet surface of the outermost layer 19a and graphene of the inner layer 19b inside the outermost layer. Incident on the sheet surface. Then, it is diffracted by the optical path difference between both the graphene sheet surfaces and emitted as diffracted X-rays 16. These individual multilayer CNTs 19 are emitted as diffracted X-rays 16 as a whole as an aggregate structure 14.

  A method for evaluating the multilayer CNT aggregate structure 14 of the embodiment will be described with reference to FIGS. FIG. 6 corresponds to FIG. 3, and the aggregate structure 14 of the multilayer CNT 19 is an aggregate of a large number of multilayer CNTs 19 on the substrate 17, and the outer surface 14 a of the aggregate structure 14 is a part of a circular shape in plan view. It has an arc shape. Incident X-rays 15 are incident on the side surface 14 a of the multilayer CNT aggregate structure 14 and are emitted from the side surfaces 14 b and 14 c forming the arc shape of another part of the circular CNT aggregate structure 14. Among the emitted X-rays, X-rays emitted from the side surface 14b are detected as diffracted X-rays 16 and X-rays emitted from the side surface 14c are detected as transmitted X-rays 20 at each detection position of the X-ray detector 21. The

  In FIG. 7, the intensity of the diffracted X-ray 16 is plotted on the vertical axis, the detected position 2θχ of the X-ray detector 21 is plotted on the horizontal axis, and the diffracted X-ray intensity at each detected position is indicated by lines L1, L2, and L3. Of these lines L1, L2, and L3, L1 indicates the X-ray intensity between the detection positions 0-A, and constitutes a base line in which the X-ray intensity changes substantially constant. L2 constitutes a peak line in which the X-ray intensity changes in a peak shape between the detection positions A and C. L3 constitutes a baseline in which the X-ray intensity changes substantially after the detection position C.

In the peak line L2 region, the detection position A has a minimum peak, and the X-ray intensity changes from the detection position A in a direction in which the X-ray intensity increases toward the peak. The X-ray intensity changes toward the position C in the direction of weakening, and the peak is minimized at the detection position C. When there is no peak with respect to the peak line L2 between the detection positions A and C, the X-ray intensity forms a base line L4 (broken line) together with the base lines L1 and L3. An area surrounded by the base line L4 and the peak line L2 between the detection positions A and C can be defined as a peak area. Here, the base line L4 is a line that connects the detection position direction end of the base line L1 and the detection position direction start end of the base line L3 with a substantially straight line. From this peak area, the orientation and aggregate density of the multi-walled CNT 19 in the aggregate structure 14 can be seen.

  As shown in FIG. 8, when the incident X-ray 15 is scanned in the range of Z1-Z2 in the height direction Z of the multilayer CNT aggregate structure 14, the intensity of the transmitted X-ray 20 with respect to the incident X-ray 15 is measured in this scanning. 9, the intensity of the transmitted X-ray 20 at each height position can be seen from a waveform diagram in which the horizontal axis in FIG. 9 is the height position Z of the aggregate structure 22 and the vertical axis is the intensity of the transmitted X-ray 20. In this case, the portion indicated by ΔA is the attenuation amount of the transmitted X-ray 20 intensity. In FIG. 8, Z <b> 1 and −Z <b> 1 in FIG. 9 indicate the highest position of the aggregate structure 14, Z <b> 2 in FIG. 8, and −Z <b> 2 in FIG. In FIG. 9, the difference in transmitted X-ray intensity at the height positions −Z1 and −Z2 of the multilayer CNT aggregate structure 14, that is, ΔA shown in FIG. 9 is the output X-ray after the incident X-ray enters the aggregate structure 14. Represents the X-ray intensity attenuation at the incident height of the incident X-ray with respect to the X-ray intensity until it is emitted. This X-ray intensity attenuation amount indicates the aggregate density in the height direction of the multilayer CNT 19 of the multilayer CNT aggregate structure 14.

  Specifically, the line indicating the transmitted X-ray intensity when the incident height of incident X-rays is higher than −Z1 is defined as a base line L5, and the incident height of incident X-rays is in the range of −Z1 to −Z2. When the line indicating the transmitted X-ray intensity is the attenuation line L6 and the line indicating the transmitted X-ray intensity when the incident height of the incident X-ray is lower than −Z2 is the base line L7, the X-ray intensity attenuation is This is the difference between the X-ray intensity of the base line L5 and the X-ray intensity of the attenuation line L6.

  Accordingly, the orientation of the multilayer CNT 19 constituting the multilayer CNT aggregate structure 14 can be determined by calculating the peak area / attenuation expression from the peak area of FIG. 7 and the X-ray intensity attenuation of FIG. Since the peak area indicates the orientation and density of the multilayer CNT 19 and the attenuation amount indicates the density information, the orientation can be determined from the above formula.

  Next, the linearity of the multilayer CNT 19 constituting the multilayer CNT aggregate structure 14 will be described with reference to FIG. 10, FIG. 11, and FIG.

  FIG. 10 shows SEM photographs at the same magnification at the center in the height direction for three samples 1, 2, and 3 having different linearities in the multilayer CNTs constituting the multilayer CNT aggregate structure. As is clear from the SEM photograph, the multi-wall CNT in sample 1 has the lowest linearity among the three samples 1, 2, and 3, and the multi-wall CNT in sample 2 has a medium linearity. Is clearly the most linear.

FIG. 11 shows diffracted X-ray intensity waveforms (corresponding to FIG. 7) at the respective detection positions for the samples 1, 2, and 3, respectively. However, for the sake of illustration, the vertical axis direction in FIG. 11 indicates the diffracted X-ray intensity, but the vertical axis is omitted because it does not indicate the diffracted X-ray intensity of each sample 1, 2, 3. As shown in FIG. 11, the peak positions and heights of the diffraction X-rays of the samples 1, 2, and 3 are different from each other. It can be seen that the peak of the diffraction X-ray intensity clearly appears in the sample having the highest linearity than the sample having the lower linearity, and from this, the structure of the multilayer CNT aggregate structure can be evaluated. That is, in sample 1, the amplitude of the diffracted X-ray intensity greatly changes with respect to the detection position change, and the peak is unclear. In sample 2, the amplitude of the diffracted X-ray intensity changes smaller than that in sample 1 at each detection position, and the peak appears relatively clearly. In sample 3, the amplitude of the diffracted X-ray intensity changes the smallest with respect to each detection position change, and the peak height at a specific detection position appears very clearly. From this, the linearity of the multilayer CNT in the sample can be relatively evaluated even from the diffraction X-ray intensity waveform.

  FIG. 12 shows the full width at half maximum (d002FWHM) of each sample 1, 2, and 3 with respect to the c-plane interval (d002) in the peak waveform constituting the peak area in the diffraction X-ray intensity waveform shown in FIG. As shown in FIG. 12, among samples 1, 2 and 3, sample 1 with low linearity has a large c-plane spacing and half-width, and sample 2 with medium linearity has a c-plane spacing and half-width. In Sample 1 which is both in the middle and has high linearity, both the c-plane spacing and the half-value width are small. From this, the linearity of the multilayer CNT in the multilayer CNT aggregate structure can be judged and evaluated.

  10 to 12 show the relationship between the c-plane spacing and the half-value width based on the X-ray intensity waveform at the center detection position in the height direction of each of the multilayer CNT aggregate structures of Samples 1, 2, and 3. This is an evaluation of the linearity at the central portion in the direction, and is not the entire multilayer CNT aggregate structure height direction. Therefore, with reference to FIGS. 13 and 14, the linearity evaluation in the entire height direction of the multilayer CNT aggregate structure will be described.

  FIG. 13 shows X-ray intensity waveforms at a plurality of detection positions in the height direction of each of the multilayer CNT aggregate structures of Samples 1, 2, and 3. The X-ray intensity waveforms at the detection positions of Samples 1, 2, and 3 are shown separated in the height direction for illustration.

  In the case of sample 1, the peak height in the X-ray intensity at a plurality of positions in the height direction is low. From this, it can be seen that the multilayer CNT aggregate structure having a low peak height in X-ray intensity at a plurality of positions in the height direction is a structure in which multilayer CNTs having low linearity are aggregated.

  In the case of sample 2, the peak height in the X-ray intensity at a plurality of positions in the height direction is higher than that of sample 1. From this, it can be seen that the multilayer CNT aggregate structure having a medium peak height in the X-ray intensity at a plurality of positions in the height direction is a structure in which multilayer CNTs having medium linearity are aggregated.

  In the case of sample 3, the peak height in the X-ray intensity at the plurality of positions in the height direction is the highest. From this, it can be seen that the multilayer CNT aggregate structure having a high peak height in the X-ray intensity at a plurality of positions in the height direction is a structure in which multilayer CNTs having high linearity are aggregated.

  FIG. 14 shows the half-value widths of samples 1, 2, and 3 with respect to the c-plane interval (d002) in the X-ray intensity waveforms of samples 1, 2, and 3 shown in FIG. Each sample 1, 2 and 3 is indicated by a square (□), a triangle (Δ) and a circle (◯) corresponding to a plurality of detections in the height direction. As shown in FIG. 14, sample 1 with low linearity concentrates in a region where both the c-plane spacing and half-value width are large, and sample 2 with medium linearity has both c-plane spacing and half-width values. In Sample 3, which is concentrated in the middle region and has high linearity, both the c-plane spacing and the half width are concentrated in a small region.

  From this, in the X-ray intensity waveform, the linearity of the multilayer CNTs in the multilayer CNT aggregate structure can be determined and evaluated from the relationship between the half width with respect to the c-plane interval (d002).

  In particular, FIGS. 13 and 14 can evaluate the linearity of the multi-walled CNTs constituting the multi-walled CNT aggregate structure in the height direction. The overall linearity can be evaluated.

  As described above, in the present embodiment, there is a method for evaluating an aggregate structure of a plurality of multi-walled CNTs grown by the action of catalyst fine particles on a substrate, the step of making X-rays incident on an arbitrary side of the aggregate structure; The X-ray detector is scanned around another side surface of the aggregate structure, and the intensity of the diffracted X-rays emitted around the aggregate structure side surface is measured from the X-ray detector output at each scanning position, and the measurement is performed. And calculating a peak area from the intensity of the diffracted X-ray, and information on the orientation and aggregate density of the multilayer CNT can be obtained from the calculated peak area.

  The incident X-ray is scanned in the height direction of the collective structure, the intensity of the transmitted X-ray transmitted through the collective structure is measured from the X-ray detector output at each scanning position, and the measured transmitted X-ray is measured. When the step of calculating the amount of attenuation from the intensity of is included, the orientation of the aggregate structure can be analyzed from the calculated peak area and amount of attenuation.

  Further, in the case of including a step of calculating the c-plane interval and the peak area half-width of the graphene sheet in the diffraction X-ray intensity waveform line constituting the peak area, the multi-wall CNT aggregate structure is calculated from the c-plane interval and the peak area half-width. The linearity of the multilayer CNT can be evaluated.

10-13 Slit 14 Multilayer CNT aggregate structure 15 Incident X-ray 16 Diffracted X-ray 17 Substrate 18 Turntable 19 Multilayer CNT
20 Transmitted X-ray

Claims (3)

A method for evaluating an aggregate structure of a plurality of multilayer CNTs arranged on a substrate,
Incident X-rays on an arbitrary side of the aggregate structure; measuring X-ray intensity emitted from the aggregate structure at a plurality of detection positions on another side of the aggregate structure; and X at each detection position And a step of calculating a peak area of the X-ray intensity from the line intensity.   Scanning X-rays in the height direction of the collective structure, measuring the X-ray intensity emitted from the collective structure at each scanning position, and calculating the X-ray intensity attenuation from the measured X-ray intensity; The orientation of the multilayer CNT in the aggregate structure is analyzed from the peak area calculated in claim 1 and the attenuation calculated in the step.   A step of calculating a half-value width from an X-ray intensity peak value within the peak area calculated in claim 1 corresponding to the c-plane interval of the multi-wall CNT, and from the correspondence relationship of the half-value width to the c-plane interval The method according to claim 1, wherein the linearity of is evaluated.