Photocathode and method for manufacturing the same

Abstract

The photocathode (4) includes a light-transmitting conductive layer (22) arranged between a light-transmitting substrate (21) and a photoelectric conversion layer (24). The light-transmitting conductive layer (22) is formed of a carbon-containing constituent material, and the Raman spectrum of the constituent material has a peak P1 of the D1 band, a peak P2 of the G band, a peak P3 of the 2D1 band, and a peak P4 of the (D1+G) band.

Description

Technical Field

[0001] The present invention relates to a photocathode and a method for manufacturing the photocathode. Background Art

[0002] For example, a photocathode is provided with a photoelectric conversion layer on one side of a translucent substrate. It is desirable for the photocathode to achieve linear detection across a wide range of light intensities, from low to high, that is, to improve the cathode's linearity. The so-called cathode linearity refers to the linearity of the cathode output current when it increases or decreases in proportion to the increase or decrease in the amount of incident light. Improving this cathode linearity requires an appropriate charge supply to the photoelectric conversion layer.

[0003] To address this technical issue, research is underway to investigate methods for reducing the surface resistance of a photoelectric conversion layer by providing a light-transmitting conductive layer as a base between a light-transmitting substrate and the photoelectric conversion layer. For example, Patent Document 1 discloses a photocathode having an intermediate layer composed of graphite, carbon nanotubes, or the like, provided between the light-transmitting substrate and the photoelectric conversion layer.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 2001-202873 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] Photocathodes such as those described above have a variety of applications, including photomultiplier tubes, phototubes, image amplifiers, and streak tubes. The properties required of photocathodes vary greatly depending on their application. Therefore, it is hoped that photocathodes with desired properties can be easily obtained even when a light-transmitting conductive layer is provided as a base between a light-transmitting substrate and a photoelectric conversion layer.

[0009] The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a photocathode that can easily obtain desired characteristics even when a light-transmitting conductive layer is provided as a base between a light-transmitting substrate and a photoelectric conversion layer.

[0010] Methods used to solve problems

[0011] The photocathode involved in one aspect of the present invention includes: a transparent substrate having a side for incident light and the other side for emitting light incident from one side; a photoelectric conversion layer arranged on the other side of the transparent substrate and converting light emitted from the other side into photoelectrons; and a light-transmitting conductive layer arranged between the transparent substrate and the photoelectric conversion layer, the light-transmitting conductive layer being formed of a carbon-containing constituent material, and the Raman spectrum of the constituent material has: a peak of the D1 band; a peak of the G band; a peak of the 2D1 band; and a peak of the (D1+G) band.

[0012] In this photocathode, the light-transmitting conductive layer disposed between the light-transmitting substrate and the photoelectric conversion layer contains carbon as a constituent material. The Raman spectrum of this constituent material exhibits four peaks: the D1 band, the G band, the 2D1 band, and the (D1+G) band. In the light-transmitting conductive layer formed from a constituent material having such a Raman spectrum, regions with different carbon atom bonding states are microscopically mixed, and the light transmittance and resistance of each region are considered to vary depending on the configuration of each region. Therefore, in this photocathode, the light transmittance and conductivity of the light-transmitting conductive layer can be adjusted by adjusting the thickness of the light-transmitting conductive layer. Even when the light-transmitting conductive layer is disposed as a base between the light-transmitting substrate and the photoelectric conversion layer, desired characteristics can be easily obtained.

[0013] The minimum value of the Raman intensity between the peak of the D1 band and the peak of the G band may also be greater than the base value of the Raman intensity between the peak of the G band and the peak of the 2D1 band. In a photocathode having a light-transmitting conductive layer exhibiting such a Raman spectrum, it is easier to obtain a structure having a mixture of regions having different bonding states of carbon atoms, making it easier to adjust light transmittance and conductivity.

[0014] The Raman intensity of the peak of the D1 band may be greater than the Raman intensity of the peak of the G band. In a photocathode having a light-transmitting conductive layer having such a Raman spectrum, the thickness of the light-transmitting conductive layer is small, so a photocathode with excellent light transmittance can be obtained.

[0015] The Raman intensity of the peak of the D1 band may be smaller than the Raman intensity of the peak of the G band. In a photocathode having a light-transmitting conductive layer having such a Raman spectrum, the light transmittance and conductivity can be adjusted more easily due to the thickness of the light-transmitting conductive layer.

[0016] The manufacturing method of the photocathode involved in one aspect of the present invention is a manufacturing method for the above-mentioned photocathode, including: the step of arranging a translucent substrate in a vapor deposition device; the step of introducing a carbon-containing gas into the vapor deposition device, and vapor-depositing a carbon-containing constituent material on the translucent substrate to form a light-transmitting conductive layer; and the step of forming a photoelectric conversion layer on the light-transmitting conductive layer.

[0017] In this photocathode manufacturing method, a light-transmitting conductive layer is formed on a light-transmitting substrate by vapor deposition using a carbon-containing gas. This method facilitates the formation of the light-transmitting conductive layer by vapor deposition using only a vapor deposition apparatus, as opposed to methods that transfer a separately formed light-transmitting conductive layer onto the light-transmitting substrate. Furthermore, the thickness of the light-transmitting conductive layer can be easily adjusted by adjusting the vapor deposition time using the vapor deposition apparatus, making it easy to obtain desired properties even when the light-transmitting conductive layer is provided as a base between the light-transmitting substrate and the photoelectric conversion layer.

[0018] The vapor deposition time of the constituent materials may be 60 minutes or less. In this case, a light-transmitting conductive layer having the above-mentioned peaks can be appropriately obtained.

[0019] Effects of the Invention

[0020] According to the present invention, even when a light-transmitting conductive layer is provided as a base between a light-transmitting substrate and a photoelectric conversion layer, desired characteristics can be easily obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a cross-sectional view showing an example of a photomultiplier tube using a photocathode according to an embodiment of the present invention.

[0022] Figure 2 yes Figure 1 An enlarged cross-sectional view of the main parts of the photomultiplier tube is shown.

[0023] Figure 3 (a) is a diagram showing an example of a constituent material of a light-transmitting conductive layer. Figure 3 (b) is Figure 3 An enlarged view of the main part of (a).

[0024] Figure 4 (a) to (d) are diagrams showing examples of Raman spectra of glassy carbon constituting the light-transmitting conductive layer.

[0025] Figure 5 (a) and (b) are cross-sectional views illustrating a method for manufacturing a photocathode according to one embodiment of the present invention.

[0026] Figure 6 (a) and (b) represent Figure 5 Cross-sectional view of the subsequent process.

[0027] Figure 7 This is a graph showing the results of an evaluation test on the spectral sensitivity characteristics of the photocathode.

[0028] Figure 8 This is a graph showing the results of an evaluation test on cathode linearity characteristics of a photocathode. DETAILED DESCRIPTION

[0029] Hereinafter, preferred embodiments of a photocathode and a method for manufacturing the photocathode according to one aspect of the present invention will be described in detail with reference to the accompanying drawings.

[0030] [Structure of a photomultiplier tube]

[0031] Figure 1 1 is a cross-sectional view showing a photomultiplier tube 1 using a photocathode 4 according to an embodiment of the present invention. Figure 1 The photomultiplier tube 1 shown is a detector that amplifies photoelectrons generated by the photoelectric effect and detects incident light L with high sensitivity. As shown in the figure, the photomultiplier tube 1 is constructed by housing an electron multiplier section 3 within a roughly cylindrical housing 2, which serves as a vacuum container. The housing 2 includes a photocathode 4, which performs photoelectric conversion on incident light L; a metal side tube 5, which holds the photocathode 4 at one end; and a stem 6 made of an insulating material, which seals the other end of the side tube 5. Multiple pins 7 protrude from the other end of the side tube 5 and are inserted into the stem 6.

[0032] The photocathode 4 utilizes the photoelectric effect to convert incident light L into photoelectrons, releasing them into the electron multiplying section 3. The photocathode 4 comprises a light-transmitting substrate 21, a photoelectric conversion layer 24, and a light-transmitting conductive layer 22 disposed therebetween. The photocathode 4 is bonded to the side tube section 5, for example, via a bonding member 23. The photoelectric conversion layer 24 is also formed on a portion of the inner wall surface of the side tube section 5. Details of the photocathode 4 will be described later.

[0033] The side tube section 5 includes a first side tube section 8 that primarily covers the electron multiplier section 3 and a second side tube section 9 that primarily covers the column 6. An outward flange section 8a is provided at the base end of the first side tube section 8, and an inward flange section 13 is provided at the front end of the first side tube section 8. An outward flange section 9a having the same diameter as the flange section 8a is provided at the second side tube section 9. By airtightly joining these flange sections 8a and 9a, the first and second side tube sections 8 and 9 are securely connected.

[0034] The electron multiplying section 3 comprises a convergent electrode 10, a dynode 11, and an anode 12. The convergent electrode 10 is a flat-plate electrode positioned between the photocathode 4 and the dynode 11. It converges the photoelectrons emitted from the photocathode 4 and guides them to the dynode 11. The dynode 11 is a thin-plate electrode with a large number of electron multiplying holes, arranged in multiple stages from the photocathode 4 to the column 6. The anode 12 is a flat-plate electrode that extracts the electrons multiplied by the electron multiplying section 3 as an output signal. For example, the anode 12 is positioned in the stage preceding the final dynode 11.

[0035] When a specified voltage is applied to the electron multiplying section 3 and the anode 12 via the pin 7, the photoelectric conversion layer 24 and the convergence electrode 10 become at the same potential, and each stage of the dynode 11 gradually becomes at a high potential from the photocathode 4 side to the column 6 side. In this state, when incident light L is incident on the photoelectric conversion layer 24 from the translucent substrate 21, the incident light L is photoelectrically converted, and photoelectrons are released into the housing 2. The released photoelectrons are converged to the first-stage dynode 11 by the convergence electrode 10, and then multiplied by secondary electrons in sequence by each stage of the dynode 11. A group of secondary electrons is released from the final stage dynode 11. The group of secondary electrons is guided to the anode 12 and output to the outside via the pin 7 (anode pin) connected to the anode 12.

[0036] In this embodiment, the photomultiplier tube 1 using the photocathode 4 is exemplified. However, the photocathode according to the present invention is not limited to the photomultiplier tube, and may be replaced by other electron tubes such as a phototube, an image amplifier, or a streak tube.

[0037] [Structure of the photocathode]

[0038] Figure 2 yes Figure 1 The main part of the photomultiplier tube 1 is enlarged and sectional. Figure 2 As shown, the photocathode 4 includes a light-transmitting substrate 21 , a light-transmitting conductive layer 22 , a bonding member 23 , and a photoelectric conversion layer 24 .

[0039] The translucent substrate 21 is formed into a disk shape from a glass material such as quartz glass or a crystalline material such as MgF2, and allows incident light L to enter the housing 2. The translucent substrate 21 has a surface 21a, into which the incident light L enters, and another surface 21b, opposite to the surface 21a, which allows the incident light L to exit toward the electron multiplier 3. The translucent substrate 21 is airtightly secured to the inward flange portion 13 provided at the distal end of the side tube portion 5 on the outer surface of the housing 2 via a bonding member 23.

[0040] The light-transmitting conductive layer 22 is a base layer of the photoelectric conversion layer 24 relative to the light-transmitting substrate 21, and is made of a carbon-containing constituent material C ( Figure 3 The light-transmitting conductive layer 22 transmits incident light L to the photoelectric conversion layer 24 and reduces the surface resistance of the photoelectric conversion layer 24. The light-transmitting conductive layer 22 has one surface 22a in contact with the light-transmitting substrate 21 and another surface 22b in contact with the photoelectric conversion layer 24. The light-transmitting conductive layer 22 is formed by vapor-depositing a carbon-containing constituent material C onto the other surface 21b of the light-transmitting substrate 21 in a circular shape having a larger diameter than the inner diameter of the inward flange portion 13 (i.e., a size that covers the opening formed by the flange portion 13).

[0041] The bonding member 23 is made of a conductive material such as aluminum. The bonding member 23 is arranged to fill the gap between the peripheral edge of the light-transmitting substrate 21 and the peripheral edge of the light-transmitting conductive layer 22 and the flange 13. The bonding member 23 serves as a substantial fixing member relative to the side tube 5 of the photocathode 4 and electrically connects the light-transmitting conductive layer 22 and the side tube 5.

[0042] The photoelectric conversion layer 24 is, for example, a multi-alkali photoelectric surface having sensitivity extending into the infrared region, and may contain, for example, antimony (Sb), potassium (K), and cesium (Cs). The photoelectric conversion layer 24 converts incident light L transmitted through the light-transmitting substrate 21 and the light-transmitting conductive layer 22 into photoelectrons, and emits the converted photoelectrons toward the electron multiplying section 3. The photoelectric conversion layer 24 is provided so as to cover the inner surface 13a of the flange 13 and the area of the other surface 22b of the light-transmitting conductive layer 22 exposed from the flange 13, and to contact the bonding member 23 and the inner peripheral edge of the flange 13.

[0043] [Structure of Light-Transmitting Conductive Layer]

[0044] Next, the above-mentioned light-transmitting conductive layer 22 will be described in more detail.

[0045] Figure 3 (a) is a diagram showing an example of a constituent material of a light-transmitting conductive layer. Figure 3 (b) is Figure 3 An enlarged view of the main part of (a). Figure 3 (a) and Figure 3 (b) are all observation results of the light-transmitting conductive layer 22 under a scanning electron microscope. Figure 3 (a) is an image with a magnification of 10,000 times. Figure 3 (b) is an image with a magnification of 50,000 times. Figure 3 As shown in (b), microscopically, a graphite-like two-dimensional layered film is formed with boundaries due to the carbon-containing constituent material C. This two-dimensional layered film has light transparency and conductivity, so adjacent two-dimensional layered films are electrically connected to each other, ensuring light transparency and conductivity as the light-transmitting conductive layer 22. In the following description, this basic structural region is referred to as region G.

[0046] In the light-transmitting conductive layer 22, in addition to the region G, as the deformation region 31, there are irregularly present block portions 31a retaining the graphene structure, layered film structure fragment boundaries 31b, and opening portions 31c that are not covered by the constituent material C and through which the light-transmitting substrate 21 is visible. In the block portion 31a, for example, the graphene structure exists as a certain block. In the layered film structure fragment boundaries 31b, which are discontinuous portions, defects are formed, for example, due to the twisting or breaking of carbon bonds, and the opening portions 31c are formed due to these twists and breaks. The incident light L is mainly transmitted from the region G and the opening portions 31c. In this embodiment, in particular, due to the presence of the opening portions 31c that do not exist in the existing graphene structure, the light transmittance can be significantly improved. In the following description, the substance in the above-mentioned state is referred to as "glassy carbon" for convenience.

[0047] In this embodiment, glassy carbon is evaporated on the light-transmitting substrate 21 using a carbon supply material, and a light-transmitting conductive layer 22 is formed on the light-transmitting substrate 21. The evaporation time of the glassy carbon is, for example, less than 60 minutes. The evaporation time of the glassy carbon can also be less than 30 minutes, or less than 10 minutes. Generally speaking, there is a trend that the shorter the evaporation time is, the more opening portions 31c are visible, and the area of the opening portions 31c also becomes larger. In this case, light transmittance is improved and conductivity is reduced. On the other hand, when the growth of the two-dimensional layered film progresses as the evaporation time becomes longer, there is a trend that the number of opening portions 31c decreases and the area of the opening portions 31c becomes smaller. In this case, light transmittance is reduced and conductivity is improved. Figure 3 (a) and Figure 3 The state of the light-transmitting conductive layer 22 shown in (b) is merely an example, and the light-transmitting conductive layer 22 having desired light transmittance and conductivity can be obtained by appropriately adjusting the vapor deposition time.

[0048] Furthermore, when viewing the light-transmitting conductive layer 22 in the thickness direction (the direction connecting one surface 22a and the other surface 22b), the area of the region G within the plane increases as the thickness of the light-transmitting conductive layer 22 increases, and decreases as the thickness of the light-transmitting conductive layer 22 decreases. This means that, when viewing the light-transmitting conductive layer 22 in the thickness direction, the area of the opening 31c within the plane increases as the thickness of the light-transmitting conductive layer 22 decreases, and decreases as the thickness of the light-transmitting conductive layer 22 increases. Therefore, it can be seen that there is a trade-off between conductivity and light transmittance depending on the thickness of the light-transmitting conductive layer 22. The thicker the light-transmitting conductive layer 22, the higher the conductivity and the lower the light transmittance of the light-transmitting conductive layer 22. The thinner the thickness of the light-transmitting conductive layer 22, the lower the conductivity and the higher the light transmittance of the light-transmitting conductive layer 22.

[0049] Figure 4 : is a diagram showing an example of the Raman spectrum of glassy carbon constituting the light-transmitting conductive layer 22. Figure 4 In the figure, the horizontal axis represents the Raman shift (cm -1 ), the vertical axis represents the Raman intensity (au). Figure 4 (a)~ Figure 4 (c) is the Raman spectrum of glassy carbon with different evaporation times. Figure 4 (d) is a Raman spectrum of highly oriented pyrolytic graphite (HOPG) as a comparative example. Figure 4 (a)~ Figure 4 The vapor deposition times in the case of (c) were 10 minutes, 30 minutes, and 60 minutes, respectively.

[0050] Raman spectroscopy is a spectrum obtained through methods such as Raman spectroscopy and electron energy loss spectroscopy and is used to analyze the state of a substance. The peak intensity of a Raman spectrum indicates the state of polarizability and orientation, while the wavenumber information indicates the composition. Furthermore, the peak ratio indicates the relative ratio of each substance, the full width at half maximum of the peak indicates crystallinity and defects / impurities, and the peak shift indicates distortion, stress, temperature, and other factors.

[0051] exist Figure 4 The four bands shown in the figure are D1 band, G band, 2D1 band and (D1+G) band. The D1 band is a band indicating structural disorder and defects. The peak P1 of the D1 band is caused by lattice motion in the direction away from the center of the Brillouin zone. If the peak P1 of the D1 band exists, it indicates that the material contains defects and edge parts. The G band is a band originating from the in-plane motion of atoms. The peak P2 of the G band changes due to the influence of structural distortion and is also used as an indicator of the number of layers. The peak P2 of the G band tends to become very sharp and strong in a single layer, and tends to become wider as the number of layers increases.

[0052] The 2D1 band originates from double scattering of hexagonal rings. Peak P3 of the 2D1 band is equivalent to the doublet of the D1 band. It arises from a double resonance process linking the phonon wavenumber vector to the electronic band structure and exhibits a strong frequency dependence on the excitation light. Like peak P2 of the G band, peak P3 of the 2D1 band tends to broaden with increasing layer number. The (D1+G) band originates from double scattering of the D1 and G bands. Peak P4 of the (D1+G) band is located at a higher wavenumber than peak P3 of the 2D1 band and tends to broaden with increasing layer number.

[0053] The range of each band's peak depends on the excitation wavelength of the Raman spectrum. The D1 band is, for example, located at 1580 to 1600 cm-1 The G band is located at 1580~1600cm -1 The 2D1 band is located at 2700-2750 cm -1 The (D1+G) band is located at 2930~3000cm -1 In the range. Figure 4 In the example, the excitation wavelength of the Raman spectrum is 457 nm, and the wave number of the peak P1 of the D1 band is about 1360 cm -1 In addition, the wave number of the peak P2 of the G band is about 1580 cm -1 The wave number of peak P3 of D2 band is about 2700 cm -1 The wave number of the peak P4 of the (D1+G) band is about 2930 cm -1 .

[0054] like Figure 4 As shown in (a) to (c), the Raman spectra of glassy carbon have four peaks: peak P1 of the D1 band, peak P2 of the G band, peak P3 of the 2D1 band, and peak P4 of the (D1+G) band. Figure 4 As shown in (d), the Raman spectrum of highly oriented pyrolytic graphite has no peak P1 of the D1 band and no peak P4 of the (D1+G) band, but only two peaks: peak P2 of the G band and peak P3 of the 2D1 band.

[0055] In the Raman spectrum of glassy carbon, peak P1 of the D1 band and peak P2 of the G band are more prominent than peak P3 of the 2D1 band and peak P4 of the (D1+G) band. As the deposition time during the formation of glassy carbon increases (the thickness of the light-transmitting conductive layer 22 increases), the magnitude relationship between the peak intensity of peak P1 of the D1 band and the peak intensity of peak P2 of the G band gradually changes.

[0056] exist Figure 4 In the example shown in Figure 2, when the deposition time is 10 minutes, the peak intensity of peak P1 of the D1 band is greater than the peak intensity of peak P2 of the G band. In contrast, when the deposition time is 30 and 60 minutes, the peak intensity of peak P2 of the G band is greater than the peak intensity of peak P1 of the D1 band. This shows that when the deposition time is short, the glassy carbon contains many relatively small crystals with a large number of defects. As the deposition time increases, the structure of the glassy carbon becomes more polycrystalline, gradually approaching a graphene structure.

[0057] The peak P3 of the 2D1 band and the peak P4 of the (D1+G) band gradually broaden and their peak intensities gradually decrease as the deposition time increases during the formation of glassy carbon. The magnitude relationship between the peak intensity of the 2D1 band peak P3 and the peak intensity of the (D1+G) band peak P4 does not depend on the deposition time and does not change. Figure 4In the example, when the evaporation time is 10 minutes, 30 minutes, and 60 minutes, the peak intensity of the peak P3 of the 2D1 band is still greater than the peak intensity of the peak P4 of the (D1+G) band.

[0058] In addition, if Figure 4 As shown in Figures (a) to (c), in the Raman spectrum of glassy carbon, the lower edge of peak P1 of the D1 band and the lower edge of peak P2 of the G band overlap. Therefore, the minimum Raman intensity R1 between peak P1 of the D1 band and peak P2 of the G band is greater than the base value R2 of the Raman intensity between peak P2 of the G band and peak P3 of the 2D1 band. The base value R2 can be either the average value of the Raman intensity in the range where the spectrum is flat between peak P2 of the G band and peak P3 of the 2D1 band, or the maximum value of the Raman intensity in that range.

[0059] [Method for manufacturing photocathode]

[0060] When manufacturing the photocathode 4 having the above structure, first, prepare the light-transmitting substrate 21. The light-transmitting substrate 21 is cleaned with acetone and ethanol, for example, and then rinsed with water. Figure 5 As shown in (a), the translucent substrate 21 is placed on a mounting table 52 in a vapor deposition apparatus 51 with the other surface 21b of the translucent substrate 21 facing upward. After the translucent substrate 21 is placed, the pressure in the vapor deposition apparatus 51 is reduced to approximately 0.01 Torr. For example, ethanol vapor can be used as the carbon supply source, and for example, argon gas can be used as the carrier gas.

[0061] Next, a carrier gas is introduced into the evaporation device 51 at a flow rate of approximately 180 sccm, causing the pressure to rise to approximately 10 Torr and the temperature to rise to approximately 1000°C. After the pressure and temperature in the evaporation device 51 are stabilized, a carbon supply raw material, which will become the source of the constituent material C, is introduced into the evaporation device 51 through the shower head 53 at a flow rate of approximately 1 sccm. Thereafter, the supply of the carbon supply raw material is maintained for approximately 10 to 60 minutes, and glassy carbon is grown to a desired thickness on the other surface 21b of the translucent substrate 21. After the glassy carbon of the desired thickness has grown, the supply of the carbon supply raw material is stopped, and the glassy carbon is allowed to cool naturally to room temperature. Thus, a light-transmitting conductive layer 22 is formed on the other surface 21b of the translucent substrate 21.

[0062] Next, the translucent substrate 21 on which the translucent conductive layer 22 is formed is taken out from the evaporation device 51, and the translucent conductive layer 22 on the peripheral portion of the other surface 21b of the translucent substrate 21 is selectively removed. When removing the translucent conductive layer 22, for example, a circular mask having a smaller diameter than the translucent substrate 21 is placed in the center of the translucent conductive layer 22, and the translucent conductive layer 22 is irradiated with plasma. As a result, the portion of the translucent conductive layer 22 exposed from the mask is removed, as shown in FIG. Figure 5 As shown in FIG. 2( b ), a light-transmitting conductive layer 22 having a smaller diameter than that of the light-transmitting substrate 21 is coaxially formed on the other surface 21 b of the light-transmitting substrate 21 .

[0063] Then, if Figure 6 As shown in (a), the flange portion 13 is arranged to overlap the peripheral portion of the light-transmitting conductive layer 22 , and the other surface 21 b of the light-transmitting substrate 21 and the flange portion 13 are airtightly bonded to each other by a bonding member 23 .

[0064] Furthermore, antimony is deposited on the inner surface 13a of the flange 13, the area exposed from the flange 13 on the other surface 22b of the light-transmitting conductive layer 22, the bonding member 23, and the inner peripheral edge of the flange 13. Then, potassium and cesium are reacted with antimony using a conveyor device, thereby Figure 6 As shown in (b), a bialkali photoelectric surface (photoelectric conversion layer 24) is formed on the other side 22b of the light-transmitting conductive layer 22 as the base layer. Figure 1 and Figure 2 The photocathode 4 is shown. Alternatively, the other surface 21b of the light-transmitting substrate 21 may be airtightly fixed to the flange portion 13 in advance, and then the light-transmitting conductive layer 22 may be formed on the other surface 21b of the light-transmitting substrate 21.

[0065] [Effects]

[0066] As described above, in the photocathode 4, the light-transmitting conductive layer 22 disposed between the light-transmitting substrate 21 and the photoelectric conversion layer 24 contains carbon as its constituent material C. The Raman spectrum of this constituent material C exhibits four peaks: the D1 band, the G band, the 2D1 band, and the (D1+G) band. In the light-transmitting conductive layer 22 formed from the constituent material C having such a Raman spectrum, the light-transmitting conductive layer 22 microscopically contains, for example, blocky portions 31a retaining a carbon atomic lattice structure and layered film structure fragment boundaries 31b containing defects such as distortions and breaks in the carbon atomic lattice structure. The light transmittance and electrical resistance of the layered film structure vary depending on the arrangement of the deformed regions 31. Therefore, in this photocathode 4, the light transmittance and electrical conductivity of the light-transmitting conductive layer 22 can be adjusted by adjusting the thickness of the light-transmitting conductive layer 22. This makes it possible to easily obtain desired characteristics even when the light-transmitting conductive layer 22 is disposed as a base between the light-transmitting substrate 21 and the photoelectric conversion layer 24.

[0067] In this embodiment, the minimum value R1 of the Raman intensity between the peak P1 of the D1 band and the peak P2 of the G band is greater than the base value R2 of the Raman intensity between the peak P2 of the G band and the peak P3 of the 2D1 band. In a light-transmitting conductive layer 22 having such a Raman spectrum, a structure incorporating the above-described deformed regions 31 can be more easily obtained, making it easier to adjust light transmittance and conductivity.

[0068] In this embodiment, when the vapor deposition time of the constituent material C is relatively short, the Raman intensity of peak P1 of the D1 band is greater than the Raman intensity of peak P2 of the G band. In a photocathode 4 having a light-transmitting conductive layer 22 with such a Raman spectrum, the thickness of the light-transmitting conductive layer 22 is reduced, thereby achieving a photocathode 4 with excellent light transmittance. On the other hand, when the vapor deposition time of the constituent material C is relatively long, the Raman intensity of peak P1 of the D1 band is less than the Raman intensity of peak P2 of the G band. In a photocathode 4 having a light-transmitting conductive layer 22 with such a Raman spectrum, the thickness of the light-transmitting conductive layer 22 is increased, thereby making it easier to adjust the light transmittance and conductivity.

[0069] In the method for manufacturing the photocathode 4 according to this embodiment, a light-transmitting conductive layer 22 is formed on a light-transmitting substrate 21 by vapor deposition using a carbon-containing gas. This method facilitates the formation of the light-transmitting conductive layer 22 by simply vapor-depositing the constituent material C using the vapor deposition apparatus 51, compared to methods in which a separately formed light-transmitting conductive layer 22 is transferred onto the light-transmitting substrate 21. Furthermore, the light-transmitting conductive layer 22 can be uniformly formed even when the light-transmitting substrate 21 has some irregularities, and a stable light-transmitting conductive layer 22 can be formed even when the area is large. Furthermore, by adjusting the vapor deposition time using the vapor deposition apparatus 51, the thickness and transmittance of the light-transmitting conductive layer 22 can be easily adjusted. Even when the light-transmitting conductive layer 22 is provided as a base between the light-transmitting substrate 21 and the photoelectric conversion layer 24, desired characteristics can be easily obtained.

[0070] In this embodiment, the vapor deposition time of the constituent material C is 60 minutes or less. In this case, the light-transmitting conductive layer 22 having the above-mentioned peaks can be appropriately obtained.

[0071] [Photocathode evaluation test results]

[0072] Figure 7 This is a graph showing the results of an evaluation test on the spectral sensitivity characteristics of the photocathode. Figure 7 In the graph, the wavelength (nm) of the incident light is shown on the horizontal axis, and the transmittance (%) is shown on the vertical axis. Curve E shown in the figure represents the transmittance of a photocathode (comparative example) using a single layer of graphene to form a light-transmitting conductive layer, and curves G7 and G8 shown in the figure represent the transmittance of a photocathode (example) using glassy carbon to form a light-transmitting conductive layer. Curve G7 represents the transmittance formed by maintaining the supply of the carbon supply raw material for about 7 minutes, and curve G8 represents the transmittance formed by maintaining the supply of the carbon supply raw material for about 8 minutes. Figure 7 The results shown confirm that the photocathode using glassy carbon to form a light-transmitting conductive layer exhibits higher transmittance in the ultraviolet wavelength region of 230 nm to 330 nm compared to the photocathode using graphene to form a light-transmitting conductive layer.

[0073] Figure 8 This is a graph showing the results of an evaluation test on the cathode linearity characteristics of a photocathode. Figure 8In the graph, the horizontal axis represents the cathode output current value (A), and the vertical axis represents the rate of change (%) of the cathode output current value relative to the current value (ideal value) in the case of ideal linearity. The dotted curve H in the figure represents the cathode linear characteristics of the photocathode (comparative example) using graphene to form a light-transmitting conductive layer, and the solid curve I in the figure represents the cathode linear characteristics of the photocathode (example) using glassy carbon to form a light-transmitting conductive layer. Figure 8 The results shown confirm that in the photocathode using glassy carbon to form a light-transmitting conductive layer, the rate of change when the current value increases (the amount of incident light increases) remains stable at around 0% until the measurement limit is reached, and the same degree of cathode linear characteristics as in the case of the photocathode using graphene to form a light-transmitting conductive layer can be obtained.

[0074] The present invention is not limited to the above-mentioned embodiments. For example, various manufacturing conditions in the method for manufacturing the photocathode may be arbitrarily changed in terms of flow rate and time, etc., depending on the thickness of the glassy carbon to be formed and the type and concentration of the carbon supply raw material. In addition, as a carbon supply raw material, any gas containing carbon may be used, and materials other than ethanol may also be used. Examples of other carbon supply raw materials include alcohols (such as methanol, propanol, butanol, etc.), hydrocarbons (methane, ethane, propane, butane, etc.), phenols, aldehydes, and ketones. In addition, these vaporized gases (including substances that evaporate, sublimate, or dissolve in a solvent to become gas) may also be used. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] 1 Photomultiplier tube

[0077] 4 Photocathode

[0078] 21Transparent substrate

[0079] 21a side

[0080] 21b The other side

[0081] 22 Light-transmitting conductive layer

[0082] 24 Photoelectric conversion layer

[0083] 51 evaporation device

[0084] CConstituent materials

[0085] LIncident light (light)

[0086] Peak of P1 D1 band

[0087] The peak of the P2 G band

[0088] Peak of P3 2D1 band

[0089] Peak of P4(D1+G) band

[0090] R1 minimum

[0091] R2 base value.

Claims

1. A photocathode comprising: A light-transmitting substrate having a surface on which light is incident and another surface on which the light incident from the surface is emitted; A photoelectric conversion layer provided on the other surface side of the light-transmitting substrate and converting the light emitted from the other surface into photoelectrons; and a light-transmitting conductive layer provided between the light-transmitting substrate and the photoelectric conversion layer; The light-transmitting conductive layer is formed of a constituent material containing carbon, The Raman spectrum of the constituent material has: The peak of the D1 band; The peak of the G band; The peak of the 2D1 band; and The peak of the (D1+G) band.

2. The photocathode according to claim 1, wherein A minimum value of the Raman intensity between the peak of the D1 band and the peak of the G band is greater than a base value of the Raman intensity between the peak of the G band and the peak of the 2D1 band.

3. The photocathode according to claim 1 or 2, wherein The Raman intensity of the peak of the D1 band is greater than the Raman intensity of the peak of the G band.

4. The photocathode according to claim 1 or 2, wherein The Raman intensity of the peak of the D1 band is smaller than the Raman intensity of the peak of the G band.

5. A method for manufacturing the photocathode according to any one of claims 1 to 4, comprising: The step of placing a light-transmitting substrate in a vapor deposition device; A step of introducing a carbon-containing gas into the vapor deposition device to vapor-deposit a carbon-containing constituent material on the light-transmitting substrate to form a light-transmitting conductive layer; and forming a photoelectric conversion layer on the light-transmitting conductive layer.

6. The method for manufacturing a photocathode according to claim 5, wherein: The vapor deposition time of the constituent materials is 60 minutes or less.

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