Patent Number: 
Section: claims

1. A thermal interface material for a high vacuum condition, comprising a graphite sheet having a thickness of from 9.6 μm to 50 nm and a thermal conductivity in an a-b surface direction at 25° C. of not less than 1800 W/mK. 2. The thermal interface material according to claim 1, wherein the graphite sheet is obtained by thermally treating a polymer film at a temperature of not less than 2900° C. 3. The thermal interface material according to claim 2, wherein the polymer film is an aromatic polyimide. 4. A graphite substrate material for high vacuum condition, being prepared from the thermal interface material according to claim 1. 5. A target substrate material for high vacuum condition, being prepared from the thermal interface material according to claim 1. 6. The thermal interface material according to claim 1, wherein the graphite sheet has the thermal conductivity in an a-b surface direction at 25° C. of not less than 1960 W/mK. 7. The thermal interface material according to claim 1, wherein the graphite sheet has the thermal conductivity in an a-b surface direction at 25° C. of not less than 2000 W/mK. 8. The thermal interface material according to claim 1, wherein the graphite sheet has the thickness of from 100 nm to 5.0 μm. 9. A layered target material for generating neutrons, comprising a neutron-producing metal member and a proton-absorbing metal substrate which are layered, wherein the thermal interface material according to claim 1 is interposed between the neutron-producing metal member and the proton-absorbing metal substrate. 10. A target module for generating neutrons, comprising:a plurality of the thermal interface materials according to claim 1;a neutron-producing metal member;a proton-absorbing metal substrate; anda heat sink member,wherein the proton-absorbing metal substrate is interposed between the neutron-producing metal member and the heat sink member,wherein one of the thermal interface materials is interposed between the neutron-producing metal member and the proton-absorbing metal substrate, andwherein one of the thermal interface materials is interposed between the proton-absorbing metal substrate and the heat sink member. 11. The target module for generating neutrons according to claim 10, wherein the neutron-producing metal member is a beryllium target, the proton-absorbing metal substrate is formed of at least one kind of material selected from among vanadium, niobium and tantalum, and the heat sink member is formed of at least one kind of material selected from among aluminum and titanium. 12. A method for transferring heat, the method comprising:inserting a graphite sheet between two components; andtransferring heat between the two components under a high vacuum condition, whereinthe graphite sheet has a thickness of from 9.6 μm to 50 nm and a thermal conductivity in an a-b surface direction at 25° C. of not less than 1800 W/mK. 13. The method according to claim 12, wherein the graphite sheet is obtained by thermally treating a polymer film at a temperature of not less than 2900° C. 14. The method according to claim 13, wherein the polymer film is an aromatic polyimide. 15. The method according to claim 12, wherein the two components are a neutron-producing metal member and a proton-absorbing metal substrate. 16. The method for transferring heat according to claim 12, wherein the graphite sheet has the thermal conductivity in an a-b surface direction at 25° C. of not less than 1960 W/mK. 17. The method for transferring heat according to claim 12, wherein the graphite sheet has the thermal conductivity in an a-b surface direction at 25° C. of not less than 2000 W/mK. 18. The method for transferring heat according to claim 12, wherein the graphite sheet has the thickness of from 100 nm to 5.0 μm.