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A low-friction sliding member such as a piston, a piston ring, a piston skirt section and a cylinder liner section of an internal combustion engine. The low-friction sliding member includes a base material having a surface. A hard carbon thin film is formed at at least a part of the surface of the b

A low-friction sliding member such as a piston, a piston ring, a piston skirt section and a cylinder liner section of an internal combustion engine. The low-friction sliding member includes a base material having a surface. A hard carbon thin film is formed at at least a part of the surface of the base material. Here, a tribo-film having at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group is formed on the hard carbon thin film when the hard carbon thin film is in slidable contact with an opposite member in presence of an organic oxygen-containing compound.

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What is claimed is: 1. A low-friction sliding member comprising: a base material having a surface; and a hard carbon thin film formed on at least a part of the surface of the base material the hard carbon thin film being formed of diamond-like carbon containing hydrogen in an amount not more than 1

What is claimed is: 1. A low-friction sliding member comprising: a base material having a surface; and a hard carbon thin film formed on at least a part of the surface of the base material the hard carbon thin film being formed of diamond-like carbon containing hydrogen in an amount not more than 10 atomic %; wherein a tribo-film having at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group is formed on the hard carbon thin film when the hard carbon thin film is in slidable contact with an opposite member in presence of an organic oxygen-containing compound capable of forming the tribo-film having at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group, wherein the organic oxygen-containing compound is at least one selected from the group consisting of an alcohol, carboxylic acid, ester, ether, ketone, aldehyde, carbonate, and a derivative of the alcohol, the carboxylic acid, the ester, the ether, the ketone, the aldehyde and the carbonate. 2. A low-friction sliding member as claimed in claim 1, wherein the tribo-film has a thickness of not more than 10 nm. 3. A low-friction sliding member as claimed in claim 1, wherein the tribo-film has a lower friction characteristics than a tribo-film which does not have at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group. 4. A low-friction sliding member as claimed in claim 1, wherein the hard carbon thin film is formed of diamond-like carbon of a-C type containing substantially no hydrogen. 5. A low-friction sliding member as claimed in claim 1, wherein the hard carbon thin film has a surface roughness (Ra) not more than 0.1 μm. 6. A low-friction sliding member as claimed in claim 1, wherein the hard carbon thin film has a surface hardness (Hv) ranging from 1000 to 3500 in micro-Vickers hardness (under a load of 10 g), and a film thickness ranging from 0.3 to 2.0 μm. 7. A low-friction sliding member as claimed in claim 2, wherein the tribo-film is formed within a range from a sliding surface of the sliding member to a depth of 10 nm from the sliding surface during friction between the hard carbon thin film and the opposite member, the sliding surface of the sliding member being in sliding contact with the opposite member. 8. A low-friction sliding mechanism comprising: a first low-friction sliding member including a base material having a surface, and a hard carbon thin film formed on at least a part of the surface of the base material the hard carbon thin film being formed of diamond-like carbon containing hydrogen in an amount not more than 10 atomic %, wherein a tribo-film having at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group is formed on the hard carbon thin film when the hard carbon thin film is in slidable contact with an opposite member in presence of an organic oxygen-containing compound; at least one of a second low-friction sliding member and a metal member having a sliding surface, serving as the opposite member, the second low-friction sliding member including a base material having a surface of the base material, and a hard carbon thin film formed on at least a part of the surface the hard carbon thin film being formed of diamond-like carbon containing hydrogen in an amount not more than 10 atomic %, wherein a tribo-film having at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group is formed on the hard carbon thin film when the hard carbon thin film is in slidable contact with the opposite member in presence of the organic oxygen-containing compound; and the organic oxygen-containing compound present in a sliding surface site formed between a sliding surface of the first low-friction sliding member and the sliding surface of at least one of the second low-friction sliding member and the metal member, wherein the organic oxygen-containing compound is at least one selected from the group consisting of an alcohol, carboxylic acid, ester, ether, ketone, aldehyde, carbonate, and a derivative of the alcohol, the carboxylic acid, the ester, the ether, the ketone, the aldehyde and the carbonate. 9. A low-friction sliding mechanism comprising: a first low-friction sliding member including a base material having a surface, and a hard carbon thin film formed on at least a part of the surface of the base material the hard carbon thin film being formed of diamond-like carbon containing hydrogen in an amount not more than 10 atomic %, wherein a tribo-film having at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group is formed on the hard carbon thin film when the hard carbon thin film is in slidable contact with an opposite member in presence of an organic oxygen-containing compound; at least one of a second low-friction sliding member and a metal member having a sliding surface, serving as the opposite member, the second low-friction sliding member including a base material having a surface of the base material, and a hard carbon thin film formed on at least a part of the sliding surface the hard carbon thin film being formed of diamond-like carbon containing hydrogen in an amount not more than 10 atomic %, wherein a tribo-film having at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group is formed on the hard carbon thin film when the hard carbon thin film is in slidable contact with the opposite member in presence of the organic oxygen-containing compound; and lubricating oil present in a sliding surface site formed between a sliding surface of the first low-friction sliding member and the sliding surface of at least one of the second low-friction sliding member and the metal member, the lubricating oil containing the organic oxygen-containing compound, wherein the organic oxygen-containing compound is at least one selected from the group consisting of an alcohol, carboxylic acid, ester, ether, ketone, aldehyde, carbonate, and a derivative of the alcohol, the carboxylic acid, the ester, the ether, the ketone, the aldehyde and the carbonate. 10. A process for reducing friction of a sliding member including a base material having a surface, the process comprising: forming a hard carbon thin film on at least a part of the surface of the base material the hard carbon thin film being formed of diamond-like carbon containing hydrogen in an amount not more than 10 atomic %; and forming a tribo-film having at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group on the hard carbon thin film when the hard carbon thin film is in slidable contact with an opposite member in presence of an organic oxygen-containing compound, wherein the organic oxygen-containing compound is at least one selected from the group consisting of an alcohol, carboxylic acid, ester, ether, ketone, aldehyde, carbonate, and a derivative of the alcohol, the carboxylic acid, the ester, the ether, the ketone, the aldehyde and the carbonate. 11. A low-friction sliding mechanism, comprising: a first sliding member having a sliding surface, at least the sliding surface of the first sliding member comprising a diamond-like carbon material containing hydrogen in an amount not more than 10 atomic % and; a second sliding member having a sliding surface slidable relative to the sliding surface of the first sliding member; and a lubricant applied to the sliding surfaces of the first and second sliding members, the lubricant comprising an oxygen-containing organic compound or a nitrogen-containing organic compound, wherein the oxygen-containing organic compound is at least one selected from the group consisting of at alcohol, carboxylic acid, ester, ether, ketone, aldehyde, carbonate, and derivative of the alcohol, the carboxylic acid, the ester, the ether, the ketone, the aldehyde and the carbonate. 12. A low-friction sliding mechanism, comprising: a first sliding member having a sliding surface, at least the sliding surface of the first sliding member comprising a diamond-like carbon material containing hydrogen in an amount not more than 10 atomic % and; a second sliding member having a sliding surface slidable relative to the sliding surface of the first sliding member, at least the sliding surface of the second sliding member comprising a diamond-like carbon material containing hydrogen in an amount not more than 10 atomic %; and a lubricant applied to the sliding surfaces of the first and second sliding members, the lubricant comprising glycerin. 13. A low-friction sliding member comprising: a base material having a surface; and a hard carbon thin film formed on at least a part of the surface of the base material, the hard carbon thin film being formed of diamond-like carbon containing hydrogen in an amount not more than 10 atomic %; wherein a tribo-film having at least one functional group selected from the group consisting of either linkage, oxide and hydroxyl group is formed on the hard carbon thin film when the hard carbon thin film is in slidable contact with an opposite member in presence of an organic oxygen-containing compound containing at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group, wherein the organic oxygen-containing compound is at least one selected from the group consisting of an alcohol, carboxylic acid, ester, ether, ketone, aldehyde, carbonate, and a derivative of the alcohol, the carboxylic acid, the ester, the ether, the ketone, the aldehyde and the carbonate. 14. A low-friction sliding mechanism comprising: a first sliding member including a base material having a surface; a second sliding member including a base member having a surface, the second sliding member being in slidable contact with the first sliding member, wherein at least a part of the surface of the base member of one of the first and second sliding members is coated with a hard carbon thin film; and an organic oxygen-containing compound present between the first and second sliding members and capable of forming a tribo-film having at least one functional group selected from the group consisting of ether linkage, oxide and hydroxyl group, on the hard carbon thin film when the first and second sliding members are in slidable contact with each other in presence of the organic oxygen-containing compound, wherein the organic oxygen-containing compound is at least one selected from the group consisting of an alcohol, carboxylic acid, ester, ether, ketone, aldehyde, carbonate, and a derivative of the alcohol, the carboxylic acid, the ester, the ether, the ketone, the aldehyde and the carbonate. 15. A low-friction sliding mechanism comprising: a first sliding member including a base material having a surface; a second sliding member including a base member having a surface, the second sliding member being in slidable contact with the first sliding member; a first film of a-C type diamond-like carbon formed on at least a part of the surface of the base material of the first sliding member; a second film of a-C type diamond-like carbon formed on at least a part of the surface of the base material of the second sliding member; and an organic oxygen-containing compound present between the first and second sliding members and capable of forming a tribo-film having at least one functional group selected from the group consisting of ether linkage, oxido and hydroxyl group, on the first and second films when the first and second sliding members are in slidable contact with each other in presence of the organic oxygen-containing compound, wherein the organic oxygen-containing compound is at least one selected from the group consisting of an alcohol, carboxylic acid, ester, ether, ketone, aldehyde, carbonate, and a derivative of the alcohol, the carboxylic acid, the ester, the ether, the ketone, the aldehyde and the carbonate.