▎ 摘　　要

NOVELTY - Unitary graphene layer or graphene single crystal (I) comprises closely packed and chemically bonded parallel graphene planes having an inter-graphene plane spacing of 0.335-0.4 nm, a thickness greater than 10 nm, and an oxygen content of 0.01-10 wt.%, in which the unitary graphene layer or graphene single crystal is obtained from heat-treating a graphene oxide gel at a temperature higher than 100 degrees C. An average misorientation angle between two graphene planes is less than 10 degrees . USE - The unitary graphene layers or graphene single crystals are useful for heat-spreading applications (claimed) e.g. as a heat spreader or a heat sink product in a hand-held device e.g. a power tool, a microelectronic or telecommunication device (e.g. mobile phone, tablet, laptop computer, notebook computer, electronic book and LCD display), a flexible display, LED, power tool, computer CPU and power electronics. ADVANTAGE - The unitary graphene layer or graphene single crystal (I): contains no discrete graphite flake or graphene platelet dispersed, and no complete grain boundary; has a Rockwell hardness value greater than 60; has an electrical conductivity greater than 1500 S/cm, preferably greater than 5000 S/cm, a thermal conductivity greater than 600 W/mK, preferably greater than 1500 W/mK, a physical density greater than 1.8 g/cm3, preferably greater than 2.1 g/cm3, and/or a tensile strength greater than 40 MPa, preferably greater than 100 MPa; has a thermal conductivity greater than 600 W/mK or electrical conductivity greater than 2000 S/cm (when the heat-treating temperature is 100-1000 degrees C); has a thermal conductivity greater than 1300 W/mK or electrical conductivity greater than 3000 S/cm (when the heat-treating temperature is 1000-1500 degrees C); has a thermal conductivity greater than 1600 W/mK or electrical conductivity greater than 5000 S/cm (when the heat-treating temperature is 1500-2500 degrees C); and has a thermal conductivity greater than 1700 W/mK or electrical conductivity greater than 10000 S/cm (when the heat-treating temperature is 2500-3250 degrees C) (all claimed). DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for: (1) a unitary graphene layer (II) for heat-spreading applications, containing closely packed, gap-free, and chemically bonded parallel graphene planes having an inter-graphene plane spacing of 0.336 to 0.5 nm and an oxygen content less than 1 wt.%, where the unitary graphene layer has a thickness greater than 10 nm, contains no discrete graphite flake or graphene platelet dispersed in that, and has an average misorientation angle between two graphene planes less than 10 degrees and is obtained from heat-treating a graphene oxide gel at a temperature higher than 500 degrees C; (2) a unitary graphene layer (III) for heat-spreading applications, containing closely packed and chemically bonded parallel graphene planes having an inter-graphene plane spacing of 0.335 to 0.5 nm and an oxygen content less than 1 wt.%, where the unitary graphene layer contains a polycrystal having an incomplete grain boundary, contains no discrete graphite flake or graphene platelet dispersed in that, and is obtained from heat-treating a graphene oxide gel at a temperature higher than 500 degrees C; and (3) producing the unitary graphene layer or graphene single crystal (I), comprising: (a1) preparing a graphene oxide gel having graphene oxide molecules dispersed in a fluid medium, where the graphene oxide gel is optically transparent or translucent; (b1) depositing a layer of the graphene oxide gel onto a surface of a supporting substrate to form a deposited graphene oxide gel; (c1) partially or completely removing the fluid medium from the deposited graphene oxide gel layer to form a graphene oxide layer; and (d1) heat-treating the graphene oxide layer to form the unitary graphene layer or graphene single crystal at a temperature higher than 500 degrees C.