Self-healing method for fractured SiC single crystal nanowires

Abstract

A self-healing method for fractured single crystal SiC nanowires. A hair in a Chinese brush pen of yellow weasel's hair moves and transfers nanowires, which are placed on an in-situ TEM mechanical microtest apparatus. An in-situ nanomechanical tension test is realized. The nanowires are loaded. Displacement is 0-200 nm. Fracture strength of the single crystal nanowires is 12-15 GPa. After the nanowires are fractured, unloading causes slight contact between the fractured end surfaces, electron beam is shut off, and self-healing of the nanowires is conducted in a vacuum chamber. Partial recrystallization is found at a fracture after self-healing through in-situ TEM representation. A fracture strength test is conducted again after self-healing. A fractured position after healing is the same as the position before healing. The fracture strength of the single crystal nanowires after self-healing is 1-2.5 GPa. The recovery ratio of the fracture strength is 10-20%.

Claims

1. A self-healing method for fractured single crystal SiC nanowires, realizing self-healing of single crystal nanowires without external intervention, the method comprising: (1) providing the single crystal SiC nanowires having a diameter of 60-90 nm; (2) fixing one end of a yellow weasel's hair taken from a Chinese brush pen to a mobile platform of an optical microscope using a conductive silver epoxy; operating a millimeter and micrometer movement of the yellow weasel's hair through the mobile platform; moving and transferring the single crystal SiC nanowires to an in-situ transmission electron microscope (TEM) mechanical testing device using an other end of the yellow weasel's hair; (3) fixing both ends of the single crystal SiC nanowires to the TEM mechanical testing device using the conductive silver epoxy; (4) installing the TEM mechanical testing device on an in-situ TEM nanomechanical test holder; an in-situ nanomechanical tension testing is realized in the TEM; (5) loading the single crystal SiC nanowires using a displacement control mode; wherein a loading rate is 0.5-15 nm/s; a displacement is 0-200 nm; (6) fracturing the single crystal SiC nanowires by tension, wherein fractured surfaces are formed; a fracture strength of the single crystal SiC nanowires is 12-15 GPa; (7) after the single crystal SiC nanowires are fractured, unloading the single crystal SiC nanowires, wherein the unloading causes a contact between the fractured surfaces; a load of end surfaces is 0; shutting off electron beam in TEM; conducting a self-healing of the single crystal SiC nanowires after waiting for 15-30 min in a vacuum chamber of the TEM; (8) after the self-healing, conducting a second in-situ TEM mechanical tension testing; wherein the single crystal SiC nanowires are loaded; the displacement control mode is used; the loading rate is 0.5-15 nm/s; the displacement is 0-100 nm; wherein partial recrystallization is found at the fractured surfaces after the self-healing through in-situ TEM representation; a fractured position after healing is the same as the fractured position before healing; wherein the fracture strength of the single crystal SiC nanowires after the self-healing is 1-2.5 GPa; and a recovery ratio of the fracture strength is 10-20%.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows loading and unloading curves of in-situ TEM tension test of single crystal SiC nanowires.

(2) FIG. 2 is a TEM micrograph of a self-healing fracture of single crystal SiC nanowires after self-healing.

(3) FIG. 3 shows in-situ TEM tension loading and unloading curves of single crystal SiC nanowires after self-healing.

DETAILED DESCRIPTION

(4) Specific embodiments of the present invention are further described below in combination with accompanying drawings and the technical solution.

(5) A self-healing method for fractured single crystal SiC nanowires realizes self-healing of single crystal nanowires without external intervention, wherein:

(6) (1) single crystal SiC nanowires have a diameter of 60-90 nm;

(7) (2) one end of a Chinese brush pen of yellow weasel's hair is fixed to a mobile platform of an optical microscope using conductive silver epoxy; the Chinese brush pen realizes millimeter movement and micrometer movement through the mobile platform; a yellow weasel's hair at the other end of the Chinese brush pen of yellow weasel's hair moves and transfers nanowires to place the nanowires on an in-situ mechanical microtest apparatus of a TEM;

(8) (3) both ends of the nanowires are fixed to the microtest apparatus using conductive silver epoxy;

(9) (4) the microtest apparatus is installed on an in-situ TEM nanomechanical test system; an in-situ nanomechanical tension test is realized in a TEM;

(10) (5) the nanowires are loaded; a displacement control mode is used; loading rate is 0.5-15 nm/s; displacement is 0-200 nm;

(11) (6) fracture strength of the single crystal nanowires is 12-15 GPa;

(12) (7) after the nanowires are fractured, unloading causes a slight contact between the fractured end surfaces; the load of the end surfaces is 0; the electron beam is shut off; self-healing of the nanowires is conducted after waiting for 15-30 min in a vacuum chamber of the TEM;

(13) (8) after self-healing, a second fracture strength test is conducted; the nanowires are loaded; the displacement control mode is used; loading rate is 0.5-15 nm/s; displacement is 0-100 nm;

(14) (9) partial recrystallization is found at a fracture after self-healing through in-situ TEM representation; a fractured position after healing is the same as the position before healing;

(15) (10) The fracture strength of the single crystal nanowires after self-healing is 1-2.5 GPa; and the recovery ratio of the fracture strength is 10-20%.

Embodiments

(16) 3C-single crystal SiC nanowires have a diameter of 80-90 nm are selected as self-healing material. The single crystal nanowires are placed in an acetone solution for ultrasonic dispersion for 30-50 s. A 200-mesh copper grid having a plastic film and a diameter of 3 mm and used for preparing a TEM sample is used; and the plastic film on the copper grid is ignited with a cigarette lighter to remove the film. Then, the copper grid without the film is clamped with tweezers and is subjected to ultrasonic cleaning in the acetone solution for 15-25 s to remove traces and pollution on the copper grid. After ultrasonic cleaning for the copper grid is completed, the copper grid is clamped with the tweezers to gain SiC nanowires from the SiC acetone solution of ultrasonic dispersion. The copper grid is placed on the mobile platform of an optical microscope. After acetone evaporates, the nanowires appear on the surface of the copper grid. The nanowires are found from the optical microscope and are focused clearly. The tail end of the Chinese brush pen of yellow weasel's hair is fixed to another optical microscope. A clip is straightened, turns red by burning on a candle, and makes a hole at the lower part in a plastic brush cap of the Chinese brush pen of yellow weasel's hair. One yellow weasel's hair is threaded out from the hole, and other yellow weasel's hairs are covered with the plastic brush cap. Three-dimensional millimeter and micrometer movement of a single yellow weasel's hair are realized through the mobile platform of the optical microscope. Under another optical microscope, the nanowires are moved and transferred through electrostatic attraction between the yellow weasel's hair and the nanowires, and are placed on the in-situ TEM mechanical microtest apparatus. The tip of the yellow weasel's hair is dipped in a small drop of conductive silver epoxy, and the conductive silver epoxy is respectively dropped on both ends of the nanowires. After the conductive silver epoxy is solidified, the nanowires can be fixed to the microtest apparatus.

(17) The microtest apparatus is placed in the in-situ nanomechanical test system of PI 95 TEM PicoIndenter. The test system is inserted into FEI Tecnai F20 FETEM. Operation voltage is 200 kV. The fracture strength test is conducted on the nanowires through an in-situ TEM tension test method. A displacement control mode is used; loading rate is 4 nm/s; and displacement is 0-180 nm. Loading and unloading curves are shown in FIG. 1. After the test, the fracture strength of the single crystal SiC nanowires is 13.4 GPa. The nanowires are unloaded, and the end surfaces of the fractured single crystal SiC nanowires come into slight contact, with a load of 0. The electron beam is shut off; and self-healing of the single crystal SiC nanowires is conducted after waiting for 20 min. After 20 min, the electron beam is turned on to shoot a TEM micrograph of the fracture after self-healing, as shown in FIG. 2. It is found that recrystallization occurs at the fracture after self-healing. Then, the in-situ TEM fracture strength test is conducted on the SiC nanowires after healing. A loading mode is a displacement control mode. The loading rate is 4 nm/s; and displacement is 0-60 nm. Loading and unloading curves of the fracture strength test of the SiC nanowires after self-healing are shown in FIG. 3. The test result shows that the fracture strength of the single crystal SiC nanowires after self-healing is 1.7 GPa; and the recovery ratio of the fracture strength is 12.7%.