Figure 1 Expansion of gallium inside a carbon nanotube with increasing temperature. a-c, Changing level of the gallium meniscus at 58℃ (a), 490℃ (b) and 45℃ (c); scale bar, 75nm. d, Height of the gallium meniscus plotted against temperature, measured in steps of 30–50℃; results are averaged (green curve) from closely similar measurements obtained during heating (red) and cooling (blue). The nanothermometer was synthesized in a vertical radiofrequency furnace (which differs from a one-step arc-discharge method). A homogeneous mixture of Ga2O3 and pure, amorphous, active carbon (weight ratio, 7.8:1) was reacted in an open carbon crucible under a flow of pure N2 gas: at 1,360℃, the reaction Ga2O3(solid)&2C(solid)ÕGa2O(vapour)&2CO(vapour) occurs. However, on the inner surface of a pure graphite outlet pipe at the top of the furnace, the temperature is lower (around 800℃), causing the reaction Ga2O(vapour)&3CO(vapour)Õ 2Ga(liquid)&C(solid)&2CO2(vapour) to occur, during which the nanothermometers' are created.

A variety of silicon based multilevel branched submicrometer/ nanostructures, such as branched nanowheatheads, big branched nanowheat-heads, and branched nanowires, have been rationally synthesized via a simple one-step, inexpensive, and catalyst-free fabrication technique. High-resolution transmission electron microscopy studies suggested that the main stem of wheat head and the nanotips of silicon branched nanowheat-heads are single crystals with the preferential growth direction along the [112] and [112] and orientation, respectively. Compared with big branched nanowheat-heads and branched nanowires, the room-temperature Raman frequency of branched nanowheat-heads is blue-shifted and its full width at half-maximum broadens. A moderately strong photoluminescence emission at 550 nm was suggested to be induced by defects, such as stacking faults or the SiOx surface in the branched nanowheat-heads, suggesting potential applications in light-emitting nanodevices. These studies shed light on new opportunities for fabricating different 3-dimensional nanostructures based on their property investigation.

We report here temperature measurement by means of a Ga-filled C nanotube thermometer with diameter,150 nm and length; 12mm. The method relies on the initial identification and calibration of a nanothermometer in a transmission electron microscope TEM, followed by placing it into an air-filled furnace whose temperature is to be measured, and final TEM reading of a postmeasurement gradation mark visible inside the tubular channel. The mark originates from the fact that, at high temperature, the Ga column tip exposed to the air through the open C nanotube end oxidizes, and a thin Ga oxide layer sticks to the nanotube walls upon cooling. The temperature according to this gradation mark coincides closely with nominal furnace temperature controlled by standard means. The method paves the way for practical temperature measurements using a C nanothermometer in air and within spatially localized regions e.g., dimensions of tens of micrometers.

Thermodynamic analysis was performed with respect to the effect of surface tension on the expansion characteristics of a one-dimensional nanoscale liquid Ga column inside a carbon nanotube. The analysis showed that the surface tension affects the column inner pressure, and that the smaller the column diameter, the greater the surface effect. Based on the analysis, it is quantitatively explained why a liquid Ga column with 75 nm diameter has virtually the same expansion coefficient as that of Ga in a macroscopic state in the range of 50 to 500℃, and suggested that the volumetric expansion coefficient can be directly used for the calibration of a given nanothermometer with a diameter larger than 10nm.

Indium-filled carbon nanotubes were synthesized via a simple chemical vapor deposition. The carbon nanotubes had diameters of 100-200 nm and length of; 10mm. The melting and expansion behavior of the indium in carbon nanotubes were investigated in an analytical transmission electron microscope. It was found that the melting and expansion behavior of indium were different from that in a macroscopic state. The melting behavior was explained using a particular equation developed for a nanoscale indium column. The analysis of the expansion behavior allows us to clarify the problems of indium filling usage in carbon nanotube-based nanothermometer.