# Low Temperature RF-Plasma Initiated Rapid and Highly Ordered Fracture on Ag Nanowires
## 3 Results and Discussion  
AgNWs were deposited on Si substrates (samples) as thin circle layers (\"coffee rings\") due to the natural spreading and drying of their ethanol suspension [16; 17], as shown in Figure 1a. From the element analysis, the spreading treatment of ethanol suspension AgNPs deposited on Si substrate is \"a clean way\" without introducing impurities, as shown in Figure 1b. This element analysis was exerted on the sample in Figure 1a. As a result, AgNPs adhered on Si substrate are mainly contributed by weak Van der Waals forces [16]. Then, the prepared samples were put in a chemical vapour deposition and treated by RF plasma, as shown in Figure 1c. In our case, 60 W power of RF (Ar\({}^{+}\) average energy with about 10-30 eV, which is around the 15 eV sputtering threshold energy of Ag [18; 19]) was chosen to exert on samples. Such power of plasma can provide enough kinetic energy on the surfaces of AgNPs and meanwhile avoid sputtering. By 3 min RF plasma treatment, partial breakage occurs to AgNPs, which then converts into uniform particle-chains on a macro scale (Figure 1d). Furthermore, the centre-to-centre distances between Ag nanoparticles show strong relations with their diameters. Similar phenomenon can be also found on AgNWs after 5 min RF plasma treatment. In contrast to 3 min RF plasma treatment, nearly all AgNPsNWs with various diameters convert to highly ordered particle-chains (Figure 1e). Apparently, the conversion of AgNPsNWs is more thorough with a little longer treatment. What's more, the temperature of the Si substrates obtained by a thermocouple (measurement accuracy 0.1 \({}^{\circ}\)C) is from room temperature to about 95 \({}^{\circ}\)C during the process, which is much lower than the melting point of bulk Ag. Note that the temperature increase in Si substrates are polyphyletic, which can be separated into three parts: 1) heat conduction from AgNWs; 2) heat conduction from equipment; and 3) heat generated on silicon substrate by plasma. Obviously, the heat conduction from AgNPsNWs is the minimum part. The temperature increase cannot simply be evacuated by the test results by the thermocouple. However, the total temperature increment is no more than 80 \({}^{\circ}\)C during the whole plasma treatment. As a result, the RF plasma treatment can be deemed as a low temperature way for AgNPs fabrication from AgNPs. A contrast test based on the traditional heat treatment has been carried out. AgNPsNWs with diameters ranging from about 60 to 300 nm have been adopted in our case, as shown in Figure 2a. Calculations of melting points (\(T_{m}\)) of three typical Ag nanostructures (nanowire, hemisphere, and nanoparticle) with various sizes are based on the [PERSON]. [PERSON] liquid-drop model [20; 21], which have been presented in Figure 2b. Furthermore, their melting points can be expressed by \(T_{m}=T_{mb}(1-k\beta/D)\), in which \(T_{mb}\) is the melting point of bulk Ag, the value of \(\beta\) is obtained from the empirical relation, \(D\) are their diameters, and \(k\) the constant of 2/3, 5/6 and 1 for nanowire, hemisphere, and nanoparticle respectively. For nanostructures with relatively free surfaces, the melting temperature decreases with their size  
Figure 1: (**a**), “Coffee ring” and optical image of hydrothermal synthesized Ag nanowires (AgNWs) on silicon surface; inset image is the AgNPsNWs ethanol suspension with 0.5 wt%; (**b**), element analysis on sample (Figure 1e) with energy dispersive spectrometer; (**c**)–(**e**) the radio frequency (RF) plasma device and morphologies of AgNPsNWs treated by RF plasma for 3 min and 5 min. reduction. It can be clearly observed that melting points of all these structures are greater than 930 \({}^{\circ}\)C. Owing to the minimum temperature of secondary (or abnormal) grain growth of Ag (about 0.2\(T_{m}\)), 200 \({}^{\circ}\)C heat treatment has been chosen. As reported, no visible change or broken junction points can be observed under 200 \({}^{\circ}\)C within 30 min heat treatment [9].