Fabrication of Free-Standing Tungsten-Nanowhiskers on SiO<SUB>2</SUB> Substrates with Electron-Beam Induced Deposition

Abstract

Free-standing tungsten-nanowhiskers about 3 nm in thickness were fabricated on SiO 2 substrates with electron-beam induced deposition in a transmission electron microscope operated at 400 kV at room temperature. The growth process of the nanowhisker was observed in-situ and analyzed. The nanowhisker was characterized with high-resolution transmission electron microscopy. Nucleus-deposits smaller than 1 nm formed on the surface of the substrate, grew to 2$3 nm and then grew out of the surface to form nanowhiskers under the electron irradiation. The nanowhisker grew long at its tip. The density and growth rate of the nanowhiskers were different at different places of the same substrate. A part of the nanowhiskers grew long to about 20 nm at the electron dose of 1:16 Â 10 25 e m À2 for an irradiation time of 223 s. The nanowhisker contained nanometer-sized grains of body-centred cubic structural tungsten and an amorphous part. It was found that there exists a critical size about 2-3 nm for a nucleus to grow to a nanowhisker. It is suggested that the nucleation site of the nanowhisker may be controlled by putting appropriate conductive particles in the critical size on the surface of an insulator substrate.

Fabrication and characterization of nanostructures on insulator substrates by electron-beam-induced deposition

“…Thus, molecules are attracted to the tip, and the deposit increases in length upon further EB irradiation. The formation of W nanodot deposits on the surface of a SiO 2 substrate and the growth of W nanowhiskers from these nanodots [20] are consistent with the above mechanism. The growth of a nanobush can also be understood qualitatively on the basis of the above mechanism [19].…”

“…It was confirmed that body-centered cubic (bcc) W nanocrystals are contained in as-prepared W nanowhiskers [20] and W nanodendrites [18,[21][22][23] by high-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED) or microbeam electron diffraction (MBED). Figure 9 shows HRTEM and SAED images of W nanodendrites [18].…”

“…EBID by elongated irradiation with an EB results in the morphology of a nanobush, as shown in figure 2 [19]. Another experiment was carried out to fabricate W nanowhiskers on SiO 2 substrates by EBID using a 400 keV EB at an intensity of 5.2 × 10 18 e cm −2 s −1 (0.83 A cm −2 ) [20]. The nucleation and growth of the nanowhiskers were investigated.…”

Nanofabrication by advanced electron microscopy using intense and focused beam∗

“…This may be due to the charged-up electrons, which induced the nonequilibrium chemical decomposition of the precursor gas. It was confirmed that body-centered cubic (bcc) tungsten nanocrystals with an amorphous structure comprised the nanostructures and that the fraction of the crystalline structure increased with increasing energy of the electron beam [17,27,30,31].…”

“…Thin films of Al 2 O 3 [17][18][19][24][25][26] and SiO 2 [27][28][29][30] were irradiated by an electron beam in TEMs with organometallic precursor gases at room temperature. Figure 2(a) shows a micrograph of the initial stage of the growth of nanostructures under a current density of about 0.75 A cm −2 .…”