High-yield single-step catalytic growth of graphene nanostripes by plasma enhanced chemical vapor deposition

Abstract

a b s t r a c tWe report a single-step growth process of graphene nanostripes (GNSPs) by adding certain substituted aromatics (e.g., 1,2-dichlorobenzene) as precursors during the plasma enhanced chemical vapor deposition (PECVD). Without any active heating and by using low plasma power ( 60 W), we are able to grow GNSPs vertically with high yields up to (13 ± 4) g/m 2 in 20 min. These GNSPs exhibit high aspect ratios (from 10:1 to >~130:1) and typical widths from tens to hundreds of nanometers on various transitionmetal substrates. The morphology, electronic properties and yields of the GNSPs can be controlled by the growth parameters (e.g., the species of seeding molecules, compositions and flow rates of the gases introduced into the plasma, plasma power, and the growth time). Studies of the Raman spectra, scanning electron microscopy images, ultraviolet photoelectron spectroscopy, transmission electron microscopy images, energy-dispersive x-ray spectroscopy and electrical conductivity of these GNSPs as functions of the growth parameters confirm high-quality GNSPs with electrical mobility~10 4 cm 2 /V-s. These results together with residual gas analyzer spectra and optical emission spectroscopy taken during PECVD growth suggest the important roles of both substituted aromatics and hydrogen plasma in the rapid vertical growth of GNSPs with large aspect ratios.

Single-step growth of graphene and graphene-based nanostructures by plasma-enhanced chemical vapor deposition

“…Exemplifying Raman spectra for PECVD-grown monolayer graphene sheet and GNSPs are shown in Figure 2.1(a) and Figure 3.1(g), respectively. Generally the Raman spectra of pristine graphene monolayer do not include the D-band, whereas the Raman spectra of GNSPs and of all VG-GNs always include a D-band due to many exposed edges in the nanostructures [61,173]. We further note that the ratio of the 2D-band to G-band, (I 2D /I G ), is an important identifier of graphene quality.…”

“…In the latter case the resulting nanostructures were mostly "wall-like" with typical length-to-width aspect ratios <~ 10, whereas the growth rate may be increased with increasing plasma power [10]. Additionally, we found that DCB precursors further enhanced the presence of C 2 radicals (Figure 3.2(c)), which also contributed to the high-yield growth of GNSPs [61]. Hydrophobicity/hydrophilicity is generally an important characteristic of nanomaterials.…”

“…These GNSPs with large aspect ratios are also high quality materials that can be produced with high yield and at room temperature. We further found that although the as-grown GNSPs formed highly interconnected networks and the distance between joint points was typically short (e.g., 1 μm, see Figure 3.1(b)), long GNSPs could be isolated from samples because GNSPs network joint points did not represent the end of a GNSP, but rather represented splitting points where the multiple GNSP layers split in different directions [61]. This notion was confirmed by studying the SEM images of all transferred samples after sonication in solvent, which always revealed combinations of long and straight GNSPs together with interconnected webs of short graphene pieces, as exemplified in Figure 3.1(c).…”

“…Other than these typical gases to grow large-area graphene sheets, a quartz container stored with some substituted aromatics may be attached to the growth chamber via a leak valve and a quarter-turn, shut-off valve. With the addition of substituted aromatics such as 1,2dicholorobenzene (1,2-DCB), 1,2-dibromobenzene(1,2-DBB), 1,8-dibromonaphthalene (1,8-DBN) and toluene as the seeding molecules, we can choose to grow graphene nanostripes (GNSPs) [61] and carbon nanotubes (CNTs) vertically, which will be elaborated later in Sections 3 and 4. A c c e p t e d M a n u s c r i p t 8…”

“…Page 10 of 30 AUTHOR SUBMITTED MANUSCRIPT -NANO-119760 .R1 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t Recently, we have demonstrated VG-GN materials with large aspect ratios (>~ 100) by using aromatic molecules in the PECVD growth as the seeding molecules [61]. These VG-GNs are dubbed as graphene nanostripes (GNSPs) to emphasize their large aspect ratios and also to differentiate them from graphene nanoribbons (GNRs) that typically referred to quasi-one-dimensional graphene nanostructures that exhibit quantum confinement effects [61]. As exemplified in Figure 3.1(c) for an GNSP that was transferred and isolated on a silicon substrate, the GNSP exhibited dimensions of <~ 1 μm in width and 125 μm in length, which corresponded to a large aspect ratio of ~ 125:1.…”