Bottom-up assembly of large-area nanowire resonator arrays

Abstract

Directed-assembly of nanowire-based devices 1 will enable the development of integrated circuits with new functions that extend well beyond mainstream digital logic. For example, nanoelectromechanical resonators are very attractive for chip-based sensor arrays 2 because of their potential for ultrasensitive mass detection 3-6 . In this letter, we introduce a new bottom-up assembly method to fabricate large-area nanoelectromechanical arrays each having over 2,000 single-nanowire resonators. The nanowires are synthesized and chemically functionalized before they are integrated onto a silicon chip at predetermined locations. Peptide nucleic acid probe molecules attached to the nanowires before assembly maintain their binding selectivity and recognize complementary oligonucleotide targets once the resonator array is assembled. The two types of cantilevered resonators we integrated here using silicon and rhodium nanowires had Q-factors of ~4,500 and 1,150, respectively, in vacuum. Taken together, these results show that bottom-up nanowire assembly can offer a practical alternative to top-down fabrication for sensitive chip-based detection.Our hybrid nanoelectromechanical systems (NEMS) array integration strategy combines deterministic bottom-up nanowire (NW) assembly with conventional top-down microfabrication as illustrated in Fig. 1. Here we show the flexibility of this approach by fabricating resonators using two types of NWs-semiconducting silicon (Si) or metallic rhodium (Rh)-synthesized off-chip with different growth methods. The SiNWs grown by the Au-catalysed vapour-liquid-solid (VLS) technique are predominately single-crystal and oriented in the 〈111〉 or 〈112〉 growth directions 7 . In contrast, RhNWs electrodeposited within the pores of anodic aluminium oxide membranes are polycrystalline, with an average grain size of 5 nm (ref. 8). This assembly method is quite general and can be extended to many other NW materials 1,9 (for example, multisegment metal, magnetic, oxide or piezoelectric materials) and geometries 10 (for example, hollow tube or flat belt).Correspondence and requests for materials should be addressed to R.B.B. and T.S.M. † These authors contributed equally to this work. Bottom-up assembly is used to position single NWs at lithographically defined locations on a Si chip for fabricating multiplexed arrays. Unlike earlier reports of NW assembly 11-15 , three separate mechanisms are combined to achieve high-yield NW integration over centimetre-scale chip areas: electric-field forces, capillary forces and NW lift-off. As illustrated in Fig. 1, we patterned arrays of wells in a sacrificial insulating photoresist layer covering metal guiding electrodes defined on the chip surface. An alternating voltage in the kilohertz range was applied between the guiding electrodes to produce spatially confined electric fields that polarize NWs in suspension 11 . Long-range dielectrophoretic forces attract the NWs to the surface and align them along the electric-field gradient. Single NWs are further centr...

Recent advances in large-scale assembly of semiconducting inorganic nanowires and nanofibers for electronics, sensors and photovoltaics

“…8,10,[59][60][61][62][63][64][65][66][67][68][69] The applied electric fields can be used effectively to attract and align NWs normally by the dielectrophoresis forces, which are exerted on the dielectric NWs through the induced dipoles. 60,61 Up to now, various nanostructures, such as Au NWs, 60 Rh NWs, 9 Ag NWs, 65 Si NWs, 9 Se NWs, 65 axially modulated pn Si NWs, 67 InP NWs, 8 ZnO NWs, 62,64 CdSe NWs, 63 as well as polymer nanofibers 68 have been assembled by this approach.…”

“…10,66 For example, Freer et al 66 refined a fluid flowassisted dielectrophoresis to place single Si NWs on electrodes and attained 98.5% single nanowire yield on >16 000 electrode pairs fabricated within an area of 4 cm 2 . As shown in Fig.…”

“…Nanoelectromechanical resonators are very attractive for a new class of ultrafast, ultrasensitive devices, 10,172,198,199 Melosh et al 172 reported a high-frequency nanomechanical resonator, which was fabricated by a technique named superlattice nanowire pattern transfer. The resonator contains nine Pt nanowires with 20 nm in diameter and 150 nm in pitch, suspended over a 0.75 mm trench on a bare Si wafer.…”

Self-Assembly in Micro- and Nanofluidic Devices: A Review of Recent Efforts

“…In addition to that, Fan et al developed a combination of alternating and constant electric fields applied by means of lithographically patterned electrodes where gold nanowires were moved along any arbitrary trajectory with speeds up to 50 μm/s and positioned at an arbitrary location with a precision better than 300 nm [113]. Hybrid nanoelectromechanical systems array integration strategy which combined deterministic bottom-up silicon and rhodium nanowire assembly with conventional top-down microfabrication could also produce higher assembly yields (>80%) [114]. Figure 14.…”

Highly Exfoliated Graphite Fluoride as a Precursor for Graphene Fluoride Dispersions and Films

“…37 For exfoliating a layered precursor material to the state of individual layers or few-layers, it is necessary to overcome the attracting forces between adjacent layers and to further stabilize the layers. This may be achieved by either covalent modification of the graphene surface by functional groups [16][17][18][19][20][21][22][23][24] or by non-covalent modification using specific solvents, 38,39 surfactants, 40 polymers 41 or donor-acceptor aromatic molecules. 42 The processes for producing graphene by liquid-phase have been recently reviewed by our group.…”