Atomic-Scale Mass Sensing Using Carbon Nanotube Resonators

Abstract

Ultraminiaturized mass spectrometers are highly sought-after tools, with numerous applications in areas such as environmental protection, exploration, and drug development. We realize atomic scale mass sensing using doubly clamped suspended carbon nanotube nanomechanical resonators, in which their single-electron transistor properties allows self-detection of the nanotube vibration. We use the detection of shifts in the resonance frequency of the nanotubes to sense and determine the inertial mass of atoms as well as the mass of the nanotube. This highly sensitive mass detection capability may eventually enable applications such as on-chip detection, analysis, and identification of compounds.Because of their small size, nanoscale systems are highly sensitive to their environment, affording great potential for sensing applications. Chemical and biological charge-based sensors using carbon nanotubes 1,2 and nanowires 3 have already been demonstrated. Nanoelectromechanical systems have been proposed for highly sensitive mass detection of neutral species, 4,5 and significant progress has been made in using nanofabricated resonators 6-8 and carbon nanotubes 9-12 for mass sensing. However, the ultimate limit of atomic resolution mass sensitivity remains unrealized. Here we demonstrate that individual double-clamped single-walled carbon nanotube resonators are capable of atomic-scale mass sensing and determining the inertial mass of atomic species. Analysis of our data also yields the nanotube mass, giving a general approach to determining the mass of molecular nanostructures. Our results open the door to ultraminiaturized mass spectroscopy or arrays, potentially enabling on-chip detection and identification of unknown analytes, as well as the study of single atom adsorption and desorption.We fabricate our devices by first growing nanotubes from catalyst islands 13 under either pure CH 4 13 or a CH 4 /H 2 mixture 14 on an oxidized Si wafer. We then attach Pd/Au source/drain electrodes and a side gate using electron beam lithography (EBL). In a second step, a layer of poly(methyl methacrylate) (PMMA) is spun on the chip, and a ∼450 nm window is opened over a segment of the nanotube between the electrodes, again using EBL. The SiO 2 is etched using buffered HF to suspend the carbon nanotube within the window. Following a critical point drying step, the samples are electrically tested at room temperature; we then load selected devices into a custom-built cryostat, which is maintained at a high vacuum. Figure 1a shows a scanning electron microscope (SEM) image of a completed suspended nanotube transistor device.At the temperature T ≈ 6 K of our experiment, the nanotubes act as single-electron transistors (SET) in which the charge on the nanotube is an integer multiple of the electron charge e. 15 As the gate voltage V g is swept, electrons enter the SET one at a time, with each transition between discrete charge states producing a Coulomb peak in the source-drain conductance (see e.g. ref 16). Figure 1b shows this b...

Nanoscale Electromechanics To Measure Thermal Conductivity, Expansion, and Interfacial Losses

“…1,2 Resonators of thin membranes, carbon nanotubes, 3,4 graphene, 5 and other two dimensional materials have been studied for their use as sensors 6,7 and for probing fundamental physics of mechanical motion. 8,9 In order to improve the sensitivity of the NEMS sensors microscopic mechanisms of energy loss have also been studied extensively.…”

Symmetry breaking in a mechanical resonator made from a carbon nanotube

“…Its crystallinity confers excellent mechanical properties to nanotube-based resonators [1][2][3][4][5][6] , such as high resonant frequencies 7,8 and low dissipation at low temperature 9,10 . As a result, these resonators are well suited for ultra-sensitive detection of mass 11,12 , charge 2,3 and force 13 . A nanotube has also much in common with a polymer as both can bend by a large amount.…”

Capacitive Spring Softening in Single-Walled Carbon Nanotube Nanoelectromechanical Resonators

“…Due to their low mass density and high Young's modulus [1][2][3][4] , SWNTs offer great promise as ultrahigh frequency NEM resonators with applications in ultrasmall mass and force sensing [5][6][7][8][9][10]. To detect the mechanical vibration of nanotube resonators, various methods have been explored so far [7,[11][12][13].…”