The dominant mechanism behind dissipation varies significantly with the critical length of the resonator, the time scale of operation, and the mode of actuation. In this regard, 1D or 2D high-frequency nanoresonators in a fluid environment is a platform not only to understand the individual dissipative processes and their coupling but also to probe the nature of fluid–structure interaction at the lower extremes of length and time scale. Secondly, the response of the interacting media, fluid, in the parameter space of the resonant motion, which are gigahertz frequency and nanometer dimension is poorly understood and consequently, the resulting extrinsic dissipation, i.e., fluid dissipation, is difficult to estimate. Firstly, because the sources of dissipation can couple with each other and the coupling effect can manifest in each dissipation mechanism. In such scenarios of a resonator in a fluid environment, estimating the net energy loss is not straightforward. But, such characterization may prove insufficient to assess their quality for applications involving biological 16, 17 and chemical 18, 19, 20 sensing where an external gas or liquid environment is inevitably present. Typically, the ultimate performance of a resonator is evaluated under near-vacuum condition 13, 14, 15, in which case only the intrinsic dissipation mechanisms are operative. The dissipation takes place due to the coupling of the resonant motion of interest, either with other internal degrees of freedom in the resonator, classified as an intrinsic source or with the external environment, classified as an extrinsic source. However, different dissipative processes can interfere with the mechanical response of the resonators and limit their performance. During any such sensing process, ultra-high sensitivity can be attained when the resonator has low mass, large surface area, and very high resonant frequency 12, 13, all of which are inherently offered by 1D and 2D materials of nanometer dimension. The unique optical 7, 8 and electronic properties 9, 10, 11 of these low-dimensional materials can be coupled with their mechanical degrees of freedom to make the next generation sensors. One motivation towards miniaturization is making high-precision resonant mechanical sensors which can detect extremely small foreign mass, charge, force, etc. In the pursuit of miniaturization of devices, low-dimensional nanomaterials like carbon nanotubes 1, 2, graphenes 3, and monolayer transition metal dichalcogenides 4 (TMDCs) have been drawing enormous attention for nearly two decades. Our finding highlights a unique feature of confined fluid–structure interaction and evaluates its effect on the performance of high-frequency nanoresonators. We also emphasize on the difference in dissipative response of the fluid under nanoconfinement when compared to a fluid exterior case. Our systematic dissipation analysis helps us to infer the origin of the intrinsic dissipation. The damping kernel-based analysis shows that the unexpected behavior stems from time dependence of the hydrodynamic response under nanoconfinement. Using linear response theory, we construct a fluid damping kernel which characterizes the hydrodynamic force response due to the resonant motion. Analyzing the sources of dissipation reveals that (i) the phonon dissipation remains unaltered with fluid density and (ii) the anomalous dissipation scaling in the fluid interior case is solely a characteristic of the fluid response under confinement. A scaling study of dissipation shows an anomalous behavior in case of interior fluid where the dissipation is found to be extremely low and scaling inversely with the fluid density. Here, we report the mechanical damping behavior of a 1D single-walled carbon nanotube (SWCNT) resonator operating in the fundamental flexural mode and interacting with a fluid environment, where the fluid is placed either inside or outside of the SWCNT. Though numerous studies have demonstrated an unparalleled sensitivity of these materials as resonant nanomechanical sensors under vacuum isolation, an assessment of their performance in the presence of an interacting medium like fluid environment is scarce. Various one and two-dimensional (1D and 2D) nanomaterials and their combinations are emerging as next-generation sensors because of their unique opto-electro-mechanical properties accompanied by large surface-to-volume ratio and high quality factor.
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