Electrical Control Of Scalable Nanoelectromechanical Systems

The electrically controlled mechanical resonators that miniaturize to micro and nanoscale have a major impact both on technological and fundamental physical researches.Microelectromechanical systems(MEMS)are widely used in daily life and scientific research scenarios,including antennas and gyroscopes in smart-phones,accelerometers in cars,blood pressure sensors in hospitals,and atomic force microscopes in surface imaging.With the progress of micro and nano processing technology,as an extension of the concept of microelectromechanical systems at the nanoscale,nanoelectromechanical systems(NEMS)have also attracted widespread attention in recent years.The smaller size enables nanoelectromechanical systems to have higher sensitivity compared to microelectromechanical systems.Nanoelectromechanical systems have outstanding advantages in force detection,mass detection,and coupling between distant quantum bits.The multifunction of microelectromechanical systems and nanoelectromechanical systems arises from their ability to efficiently couple mechanical vibration modes with other physical degrees of freedom.By now,micro/nanoelectromechanical systems can couple multiple physical systems,including but not limited to gate-defined quantum dots,superconducting qubits,and NV centers.Based on such ability,nanoelectromechanical systems have the potential to act as couplers of multiple physical systems.However,in order to achieve this goal,we still need to solve a series of practical problems.On one hand,the resonant frequency,quality factor,boundary conditions and other parameters of nanoelectromechanical systems have a direct impact on the properties of devices as couplers.The ability to adjust these parameters has important significance for the application of couplers.On the other hand,multiple physical systems that need to be coupled are often separated in different spatial locations,and it is usually not possible to couple them using a single resonator device.In order to couple distant systems,it is necessary to realize scalable nanoelectromechanical systems by using the coupling between mechanical resonators.In addition,the specific mechanism by which this extended resonator system couples with other physical systems is also worth considering.Based on these considerations,a natural issue is how to achieve electrical control of scalable nanoelectromechanical systems.In order to achieve the goal of electrically controlled and scalable nanoelectromechanical systems,three studies have been conducted in this thesis,including:(1)A new control method for a resonator device has been studied.We observed the hysteresis loop of the resonant frequency of the graphene resonator device when scanning the gate voltage back and forth.Through analysis,we pointed out that this hysteresis property is caused by sliding motion.The possibility of using sliding motion to study nanofriction and explain the coupling between resonators was also discussed.(2)A scalable resonator system has been studied.The two-dimensional array expansion of coupled graphene resonator devices was realized.The gate tunable quasicontinuous vibration modes were observed as evidence of coupling between array elements.(3)The hybrid devices consisting of mechanical resonators and gatecontrolled quantum dots were studied.The mechanical resonators that can work as gatecontrolled quantum dots were realized here.The electrical tunability of the gate on the electrical transport properties of quantum dots and the mechanical vibration properties of mechanical resonator has also been demonstrated.Based on this,we observed the coupling between mechanical resonant and quantum dot transport.The main content of the thesis is organized as follows:1.A brief introduction to basic concepts and research status of nanoelectromechanical resonator systems was given in this chapter.An introduction to the characteristics of the two resonator systems we specifically studied was also introduced.2.A brief introduction to the general properties and related theories of nanoelectromechanical resonators were given in this chapter.The electrical device characterization methods developed based on these theories were also introduced.3.We observed the hysteresis phenomenon of the resonant frequency of graphene nanoelectromechanical resonator experimentally.A theoretical model including sliding motion was established to explain this phenomenon.We discussed the possibility of using sliding motion to study nanofriction,and a new understanding of the coupling mechanism between nanoelectromechanical resonators was proposed.4.We realized the two-dimensional extension of graphene nanomechanical resonators in experiments to build a phononic crystal structure.We observed gate tunable quasi-continuous resonance modes in experiments,and demonstrated that the resonators in the extended resonator array were coupled to each other by analyzing the experimental results.5.We studied a hybrid device consisting of a beam resonator and gate-controlled quantum dots.The device worked as a high-frequency mechanical resonator and a single hole transistor at the same time.Its resonant frequency and transport properties can be modulated by gate voltage.The possibility of coupling quantum dots using mechanical resonators has been preliminarily explored.The main innovations of this thesis include:1.Tunable resonant frequency hysteresis of graphene nanoelectromechanical resonators was observed.This result not only provided a new approach for electrical tuning of graphene nanoelectromechanical resonators,but also provided a new method for studying nanofriction.2.We provided a design scheme for a two-dimensional resonator array.The twodimensional extension of graphene nanoelectromechanical resonator system was realized.And a quasi-band structure which can be tuned by gate voltage was observed.3.A hybrid device consisting of a beam resonator and gate-controlled quantum dots was realized by using a suspended silicon nanowire system.The single hole tunneling in quantum dots and mechanical resonance phenomena have been observed simultaneously in the device.And the coupling between the single hole tunneling and mechanical resonance was preliminarily observed.