Atomic scale mechanical breakjunction.
Nano-scale quantum electronics and mechanics
We specialize in:
Part of the widespread interest in nanometer-sized systems is motivated by their capability to combine and hybridize mechanical and electronic properties of materials at the nanoscale. The long term goals of our research are to understand at a fundamental level, and harness into applications, the interplays of structure, electronic degrees of freedom, and correlated electronic phases in nano and mesoscopic systems.
Four specific projects on which we are currently working are:
Our work focuses on graphene (both a single-molecule and a 2-dimensional electron gas where electrons behave like relativistic particles), carbon nanotubes (1-d nanosystems) and topological insulators which are ideal testing grounds for the interplays of mechanical degrees of freedom with electrons and their many body-states.
A suspended g-MCBJ. We electromigate the junction to connect single molecules and study their electronic spectrum.
A suspended carbon nanotube inside a gated-Mechanical Breakjunction (g-MCBJ)
We make use of a low temperature gated-mechanical breakjunction system (see Figure), which can controllably stress a nanosystem to tune its shape and strain, while simultaneously making detailed transport measurements. We want to understand how the interplays between structure (lattice, defects, shape, strain, boundaries, phonons) and electronic interactions (Coulomb interactions, screening, charged excitations) determine the properties of nanosystems (scattering, band structure, ground states, coherence, excited states).
Heat transport measures the energy carried by both electrons and phonons and is fundamental to understanding a material, its ground states, excitations and scattering mechanisms.
Image of a 1 micron long suspended graphene(one-atom thick) crystal.
Optical image of micron scale heater and thermometers on a graphene flake.
Measurements of thermal conductivity and thermopower over a broad temperature range (1.5-300 Kelvin) will assess graphene's promising potential for thermal management in nanoscale electronics. We also aim to test the theoretical models of heat propagation in graphene, its phonon modes and their scattering mechanisms, as well as heat transport in the quantum Hall regime.
We are fabricating nanometer-size few-layer thick graphene nanoribbons or carbon nanotubes oscillators. Using a low-temperature mechanical breakjunction system, we will study their potential as tunable ultra-high frequency nano-electro-mechanical systems (NEMS) and we expect these very short ribbons to have resonant frequencies in the THz range.
Cartoon of electron transport in a quantum dot nano-oscillators
These NEMS will make very sensitive nanoscale sensors, since even a very small force or mass on the oscillator will cause a shift of its resonant frequency.
We also want to use these sensors as laboratories to explore the physics of carbon nanotube and graphene quantum dots.
In collaboration with the group of Prof. Oussama Moutanabbir (École Polytechnique), we investigate how engineered defects (stacking faults) in silicon nanowires (Si-NWs) affect charge carrier and phonon transport. We study individual Si-NWs grown by the VLS method (Moutanabbir), see figure below, with ordered lattice defect planes along the growth direction. Characterization of the Si-NWs is done by micro-Raman spectroscopy which is sensitive to the presence of crystal faults. Transport and magneto-transport measurements are done at low temperature in single suspended Si-NWs transistors.
We are interested in exploring fundamental quantum transport in Si-NW quantum dots, as well as their application in thermal energy harvesting. The thermal conductivity, K, of Si-NWs is lower than for bulk silicon. Defect and surface engineering of Si-NWs can further reduce K, improving the thermoelectric efficiency (ability to harvest energy) to maximizing the figure of merit ZT = (S2)·σ·T/K. This would have applications in industry such as improving thermocouples to gather more thermal energy from vapor exhausts.
Left panel, high-resolution TEM image of a Si-NW crystal’s structure showing stacking faults along the growth direction. Right panel, SEM image of our Si-NWs grown by the VLS method (Credit: O. Moutanabbir).
Alexandre Champagne, Ph.D.
Email: a.champagne@concordia.ca
M.Sc. student
Graphene Quantum Strain Transistors
Email: guoqing.wei@mail.concordia.ca
M.Sc. student
Electro-optics of graphene/boron-nitride heterostructures
Email: rebollo_27@hotmail.com
M.Sc. student
Carbon nanotubes
Email: linxiang.huang@mail.concordia.ca
M.Sc. student
Bilayer Graphene NEMS
Email: wyatt.wright.concordia@gmail.com
North side of the lab.
Our laboratory in located in the basement of the Science Pavillion on the Loyola campus. It is a brand new 65 square-meter laboratory space with a low vibration floor, 5 meter high ceiling, sound proofed pump and service room, fume hood, gas (He, N, compressed air) and vacuum service all around the lab, as well as 2 electrical panels with isolated grounds. We have two low-temperature cryostats, a chemical vapor deposition growth chamber, and many other toys.
We make use of a broad array of micro- and nano-fabrication tools at open access clean room facilities located at the Polytechnique Montréal and McGill University in Montreal.
Our group is a member of the Nanoscience Group at Concordia which shares a large number of facilities.
Low-temperature cryostat (0.3 - 300 Kelvin). Allows a wide range of electron transport experiments in nanosystems as a function of temperature, electric and magnetic field.
Low-temperature cryostat (1.5 - 420 Kelvin). Allows a wide range of electron transport experiments in nanosystems as a function of temperature, electric and magnetic field.
Low-temperature cryostat (4.2 - 300 Kelvin) equipped with a mechanical breakjunction assembly. Allows a wide range of electron transport experiments in nanosystems as a function of mechanical strain.
14 Tesla magnet and its dewar which can be used with both cryostats (VTI and MBJ).
Five-probe probe station for sample characterization during microfabrication.
Four-source thermal evaporator for thin film depostions.
Gas flowmeters and furnace making up the CVD. The CVD is used for the growth of single-wall carbon nanotubes (SWCNT) and microcrystals of topological insulators (Bi2Se3).
High precision helium-3 and helium-4 leak detector equipped with a turbo-molecular pump. An additional high-volume turbo-pumping station is used for high vacuum pumping. Permits the operation and maintenance of helium-3 and helium-4 low-temperature cryostats.
High resolution Olympus BX51 optical microscope and XC-50 color digital camera system. Allows easy identification of graphene (carbon monolayer) crystals and characterization of micro-lithography.
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