Poya Yasaei | Northwestern University (original) (raw)
Address: Chicago, Illinois, United States
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Papers by Poya Yasaei
Graphene has served as the model 2D system for over a decade, and the effects of grain boundaries... more Graphene has served as the model 2D system for over a decade, and the effects of grain boundaries (GBs) on its electrical and mechanical properties are very well investigated. However, no direct measurement of the correlation between thermal transport and graphene GBs has been reported. Here, we report a simultaneous comparison of thermal transport in supported single crystalline graphene to thermal transport across an individual graphene GB. Our experiments show that thermal conductance (per unit area) through an isolated GB can be up to an order of magnitude lower than the theoretically anticipated values. Our measurements are supported by Boltzmann transport modeling which uncovers a new bimodal phonon scattering phenomenon initiated by the GB structure. In this novel scattering mechanism, boundary roughness scattering dominates the phonon transport in low-mismatch GBs, while for higher mismatch angles there is an additional resistance caused by the formation of a disordered region at the GB. Nonequilibrium molecular dynamics simulations verify that the amount of disorder in the GB region is the determining factor in impeding thermal transport across GBs.
and examined their performance for BP exfoliation (see Section S1, Supporting Information). Initi... more and examined their performance for BP exfoliation (see Section S1, Supporting Information). Initially, a chunk of black phosphorous crystal (0.02 mg mL −1 ) was immersed into different solvents and was sonicated for 15 h (total input energy -1 MJ). We noticed that aprotic and polar solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) are appropriate solvents for the synthesis of atomically thin BP nanofl akes and can produce uniform and stable dispersions after the sonication (see Section S2, Supporting Information). The solutions were then centrifuged and their supernatants were carefully collected by a pipette. A shows the BP nanofl ake dispersions in DMSO and DMF after sonication for 15 h (left image) and after the centrifugation (right image), having concentrations up to 10 µg mL −1 (see Experimental Section).
A fundamental understanding of chemical sensing mechanisms in graphene-based chemical field-effec... more A fundamental understanding of chemical sensing mechanisms in graphene-based chemical field-effect transistors (chemFETs) is essential for the development of next generation chemical sensors. Here we explore the hidden sensing modalities responsible for tailoring the gas detection ability of pristine graphene sensors by exposing graphene chemFETs to electron donor and acceptor trace gas vapors. We uncover that the sensitivity (in terms of modulation in electrical conductivity) of pristine graphene chemFETs is not necessarily intrinsic to graphene, but rather it is facilitated by external defects in the insulating substrate, which can modulate the electronic properties of graphene. We disclose a mixing effect caused by partial overlap of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of adsorbed gas molecules to explain graphene's ability to detect adsorbed molecules. Our results open a new design space, suggesting that control of external defects in supporting substrates can lead to tunable graphene chemical sensors, which could be developed without compromising the intrinsic electrical and structural properties of graphene.
Grain boundaries can markedly affect the electronic, thermal, mechanical and optical properties o... more Grain boundaries can markedly affect the electronic, thermal, mechanical and optical properties of a polycrystalline graphene. While in many applications the presence of grain boundaries in graphene is undesired, here we show that they have an ideal structure for the detection of chemical analytes. We observe that an isolated graphene grain boundary has B300 times higher sensitivity to the adsorbed gas molecules than a single-crystalline graphene grain. Our electronic structure and transport modelling reveal that the ultrasensitivity in grain boundaries is caused by a synergetic combination of gas molecules accumulation at the grain boundary, together with the existence of a sharp onset energy in the transmission spectrum of its conduction channels. The discovered sensing platform opens up new pathways for the design of nanometre-scale highly sensitive chemical detectors.
Graphene has served as the model 2D system for over a decade, and the effects of grain boundaries... more Graphene has served as the model 2D system for over a decade, and the effects of grain boundaries (GBs) on its electrical and mechanical properties are very well investigated. However, no direct measurement of the correlation between thermal transport and graphene GBs has been reported. Here, we report a simultaneous comparison of thermal transport in supported single crystalline graphene to thermal transport across an individual graphene GB. Our experiments show that thermal conductance (per unit area) through an isolated GB can be up to an order of magnitude lower than the theoretically anticipated values. Our measurements are supported by Boltzmann transport modeling which uncovers a new bimodal phonon scattering phenomenon initiated by the GB structure. In this novel scattering mechanism, boundary roughness scattering dominates the phonon transport in low-mismatch GBs, while for higher mismatch angles there is an additional resistance caused by the formation of a disordered region at the GB. Nonequilibrium molecular dynamics simulations verify that the amount of disorder in the GB region is the determining factor in impeding thermal transport across GBs.
and examined their performance for BP exfoliation (see Section S1, Supporting Information). Initi... more and examined their performance for BP exfoliation (see Section S1, Supporting Information). Initially, a chunk of black phosphorous crystal (0.02 mg mL −1 ) was immersed into different solvents and was sonicated for 15 h (total input energy -1 MJ). We noticed that aprotic and polar solvents such as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) are appropriate solvents for the synthesis of atomically thin BP nanofl akes and can produce uniform and stable dispersions after the sonication (see Section S2, Supporting Information). The solutions were then centrifuged and their supernatants were carefully collected by a pipette. A shows the BP nanofl ake dispersions in DMSO and DMF after sonication for 15 h (left image) and after the centrifugation (right image), having concentrations up to 10 µg mL −1 (see Experimental Section).
A fundamental understanding of chemical sensing mechanisms in graphene-based chemical field-effec... more A fundamental understanding of chemical sensing mechanisms in graphene-based chemical field-effect transistors (chemFETs) is essential for the development of next generation chemical sensors. Here we explore the hidden sensing modalities responsible for tailoring the gas detection ability of pristine graphene sensors by exposing graphene chemFETs to electron donor and acceptor trace gas vapors. We uncover that the sensitivity (in terms of modulation in electrical conductivity) of pristine graphene chemFETs is not necessarily intrinsic to graphene, but rather it is facilitated by external defects in the insulating substrate, which can modulate the electronic properties of graphene. We disclose a mixing effect caused by partial overlap of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of adsorbed gas molecules to explain graphene's ability to detect adsorbed molecules. Our results open a new design space, suggesting that control of external defects in supporting substrates can lead to tunable graphene chemical sensors, which could be developed without compromising the intrinsic electrical and structural properties of graphene.
Grain boundaries can markedly affect the electronic, thermal, mechanical and optical properties o... more Grain boundaries can markedly affect the electronic, thermal, mechanical and optical properties of a polycrystalline graphene. While in many applications the presence of grain boundaries in graphene is undesired, here we show that they have an ideal structure for the detection of chemical analytes. We observe that an isolated graphene grain boundary has B300 times higher sensitivity to the adsorbed gas molecules than a single-crystalline graphene grain. Our electronic structure and transport modelling reveal that the ultrasensitivity in grain boundaries is caused by a synergetic combination of gas molecules accumulation at the grain boundary, together with the existence of a sharp onset energy in the transmission spectrum of its conduction channels. The discovered sensing platform opens up new pathways for the design of nanometre-scale highly sensitive chemical detectors.