Photocurrent measurements of supercollision cooling in graphene

Graham, Mary; Shi, Su‐Fei; Ralph, Daniel; Park, Jiwoong; McEuen, Paul L.

doi:10.1038/nphys2493

Cited by 311 publications

(524 citation statements)

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“…Metal nanoparticles are known to dope graphene underneath, which leads to an in-plane electric field in the graphene areas surrounding them 18,20 . It is also known that illumination of such built-in junctions creates long-lived (>1 ps) hot electrons in graphene 24,25 , and these electrons generate a photovoltage 5,26,27 , similar to illumination of semiconducting p-n junctions. The photovoltage V ph in graphene is proportional to its electron temperature, T e .…”

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confidence: 99%

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Giant photoeffect in proton transport through graphene membranes

Lozada-Hidalgo

Zhang

et al. 2018

Nature Nanotech

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Graphene has recently been shown to be permeable to thermal protons 1 , the nuclei of hydrogen atoms, which sparked interest in its use as a proton-conducting membrane in relevant technologies 1-4 . However, the influence of light on proton permeation remains unknown. Here we report that proton transport through Pt-nanoparticle-decorated graphene can be enhanced strongly by illuminating it with visible light. Using electrical measurements and mass spectrometry, we find a photoresponsivity of 10 4 A W -1 , which translates into a gain of 10 4 protons per photon with response times in the microsecond range. These characteristics are competitive with those of state-of-the-art photodetectors that are based on electron transport using silicon and novel two-dimensional materials 5-7 . The photo-proton effect can be important for graphene's envisaged use in fuel cells and hydrogen isotope separation. Our observations can also be of interest for other applications such as light-induced water splitting, photocatalysis and novel photodetectors.Recent experiments have established that graphene monolayers are surprisingly transparent to thermal protons, even in the absence of lattice defects 1,2 . The proton transport through graphene was found to be thermally activated 1 with a relatively low energy barrier of about 0.8 eV. Further measurements involving hydrogen's isotope deuterium have shown that this barrier is in fact 0.2 eV higher than the measured activation energy because the initial state of incoming protons is lifted by zero-point oscillations at oxygen bonds within the proton-conducting media used in the experiments 2 . The resulting value of 1.0 eV for the graphene barrier is somewhat lower (by at least 30%) than the values obtained theoretically for ideal graphene 1,[8][9][10] , which triggered a debate about the exact microscopic mechanism behind the proton permeation [8][9][10][11][12] . For example, it was recently suggested that graphene's hydrogenation could be an additional ingredient involved in the process 11 . Independently of fundamentals of the involved mechanisms, the high proton conductivity of graphene membranes combined with their impermeability to other atoms and molecules entices their use for various applications including fuel cell technologies and hydrogen isotope separation 1-4 . For example, it was argued that mass-produced membranes based on chemical-vapor-deposited graphene can dramatically increase efficiency and decrease costs of heavy water production 1,2,4 .In this Letter, we describe an unexpected enhancement of proton transport through catalyticallyactivated 1 graphene under low-intensity illumination. The devices used in this work were made from monocrystalline graphene obtained by mechanical exfoliation. The graphene crystals were suspended

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confidence: 99%

“…It also explains naturally the observed I ∝ P 1/4 dependence. In graphene the electronic temperature depends on illumination power density as 24,27 T e ∝ P 1/n , with n≥3. Accordingly, we obtain V ph ∝ T e ∝ P 1/n and, hence, I ∝ P 1/n .…”

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confidence: 99%

Giant photoeffect in proton transport through graphene membranes

Lozada-Hidalgo

Zhang

et al. 2018

Nature Nanotech

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“…1c) when k B T g ≈ φ/2, dominating over acoustic and optical phonon cooling [12,13] in pristine graphene Schottky junctions; J ⊥ q also overwhelms in-plane (lateral) diffusive energy transport. We find that the values of J ⊥ q are competitive with disorder-assisted cooling [14][15][16] in more dirty devices.Graphene is essential to our proposal due to a unique combination of electronic characteristics. First, fast intraband Auger-type scattering [19,20] allows the absorbed photon energy flux, J in q , to be efficiently captured as heat by ambient carriers in graphene; this process results in a thermalized hot carrier distribution [19,20].…”

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confidence: 81%

“…These junctions are characterized by Schottky barriers φ that span two orders of magnitude φ ≈ 0.01−1 eV and exhibit in situ control through applied bias or by using gate potentials [7][8][9][10][11]. The wide range of φ achievable across the g/X interface, combined with the unique graphene photoresponse mediated by long-lived hot carriers (elevated electronic temperatures, T g , different from those of the lattice, T 0 [12][13][14][15][16][17]), make graphene Schottky junctions a prime target for accessing novel vertical energy transport regimes [18].…”

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confidence: 99%

Enhanced Thermionic-Dominated Photoresponse in Graphene Schottky Junctions

Rodriguez-Nieva¹,

Dresselhaus²,

Song

2016

Nano Lett.

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Vertical heterostructures of van der Waals materials enable new pathways to tune charge and energy transport characteristics in nanoscale systems. We propose that graphene Schottky junctions can host a special kind of photoresponse which is characterized by strongly coupled heat and charge flows that run vertically out of the graphene plane. This regime can be accessed when vertical energy transport mediated by thermionic emission of hot carriers overwhelms electron-lattice cooling as well as lateral diffusive energy transport. As such, the power pumped into the system is efficiently extracted across the entire graphene active area via thermionic emission of hot carriers into a semiconductor material. Experimental signatures of this regime include a large and tunable internal responsivity R with a non-monotonic temperature dependence. In particular, R peaks at electronic temperatures on the order of the Schottky potential φ and has a large upper limit R ≤ e/φ (e/φ = 10 A/W when φ = 100 meV). Our proposal opens up new approaches for engineering the photoresponse in optically-active graphene heterostructures.Keywords: graphene; hot carriers; Schottky junction; photocurrent Vertical heterostructures comprising layers of van der Waals (vdW) materials have recently emerged as a platform for designer electronic interfaces [1]. Of special interest are heterostructures which feature tunable interlayer transport characteristics, as exemplified by g/X Schottky junctions [2-10]; here 'g' denotes graphene, and X is a semiconductor material, such as Si, MoS 2 or WSe 2 . These junctions are characterized by Schottky barriers φ that span two orders of magnitude φ ≈ 0.01−1 eV and exhibit in situ control through applied bias or by using gate potentials [7][8][9][10][11]. The wide range of φ achievable across the g/X interface, combined with the unique graphene photoresponse mediated by long-lived hot carriers (elevated electronic temperatures, T g , different from those of the lattice, T 0 [12-17]), make graphene Schottky junctions a prime target for accessing novel vertical energy transport regimes [18].Here we show that specially designed graphene Schottky junctions can host an enhanced thermionicdominated photoresponse driven by strongly coupled charge and energy currents. Such photoresponse proceeds, as illustrated in Fig. 1a, via the thermionic emission of graphene hot carriers with energy larger than the Schottky barrier. At steady state, an equal number of cold carriers are injected at the Fermi surface through an ohmic contact, giving a net flow of heat J ⊥ q out of the graphene electronic system balancing the energy pumped into the system. Strikingly, thermionic emission yields strong heat transport running vertically out of the hot electron system, which dominates over more conventional electronic cooling channels, e.g. electron-lattice cooling. Indeed, we find that J ⊥ q can be significant in graphene (see Fig. 1c) when k B T g ≈ φ/2, dominating over acoustic and optical phonon cooling [12,13] in pristine graphene Sch...

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“…In addition, they are very similar in magnitude and in the range of ∼ 1 − 2 ps with sample-to-sample variation within ∼ 20 − 30%. On average, MEG samples exhibit slightly longer relaxation times than sCVDG and pCVDG samples, which can be attributed to a degree of disorder arising from charge impurities, substrate roughness, wrinkling and breaking of the transferred CVDG samples that can provide additional parallel channels for carrier cooling [105,118,119]. However, the relaxation times of some CVDG samples can approach or exceed these of MEG samples, indicating that disorder-assisted electron-phonon (supercollision) cooling is not the dominant cooling mechanism in our high quality graphene samples, but generally provides at most only a modest correction.…”

Section: Highly Doped Graphenementioning

confidence: 99%

Relaxation Dynamics in Graphene

Malić

Knorr

2013

Graphene and Carbon Nanotubes

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In this thesis, the relaxation dynamics of nonequilibrium carriers in graphene is investigated. Based on the density matrix approach, the interaction of carriers with light, phonons and electrons is theoretically modelled. The resulting time-, momentum-, and angle-resolved simulation of the carrier dynamics enables the interpretation of recent experimental observations. Typically, the carrier relaxation has been accessed via high-resolution pump-probe experiments. Common to all studies is a bi-exponential decay of the pump-induced differential transmission (DT) spectrum. The fast decay component in the range of few tens of femtoseconds is assigned to an ultrafast Coulomb-dominated carrier redistribution towards a hot Fermi-Dirac distribution, whereas the slower decay component in the range of a picosecond reflects the equilibration between the electron and the phonon system. However, many studies report a zero-crossing after the initial decay in the transient DT spectrum, where the second decay component characterizes the recovering of the DT signal. In very good agreement with recent pump-probe experiment performed by the group of Prof. Manfred Helm (Helmholtz-Zentrum Dresden-Rossendorf), a microscopic explanation for the occurrence of transient negative differential transmission in graphene is found, where a detailed interplay of intraand interband absorption processes on the transient DT in graphene is investigated. In particular, phonon-assisted intraband processes are shown to lead to an enhanced absorption giving rise to the experimentally observed zero-crossing from positive to negative DT signals.In collaboration with the group of Prof. Theodore B. Norris (Michigan University, USA), theoretical studies combined with ultrafast time-resolved THz spectroscopy were performed to systematically investigate the hot-carrier dynamics in an array of graphene samples. The theory calculates explicitly the time-dependent response of the system to a THz probe pulse. The calculations reveal that the observed dynamics can be accounted for qualitatively without including any fitting parameters, phenomenological models or extrinsic effects. Specifically, the hot-carrier dynamics are governed by the coupling of extraordinarily efficient carrier-carrier and carrier-phonon interactions. Furthermore, the theory demonstrates that the simple Drude model is insufficient to fully account for the THz interactions.Beside pump-probe studies, the thesis presents the absorption spectra of mono-and bilayer graphene including the impact of the fully momentum-dependent optical and Coulomb matrix elements. In agreement with recent experiments, the absorbance of graphene is characterized by a frequency-independent value in the near-infrared spectral region and a pronounced peak in the ultraviolet region resulting from interband transition. In contrast to the linear band structure of graphene, the energy dispersion of bilayer graphene exhibits four parabolic bands resulting in interesting optical features: The absorbance exhibits in...

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Photocurrent measurements of supercollision cooling in graphene

Cited by 311 publications

References 23 publications

Giant photoeffect in proton transport through graphene membranes

Giant photoeffect in proton transport through graphene membranes

Enhanced Thermionic-Dominated Photoresponse in Graphene Schottky Junctions

Relaxation Dynamics in Graphene

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