Extreme sensitivity of graphene photoconductivity to environmental gases

Docherty, Callum J.; Lin, Cheng‐Te; Joyce, Hannah J.; Nicholas, R.J.; Herz, Laura M.; Li, Lain‐Jong; Johnston, Michael B.

doi:10.1038/ncomms2235

Cited by 133 publications

(112 citation statements)

References 41 publications

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“…So a lower cooling rate (longer lifetime of hot electrons) leads to a larger photocurrent. The electron heating and cooling dynamics in bulk graphene have been studied using pump-probe measurements, such as optical pumpprobe [22,31,33,34], femtosecond time-resolved angleresolved photo-electron spectroscopy (ARPES) [30,32], and time-resolved optical pump-terahertz (THz) probe spectroscopy [26,[35][36][37][38][39][40][41]. The photoexcited carrier dynamics have also been studied in graphene-based devices through time-resolved photocurrent scanning microscopy [7,8,17,29].…”

Section: Time-resolved Photocurrentmentioning

confidence: 99%

Hot-carrier photocurrent effects at graphene–metal interfaces

Tielrooij¹,

Massicotte²,

Piątkowski³

et al. 2015

J. Phys.: Condens. Matter

102

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Photoexcitation of graphene leads to an interesting sequence of phenomena, some of which can be exploited in optoelectronic devices based on graphene. In particular, the efficient and ultrafast generation of an electron distribution with an elevated electron temperature and the concomitant generation of a photo-thermoelectric voltage at symmetry-breaking interfaces is of interest for photosensing and light harvesting. Here, we experimentally study the generated photocurrent at the graphene-metal interface, focusing on the time-resolved photocurrent, the effects of photon energy, Fermi energy and light polarization. We show that a single framework based on photo-thermoelectric photocurrent generation explains all experimental results.

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Section: Time-resolved Photocurrentmentioning

confidence: 99%

Hot-carrier photocurrent effects at graphene–metal interfaces

Tielrooij¹,

Massicotte²,

Piątkowski³

et al. 2015

J. Phys.: Condens. Matter

102

View full text Add to dashboard Cite

show abstract

“…Moreover, the theory allows us to go beyond idealized Drude models for the dynamic THz response, and determine the limitations of such simplified models [13][14][15][16][17][18][19][20][21] . This work establishes that the hot-carrier dynamics are governed by the coupling of extraordinarily efficient carrier-carrier and carrier-optical-phonon interactions.…”

mentioning

confidence: 99%

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

et al. 2015

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The ultrafast dynamics of hot carriers in graphene are key to both understanding of fundamental carrier-carrier interactions and carrier-phonon relaxation processes in two-dimensional materials, and understanding of the physics underlying novel high-speed electronic and optoelectronic devices. Many recent experiments on hot carriers using terahertz spectroscopy and related techniques have interpreted the variety of observed signals within phenomenological frameworks, and sometimes invoke extrinsic effects such as disorder. Here, we present an integrated experimental and theoretical programme, using ultrafast timeresolved terahertz spectroscopy combined with microscopic modelling, to systematically investigate the hot-carrier dynamics in a wide array of graphene samples having varying amounts of disorder and with either high or low doping levels. The theory reproduces the observed dynamics quantitatively without the need to invoke any fitting parameters, phenomenological models or extrinsic effects such as disorder. We demonstrate that the dynamics are dominated by the combined effect of efficient carrier-carrier scattering, which maintains a thermalized carrier distribution, and carrier-optical-phonon scattering, which removes energy from the carrier liquid.

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“…Studies of changes to these properties have led to an understanding of the orientation of adsorbed molecular species [11], chemical activity mediated by the surface [12], and the type of electron scattering caused [13]. Adsorbed gases have also been shown to affect the THz conductivity of graphene [14]. Of particular interest is the interaction of graphene with molecular oxygen.…”

mentioning

confidence: 99%

Optically induced oxygen desorption from graphene measured using femtosecond two-pulse correlation

et al. 2014

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Recently, there has been a great deal of interest in the effect of atmospheric gases on the properties of graphene. We investigate the electrical and optical response of graphene-based field effect transistors that have been exposed to high purity oxygen gas using a combination of ultrafast two-pulse correlation (to give high temporal resolution) and low-frequency transport measurements (to monitor the photoinduced changes in the Fermi level). By measuring the Fermi level shifts, we are only sensitive to the oxygen atoms that interact directly with the surface. We compare our results to predictions of the empirical friction model for molecular desorption. We show the time scale of the relaxation associated with oxygen desorption to be ∼100 fs, suggesting the desorption proceeds through hot electron generation in the graphene rather than heating of the lattice through hot phonon generation. Ultrafast laser measurements on graphene have afforded great insight into quasiparticle relaxation mechanisms and lifetimes in this material [1][2][3][4]. For example, it is now known that, after ultrafast photoexcitation of the electrons, energy relaxation occurs through mechanisms with markedly different time scales: first through energy redistribution by electron-electron scattering (∼10 fs), then thermalization with optical phonons (∼100 fs), and finally, anharmonic decay of optical phonons and/or coupling to substrate phonons (∼1 ps) [2][3][4]. More recently, ultrafast laser measurements have been used to probe the time scales of charge transfer to graphene from photoexcited adsorbed molecules [5]. However, experimentally the exact time scales and mechanisms associated with the adsorption and desorption of molecular species are not well known [6].Molecules that interact with graphene can significantly influence its electrical, optical, and mechanical properties [7][8][9]. This has led to graphene being used as the active element in a range of sensing applications [10]. Studies of changes to these properties have led to an understanding of the orientation of adsorbed molecular species [11], chemical activity mediated by the surface [12], and the type of electron scattering caused [13]. Adsorbed gases have also been shown to affect the THz conductivity of graphene [14]. Of particular interest is the interaction of graphene with molecular oxygen. Oxygen molecules can adsorb onto the surface of a pristine graphene sheet resulting in fractional charge transfer from the graphene to the oxygen. Recent studies have shown the importance of the substrate and environmental conditions to this charge transfer [15,16]. However, the nature of the interaction with oxygen has yet to be fully explored, and it is unclear exactly how and where the oxygen molecules bind to graphene and how efficiently molecules can dissociate at these sites.Here, we investigate the mechanisms, energies, and time scales relevant for the molecular adsorption of oxygen molecules on graphene. To do this, we have designed an experiment which permits high electrica...

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Extreme sensitivity of graphene photoconductivity to environmental gases

Cited by 133 publications

References 41 publications

Hot-carrier photocurrent effects at graphene–metal interfaces

Hot-carrier photocurrent effects at graphene–metal interfaces

Microscopic Origins of the Terahertz Carrier Relaxation and Cooling Dynamics in Graphene

Optically induced oxygen desorption from graphene measured using femtosecond two-pulse correlation

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