Showing papers by "Philip Kim published in 2010"
TL;DR: Graphene devices on h-BN substrates have mobilities and carrier inhomogeneities that are almost an order of magnitude better than devices on SiO(2).
Abstract: Graphene devices on standard SiO(2) substrates are highly disordered, exhibiting characteristics that are far inferior to the expected intrinsic properties of graphene. Although suspending the graphene above the substrate leads to a substantial improvement in device quality, this geometry imposes severe limitations on device architecture and functionality. There is a growing need, therefore, to identify dielectrics that allow a substrate-supported geometry while retaining the quality achieved with a suspended sample. Hexagonal boron nitride (h-BN) is an appealing substrate, because it has an atomically smooth surface that is relatively free of dangling bonds and charge traps. It also has a lattice constant similar to that of graphite, and has large optical phonon modes and a large electrical bandgap. Here we report the fabrication and characterization of high-quality exfoliated mono- and bilayer graphene devices on single-crystal h-BN substrates, by using a mechanical transfer process. Graphene devices on h-BN substrates have mobilities and carrier inhomogeneities that are almost an order of magnitude better than devices on SiO(2). These devices also show reduced roughness, intrinsic doping and chemical reactivity. The ability to assemble crystalline layered materials in a controlled way permits the fabrication of graphene devices on other promising dielectrics and allows for the realization of more complex graphene heterostructures.
6,261 citations
TL;DR: The density dependence of the characteristic temperature Θ( BG) defining the crossover between the two distinct regimes is mapped out, and it is shown that, for all n, ρ(T) scales as a universal function of the normalized temperature T/Θ(BG).
Abstract: We report on the temperature dependent electron transport in graphene at different carrier densities $n$. Employing an electrolytic gate, we demonstrate that $n$ can be adjusted up to $4\ifmmode\times\else\texttimes\fi{}{10}^{14}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}2}$ for both electrons and holes. The measured sample resistivity $\ensuremath{\rho}$ increases linearly with temperature $T$ in the high temperature limit, indicating that a quasiclassical phonon distribution is responsible for the electron scattering. As $T$ decreases, the resistivity decreases more rapidly following $\ensuremath{\rho}(T)\ensuremath{\sim}{T}^{4}$. This low temperature behavior can be described by a Bloch-Gr\"uneisen model taking into account the quantum distribution of the two-dimensional acoustic phonons in graphene. We map out the density dependence of the characteristic temperature ${\ensuremath{\Theta}}_{\mathrm{BG}}$ defining the crossover between the two distinct regimes, and show that, for all $n$, $\ensuremath{\rho}(T)$ scales as a universal function of the normalized temperature $T/{\ensuremath{\Theta}}_{\mathrm{BG}}$.
848 citations
TL;DR: It is proposed that oxygen molecular anions are stabilized by water solvation and electrostatic binding to the silicon dioxide surface and become stronger and more irreversible in the presence of moisture and over long periods of time.
Abstract: Using micro-Raman spectroscopy and scanning tunneling microscopy, we study the relationship between structural distortion and electrical hole doping of graphene on a silicon dioxide substrate. The observed upshift of the Raman G band represents charge doping and not compressive strain. Two independent factors control the doping: (1) the degree of graphene coupling to the substrate and (2) exposure to oxygen and moisture. Thermal annealing induces a pronounced structural distortion due to close coupling to SiO2 and activates the ability of diatomic oxygen to accept charge from graphene. Gas flow experiments show that dry oxygen reversibly dopes graphene; doping becomes stronger and more irreversible in the presence of moisture and over long periods of time. We propose that oxygen molecular anions are stabilized by water solvation and electrostatic binding to the silicon dioxide surface.
745 citations
Journal Article•
TL;DR: In this article, the fractional quantum Hall effect (FQHE) is observed in suspended sheets of graphene, probed in a two-terminal measurement setup, and it is shown that at low carrier density, graphene becomes an insulator with a magnetic-field-tunable energy gap.
Abstract: The fractional quantum Hall effect is a quintessential manifestation of the collective behaviour associated with strongly interacting charge carriers confined to two dimensions and subject to a strong magnetic field. It is predicted that the charge carriers present in graphene — an atomic layer of carbon that can be seen as the 'perfect' two-dimensional system — are subject to strong interactions. Nevertheless, the phenomenon had eluded experimental observation until now: in this issue two groups report fractional quantum Hall effect in suspended sheets of graphene, probed in a two-terminal measurement setup. The researchers also observe a magnetic-field-induced insulating state at low carrier density, which competes with the quantum Hall effect and limits its observation to the highest-quality samples only. These results pave the way for the study of the rich collective behaviour of Dirac fermions in graphene. The fractional quantum Hall effect (FQHE) is the quintessential collective quantum behaviour of charge carriers confined to two dimensions but it has not yet been observed in graphene, a material distinguished by the charge carriers' two-dimensional and relativistic character. Here, and in an accompanying paper, the FQHE is observed in graphene through the use of devices containing suspended graphene sheets; the results of these two papers open a door to the further elucidation of the complex physical properties of graphene. When electrons are confined in two dimensions and subject to strong magnetic fields, the Coulomb interactions between them can become very strong, leading to the formation of correlated states of matter, such as the fractional quantum Hall liquid1,2. In this strong quantum regime, electrons and magnetic flux quanta bind to form complex composite quasiparticles with fractional electronic charge; these are manifest in transport measurements of the Hall conductivity as rational fractions of the elementary conductance quantum. The experimental discovery of an anomalous integer quantum Hall effect in graphene has enabled the study of a correlated two-dimensional electronic system, in which the interacting electrons behave like massless chiral fermions3,4. However, owing to the prevailing disorder, graphene has so far exhibited only weak signatures of correlated electron phenomena5,6, despite intense experimental and theoretical efforts7,8,9,10,11,12,13,14. Here we report the observation of the fractional quantum Hall effect in ultraclean, suspended graphene. In addition, we show that at low carrier density graphene becomes an insulator with a magnetic-field-tunable energy gap. These newly discovered quantum states offer the opportunity to study correlated Dirac fermions in graphene in the presence of large magnetic fields.
655 citations
TL;DR: For a given optical phonon temperature, the anharmonic downshift of the Raman G mode is smaller than expected under equilibrium conditions, suggesting that the electrons and high-energy optical phonons are not fully equilibrated with all of the phonon modes.
Abstract: We examine the intrinsic energy dissipation steps in electrically biased graphene channels. By combining in-situ measurements of the spontaneous optical emission with a Raman spectroscopy study of the graphene sample under conditions of current flow, we obtain independent information on the energy distribution of the electrons and phonons. The electrons and holes contributing to light emission are found to obey a thermal distribution, with temperatures in excess of 1500 K in the regime of current saturation. The zone-center optical phonons are also highly excited and are found to be in equilibrium with the electrons. For a given optical phonon temperature, the anharmonic downshift of the Raman G mode is smaller than expected under equilibrium conditions, suggesting that the electrons and high-energy optical phonons are not fully equilibrated with all of the phonon modes.
214 citations
TL;DR: Measurements of the activation energy gaps for the nu=2 and 3 filling factors in tilted magnetic fields exhibit no appreciable dependence on the in-plane magnetic field, suggesting that these Landau level splittings are independent of spin.
Abstract: The quantum Hall effect near the charge neutrality point in bilayer graphene is investigated in high magnetic fields of up to 35 T using electronic transport measurements. In the high-field regime, the eightfold degeneracy in the zero-energy Landau level is completely lifted, exhibiting new quantum Hall states corresponding to filling factors nu=0, 1, 2, and 3. Measurements of the activation energy gaps for the nu=2 and 3 filling factors in tilted magnetic fields exhibit no appreciable dependence on the in-plane magnetic field, suggesting that these Landau level splittings are independent of spin. In addition, measurements taken at the nu=0 charge neutral point show that, similar to single layer graphene, the bilayer becomes insulating at high fields.
137 citations
01 Dec 2010
TL;DR: Graphene field effect transistors are fabricated utilizing single-crystal hexagonal boron nitride (h-BN), an insulating isomorph of graphene, as the gate dielectric.
Abstract: Graphene field-effect transistors are fabricated utilizing single-crystal hexagonal boron nitride (h-BN), an insulating isomorph of graphene, as the gate dielectric The devices exhibit mobility values exceeding 10,000 cm2/V-sec and current saturation down to 500 nm channel lengths with intrinsic transconductance values above 400 mS/mm The work demonstrates the favorable properties of using h-BNas a gate di-electric for graphene FETs
132 citations
TL;DR: The large Raman signal for both adsorbed iodine and intercalated bromine species is attributed to intramolecular electronic resonance enhancement, and the signal evolution with varying graphene thickness is explained by multiple reflection electromagnetic calculations.
Abstract: Strong Raman scattering is observed from iodine anions adsorbed at ca. 3% coverage on single layer graphene. In addition, the Raman signal from just one bromine intercalation layer inside three and four layer thick graphenes is observed. We analyze and model the intramolecular electronic, charge-transfer, and multiple reflection electromagnetic mechanisms responsible for this unusual sensitivity. Graphene is an excellent Raman substrate for adsorbed species showing intramolecular electronic resonance, because graphene efficiently quenches interfering excited-state luminescence. The Raman sensitivity for adsorbed and intercalated molecular species is highest for single layer graphene and decreases with increasing thickness. These phenomena are compared with surface enhanced Raman spectroscopy field enhancement and "chemical" Raman processes in aggregated Ag particles and on flat, highly reflective metal surfaces. The Raman spectra of adsorbed bromine layers are not observed, despite significant charge transfer to graphene. Charge transfer from adsorbed bromine is about one-half of charge transfer from intercalated bromine. We attribute the large Raman signal for both adsorbed iodine and intercalated bromine species to intramolecular electronic resonance enhancement. The signal evolution with varying graphene thickness is explained by multiple reflection electromagnetic calculations.
130 citations
TL;DR: In this article, a vector network analyzer is used to detect the mechanical motion of graphene mechanical resonators, and a local gate is employed to minimize the parasitic capacitance of graphene resonators.
Abstract: We report radio frequency (rf) electrical readout of graphene mechanical resonators. The mechanical motion is actuated and detected directly by using a vector network analyzer, employing a local gate to minimize parasitic capacitance. A resist-free doubly clamped sample with resonant frequency ∼34 MHz, quality factor ∼10 000 at 77 K, and signal-to-background ratio of over 20 dB is demonstrated. In addition to being over two orders of magnitude faster than the electrical rf mixing method, this technique paves the way for use of graphene in rf devices such as filters and oscillators.
109 citations
TL;DR: In this paper, the magnetic properties of single crystal antimony telluride (Sb2Te3) nanowires with diameters in the range of 20−100 nm were investigated.
Abstract: We report measurements of electronic, thermoelectric, and galvanomagnetic properties of individual single crystal antimony telluride (Sb2Te3) nanowires with diameters in the range of 20−100 nm. Temperature-dependent resistivity and thermoelectric power (TEP) measurements indicate hole dominant diffusive thermoelectric generation with an enhancement of the TEP for smaller diameter wires up to 110 μV/K at T = 300 K. We measure the magnetoresistance in magnetic fields both parallel and perpendicular to the nanowire [110] axis, where strong anisotropic positive magnetoresistance behavior was observed.
108 citations
Journal Article•
TL;DR: Measurements of electronic, thermoelectric, and galvanomagnetic properties of individual single crystal antimony telluride (Sb(2)Te(3)) nanowires with diameters in the range of 20-100 nm indicate hole dominant diffusive thermoeLECTric generation with an enhancement of the TEP for smaller diameter wires up to 110 microV/K.
Abstract: We report measurements of electronic, thermoelectric, and galvanomagnetic properties of individual single crystal antimony telluride (Sb(2)Te(3)) nanowires with diameters in the range of 20-100 nm. Temperature-dependent resistivity and thermoelectric power (TEP) measurements indicate hole dominant diffusive thermoelectric generation with an enhancement of the TEP for smaller diameter wires up to 110 microV/K at T = 300 K. We measure the magnetoresistance in magnetic fields both parallel and perpendicular to the nanowire [110] axis, where strong anisotropic positive magnetoresistance behavior was observed.
TL;DR: The magnitude of these shifts, and their magnetic field dependence, suggests that an interaction-enhanced energy gap opens in the n=0 level at high magnetic fields.
Abstract: We report a study of the cyclotron resonance (CR) transitions to and from the unusual $n=0$ Landau level (LL) in monolayer graphene. Unexpectedly, we find the CR transition energy exhibits large (up to 10%) and nonmonotonic shifts as a function of the LL filling factor, with the energy being largest at half filling of the $n=0$ level. The magnitude of these shifts, and their magnetic field dependence, suggests that an interaction-enhanced energy gap opens in the $n=0$ level at high magnetic fields. Such interaction effects normally have a limited impact on the CR due to Kohn's theorem [W. Kohn, Phys. Rev. 123, 1242 (1961)], which does not apply in graphene as a consequence of the underlying linear band structure.
TL;DR: Low-energy electron microscopy and microprobe diffraction are used to image and characterize corrugation in SiO(2)-supported and suspended exfoliated graphene at nanometer length scales and reveal quantitative differences in surface roughness on length scales below 20 nm which depend on film thickness and interaction with the substrate.
Abstract: Low-energy electron microscopy and microprobe diffraction are used to image and characterize corrugation in SiO2-supported and suspended exfoliated graphene at nanometer length scales. Diffraction line-shape analysis reveals quantitative differences in surface roughness on length scales below 20 nm which depend on film thickness and interaction with the substrate. Corrugation decreases with increasing film thickness, reflecting the increased stiffness of multilayer films. Specifically, single-layer graphene shows a markedly larger short-range roughness than multilayer graphene. Due to the absence of interactions with the substrate, suspended graphene displays a smoother morphology and texture than supported graphene. A specific feature of suspended single-layer films is the dependence of corrugation on both adsorbate load and temperature, which is manifested by variations in the diffraction line shape. The effects of both intrinsic and extrinsic corrugation factors are discussed.
TL;DR: The topological nature of a certain type of grain boundary in polycrystalline graphene may be used to tailor the electrical transport properties of graphene.
Abstract: The topological nature of a certain type of grain boundary in polycrystalline graphene may be used to tailor the electrical transport properties.
TL;DR: In this article, the relationship between structural distortion and electrical hole doping of graphene on a silicon dioxide substrate was studied using micro-Raman spectroscopy and scanning tunneling microscopy.
Abstract: Using micro-Raman spectroscopy and scanning tunneling microscopy, we study the relationship between structural distortion and electrical hole doping of graphene on a silicon dioxide substrate. The observed upshift of the Raman G band represents charge doping and not compressive strain. Two independent factors control the doping: (1) the degree of graphene coupling to the substrate, and (2) exposure to oxygen and moisture. Thermal annealing induces a pronounced structural distortion due to close coupling to SiO2 and activates the ability of diatomic oxygen to accept charge from graphene. Gas flow experiments show that dry oxygen reversibly dopes graphene; doping becomes stronger and more irreversible in the presence of moisture and over long periods of time. We propose that oxygen molecular anions are stabilized by water solvation and electrostatic binding to the silicon dioxide surface.
TL;DR: The greatly reduced carrier broadening to values below the graphene electron-phonon coupling constant explains the appearance of sharp resonances that reveal a fundamental interaction of Dirac fermions.
Abstract: Coherent coupling of Dirac fermion magnetoexcitons with an optical phonon is observed in graphite as marked magnetic-field dependent splittings and anticrossing behavior of the two coupled modes. The sharp magnetophonon resonance occurs in regions of the graphite sample with properties of superior single-layer graphene having enhanced lifetimes of Dirac fermions. The greatly reduced carrier broadening to values below the graphene electron-phonon coupling constant explains the appearance of sharp resonances that reveal a fundamental interaction of Dirac fermions.
Patent•
19 Jul 2010TL;DR: In this paper, a polyvinyl alcohol (PVA) layer was applied to the working surface of the graphene layer and a dielectric layer was added to the PVA layer.
Abstract: An apparatus or method can include forming a graphene layer including a working surface, forming a polyvinyl alcohol (PVA) layer upon the working surface of the graphene layer, and forming a dielectric layer upon the PVA layer In an example, the PVA layer can be activated and the dielectric layer can be deposited on an activated portion of the PVA layer In an example, an electronic device can include such apparatus, such as included as a portion of graphene field-effect transistor (GFET), or one or more other devices
TL;DR: In this paper, a few-layer graphene films are grown using a Molecular Beam Deposition (MBD) technique in ultra-high vacuum by evaporation of atomic carbon and subsequent annealing of the samples at 800-900°C.
TL;DR: In this article, the energy loss of the non-equilibrium electron system in individual metallic single-walled carbon nanotubes at low temperature was characterized using Johnson noise thermometry.
Abstract: We characterize the energy loss of the non-equilibrium electron system in individual metallic single-walled carbon nanotubes at low temperature. Using Johnson noise thermometry, we demonstrate that, for a nanotube with ohmic contacts, the dc resistance at finite bias current directly reflects the average electron temperature. This enables a straightforward determination of the thermal conductance associated with cooling of the nanotube electron system. In analyzing the temperature- and length-dependence of the thermal conductance, we consider contributions from acoustic phonon emission, optical phonon emission, and hot electron outdiffusion.
TL;DR: In this paper, a vector network analyzer is used to detect the mechanical motion of graphene mechanical resonators, and a local gate is employed to minimize the parasitic capacitance of graphene resonators.
Abstract: We report radio frequency (rf) electrical readout of graphene mechanical resonators. The mechanical motion is actuated and detected directly by using a vector network analyzer, employing a local gate to minimize parasitic capacitance. A resist-free doubly clamped sample with resonant frequency ~ 34 MHz, quality factor ~ 10000 at 77 K, and signal-to-background ratio of over 20 dB is demonstrated. In addition to being over two orders of magnitude faster than the electrical rf mixing method, this technique paves the way for use of graphene in rf devices such as filters and oscillators.
Posted Content•
30 Apr 2010
TL;DR: In this paper, a capacitance study of dual gated bilayer graphene was performed, where the authors measured the electronic compressibility as a function of carrier density, temperature, and applied perpendicular electrical displacement.
Abstract: We report on a capacitance study of dual gated bilayer graphene. The measured capacitance allows us to probe the electronic compressibility as a function of carrier density, temperature, and applied perpendicular electrical displacement D. As a band gap is induced with increasing D, the compressibility minimum at charge neutrality becomes deeper but remains finite, suggesting the presence of localized states within the energy gap. Temperature dependent capacitance measurements show that compressibility is sensitive to the intrinsic band gap. For large displacements, an additional peak appears in the compressibility as a function of density, corresponding to the presence of a 1-dimensional van Hove singularity (vHs) at the band edge arising from the quartic bilayer graphene band structure. For D > 0, the additional peak is observed only for electrons, while D < 0 the peak appears only for holes. This asymmetry that can be understood in terms of the finite interlayer separation and may be useful as a direct probe of the layer polarization.
TL;DR: In this article, the microwave conductance of mechanically exfoliated graphene at frequencies up to 8.5 GHz was measured and the conductance at 4.2 K exhibits quantum oscillations, and is independent of the frequency.
Abstract: We have measured the microwave conductance of mechanically exfoliated graphene at frequencies up to 8.5 GHz. The conductance at 4.2 K exhibits quantum oscillations, and is independent of the frequency.
TL;DR: In this paper, the microwave conductance of mechanically exfoliated graphene at frequencies up to 8.5 GHz was measured and the conductance at 4.2 K exhibits quantum oscillations, and is independent of the frequency.
Abstract: We have measured the microwave conductance of mechanically exfoliated graphene at frequencies up to 8.5 GHz. The conductance at 4.2 K exhibits quantum oscillations, and is independent of the frequency.
TL;DR: In this paper, the magnetic properties of single crystal antimony telluride (Sb2Te3) nanowires with diameters in the range of 20-100 nm were investigated.
Abstract: We report measurements of electronic, thermoelectric, and galvanomagnetic properties of individual single crystal antimony telluride (Sb2Te3) nanowires with diameters in the range of 20-100 nm. Temperature dependent resistivity and thermoelectric power (TEP) measurements indicate hole dominant diffusive thermoelectric generation, with an enhancement of the TEP for smaller diameter wires up to 110 uV/K at T = 300 K. We measure the magnetoresistance, in magnetic fields both parallel and perpendicular to the nanowire [110] axis, where strong anisotropic positive magnetoresistance behavior was observed.
01 Jan 2010
TL;DR: In this paper, strong Raman scattering is observed from iodine anions adsorbed atca. 3% coverage on single layer graphene, and the Raman sensitivity for both adorbed and intercalated molecular species is highest for single layer graphene and decreases with increasing thickness.
Abstract: Strong Raman scattering is observed from iodine anions adsorbed atca. 3% coverage on single layergraphene.Inaddition,theRamansignalfromjustonebromineintercalationlayerinsidethreeandfourlayer thick graphenes is observed. We analyze and model the intramolecular electronic, charge-transfer, and multiple reflection electromagnetic mechanisms responsible for this unusual sensitivity. Graphene is an excellent Raman substrate for adsorbed species showing intramolecular electronic resonance, because graphene efficiently quenches interfering excited-state luminescence. The Raman sensitivity for adsorbed and intercalated molecular species is highest for single layer graphene and decreases with increasing thickness. These phenomena are compared with surface enhanced Raman spectroscopyfield enhancement and "chemical" Raman processes in aggregated Ag particles and onflat, highly reflective metal surfaces. The Raman spectra of adsorbed bromine layers are not observed, despite significant charge transfer to graphene. Charge transfer from adsorbed bromine is about one-half of charge transfer from intercalated bromine. We attribute the large Raman signal for both adsorbediodineandintercalatedbrominespeciestointramolecularelectronicresonanceenhancement.Thesignal evolution with varying graphene thickness is explained by multiple reflection electromagnetic calculations.
Journal Article•
TL;DR: In this article, the authors describe a new regime of magnetotransport in two dimensional electron systems in the presence of a narrow potential barrier imposed by external gates, where the Landau level states, confined to the barrier region in strong magnetic fields, undergo a deconfinement transition as the field is lowered.
Abstract: We describe a new regime of magnetotransport in two dimensional electron systems in the presence of a narrow potential barrier imposed by external gates. In such systems, the Landau level states, confined to the barrier region in strong magnetic fields, undergo a deconfinement transition as the field is lowered. We present transport measurments showing Shubnikov-de Haas (SdH) oscillations which, in the unipolar regime, abruptly disappear when the strength of the magnetic field is reduced below a certain critical value. This behavior is explained by a semiclassical analysis of the transformation of closed cyclotron orbits into open, deconfined trajectories. Comparison to SdH-type resonances in the local density of states is presented.
Journal Article•
TL;DR: Using Johnson noise thermometry, it is demonstrated that, for a nanotubes with Ohmic contacts, the dc resistance at finite bias current directly reflects the average electron temperature, which enables a straightforward determination of the thermal conductance associated with cooling of the nanotube electron system.
Abstract: We characterize the energy loss of the nonequilibrium electron system in individual metallic single-walled carbon nanotubes at low temperature. Using Johnson noise thermometry, we demonstrate that, for a nanotube with Ohmic contacts, the dc resistance at finite bias current directly reflects the average electron temperature. This enables a straightforward determination of the thermal conductance associated with cooling of the nanotube electron system. In analyzing the temperature- and length-dependence of the thermal conductance, we consider contributions from acoustic phonon emission, optical phonon emission, and hot electron outdiffusion.
01 Jan 2010
TL;DR: In this article, a line-shape analysis of a single-layer graphenes shows that it is significantly larger than a multilayer graphene, and the effect of both intrinsic and extrinsic corrugation is investigated.
Abstract: Low-energyelectronmicroscopyandmicroprobediffractionareusedtoimageandcharacterizecorrugationinSiO 2 -supportedandsuspendedexfoliatedgrapheneatnanometerlengthscales.Diffractionline-shapeanalysisrevealsquantitativedifferencesinsurfaceroughnessonlengthscalesbelow20nmwhichdependonfilmthicknessandinteractionwiththesubstrate.Corrugationdecreaseswithincreasingfilmthickness,reflectingtheincreasedstiffnessofmultilayerfilms.Specifically,single-layergrapheneshowsamarkedlylargershort-rangeroughnessthanmultilayergraphene.Duetotheabsenceofinteractionswiththesubstrate,suspendedgraphenedisplaysasmoothermorphologyandtexturethansupportedgraphene.Aspecificfeatureofsuspendedsingle-layerfilmsisthedependenceofcorrugationonbothadsorbateloadandtemperature,whichismanifestedbyvariationsinthediffractionlineshape.Theeffectsofbothintrinsicandextrinsiccorrugationfactorsarediscussed. KEYWORDS: graphene · exfoliated graphene · corrugation · roughness ·morphology · -LEED · LEEM ARTICLE www.acsnano.org VOL. 4 ▪ NO. 8 ▪ 4879–4889 ▪ 2010