Since opening sizable bandgaps in bilayer graphene （BLG） was proven possible, BLG has attracted considerable attention as a promising high-mobility candidate material for many electronic and optoelectronic applicati...Since opening sizable bandgaps in bilayer graphene （BLG） was proven possible, BLG has attracted considerable attention as a promising high-mobility candidate material for many electronic and optoelectronic applications. However, the bandgaps observed in the transport experiments reported in the literature are far smaller than both the theoretical predictions and the bandgaps extracted from optical measurements. In this study, we investigate the factors preventing the formation of large bandgaps and demonstrate that a -200-meV transport bandgap can be opened in BLG by scaling the gate dielectric and employing a ribbon channel to suppress the percolative transport. This is the largest transport bandgap that has been achieved in BLG to date.展开更多
We theoretically investigate the spin filtering transport of double parallel quantum wires(QWs) side-coupled to a grapheme sheet and sandwiched between two ferromagnetic(FM) leads.The dependences of the wire-graphene ...We theoretically investigate the spin filtering transport of double parallel quantum wires(QWs) side-coupled to a grapheme sheet and sandwiched between two ferromagnetic(FM) leads.The dependences of the wire-graphene coupling strength,wire-wire coupling strength,as well as the spin polarization of the ferromagnetic leads are studied.It is found that the wire-graphene coupling strength tends to reduce the current and the wire-wire coupling strength can first reinforce and then decrease the current.The spin polarization strength has an enhanced(identical) effect on the current under the parallel(anti-parallel) alignment of the FM leads,which gives rise to an obvious spin-filter and tunnel magnetoresistance(TMR) effect.Our results suggest that such a theoretical model can stimulate some experimental investigations about the spin-filter devices.展开更多
Sodium ions(Na+) and ether electrolyte coinserted graphite possesses a considerable volume expansion effect. However, the mechanism fails to clearly explain its stability. In response to this deficiency, the co-insert...Sodium ions(Na+) and ether electrolyte coinserted graphite possesses a considerable volume expansion effect. However, the mechanism fails to clearly explain its stability. In response to this deficiency, the co-inserted reaction is proposed, which is affected by the Lorentz force of the applied electric field under the high-current condition. The Na^(+) ions are separated out, while the ethylene glycol dimethyl ether molecules remain between the graphite layers. This insight provides a reasonable explanation for the extraordinary stability of this material. In situ X-ray diffraction and density functional theory calculations confirm the separation and release of Na+. On the basis of this result, unmodified commercial graphite was stably cycled 6400 times at a current density of up to 10 A g^(-1), and the capacity retention rate was as high as 97.2%. The full battery assembled in the laboratory has a maximum output power of 14,846 W kg^(-1)and an output energy density of 103 W h kg^(-1)(relative to the weight of anodic and cathodic active materials). The new mechanism provides innovative ideas for the design of large-scale energy storage devices.展开更多
Electron transport through short, phase-coherent metal-graphene-metal devices occurs via resonant transmission through particle-in-a-box-like states defined by the atomically-sharp metal leads. We study the spectrum o...Electron transport through short, phase-coherent metal-graphene-metal devices occurs via resonant transmission through particle-in-a-box-like states defined by the atomically-sharp metal leads. We study the spectrum of particle-in-a-box states for single- and bi-layer graphene, corresponding to massless and massive two-dimensional （2-D） fermions. The density of states D as a function of particle number n shows the expected relationships D（n） -n1/2 for massless 2-D fermions （electrons in single-layer graphene） and D（n） -constant for massive 2-D fermions （electrons in bi-layer graphene）. The single parameters of the massless and massive dispersion relations are found, namely Fermi velocity vF = 1.1 × 10^6 m/s and effective mass m＊ = 0.032 me, where me, is the electron mass, in excellent agreement with theoretical expectations.展开更多
文摘Since opening sizable bandgaps in bilayer graphene （BLG） was proven possible, BLG has attracted considerable attention as a promising high-mobility candidate material for many electronic and optoelectronic applications. However, the bandgaps observed in the transport experiments reported in the literature are far smaller than both the theoretical predictions and the bandgaps extracted from optical measurements. In this study, we investigate the factors preventing the formation of large bandgaps and demonstrate that a -200-meV transport bandgap can be opened in BLG by scaling the gate dielectric and employing a ribbon channel to suppress the percolative transport. This is the largest transport bandgap that has been achieved in BLG to date.
基金Supported by the National Natural Science Foundation of China under Grant Nos.11174214,11204192the NSAF Joint Fund Jointly set up by the National Natural Science Foundation of Chinathe Chinese Academy of Engineering Physics under Grant Nos.U1230201and U1430117
文摘We theoretically investigate the spin filtering transport of double parallel quantum wires(QWs) side-coupled to a grapheme sheet and sandwiched between two ferromagnetic(FM) leads.The dependences of the wire-graphene coupling strength,wire-wire coupling strength,as well as the spin polarization of the ferromagnetic leads are studied.It is found that the wire-graphene coupling strength tends to reduce the current and the wire-wire coupling strength can first reinforce and then decrease the current.The spin polarization strength has an enhanced(identical) effect on the current under the parallel(anti-parallel) alignment of the FM leads,which gives rise to an obvious spin-filter and tunnel magnetoresistance(TMR) effect.Our results suggest that such a theoretical model can stimulate some experimental investigations about the spin-filter devices.
基金supported by the National Natural Science Foundation of China (21978088, 91534202 and 51673063)sponsored by the Program of Shanghai Academic/Technology Research Leader (20XD1433600)+4 种基金the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutes of High Learningthe Basic Research Program of Shanghai (17JC1402300)the Social Development Program of Shanghai (17DZ1200900)the Shanghai City Board of education research and innovation projectthe Fundamental Research Funds for the Central Universities (222201718002)。
文摘Sodium ions(Na+) and ether electrolyte coinserted graphite possesses a considerable volume expansion effect. However, the mechanism fails to clearly explain its stability. In response to this deficiency, the co-inserted reaction is proposed, which is affected by the Lorentz force of the applied electric field under the high-current condition. The Na^(+) ions are separated out, while the ethylene glycol dimethyl ether molecules remain between the graphite layers. This insight provides a reasonable explanation for the extraordinary stability of this material. In situ X-ray diffraction and density functional theory calculations confirm the separation and release of Na+. On the basis of this result, unmodified commercial graphite was stably cycled 6400 times at a current density of up to 10 A g^(-1), and the capacity retention rate was as high as 97.2%. The full battery assembled in the laboratory has a maximum output power of 14,846 W kg^(-1)and an output energy density of 103 W h kg^(-1)(relative to the weight of anodic and cathodic active materials). The new mechanism provides innovative ideas for the design of large-scale energy storage devices.
文摘Electron transport through short, phase-coherent metal-graphene-metal devices occurs via resonant transmission through particle-in-a-box-like states defined by the atomically-sharp metal leads. We study the spectrum of particle-in-a-box states for single- and bi-layer graphene, corresponding to massless and massive two-dimensional （2-D） fermions. The density of states D as a function of particle number n shows the expected relationships D（n） -n1/2 for massless 2-D fermions （electrons in single-layer graphene） and D（n） -constant for massive 2-D fermions （electrons in bi-layer graphene）. The single parameters of the massless and massive dispersion relations are found, namely Fermi velocity vF = 1.1 × 10^6 m/s and effective mass m＊ = 0.032 me, where me, is the electron mass, in excellent agreement with theoretical expectations.
