J. Yin

Electronic and magnetic properties of zigzag graphene nanoribbon with one edge saturated

We investigated the energetic stability, electronic, and magnetic properties of the zigzag graphene nanoribbons with one edge saturated by two hydrogen atoms, the other edge saturated by one hydrogen atom by using density-functional theory (DFT). The energy of the ferromagnetic semiconductor state is the lowest state for these nanoribbons. The energy difference between the antiferromagnetic states and the ferromagnetic states varies inversely with the nanoribbon width. Both the band gaps and the magnetic moments in the zigzag graphene nanoribbons with one edge saturated are larger than those of zigzag graphene nanoribbons.

Ferroelectric and dielectric properties of ferroelectromagnet Pb(Fe1/2Nb1/2)O3 ceramics and thin films

The ferroelectric and dielectric properties of ferroelectromagnet Pb(Fe1/2Nb1/2)O3 (PFN) ceramics and thin films prepared by pulsed laser deposition (PLD) have been investigated systematically. PFN ceramics experienced a para-ferroelectric transition and a para-antiferromagnetic transition at 380 K and 145 K, respectively. At room temperature, it has an electrical remnant polarization of 11.5 μC/cm2 and a coercive field of 4.04 kV/cm. The dielectric behaviors show characteristics of diffusive phase transition at a wide temperature range around 380 K. Anomalies in the dielectric constant and loss tangent have been observed near the Neel temperature of 145 K, indicating a coupling between the ferroelectric and antiferromagnetic orders in PFN ceramics. At room temperature, the PFN films exhibited a remnant electric polarization of 7.4 μC/cm2, a coercive field of 10.5 kV/cm, and a dielectric constant of 486 at frequency of 10 kHz, indicating their potential applications in memory devices.

Large polarization and enhanced magnetic properties in BiFeO3 ceramic prepared by high-pressure synthesis

The BiFeO3 ceramics were prepared by sol-gel method (BFO-1) and high-pressure synthesis (BFO-2). X-ray diffraction showed that these ceramics are almost of single phase. It is difficult to observe a ferroelectric loop of BFO-1 even at an electric field of 6kV∕cm. Compared to BFO-1, the high-pressure synthesized one has higher resistivity, higher density, and better crystallization. Under an applied electric field of 120kV∕cm, the values of remanent polarization and the coercive field are 46μC∕cm2 and 73kV∕cm, respectively. At room temperature, a magnetic hysteresis loop with enhanced magnetization can be observed in BFO-2.

Effects of the electroforming polarity on bipolar resistive switching characteristics of SrTiO3―δ films

The effects of the electroforming polarity on the bipolar resistive switching characteristics in SrTiO3−δ thin films have been investigated. The conduction mechanisms of high resistance state and low resistance state are Poole–Frenkel emission and tunneling, respectively. The temperature dependences of the resistance at high and low resistance state are both semiconductorlike. The impact of the polarity of the electroforming voltage on the resistive switching mechanism and the distribution of defects was discussed. A simple model describing the combination of bulk and the interface effect was proposed to explain the resistive switching in this material.

Ferromagnetic and antiferromagnetic properties of the semihydrogenated SiC sheet

The intriguing electronic and magnetic properties of the semihydrogenated SiC sheet are investigated by means of the first-principles calculations. The semihydrogenated SiC sheet exhibits diverse electronic and magnetic properties: a ferromagnetic semiconductor when Si atoms are hydrogenated, while an antiferromagnetic semiconductor with C atoms hydrogenated. The semihydrogenated SiC sheet with the C atoms hydrogenated is found to be more stable than the sheet with the Si atoms hydrogenated. Thus, controlling the hydrogenation on the different atom sites can precisely modulate the electronic and magnetic properties of the semihydrogenated SiC sheet, which endues the semihydrogenated SiC sheet great potential applications in the future functional nanodevices.

Studies of metal–ferroelectric–GaN structures

A GaN-based metal–insulator–semiconductor (MIS) structure has been fabricated by using ferroelectric Pb(Zr0.53Ti0.47)O3 instead of conventional oxides as insulator gate. Because of the polarization field provided by ferroelectric and the high dielectric constant of ferroelectric insulator, the capacitance–voltage characteristics of GaN-based metal–ferroelectric–semiconductor (MFS) structures are markedly improved compared to those of other previously studied GaN MIS structures. The GaN active layer in MFS structures can reach inversion just under the bias of smaller than 5 V, which is the generally applied voltage used in semiconductor-based integrated circuits. The surface carrier concentration of the GaN layer in the MFS structure is decreased by one order compared with the background carrier concentration. The GaN MFS structures look promising for the practical application of GaN-based field effect transistors.

Enhanced fatigue and retention properties of Pb(Ta0.05Zr0.48Ti0.47)O3 films using La0.25Sr0.75CoO3 top and bottom electrodes

Ferroelectric perovskite Pb(Ta0.05Zr0.48Ti0.47)O3 thin-film capacitors having LaxSr1−xCoO3 bottom and top electrodes have been prepared on Pt/TiO2/SiO2/Si(001) substrates by pulsed-laser deposition. It is found that La0.25Sr0.75CoO3 bottom electrodes with cubic structure strongly promote the formation of (001) texture of PTZT films and improve the fatigue and retention properties of the capacitors. The polarization of the La0.25Sr0.75CoO3/Pb(Ta0.05Zr0.48Ti0.47)O3/La0.25Sr0.75CoO3 capacitors with a Pb(Ta0.05Zr0.48Ti0.47)O3 thickness of 400 nm were subjected to no degradation after 1×1010 switching cycles at an applied voltage 5 V with a frequency of 1 MHz. The capacitor retains more than 92.6% of its polarization after a retention time up to 105u200as. The possible microstructural background responsible for the excellent fatigue and retention properties was discussed.

The effect of acoustic phonon scattering on the carrier mobility in the semiconducting zigzag single wall carbon nanotubes

Carrier mobilities of the semiconducting single wall carbon nanotubes (SWCNTs) have been studied by using the first-principles calculations with the deformation potential approximation, which only considers the scattering by the longitudinal acoustic phonons based on the adapting Bardeen–Shockley theory [J. Bardeen and W. Shockley, Phys. Rev. 80, 72 (1950)] to one-dimensional case. From the band structures of the semiconducting SWCNTs, we calculated the effective masses, the stretching modulus, the deformation potential constants. We demonstrated that the calculated intrinsic carrier mobility can reach 106u2002cm2/Vu2009s at room temperature, and the carrier mobilities of the semiconducting SWCNTs show the intriguing alternating behavior.

The epitaxial growth of wurtzite ZnO films on LiNbO3 (0001) substrates

Abstract ZnO epitaxial films were deposited on LiNbO 3 (0xa00xa00xa01) substrates by pulsed laser deposition. The smaller lattice misfit (−8.5%) between ZnO along 〈1 0 1 0〉− direction and LiNbO 3 (0xa00xa00xa01) along 〈1 1 2 0〉− direction, as compared with that in the case of normally used sapphire (0xa00xa00xa01) substrates, favored the epitaxial growth of ZnO films. The transmittance spectra of ZnO films deposited in vacuum after annealed in pure oxygen show a sharp absorption edge at 375.6xa0nm (E g =3.31 eV ) .

The Resistive Switching Mechanism of Ag / SrTiO3 / Pt Memory Cells

Reproducible and reliable bipolar resistive switching was obtained from Ag/SrTiO 3 (STO)/Pt memory cells. The current-voltage characteristic of the Ag/STO/Pt cells with a positive voltage applied to the Pt electrode and the results of X-ray photoelectron spectroscopy imply that the electrochemical reaction and the diffusion of Ag + ions play a critical role in the resistive switching effect. The temperature dependence of the on-state resistance, combined with the time dependence of the on- and off-state resistances under a constant voltage, provides further evidence that the resistive switching mechanism should be ascribed to the formation and dissolution of the metallic Ag nanofilaments.