Lizhu Huang

Epitaxial growth and structural property of graphene on Pt(111)

We report on epitaxial growth of graphene on Pt(111) surface. It was found out that the proportion of different rotational domains varies with growth temperature and the graphene quality can be improved by adjusting both the growth temperature and ethylene exposure. Rippled and unrippled domains of high quality graphene are observed. The adhesive energy and electronic structure of two models, representing rippled and unrippled graphene, are obtained with density functional theory calculation, which shows that the interaction between graphene and Pt(111) surface is very weak and the electronic structure is nearly the same as that of a free standing graphene.

Efficiency exceeding 10% for inverted polymer solar cells with a ZnO/ionic liquid combined cathode interfacial layer

The interlayer inserted between the active layer and ITO has been demonstrated to be crucial for the performance of inverted polymer solar cells (i-PSCs). In this work, we find that ionic liquids (ILs) can significantly enhance the efficiency of i-PSCs. With the ZnO/IL interfacial layer, PTB7-Th : PC71BM i-PSCs can exhibit a champion power conversion efficiency (PCE) of 10.15%, which is among the highest PCEs reported thus far for single-junction bulk heterojunction solar cells through the solution process. The IL layer and ZnO/IL combination layer with low work function, good optical transmittance, improved electron extraction and reduced resistance at the cathode interface have been demonstrated to be excellent and general interfacial layers for i-PSCs.

Synthesis of novel core-shell nanocomposites for fabricating high breakdown voltage ZnO varistors

A novel varistor-composite synthesis for the fabrication of high breakdown voltage ZnO varistors has been successfully developed. It involves coating ZnO nanoparticles with SiO2 through the hydrolysis of tetraethyl orthosilicate (TEOS) and the subsequent coating of additives on the core of the SiO2-coated ZnO particles, producing a double core-shell structure. The effect of the amount of TEOS used on the morphology of the synthesized composites and the microstructure, as well as the electrical property of the sintered samples from the double core-shell composites are fully studied. Such materials, with the appropriate amount of TEOS added (Si4+/Zn2+ = 0.15 moles) enables the superior electrical performance of ZnO varistors: high breakdown voltage (VB = 1123 V mm−1), excellent nonlinear coefficient (α = 42.5) and low leakage current (IL = 8.5 μA), compared with current commercial varistors and the sample from single core-shell composites. The high performance is attributed to the smaller ZnO grain size and perfect additive homogeneity. The SiO2-coating provides a better way to control the varistor microstructure through the formation of a nearly circular distribution of blocky Zn2SiO4 around the ZnO grains.

Observation of an unusual optical switching effect in relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3-Pb(Zr0.53,Ti0.47)O3 transparent ceramics

We present an unusual optical switching effect in relaxor ferroelectrics Pb(Mg1/3Nb2/3)O3-Pb(Zr0.53,Ti0.47)O3 transparent ceramics under strong AC electric fields, which is accompanied by a peculiar dielectric response rarely reported previously and attributed to the disruption of the ferroelectric domain structure by the strong AC field. The results provide further understanding on the domain behaviors under electric fields of the relaxor ferroelectrics and the potential for advancing electro-optic applications.

Large and temperature-independent piezoelectric response in Pb(Mg1/3Nb2/3)O3-BaTiO3-PbTiO3

The temperature dependence of elastic, dielectric, and piezoelectric properties of (65-x)[Pb(Mg1/3Nb2/3)O3]–xBaTiO3-35PbTiO3 ceramics with x=0, 1, 2, 3, and 4 was investigated. Compound with x=2 was found to exhibit a large piezoelectric response (d31=170 pC/N, d33=530 pC/N at 300 K). Particularly, its d31 value was nearly a constant over a temperature range from 185 to 360 K. A broad ferroelectric phase transition tuned by BaTiO3 doping was deduced from the dielectric constant, elastic compliance constant, and Raman spectra. The temperature-stable piezoelectric response was attributed to the counter-balance of contributions from the dielectric and elastic responses.

Enhancement of Piezoelectric Properties of PMN-PT Ceramics at Low Temperatures

The temperature dependence of dielectric, elastic, electromechanical, and piezoelectric properties of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) ceramics near MPB with x = 0.33, 0.35, 0.36, 0.37, and 0.38 was systematically investigated within the temperature range 120–360 K. Compositions of x = 0.37 and 0.38 were found to exhibit temperature-independent piezoelectric properties over a temperature range from 185 to 360 K. The temperature-stable piezoelectric response was attributed to a counter-balance among the dielectric, elastic, and electromechanical responses in a broad ferroelectric phase transition that was revealed from the dielectric constant, elastic compliance constant, and electromechanical coupling factor.

Study of spin-orbit torque induced magnetization switching in synthetic antiferromagnet with ultrathin Ta spacer layer

Spin manipulation in magnetic materials based on spin-orbit torque gives rise to promising families of magnetic memory and logic devices. In the synthetic antiferromagnetic structure of CoFeB/Ta/CoFeB where both CoFeB layers exhibit perpendicular anisotropy, we study the magnetization switching process based on the mechanism of spin-orbit torque and interlayer exchange coupling mediated by a Ta layer. The magnetization switching trigged by in-plane current is achieved. Though the heavy metal Ta layer is ultrathin, the critical current density is 8 × 106–1 × 107 A/cm2 with a bias field of 5–10 mT. Meanwhile, the current induced anti-damping-like field and field-like field are determined by the harmonic lock-in technique. Harmonic results suggest that the generation efficiency of the field-like field is ∼1.24 times that of the anti-damping-like field. The effective spin Hall angle of a Ta layer is derived to be around −0.158. Finally, we examine the magnetic properties of CoFeB layers as a function of temperature which indicates that the magnetic properties of bottom and top CoFeB layers have a close correlation with the interface quality and growth order.Spin manipulation in magnetic materials based on spin-orbit torque gives rise to promising families of magnetic memory and logic devices. In the synthetic antiferromagnetic structure of CoFeB/Ta/CoFeB where both CoFeB layers exhibit perpendicular anisotropy, we study the magnetization switching process based on the mechanism of spin-orbit torque and interlayer exchange coupling mediated by a Ta layer. The magnetization switching trigged by in-plane current is achieved. Though the heavy metal Ta layer is ultrathin, the critical current density is 8 × 106–1 × 107 A/cm2 with a bias field of 5–10 mT. Meanwhile, the current induced anti-damping-like field and field-like field are determined by the harmonic lock-in technique. Harmonic results suggest that the generation efficiency of the field-like field is ∼1.24 times that of the anti-damping-like field. The effective spin Hall angle of a Ta layer is derived to be around −0.158. Finally, we examine the magnetic properties of CoFeB layers as a function of tempe...

Origin of temperature independent piezoelectric coefficient in Pb(Mg1/3Nb2/3)O3-BaTiO3-PbTiO3 ceramics

The temperature dependence of piezoelectric resonance frequency, dielectric, and piezoelectric properties of (65-x)[Pb(Mg1/3Nb2/3)O3]–xBaTiO3-35PbTiO3 (x = 0, 1, 2, 3) ceramics has been investigated. Sample compositions with x = 2 and 3 were found to exhibit a large piezoelectric response. Particularly, d31 value was nearly a constant over a temperature range from 150 to 325 K. A broad ferroelectric phase transition tuned by BaTiO3 ratio in the sample was deduced from the dielectric constant, piezoelectric resonance frequency, and Raman spectra. The temperature dependence of the Raman modes wavenumber positions and intensities provides a clear evidence for the occurrence of the phase transition. The temperature-stable piezoelectric response was attributed to the counter-balance of contributions from the dielectric and elastic responses.The temperature dependence of piezoelectric resonance frequency, dielectric, and piezoelectric properties of (65-x)[Pb(Mg1/3Nb2/3)O3]–xBaTiO3-35PbTiO3 (x = 0, 1, 2, 3) ceramics has been investigated. Sample compositions with x = 2 and 3 were found to exhibit a large piezoelectric response. Particularly, d31 value was nearly a constant over a temperature range from 150 to 325 K. A broad ferroelectric phase transition tuned by BaTiO3 ratio in the sample was deduced from the dielectric constant, piezoelectric resonance frequency, and Raman spectra. The temperature dependence of the Raman modes wavenumber positions and intensities provides a clear evidence for the occurrence of the phase transition. The temperature-stable piezoelectric response was attributed to the counter-balance of contributions from the dielectric and elastic responses.

Relaxor ferroelectric properties of 85PZN–15BT transparent ceramic at low temperatures

Dielectric, hysteresis (P–E) loops and TSDC properties of transparent 85PZN–15BT ceramic over -150–150°C were investigated. The sample was found to exhibit a strong relaxor behavior and a relatively small remanent polarization. TSDC studies showed that there existed an electric field-dependent peak in the p versus T. Such interesting features were attributed to the electric field-induced transition and coexistence of polar nanoregion, long-range ordered polar region and nonpolarizable BZN-rich region.

Microstructure and Electrical Properties of Pb(Mg1/3Nb2/3)O3-BaTiO3-PbTiO3Ceramics

The study of (65-x)Pb(Mg1/3Nb2/3)O3-xBaTiO3-35PbTiO3ceramics where x is 0, 1, 2, 3 and 4 were carried out. Phase structures of the system were examined by X-ray diffraction. The microstructure, piezoelectric and dielectric properties were investigated as a function of BaTiO3concentration, and their relationships were discussed. A dielectric anomaly at just 300 K was observed in the sample with x of 1 which exhibited the largest piezoelectric coefficient among all samples.