弛豫铁电体因其卓越的介电和压电特性,在传感器、光电器件、高密度存储器、类脑计算等领域展现出广泛的应用潜力。然而,纳米尺度超薄膜的弛豫特性研究受到严重漏电流的限制,基于Sawyer-Tower电路和Positive-Up-Negative-Down(PUND)脉冲...弛豫铁电体因其卓越的介电和压电特性,在传感器、光电器件、高密度存储器、类脑计算等领域展现出广泛的应用潜力。然而,纳米尺度超薄膜的弛豫特性研究受到严重漏电流的限制,基于Sawyer-Tower电路和Positive-Up-Negative-Down(PUND)脉冲波形的测试方法存在显著挑战。本研究提出了一种基于压电力显微镜(Piezoresponse Force Microscopy, PFM)的测试方法,来研究纳米尺度弛豫薄膜的极化特性。以Pb(Mg,Nb)O_(3)-PbTiO_(3)(PMN-PT)超薄膜为例,比较了不同厚度的PMN-PT弛豫薄膜与铁电Pb(Zr,Ti)O_(3)(PZT)薄膜在双频追踪PFM(DART-PFM)测量中On-field和Off-field两种模式下的极化回滞行为。通过调节PFM回线测量中的用于极化读出的交流信号电压振幅,系统表征了纳米厚度PMN-PT薄膜的弛豫特性。进一步对不同面内应变和厚度的PMN-PT超薄膜进行PFM测试,发现在较大压缩应变(3.19%)下,弛豫特性被抑制,表现出显著的铁电特性,并观测到铁电-弛豫转变的临界厚度。这些实验结果验证了所提出测试方法的有效性。本研究不仅为超薄膜弛豫特性的探索提供了一种新的表征方法,也为理解铁电材料的弛豫极化行为奠定了基础,推动了弛豫铁电材料在低维电子学器件中的应用。展开更多
A series of researches were carried out for the soil samples in the Pearl River Delta under the action of consolidation loads,such as the quantitative analyses of the pore scale,shape and size distributions of micro-s...A series of researches were carried out for the soil samples in the Pearl River Delta under the action of consolidation loads,such as the quantitative analyses of the pore scale,shape and size distributions of micro-structure units,with an environmental scanning electron microscope (ESEM),a mercury intrusion analyzer and a mineral diffractometer. The experimental results show that the consolidation pressures remarkably change the pore sizes and distribution characteristics of the silt,thus changing its compressibility and permeability. This can be proved by the fact that,in the earlier stage with a consolidation pressure of p<200 kPa,the pore sizes are greater and the compressibility and permeability coefficients are larger. However,they rapidly decrease with the increase in consolidation pressure. And in the later stage with a consolidation pressure of p>200 kPa,the pore sizes are smaller and the compressibility and permeability coefficients are less. Therefore,the empirical formulas of compression coefficient and permeability coefficient vs consolidation load and average pore diameter are deduced.展开更多
文摘弛豫铁电体因其卓越的介电和压电特性,在传感器、光电器件、高密度存储器、类脑计算等领域展现出广泛的应用潜力。然而,纳米尺度超薄膜的弛豫特性研究受到严重漏电流的限制,基于Sawyer-Tower电路和Positive-Up-Negative-Down(PUND)脉冲波形的测试方法存在显著挑战。本研究提出了一种基于压电力显微镜(Piezoresponse Force Microscopy, PFM)的测试方法,来研究纳米尺度弛豫薄膜的极化特性。以Pb(Mg,Nb)O_(3)-PbTiO_(3)(PMN-PT)超薄膜为例,比较了不同厚度的PMN-PT弛豫薄膜与铁电Pb(Zr,Ti)O_(3)(PZT)薄膜在双频追踪PFM(DART-PFM)测量中On-field和Off-field两种模式下的极化回滞行为。通过调节PFM回线测量中的用于极化读出的交流信号电压振幅,系统表征了纳米厚度PMN-PT薄膜的弛豫特性。进一步对不同面内应变和厚度的PMN-PT超薄膜进行PFM测试,发现在较大压缩应变(3.19%)下,弛豫特性被抑制,表现出显著的铁电特性,并观测到铁电-弛豫转变的临界厚度。这些实验结果验证了所提出测试方法的有效性。本研究不仅为超薄膜弛豫特性的探索提供了一种新的表征方法,也为理解铁电材料的弛豫极化行为奠定了基础,推动了弛豫铁电材料在低维电子学器件中的应用。
文摘采用脉冲激光沉积技术(pulsed laser deposition,PLD),在Pt/Ti/SiO_2/Si基片上制备了La_(0.1)Bi_(0.9)FeO_3(BFO),Bi_(0.5)(Na_(0.85)K_(0.15))0.5TiO_3(BNKT)和BFO/BNKT纳米复合薄膜。结果表明,复合薄膜的铁电特性比单层的BFO、BNKT薄膜有所增强。利用压电力显微镜(piezoresponse force microscopy,PFM)观察到了铁电畴。由于畴结构内部矫顽力分布不均匀,导致极化反转随时间改变,疲劳测试结果也证实了该结论。随着转换周期的增加,极化随之增强。运用PFM测量了纳米级的压电响应,同样证实了BFO/BNKT复合薄膜中的畴反转现象。
基金Project(2008ZA11) supported by State Key Laboratory of Subtropical Building Science in South China University of Technology, ChinaProject(20080430815) supported by China Postdoctoral Science Foundation
文摘A series of researches were carried out for the soil samples in the Pearl River Delta under the action of consolidation loads,such as the quantitative analyses of the pore scale,shape and size distributions of micro-structure units,with an environmental scanning electron microscope (ESEM),a mercury intrusion analyzer and a mineral diffractometer. The experimental results show that the consolidation pressures remarkably change the pore sizes and distribution characteristics of the silt,thus changing its compressibility and permeability. This can be proved by the fact that,in the earlier stage with a consolidation pressure of p<200 kPa,the pore sizes are greater and the compressibility and permeability coefficients are larger. However,they rapidly decrease with the increase in consolidation pressure. And in the later stage with a consolidation pressure of p>200 kPa,the pore sizes are smaller and the compressibility and permeability coefficients are less. Therefore,the empirical formulas of compression coefficient and permeability coefficient vs consolidation load and average pore diameter are deduced.
