Equivalent circuit modeling of the ac response of Pd-ZrO2 granular metal thin films using impedance spectroscopy
Equivalent circuit modeling of the ac response of Pd-ZrO2 granular metal thin films using impedance spectroscopy
复制标题
DOI：
10.1088/0022-3727/48/33/335306
复制
发表时间：
2015-08-26
影响因子：
3.4
通讯作者：
Labarta, Amilcar
中科院分区：
文献类型：
--
作者：
Bakkali, Hicham;Dominguez, Manuel;Labarta, Amilcar
交流响应的介电制度的薄膜组成的Pd纳米粒子嵌入在ZrO 2绝缘矩阵，通过共溅射制造，从阻抗谱测量（11 Hz-2 MHz）在30-290 K的温度范围内获得。的响应被拟合到一个等效电路模型，其参数进行了评估，假设，作为一个后果的双峰粒径分布的Pd颗粒，出现两种机制。在低频时，由于两个竞争路径，类似于并联RC电路的第一元件主导响应。其中之一是与大多数最小的Pd颗粒（尺寸类似于2 nm），这使得直流隧穿骨干的样品之间的热激活隧穿电导。另一个是与较大的Pd颗粒（尺寸> 5 nm）之间的电容路径相关的电导。在低温和中频（类似于1 kHz）下，较大颗粒之间的捷径过程连接了最初在低频下与主链隔离的区域。这些区域由位于两个较大粒子周围的一些额外的较小粒子填充，被隔离，因为较大粒子的间隔对于隧穿电流来说太大。一旦连接到主干，电流也可以通过所谓的热激活辅助隧穿电阻路径流过它们，产生等效电路的第二元件（并联RLC元件）。在高温下，热能将短路过程的开始移动到高频，因此仅观察到第一个元素。考虑到这些结果，控制颗粒尺寸分布可能有助于调整频率，在该频率下隧穿电导主导这些颗粒金属的交流响应。
The ac response in the dielectric regime of thin films consisting of Pd nanoparticles embedded in a ZrO2 insulating matrix, fabricated by co-sputtering, was obtained from impedance spectroscopy measurements (11 Hz-2 MHz) in the temperature range 30-290 K. The response was fitted to an equivalent circuit model whose parameters were evaluated assuming that, as a consequence of the bimodal size distribution of the Pd particles, two mechanisms appear. At low frequencies, a first element similar to a parallel RC circuit dominates the response, due to two competing paths. One of them is associated with thermally-activated tunneling conductance among most of the smallest Pd particles (size similar to 2 nm), which make up the dc tunneling backbone of the sample. The other one is related to the conductance associated with the capacitive paths among larger Pd particles (size > 5 nm). At low temperature and intermediate frequencies (similar to 1 kHz), a shortcut process between the larger particles connects regions initially isolated from the backbone at low frequencies. These regions, populated by some additional smaller particles located around two bigger particles, were isolated because the bigger particles separation is too large for the tunneling current. Once connected to the backbone, current may also flow through them by means of the so-called thermally-activated assisted tunneling resistive paths, yielding the second element of the equivalent circuit (a parallel RLC element). At high temperature, the thermal energy shifts the onset of the shortcut process high frequencies and, thus, only the first element is observed. Considering these results, controlling the particle size distribution could be helpful to tune up the frequency at which tunneling conductance dominates the ac response of these granular metals.