Electro-mechanical sensing in freestanding monolayered gold nanoparticle membranes (original) (raw)
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Applied Physics Letters, 2010
The use of nanoparticle materials in the manufacture of electronic polymer memory devices is on the rise. Organic memory devices are fabricated by depositing a blend of organic polymer, small organic molecules, and nanoparticles between two metal electrodes. The primary aim is to produce devices that exhibit two distinct electrical conductance states when control voltages are applied. By retaining the states when power is removed can be viewed as the realization of nonvolatile memory. In this letter, an attempt is made to further understand the conundrums that scholars in this field are currently facing, with questions about the nanoparticle charging mechanism being investigated.
Physical Chemistry Chemical Physics, 2006
In this article, the effect of interparticle interactions of 4.63 nm sized monolayer protected gold clusters (Au MPCs) during quantized double layer (QDL) charging has been investigated using electrochemical techniques. Voltammetry and scanning tunneling microscopy have been used to compare their electron transfer behavior. Furthermore, since the QDL process is diffusion controlled, the diffusion coefficient values have been estimated at various charge steps using two independent electroanalytical techniques, viz. chronoamperometry and impedance. These results show that higher core charge facilitates higher diffusion coefficient values, and indicate that repulsive interactions dominate for charged MPCs compared to those of its neutral analogue, which are mainly attractive in nature. Additionally, the electron transfer rate constants at various charge steps have been estimated from the impedance results, showing comparatively faster electron transfer rate at higher charge states.
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Applied Physics Letters, 2014
A unique positive-to-negative transition of temperature coefficient of conductance (TCC) was observed in self-assembled close-packed Au nanoparticle (AuNP) arrays. The transition of TCC can be interpreted properly with a diffusive hopping model, in which the Coulomb charging energy E a plays a significant role. Two parameters of AuNP arrays, the nearest neighboring number and the particle core size, have been varied to tune E a . Our data show that the positive-to-negative transitions of TCC are relevant to both parameters, which confirms the validity of the diffusive hopping model. V C 2014 AIP Publishing LLC. [http://dx.
Analytical Chemistry, 1999
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International Journal of …, 2011
Gold nanoparticles (GNPs) offer a great possibility for biomedical application, not only to pharmaceutics approaches, but also as novel diagnostic and therapeutic approaches. One of the important concerns is about their safety in clinical applications. Nanoparticle size has been shown to be an extremely important parameter affecting the nanoparticle uptake and cellular internalization. The aim of the present study was to investigate the dielectric constant, electrical conductivity and relaxation time of different GNP sizes. The electrical parameters were measured in the frequency range of 20 Hz up to 1 MHz using a WAYNE KERR precision component analyzer. The sample cell has two squared platinum black electrodes each having an area of 1 × 1 cm 2 with an inner electrode distance of 1 cm. For a dielectric material placed between two parallel plate capacitor, the measured value of capacitance (C) and resistance (R) were used to calculate the real ( ε ′ ) and imaginary part (ε ′′ ) of the complex permittivity * j ε ε ε ′ ′′ = − , in addition to calculating the conductivity (σ σ σ σ ) and the relaxation time ( τ τ τ τ). The sizes of GNPs were calculated from the images taken by the transmission electron microscope (TEM). It became evident that relatively simple methods can be used to obtain the populations of different GNP sizes, which allow simultaneous detection of several targets. The presented dielectric data indicates that GNPs have strong dielectric dispersion corresponding to the alpha relaxation region in the frequency range of 20 Hz to 100 kHz which was identified as anomalous frequency dispersion. The measured conductivity values decreased with increasing GNPs size. Moreover, at high frequencies, the conductivity rapidly increased for all the examined GNPs size. The GNPs show a relaxation process. The relaxation time decreased with increasing GNPs size and was found to be 2.5, 3.5 and 4 ms for 10, 20 and 50 nm GNP size, respectively. A rapid decrease in the dielectric constant may be attributed to the tendency of dipoles in the GNPs to orient themselves in the direction of the applied field in the lowfrequency range. However, in the high-frequency range, the dipoles will hardly be able to orient themselves in the direction of the applied field and hence, the value of the dielectric constant is nearly constant. The relaxation time may be attributed to increase in the localized charges distribution within the medium which was confirmed by the conductivity data. This study demonstrates that the dielectric, electrical conductivity and relaxation time values decreased with increasing the GNPs size, e.g. these changes are particle-size dependent. This study suggests that the increase in dielectric constant, electrical conductivity and relaxation time observed with the smaller 10 and 20 nm GNPs compared with 50 nm GNPs may be used as important risk factors for bioaccumulation and toxicity of the smaller GNPs. Thus additional histological and histochemical experiments are needed to confirm this hypothesis.
Aerosol Science and Technology, 2015
Theoretical and experimental analyses of the steady state, bipolar diffusion charge distribution on nanoparticles are reviewed. This charge distribution plays a critical role in electrical mobility measurements of nanoparticle size distribution functions, where it is approximated via empirical regression equations. While the regression approach has been broadly successful, there remain several unresolved issues related to charge distribution calculations. Specifically, research to date has not revealed a method to reliably calculate nanoparticle-ion collision rates in the presence of strong attractive potentials, charge distribution predictions do not routinely consider the mass and (electrical) mobility distributions of the charging ions, and calculation approaches applicable to both spherical and nonspherical particles have not been compared to experimental data. In light of these issues, we examine the steady-state bipolar charge distribution on gold nanospheres and gold nanorods via tandem differential mobility analysis (TDMA). We compare measurements to regression equations as well as to Brownian Dynamics (BD) simulations, which take ion mobility and mass distributions as inputs. These distributions were measured using a DMA coupled to a mass spectrometer. Both regression equations and BD simulations are found to agree reasonably well with measurements in air, and we find that particle mobility diameter has a much greater influence on charging than particle morphology. Results support the use of BD calculations to predict bipolar charge distributions when ion properties are known. Nevertheless, our work supports continued use of regression equations when such information is not available.
Journal of Nanoparticle Research, 2014
We performed admittance measurements to investigate the particle size dependence of the conductivity of gold nanoparticle (Diameters: 6-100 nm) colloids in electrophoresis microchip in the frequency range of 0.03-1.00 MHz. The admittance was measured with two electrodes capacitively coupled to the colloid contained in a microchip capillary channel. The imaginary and real components of the admittance showed low-frequency dispersion associated with the polarization of the nanoparticles induced by the AC electric field. This was evident from the linear dependence of the process relaxation time as a function of the square of the radius of the nanoparticle.