Influence of post-annealing treatment on the structure properties of ZnO films

We review case studies of diffusion in nanocrystalline ceramics, i.e. polycrystalline non-metallic materials with average grain sizes typically in the range from 5 to 50 nm. The experimental methods applied are, on the one hand, tracer diffusion or conductivity methods which are sensitive to macroscopic transport, and, on the other hand, NMR techniques which, complementarily to the previous ones, give access to microscopic diffusion parameters like atomic hopping rates and jump barrier heights. In all cases the diffusion properties of the samples, whether single-phase systems or composites, are dominated by their grain boundaries and interfacial regions, respectively. In principle, all experimental techniques allow one to discriminate between contributions to the diffusion from the crystalline grains and those from the interfacial regions. Corresponding examples are presented for SIMS and impedance measurements on oxygen conductors. NMR studies for various nanocrystalline lithium ion conductors reveal that two lithium species with different diffusivities are present. Comparison with the coarse grained counterparts shows that the slower ions are located inside the crystallites and the faster ones in the structurally disordered interfacial regions. Investigations on composite materials exhibit phenomena which can be explained by the percolation of fast diffusion pathways being formed by the interfaces between the two components.

https://iopscience.iop.org/article/10.1088/0953-8984/15/30/202/pdf

Diffusion and ionic conduction in nanocrystalline ceramics

Grain boundary segregation, chemical ordering and stability of nanocrystalline alloys: Atomistic computer simulations in the Ni–W system

Poly(styrene butylacrylate) latex/nano-ZnO composites were prepared by blending poly(styrene butylacrylate) latex with a water slurry of nano-ZnO particles, and the effects of certain parameters, such as particle size, dispersant type, dispersing time and others, on the dispersibility, mechanical properties, ultraviolet (UV) shielding and near infrared (NIR) shielding were investigated with transmission electron microscopy (TEM), an Instron testing machine, dynamic mechanical analysis and ultraviolet-visible-near infrared (UV-VIS-NIR) spectrophotometry. TEM observation showed that dispersants with long chains are better than those with short chains at enhancing the dispersibility of nano-ZnO particles in a matrix; extending dispersing time also improves the dispersibility of nano-ZnO particles in a matrix. Instron tests showed that the nanocomposite polymers embedded with nano-ZnO particles had much higher tensile strength than the corresponding composite polymers with micro-ZnO particles. As the nano-ZnO content increased, the temperature of glass transition (Tg) of the nanocomposite polymer embedded with 60 nm ZnO particles first increased then decreased, but 100 nm ZnO and micro-ZnO particles seemed to have no influence on the Tg of the composite polymers. The better dispersibility of nano-ZnO particles resulted in higher Tg values. Increasing nano-ZnO content or dispersibility could enhance the UV shielding properties of the nanocomposite polymers, and 60 nm ZnO particles could more effectively shield UV rays than 100 nm ZnO particles. Micro-ZnO particles basically had no effect on the UV absorbance of the composite polymers. A blue-shift phenomenon was observed at 365 nm when nano-ZnO particles were present in the nanocomposite polymers. NIR analysis indicated that as nano-ZnO content increased, the NIR shielding of the nanocomposite polymers increased, but the NIR shielding properties seemed to be more influenced by particle size than by the nano-effect. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1923–1931, 2003

Preparation and characterization of poly(styrene butylacrylate) latex/nano‐ZnO nanocomposites

SnO2 thin films were grown on p-InP (100) substrates by using radio-frequency magnetron sputtering at low temperature. Transmission electron microscopy (TEM) and electron diffraction pattern measurements showed that these SnO2 thin films were nanocrystalline. The capacitance–voltage measurements at room temperature showed that the type and the carrier concentration of the nominally undoped SnO2 film were n type and approximately 1.62×1016 cm−3, respectively. Raman scattering measurements showed that the grain sizes of the nanocrystalline films were below 10 nm, which was in reasonable agreement with the result obtained from the high-resolution TEM measurements. Photoluminescence measurements showed a broad peak below the band-to-band emission. These results can help improve the understanding of SnO2 nanocrystalline films grown on p-InP (100) substrates for applications in high-sensitivity gas sensors.

Microstructural, electrical, and optical properties of SnO2 nanocrystalline thin films grown on InP (100) substrates for applications as gas sensor devices

Undoped and Bi-doped nanocrystallineZnO was prepared by the inert gas condensation method. Samples of different grain sizes were obtained by annealing treatments at various temperatures. The dc and acelectrical conductivity of undoped and Bi-doped nanocrystallineZnO was investigated as a function of grain size. In dcmeasurements,nanocrystallineZnO of small grain size ( 40 nm) did not exhibit time dependent conduction but exhibited ohmic behavior. This difference in dc conductivity is discussed in terms of the grain size dependence of the average trap density. A small amount of Bi dopant had no measurableeffect on the electrical behavior in the small grain size range but resulted in higher specimen resistance in the large grain size range. acelectrical properties were characterized by impedance spectroscopy. The impedance spectra of undoped and Bi-doped samples of small grain sizes were rather similar and exhibited two semicircles. In contrast, the impedance spectra of samples with larger grain sizes were single, depressed circles with much higher impedances for the Bi-doped sample, in agreement with the dcmeasurements. A consistent assignment of the contributions due to bulk conductivity, porosity, and grain boundary effects to the overall impedance is presented.

Grain size-dependent electrical properties of nanocrystalline ZnO

Anomalous Space‐Charge Limited Currents in Nanocrystalline ZnO

This study describes the deposition and recording of surface charges on polyimide with a scanning Kelvin probe microscope. The apparatus used here works with a needle tip whose movements and oscillations are controlled and driven by an electromechanical system. To deposit charges the probe tip touches down to the insulator surface and with an external voltage the contact charging is performed. After the charge deposition the same system works as a vibrating scanning Kelvin probe to measure the charged surface area. This Kelvin probe system has the advantage of a controlled tip oscillation compared to a conventional AFM probe with a free oscillating cantilever. Electrostatic forces cannot stick the tip to the surface. In an additional experiment the charges deposited around an electrode as known from Lichtenberg figures are detected.

H. Kliem

Papers

Grain size-dependent electrical properties of nanocrystalline ZnO

Anomalous Space‐Charge Limited Currents in Nanocrystalline ZnO

Contact Charging and Surface Charge Measurement Using a Scanning Kelvin Technique