The effect of surface roughness on the response of the QCM has been considered, both theoretically and experimentally. A new theoretical approach to the description of the effect of roughness on the response of the QCM is proposed that accounts for the multiscale nature of roughness. Performing experiments in liquids having a wide range of viscosity and density made it possible to understand, for the first time, what characteristics of roughness influence the QCM experiments. The most important conclusion of the current study is that, to understand the experimental data, one has to take into account at least two types of roughness: slight and strong. We found that measurements of the frequency shift observed are not sufficient for the interpretations of the experimental data observed, and a full analysis of the impedance spectrum is called for.

The electroplating of silver and copper has been studied using an electrochemical quartz crystal microbalance (EQCM). Deposition of Ag on Ag follows the expected behavior. For deposition of Cu, the linearity between frequency shift and added mass is maintained, but the slope is smaller (in absolute value). This is attributed to the formation of Cu ϩ ions, which diffuse in part into the bulk of the solution, without being further reduced. Pourbaix-type diagrams have been developed, showing the regions of thermodynamic stability of the cuprous ions in aqueous solutions, in the absence of complexing agents. In the early stages of deposition of both metals on a gold surface, large deviations of the frequency shift from its calculated value are observed. For Ag, this deviation is due to the difference in the interaction of Au and Ag with the solvent. When Cu is deposited on gold, the deviation is also due to stress in the deposit. This stress, resulting from the difference in crystal parameters between gold and copper, can be relaxed partially at open circuit at room temperature.

The quartz crystal microbalance has been used to study adsorption from the gas phase onto a gold surface. The commercial device used in our measurements has a resolution of 0.15 Hz, corresponding to 1.8 ng/cm* 12 345.Changes of frequency are caused by a change of mass, but factors such as the total pressure, the viscosity, the density, the surface roughness, the temperature, and the thermal conductivity of the medium may also cause a shift in frequency. A new method, which we call the supporting gas method (SGM), was developed to eliminate the effect of these factors on the frequency of the crystal. In this method the substance being studied is mixed with a large excess of an inert gas (Ar was mostly used, but H2 and He yielded identical results). In the course of measurement, the total pressure is maintained constant, while the partial pressure of the substance being studied is varied. The adsorption isotherms of a number of substances were determined. A comparison between benzene and pyridine showed that the former is adsorbed flat on the surface, while the latter is attached to it in an upright orientation, through the nitrogen atom. The saturated homologues of these two compounds, cyclohexane and piperidine, respectively, do not exhibit monolayer adsorption. Water, methanol, and 1-propanol are all adsorbed, occupying the same number of sites per molecule on the surface. It may be concluded that these compounds are attached to the surface through the OH group, with the other atoms facing away. The SGM can be a powerful tool in the study of submonolayer adsorption from the gas phase. The sensitivity is high, on the order of a few percent of a monolayer, and can be increased further. The stability is excellent, and seems to be determined by the parameters of the system as a whole, and not by the inherent properties of the quartz crystal microbalance itself. There are several sources of error which can lead to misinterpretation of the results. These can be reduced to an insignificant level by making measurements at a constant total pressure, employing an inert gas in large excess.

low-pressure flat flames doped with iron pentacarbonyl IJFeIJCO) 5 ) were used to investigate the initial steps towards the formation of iron-oxide nanoparticles. The particles were extracted from the flame using a molecular beam sampling probe and the mass flow rate of condensed material was measured by a quartz crystal microbalance (QCM). It was observed that particles are already formed on the cold side of the flame, and vanish quickly once they pass through the flame front. To understand the process and assess the perturbations caused by the sampling probe, spatially resolved laser-based measurements of temperature, Fe and FeO concentration as well as molecular-beam sampling with particle mass spectrometry (PMS) were carried out. Numerical flow simulations of the synthesis flames, the reactor, and the sampling were performed and the simulations confirmed the experimental findings of very early particle formation. The detailed knowledge of the perturbation caused by invasive probing enabled further insight into the iron-oxide nanoparticle formation mechanism. From the results it is concluded that neither Fe atoms nor FeO molecules belong to the growth species of iron-oxide nanoparticles from flame synthesis. 6930 | CrystEngComm, 2015, 17, 6930-6939This journal is

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The response of the electrochemical quartz crystal microbalance (EQCM) was studied in 0.1 M HClO4,KNO3 and KOH. The gold coating on the crystal served as the working electrode, and the frequency was determined as a function potential in the double‐layer region. Frequency shifts up to −5 Hz were observed, even though the ions of the electrolytes employed are not specifically adsorbed and there is no faradaic reaction which could lead to the formation of adsorbed species through charge‐transfer. The added weight which would cause a similar shift in frequency in our experimental setup is ca. 60 ng/cm2, which is equivalent to about a monolayer of chlorine atoms adsorbed on the surface. Thus, elucidation of the origin of this effect is essential for the proper use of the EQCM in the submonolayer region. The effects observed are due to the surface excess of ions in the diffuse double layer. A model was developed in which the liquid in a thin layer near the surface has a higher viscosity than in the bulk, because of the high concentration of ions and the high electrical field in this region. The value of this viscosity can neither be calculated independently nor measured experimentally, since the liquid in this region is charged (electroneutrality is maintained across the interface but not on each side separately). Using the viscosity of the film as a parameter, we were able model the experimental behavior.

The admittance of the quartz crystal microbalance (QCM) was used to study properties of a liquidlike layer (LLL) at the gold/frozen electrolyte interface. It was shown that in a certain range of temperature, below the melting point, the resonance of the QCM is readily detectable suggesting the presence of a LLL. Treatment of the experimental data within the framework of the models proposed here allowed us to conclude that, depending on the temperature, the LLL exists in two states: at temperatures above -4 °C, it can be considered as a viscous liquid, while at lower temperatures down to -7 °C, it behaves as a viscoelastic medium. Data handling enabled us to evaluate the temperature dependence of the thickness of the LLL, which increases from a few tens of nanometers at -7 °C up to ca. 200 nm at -1 °C in the systems studied here (aqueous solutions of 0.1 M Na 2 SO 4 and 0.1 M HClO 4 ).

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