Changes In Interface Properties Research Articles

Depiction of a non-aqueous ionic liquid surfactant-free microemulsion by dielectric relaxation spectroscopy

A dielectric relaxation was observed at approximately 700 MHz in the surfactant-free microemulsion which is composed of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), ethanol and toluene. The measured frequency was between 1 MHz and 3 GHz. Two inflection points (22.39 and 31.09 wt%) on the curve of the dielectric parameters vs weight fraction of IL give the phase boundaries between IL/O and B.C., B.C. and O/IL sub-regions. The permittivity of the frequency at the beginning of the relaxation phenomenon and the maximum of the derivative of dc conductivity both give 31.09 wt% as the percolation threshold. Both frequency dependences of permittivity and loss angle provide the critical exponent u = 0.72, which suggest that a static percolation occurs in the microemulsion near the critical threshold. This conclusion is also supported by the scaling dependence of dc conductivity on IL weight fraction. The results of phase parameters obtained by Hanai theory show that: the dielectric relaxation of this system is proved to be caused by the interfacial polarization, which indicates that dispersed particles indeed exist in this surfactant-free microemulsion; in the IL/O sub-region, disperse particle not only contains IL and TX-100, but also includes oil molecule; and for the O/IL sub-region the continuous phase should be the IL/ethanol binary solvent rather than the pure IL; the main reasons for the occurring of the static percolation in this system may be the large volume fraction of dispersed particle and the existent of IL molecule. The substitution of ethanol for surfactant causes change in interface properties but no change in percolation mechanism, indicating that ethanol indeed distributes at the interface and molecular details at the interface do not determine the mechanism of percolation

The Preparation, Characterization, Mechanical and Antibacterial Properties of GO-ZnO Nanocomposites with a Poly(l-lactide)-Modified Surface.

Graphene oxide (GO) was employed for the preparation of GO-zinc oxide (ZnO). The hydroxyl group on the surface was exploited to trigger the l-lactide ring-opening polymerization. A composite material with poly(l-lactide) (PLLA) chains grafted to the GO-ZnO surface, GO-ZnO-PLLA, was prepared. The results demonstrated that the employed method allowed one-step, rapid grafting of PLLA to the GO-ZnO surface. The chemical structure of the GO surface was altered by improved dispersion of GO-ZnO in organic solvents, thus enhancing the GO-ZnO dispersion in the PLLA matrix and the interface bonding with PLLA. Subsequently, composite films, GO-ZnO-PLLA and GO-ZnO-PLLA/PLLA, were prepared. The changes in interface properties and mechanical properties were studied. Furthermore, the antibacterial performance of nano-ZnO was investigated.

Comparison of implant stability measurement devices for bone-anchored hearing aid systems

Statement of problemThe success of implants for bone-anchored hearing aids (BAHA) relies on proper osseointegration at the bone-implant interface. Clinical evaluation of implant stability is important in prescribing loading, identifying the risk of failure, and monitoring the long-term health of the implant. PurposeThe purpose of this in vitro study was to evaluate 2 measurement systems for BAHA implant stability: the most commonly used, Osstell implant stability quotient (ISQ), and a newly developed advance system for implant stability testing (ASIST). Material and methodsBAHA implants (Oticon Medical Ponto and Cochlear BAHA Connect systems) were installed in plastic materials with adhesive to simulate implants integrated in bone with varying levels of interface stiffness. Different lengths of BAHA abutments were used with each implant specimen, and stability measurements were obtained with both the Osstell ISQ and the ASIST systems. The measurement systems were evaluated in terms of sensitivity to differences in interface stiffness and the effect of abutment length on the stability measurement. Repeated measures ANOVA followed by post hoc t tests were used for the comparisons with a Bonferroni adjusted alpha value of .05/15 = .003 to control for potential type 1 errors. ResultsChanging the abutment length of a single implant installation had minimal effect on the ASIST stability coefficient, whereas large variations were observed in the Osstell implant stability quotient (ISQ). The Osstell showed a clear relationship of decreasing ISQ with increasing abutment length for both the Oticon Medical and the Cochlear implant systems. Both the ASIST and the Osstell were found to be sensitive to changes in interface properties, with the ASIST being more sensitive to these changes. ConclusionsThe ASIST system is more sensitive to changes in interface properties and shows smaller variation because of changes in abutment length than the Osstell ISQ system.

Changing interfaces: Photoluminescent ZnO nanoparticle powders in different aqueous environments

We transformed vapor phase grown ZnO nanoparticle powders into aqueous ZnO nanoparticle dispersions and studied the impact of associated microstructure and interface property changes on their spectroscopic properties. With photoluminescence (PL) spectroscopy, we probed oxygen interstitials Oi2− in the near surface region and tracked their specific PL emission response at hvEM=2.1eV during the controlled conversion of the solid–vacuum into the solid–liquid interface. While oxygen adsorption via the gas phase does affect the intensity of the PL emission bands, the O2 contact with ZnO nanoparticles across the solid–liquid interface does not. Moreover, we found that the near band edge emission feature at hvEM=3.2eV gains relative intensity with regard to the PL emission features in the visible light region.Searching for potential PL indicators that are specific to early stages of particle dissolution, we addressed for aqueous ZnO nanoparticle dispersions the effect of formic acid adsorption. In the absence of related spectroscopic features, we were able to consistently track ZnO nanoparticle dissolution and the concomitant formation of solvated Zinc formate species by means of PL and FT-IR spectroscopy, dynamic light scattering, and zeta potential measurements. For a more consistent and robust assessment of nanoparticle properties in different continuous phases, we discuss characterization challenges and potential pitfalls that arise upon replacing the solid–gas with the solid–liquid interface.

Assembling ellipsoidal particles at fluid interfaces using switchable dipolar capillary interactions.

How to dynamically tune an assembly of anisotropic colloidal particles adsorbed at fluid-fluid interfaces using dipolar capillary interactions is demonstrated. A previously discovered first-order phase transition is exploited and it is shown how to spontaneously turn off these dipolar capillary interactions by exceeding a critical field strength, providing unprecedented control of the bottom-up fabrication of soft materials.

Changes in Interface Properties of TCO/a-Si:H Layer by Zn Buffer Layer in Silicon Heterojunction Solar Cells

In this study, we inserted a Zn buffer layer into a AZO/p-type a-si:H layer interface in order to lower the contact resistance of the interface. For the Zn layer, the deposition was conducted at 5 nm, 7 nm and 10 nm using the rf-magnetron sputtering method. The results were compared to that of the AZO film to discuss the possibility of the Zn layer being used as a transparent conductive oxide thin film for application in the silicon heterojunction solar cell. We used the rf-magnetron sputtering method to fabricate Al 2 wt.% of Al-doped ZnO (AZO) film as a transparent conductive oxide (TCO). We analyzed the electro-optical properties of the ZnO as well as the interface properties of the AZO/p-type a-Si:H layer. After inserting a buffer layer into the AZO/p-type a-Si:H layers to enhance the interface properties, we measured the contact resistance of the layers using a CTLM (circular transmission line model) pattern, the depth profile of the layers using AES (auger electron spectroscopy), and the changes in the properties of the AZO thin film through heat treatment. We investigated the effects of the interface properties of the AZO/p-type a-Si:H layer on the characteristics of silicon heterojunction solar cells and the way to improve the interface properties. When depositing AZO thin film on a-Si layer, oxygen atoms are diffused from the AZO thin film towards the a-Si layer. Thus, the characteristics of the solar cells deteriorate due to the created oxide film. While a diffusion of Zn occurs toward the a-Si in the case of AZO used as TCO, the diffusion of In occurs toward a-Si in the case of ITO used as TCO.

Cellulose-Based Liquid Crystalline Photoresponsive Films with Tunable Surface Wettability

We report on a new type of liquid crystalline cellulosic films with light controllable reversible wettability. The films are prepared from a thermotropic cellulose derivative functionalized with azo-containing groups. These groups exhibit dynamic changes in interfacial properties in response to UV irradiation. The UV irradiation induces trans-to-cis isomerization in the azobenzene moiety, which causes a conformational change in the upper molecular layers of the thin films. These changes originate a hydrophobic to comparatively hydrophilic transformation of the surface. The reversible wettability of the surface results from the cis/trans photo and thermal isomerization. The UV-vis absorption spectra, as well as contact angle measurements with UV irradiation, clearly support the understanding of the phenomenon. This type of surface design enables the amplification of molecular level conformational transitions to macroscopic changes in interface properties using the means of isomerism. This opens new opportunities in surface engineering using eco-friendly cellulose manipulation.

Effects of interfacial stability between electron transporting layer and cathode on the degradation process of organic light-emitting diodes

The authors have demonstrated that the increase of electron injection barrier height between tris(8-hydroxyquinoline)aluminum (Alq3) and LiF∕Al cathode is one of the most critical parameters to determine the reliability of organic light-emitting diode with the typical structure of indium tin oxide/N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl) benzidine/Alq3∕LiF∕Al. The electrical properties of several devices (hole only, electron only, and integrated double-layered devices) have been measured in the function of operating time to analyze the bulk and interface property changes. Bulk properties of trap energy and mobility in an organic layer have been estimated by using trap-charge-limited currents and transient electroluminescence measurements.

Treatment of Polishing Wastewater from Semiconductor Manufacturer by Dispersed Air Flotation

Treatment of chemical mechanical polishing wastewater containing nanosized silica from semiconductor industry by dispersed air flotation was investigated. Very effective removal of particles from wastewater was found when cationic surfactant, cetyltrimethyl ammonium bromide (CTAB), was used as a collector. The flotation efficiency decreased slightly under a pH of 4.5. The zeta potential increased with a increasing concentration of CTAB, and flocculation of particles by CTAB was found. It is proposed that both the change of interface properties and the aggregation of particles contributed to flotation removal of particles. Longer reaction time and higher dosage were needed when n-dodecyl amine chloride (DAC) was used as a collector, owing to its relatively weak adsorption. The flotation efficiency increased with increasing DAC concentration. The improved flotation efficiency at pH of 10.0 was probably due to the formation of DAC precipitate.

Mobility improvement after HCl post-deposition cleaning of high-/spl kappa/ dielectric: a potential issue in wet etching of dual metal gate Process technology

The effect of deionized water and dilute hydrochloric acid, 500:1 (HCl) post-Hf-silicate deposition cleaning on the device characteristics of Hf-silicate MOSFETs have been investigated. The results suggest that a significant improvement in mobility and equivalent oxide thickness scaling can be obtained using HCl post-treatment in comparison to control and H/sub 2/O post-treated devices. The enhancement in bulk trapping immunity has been attributed to the reduced charge trapping in the bulk high-/spl kappa/ layers, whereas no apparent change in interface properties could be observed. The effect of the post-deposition cleaning might have important implications on the wet etching of gate metals in dual-metal-gate technology.

Decarboxylation of 6-nitrobenzisoxazole-3-carboxylate as kinetic probe for piperazinium-based cationic micelles

A new class of cationic surfactants containing the heterocyclic piperazinium ring in their covalent structure was prepared; cetyldialkylpiperazinium halides, CRPX, with alkyl=Me (CMPX), Et (CEPX), n-Pr (CPPX), and with halide=Br and Cl. They were characterized by measures of critical micellar concentration, cmc, and ionization degree, α, and also by use of the decarboxylation of 6-nitrobenzisoxazole-3-carboxylate as a kinetic probe to investigate the properties of the microinterface they provide in aqueous solutions. The pseudophase kinetic treatment fails to fit the data at high [surfactant], which show anomalies with abrupt increase in k obs, especially for CEPX and CPPX. Data can be fitted up to [surfactant] ca. 0.1 M, and 0.2 M in some cases. Compared with cetyltrialkylammonium halides, values of k′ M indicate a water-richer microenvironment and less important interface property changes with increasing head group bulk. The reaction could be studied both in the presence and in the absence of NaOH; comparison shows that NaOH affects only the shape of the kinetic profile at low [surfactant], without affecting the microenvironment provided by mature micelles.

Spectroscopic ellipsometry of oxides and interfaces thermally formed on (100)Si and (111)Si

Thin oxides and their interface, formed by dry oxidation of hydrogen-enriched (100)Si and (111)Si substrates via r.f. hydrogen plasma exposure at 850°C, are studied by multiple-angle spectroscopic ellipsometry in the range 280–632.8 nm. Comparison with the standard oxidation of RCA cleaned Si shows that on plasma treated Si the initial oxide growth rate is higher and a thicker interface is formed with a different composition. Various processes involving hydrogen are suggested to be responsible for changes in interface properties.

Reactive ion etching induced damage with gas mixtures CHF3/O2 and SF6/O2

In this work, reaction ion etching (RIE) induced damage and its impact on device performance have been characterized and evaluated using a variety of characterization techniques for two technologically important gas mixtures: CHF3/O2 for selective oxide etching, and SF6/O2 for selective poly Si or crystalline Si etching. Current–voltage characteristics of Al/Si Schottky diodes fabricated on the RIE exposed Si surface reveal significant barrier height shifts for the CHF3/O2 process while showing little change for the SF6/O2 processes. Carrier generation lifetime is degraded by at least one order of magnitude, with the degradation due to CHF3/O2 processes being more severe. Scanning electron microscopy and Auger electron spectroscopy support the idea that the defects that give rise to the altered electrical behavior are most likely Si lattice damage instead of metal contamination and/or morphologic modification. Rapid thermal annealing of the CHF3/O2 etched samples has a negative effect on I–V recovery precluding simple application of RTA for removing RIE damage. In the RIE exposed oxide, the two distinctively different gas mixtures induce very similar C–V and Si/SiO2 interface property changes, suggesting that the high energy photons present in the plasma glow are the most probable source of damage in the oxide.