Au Grains Research Articles

Supergene gold transformations of the placer gold deposits from the Gamba district in northern Cameroon: Implications for secondary and nano-particulate gold formations

The northern part of Cameroon is a Sudanese or Sudano-Sahelian type characterized mainly by a dry climate, a significant landscape position, and distance from the primary gold (Au) sources, giving the occasion to explore the study of complex supergene Au transformations. This study on the biogeochemical transformation of Au in Cameroon will expand understanding of this process and provide advantageous results for Au recovery from materials that are ultimately regarded as waste. In this study, placer Au particles were collected from four individual sites, Djaba, Bigbal, Bougma, and Mayo Salah, and analyzed using a scanning electron microscope (SEM), electron probe microanalysis (EPMA) and LA-ICP-MS Time of Flight (ToF) to observe nanometer-sized Au grain morphologies, the Au mobility and spatial association between Au and related major and minor elements by element distributions in Au particles, respectively. The results from the examination of Au samples across all sampling sites show that Au particles are formed by the binary Au/Ag alloys and that the formation of Au nano- and micro-particles is associated with Au/Ag dissolution and Au re-precipitation. The abundant nano- and micro-particles of Au morphotypes within the cavities of primary Au grains across all the sampling locations were associated with the polymorphic layers formed by clays, iron-oxides, and silicate minerals. The nano- and micro-particles of Au overgrow as colloids and crystalline phases of triangular, spherical, hexagonal, and octahedral platelet aggregates of bacteriomorphic Au and were indicative of biogeochemical transformation. The high Au concentrations in the rim suggest the dissolution of Ag and Cu involving Au mobility identified in placer Au grains across the individual sites. Hence, the minor elements, such as Ag and Cu, occur in solid solution in the Au cores, while trace elements, such as Si, Al, Fe, Cr, Ti, Ga, Ni, Pb, Mn, V, and As, form impurities or micro inclusions in the rim of native gold which was interpreted as evidence of Au mobility. Furthermore, the Au grains are commonly associated with pyrite, chalcopyrite, bornite, and galena. This can only be attributed to the hypogene orogenic precipitation environment, implying that Au grains were transported from primary sources. Overall, the Au particle transformation and mobility of placer Au highlighted in this study was a good indicator for understanding biogeochemical mechanisms affecting gold particles in the northern Cameroon supergene environments.

Anti-friction gold-based stretchable electronics enabled by interfacial diffusion-induced cohesion

Stretchable electronics that prevalently adopt chemically inert metals as sensing layers and interconnect wires have enabled high-fidelity signal acquisition for on-skin applications. However, the weak interfacial interaction between inert metals and elastomers limit the tolerance of the device to external friction interferences. Here, we report an interfacial diffusion-induced cohesion strategy that utilizes hydrophilic polyurethane to wet gold (Au) grains and render them wrapped by strong hydrogen bonding, resulting in a high interfacial binding strength of 1017.6 N/m. By further constructing a nanoscale rough configuration of the polyurethane (RPU), the binding strength of Au-RPU device increases to 1243.4 N/m, which is 100 and 4 times higher than that of conventional polydimethylsiloxane and styrene-ethylene-butylene-styrene-based devices, respectively. The stretchable Au-RPU device can remain good electrical conductivity after 1022 frictions at 130 kPa pressure, and reliably record high-fidelity electrophysiological signals. Furthermore, an anti-friction pressure sensor array is constructed based on Au-RPU interconnect wires, demonstrating a superior mechanical durability for concentrated large pressure acquisition. This chemical modification-free approach of interfacial strengthening for chemically inert metal-based stretchable electronics is promising for three-dimensional integration and on-chip interconnection.

Micro- to nanoscale textures of gold in arsenopyrite and scorodite from the As-Au-Bi assemblage of Drenjak locality (Serbia)

Arsenopyrite and pyrite are important carriers of Au that is present in the form of microscopic and “invisible” gold. Such gold can be expected to be released upon the process of oxidation of these sulfides. In studied gold mineralization at Drenjak, related to the granitoids of the Oligocene-Miocene Kopaonik Ore District, the main arsenopyrite-pyrite-(bismuthinite) sulfide assemblage was formed in the quartz bodies and partly replaced by scorodite (FeAsO4·2H2O) and Bi-arsenate. With only up to 5 ppm of gold recorded by LA-ICP-MS, aforementioned sulfide minerals are here practically free from lattice-bound gold. Native gold is present in the mineralization, generally ranging in grain size from 20 µm down to the nanoparticles, as revealed by TEM. It is mainly hosted by arsenopyrite and scorodite. In arsenopyrite, gold is polycrystalline and consists of nanocrystallites 20–30 nm in size. It was deposited after arsenopyrite, healing its cavities and microcracks, often associated with native bismuth and bismuthinite. The abundance of gold and Bi minerals correlates with the presence of scorodite. Two types of gold are present in scorodite and Bi arsenate: i) prevailing relict Au grains retained after arsenopyrite oxidation, ii) colloidal-like gold co-precipitated with the arsenates. Based on our observations, we additionally present and discuss indications of low-temperature hydrothermal origin of scorodite, formerly known only as a weathering product

Neoproterozoic potassic andesitic and lamprophyric rocks in the tupanci area, southernomost Brazil: Petrology and associated mineralization

Au and sulfide mineralizations occur in the Sul-Rio-Grandense Shield, and important occurrences of these metals are reported and attributed to the Lavras do Sul Shoshonitic Association (LSSA). Several authors point to a significant participation of andesitic and lamprophyric rocks in the formation of these deposits. The Tupanci area has the presence of andesites and lamprophyres, stratigraphically correlated to LSSA volcanic rocks (Hilário Formation), representing the northernmost exposures of this magmatism. The LSSA is one of the most complete Neoproterozoic Shoshonitic associations (ca. 592-590 Ma) in southern Brazil, containing plutonic, volcanic and hypabyssal rocks, related to the post-collisional stage of the Brasiliano/Pan-African orogeny. The andesitic rocks of the Tupanci area occur in the form of the lava flows, overlayed by volcanoclastic deposits, product of the reworking of the volcanic unit. Lamprophyres occur in the form of dykes, with N-NW direction, which are intruded in rocks of the metamorphic basement and in andesitic lava flows, being texturally separated and classified as spessartite and lamprophyric lapilli-tuff. The singular occurrence of the lamprophyric lapilli-tuff stands out, is analogous to Kimberley-type pyroclastic kimberlitic intrusions, depicting explosive manifestations linked to LSSA lamprophyres. The andesites and lamprophyres that ocour in Tupanci area show characteristics of high-K calc-alkaline or shoshonitic rocks, evidenced by LILE and LREE enrichment, negative Ti and Nb anomalies, plus positive Pb anomalies and the absence of Eu anomalies. These attributes reinforce the relationship of andesitic and lamprophyric rocks with related LSSA rocks. The presence of Au and Pt grains in the matrix of lamprophyric lapilli-tuff, highlights the economic importance of these rocks for the mineral occurrences in the region, where future studies can better define the metallogenetic potential for the rocks of the Tupanci area.

Spiked nanorosette: A novel zinc oxide-gold textured nanostructure for impedance biosensing of target DNA signatures.

The creation of nanostructure is profound for the generation of nanobiosensors in several medical diagnosis. Here, we employed an aqueous hydrothermal route using Zinc-oxide (ZnO) and Gold (Au), which under optimal conditions formed an ultra-crystalline rose-like nanostructure textured with nanowires on the surface, coined as "spiked nanorosette." The spiked nanorosette structures was further characterized to possess crystallites of ZnO and Au grains with average sizes of 27.60 and 32.33nm, respectively. The intensity for both ZnO (002) and Au (111) planes of the nanocomposite was inferred to be controlled by fine-tuning the percentage of Au nanoparticles doped in the ZnO/Au matrix, as referred by X-ray diffraction analysis. The formation of ZnO/Au-hybrid nanorosettes were additionally verified by the distinct corresponding peaks from photoluminescence and X-ray photoelectron spectroscopy, supported by electrical validations. The biorecognition properties of the spiked nanorosettes were also examined using custom targeted and non-target DNA sequences. The DNA targeting capabilities of the nanostructures were analyzed by Fourier Transform Infrared and electrochemical impedance spectroscopy. The fabricated nanowire-embedded nanorosette exhibited a detection limit at the lower picomolar range of 1×10-12M, with high selectivity, stability and reproducibility and good linearity, under optimal conditions. Impedance-based techniques are more sensitive to the detection of nucleic acid molecule whereas this novel spiked nanorosette demonstrate promising attributes as excellent nanostructures for nanobiosensor developments and their potential future application for nucleic-acids or disease diagnostics.

Direct atomic layer deposition of ultra-thin Al2O3 and HfO2 films on gold-supported monolayer MoS2

In this paper, the atomic layer deposition (ALD) of ultra-thin films (<4 nm) of Al2O3 and HfO2 on gold-supported monolayer (1L) MoS2 is investigated, providing an insight on the mechanisms ruling the nucleation in the early stages of the ALD process. A preliminary multiscale characterization of large area 1L-MoS2 exfoliated on sputter-grown Au/Ni films demonstrated: (i) a tensile strain (from 0.1 to 0.3%) and p-type doping (from 1 × 1012 to 4 × 1012 cm−2) distribution at micro-scale; (ii) an almost conformal MoS2 membrane to the Au grains topography, with some locally detached regions, indicating the occurrence of strain variations at the nanoscale; (iii) atomic scale variability (from ∼ 4.0 to ∼ 4.5 Å) in the Mo-Au atomic distances was detected, depending on the local configuration of Au nanograins. Ab initio DFT calculations of a free-standing MoS2 layer and a simplified MoS2/Au(111) interface model showed a significant influence of the Au substrate on the MoS2 energy band structure, whereas small differences were accounted for the adsorption of H2O, TMA (co-reactant, and Al-precursor, respectively) molecules, and a slight improved adsorption was predicted for TDMAHf (Hf-precursor). This suggests a crucial role of nanoscale morphological effects, such as the experimentally observed local curvature and strain of the MoS2 membrane, in the enhanced physisorption of the precursors. Afterwards the nucleation and growth of Al2O3 an HfO2 films onto 1L-MoS2/Au was investigated in detail, by monitoring the surface coverage as a function of the number (N) of ALD cycles, with N from 10 to 120. At low N values, a slower growth rate of the initially formed nuclei was observed for HfO2, probably due to the bulky nature of the TDMAHf precursor as compared to TMA. On the other hand, the formation of continuous films was obtained in both cases for N > 80 ALD cycles, corresponding to ∼ 3.6 nm Al2O3 and ∼ 3.1 nm HfO2. Current mapping on these ultra-thin films by conductive-AFM showed, for the same applied bias, a uniform insulating behavior of Al2O3 and the occurrence of few localized breakdown spots in the case of HfO2, associated to a less compact films regions. Finally, an increase of the 1L-MoS2 tensile strain was observed by Raman mapping after encapsulation with both high-κ films, accompanied by a reduction in the PL intensity, explained by the effects of strain and the higher effective dielectric constant of the surrounding environment.

Fine gold grains inside the limonite in the supergene Shangmanggang gold deposit, SW China: Implications for gold mobilization and mineral exploration

Supergene Au deposits have attracted economical attention because of their increased grades and more environmentally leaching. Understanding the supergene processes responsible for the Au mobilization in the surface environments is important to determine the location of concealed Au deposits. In this study, we recognized and sampled three Au-rich spatial zones in the Shangmanggang deposit in southwestern China: the hypogene, semi-oxidized, and red clay zones. The microscopic and chemical analyses of Au-bearing minerals show that (i) gold is mostly present as lattice-bound Au+ in the pyrite within the hypogene zone and (ii) numerous fine Au grains, mostly 100 × n nm to 1 × n μm in size, with a granular, spindle, or irregular shape, have been widely observed in the semi-oxidized and red clay zones, mainly inside the fissures and cavities of limonite. When exposed to an oxidizing environment, primary pyrite in the hypogene zone is gradually oxidized into limonite. With S diffusing out of the limonite, the Au in pyrite becomes rapidly activated and also diffuses into the environment as Au(S2O3)23− with a neutral or weakly alkaline pH in karst terrains. When meteoric water containing Au(S2O3)23− infiltrated the regolith profile, Au+ was reduced to elemental Au and precipitated in the limonite cavities and fissures due to their difference in the pH with the soil solution, which is an important insight into the formation of Au grains inside the limonite in the regolith. These results could provide a reference to better understand Au mobilization in the immature laterite in SW China, as well as the exploration of a potential hypogene Au deposit covered by the lateritic profile.

An explanation for the effect of Au surface finish on the quality of sintered Ag-Au joints

As an environmentally friendly interconnection material in power electronics, silver paste is widely used in gold surface finish. To explain the delamination at the Ag-Au interface and clarify the mechanism of Ag-Au interconnection, the bonding properties of sintered silver joints on different gold-plated substrates are studied. It was concluded that the effect of grain size on Ag-Au diffusion is greater than that of grain boundary type. The gold-plating layer with larger grains provides fewer grain boundaries, which inhibits the rapid diffusion of Ag atoms due to high angle grain boundaries. In addition, to investigate the effects of Au grain boundary misorientation on Ag-Au interdiffusion, molecular dynamics simulation is carried out on the sintering process. It is not found that high angle grain boundary of Au layer promotes the diffusion of Ag atoms during pre-drying. However, in the sintering stage, the MSD (mean square displacement) of Ag atoms in the substitute-model with high angle grain boundaries is about 4 times that of with low angle grain boundaries. It is proved that owing to lots of high angle grain boundaries in the gold-plated substrate, the diffusion of Ag atoms is faster in the sintering stage.

Controllable fabrication of Au-nanoprotrusion arrays as a platform for the materials design and characterization

Au-nanoprotrusions (AuNPs) were fabricated on a gold substrate using obliquely incident Ar+ ions with a simultaneous supply of carbon at room temperature. The sputter erosion rate was kept almost constant at 49 nm/min, while the deposition rate of carbon ranged from 1.2 to 0.6 nm/min. Scanning electron microscopy (SEM) observation revealed the variation in the number density and shape of the AuNPs ranging from slender needles to cones with a large apex angle, depending on the carbon deposition rate. Transmission electron microscopy (TEM) demonstrated that the slender needles were characterized by the bi-metal like structure of the large Au grain-rich phase and amorphous carbon phase with a dispersion of fine Au nanoparticles, while the conical structures consisted of Au grains with an amorphous carbon cap region on top. Those structures were selectively prepared, depending on the application. Li-C nanocomposite films deposited on conical structures, for instance, were readily observed cross-sectionally by TEM without any post treatment, revealing the instantaneous formation of a solid electrolyte interphase (SEI) after only 2 charge-discharge cycles in the cyclic voltammetry (CV) measurement. Thus, AuNPs are promising as a platform for the materials design and characterization in atomic dimensions.

Metallogenesis of the Bakoshi-Kundila gold deposit in northern West Nigerian Subshield: Insights from pyrite chemical and sulfur isotopic compositions and zircon U-Pb geochronology

The Bakoshi-Kundila gold deposit, located in northern West Nigerian Subshield, in the southern trans-Saharan Orogenic Belt of West Africa, is a recent discovery and artisanally mined deposit. Like other Nigerian gold deposits, the mechanism and timing of gold precipitation remains unknown. In this study, we report the results of an integrated study of pyrite chemical and isotopic compositions and U-Pb on zircon geochronology to determine the gold precipitation mechanisms, fluid sources, and formation age of the gold mineralization. Two mineralization stages are recognized: (i) the Au-pyrite-quartz vein-type mineralization, including two generations of pyrite referred to as Py1a and Py1b, and (ii) wall rock disseminated-type Au-pyrite mineralization, comprising three pyrite types, Py2a, Py2b, and Py3. Py1 is Au-rich and As-poor pyrite and contain lattice-bound Au (Au+), nanoparticle Au (Au0), and native Au grains adsorbed on Py1b surface. Associated with Py1 are Ag-Te-Au bearing minerals. In contrast, Py2 and Py3 are As-rich and are less in Au; they contain only lattice-bound Au. Py1 grains have higher contents of Ag, Pb, Bi, Sb, Tl, and Cu which correlate with Au compared to those from Py2 and Py3. Py1 generations has lower δ34SV-CDT from –5.43 to –2.11 ‰ compared to the higher values of +3.63 to +5.47 ‰ obtained for the Py2 and Py3. These sulfur isotopes data are within the δ34S values of 0 ± 5 ‰ of the magmatic reservoir. U-Pb on zircon from Au-pyrite-quartz vein stage yielded older ages of 644.5 ± 2.2 Ma and 681.5 ± 1.8 Ma, compared to younger age of 606. 4 ± 1.8 Ma yielded by zircon grains from wall rock-type mineralization. Additionally, zircon grains from Au-bearing Tourmalinite yielded ages of 679 ± 1.3 Ma and 609.6 ± 7.1 Ma. We propose that Au mineralization at the Bakoshi-Kundila occurred during two periods in the Neoproterozoic: (i) an early ∼ 682 Ma (Cryogenian), possibly related to the emplacement of 683 Ma Yettiti granite and (ii) a second-stage Au disseminated in wall rock of granites and might have experienced 606–610 Ma Ediacaran metamorphism during the late tectonic events in West Nigerian Subshield.

Conversion of the anomalous skin effect to the normal one in thin-film metallic microwave systems

The main morphology parameters of microstrip Au/i-GaAs coplanar microwave transmission lines (CTL) with length l W influenced on its skin depth resistance R wide of δ and inductivity L are defined at frequencies f > 10 GHz. Due to the sizes of Au grains formed CTL d x < 130 nm, surface roughness h ≥ 400 nm and fractal character of its lateral distribution in CTL plane, the features in electron scattering processes arise and lead to the formation of significant size effects in local approximation. Necessary condition l ball < d x ≪ δ for transition from anomalous skin effect to normal skin effect start up owing to limited grain size d x ≪ δ. Moreover, in local approximation nonlinear dependence of R from l W is provided by fractal geometry of relief and grain lateral distribution. Nonlinear dependence of L from l W is provided by not only fractal features of CTL two-dimensional surface but fractal features of three-dimensional Au grain distribution over skin depth wide.

Analysis of Grain Morphology, Mineral Composition, and Ore Grade on Gold Placer Deposits in Bantimurung, Pangkep Regency, South Sulawesi, Indonesia

The information through social media shows that there is quite an intense placer mining activity by local residents in the Bantimurung area, Tondong Tallasa District, Pangkep Regency. This study as a preliminary research aims to determine the grain morphology characteristics of mineral composition and metal grade in gold placer deposits in the study area. The data collected were eight samples. The collected samples were prepared into thin section, polished and observed using a microscope to identify the mineral composition and grain morphology. The grades of Au metal and its associated metals consisting of Ag, Zn, Pb, and Cu in the placer samples were analyzed by the AAS method. Petrography shows abundant of quartz, plagioclase, biotite and pyroxene minerals it might be indication of mineralization of epithermal. Ore petrography shows pyrite present along the river, silver is also found quite a lot along the river. Meanwhile, covellite, magnetite, sphalerite, and garnet were found only slightly at the sampling station this mineral composition indicates that the source of the placer deposits was epithermal. The grain morphology of the thin-section observation shows that quartz dominant has a high sphericity with character of roundness tends to be very angular to sub-rounded from upstream to downstream of the river. Plagioclase tends to have sub rounded roundness and high sphericity. Biotite tends to have a high sphericity with roundness from upstream to downstream is very angular, then angular, then sub-rounded. Pyroxenes tend to have high sphericity with very angular and angular roundness. Au content is directly proportional to Cu and inversely proportional to Zn, Pb, and Ag. Statistically Au affects the content of Cu by 50.97%. It can be concluded that Au is genetically associated with Cu, however Au grains that were still attached to the mineral and had not been separated from other minerals so that it could not be seen visually. This can also indicate that the source of this placer deposit is not far from the study site. Au grade corelated with stream sediment types it is 97,86 ppm for channel bar and 94,16 ppm for point bar, based on this we conclude the downstream has higher grade of Au compare to the upstream.

Magnetic and Optical Properties of Au-Co Solid Solution and Phase-Separated Thin Films and Nanoparticles.

The chemical composition and morphology of AuxCo1-x thin films and nanoparticles are controlled via a combination of cosputtering, pulsed laser-induced dewetting (PLiD), and annealing, leading to tunable magnetic and optical properties. Regardless of chemical composition, the as-deposited thin films and as-PLiD nanoparticles are found to possess a face-centered cubic (FCC) AuxCo1-x solid-solution crystal structure. Annealing results in large phase-separated grains of Au and Co in both the thin films and nanostructures for all chemical compositions. The magnetic and optical properties are characterized via vibrating sample magnetometry (VSM), ellipsometry, optical transmission spectroscopy, and electron energy loss spectroscopy (EELS). Despite the exceptionally high magnetic anisotropy inherent to Co, the presence of sufficient Au (72 atom %) in the AuxCo1-x solid solution results in superparamagnetic thin films. Among the as-PLiD nanoparticle samples, an increased Co composition leads to a departure from traditional ferromagnetism in favor of wasp-waisted hysteresis caused by magnetic vortices. Phase separation resulting from annealing leads to ferromagnetism for all compositions in both the thin films and nanoparticles. The optical properties of AuxCo1-x nanostructures are also largely influenced by the chemical morphology, where the AuxCo1-x intermixed solid solution has significantly damped plasmonic performance relative to pure Au and comparable to pure Co. Phase separation greatly enhances the quality factor, optical absorption, and electron energy loss spectroscopy (EELS) signatures. The enhancement of the localized surface plasmon resonances (LSPRs) scales with the reduction in Co composition, despite EELS evidence that excitation of the Co portions of a nanoparticle can provide a similar, and in some instances enhanced, LSPR resonance compared to Au. This behavior, however, is seemingly limited to the LSPR dipole mode, while higher-order modes are greatly damped by a Co aloof position. This observed magneto-plasmonic functionality and tunability could be applicable in biomedicine, namely, cancer therapeutics.

Sensing Alzheimer’s Disease Utilizing Au Electrode by Controlling Nanorestructuring

This paper reports the development of Alzheimer’s disease (AD) sensor through early detection of amyloid-beta (Aβ) (1–42) using simple nanorestructuring of Au sheet plate by oxidation-reduction cycle (ORC) via the electrochemical system. The topology of Au substrates was enhanced through the roughening and Au grains grown by a simple ORC technique in aqueous solutions containing 0.1 mol/L KCl electrolytes. The roughened substrate was then functionalized with the highly specific antibody β-amyloid Aβ (1–28) through HS-PEG-NHS modification, which enabled effective and direct detection of Aβ (1–42) peptide. The efficacy of the ORC method had been exhibited in the polished Au surface by approximately 15% larger electro-active sites compared to the polished Au without ORC. The ORC polished structure demonstrated a rapid, accurate, precise, reproducible, and highly sensitive detection of Aβ (1–42) peptide with a low detection limit of 10.4 fg/mL and a wide linear range of 10−2 to 106 pg/mL. The proposed structure had been proven to have potential as an early-stage Alzheimer’s disease (AD) detection platform with low-cost fabrication and ease of operation.

Early and direct detection of bacterial signaling molecules through one-pot Au electrodeposition onto paper-based 3D SERS substrates

The rapid detection of bacterial metabolites responsible for cell communication is important for the early diagnosis of bacterial infection and treatment with appropriate antibiotics. Surface-enhanced Raman spectroscopy (SERS) has provided amplified molecular fingerprints, serving as one of the most promising nondestructive and label-free direct detection methods. However, direct analysis of complex bacterial cultures using the conventional SERS approach is difficult. Here, we design a new paper-based 3D SERS substrate and establish a facile one-pot Au electrodeposition protocol to directly detect pyocyanin, a signaling molecule of Pseudomonas aeruginosa, secreted in the culture medium, without pretreatment steps. During one-pot Au electrodeposition in the presence of an Au precursor and culture medium, the bacterial pathogen molecule (i.e., pyocyanin) is captured in the interstitial voids of the 3D hydrogel matrix among growing Au grains, resulting in high amplification of the Raman signal intensity. Because the hydrogel skin excludes macromolecules (i.e., proteins) in the culture medium, thereby maintaining an uncontaminated surface, our approach achieves the direct and rapid detection of pyocyanin in a complex bacteria culture sample without any purification steps. Therefore, the pyocyanin concentration during bacterial culturing is easily and directly monitored, which is important for the early diagnosis of infection and in-depth studies of bacterial cell communication.

Reirradiation Using 198Au Grain Brachytherapy for Recurrent Oral Cancer Cases Previously Treated by Definitive Radiotherapy.

We investigated treatment outcomes and complications during reirradiation of patients with oral cancers. Six patients who received definitive radiotherapy for oral cancer as the initial treatment and brachytherapy for recurrence were included. Local control and overall survival rates, soft tissue and mandibular complications, and tooth extraction were investigated. The five-year local control and overall survival rates were 83.3% and 100%, respectively. The occurrence rate of grade 2 soft tissue and mandible complications was 33.3%, and the primary sites were the buccal mucosa and the floor of mouth. The positions of the extracted tooth in the two cases were adjacent to the tumor, and one case developed grade 2 complication of the mandible. During recurrence of the buccal mucosa and the floor of mouth cancers, reirradiation should be avoided considering mandibular complications. To avoid reirradiation-related complications, tooth extraction near the radiation field should be avoided.

Electronic Structure and Stacking Arrangement of Tungsten Disulfide at the Gold Contact.

There is an intensive effort to control the nature of attractive interactions between ultrathin semiconductors and metals and to understand its impact on the electronic properties at the junction. Here, we present a photoelectron spectroscopy study on the interface between WS2 films and gold, with a focus on the occupied electronic states near the Brillouin zone center (i.e., the Γ point). To delineate the spectra of WS2 supported on crystalline Au from the suspended WS2, we employ a microscopy approach and a tailored sample structure, in which the WS2/Au junction forms a semi-epitaxial relationship and is adjacent to suspended WS2 regions. The photoelectron spectra, as a function of WS2 thickness, display the expected splitting of the highest occupied states at the Γ point. In multilayer WS2, we discovered variations in the electronic states that spatially align with the crystalline grains of underlying Au. Corroborated by density functional theory calculations, we attribute the electronic structure variations to stacking variations within the WS2 films. We propose that strong interactions exerted by Au grains cause slippage of the interfacing WS2 layer with respect to the rest of the WS2 film. Our findings illustrate that the electronic properties of transition metal dichalcogenides, and more generally 2D layered materials, are physically altered by the interactions with the interfacing materials, in addition to the electron screening and defects that have been widely considered.

Abstract P-8:Fe2O3-SiO2-Au Core-Shell Nanoparticles for Theranostics

Background: Core-shell nanoparticles (NPs) Fe3O4-SiO2 covered with Au grains due to their unique magnetic, biological, optical and mechanical properties are promising nanostructured material especially in biomedical field. Magnetic core allows controlling the position of NPs, SiO2 shell makes them biocompatible and decrease magnetostatic interactions between them, and Au NPs on the surface allow creating additional matrix around them and using such systems as controlled nanocontainers in tasks of drug delivery, magnetic resonance imaging and target cancer cell therapy. Methods: Inner magnetic core of the NPs was synthesized using polyol method, a 3-step process which resulting in magnetite NPs with hydrophilic surface. Shell was made by covering Fe3O4 particles in surfactant and growing SiO2 on top of them by sol-gel method. Covering core-shell NPs with 3.5 nm Au seed grains using monosilane and their further growth to control diameter. Structural properties were studied using TEM and Dual Beam SEM. Magnetic properties were investigated using LakeShore VSM 7400 magnetometer. Results: Two samples with different concentration of Au NPs were investigated. SEM observations show that core-shell Fe3O4-SiO2 are spherical with average diameter of 200 nm and Au NPs with diameter of 15 nm are evenly dispersed on their surface. Magnetic measurements showed that different concentration of Au NPs results in different coercive forces of the sample. Decreasing the temperature to 77 K showed up to 6 times increase of coercive force and slight increase in magnetization. Conclusion: Biocompatible magnetic nanoparticles are critical advances in biomedical applications. In this work, we studied the morphology of the samples, demonstrated the change of coercive force of NPs with different Au concentration and investigated their magnetic properties in low temperatures.

Tailoring of Gas Sensing Characteristics Using Bilayer Sensor with Oxide Semiconductor Sensing Layer and Nanoscale Au Catalytic Overlayer

Introduction Gas sensing characteristics of oxide semiconductor chemiresistors can be enhanced or controlled by loading noble metal catalysts to the entire sensing materials. Although uniform catalyst loading generally promotes the sensing reaction between analyte gas and ionized oxygen on the surface, it may induce other adverse effects such as 1) the excessive increase of sensor resistance depending on work function of metal catalyst, 2) the gas oxidation at the upper part of sensing film, and 3) the gas reforming during the gas transport within sensing film. Excessively high sensor resistance hampers the cost-effective signal measurement using conventional electric circuits, while it is difficult to separate the gas sensing, reforming, and oxidation reactions, leading to low controllability of gas sensing characteristics. Herein, a novel bilayer design with an oxide chemiresistors sensing layer (SnO2, ZnO, and Co3O4) and nanoscale catalytic Au overlayer was suggested to solve above problems. Bilayer sensor design effectively separated the sensing and catalytic reaction, leading to the excellent control of gas sensing characteristics without affecting the sensor resistance in air. Method Sensing materials SnO2 hollow spheres were prepared using ultrasonic spray pyrolysis of mixed solution consisting of 0.1 M of Tin (II) chloride dihydrate (SnCl2•2H2O, ≥ 99.99%) and 0.025 M of citric acid monohydrate (C6H8O7•H2O, ≥ 99.0%). Droplets of this source solution were then generated by six ultrasonic transducers (resonance frequency: 1.7 MHz) and transferred into a quartz tube (inner diameter: 55 mm) in an electric furnace heated to 700 ºC in air (flow rate : 10 L/min) for pyrolysis. As-prepared precursor powders were converted into SnO2 hollow spheres via heat treatment at 600 ºC for 2 h in air. SnO2 sensing films were fabricated by screen printing onto Pt interdigitated electrode (IDE) (electrode gap: 100 mm) patterns on SiO2/Si substrates (size = 8 mm x 8 mm). Catalytic Au nanoparticles were deposited on the SnO2 thick films through e-beam evaporation of Au grains (99.998%) in a vacuum chamber (below 2×10-6 Torr) at a rate of 0.1 Å sec−1 (nominal thicknesses: 0.5, 1, and 3 nm), as calibrated by a quartz crystal microbalance, which were converted into discrete configurations of Au nanoparticles through heat treatment at 550 ºC for 2 h. Additionally, SnO2 thick films with 1-nm-thick Au overlayer were also heat treated at 550 ºC for 0.5 and 4 h to investigate the effects of Au configuration on gas sensing characteristics. Results and Conclusions The configuration of Au nanoparticle overlayer was changed by controlling the Au-coating thickness and annealing time and investigated the gas sensing characteristics of SnO2 sensors with various configurations of Au nanoparticles overlayer. The Au nanoparticle overlayer significantly enhanced the methylbenzene selectivity and response of SnO2 thick film sensor by reforming of less reactive methylbenzenes into more reactive species and suppressing the cross-responses to relatively reactive interference gases (e.g. ethanol and HCHO) through oxidative filtering. Furthermore, the methylbenzene selectivity and response of ZnO and Co3O4 were also significantly enhanced by introducing the Au nanoparticle overlayer, confirming the general validity on the role of Au nanoparticle overlayer. In all the sensing films, the gas transport as well as sensor resistance is hardly influenced by nanoscale catalytic Au overlayer, demonstrating that the bilayer sensor is promising platform to control the gas sensing characteristics by separating catalytic reaction and sensing reaction and by tuning the catalyst-induced gas reforming and oxidation reaction. These sensors can be used for various sensor applications with new functionality.

The Effect of Aerophine 3418A Collector Dosage on Niğde (Ulukışla-Madenköy) Complex Pb-Zn Sulphide Ore Flotation

In this study, grinding + flotation experiments were performed on the sample of complex Pb-Zn sulphide ore taken from Niğde (Ulukışla-Madenköy) region in Turkey. According to the mineralogical analysis of the ore sample used in experimental studies, it was determined that the ore composition contains calcite, quartz, pyrite, chalcopyrite, hematite, goethite, limonite, gypsum, galena, sphalerite, jarosite, arsenopyrite and marcasite minerals. In addition, Au and Ag grains were found to be inclusions in hematite, goethite and jarosite minerals. The experiments were carried out at a solid ratio of 30%, a flow rate of 10 L/min, a stirring rate of 1250 rpm and pH = 9. In flotation tests, lime is used as the pH regulator, zinc sulphate, sodium silicate as the depressant, sodium isobutyl dithiophosphine as the collector and methyl isobutyl carbinol as the frother. In the flotation studies, the effect of Aerophine 3418A collector dosage on flotation was investigated. As a result, a lead concentrate of 55.13% Pb was obtained and it was found that this concentrate contained 2489 ppm of Ag. The amount of Aerophine 3418A collector was determined as 10 g/t.