Flame Annealing Research Articles

Hollow tubular MnOx prepared by flame annealing with cotton fiber as sacrificial template and its applications for Hg0 adsorption in flue gas

The mass discharge of mercury from coal-fired power plant has caused great harm, abating mercury emissions is of preoccupation for protecting public environmental safety and human health. Metal oxides are often used for Hg0 removal in the flue gas. In this paper, a hollow tubular MnOx(MnCot) was successfully prepared by rapid flame annealing using cotton fiber as a sacrificial template. The MnCot were then well characterized and tested for its capability for Hg0 removal in flue gas. The results indicate that the flame assisted synthesis method for rapidly prototyping metal oxides with typical structures is achievable. The hollow tubular structure of the cotton fiber is well reprinted with good crystallization of Mn3O4. The inner diameter of the hollow tubular MnCot is about 10 μm, and the thickness of the tube is about 1 μm. The Hg0 removal efficiency on MnCot can be maintained as high as 90 % under simulated flue gas atmosphere below 240°C. O2 and NO have a positive effect on the Hg0 removal, which can act as the fresh active sits thus enhancing its capability for Hg0 removal. However, the presence of SO2 will result in the surface sulfation on MnCot, thus deteriorating its capability for Hg0 removal. Further, the competitive adsorption between SO2 and Hg0 on the material will also weaken its capability for Hg0 removal. The hollow tubular MnOx rapidly prepared by one-step flame annealing has a good industrial application potential for Hg0 removal in coal-fired flue gas.

Oxygen vacancies boosted photoelectrochemical performance of α-Fe2O3 photoanode via butane flame annealing

In this study, oxygen vacancies were introduced into the hematite (α-Fe2O3) photoanode via a simple and rapid butane flame annealing method. The presence of oxygen vacancies were demonstrated by high-resolution transmission electron microscopy (HRTEM), electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS). The photocurrent density of optimum α-Fe2O3 electrodes was 0.67 mA cm-2 at 1.23 VRHE, about 2.7 times higher than that of N2 annealed electrode. Our study showed that butane flame annealing process can introduce oxygen vacancies defects in Fe2O3 electrodes, which would improve carrier transfer efficiency, increase electron density, enhance water oxidation activity, and narrow the light optical bandgap. The use of butane flame annealing is a simple and effective strategy to enhance the PEC performance of hematite thin films.

Electromagnetic alternators with composite amorphous alloy shell for improving characteristics

In this study, a magnetic casing encapsulating a generator is used to improve the electromagnetic and power characteristics of the generator. Two types of two-pole AC generators are proposed: one is a bare-bonded (NC) type and the other is an iron-based amorphous alloy material covering the generator casing. In this study, Fe-Si-B amorphous thin strips were annealed between 300 and 380 °C and soaked for 60 min to observe and analyze the structural changes and the evolution of properties under different temperature conditions. After the thin strip is annealed at 400 °C, α-Fe dendrites begin to appear, and at 450 °C, a large number of α-Fe dendrites are formed. The demagnetization rate of the permanent magnet area near the bottom of the pole piece is the highest for the generator with an amorphous alloy shell because the magnetic flux leakage from the side frame of the pole piece changes the magnetic flux path, thereby affecting the demagnetization performance. In this study, three amorphous alloys, HB1-M, HB1, and SA1, were used as the cladding permanent magnet generator shell, and annealing and non-annealing procedures were conducted to observe the influence on the magnetic power of the generator. The magnetic flux on the surface of the amorphous shell was measured by a magnetic fluxmeter. For experiments with an amorphous shell, the results show that the annealed center point magnetic flux densities were approximately HB1-M (15 mT), HB1 (12 mT), and SA1 (10 mT), and the marginal non-annealed amorphous thin strip could reach ∼7–5 mT. The measured generator harmonic component of SA1 is higher than the voltage and current harmonics, reflecting that the magnetization direction of the magnetic shell in the demagnetization region is covered by the magnetic flux density. Because of central flame annealing, the magnetic shell is paramagnetic, and it helps to reduce the noise by at least 5 dB. The generator current harmonic characteristic of the HB1-M material is smaller than that of the HB1 and SA1 materials. In this study, a composite amorphous material was used to cover the generator casing; it was verified that HB1-M + HB1 + SA1 has the lowest noise characteristics for the generator. The generator noise of the composited material (HB1-M + HB1 + SA1) can be reduced to below 69 dB, which is ∼7–9 dB lower than that of a single amorphous material.

Nanostructured Ag‐Bioglass Implant Coatings with Antibacterial and Osteogenic Activity

AbstractBone implant failure due to aseptic loosening and biofilm infections is an increasing healthcare problem. Implants may be coated with nanoparticles to avoid bacterial colonization and promote osseointegration. However, these nanocoatings often require long, expensive, and complex manufacturing routes with limited clinical translation potential. Here, a multifunctional nanoparticle coating consisting of silver (Ag) and bioglass (BG) is investigated to overcome current limitations by providing synchronously antibacterial and osteogenic effect. Flame spray pyrolysis (FSP) is exploited as a scalable and reproducible process to synthesize large quantities of nanoparticles and deposit them on titanium (Ti) substrates. The deposited nanocoatings show a homogeneous morphology and biomineralize after soaking in simulated body fluid (SBF), while their adhesion on Ti substrates is promoted by in situ flame annealing. The Ag+ ion release from Ag containing BG samples inhibits Staphylococcus aureus biofilm formation up to 3 log units, while the osteogenic responses of pre‐osteoblastic cells directly grown on AgBG samples show similar levels of alkaline phosphatase activity, calcium and collagen production when compared to pure Ti. The inexpensively synthesized multifunctional AgBG nanostructured implant coatings exert a high bioactivity and antibacterial response while maintaining high biocompatibility. The insights of this study can direct the development of multifunctional implant coatings.

Flame-annealed porous TiO2/CeO2 nanosheets for enhenced CO gas sensors

CO sensor is helpful to monitor the working state of combustion equipment, such as industrial boilers and engines, and to ensure the production process and human life safety. However, balancing fast response/recovery and high response value for metal oxide CO sensors remains a challenge. In this work, based on band gap engineering, porous TiO2/CeO2 NSs with different TiO2 coupling amounts were prepared by hydrothermal method combined with flame annealing. The heterojunction composed of TiO2 and CeO2 narrowed the energy band width of the composite system and made the electron transmission more efficient, which endowed TiO2/CeO2 NSs with good gas sensing properties. The results indicated that the response value of TiO2/CeO2 NSs is 9.78 time that of CeO2 NSs. Its ultrafast response/recovery time (2 s/6 s), good CO selectivity and wide CO monitoring range (500 ppb-5000 ppm) are also impressive. The TiO2/CeO2 NSs sensor has great potential for rapid CO monitoring.

Candle flame fabrication of carbon coated CuO-Cu2O composite photocathode for photoelectrochemical water reduction

In this work, carbon coated-CuO-Cu2O composite on copper foam (C-CuO-Cu2O/CF) is synthesized by candle flame treatment and is evaluated as a photocathode of photoelectrochemical water splitting (PEC). The photocurrent density of C-CuO-Cu2O/CF electrode can reach −1.2 mA cm−2 (at 0 V vs. RHE), which is about 12 times higher than that of Cu2O/CF. The high PEC performance is due to the carbon modification and the unique composition which increase the carrier concentration and reduce the carrier recombination rate and promote charge transfer at electrode-electrolyte interface. Our results proves that candle flame annealing is a promising way for the rational design of carbon modified photoelectrodes.

Electrochemical Reduction of CO2 on Flame Annealed Cu

AbstractSurface modification of metallic Cu by conventional oxidation and an alternative method of oxidation using flame annealing and its influence on electrochemical reduction (ECR) of CO2 are reported in this study. The ECR of CO2 in aqueous KCl electrolyte yielded methane, ethane, ethylene, and hydrogen as the major products. The faradaic efficiency of ethane obtained at −1.2 V vs NHE for flame‐annealed Cu (34 %) was comparable to the conventionally oxidised Cu (40 %), while bare Cu yielded methane (10 %). The metal–metal oxide interface on the electrode aids in the formation of C2‐based products. Flame annealing can be regarded as an alternative electrode preparation method for C2 product formation, with its merits in high specific surface area, self‐rejuvenating mode on deactivation and ease of preparation.

Observation of Substituent Effects in the Electrochemical Adsorption and Hydrogenation of Alkynes on Pt{hkl} Using SHINERS.

By combining cyclic voltammetry (CV) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS), the adsorption behavior of two alkynes, propargyl alcohol (PA) and 2-methyl-3-butyn-2-ol (MeByOH), undergoing hydrogenation on Pt basal plane single-crystal electrodes is investigated. It is found that PA and MeByOH give rise to strong surface sensitivities in relation to both hydrogenation activity and molecular fragmentation into adsorbed species such as CO. For PA, irreversible adsorption is strongly favored for Pt{100} and Pt{110} but is weak in the case of Pt{111}. It is suggested that the presence of the primary alcohol substituent is key to this behavior, with the order of surface reactivity being Pt{100} > Pt{110} > Pt{111}. In contrast, for MeByOH, strong irreversible adsorption is observed on all three basal plane Pt surfaces and we propose that this reflects the enhanced activity of the alkyne moiety arising from the inductive effect of the two methyl groups, coupled with the decreased activity of the tertiary alcohol substituent toward fragmentation. Pt{111} also exhibits singular behavior in relation to MeByOH hydrogenation in that a sharp Raman band at 1590 cm–1 is observed corresponding to the formation of a di-σ/π-bonded surface complex as the alkyne adsorbs. This band frequency is some 20 cm–1 higher than the analogous broadband observed for PA and MeByOH adsorbed on all other basal plane Pt surfaces and may be viewed as a fingerprint of Pt{111} terraces being present at a catalyst surface undergoing hydrogenation. Insights into the hydrogenation activity of different Pt{hkl} surfaces are obtained using quantitative comparisons between Raman bands at hydrogenation potentials and at 0.4 V vs Pd/H, the beginning of the double-layer potential region, and it is asserted (with support from CV) that Pt{110} is the most active plane for hydrogenation due to the presence of surface defects generated via the lifting of the (1 × 2) to (1 × 1) clean surface reconstruction following flame annealing and hydrogen cooling. Our findings are also consistent with the hypothesis that Pt{111} planes are most likely to provide semihydrogenation selectivity of alkynes to alkenes, as reported previously.

Catalytic Filter for Continuous and Selective Ethanol Removal Prior to Gas Sensing.

Ethanol is a major confounder in gas sensing because of its omnipresence in indoor air and breath from disinfectants or alcoholic beverages. In fact, most modern gas sensors (e.g., graphene, carbon nanotubes, or metal oxides) are sensitive to ethanol. This is challenging because ethanol is often present at higher concentrations than target analytes. Here, a simple and modular packed bed filter is presented that selectively and continuously removes ethanol (and other alcohols like 1-butanol, isopropanol, and methanol) over critical acetone, CH4, H2, toluene, and benzene at 30-90% relative humidity. This filter consists of catalytically active ZnO nanoparticles (dBET = 55 nm) made by flame aerosol technology and annealing. Continuous oxidation of ethanol to CO2 and H2 was observed at filter temperatures above 260 °C while below that, unwanted acetaldehyde was formed. Most remarkably, ethanol concentrations up to 185 ppm were removed from exhaled breath in preliminary tests with an alcohol intoxicated volunteer, as confirmed by mass spectrometry. At the same time, almost 4 orders of magnitude lower (e.g., 0.025 ppm) acetone concentrations were preserved. This was superior to previous catalyst filters (e.g., CuO, SnO2, and Fe2O3) with overlapping ethanol and acetone conversions and related to ZnO's surface basicity. The ZnO filter performance was stable (±2.5% conversion variability) for, at least, 21 days. Finally, when combined with a Si-doped WO3 sensor, the filter effectively mitigated ethanol interference when sensing acetone without compromising the sensor's fast response and recovery times. Such catalytic filters can be combined readily with all gas sensors.

Surface microstructural controls on electrochemical hydrogen absorption at polycrystalline palladium

The ease by which hydrogen is absorbed into a metal can be either advantageous or deleterious, depending on the material and application in question. For instance, in metals such as palladium (Pd), rapid absorption kinetics are seen as a beneficial property for hydrogen purification and storage applications, whereas the contrary is true for structural metals such as steel, which are susceptible to mechanical degradation in a process known as hydrogen embrittlement. It follows that understanding how the microstructure of metals (i.e., grains and grain boundaries) influences adsorption and absorption kinetics would be extremely powerful to rationally design materials (e.g., alloys) with either a high affinity for hydrogen or resistance to hydrogen embrittlement. To this end, scanning electrochemical cell microscopy (SECCM) is deployed herein to study surface structure-dependent electrochemical hydrogen absorption across the surface of flame annealed polycrystalline Pd in aqueous sulfuric acid (considered to be a model system for the study of hydrogen absorption). Correlating spatially-resolved cyclic voltammetric data from SECCM with co-located structural information from electron backscatter diffraction (EBSD) reveals a clear relationship between the crystal orientation and the rate of hydrogen adsorption-absorption. Grains that are closest to the low-index orientations [i.e., the {100}, {101}, and {111} facets, face-centered cubic (fcc) system] facilitate the lowest rates of hydrogen absorption, whereas grains of high-index orientation (e.g., {411}) promote higher rates. Apparently enhanced kinetics are also seen at grain boundaries, which are thought to arise from physical deformation of the Pd surface adjacent to the boundary, resulting from the flame annealing and quenching process. As voltammetric measurements are made across a wide potential range, these studies also reveal palladium oxide formation and stripping to be surface structure-dependent processes, and further highlight the power of combined SECCM-EBSD for structure-activity measurements in electrochemical science.

Organic thin-film transistors with flame-annealed contacts

Reducing contact resistance is critical to developing high-performance organic field-effect transistors (OFETs) since it impacts both the device mobility and switching speed. Charge injection and collection has been optimized by applying chemical treatments to the contacts, such as self-assembled monolayers (SAMs), oxide interlayers, or dopants. Here, we tested how flame annealing the surface of the electrodes impacts the interface and bulk components of the contact resistance, as well as the overall device performance. A butane micro torch was used to flash-anneal the gold electrodes, which allowed gold grains to crystallize into larger domains. We found that, along with the grain size, the surface roughness of the contacts was also increased. SAM treatment created a lower work function shift on a flame annealed electrode than when deposited on an untreated surface, due to the greater surface roughness. This resulted in a larger interface contact resistance. However, flame annealing also produced an order of magnitude reduction in the density of trap states in the semiconductor layer, which reduced the bulk contact resistance and channel resistance. These competing effects yielded OFETs with similar performance as untreated devices.

Making Copper and Alloyed Single Crystal Beads By Oxygen-Hydrogen Flame in Air and Boosting the Electrocatalytic Activity Toward Formaldehyde Oxidation By the Factor of 12 with 1.5 % of Ni

This work shows that it is feasible to prepare chemically pure or bimetallic, non-precious metal (Cu, Ni, Co) single crystal electrodes by melting the end of a polycrystalline metal wire in the air by a tactfully designed oxygen-hydrogen torch. The structures and chemical compositions of the as-prepared Cu and CuNi beads were characterized by X-ray photoelectron spectroscopy (XPS). Obtained results show that Cu and the CuNi single crystal beads are free of oxide in the bulk and Cu to Ni molar ratio is 98.5:1.5 in the CuNi bead. After flame annealing, the thickness of cuprous oxide on the (111) surface is less than 10 Å. The (111) planes of Cu and Cu/Ni electrodes are exposed to study their electrocatalysis toward the oxidation of formaldehyde (HCHO) in 0.1 M KOH, which is relevant to the development of fuel cells, hydrogen carrier and the removal of HCHO in waste water. The HCHO fuel cell employs Cu/Ni anode can have multiple advantages. First, the cell potential for HCHO/CuNi anode is ~ 0.5V more greater than a typical CH3OH/Pt anode if the same cathode is used. Second, Cu and Ni metals are the inexpensive and abundant. Third, the aqueous HCHO has a relatively lower vapor pressure than methanol. Fourth, paraformaldehyde, the source of HCHO, is a solid at room temperature, which makes it easy to be transported and stored. Although bulk Ni is inactive toward HCHO oxidation, a tiny Ni in the Cu electrode increases the exchange current density, due to HCHO oxidation, by 12 times. The durability of Cu(111) and Cu98.5Ni1.5(111) electrode in catalyzing HCHO oxidation is researched by stepping the potential from their OCP (-0.9 and -1V vs. Ag/AgCl) to -0.4 and -0.54V. For Cu(111), the current surges after the switch of potential, followed by an exponential drop from 0.9 to 0.06 mA/cm2 within 100 s. For Cu98.5Ni1.5, the current decrease to 1/4 (1mA/cm2) of its original value in 300 sec and then fluctuates between 0.8 and 0.7 mA/cm2. The activity is restored after the interface is refreshed by removing and re-immersing the electrode in the electrolyte. The kinetics of HCHO oxidation at Cu98.5Ni1.5 and Cu(111) electrodes are scrutinized by conducting voltammetry in 0.1 M KOD/KOH + 0.1 M HCHO. The current observed at Cu98.5Ni1.5 in KOD is markedly lower than that recorded in KOH; whereas no effect is seen with Cu(111). This contrast implies that a cleavage of a O-D bond is involved in the rate-determining step of HCHO oxidation at Cu98.5Ni1.5, but not at the Cu(111) electrode. Figure 1

Peroxodisulfate reduction on platinum stepped surfaces vicinal to the (110) and (100) poles

The reduction of peroxodisulfate anion at stepped platinum single crystal electrodes vicinal to the (110) and (100) poles has been investigated using cyclic voltammetry. Particular emphasis is made in understanding the effect of the cooling atmosphere used after the flame annealing. Two cooling atmospheres have been used: H2/Ar and CO. The cooling procedure has a significant influence on the reactivity obtained with the stepped surfaces belonging to both crystallographic zones. For the surfaces composed of (110) terraces and (111) or (100) steps cooled in H2/Ar, only one peroxodisulfate reduction peak is observed. On the contrary, for the same surfaces cooled in CO, more than one peak is observed for wide terraces. For surfaces vicinal to the pole (100), the cooling in CO atmosphere seems to produce a surface with higher order than those cooled in H2/Ar. The implications of the results on the understanding of the local distribution of charges at heterogeneous surfaces are discussed, identifying local values of the potential of zero charge. Those results are compared, when possible, with results obtained with other techniques.

Synergistic effect of crystalline phase on protein adsorption and cell behaviors on TiO2 nanotubes

The objective of this study is to explore the structure–property relationships of TiO2 nanotubes (TNTs) with different crystalline phases that link to protein adsorption and cell responses. Given the formation of intact rutile nanotubular structures by furnace annealing is challenge, a combination of furnace annealing and flame annealing is employed for the preparation of rutile TNTs. TNTs with pure anatase phase and mixed anatase/rutile phases are obtained by simple furnace annealing of amorphous TNTs. Results show that BSA and FBS adsorptions are greatly enhanced on rutile TNTs, whereas no discernable difference on other crystalline phases. Rutile TNTs also present highest adsorption of fibronectin and collagen which are diminished on anatase and dual anatase–rutile phases. Interestingly, however, there is no significant difference in cell proliferation or differentiation on TNTs with different crystallites. Scrutinization of the surface properties involved in protein adsorption and cell activities, a synergistic effect of surface charge, hydroxyl groups, and roughness is found on protein adsorption which further regulates cell behaviors. Those findings provide a better understanding of the structure–property relationships of titanium-based biomaterials.

Water Electrolysis using Flame-Annealed Pencil-Graphite Rods

Inexpensive and sensitive graphite electrodes were fabricated by applying flame annealing to pencil-graphite rods (PGRs) as electrodes for water electrolysis cells. The resin (polymer, binder) on the surface of PGR was removed by flame annealing to make it porous, and the graphite electrodes with high activity and low cost were obtained. By flame annealing the PGR, although the PGR electrode became active upon water electrolysis, the PGR electrode became instable for long-time operation. The effects of flame annealing on PGR for water electrolysis were analyzed by SEM, FT-IR spectroscopy, Raman spectroscopy, NEXAFS, and electrochemical impedance spectroscopy (EIS).

Carbon monoxide oxidation assisted by interfacial oxygen-water layers

Based on the fact that oxygenated species promotes the oxidative desorption of carbon monoxide adsorbates, a simple methodology is described here to prepare platinum electrodes with oxygen/water ensembles. Platinum fast quenching (thermal shocking) in oxygenated water after flame annealing in an oxygen atmosphere offers features not seen before. We propose the formation of interfacial oxygen/water ensembles as partially soluble species between platinum rows at stepped n x (110) surfaces. Depending on the temperature of quenching and time of cooling, it is possible to almost completely oxidize carbon monoxide adsorbates, via two processes, i.e., chemical oxidation by molecular oxygen and Langmuir-Hinshelwood surface oxidation.

Fast Flame Annealed Porous CuFe2O4 for Photoelectrochemical Hydrogen Production

Photoelectrochemical (PEC) water splitting is one of the promising renewable energy techniques that can store solar energy into one of the clean and renewable energy resources, hydrogen (H2). However, facilitating the renewable PEC water splitting system on a global scale is still challenging. Especially, finding suitable p-type photocathodes is critical which have a narrow bandgap, a great solar to hydrogen (STH) efficiency and economical fabrication processes with earth abundant elements. Metal oxides have shown remarkable advantages that satisfy the important requirements to be an excellent photocathode among the suggested candidates. Copper ferrite (CuFe2O4) is a promising but rarely studied p-type photocathode based on the relatively narrow bandgap (~1.7eV) which can utilize a great portion of solar light to realize the maximum STH efficiency of ~30% and photocurrent of ~25mA/cm2 theoretically. In addition, CuFe2O4 has positive flat band and photocurrent onset potentials (~1.0 VRHE) that are critical to achieve high operating photocurrent with n-type photoanode for an ideally unbiased entire solar water splitting system. Moreover, it consists of earth abundant elements. However, there are still limiting features for the use of CuFe2O4 photocathode since it has shown a relatively poor photocurrent and the synthesis process inevitably requires long time annealing at high temperature to produce less defective and better crystalline material for a high charge transport property. Here, we employed the rapid and high temperature (>980°C) flame as an annealing process for CuFe2O4 photocathode synthesis, demonstrating the significantly enhanced photocurrent (-1.82 mA/cm2 at 0.4VRHE in Ar purged 1M NaOH) as a single material photocathode whose photoactivity is greater than that of most studied photocathodes. There are several unique advantages of the flame annealing compared with other conventional annealing methods for the synthesis. For example, the flame does have negligible ramping time to reach high temperature above 980°C due to its short ignition delay time that finally makes the high crystalline CuFe2O4 in only 16 minutes. Moreover, the flame is operated in the open atmospheric environment and the amount of oxygen can be easily controlled by adjusting the fuel to oxygen equivalence ratio as a combustion parameter. Oxygen rich environment was employed for CuFe2O4 annealing to provide fully oxidized condition for an amorphous Cu and Fe mixture prepared by sol-gel method. Finally, the porosity of CuFe2O4 was highly increased by flame annealing, and the physical structural change positively affects the enhancement of the light absorption property and the specific surface area increase.

Ultrafast Flame Annealing of TiO2 Paste for Fabricating Dye-Sensitized and Perovskite Solar Cells with Enhanced Efficiency.

Mesoporous TiO2 nanoparticle (NP) films are broadly used as electrodes in photoelectrochemical cells, dye-sensitized solar cells (DSSCs), and perovskite solar cells (PSCs). State-of-the-art mesoporous TiO2 NP films for these solar cells are fabricated by annealing TiO2 paste-coated fluorine-doped tin oxide glass in a box furnace at 500 °C for ≈30 min. Here, the use of a nontraditional reactor, i.e., flame, is reported for the high throughput and ultrafast annealing of TiO2 paste (≈1 min). This flame-annealing method, compared to conventional furnace annealing, exhibits three distinct benefits. First, flame removes polymeric binders in the initial TiO2 paste more completely because of its high temperature (≈1000 °C). Second, flame induces strong interconnections between TiO2 nanoparticles without affecting the underlying transparent conducting oxide substrate. Third, the flame-induced carbothermic reduction on the TiO2 surface facilitates charge injection from the dye/perovskite to TiO2 . Consequently, when the flame-annealed mesoporous TiO2 film is used to fabricate DSSCs and PSCs, both exhibit enhanced charge transport and higher power conversion efficiencies than those fabricated using furnace-annealed TiO2 films. Finally, when the ultrafast flame-annealing method is combined with a fast dye-coating method to fabricate DSSC devices, its total fabrication time is reduced from over 3 h to ≈10 min.

Electrochemical Nature of Silver Halide Underpotential Deposition on Au(111)

In previous research completed by Iski et al.1, it was found that through specific electrochemical methods, a silver (Ag) monolayer could be formed on a Au(111) surface in both a chloride-free and chloride-rich solution. The electrochemical method used was under potential deposition (UPD) and reduced Ag+ to the surface. The previous study showed that, in a chloride-free environment, the Ag monolayer could be formed and atomically resolved; however, once removed from the cell, it could be completely destroyed via hydrogen flame annealing. Interestingly, in the presence of chloride, the same Ag monolayer was formed and was found to be extremely thermally stable after removal from the cell and was resistive to temperatures as high as 1,000 K. The atomic structure of these films can be studied with electrochemical scanning tunneling microscopy (EC-STM), which not only allows for atomic scale imaging of the surface layer within an electrochemical environment, but also facilitates the taking of cyclic voltammograms (CVs), which can be used to examine the redox behavior of the systems. Through this electrochemical manipulation, a newly hypothesized mechanism for the reduction of AgCl to the surface rather than bare Ag+ ions is proposed. Despite many studies on these types of surface layers2, very few publications have directly studied their extreme thermal stability. Since it is known that the stability of bulk metal halide structures decreases as the halogen ion increases in size, an investigative study was performed following the same procedure, substituting chloride with bromide and iodide. As with the AgClx system, once AgBrx was used to form the Ag monolayer, a new surface structure formed which was also thermally resistive to a hydrogen flame. Conversely, the surface formed by the AgIx was not maintained and formed silver oxide insulating species after thermal treatment. CVs taken in the same region as those of the previous work show a definite surface modification by both AgBrx and AgIx before annealing which persists after the thermal treatment for the AgBrx. Further electrochemical studies into these Ag monolayers formed in a halogenated environment are being conducted in an attempt to better understand the properties of these surfaces and the type of redox chemistry occurring at the relevant potentials. Using EC-STM, we plan to study the ways in which this remarkable stability is imparted to the single crystal surface under ambient conditions. [1] Iski, E. V. et al. Electrochimica Acta 2011, 56 (3), 1652–1661. [2] Michalitsch, R.; Laibinis, P. E. Angewandte Chemie International Edition 2001, 40 (5), 941–94.

Mixed carboranethiol self-assembled monolayers on gold surfaces

Carboranethiol self-assembled monolayers on metal surfaces have been shown to be very convenient systems for surface engineering. Here we have studied pure and mixed self-assembled monolayers (SAMs) of three different carboranethiol (CT) isomers on gold surfaces. The isomers were chosen with dipole moments pointing parallel to (m-1-carboranethiol, M1), out of (m-9-carboranethiol, M9) and into (o-1-carboranethiol, O1) the surface plane, in order to investigate the effect of dipole moment orientation on the film properties. In addition, influence of the substrate surface morphology on the film properties was also studied by using flame annealed (FA) and template stripped (TS) gold surfaces. Contact angle measurements indicate that in M1/M9 and M1/O1 mixed SAMs, M1 is the dominant species on the surface even for low M1 ratio in the growth solution. Whereas for O1/M9 mixed SAMs no clear evidence could be observed indicating dominance of one of the species over the other one. Though contact angle values were lower and hysteresis values were higher for SAMs grown on TS gold surfaces, the trends in the behavior of the contact angles with changing mixing ratio were identical for SAMs grown on both substrates. Atomic force microscopy images of the SAMs on TS gold surfaces indicate that the films have similar morphological properties regardless of mixing ratio.