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Summary High saturation magnetization, hysteresis-less long linear response range, and resistance to device fabrication conditions are figures of merit for magnetic materials. Despite advances in materials research, many high-saturating micro- and nanomagnetic materials are hysteresis-prone, have short linear ranges, and are sensitive to oxidation, resulting in device inefficiencies in high-frequency electronics and unpredictable responses in magnetic sensing applications. Holmium oxide is a promising material because of its high magnetic susceptibility, but synthetic options are limited, with low-temperature magnetism incompletely characterized. Here, we present physical vapor deposition synthesis and material characterization of polycrystalline holmium oxide thin films. The product has saturation magnetization exceeding 2 Tesla, linear range (μ0H) also exceeding 2 Tesla, zero magnetic remanence and coercivity, and resistance to harsh processing conditions including oxygen plasma and concentrated hydrofluoric acid etching, making these thin films ideal for fabricating next-generation nanoscale magnetic devices in advanced scientific and engineering applications.

We report the promoting effect of graphitic carbon nitride in Cu-catalyzed N-arylation. The abundance of pyridinic coordination sites in this host permits the adsorption of copper iodide from the r...

The worldwide replacement of the toxic mercuric chloride catalyst in vinyl chloride manufacture via acetylene hydrochlorination is slowed by the limited durability of alternative catalytic systems at high space velocities. Here, we demonstrate that platinum single atoms on carbon carriers are substantially more stable (up to 1,073 K) than their gold counterparts (up to 473 K), enabling facile and scalable preparation and precise tuning of their coordination environment by simple temperature control. By combining kinetic analysis, advanced characterization, and density functional theory, we assess how the Pt species determines the catalytic performance and thereby identify Pt(ii)−Cl as the active site, being three times more active than Pt nanoparticles. We show that Pt single atoms exhibit outstanding stability in acetylene hydrochlorination and surpass the space–time yields of their gold-based analogues after 25 h time-on-stream, qualifying them as a candidate for sustainable vinyl chloride production. Platinum nanoparticles have been neglected as a catalyst for acetylene hydrochlorination due to their limited activity. Here, the authors show that nanostructuring to the single-atom level renders platinum on carbonaceous supports a superior catalyst for this important industrial process.

A dual system comprising two catalytic reactors connected in series was developed for the direct conversion of ethene to vinyl chloride monomer (VCM). The first reactor uses ZrO2-supported ceria (CeO2/ZrO2) to perform ethene oxychlorination to 1,2-dichloroethene (EDC) that is dehydrochlorinated to VCM in the second reactor over calcium-promoted γ-Al2O3. The choice of carrier for ceria is of critical importance to maximize the EDC production by reducing combustion products. While MgO, SiO2, SiC, TiO2, ZSM-5, and γ-Al2O3 carriers induced higher overoxidation compared to bulk ceria, ZrO2 was the only carrier that suppressed COx formation. Moreover, the latter carrier led to the highest oxychlorination activity. The unique performance of the CeO2/ZrO2 catalyst was rationalized by its ability to promote chlorine evolution and to suppress the combustion of chlorinated products, as inferred from the activity evaluation in HCl and VCM oxidation, respectively. The outstanding redox properties, enabling operation at low temperature and thus high selectivity, are associated with the formation of defective CeO2 nanoparticles, contrasting the low activity over Ce–Zr mixed oxide. In order to subsequently form VCM, an efficient EDC dehydrochlorination catalyst was designed by moderating the acidity of γ-Al2O3via calcium doping and used in a reactor after CeO2/ZrO2. This dual catalyst system displayed 100% selectivity to VCM at 25% ethene conversion, surpassing the space time yield of the best ethene-to-VCM catalyst EuOCl by a factor of four, where the first step is operated at an elevated temperature of about 100–150 K with respect to cupric chloride benchmarks. In addition, the catalytic dehydrochlorination, operated at a lower temperature of 100 K than the current non-catalytic process, showed minimized coke formation. This developed system rendered stable after slight initial deactivation, offering promising potential to intensify VCM production.

Monoclinic zirconia has been uncovered as a carrier able to substantially boost the activity of indium oxide for CO2 hydrogenation to methanol. Here, electronic, geometric, and interfacial phenomen...

Monolithic, nitrogen-doped carbon sorbents were prepared from resorcinol-urea-formaldehyde resins and physically activated with CO2 for different activation times. The effect of the activation time on the water sorption behavior and the physicochemical properties were investigated. Longer activation times lead to a steeper slope of the water sorption isotherm and, due to a higher specific surface area and micropore volume, an increased water sorption capacity. It was found that, after physical activation for 3 h at 800 °C, the physically activated, nitrogen-doped carbon has a high surface area (>1000 m2/g) and a high water sorption capacity (50 wt%). In a miniaturized adsorption heat pump test stand, the best candidate material was assessed alongside commercial silica gel for reference. At a temperature swing from 90 °C → 50 °C, the CO2-activated carbon exhibits a maximal specific cooling power which is a factor of 1.7 higher in comparison with the reference silica gel (429 W/kg versus 255 W/kg). At a more applicable temperature swing, 60 °C → 30 °C, the CO2-activated carbon yields a specific cooling power 3.8 times higher than that of the silica gel reference (932 W/kg versus 240 W/kg).

A combinatorial screening approach has been designed for identification of Hf-Ta anodic memristors with enhanced properties. Three distinct compositional zones with similar characteristics have been identified, two of which are relevant for memristive applications. In a Hf-poor zone, (

An improved understanding of the nature and distribution of boron and cesium species in BCsX zeolites is a prerequisite to guide future developments in the environmentally attractive, yet challenging, production of styrene through the side-chain alkylation of toluene with methanol. Herein, standard characterization and catalytic tests are complemented by integrated visualization through time-of-flight secondary-ion mass spectrometry and energy-dispersive X-ray spectroscopy and detailed assessment by 133 Cs and 11 B NMR spectroscopy, to correlate the properties and performance during successive ion-exchange and impregnation steps in the preparation of both powders and millimeter-sized granules. The results highlight a significant impact of catalyst scaleup on the effective introduction of boron species, which originates chemical heterogeneity that is linked to selectivity losses. They also illustrate the complexity of elucidating the role of this promotor, which interacts with cesium cations and exhibits different coordination states and chemical environments, depending on the pretreatment.

The electroreduction of CO2 to fuels and chemicals is an attractive strategy for the valorization of CO2 emissions. In this study, a Cu2 O electrocatalyst prepared by a simple and potentially scalable solvothermal route effectively targeted CO evolution at low-to-moderate overpotentials [with a current efficiency for CO (CECO ) of ca. 60 % after 12 h at -0.6 V vs. reversible hydrogen electrode, RHE], and its selectivity was tuned by the introduction of p-block elements (In, Sn, Ga, Al) into the catalyst. SEM, HRTEM, and voltammetric analyses revealed that the Cu2 O catalyst undergoes extensive surface restructuring (favorable for CO evolution) under the reaction conditions. The modification of Cu2 O with Sn and In further enhanced the current efficiency (CE) for CO (ca. 75 % after 12 h at -0.6 V). In contrast, the introduction of Al altered the selectivity profile of the catalyst significantly, decreasing the selectivity toward CO but promoting the reduction of CO2 to ethylene (CE≈7 %), n-propanol, and ethanol (CE≈2 % each) at -0.8 V vs. RHE. This result is related to a decreased reducibility of Al-doped Cu2 O that might preserve Cu+ species (favorable for C2 H4 production) under the reaction conditions, which is supported by XRD, X-ray photoelectron spectroscopy, and H2 temperature-programmed reduction observations.

Journal of Materials Chemistry A, 5 (31), ISSN:2050-7488, ISSN:2050-7496

ISSN:1867-3880 ISSN:1867-3899

Carbon nitrides are promising hosts for single-atom catalysts (SACs) based on small amounts of precious metals dispersed as isolated atoms, presenting tantalizing opportunities to reduce the cost a...

Chemical Science, 10 (2), ISSN:2041-6520, ISSN:2041-6539

Controlling the structure sensitivity of catalyzed reactions over metals is central to developing atom-efficient chemical processes. Approaching the minimum ensemble size, the properties enter a non-scalable regime in which each atom counts. Almost all trends in this ultra-small frontier derive from surface science approaches using model systems, because of both synthetic and analytical challenges. Exploiting the unique coordination chemistry of carbon nitride, we discriminate through experiments and simulations the interplay between the geometry, electronic structure, and reactivity of palladium atoms, dimers, and trimers. Catalytic tests evidence applicationdependent requirements of the active ensemble. In the semihydrogenation of alkynes, the nuclearity primarily impacts activity, whereas the selectivity and stability are affected in Suzuki coupling. This powerful approach will provide practical insights into the design of heterogeneous catalysts comprising well-defined numbers of atoms.

Although amorphous silica-alumina catalysts (ASA) are a promising candidate for the replacement of HCl in the production of methylenedianiline (MDA) and higher homologues, their industrial implementation has been hampered by the lack of systematic studies targeting their design. The complexity of both, the materials as well as the reaction, necessitates the development of synthesis-structure-performance relationships to indicate if, and how, the stringent specifications in terms of activity, selectivity, and stability can be met. Herein, we investigate a large set of ASA obtained by coprecipitation, deposition-precipitation, grafting, and from commercial sources. A detailed analysis of their porosity, composition, Al speciation, acidity, and morphology reveals that every synthesis method leads to a unique combination of material properties. Through high-throughput batch experiments we investigate the importance of each of these parameters for the catalytic performance. The properties that determine the activity relate to the specific surface area, which should be as large as possible while featuring tetrahedrally-coordinated aluminum atoms in the silica matrix. In contrast, the selectivity is determined by the employed reaction conditions, namely the reaction temperature and the aniline content of the feed. Continuous tests under industrial conditions reveal that ASA deactivate via fouling during the initial restructuring of aminal. Pore-mouth blockage by fouling was minimized and optimal lifetimes ensured by employing mesopore networks consisting primarily of pyramidal or cylindrical pores. Based on these insights, we demonstrate that ASA can outperform hierarchical zeolites in terms of activity, while approaching industrially attractive oligomer contents and keeping the concentration of byproducts low at a high catalyst lifetime, advertising their potential for large-scale implementation.

The emergence of synergistic effects in multicomponent systems opens new opportunities to design improved catalysts for the electrochemical CO 2 reduction reaction (eCO 2 RR). Targeting the selective formation of CO, we have evaluated a comprehensive set of silver–indium electrocatalysts with different architectures, ranging from bulk intermetallic compounds to Ag nanoparticles supported on In 2 O 3 and In(OH) 3 . This approach allowed the design of a supported electrocatalyst with maximized performance. Despite very different bulk compositions, XPS analyses on Ag–In alloy electrodes revealed a near-surface indium enrichment, leading to a comparatively poor electrocatalytic performance. In contrast, the presence of oxidized indium deposits on the surface of bulk silver had a positive effect on the selectivity for CO at moderate overpotential. Based on these findings, we studied the interactions between silver and oxidic indium phases by preparing sets of In 2 O 3 - and In(OH) 3 -supported Ag catalysts, which were characterized with XRD, N 2 sorption, H 2 -TPR, CO 2 -TPD, STEM and EDX. With respect to the pristine supports and to similarly prepared Ag catalysts on carbon black, these nanostructured systems exhibited an enhanced current efficiency for CO at moderate overpotential, evidencing a synergistic effect between the metal nanoparticles and the supports. This effect was particularly marked at higher Ag loadings and with In(OH) 3 as support which, unlike In 2 O 3 , was stable against reduction under eCO 2 RR conditions. As a final step, the selectivity enhancement achieved in Ag/In(OH) 3 was combined with the known activity-promoting role of P25 TiO 2 by depositing Ag on a composite support. The Ag/In(OH) 3 –TiO 2 catalyst showed concurrent gains in selectivity and activity for CO. The findings highlight the potential of stable metal (hydr)oxide supports to act as promoters in the eCO 2 RR and the importance of the structural configuration in multicomponent electrocatalysts.

Copper–indium catalysts have recently shown promising performance for the selective electrochemical reduction of CO2 to CO. In this work, we prepared Cu–In nanoalloys by the in situ reduction of CuInO2 and In2O3-supported Cu nanoparticles and found that the structure of these nanoalloys evolves substantially over several electrocatalytic cycles, in parallel with an increase in the activity and selectivity for CO evolution. By combining electrochemical measurements with ex situ characterization techniques, such as XRD, STEM, elemental mapping, and XPS, we show that this behavior is caused by the segregation of copper and indium in these materials, resulting in the formation of a heterogeneous nanostructure of Cu-rich cores embedded within an In(OH)3 shell-like matrix. The evolved catalysts show high electrocatalytic performance at moderate overpotential (i.e., jCO > 1.5 mA cm–2 at −0.6 V vs RHE). We found that the removal of In(OH)3 from these heterogeneous nanostructures decreases the performance of the e...

Methanol synthesis by CO2 hydrogenation is attractive in view of avoiding the environmental implications associated with the production of the traditional syngas feedstock and mitigating global warming. However, there still is a lack of efficient catalysts for such alternative processes. Herein, we unveil the high activity, 100 % selectivity, and remarkable stability for 1000 h on stream of In2 O3 supported on ZrO2 under industrially relevant conditions. This strongly contrasts to the benchmark Cu-ZnO-Al2 O3 catalyst, which is unselective and experiences rapid deactivation. In-depth characterization of the In2 O3 -based materials points towards a mechanism rooted in the creation and annihilation of oxygen vacancies as active sites, whose amount can be modulated in situ by co-feeding CO and boosted through electronic interactions with the zirconia carrier. These results constitute a promising basis for the design of a prospective technology for sustainable methanol production.

In this work, nitrogen doped resorcinol–melamine–formaldehyde (RMF) resins were synthesized, pyrolyzed and physically activated with CO2. The influence of the activation time on the physicochemical properties and the water sorption behavior produced in this way was investigated. Furthermore, a comparison between physical activation with CO2 and chemical activation with KOH is presented. Materials performance was validated in an adsorption chiller test setup with a temperature step from 90 °C → 50 °C. The CO2 activated RMF carbon exhibits a maximal specific cooling power which is a factor of 1.7 higher in comparison to a commonly used, commercial silica gel reference material (430 W kg−1 compared to 255 W kg−1). This is surprising considering that the hydrophilicity of the CO2 activated carbon is rather low. The superior performance of carbon based sorbents is attributed to originate from the superior thermal transport properties of monolithic carbons over commercial silica gels. At a more feasible temperature swing 60 °C → 30 °C, the RMF derived carbon yields a specific cooling power 3.2 times greater than that of the silica gel reference.

In the present study, we report on the development of carbon adsorbents for water adsorption heat pumps. Resorcinol-melamine-formaldehyde (RMF) resins were synthesized and molded into monolithic shapes before pyrolysis and chemical activation with KOH. The influence of the carbonization and activation treatments on the physicochemical properties and the water sorption behavior of the final adsorbent materials were investigated. Activated carbons with a one-to-one (C to KOH) impregnation mass ratio, an activation temperature of 800 °C and an activation time of one hour exhibited the highest water cycling ability. For isobaric adsorption at 23 mbar, the peak specific cooling power of the best monolithic activated carbon produced in this way was 192 W kg−1 for a temperature step from 90 °C to 50 °C compared to 255 W kg−1 for silica gel for a finned tube heat exchanger of comparable fin spacing. For a temperature step from 60 °C to 30 °C, the monolithic activated carbon exhibited a higher peak specific cooling power (389 W kg−1) compared to silica gel (240 W kg−1). In situ infrared thermography revealed superior thermal transport properties of the monolithic carbons compared to commercial silica gel.

Cellulose, 18 (6), ISSN:1572-882X, ISSN:0969-0239

ACS Catalysis, 8 (2), ISSN:2155-5435

ACS Catalysis, 8 (1), ISSN:2155-5435

Local contact damage as well as cohesive and adhesive failure can limit the lifetime and applicability of hydrogenated diamond-like carbon (DLC) films on metallic substrates. DLC on titanium (Ti) is very interesting for industrial applications (e.g. biomedical applications), while also an excellent model system for the general understanding of hard and brittle films on ductile metallic substrates. Interlayers deposited between the DLC film and the Ti substrate have been shown to affect failure of such DLC coated Ti substrates. In this study, the effect of interlayer structure on contact damage and cohesive and adhesive failure is studied with tantalum (Ta) in its α- and β-phase. In all investigated cases the more ductile α-Ta provides improved results over the hard and brittle β-Ta interlayer. Due to plastic deformation effects, the resistance to contact damage is significantly increased with an α-Ta interlayer. Delamination occurs at the interface between the Ti substrate and the Ta interlayer. Compared to DLC on Ti without a Ta interlayer no enhancement in onset strain of fragmentation and delamination was achieved. A finite-element analysis shows that stress concentrations can be distributed over both interfaces if the Young's modulus of the interlayer material is of the order of the Young's modulus of the DLC.

In this study, we gathered further understanding of the function of the components in the Cu-ZnO-Al2O3 catalyst for methanol synthesis from mixed syngas feeds (CO/CO2/H2) to rationally develop systems displaying superior performance. In order to unravel the role of ZnO in the hydrogenation of the preferred methanol source, CO2, and in the (reverse) water–gas shift ((R)WGS) reaction, we tested coprecipitated materials with variable surface zinc content under industrially relevant conditions (5.0 MPa, 503–543 K). We found that a surface enrichment in zinc leads to higher activity and selectivity due to (i) the enhancement of the unique synergistic Cu-ZnO interactions boosting CO2 hydrogenation, (ii) the inhibition of the RWGS reaction which produces the undesired CO, and (iii) the electronic stabilization of the Cu sites against reoxidation by CO2 or H2O. Thus, a catalyst with a surface Zn/(Cu + Zn) ratio of 0.8 displayed superior catalytic properties than a commercial benchmark sample, which featured only ...

After base treatment of ZSM-5 crystals below 100 nm in size, TEM shows hollow single crystals with a 10 nm shell. SEM images confirm that the shell is well- preserved even after prolonged treatment. Determination of the Si/Al ratios with AAS and XPS in combination with argon sputtering reveals aluminum zoning of the parent zeolite, and the total pore volume increases in the first two hours of base treatment. In corresponding TEM images, the amount of hollow crystals are observed to increase during the first two hours of base treatment, and intact crystals are visible even after 10 h of leaching; these observations indicate different dissolution rates between individual crystals. TEM of large, commercially available ZSM-5 crystals shows inhomogeneous distribution of mesopores among different crystals, which points to the existence of structural differences between individual crystals. Only tetrahedrally coordinated aluminum is detected with (27) Al MAS NMR after the base leaching of nano-sized ZSM-5.

Friction and wear minimizing coatings are crucial for applications in combustion engines and medical implants. Their performance is typically limited by mechanical failure especially due to local overload. In this work, the contact damage creation, evolution, and final morphology of hydrogenated diamond-like carbon (DLC)-coated titanium (Ti) substrates are investigated. The influence of the DLC film thickness and the elastic–plastic deformation of the Ti on the contact damage are studied by microindentation and static finite-element analysis. Film thickness, indenter radius, and applied load as well as the elastic–plastic deformation of the Ti are shown to significantly affect contact damage. A failure plot is presented with the location of first failure in the DLC and compared to the experimental observation. In addition, a case study with variable fracture toughness of the DLC and its influence on the failure plot is shown. The stress distribution in the DLC follows a transition from a membrane-like to a plate-like deformation behavior upon increasing the DLC film thickness. Thin DLC films reveal increased cracking in the inner zone of the indent, while thicker DLC films reveal pronounced edge cracking. These edge cracks were correlated to pop-ins in force–displacement curves upon microindentation. Finally, a film thickness optimization process is presented for hard and brittle films on soft and ductile metallic substrates.

Using the model system hydrogenated diamond-like carbon (a-C:H) on titanium (Ti) substrates the effect of a changing film thickness on the cohesive and adhesive failure of hard and brittle films on ductile metallic substrates is analyzed by uniaxial loading. A film thickness size effect has been observed for the fracture strength and the onset strain of delamination. For a a-C:H film thickness 1 μm, whereas for film thicknesses of 200 and 500 nm the effect of the strain is only secondary. Upon uniaxial loading the Ti substrate exhibits an anisotropic deformation which affects the cohesive and adhesive failure of thin a-C:H films. The energy release rates for cohesive and adhesive failure and the fracture toughness of a-C:H are all independent of film thickness. The corresponding values have been determined to be 63.5 ± 2.6 J m −2 , 579 ± 20 J m −2 and 3.2 ± 0.1 MPa m 1/2 , respectively. Finally, a schematic is presented to determine qualitatively the adhesion of ductile and moderately brittle films on any kind of substrate.

Angewandte Chemie. International Edition, 56 (33), ISSN:1433-7851, ISSN:1521-3773, ISSN:0570-0833

The electronic transport properties of perovskite-type oxides with promising thermoelectric properties can be tuned by cationic substitutions as well as by creating oxygen vacancies. Here, two series of SrxEu1–xTiO3-δ (x = 0.00, 0.03, 0.25, 0.75, 0.97) samples with different oxygen stoichiometries are synthesized using various reductive atmospheres. Oxygen deficiencies in the series produced in highly reducing atmosphere are confirmed by thermogravimetric analysis. Electrical resistivity (ρ) and Seebeck coefficient (S) data reflect the strong influence of the oxygen nonstoichiometry on the transport properties. Samples from the strongly reduced series possess up to 5 orders of magnitude lower electrical resistivities than samples from the less reduced series, confirming that oxygen vacancies act as electron donors in the former. Their Seebeck coefficients strongly decrease with the increase of the charge carrier concentration (lower ρ). Pronounced S(T) peaks are observed, and are attributed to strong hybr...

Alkaline treatment of hydrothermally synthesised Sn-MFI and alkaline-assisted stannation of silicalite-1 were investigated as industrially amenable post-synthetic strategies to generate hierarchical Lewis-acidic MFI zeolites for the isomerisation of mono- and disaccharides. The mesoporosity introduced upon both treatments produced materials that are able to convert glucose, xylose, and lactose, which suffer from access or diffusion limitations to the active sites of the purely microporous Sn-MFI. The stannation of silicalite-1 rendered more active catalysts than the base leaching of Sn-MFI. This is due to a better utilisation of Sn, which is mainly incorporated at the crystals' external surface in the former case but mostly remains in the inaccessible micropores in the latter. The amount of Sn introduced via stannation could also be controlled by varying the strength of the alkaline solution and the molarity of the tin salt added. A Sn loading of 0.25 wt.% already ensures remarkable activity and selectivity.

Tantalum (Ta) and tantalum nitride thin films are highly important as diffusion barriers and adhesion layers in microelectronics and hard coatings for cutting tools. In this study, the effect of the underlying substrate on the phase formation of Ta and the influence of a changing N 2 /Ar flow ratio on hardness, phase and composition of reactively formed tantalum nitride have been investigated. Ta is DC sputter deposited and forms β-Ta on amorphous diamond-like carbon and on the amorphous natural oxide layers of Ti and Si(100) while a 15 nm TaN seed layer results in the formation of α-Ta. The chemical composition of the topmost layers of a substrate influences the formation of α- and β-Ta. With increasing N 2 /Ar flow ratios a transition from amorphous Ta-rich tantalum nitride over face-centered cubic tantalum nitride (fcc-TaN) to (100) textured fcc-TaN at flow ratios above 45% is observed. The hardness of the tantalum nitride thin film reaches a maximum at a flow ratio of 45%, followed by a decrease in hardness for higher N 2 /Ar flow ratios. The increase in hardness is associated with a decrease in grain size and shows a stronger correlation for a Meyers and Ashworth relationship than for a Hall–Petch relationship.

RuO2/SnO2–Al2O3 has been recently reported as an industrial catalyst for Cl2 production through HCl oxidation. The stabilizing role of the alumina binder in the material, essential for its durable performance, is elucidated here. Al2O3 prevents chlorination of the SnO2 carrier under relevant reaction conditions, whereas, in its absence, SnO2 losses exceed 80 wt % in very short times owing to volatilization as SnCl4. Characterization by using X-ray diffraction, temperature-programmed reduction with hydrogen, and high-resolution TEM indicates expansion of the cassiterite cell in the SnO2–Al2O3 composite with respect to pure SnO2, which suggests the insertion of certain Al species upon mechanochemical and thermal activation of the oxide mixture. 27Al magic-angle spinning NMR and X-ray photoelectron spectroscopy studies reveal that the pentahedrally coordinated Al3+ cations interact with SnO2, generating an electron-depleted region near the surface of SnO2 particles. This induces some acidic character in cassiterite, which possibly makes it inert toward HCl. Besides this electronic effect, the presence of thin porous amorphous alumina films, partly covering the SnO2 surface, can offer additional geometric protection of the support. Mechanical mixing followed by calcination is essential to attain stabilization, and maximized effects are achieved with a high-surface area alumina. Other oxides such as SiO2 are ineffective in preventing tin losses during HCl oxidation. The practical implications of these findings are very important. The metal loading (fourfold decrease) and, thus, the cost of the catalyst can be significantly lowered without compromising its long-term stability.

Reactions in the gas phase are of primary technological importance for applications in nano- and microfabrication technology and in the semiconductor industry. We present exclusively gas-phase protocols to chemically passivate oxide-free Si(111) and Si(100) surfaces with short-chain alkynes. The resulting surfaces showed equal or better oxidation resistance than most existing liquid-phase-derived surfaces and rivaled the outstanding stability of a full-coverage Si(111)-propenyl surface.1,2 The most stable surface (Si(111)-ethenyl) grew one-fifth of a monolayer of oxide (0.04 nm) after 1 month of air exposure. We monitored the regrowth of oxides on passivated Si(111) and Si(100) surfaces by X-ray photoelectron spectroscopy (XPS) and observed a significant crystal-orientation dependence of initial rates when total oxide thickness was below approximately one monolayer (0.2 nm). This difference was correlated with the desorption kinetics of residual surface Si-F bonds formed during HF treatment. We discuss applications of the technology and suggest future directions for process optimization.

CrystEngComm, 18, ISSN:1466-8033

Unwanted physiological reactions, caused by particle release in articulating joints, are still a major concern in total hip arthroplasty. Diamond-like carbon coatings (DLC) show very low wear values in many technical applications. Attempts to transfer these outstanding tribological properties to in-vivo load bearing articulating joints turned out to be extremely problematic. A DLC coated metallic metatarsophalangeal (MTP) prosthesis, with both articulating surfaces coated, was explanted after approximately 4 years. The DLC-coating was removed from the entire face of the phalangeal component and from most of the face of the metatarsal component. It appeared that the coating was scratched and then delaminated parallel to the scratches. To retrospectively investigate the reason for the in-vivo failure, the explanted prosthesis was analyzed by X-ray photoelectron spectroscopy (XPS) depth profiling and cross sectional scanning electron microscope (SEM) analysis. The coating consisted of an approximately 180 nm thick DLC film and a circa 120 nm thick silicon based adhesion promoting interlayer on a CoCrMo base material. SEM observation of transversal cuts showed that the delamination of the DLC-coatings was mainly caused by a slow in-vivo corrosion of the whole Si interlayer due to crevice corrosion. Additionally, a weak mechanical bond between the CoCrMo substrate and the Si-based interlayer further facilitated the access of body liquid below the Si interlayer. The instability of Si toward crevice corrosion was also demonstrated by a separate crevice experiment using silicon single crystals.

The corrosion mechanisms of Al Cr Fe and Al Cu Fe Cr complex metallic alloys have been investigated by potentiodynamic and potentiostatic polarization. Very good passivation of the Al Cr Fe surface is exhibited from 1 M H2SO4 to 1 M NaOH solutions which was confirmed by ICP OES analysis over a period of 273 days. Potentiostatically formed passive films analysed by XPS revealed chromium enrichment in the outermost layer of the aluminium oxy hydroxide film. Although Al Cu Fe Cr showed passivation during potentiodynamic polarization heavy active corrosion at OCP was revealed by ICP OES. For the Al Cu Fe Cr alloy the 10 content of Cr is insufficient to maintain a protective "chemically stable" Cr oxide/hydroxide. (c) 2011 Elsevier Ltd. All rights reserved.

The evolving usefulness of organic conducting polymers, of metallic or semiconducting type, is primarily dependent on their mechanisms of electrical conduction and degradation. Understanding these mechanisms is crucial for improving the effi ciency and lifetime of technologies derived from this class of polymers. There is demand for a model that provides a vivid and more precise evaluation of the electrical conduction mechanism in these polymers – especially when they act as hosts to guest species, such as acid dopant ions and nanoparticles. If, for example, the motional behavior of a host–guest organic conducting polymer structure, as related to dynamic stability, is either asynchronous or synchronous, is this refl ected in the mechanism of electrical conduction and does it account for the pace of material’s degradation? Here, we demonstrate that the answer is affi rmative: asynchronous structural motions arising due to loosely bound or free guest species within the host polymer lead to anomalous electrical conduction mechanisms, increased fragility and short lifetime, at odds with the synchronous behavior.

The influence of chemical and thermal aging effects on catalytic activity was analyzed for a vehicle (bifuel) aged pre- and underfloor three-way catalyst (p-/u-TWC) as well as an engine aged diesel oxidation catalyst (DOC). The conversion results were compared with the respective new catalysts. Although the vehicle aged p-TWC showed massive thermal aging, its CO conversion rate was comparable to that of the vehicle aged u-TWC. On the other hand, the conversion rate for methane abatement was significantly affected above 325 °C. Methane conversion appeared as the parameter mostly affected by (thermal) aging. The DOC showed massive chemical aging with typical engine oil based contaminants like P and Zn but also with Si. The contamination is likely responsible for the shift of propene and NO light-off curves to higher temperatures by about 70 °C.

Results from a study conducted between National Metrology Institutes (NMIs) for the measurements of the absolute thicknesses of ultra-thin layers of SiO2 on Si are reported. These results are from a key comparison and associated pilot study under the auspices of the Consultative Committee for Amount of Substance. ‘Amount of substance’ may be expressed in many ways, and here the measurand is the thickness of the silicon oxide layers with nominal thicknesses in the range 1.5–8 nm on Si substrates, expressed as the thickness of SiO2. Separate samples were provided to each institute in containers that limited the carbonaceous contamination to approximately < 0.3 nm. The SiO2 samples were of ultra-thin on (100) and (111) orientated wafers of Si. The measurements from the laboratories which participated in the study were conducted using ellipsometry, neutron reflectivity, X-ray photoelectron spectroscopy or X-ray reflectivity, guided by the protocol developed in an earlier pilot study. A very minor correction was made in the different samples that each laboratory received. Where appropriate, method offset values attributed to the effects of contaminations, from the earlier pilot study, were subtracted. Values for the key comparison reference values (agreed best values from a Consultative Committee study) and their associated uncertainties for these samples are then made from the weighted means and the expanded weighted standard deviations of the means of these data. These results show a dramatic improvement on previous comparisons, leading to 95% uncertainties in the range 0.09–0.27 nm, equivalent to 0.4–1.0 monolayers over the 1.5–8.0 nm nominal thickness range studied. If the sample-to-sample uncertainty is reduced from its maximum estimate to the most likely value, these uncertainties reduce to 0.05–0.25 nm or ∼1.4% relative standard uncertainties. The best results achieve ∼1% relative standard uncertainty. It is concluded that XPS has now been made fully traceable to the SI, for ultra-thin thermal SiO2 on Si layers, by calibration using wavelength methods in an approach that may be extended to other material systems. © Crown copyright 2009. Reproduced with the permission of Her Majesty's Stationery Office. Published by John Wiley & Sons, Ltd.

In this work, the ability of ashless anti-wear additives to form protective tribofilms on diamond-like carbon (DLC) and steel surfaces was investigated and compared to the reactions of ZnDTP. Reciprocating sliding tests were performed under mild tribological conditions for steel/steel and DLC/DLC contacts to avoid wearing through the DLC coating. A comparison of the friction behavior of ZnDTP with two ashless additives, a butylated triphenyl phosphorothionate (b-TPPT) and an amine phosphate (AP), indicated that the latter additive behaved in a different manner to the first two. b-TPPT shows the lowest friction coefficient for DLC/DLC contacts whereas the AP give the lowest friction coefficient for steel sliding against steel. AFM and ESEM were performed to analyze the surfaces and showed the build up of tribofilms from ZnDTP and b-TPPT onto both the steel and DLC surfaces. No evidence of such a film formation on DLC was observed when the AP were used.

Increasing use of DLC coatings in oil-lubricated, mechanical systems has led to a great deal of interest in optimising the interactions between lubricant additives and coatings. We have looked at the formation of a tribofilm from ZnDTP on diamond-like carbon (DLC) when sliding in oil against DLC on a polished steel substrate under very low wear conditions. It was found that the tribofilm formed in the absence of iron adhered very weakly to the surface and could be removed by washing in an ultrasonic bath. The wear was too low to be detected with laser profilometry. AFM imaging of the surfaces of steel and DLC after sliding of steel/steel and DLC/DLC showed that the tribofilm formed on DLC had a very different morphology to that formed on steel. EDX was used to demonstrate that the tribofilm contained zinc, sulphur and phosphorus. ToF-SIMS measurements showed that iron was neither present at the DLC surface nor in the tribofilm.

Focused ion beam physical sputtering and iodine-enhanced etching of indium phosphide (InP) were performed. Up to 15× enhanced etching rates over sputtering were measured at room temperature, due to the addition of iodine to the sputter-process. Reaction mechanisms and products are discussed and characterized. The reaction is limited by the desorption of indium triiodide (InI 3 ) at room temperature. InI 3 has to be removed by sputtering, which simultaneously amorphizes the underlying substrate. Surface roughness and stoichiometry of InP are compared for sputtering and etching. Gallium-contamination and the damaged zone in InP are significantly reduced by iodine-enhanced etching. Based on the reaction mechanisms, an optimum beam scanning strategy is proposed which allows precise microfabrication in reduced time and minimizes damage to the substrate. The method is also applicable for other halide gas etching processes of III–V semiconductors.

We report on mechanical dissipation measurements carried out on thin (∼100 nm), single-crystal silicon cantilevers with varying chemical surface termination. We find that the 1-2 nm-thick native oxide layer of silicon contributes about 85% to the friction of the mechanical resonance. We show that the mechanical friction is proportional to the thickness of the oxide layer and that it crucially depends on oxide formation conditions. We further demonstrate that chemical surface protection by nitridation, liquid-phase hydrosilylation, or gas-phase hydrosilylation can inhibit rapid oxide formation in air and results in a permanent improvement of the mechanical quality factor between three- and five-fold. This improvement extends to cryogenic temperatures. Presented recipes can be directly integrated with standard cleanroom processes and may be especially beneficial for ultrasensitive nanomechanical force- and mass sensors, including silicon cantilevers, membranes, or nanowires.

Diamond-like carbon (DLC) coatings are a class of materials and, depending on the deposition conditions and the tribological system, different outstanding tribological properties can be obtained. The most important subclasses of DLC are hydrogenated amorphous carbon (a-C:H) and hydrogen free tetrahedral amorphous carbon (ta-C). When DLC slides against a metal, the formation of the so-called transfer layer on the metallic counterpart can protect the metal from further wear. Adhesion and cohesion of this transfer layer is a critical issue and is also influenced by the environmental atmosphere including the relative humidity. When DLC is running against a hard and chemically inert counterface, such as sapphire, the formation of a transfer layer is not observed but low wear is still obtained. This is attributed to the lubricating properties of the graphitic wear residues. Due to its unique combination of properties, DLC is already used in different industrial applications such as magnetic storage media, diesel injection pumps, sliding bearings, car valve rockers, gears, tappets of racing motorcycles, laser barcode scanner windows in supermarkets, VCR head drums, textile industry parts, motor cycle forks, razor blades, etc. In medical applications, i.e. the coating of load bearing joints that slide against ultra high molecular weight polyethylene (UHMWPE), the different in vitro experiments apparently showed contradicting results, mainly due to the different experimental setups and especially the different liquids used as lubricants. However, when DLC slides against DLC in medical applications low wear rates could be demonstrated in different in vitro tests.