Surface Characterisation of Silicon Based MEMS

Polysilicon Microelectromechanical systems(MEMS) are the subject of intensive researches. Surface chemistry and topography of a MEMS test structure fabricated at Sandia National Laboratory, USA, were studied by means of scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS) and atomic force microscopy(AFM). XPS C_ 1sand Si_ 2pspectra from the polysilicon components, silicon nitride substrate and a reference silicon wafer were compared. The results confirm the presence of a self-assembled monolayer(SAM) on the MEMS surface. An island-like morphology was found on both polysilicon and silicon nitride surfaces of the MEMS. The islands take the form of caps, being up to 0.5 μm in diameter and 20 nm in height. It is concluded that the co-existence of columnar growth and equiaxed growth during the low pressure chemical vapor deposition(LPCVD) of these layers leads to the observed morphology and the islands are caps to the columnar structures.

Optimizing the oxide support composition in Pr-doped CeO_(2) towards highly active and selective Ni-based CO_(2) methanation catalysts

In this study,Ni catalysts supported on Pr-doped Ce O_(2) are studied for the CO_(2) methanation reaction and the effect of Pr doping on the physicochemical properties and the catalytic performance is thoroughly evaluated.It is shown,that Pr^(3+)ions can substitute Ce^(4+)ones in the support lattice,thereby introducing a high population of oxygen vacancies,which act as active sites for CO_(2) chemisorption.Pr doping can also act to reduce the crystallite size of metallic Ni,thus promoting the active metal dispersion.Catalytic performance evaluation evidences the promoting effect of low Pr loadings(5 at%and 10 at%)towards a higher catalytic activity and lower CO_(2) activation energy.On the other hand,higher Pr contents negate the positive effects on the catalytic activity by decreasing the oxygen vacancy population,thereby creating a volcano-type trend towards an optimum amount of aliovalent substitution.

High-energy sodium-ion hybrid capacitors through nanograin-boundary-induced pseudocapacitance of Co_(3)O_(4) nanorods

Sodium-ion hybrid capacitors (SICs) have been proposed to bridge performance gaps between batteries and supercapacitors,and thus realize both high energy density and power density in a single configuration.Nevertheless,applications of SICs are severely restricted by their insufficient energy densities (<100Wh/kg) resulted from the kinetics imbalance between cathodes and anodes.Herein,we report a nanograin-boundary-rich hierarchical Co_(3)O_(4) nanorod anode composed of~20 nm nanocrystallites.Extreme pseudocapacitance (up to 72%@1.0 mV/s) is achieved through nanograin-boundary-induced pseudocapacitive-type Na^(+) storage process.Co_(3)O_(4) nanorod anode delivers in this case highly reversible capacity (810 mAh/g@0.025 A/g),excellent rate capability (335 mAh/g@5.0 A/g),and improved cycle stability (100 cycles@1.0 A/g with negligible capacity degradation).The outstanding performance can be credited to the hierarchical morphology of Co_(3)O_(4) nanorods and the well-designed nanograinboundaries between nanocrystallites that avoid particle agglomeration,induce pseudocapacitive-type Na^(+) storage,and accommodate volume variation during sodiation-desodiation processes.Nitrogendoping of the Co_(3)O_(4) nanorods not only generates defects for extra surficial Na^(+) storage but also increases the electronic conductivity for efficient charge separation and lowers energy barrier for Na^(+) intercalation.Synergy of conventional reaction mechanism and pseudocapacitive-type Na^(+) storage enables high specific capacity,rapid Na^(+) diffusion,and improved structural stability of the Co_(3)O_(4) nanorod electrode.The SIC integrating this highly pseudocapacitive anode and activated carbon cathode delivers exceptional energy density (175 Wh/kg@40 W/kg),power density (6632 W/kg@37 Wh/kg),cycle life (6000 cycles@1.0 A/g with a capacity retention of 81%),and coulombic efficiency (~100%).

Influence of Halide Choice on Formation of Low-Dimensional Perovskite Interlayer in Efficient Perovskite Solar Cells

Recent advances in heterojunction and interfacial engineering of perovskite solar cells(PSCs)have enabled great progress in developing highly efficient and stable devices.Nevertheless,the effect of halide choice on the formation mechanism,crystallography,and photoelectric properties of the lowdimensional phase still requires further detailed study.In this work,we present key insights into the significance of halide choice when designing passivation strategies comprising large organic spacer salts,clarifying the effect of anions on the formation of quasi-2D/3D heterojunctions.To demonstrate the importance of halide influences,we employ novel neo-pentylammonium halide salts with different halide anions(neoPAX,X=I,Br,or Cl).We find that regardless of halide selection,iodide-based(neoPA)_(2)(FA)_((n-1))PbnI_((3n+1))phases are formed above the perovskite substrate,while the added halide anions diffuse and passivate the perovskite bulk.In addition,we also find the halide choice has an influence on the degree of dimensionality(n).Comparing the three halides,we find that chloride-based salts exhibit superior crystallographic,enhanced carrier transport,and extraction compared to the iodide and bromide analogs.As a result,we report high power conversion efficiency in quasi-2D/3D PSCs,which are optimal when using chloride salts,reaching up to 23.35%,and improving long-term stability.

Preparation Procedure of Liposome-Absorbed Substrate and Tip Shape Correction of Diameters of Liposome Measured by AFM

The procedure to measure liposome in aqueous solution has been examined using atomic force microscope (AFM). We concluded a chemical modified silicon wafer (substrate for AFM observation of liposome) with 3-aminopropyltrieth-oxysilane (APTES) which enabled us to scan anionic liposome softly in water because they were keeping structures as vesicles and stably adsorbed on the substrate by electrostatic force. From captured AFM topographic images, we counted the amount of liposome and analyzed the distribution of mean diameters, which were corrected by an approximated curve of the tip shape. We discussed the method of effective evaluation as practical analysis and its problems for robust analysis.

Development of a Novel Hybrid Aluminum-Based Sol-Gel Materials: Application to the Protection of AA2024-T3 Alloys in Alkaline Environment

Extensive research on environmentally complaint sol-gel coatings is currently underway for a wide range of applications. Sol-gel technology combines the synergistic properties of inorganic and organic components to design nanostructured coating materials with advanced physical properties. Through a judicious choice of precursors and additives improved performances, such as chemical resistance or pH stability, it can be achieved. This is of particular interest for copper rich AA 2024-T3 aluminium alloys used on aircraft, where increase in local pH occurs at corrosion sites. This work focuses on improving the alkaline stability and anticorrosion properties of such a sol-gel coatings on AA2024-T3 by incorporating aluminium functionality into hybrid materials prepared from hydrolysis and condensation of 3-methacryloxypropyltrimethoxysilane, zirconium n-propoxide and zirconium/alkoxide precursors. Dynamic light scattering technique was used to study the particle size nature of the sol-gel materials in colloidal form. X-ray photoelectron spectroscopy was used to study the oxidation state of the aluminium and zirconium at the sol-gel coating surface. Field emission scanning electrochemical microscopy coupled with energy dispersive spectroscopy was used to assess the microstructural features. Electrochemical characterisations employing potentiodynamic scanning and electrochemical impedance spectroscopy were performed to investigate the anticorrosion performance of the hybrid sol-gel coatings. The best anti-corrosive protection of AA2024-T3 in an alkaline saline solution (pH = 10) was achieved with materials containing 10 mol% and 15 mol% aluminium doped sol-gel coatings. This study shows that presence of aluminium has a positive effect on alkaline stability of the coatings and is a potential green candidate for the protective coatings on aerospace alloys.

Stratigraphic analysis of intercalated graphite electrodes in aqueous inorganic acid solutions

A detailed stratigraphic investigation of the intercalation mechanism when graphite electrodes are immersed inside diluted perchloric(HClO_(4))and sulfuric(H_(2)SO_(4))electrolytes is obtained by comparing results when graphite crystals are simply immersed in the same acid solutions.By combining time-of-flight secondary ion mass spectrometry(ToF-SIMS)and in-situ atomic force microscopy(AFM),we provide a picture of the chemical species involved in the intercalation reaction.The depth intensity profile of the ion signals along the electrode crystal clearly shows a more complex mechanism for the intercalation process,where the local morphology of the basal plane plays a crucial role.Solvated anions are mostly located within the first tens of nanometers of graphite,but electrolytes also diffuse inside the buried layers for hundreds of nanometers,the latter process is also aided by the presence of mesoscopic crystal defects.Residual material from the electrolyte solution was found localized in well-defined circular spots,which represent preferential interaction areas.Interestingly,blister-like micro-structures similar to those observed on the highly oriented pyrolytic graphite(HOPG)surface were found in the buried layers,confirming the equivalence of the chemical condition on the graphite surface and in the underneath layers.