In-situ wafer bowing measurements of GaN grown on Si(111) substrate by reflectivity mapping in metal organic chemical vapor deposition system

In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2 Thomas Swan close coupled showerhead metal organic chemical vapor deposition（MOCVD） system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses（tensile and compressive） during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, Ga N grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded Al Ga N buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method.

IN-SITU REFLECTION MICROSCOPIC FTIR SPECTROELECTROCHEMISTRY AT MICRO-/ULTRAMICROELECTRODE

An in-situ reflection ultramicroelectrode microscopic FTIR spectroelectrochemical cell was constructed and demonstrated by using hexacyanoferrate redox couple in aqueous sulphate solution.An excellent microscopic SNIFTIRS reflection spectra had been obtained with no difficulty of IR beam focusing.The cell is simple in construction and convenient for use,And it will have most of all advantages of micro-/ultramicroelectrode.

Advancements in Sound Reflection and Airborne Sound Insulation Measurement on Noise Barriers

The in-situ measurement of sound reflection and airborne sound insulation characteristics of a noise barrier in Europe are currently performed following the CEN/TS 1793-5 European standard guidelines (last revision published in 2003 [1]). After some years a large number of barriers measured, the original method has been significantly enhanced and validated in the frame of the EU funded QUIESST project, WP3 [2]. The sound reflection measurement method has been improved using a square 9-microphone grid not rigidly connected to the loudspeaker, an optimized alignment algorithm of free-field and reflected impulse responses, including fractional step shifts and least squares estimation of the best relative position, and a correction for geometrical divergence and sound source directivity. Each single measurement is then validated by means of the Reduction Factor calculation. The airborne sound insulation measurement method has not been markedly changed since 2003, because the procedure is robust and easily applicable as it is, but some problems may still be encountered when measuring highly insulating noise barriers, due to a poor signal to noise ratio of the transmitted impulse response. In those cases it is difficult to realize just after the measurement whether the obtained data are valid or not. A method, applicable on site, to overcome this problem is described here. It is based on the Signal to Noise Ratio estimation of critical parts of the acquired impulse responses and gives a strong validation criterion.

MECHANISM OF GLUCOSE ELECTRO-OXIDATION: VOLTAMMETRIC AND in-situ FTIR REFLECTANCE SPECTROSCOPIC STUDIES

In connection with the development of the implantable biocell for a cardiac pacemaker and the sensor for an artificial pancreas, much attention has been paid to the studies of glucose electro-oxidation. However, the mechanistic aspects still remain debatable, since most of the experiments are based only on conventional electrochemical techniques and the information about the electrode reaction in molecular level is in lack. In the present note, be-

In-situ quantification of the surface roughness for facile fabrications of atomically smooth thin films

This work presents an in-situ technique to quantify the layer-by-layer roughness of thin films and heterostructures by measuring the spectral profile of the reflection high-energy electron diffraction(RHEED).The characteristic features of the diffraction spot,including the vertical to lateral size ratio c/b and the asymmetrical ratio c_(1)/c_(2) along the vertical direction,are found to be quantitatively dependent on the surface roughness.The quantitative relationships between them are established and discussed for different incident angles of high-energy electrons.As an example,the surface roughnesses of LaCoO_(3) films grown at different temperatures are obtained using such an in-situ technique,which are confirmed by the ex-situ atomic force microscopy.Moreover,the in-situ measured layer-by-layer roughness oscillations of two LaCoO_(3) films are demonstrated,revealing drastically different information from the intensity oscillations.The experiments assisted with the in-situ technique demonstrate an outstanding high resolution down to-0.1 A.Therefore,the new quantitative RHEED technique with real-time feedbacks significantly escalates the thin film synthesis efficiency,especially for achieving atomically smooth surfaces and interfaces.It opens up new prospects for future generations of thin film growth,such as the artificial intelligence-assisted thin film growth.

Unraveling the interfacial effect of PdBi bimetallic catalysts on promoting CO_(2)electroreduction to formate

Through interface engineering and content control strategy,a PdBi bimetallic interface structure was constructed for the first time to selectively convert CO_(2)to formate with a remarkably high Faraday efficiency(FEformate)of 94%and a partial current density(jformate)of 34 mA·cm^(−2)at−0.8 V vs.reversible hydrogen electrode(RHE)in an H-cell.Moreover,the PdBi interface electrocatalyst even exhibited a high current density of 180 mA·cm^(−2)with formate selectivity up to 92%in a flow cell and could steadily operate for at least 20 h.Electrochemical in-situ attenuated total reflection surface enhanced infrared absorption spectroscopy(ATR-SEIRAS)confirmed that the PdBi interface could greatly weaken the adsorption of*CO intermediates due to electronic and geometric effects.Density functional theory(DFT)calculations also established that the PdBi interface regulated the CO_(2)-to-formate pathway by reducing the energy barrier toward HCOOH and largely weakening the adsorption of*CO intermediates on the catalyst surface.This study reveals that the unique PdBi bimetallic interface can provide a novel platform to study the reaction mechanism through combining in-situ ATR-SEIRAS and DFT calculations.

Experimental and mechanistic understanding of photo-oxidation of methanol catalyzed by CuO/TiO2-spindle nanocomposite:Oxygen vacancy engineering

We report experimental and mechanistic understanding of methanol oxidation to produce methyl formate using CuO/Ti02-spindle composite as a promising photocatalyst under mild conditions with over 97%conversion and 83%selectivity.The catalysts are obtained via precise depositing of CuO nanoclusters(size:~3.5 nm)at the{101}facet of the TiO2 to optimally tune exciton recombination through oxygen vacancies generation,evidenced by photoluminescence and Raman spectroscopy measurements.The turnover frequency(TOF)and the apparent quantum efficiency(AQE)of the 7%CuO/TiO2-spindle composites reach up to 23.8 molmethanol·gcat^-1·h^-1 and 55.2%at 25℃,respectively,which are substantially higher than these previously reported photocatalysts.Further,the in-situ attenuated total reflection infrared spectroscopy analysis reveals that the methanol oxidation most likely takes place through the conversion of adsorbed methoxy(CH30^*)to formaldehyde(CHO^*)intermediate,a subject of major debate for a long time.The adsorbed formaldehyde(CHO^*)thus produced reacts with another CH30^*species in its close proximity to form the final product of methyl formate.Results of this study provide insights into the reaction mechanism,and offer guidelines to systematically develop and apply photocatalysts for methanol conversion and related reactions via surface engineering.

Catalytic performance and reaction mechanisms of NO removal with NH_(3) at low and medium temperatures on Mn-W-Sb modified siderite catalysts

Iron-based catalysts have been explored for selective catalytic reduction(SCR)of NO due to environmentally benign characters and good SCR activity.Mn-W-Sb modified siderite catalysts were prepared by impregnation method based on siderite ore,and SCR perfor-mance of the catalysts was investigated.The catalysts were analyzed by X-ray diffrac-tion,H_(2)-temperature-programmed reduction,Brunauer-Emmett-Teller,Thermogravimetry-derivative thermogravimetry and in-situ diffused reflectance infrared Fourier transform spectroscopy(DRIFTS).The modified siderite catalysts calcined at 450℃ mainly consist of Fe_(2)O_(3),and added Mn,W and Sb species are amorphous.3Mn-5W-1.5Sb-siderite catalyst has a wide temperature window of 180-360℃ and good N_(2) selectivity at low temperatures.In-situ DRIFTS results show NH_(4)^(+),coordinated NH_(3),NH_(2),NO_(3)^(-)species(bidentate),NO_(2)-species(nitro,nitro-nitrito,monodentate),and adsorbed NO_(2) can be discovered on the sur-face of Mn-W-Sb modified siderite catalysts,and doping of Mn will enhance adsorbed NO_(2) formation by synergistic catalysis with Fe^(3+).In addition,the addition of Sb can inhibit sulfates formation on the surface of the catalyst in the presence of SO_(2) and H_(2)O.Time-dependent in-situ DRIFTS studies also indicate that both of Lewis and Br?nsted acid sites play a role in SCR of NO by ammonia at low temperatures.The mechanism of NO removal on the 3Mn-5W-1.5Sb-siderite catalyst can be discovered as a combination of Eley-Rideal and Langmuir-Hinshelwood mechanisms with three reaction pathways.The mechanism of NO,oxidized by synergistic catalysis of Fe^(3+)and Mn^(4+/3+)to form NO_(2) among three pathways,reveals the reason of high NO_(x) conversion of the catalyst at medium and low temperatures.

Catalytic Combustion of Lean Methane Assisted by Electric Field over Pd/Co_3O_4 Catalysts at Low Temperature

A series of Pd/Co_3O_4 catalysts were prepared by Self-Propagating High-Temperature Synthesis(SHS)method in this study, and electric field was applied for catalytic combustion of lean methane over Pd/Co_3O_4 catalysts at low temperature. When electric field was applied, the catalytic combustion performance of Pd/Co_3O_4 catalysts was greatly improved, and the application of electric field could reduce the load of active element Pd to some extent while maintaining the same efficiency. Based on experimental tests and the analysis results of X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), H2-temperature-programmed reduction(H2-TPR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy(in-situ DRIFTS), the mechanism of catalytic oxidation of CH_4 over Pd/Co_3O_4 catalysts in electric field was proposed. The catalytic combustion of CH_4 occurs only when the temperature is higher than 250?C normally, but when electric field was applied, the whole process of CH_4 oxidation was promoted significantly and the reaction temperature was reduced. Electric field could promote the reduction of the support Co_3O_4 to release the lattice oxygen, resulting in the increase of PdOxand the surface chemisorbed oxygen, which could provide more active sites for the low-temperature oxidation of CH_4. Furthermore, electric field could accelerate the dehydroxylation of CoOOH to further enhance the activity of the catalysts.