High-intensity X-ray Diffraction Research Articles

Characterization of polycrystalline bulk ferroelectric ZnSnS3 synthesized by hydrothermal method for photovoltaic application

ZnSnS3, a newly theoretically predicted ferroelectric material which shows promising properties for solar cell and photovoltaic applications, was successfully grown in our laboratory by hydrothermal method. The high intensity x-ray diffraction pattern from the (211), (101̅), (200), (210), (310), (320), and (321̅) planes reveal the crystalline character of the trigonal ZnSnS3 phase. The microstructural property and elemental distribution were evaluated using SEM and TEM studies. Diffuse reflectance measurement at room temperature shows a direct bandgap of 2.62 eV along with a high energy direct transition of 3.13 eV. Two broad photoluminescence peaks at various temperatures (4–300 K) were also detected around (2.61–2.73 eV) and (3.04–3.11 eV). The emission characteristics are explained considering the shallow donor level to valence band transitions. Raman study elucidates that the synthesized ZnSnS3 possess a good number of Raman active bands. A phase transition from the ferroelectric to non-ferroelectric phase of ZnSnS3 is observed around 330 °C in DSC and dielectric measurements. The P-E measurement showed that the material is ferroelectric in nature with saturation polarization value of 21.85μC/cm2. The current-voltage characteristics showgood photovoltaic response of the fabricated Ni/ZnSnS3/Ni device in the visible range indicating its application in PV devices and photodetector.

Study of GaN coalescence by dark-field X-ray microscopy at the nanoscale.

This work illustrates the potential of dark-field X-ray microscopy (DFXM), a 3D imaging technique of nanostructures, in characterizing novel epitaxial structures of gallium nitride (GaN) on top of GaN/AlN/Si/SiO2 nano-pillars for optoelectronic applications. The nano-pillars are intended to allow independent GaN nanostructures to coalesce into a highly oriented film due to the SiO2 layer becoming soft at the GaN growth temperature. DFXM is demonstrated on different types of samples at the nanoscale and the results show that extremely well oriented lines of GaN (standard deviation of 0.04°) as well as highly oriented material for zones up to 10 × 10 µm2 in area are achieved with this growth approach. At a macroscale, high-intensity X-ray diffraction is used to show that the coalescence of GaN pyramids causes misorientation of the silicon in the nano-pillars, implying that the growth occurs as intended (i.e. that pillars rotate during coalescence). These two diffraction methods demonstrate the great promise of this growth approach for micro-displays and micro-LEDs, which require small islands of high-quality GaN material, and offer a new way to enrich the fundamental understanding of optoelectronically relevant materials at the highest spatial resolution.

High strength and plasticity in Cr-Al-C composite

The microstructure and mechanical behavior of a Cr-Al-C composite rapidly consolidated by spark plasma sintering at a relatively low temperature of 900 °C were investigated. The sintered composite showed a multi-phase microstructure consisting of Cr2AlC and Al4C3 in Cr5Al8 matrix, as confirmed by high intensity X-ray diffraction and transmission electron microscopy (TEM). The multi-phase composite showed high hardness of about 11 GPa, high compressive strength of up to 5.81 GPa and strain-to-failure of 1.76%–10.82% at room temperature. High resolution TEM revealed that the dislocation slip and kink bands within the Cr2AlC MAX phase grains contribute significantly to the plasticity, whereas, the Cr5Al8 and Al4C3 improves the strength and hardness of the overall composite. These results highlight the importance of combining ceramic phases with intermetallic matrix for designing high-performance engineering materials.

Focal construct geometry for high-intensity x-ray diffraction from laser-shocked polycrystalline.

An increasing number of dynamic experiments, especially those involving laser drive, are employing in situ x-ray diffraction as a probe to interrogate structure evolution between states of matter under extreme pressure and temperature. We present an alternative configuration, focal construct geometry, for in situ x-ray diffraction to measure the structure and evolution of dynamically compressed polycrystalline materials on a laser platform. This configuration makes full use of the isotropically emitted He-α x rays by employing an annular (or semi-annular) collimator rather than a regular pinhole collimator and thus increases the flux of incident x rays reaching the sample as well as the intensity of the diffracted x rays, enabling the detection of a diffraction pattern with less laser energy. Its effectiveness and applicability are validated against the conventional Debye-Scherrer geometry through direct molecular dynamics simulations and x-ray diffraction simulations for two representative shock-induced phase transition events, solid-solid and solid-liquid (or melting). This configuration reproduces all the Debye-Scherrer diffraction profiles in good accuracy and demonstrates superior efficiency in utilizing the isotropic x-ray source and harvesting diffracted x rays while preserving the angular resolution.

Study of effect of Dy substitution on structural, dielectric, impedance and magnetic properties of bismuth ferrite

This communication mainly reports the synthesis and characterization of dysprosium (Dy)-doped bismuth ferrite [i.e., Bi(Fe0.95Dy0.05)O3 (referred as BFDO5)] compound. A conventional high-temperature solid-state reaction technique has been utilized for synthesizing the material at a temperature of 800 °C. The structural study of the prepared sample, carried out using X-ray diffraction data, reveals the creation of a single-phase compound having an orthorhombic crystal structure. The average crystallite size, obtained from the measurement of high-intensity X-ray diffraction peaks of the BFDO5 material, was found to be 38 nm. The purity of the prepared compound and concentration of its constituent elements were confirmed by energy dispersive X-ray spectroscopy (EDXS) data. The field effect scanning electron microscope (FESEM) image clearly shows the surface morphology and regular distribution of the composite grains over its surface. Detailed analysis of the dielectric and impedance data, measured in a broad range of frequency (1–1000 kHz) and temperature (25–500 °C), has shown a significant improvement in the dielectric and electrical properties of the prepared material. The electrical polarization measurement, done by P–E hysteresis loop tracer, shows the existence and enhancement of ferroelectric property of the material. Room temperature measurement of its magnetization was carried out by using vibrating sample magnetometer that shows a significant enhancement in a remnant magnetization as compared to pure bismuth ferrite.

Correlation of Local Crystal Structural and Physical Properties of the Delafossite CuCr1-xFexO2 (0 ≤ x ≤ 1) Series.

Cu-based delafossites offer multifunctional properties that include electrical, magnetic, optical, and thermal transport, and they also act as a photocathode for energy-harvesting applications. Such properties can be modified by bringing about subtle changes in the chemical environment, like introducing holes or excess electrons in the system. With the aim to understand the evolution of physical properties that take place upon systematically replacing 3d3 (Cr3+) with 3d5 (Fe3+), we performed a comprehensive study of structural, electrical and thermal transport, and magnetic properties of the CuCr1-xFexO2 series. In agreement with the different ionic radii of trivalent cations, high-intensity X-ray diffraction confirms a systematic increase of the unit cell parameters. Extended X-ray absorption fine structure spectroscopy confirms the uniform solution of mixed trivalent Cr3+/Fe3+ cations and demonstrates the changes in the hybridization between Cu 3d and O 2p orbitals. Cu K-edge near-edge spectra reflect a sharp 1s → 4p transition associated with the ligand-metal charge transfer "shakedown" process in the collinear O-Cu-O bond along c-axis, whereas the Cr and Fe K-edge absorption spectra show small reciprocal shifts in the edge energies. The charge carrier concentration increases with Fe substitution as confirmed from Hall effect measurement; both p-type conduction and a decrease in the electrical resistivity are observed. The electrical conduction follows a 3D variable range hopping at low-temperature and thermally activated transport at high temperature. The two end members of the series are well-studied, geometrically frustrated antiferromagnetic systems; the present study of magnetic properties of intermediate compositions show a systematic increase of FM interaction with rising Fe concentration and hence a competing magnetic state. A sharp transition in high-temperature (600 K) region identifies a truly paramagnetic state for Fe rich compounds. Thermal conductivity values are drastically affected by the spin fluctuation and spin-phonon scattering taking place in these compositions.

Direct Ethanol Fuel Cells: The influence of structural and electronic effects on Pt–Sn/C electrocatalysts

Carbon-supported platinum-tin electrocatalysts (Pt–Sn/C) are known to be the most efficient fuel cell anode material to oxidize ethanol in the so-called Direct Ethanol Fuel Cells (DEFC). However, the platinum-tin binary system presents distinct phases depending on the amount of Sn (i.e., the Pt:Sn ratio) and on the thermal annealing temperatures, as well as the presence of oxides (e.g. SnO2) whose influence on the performance of DEFCs is not well understood. In this work, Pt–Sn catalysts presenting distinct Pt:Sn ratios were prepared, characterized and tested in a single DEFC. The combined results from DEFC tests and structural characterization techniques showed that increasing the amount of Sn dissolved into the Pt structure enhances DEFC performance but also that Sn content alone does not explain the overall behavior. Microstructural effects on the DEFC response was further investigated by performing a comprehensive study using high intensity X-ray Diffraction and in situ–X-Ray Absorption Spectroscopy provided by synchrotron light on Pt3Sn1/C samples subjected to thermal treatments in a reducing H2 atmosphere at temperatures of 100, 200, 300, 400, and 500 °C. The results showed that best DEFC performance depends on a balance between the amount of Sn dissolved in Pt, the formation of a new phase (PtSn) and also on the presence of tin oxides, yielding a material with an optimized modified 5d-band electronic structure, which was obtained with a thermal treatment at 200 °C.

Study of stainless steel electrodes after electrochemical analysis in sea water condition

For water electrolysis, a rare earth material (eg., platinum) is often used as an electrode, but because of the high cost and toxicity of chemicals, researchers are searching for cost effective and eco-friendly alternative materials. Various alloys and metals have been long explored for use as electrode materials in different media. Stainless steel (SS 304) electrodes are cost effective and have a large surface area; further their catalytic performance is comparable to that of carbon coated noble metals cathodes. Stainless steel has good mechanical properties and durability so it is widely used in desalination plants, oil and gas industries, ship building, etc. However, over a period of time it corrodes very quickly in saline water. To improve the stability and durability of the electrodes (i.e., to minimize corrosion), we anneal the samples under two different sets of conditions and test the electrodes in 3.5% NaCl solution. The anodic peak (−0.25 V) observed for bare stainless steel result from the formation of iron (II) hydroxide [Fe(OH)2]. The Raman bands observed at 210 and 274 cm−1 for bare stainless steel result from the formation of α-Fe2O3 owing to partial, anodic, and cathodic reactions occurring on the electrode which disrupts the surface layers. High intensity X-ray diffraction (XRD) and Raman peaks of Cr2O3 and MnCr2O4 observed in argon and hydrogen annealed sample after cyclic voltammetry reveal that this sample is more stable than bare and air annealed samples. XRD reveals mixed oxide phases in addition to eskolaite and magnetite phases. Scanning electron microscope (SEM) images show that although the air-annealed sample has a soft, spongy structure, Na and Cl ions are adsorbed in the voids on the outer surface of the electrode leading to quick degradation. For the air-annealed sample the oxide appears to adhere poorly to the stainless steel. Oxygen (ie., oxide composition) may play a key role in adherence and growth of Cr2O3 formed at high temperature. X-ray photoelectron spectroscopy (XPS) reveals that large amounts of Cr and Mn are dissolved/corroded into the electrolyte for air annealed sample which is in good agreement with the Raman and SEM results.

Novel melamine modified metal-organic frameworks for remarkably high removal of heavy metal Pb (II)

Novel melamine modified metal-organic frameworks (melamine-MOFs) were synthesized and then used as an absorbent for the removal of heavy metal Pb (II) from a low-salt solution. The melamine-MOFs showed high-intensity x-ray diffraction peaks and a UiO-66-like structure. It has a sphere-like morphology and a diameter of ~50nm. The interactions between melamine and the MOFs were calculated by time dependent density function theory (TD-DFT), showing that there were charge transfer and orbital switching. Fourier transform infrared (FTIR) analysis showed successful incorporation of the melamine into the MOFs upon chemical reaction. Thermal gravimetric analysis (TGA) showed a limited weight-loss before 350°C, indicating that the melamine was not physically mixed with the MOFs. Effects of adsorption time, pH, and temperature (T) were also investigated. The melamine-MOFs showed higher adsorption capacity (122.0mgg−1) than that of the pristine MOFs (72.1mgg−1) at 120min, 40°C and pH=5. The adsorption capacity was remarkably high (about 205mgg−1) at pH of 6. The pseudo-second-order kinetic model fit the adsorption data best (R2>0.99). The adsorption mechanisms were confirmed as the coordination interaction between the amino groups (–NH2) and Pb (II). Therefore, the melamine-MOFs demonstrated a great potential in the treatment of heavy metal wastewater.

A Fundamental Study of Lithium Superoxide in Li-O2 Batteries

The electrochemical and chemical processes that are involved in Li-O2 batteries are complex, and depend strongly on electrode materials, electrolytes, interfaces, and cell operating conditions. In non-aqueous Li-O2 batteries, the main discharge products are commonly known to be lithium peroxide (Li2O2), and possibly some other parasitic solid components (e.g. Li2CO3, LiOH, Li2O, etc.). Relative to these solid compounds (i.e. Li2CO3, Li2O, LiOH, Li2O2) that are commonly found in discharge products, little is known about the solid LiO2. To have a basic understanding of lithium superoxide solid, a combined theoretical studies and experimental characterizations are necessary. Compared to sodium superoxide (NaO2) and potassium superoxide (KO2), the superoxide intermediates and lithium superoxide (O2 -, LiO2) are commonly known to be metastable and there have been no reports of a Li-O2 battery based on LiO2. With this as a motivation, a systematic studies of lithium superoxide in Li-O2 battery have been carried out in our laboratory recently [1-4]. Consistent with our previous Density Functional Theory (DFT) predictions, it has been experimentally confirmed that the LiO2 solid can be stable as a component along with Li2O2 discharge product [1] or in pristine crystalline form [2] in the battery. Consistent with DFT predicted structure [3], these LiO2 solids are found to be in crystalline form with an orthorhombic phase [shown in the attached figure] that confirmed by high intensity X-ray diffraction and transmission electron microscopy measurements. Although LiO2 is thermodynamically unstable with respect to the disproportionation process, theoretical calculations have indicated that some forms of LiO2 may have a long lifetime [4]. Based on both DFT and Ab Initio Molecular Dynamics (AIMD) simulation, we found the disproportionation process will be slower at an electrolyte/LiO2 interface compared to a vacuum/LiO2 interface [1], and this has been experimentally confirmed that the LiO2 component or solid can be possibly stable up to days when an electrolyte is left on the surface of the discharged cathode. In addition, the pristine crystalline LiO2 solid can be electrochemically synthesized and stabilized in a Li-O2cell environment using a suitable graphene-based cathode with iridium nanoparticles [2] based a novel templating growth mechanism as suggested by theory. In this presentation, the recent developments, studies and findings of this elusive metastable solid compound will be discussed systematically based on our recent efforts. This work was primarily supported by the US Department of Energy under contract DE-AC02-06CH11357 from the Vehicle Technologies Office, Department of Energy, Office of Energy Efficiency and Renewable Energy.

Annular beam high-intensity X-ray diffraction based on an ellipsoidal single-bounce monocapillary

This short communication presents a study of the use of an annular X-ray beam produced by an ellipsoidal single-bounce monocapillary (ESBC) to perform focal construct geometry (FCG) high-intensity angular-dispersive X-ray diffraction (ADXRD) in transmission mode. The ESBC optic effectively focused a large focal spot X-ray source into a smaller focal spot and produced a narrowed X-ray ring in the far-field pattern when combined with a beam stop. A CCD imaging detector was linearly translated along the principal axis of the ESBC-FCG and obtained the corresponding sequential images of diffraction concentric circular caustics and convergence points, which were formed by the constructive interference of a continuous set of Debye cones arising from the annular interrogation volume. Pixels from the central region of an approximately 0.6 mm2 area were interrogated on each sequential image; as a result, a one-dimensional diffractogram of an aluminium oxide sample was revealed. The presented ESBC-FCG ADXRD technique shows potential for increasing the diffracted intensity and streamlining the operation of crystallographic analysis.

Equipment for <i>In Situ</i> Studies of the Surface Structure of Thin Surface Layers in the Process of their Formation

The widespread use of polymeric semiconductor compositions for creating flexible and inexpensive solar cells can be achieved by providing the higher values of the coefficient of efficiency. The cost-effective production of polymer solar cells is expected at the efficiency of them not less than 10 %, while now its real level does not exceed 4 %. Many laboratories work to develop semiconductor compositions of organic materials as donors and acceptors which are fullerene derivatives or nanosize particles of semiconductor inorganic compounds [1-6]. The prospect of polymer used depends on the photovoltaic materials and the polymer purity and to a greater extent on the structure of the films formed from the compositions under development. In the search for ways to achieve higher performance of solar cells it is essential to optimize the technology of polymeric composition preparation, of which the active layer is formed, as well as optimization of the layer formation. In order to get information about the relationship between the structure of formed layer and its photovoltaic characteristics it is suggested to analyze the structure of the active layer simultaneously with the monitoring of its current-voltage characteristics. The study of the material structure directly in the process of its evolution seems an urgent task, since the majority of modern methods of structure investigation (light and electron microscopy, X-ray analysis) is not able to detect structural changes occurring in a short period of time. The most useful tool for monitoring the structure of polymer active layer is high intensity X-ray diffraction.

Interfacial effects on lithium superoxide disproportionation in Li-O₂ batteries.

During the cycling of Li-O2 batteries the discharge process gives rise to dynamically evolving agglomerates composed of lithium-oxygen nanostructures; however, little is known about their composition. In this paper, we present results for a Li-O2 battery based on an activated carbon cathode that indicate interfacial effects can suppress disproportionation of a LiO2 component in the discharge product. High-intensity X-ray diffraction and transmission electron microscopy measurements are first used to show that there is a LiO2 component along with Li2O2 in the discharge product. The stability of the discharge product was then probed by investigating the dependence of the charge potential and Raman intensity of the superoxide peak with time. The results indicate that the LiO2 component can be stable for possibly up to days when an electrolyte is left on the surface of the discharged cathode. Density functional calculations on amorphous LiO2 reveal that the disproportionation process will be slower at an electrolyte/LiO2 interface compared to a vacuum/LiO2 interface. The combined experimental and theoretical results provide new insight into how interfacial effects can stabilize LiO2 and suggest that these interfacial effects may play an important role in the charge and discharge chemistries of a Li-O2 battery.

High intensity x-ray diffraction in transmission mode employing an analog of Poisson’s spot

Poisson’s spot is a diffraction phenomenon producing an intensity maximum at the center of the geometric shadow of circular opaque objects. In an analog of the Poisson spot experiment, we show that a tubular cone of x-rays incident upon a crystalline sample produces diffraction spots or foci, corresponding to Bragg maxima within a transmission shadow. We discuss the beam geometry and the intensity gain recorded at the foci in transmission mode. We describe the geometric growth and decay of the foci over a linear axis with the aid of a movie sequence synchronized with the plotting of a diffractogram. The mean signal of a small central area in each successive camera image provides the intensity data for the diffractogram.

Analysis and characterization of a mechanical sensor to monitor stress in interconnect features

A mechanical rotating stress sensor fabricated in copper has been characterized in 100 nm single damascene technology. Geometrical variations to the structure produce a distinctive behaviour which can be used to fit the actuating stress. Existing analytical models were tested and shown to be unable to describe the structure due to geometric non-linearities not considered by these one-dimensional solutions. A model based on the large strain finite element method was developed to include this non-linearity and fully describe the sensor design for all geometrical variations. The stress determined from the Cu rotating sensors is comparable to measurements performed using high intensity X-ray diffraction on similar samples. Furthermore, the simulation methodology is validated for calibrated Al sensors. All of the studied samples show an excellent fit with the developed finite element analysis, demonstrating the validity of the model to predict smaller geometries, showing that the sensor can be utilized in future integration schemes and applied to other material systems.

Phase Transitions in Frozen Systems and During Freeze–Drying: Quantification Using Synchrotron X-Ray Diffractometry

(1) To develop a synchrotron X-ray diffraction (SXRD) method to monitor phase transitions during the entire freeze-drying cycle. Aqueous sodium phosphate buffered glycine solutions with initial glycine to buffer molar ratios of 1:3 (17:50 mM), 1:1 (50 mM) and 3:1 were utilized as model systems. (2) To investigate the effect of initial solute concentration on the crystallization of glycine and phosphate buffer salt during lyophilization. Phosphate buffered glycine solutions were placed in a custom-designed sample cell for freeze-drying. The sample cell, covered with a stainless steel dome with a beryllium window, was placed on a stage capable of controlled cooling and vacuum drying. The samples were cooled to -50 degrees C and annealed at -20 degrees C. They underwent primary drying at -25 degrees C under vacuum until ice sublimation was complete and secondary drying from 0 to 25 degrees C. At different stages of the freeze-drying cycle, the samples were periodically exposed to synchrotron X-ray radiation. An image plate detector was used to obtain time-resolved two-dimensional SXRD patterns. The ice, beta-glycine and DHPD phases were identified based on their unique X-ray peaks. When the solutions were cooled and annealed, ice formation was followed by crystallization of disodium hydrogen phosphate dodecahydrate (DHPD). In the primary drying stage, a significant increase in DHPD crystallization followed by incomplete dehydration to amorphous disodium hydrogen phosphate was evident. Complete dehydration of DHPD occurred during secondary drying. Glycine crystallization was inhibited throughout freeze-drying when the initial buffer concentration (1:3 glycine to buffer) was higher than that of glycine. A high-intensity X-ray diffraction method was developed to monitor the phase transitions during the entire freeze-drying cycle. The high sensitivity of SXRD allowed us to monitor all the crystalline phases simultaneously. While DHPD crystallizes in frozen solution, it dehydrates incompletely during primary drying and completely during secondary drying. The impact of initial solute concentration on the phase composition during the entire freeze-drying cycle was quantified.

Microbeam X-ray Diffraction Analysis of Interfacial Heterogeneous Nucleation of n-Hexadecane inside Oil-in-Water Emulsion Droplets

We have carried out X-ray microbeam analysis of the crystallization behavior of n-hexadecane (C16) in oil-in-water emulsion droplets that were formed using surfactants with different types of hydrophobic moieties. It was confirmed that molecular-shape matching between the hydrophobic moiety and C16 caused the following crystallization behavior: when the molecular shape of the hydrophobic moiety was similar to C16, high-intensity X-ray diffraction of the rotator phase of C16 was detectable at the initial stage of crystallization and the long-chain axes of C16 crystals aligned normal to the membrane interface. The present results provided the first evidence of interfacial heterogeneous nucleation caused by molecular interactions at the emulsion membrane, which is thought to be related to the interfacial freezing that was observed at the oil−water interface with surfactants in a bulk system.

Nanocrystal Assembled TiO2 Particles Prepared from Aqueous Solution

Anatase TiO2 particles, 100−200 nm in diameter, were developed in aqueous solution at 50 °C. The particles were assemblies of nano TiO2 crystals covered with nanorelief surface structures. The crystals grew anisotropically along the c-axis to form acicular crystals. The particles showed c-axis orientation due to high-intensity X-ray diffraction from the (004) planes. The particles had a BET specific surface area of 270 m2/g. BJH and DFT/Monte-Carlo analysis of adsorption isotherm indicated the existence of pores ∼3 nm and ∼1 nm in diameter. Crystallization and self-assembly of nano TiO2 were effectively utilized to fabricate nanocrystal assembled TiO2 particles having a high surface area and nanorelief surface structure.

Electrochemical behaviour of nano-sized spinel LiMn 2O 4 and LiAl xMn 2−xO 4 ( x=Al: 0.00–0.40) synthesized via fumaric acid-assisted sol–gel synthesis for use in lithium rechargeable batteries

Pristine spinel LiMn 2O 4 and LiAl x Mn 2− x O 4 ( x=Al: 0.00–0.40) with sub-micron sized particles have been synthesized using fumaric acid as chelating agent by sol–gel method. The synthesized samples were subjected to thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and cyclic voltammetry (CV) and galvanostatic cycling studies. The TGA curve of the gel shows several weight-loss regions stepwise amounting to 55% till 800 °C attributed to the decomposition of the precursors. Calcination to higher temperatures (800 °C) yields pure-phase spinel (LiAl x Mn 2− x O 4), as it is evident from the high-intensity XRD reflections matching to the standard pattern. SEM and TEM studies confirm that the synthesized grains are of uniform regular surface morphology. FT-IR studies show stretching and bending vibration bands of Li–O, Li–Al–Mn–O. LiAl 0.1Mn 1.90O 4 spinel was found to deliver discharge capacity of 139 mA h/g during the first cycle with columbic efficiency of 97%. LiAl 0.1Mn 1.90O 4 spinel exhibits the high cathodic peak current indicating better electrochemical performance. Low doping ( x=0.1) of Al is found to be beneficial in stabilizing the spinel structure.

The effect of adsorption of thiourea on the particle size of supported platinum nanocatalysts synthesized by chemical reduction

In this work, carbon-supported platinum nanoparticles were synthesized in the presence of varying concentrations of thiourea (TU). Because of the presence of the sulfur atom, thiourea adsorbs strongly on the forming Pt nuclei during the synthesis, affecting the rate and the extent of growth. High-intensity X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used to probe the effect on the crystallite size and particle size, respectively, revealing a decrease in both mean crystallite and the mean particle size for increasing concentrations of thiourea during the synthesis. An adsorption isotherm for the adsorption of thiourea on platinum nanoparticles is also discussed. Cyclic voltammetry was used to check the effect of TU on the particles as well as to obtain further knowledge on both adsorption and electrochemical oxidation behavior of thiourea on Pt surfaces. Thermal treatment effectively cleaned the electrode surface, thus providing an easy way to remove adsorbed species from the Pt surface.