Analysis Of High-resolution Transmission Electron Microscopy Images Research Articles

Formamidinium Lead Iodide‐Based Perovskite Solar Cell Fabrication With an Electrospun‐Reduced Graphene Oxide Back Electrode: A Novel Approach

AbstractIn this work, low‐cost and simple structure perovskite solar cells (PSCs) were fabricated using formamidinium lead iodide (FAPbI3) as the light absorber and reduced graphene oxide nanofibers (rGO NFs) as the counter electrode (CE). The FAPbI3 light absorber was prepared using a two‐step solution process, whereas the rGO NFs were synthesized through a simple electrospinning method. The as‐prepared FAPbI3 and rGO NFs were characterized by high‐resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), and X‐ray diffraction (XRD) pattern analysis. The surface morphology of the as‐prepared FAPbI3 and rGO NFs showed crystalline and bead‐free fiber structures, as confirmed by HRTEM and FESEM image analysis. The AFM topographical images of FAPbI3 and rGO NFs further reveal the crystalline and fiber structures. XRD pattern analysis confirmed the cubic crystalline phase of FAPbI3 and the graphitic nature of rGO NFs. From the electrochemical impedance spectroscopy studies, the PSC assembled with the FAPbI3 light absorber and rGO NFs‐based CE demonstrated an electrical conductivity of 3.64 × 10−4 S cm−1. The fabricated PSC device achieved an efficiency of 8.78% compared to the 7.49% efficiency of the device with a sputtered gold CE. This work uniquely integrates advanced materials, cost‐effective manufacturing, and enhanced efficiency in PSCs using FAPbI3 light absorbers and rGO NFs, addressing key challenges in cost and sustainability in solar technology.

Time-Dependent Size and Shape Evolution of Gold and Europium Nanoparticles from a Bioproducing Microorganism, a Cyanobacterium: A Digitally Supported High-Resolution Image Analysis

Herein, the particle size distributions (PSDs) and shape analysis of in vivo bioproduced particles from aqueous Au3+ and Eu3+ solutions by the cyanobacterium Anabaena sp. are examined in detail at the nanoscale. Generally, biosynthesis is affected by numerous parameters. Therefore, it is challenging to find the key set points for generating tailored nanoparticles (NPs). PSDs and shape analysis of the Au and Eu-NPs were performed with ImageJ using high-resolution transmission electron microscopy (HR-TEM) images. As the HR-TEM image analysis reflects only a fraction of the detected NPs within the cells, additional PSDs of the complete cell were performed to determine the NP count and to evaluate the different accuracies. Furthermore, local PSDs were carried out at five randomly selected locations within a single cell to identify local hotspots or agglomerations. The PSDs show that particle size depends mainly on contact time, while the particle shape is hardly affected. The particles formed are distributed quite evenly within the cells. HR-PSDs for Au-NPs show an average equivalent circular diameter (ECD) of 8.4 nm (24 h) and 7.2 nm (51 h). In contrast, Eu-NPs preferably exhibit an average ECD of 10.6 nm (10 h) and 12.3 nm (244 h). Au-NPs are classified predominantly as "very round" with an average reciprocal aspect ratio (RAR) of ~0.9 and a Feret major axis ratio (FMR) of ~1.17. Eu-NPs mainly belong to the "rounded" class with a smaller RAR of ~0.6 and a FMR of ~1.3. These results show that an increase in contact time is not accompanied by an average particle growth for Au-NPs, but by a doubling of the particle number. Anabaena sp. is capable of biosorbing and bioreducing dissolved Au3+ and Eu3+ ions from aqueous solutions, generating nano-sized Au and Eu particles, respectively. Therefore, it is a low-cost, non-toxic and effective candidate for a rapid recovery of these sought-after metals via the bioproduction of NPs with defined sizes and shapes, providing a high potential for scale-up.

Nanostructure quantification of turbostratic carbon by HRTEM image analysis: State of the art, biases, sensitivity and best practices

High Resolution Transmission Electron Microscopy (HRTEM) has been a widely used technique for the analysis of nanostructure of turbostratic carbon. Since the late nineties, digital imaging and image analysis has made it possible to quantify and derive structural properties from HRTEM images. A number of image analysis methodologies have been proposed, based on which numerous studies drew their conclusions about a variety of materials including soot, carbon black, char, black carbon, carbon nano-onions, fullerenes, pyrocarbon, hard carbon, etc. Recognizing the need for standardization in order to make measurements comparable, repeatable and reproducible, this study is a review of published techniques and a critical analysis of a representative set of them. Based on sensitivity analysis using an extensive dataset of micrographs, best practices for image acquisition and image analysis are provided. Measurement uncertainties and sensitivities to image analysis parameters are estimated. A set of improvements to the state-of-the-art is proposed. Computer code for the presented methods is made available.

Synthesis, Characterization and sintering of nanocrystalline (U1-yCey)O2±x

Nanocrystalline solid solutions of (U1-yCey)O2±x [y = 0.15, 0.22, 0.28, 0.35] have been synthesized by citrate gel-combustion route with a fuel to oxidant ratio of 1. The “as prepared” powders were calcined at 873 K in air for 6 h and were consolidated into pellets at 220 MPa. These green pellets were reduced at 1073 K under flowing hydrogen for 8 h and were sintered at 1873 K under flowing Ar+8% H2 for 6 h. All these powders were characterized for their X-ray crystallite size (XCS), specific surface area (SSA), particle size distribution (PSD), porosity, bulk density (BD) and residual carbon (RC). The morphology and microstructures of these powders were studied by using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM), respectively. The Hall–Williamson analysis of the X-ray diffraction (XRD) data revealed that the “as-prepared” powders consist of nano grains with a size of about 10 to 20 nm and the results have been substantiated by bright field HRTEM image analysis of these samples. These sintered pellets were characterized for their phase composition, density and microstructure. Presence of a single phase fluorite solid solution was confirmed by XRD. A sintered density of 95.88±0.62% of theoretical density (TD) could be achieved. A systematic study on the gel-combustion synthesis of nanocrystalline (U1-yCey)O2±x [y = 0.15, 0.22, 0.28, 0.35] powders is being reported for the first time.

Microstructural evolution in self-catalyzed GaAs nanowires during in-situ TEM study

The microstructural evolutions in self-catalyzed GaAs nanowires (NWs) were investigated by using in situ heating transmission electron microscopy (TEM). The morphological changes of the self-catalyst metal gallium (Ga) droplet, the GaAs NWs, and the atomic behavior at the interface between the self-catalyst metal gallium and GaAs NWs were carefully studied by analysis of high-resolution TEM images. The microstructural change of the Ga-droplet/GaAs-NWs started at a low temperature of ∼200 °C. Formation and destruction of atomic layers were observed at the Ga/GaAs interface and slow depletion of the Ga droplet was detected in the temperature range investigated. Above 300 °C, the evolution process dramatically changed with time: The Ga droplet depleted rapidly and fast growth of zinc-blende (ZB) GaAs structures were observed in the droplet. The Ga droplet was completely removed with time and temperature. When the temperature reached ∼600 °C, the decomposition of GaAs was detected. This process began in the wurtzite (WZ) structure and propagated to the ZB structure. The morphological and atomistic behaviors in self-catalyzed GaAs NWs were demonstrated based on thermodynamic considerations, in addition to the effect of the incident electron beam in TEM. Finally, GaAs decomposition was demonstrated in terms of congruent vaporization.

Experimental study of impact of lubricant-derived ash on oxidation reactivity of soot generated in diesel engines

The objective of the present study was to understand how the lubricant-derived ash-loaded diesel particulate filter (DPF) impacted the soot oxidation reactivity during the regeneration process. Four major commercial lubricant additives (i.e. Ca, Zn-P, Ca-Zn-P, and Mo-P) were heated up in a muffle furnace to generate ash particles, which were mixed with diesel soot in a loose-contact pattern for further analysis. Thermogravimetric analysis (TGA) was employed for both non-isothermal and isothermal conditions to examine the oxidation reaction parameters, including ignition temperature, peak temperature and burnout temperature. In the meantime, the sizes and nanostructures of the primary soot particles during the oxidation process were characterized by high-resolution transmission electron microscopy (HRTEM). Results showed that lubricant-derived ashes accelerated the oxidation of soot particles as indicated by the reduced oxidation characteristic temperatures and increased oxidation rate. Based on the analysis of HRTEM images, both surface and internal burning phenomena existed in the oxidation processes of pure soot conditions and soot-ash mixtures conditions. The structures of shell-core, onion- and capsule-like, hollow and carbonization fragments appeared sequentially through the entire oxidation processes. Comparing to the pure soot conditions, the tendency of surface burning of the soot particles was notably increased by the lubricant-derived ashes. It was thus concluded that, the lubricant-derived ash components played the role as catalyst to promote soot oxidation and favor the whole regeneration process, even though the ashes may deteriorate performance of DPF by increased backpressures.

An Influence of the Si(111)3-4<sup>o</sup> Vicinal Surface on the Solid Phase Epitaxy of α-FeSi<sub>2</sub> Nanorods and their Crystal Parameters

The morphology and structure of iron silicide nanorods formed on Si (111) vicinal surface by the SPE method at T = 630 °C were studied. Optimal Fe coverage and Fe deposition rate for the formation of a dense array of the nanorods (54-65% of the substrate area) on Si (111) surface with 3-4o miscut angles were established. The aspect ratio of the nanorods is 1.9 – 3.3. Cross-sectional images of a high-resolution transmission electron microscopy (HRTEM) have shown that the nanorods have α-FeSi2 crystal structure. They are strained along the “a” axis and stretched along the “c” axis, which increased the unit cell volume by 10.3%. According to HRTEM image analysis, the nanorods have the following epitaxial relationships: α-FeSi2[01]//Si [10] and α-FeSi2(112)//Si (111). All the data obtained have provided, for the first time, a direct evidence of α-FeSi2 nanorods formation on Si (111) vicinal surface without noticeable penetration of Fe atoms into the Si substrate.

Environmental and toxicological assessment of nanodiamond-like materials derived from carbonaceous aerosols

Carbonaceous aerosols (CAs) are ubiquitous and among the most significant environmental materials found in ambient air, mainly derived from anthropogenic sources (biomass burning, industrial activity, vehicle emissions, etc.). Elemental carbon (black carbon) and organic carbons are the major constituents of CAs. Due to their toxic effects, they are considered as high-risk compounds for human health. The key objective of the present work is to conduct a feasibility study for the conversion of CAs (TSP and PM10) into a value-added carbon nanostructured product by using a chemical method. High resolution-transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transforms infrared spectroscopy (FT-IR), X-ray photoelectron spectrometer (XPS), ultraviolet–visible spectroscopy (UV–visible), fluorescence spectroscopy (FL), and Zeta potential analyses indicated the formation of carbon nanomaterials with crystalline phases, which exhibit the characteristics of nanodiamonds (NDs). The HR-TEM image analysis showed that the nominal size of the CAs-derived NDs ranged from 4 to 17 nm composed of mainly carbon and oxygen. The FT-IR and XPS analysis indicated that the NDs are highly functionalized with an oxygen-containing functional group. The CAs-derived NDs showed the property of blue-fluorescence with excitation dependent. In the cytotoxicity and genotoxicity study, the NDs obtained was observed to be biocompatible and suitable for bioimaging applications. This result provides a new avenue for the conversion of CAs to high-value products leading to the mitigation of atmospheric pollution.

HRTEM and EELS investigations of flame-formed soot nanostructure

High resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) were applied to soot probed along a premixed methane flame from the inception phase up to the burnout region in order to follow the transformations of soot nanostructures. The nascent methane soot presented the predominance of large coalesced disordered structures in comparison to young, intermediate and mature soot presenting spherule aggregates. Quantitative structural information describing the shape, size and orientation of sp2-bonded (aromatic) layers and their distribution inside the carbon particle were obtained by HRTEM image analysis. A moderate structural improvement in terms of a better stacking of longer and more planar layers along with the tortuosity fringe decrease was observed along the methane flame. EELS was instead used to provide quantitative information about the relative concentrations of sp3 and sp2 hybridized carbon. It is the first time that quantitative EELS is applied to soot from the inception to maturation along a premixed laminar flame. The aromatic content for the nascent soot resulted to be rather high (84%) indicating the predominant aromatic character of soot precursors. The steep increase of sp2 content from 84 to 94% in the passage from nascent to young soot was noteworthy. The similar sp2 content (94–96%) as well as the invariance of fringe length of young, intermediate and mature soot testified that most of the structural changes occurred at the inception, after then methane soot did not undergo a significant nanostructural restructuring, possibly because of the less reactive environment generated from methane combustion.

Mesoporous CdS via Network of Self-Assembled Nanocrystals: Synthesis, Characterization and Enhanced Photoconducting Property.

Semiconduction nanoparticles are intensively studied due to their huge potential in optoelctronic applications. Here we report an efficient chemical route for hydrothermal synthesis of aggregated mesoporous cadmium sulfide (CdS) nanoparticles using supramolecular-assembly of ionic and water soluble sodium salicylate as the capping agent. The nanostructure, mesophase, optical property and photoconductivity of these mesoporous CdS materials have been characterized by using small and wide angle powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), N2-sorption, Raman analysis, Fourier transformed infrared (FT-IR), UV-Visible DSR spectroscopy, and photoconductivity measurement. Wide angle XRD pattern and high resolution TEM image analysis suggested that the particle size of the materials is within 10 nm and the nanoparticles are in well-crystallized cubic phase. Mesoporous CdS nanoparticles showed drastically enhanced photoelectrochemical response under visible light irradiation on entrapping a photosensitizer (dye) molecule in the interparticle spaces. Efficient synthesis strategy and the enhanced photo response in the mesoporous CdS material could facilitate the designing of other porous semiconductor oxide/sulfide and their applications in photon-to-electron conversion processes.

Experimental investigation into the oxidation reactivity and nanostructure of particulate matter from diesel engine fuelled with diesel/polyoxymethylene dimethyl ethers blends.

This paper focuses on oxidation reactivity and nanostructural characteristics of particulate matter (PM) emitted from diesel engine fuelled with different volume proportions of diesel/polyoxymethylene dimethyl ethers (PODEn) blends (P0, P10 and P20). PM was collected using a metal filter from the exhaust manifold. The collected PM samples were characterized using thermogravimetric analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The TGA results indicated that the PM produced by P20 had the highest moisture and volatility contents and the fastest oxidation rate of solid carbon followed by P10 and P0 derived PM. SEM analysis showed that PM generated from P20 was looser with a lower mean value than PM emitted from P10 and P0. Quantitative analysis of high-resolution TEM images presented that fringe length was reduced along with increased separation distance and tortuosity with an increase in PODEn concentration. These trends improved the oxidation reactivity. According to Raman spectroscopy data, the intensity, full width at half-maximum and intensity ratio of the bands also changed demonstrating that PM nanostructure disorder was correlated with a faster oxidation rate. The results show the use of PODEn affects the oxidation reactivity and nanostructure of PM that is easier to oxidize.

Impact of lubricating oil combustion on nanostructure, composition and graphitization of diesel particles

In this study, the impact of lubricating oil on the nanostructure, composition, and graphitization of diesel particles is studied experimentally. A 4-cylinder turbocharged light-duty diesel engine was used to generate particle samples. In the analysis, high resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TGA) were applied to study the nanostructure and the compositions of particles, respectively. Furthermore, Raman spectroscopy was used to compare the graphitization of particles. Quantitative analysis of HRTEM images suggests that lube oil-derived particles have more disordered structures with shorter fringe length, larger degree of tortuosity, and greater separation distance than diesel particles. TGA results indicate that lubricating oil leads to more low volatility volatile fraction in PMs, particularly at the low load conditions. From Raman spectrum, it has been found that there are more defective band appeared in lube oil-derived particles. This implies that the lube oil-derived particles have a lower degree of graphitization. Overall, this study shows that lubricating oil has a significant impact on the characteristics of particles.

Structural, optical and electronic properties of Ag–TiO2 nanocomposite thin film

Nanocomposite thin films of Ag nanoparticles in TiO2 matrices were synthesised by RF magnetron co-sputtering and characterised by X-ray diffraction (XRD), Rutherford back scattering (RBS) spectrometry, UV–Vis, high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). The composition of Ag was varied from 0 to 45 at.%. The thickness and the concentrations of Ag in the nanocomposite thin film were revealed by RBS. XRD analysis confirmed that the TiO2 matrix is in anatase phase and shows change in phase with Ag concentration. The UV–visible absorption spectroscopy revealed low-intense and broad surface plasmon resonance (SPR) peak at ~500 nm for the thin film with 33 at.% Ag content that was red-shifted to ~525 nm with increasing its intensity for 45 at.% of Ag. The red shift in SPR peak understood by Maxwell–Garnett theory and explained further nonexistence of SPR by interparticle separation from HR-TEM images and crystallinity. This HR-TEM image analysis confirmed the formation of Ag nanoparticles, and average radii were ~5, 12, 15 nm. The Tauc plot reveals reduction in band gap from 3.05 to 2.25 eV with increase in Ag content. Above results are understood based on the XPS analysis which shows a strong interaction between the Ag nanoparticle and TiO2. This decrease in band gap was advantageous to enhance the properties like photocatalytic and bioactivities through SPR.

Characterization of carbonaceous particulate matter emitted from marine diesel engine

In an effort to aid the Korean ship-building industry to effectively respond to the upcoming environmental regulations, a series of experimental campaigns to characterize carbonaceous Particulate matters (PMs) emitted from a cruising marine ship have been carried out. To this end, the carbonaceous PMs emitted from two-stroke marine-diesel engines burning Bunker B (Low residual fuel oil, LRFO 3%) were sampled on-board at various locations: 1) After the turbo charger (TC), 2) before the economizer (ECO), 3) after the economizer, and 4) in the funnel of the chimney. Sampled carbonaceous PM particles were then analyzed using a High-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. Results obtained from the analysis of HRTEM images and Raman spectra indicate that carbonaceous PMs are mainly fractionated into Black carbon (BC) and Organic carbon (OC), respectively and the each fraction of sampled carbonaceous PMs varies with engine operation conditions and exhaust gas temperatures at the sampling location. The present work is anticipated to provide a useful set of information for characterizing carbonaceous PMs emitted from marine diesel engines.

Nanostructure characterization of carbide-derived carbons by morphological analysis of transmission electron microscopy images combined with physisorption and Raman spectroscopy

A novel image processing method based on mathematical morphology is applied in order to characterize the nanostructure of carbide-derived carbons (CDCs) observed using high resolution transmission electron microscopy (HRTEM). The analysis provides information about the shape and disordered arrangement of the defective polyaromatic units forming the CDC nanostructure. Individual fringes, basic structural units, and continuous domains are analysed. Hierarchical polycarbosilane-based CDCs obtained at different pyrolysis/chlorination temperatures are investigated. The information collected is interpreted with respect to the different synthesis conditions. This analysis is supported by Raman spectroscopy measurements and porosity evaluation with nitrogen (−196 °C) and carbon dioxide (0 °C) physisorption. The CDCs show only minor differences in the carbon nanostructures. The HRTEM image analysis is sensitive enough to illuminate the slight variations. An increase in carbon ordering at higher synthesis temperature and a rather folded structure with higher tortuosity of the fringes with increasing micropore volume is observed. These findings are complementary to the data obtained from nitrogen and carbon dioxide physisorption experiments as well as from Raman spectroscopy, showing a less defective microstructure of the CDCs prepared at higher pyrolysis/chlorination temperatures. The results also prove the precise control over the nanostructure of CDCs provided by the synthesis temperature.

Study on CuO-CeO2/SiC catalysts in the sulfur-iodine cycle for hydrogen production

The structure and activity of ceria–copper oxides supported on nanometer silicon carbide (nano-SiC) particles for sulfuric acid decomposition were studied. The promoting activities and stabilities of CuO–CeO2 complex oxides loaded on nano-SiC grains were prominently higher than those of CuO–CeO2 without carriers, especially at <800 °C. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM) showed that copper-cerium composite oxides grains were well dispersed and fixed on the surface of SiC particle, and the average sizes of CuO–CeO2 complex oxides carried by SiC particles were considerably smaller than those of CuO–CeO2 without carriers. Based on the analysis of HRTEM images, X-ray photoelectron spectroscopy (XPS) spectra, and infrared radiation (IR) pattern, the majority of SiC surfaces were converted to SiO2 layers, in which CeO2 grains immobilized by coordination bonding Ce–O–Si bridges. From the temperature programmed reduction (TPR) patterns, compared with those of CuO–CeO2 without carrier, the reduction temperature of CuO to Cu2O in CuO–CeO2/SiC catalysts was lowered, especially at (Ce + Cu)/SiC atomic ratio of 5 mol.%. The catalysts also showed relatively high activities at 727 °C for 20 h of continuous operation. A mechanism of SO3 decomposition on CuO–CeO2/SiC was proposed according to the characterization results. Copyright © 2016 John Wiley & Sons, Ltd.

Nitrogen atom shift and the structural change in chromium nitride

The atomic configurations and structural evolution of disordered Cr2N have been investigated by CS-corrected high-resolution transmission electron microscopy (HRTEM) imaging, electron diffraction analysis, electron energy loss spectroscopy (EELS) and ab initio calculations. The atomic structure of the disordered Cr2N is experimentally confirmed by CS-corrected atomic resolution imaging. Both diffraction and HRTEM image analysis revealed that the disordered Cr2N structure possesses a hexagonal (hcp) arrangement of Cr atoms with N atom random distributions, particularly, N atoms shift away from octahedral interstices at (001) plane. The nitrogen atom shifts result in a clear reduction of the relative intensity ratio of (030) to (002) reflection. It has also been found that the disordered Cr2N can transform into a face-centered cubic (fcc) phase at the specimen surface while chemically retaining a Cr/N atomic ratio close to 2:1. Structurally, such cubic phase is similar to sub-stoichiometric fcc CrN. The analysis corroborated that the structural transformation could be achieved by shearing motion of Cr atoms in (001) planes. Based on the experimental observations and theoretical calculations, the effects of nitrogen atom redistribution on the structure and the stability of various Cr2N phases are addressed in detail.

Microstrain and growth fault structures in electrodeposited nanocrystalline Ni and Ni–Fe alloys

Nanocrystalline Ni and Ni–Fe alloys produced by electrodeposition were characterized using high-resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD). The grain sizes for these materials spanned a range of about 81–10 nm. HR-TEM analysis on a series of images revealed the presence of local strains at both high-angle and low-angle grain boundaries and twin boundaries. In addition to this, stacking faults and twins of the growth type (growth faults) were observed in both the nanocrystalline Ni and Ni–Fe alloys. The growth fault density increased with increasing Fe concentration, which is consistent with a decrease in the stacking fault energy. The microstrain for the samples was determined from XRD pattern analysis based on line broadening. A general increasing microstrain trend with decreasing grain size was observed and considered to be related to the local strains observed at grain boundaries in the HR-TEM image analysis. With respect to grain size, the microstrain values for the nanocrystalline Ni–Fe samples were noticeably higher than some of the Ni samples. Further XRD pattern analysis was performed to determine the growth fault probabilities for each of the samples and analyze their influence on the microstrain. Increasing Fe was accompanied by an increase in growth fault probability, which was consistent with the HR-TEM image analysis. In addition to the effect of grain size, there is likely a contributing effect on microstrain-induced XRD line broadening due to the presence of growth faults.

The interface of a-SiNx:H and Si: Linking the nano-scale structure to passivation quality

Surface passivation by hydrogenated amorphous silicon nitride (a-SiNx:H) is determined by the combined effect of two mechanisms: so-called chemical passivation by reducing the density of interface states (Dit) and field-effect passivation as a result of the number of fixed charges (Qf) at the interface with Si. These are related to the K defect center: *Si-N3. Defects near the interface (in both Si as in a-SiNx:H), modeled by force field Molecular Dynamics (MD) and ab initio Density Functional Theory (DFT), can be related to Qf and Dit measured experimentally using CV-MIS (Capacitance–Voltage Metal–Insulator–Semiconductor). The compositional build up at the interface as is determined by HRTEM (High Resolution Transmission Electron Microscopy) and modeled by MD corresponds to each other; a gradual change from Si to the bulk a-SiNx:H composition in the first 2 nm of the a-SiNx:H layer. At the c-Si side a highly distorted layer (about 1–3 nm) caused by the insertion of N and/or H is found. The insertion and adhesion of N into and at the Si surface is called nitridation and can be altered by using a NH3 plasma prior to a-SiNx:H deposition. HRTEM image analysis shows that by varying the nitridation of the Si surface the amount and penetration depth of N inside the Si surface is altered. Using MD modeling, it is shown that this process changes the amount of K-centers at the surface, which explains the variation in Qf and Dit that is found experimentally. Ab initio DFT studies of a-SiNx:H (x=1.17) show that K-centers and Si atoms in distorted configuration, are the dominating defects resulting in a higher Dit. For lower x (x=1) the Dit caused by K-centers increases, which is observed experimentally too.

Impact of fuel formulation on the nanostructure and reactivity of diesel soot

The work focuses on the impact of fuel on soot reactivity and nanostructure. A 2.5L, 4-cylinder, turbocharged, common rail, direct injection light-duty diesel engine was used in generating soot samples. Three test fuels were used: an ultra low sulfur diesel fuel (BP15), a pure soybean methyl-ester (B100), and a synthetic Fischer-Tropsch fuel (FT) produced in a gas-to-liquid process. A test condition of 2400rpm and 64Nm (low load), with single and split injection strategies, was chosen for studying the impacts of fuel formulation on the characteristics of diesel soot. The start of injection (SOI) and fuel rail pressures were adjusted such that the three test fuels have similar combustion phasing, thereby facilitating comparisons between soots from the different fuels. The collected soot samples were characterized using thermogravimetric analyzer (TGA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and high resolution transmission electron microscopy (HRTEM). According to TGA, B100 soot exhibits the fastest oxidation on a mass basis followed by BP15 and FT derived soots in order of apparent rate constant. XPS analysis indicates no relation between the surface oxygen content and the soot reactivity. The basal plane diameter obtained from XRD is inversely related to the apparent rate constants for soot oxidation. Quantitative analysis of HRTEM images also suggests soot nanostructure disorder correlates with a faster oxidation rate. XRD and HRTEM analysis results are compared, and they both show excellent correlation of soot nanostructure and reactivity.