Combined Scanning Research Articles

Impact of sintering method on certain properties of titanium dioxide nanopowder materials

Titanium dioxide nanopowder samples consolidated by method of cold uniaxial compaction at 200 MPa and conventionally sintered in air at 1300?? with isothermal tempering during 60 minutes or spark-plasma sintering at 1300?? and 30 MP? were studied using the method of light combination scattering spectroscopy (Raman spectroscopy) and scanning electron microscopy. The samples were found to differ significantly in terms of color, density, phase composition and microstructure.

Design of Ag-Ge-Zn braze/solder alloys: Experimental thermodynamics and surface properties

The experimental investigation of the Ag-Ge-Zn phase diagram was performed by using combined microstructural and Differential Scanning Calorimeter (DSC) analyses. The samples were subjected to thermal cycles by a heat-flux DSC apparatus with heating and cooling rate of 0.5 or 0.3?C/min. The microstructure of the samples, both after annealing and after DSC analysis, was studied by optical and scanning electron microscopy coupled with EDS (Energy Dispersive Spectroscopy) analysis. Considering the slow heating and cooling rate adopted, the isothermal section at room temperature was established. No ternary compounds were observed. On the basis of the experimental investigations the invariant reactions were identified. Combining the thermodynamic data on the Ag-Ge, Ag-Zn and Ge-Zn liquid phases by means of Butler?s model the surface tension of Ag-Ge-Zn alloys was calculated.

On the shuttling mechanism of a chlorine atom in a chloroaluminum phthalocyanine based molecular switch.

An intermediate shuttling structure of a chloroaluminum phthalocyanine(ClAlPc)-based molecular switch is transiently created and analyzed by combined scanning tunneling microcopy/spectroscopy and density-functional theory calculations, which suggests that the Cl atom is squeezed into the space between the central Al atom and the inner N-containing ring in ClAlPc.

Exploration of candidate biomarkers for human psoriasis based on gas chromatography-mass spectrometry serum metabolomics.

Recent studies have shown that dysregulated metabolic pathways are linked to psoriasis pathogenesis. However, an extensive, unbiased metabolic analysis in patients with psoriasis has not been completely explored. The metabolome represents the end products of proteomics or cellular processes that may be closely associated with the pathogenesis of psoriasis. To determine the differences in serum metabolomic profiles among patients with psoriasis and healthy controls with the goal of identifying potential biomarkers in patients with psoriasis. Serum metabolomic profiles from 29 subjects (14 patients with psoriasis and 15 sex- and age-matched healthy controls). The serum metabolites were analysed by gas chromatography-mass spectrometry based on a combined full scan and selected-ion monitoring mode. Multivariate statistical analysis of metabolomics data revealed altered serum metabolites between the patients with psoriasis and healthy individuals. Compared with healthy individuals, patients with psoriasis had higher levels of amino acids including asparagine, aspartic acid, isoleucine, phenylalanine, ornithine and proline; higher levels of lactic acid and urea; and lower levels of crotonic acid, azelaic acid, ethanolamine and cholesterol. It appears that the glycolysis pathway and amino acid metabolic activity are increased in patients with psoriasis. These metabolic perturbations may stem from increased demand for protein biosynthesis and keratinocyte hyperproliferation. Our findings may help to elucidate the pathogenesis of psoriasis and provide insights into early diagnosis and therapeutic intervention.

He+ irradiation induced cracking and exfoliating on the surface of Ti3AlC2

We report a systematic study of the effects of a 400 keV helium ion beam irradiation on the surface morphology and crystal structure of Ti3AlC2 by combined scanning electron microscopy, grazing incidence X-ray diffraction and transmission electron microscopy. Helium irradiation experiments were performed at both room temperature and 500 °C, respectively, with fluence up to 2.0 × 1017 He+/cm2. After irradiation, intragranular orientated cracks grew along the (10 1¯ 0)Ti3AlC2 plane and the surface has started to exfoliate. The formation of the cracks is mainly attributed to the reduction of the lattice parameter along the a direction induced by ion irradiation, and the crack growth is affected by the grain size and the content of impurity phase TiAl3. The surface exfoliation is due to the blistering of He bubbles at the projected depth.

TRIBOCHEMISTRY VERSUS NANO-TRIBOLOGY I. THEORETICAL CONSIDERATIONS ON MAKING A TANDEM NANOSCOPE

The most fascinating discovery of tribochemical studies was that the high activation energy of reactions between solids covered by mechanical energy has no exclusively thermal origin as that had been adopted formerly. For studying of tribochemical elemental effects, some theoretical considerations of combination atomic force microscope (AFM) and scanning tunneling microscope (STM) techniques using one dual tip cantilever have been discussed to develop a solid base to make experimental setup called Tandem NanoScope.

Epoxy-matrix composites filled with surface-modified SiO2 nanoparticles

Composites based on an epoxy resin, diglycidyl ether of bisphenol A and SiO2 nanoparticles, unmodified and surface-modified with a coupling agent 3-glycidyloxypropyltrimethoxysilane, were prepared. Successful modification of the nanoparticles was confirmed by infrared spectroscopy and combined differential scanning calorimetry and thermogravimetric analysis (DSC–TG). Composite materials were prepared by adding 0.5–5 phr (parts per hundred parts of resin) of modified and unmodified nanoparticles into the epoxy resin which was then cured with a poly(oxypropylene) diamine. Curing was followed by DSC, and cured materials were characterised by tensile and hardness testing. Morphology of fractured surfaces after tensile testing was investigated by scanning electron microscopy (SEM). Thermal stability of cured materials was studied by TG and their glass transition temperature determined by DSC. The presence of the filler was found not to influence the curing mechanism of the epoxy resin nor the degradation mechanism of the crosslinked epoxy–amine matrix. Glass transition exhibits a small shift to higher temperatures in composites, which also exhibit increased char formation—at lower filler content for the composite with unmodified nanoparticles and at higher for the one with modified nanoparticles. All composites show improved mechanical properties in comparison with the neat epoxy. For the unmodified particles, strength and modulus are particularly improved at lower nanofiller content due to their better dispersion, as observed by SEM. The modified nanoparticles contributed to a significant increase in elongation at break, increasing the toughness of the cured resin while retaining its strength and without having an adverse influence on the modulus.

Clinical and morphological characteristics of ectopic thyroid gland in children: A series of 24 patients from Northwest India

BackgroundMost adults with ectopic thyroid gland (ETG) are asymptomatic at the time of detection of ETG. Unlike adults, the clinical and morphological spectrum of ETG in children remains less characterized. MethodsWe retrospectively analyzed data of children with primary congenital hypothyroidism (CH) due to ETG who attended the pediatric endocrinology clinic of our hospital between April 2004 and March 2016. The diagnosis of ETG was based on combined scanning with technetium-99m (99mTc) pertechnetate thyroid scintigraphy and high-resolution thyroid ultrasonography. ResultsTwenty-four (18.7%) of the 128 children with primary CH were identified to have ETG. Their mean age at diagnosis was 64.3±47 months (range, 0.5–144 months); 17 (70.8%) were girls. The mode of diagnosis was based on symptoms in 20, newborn screening in 3 and incidental in 1. Symptoms included poor weight gain in 13 (54%) developmental delay in 9 (37.5%), constipation in 8 (33%), decreased activity in 6, excessive sleepiness in 5, anorexia in 1 and decreased sweating in 1. The anatomical location of ETG was lingual in 17 (71%) and sublingual in 5 (21%). Thyroid function tests showed overt hypothyroidism in 16 and subclinical in 8. The mean duration of follow up was 16±27.5 months (range 0.5–114 months). ConclusionWe found symptomatic hypothyroidism to be common at presentation in our children with ETG. This is the largest series of children with ETG based on the diagnosis by combined scanning.

Lidar combined scanning unit

Subject of Research. The results of lidar combined scanning unit development for locating leaks of hydrocarbons are presented The unit enables to perform high-speed scanning of the investigated space in wide and narrow angle fields. Method. Scanning in a wide angular field is produced by one-line scanning path by means of the movable aluminum mirror with a frequency of 20Hz and amplitude of 20 degrees of swing. Narrowband scanning is performed along a spiral path by the deflector. The deflection of the beam is done by rotation of the optical wedges forming part of the deflector at an angle of ±50. The control function of the scanning node is performed by a specialized software product written in C# programming language. Main Results. This scanning unit allows scanning the investigated area at a distance of 50-100 m with spatial resolution at the level of 3 cm. The positioning accuracy of the laser beam in space is 15'. The developed scanning unit gives the possibility to browse the entire investigated area for the time not more than 1 ms at a rotation frequency of each wedge from 50 to 200 Hz. The problem of unambiguous definition of the beam geographical coordinates in space is solved at the software level according to the rotation angles of the mirrors and optical wedges. Lidar system coordinates are determined by means of GPS. Practical Relevance. Development results open the possibility for increasing the spatial resolution of scanning systems of a wide range of lidars and can provide high positioning accuracy of the laser beam in space.

Tuning the Graphene on Ir(111) adsorption regime by Fe/Ir surface-alloying

A combined scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, and density functional theory study of graphene on a Fe–Ir(111) alloy with variable Ir concentration is presented. Starting from an intercalated Fe layer between the graphene and Ir(111) surface we find that graphene–substrate interaction can be fine-tuned by Fe–Ir alloying at the interface. When a critical Ir-concentration close to 0.25 is reached in the Fe layer, the Dirac cone of graphene is largely restored and can thereafter be tuned across the Fermi level by further increasing the Ir content. Indeed, our study reveals an abrupt transition between a chemisorbed phase at small Ir concentrations and a physisorbed phase above the critical concentration. The latter phase is highly reminiscent of the graphene on the clean Ir(111) surface. Furthermore, the transition is accompanied by an inversion of the graphene’s induced magnetization due to the coupling with the Fe atoms from antiferromagnetic when chemisorbed to weakly ferromagnetic in the physisorption regime, with spin polarizations whose magnitude may be tuned with the amount of Fe content.

Exploring site-specific chemical interactions at surfaces: a case study on highly ordered pyrolytic graphite

A material’s ability to interact with approaching matter is governed by the structural and chemical nature of its surfaces. Tailoring surfaces to meet specific needs requires developing an understanding of the underlying fundamental principles that determine a surface’s reactivity. A particularly insightful case occurs when the surface site exhibiting the strongest attraction changes with distance. To study this issue, combined noncontact atomic force microscopy and scanning tunneling microscopy experiments have been carried out, where the evolution of the local chemical interaction with distance leads to a contrast reversal in the force channel. Using highly ordered pyrolytic graphite surfaces and metallic probe tips as a model system, we find that at larger tip-sample distances, carbon atoms exhibit stronger attractions than hollow sites while upon further approach, hollow sites become energetically more favorable. For the tunneling current that is recorded at large tip-sample separations during acquisition of a constant-force image, the contrast is dominated by the changes in tip-sample distance required to hold the force constant (‘cross-talk’); at smaller separations the contrast turns into a convolution of this cross-talk and the local density of states. Analysis shows that the basic factors influencing the force channel contrast reversal are locally varying decay lengths and an onset of repulsive forces that occurs for distinct surface sites at different tip-sample distances. These findings highlight the importance of tip-sample distance when comparing the relative strength of site-specific chemical interactions.

Accurate Cure Modeling for Isothermal Processing of Fast Curing Epoxy Resins.

In this work a holistic approach for the characterization and mathematical modeling of the reaction kinetics of a fast epoxy resin is shown. Major composite manufacturing processes like resin transfer molding involve isothermal curing at temperatures far below the ultimate glass transition temperature. Hence, premature vitrification occurs during curing and consequently has to be taken into account by the kinetic model. In order to show the benefit of using a complex kinetic model, the Kamal-Malkin kinetic model is compared to the Grindling kinetic model in terms of prediction quality for isothermal processing. From the selected models, only the Grindling kinetic is capable of taking into account vitrification. Non-isothermal, isothermal and combined differential scanning calorimetry (DSC) measurements are conducted and processed for subsequent use for model parametrization. In order to demonstrate which DSC measurements are vital for proper cure modeling, both models are fitted to varying sets of measurements. Special attention is given to the evaluation of isothermal DSC measurements which are subject to deviations arising from unrecorded cross-linking prior to the beginning of the measurement as well as from physical aging effects. It is found that isothermal measurements are vital for accurate modeling of isothermal cure and cannot be neglected. Accurate cure predictions are achieved using the Grindling kinetic model.

The effects of two-dimensional bifurcations and quantum beats in a system of combined atomic force and scanning tunneling microscopes with quantum dots

The field and temperature dependence of the probability of two-dimensional dissipative tunneling is studied in the framework of one-instanton approximation for a model double-well oscillator potential in an external electric field at finite temperature with account for the influence of two local phonon modes for quantum dots in a system of a combined atomic force and a scanning tunneling microscope. It is demonstrated that in the mode of synchronous parallel transfer of tunneling particles from the cantilever tip to the quantum dot the two local phonon modes result in the occurrence of two stable peaks in the curve of the 2D dissipative tunneling probability as a function of the field. Qualitative comparison of the theoretical curve in the limit of weak dissociation and the experimental current–voltage characteristic for quantum dots that grow from colloidal gold under a cantilever tip at the initial stage of quantum-dot formation when the quantum dot size does not exceed 10 nm is performed. It is established that one of the two stable peaks that correspond to interaction of tunneling particles with two local phonon modes in the temperature dependence of the 2D dissipative tunneling probability can be split in two, which corresponds to the tunneling channel interference mechanism. It is found that the theoretically predicted and experimentally observed mode of quantum beats occurs near the bifurcation point.

The role of the density profile in the ASDEX-Upgrade pedestal structure

Experimental evidence for the impact of a region of high density localised in the high-field side scrape-off layer (the HFSHD) on plasma confinement is shown in various dedicated experiments on ASDEX Upgrade (AUG). Increasing main ion fuelling is shown to increase the separatrix density and shift the density profile outwards. Predictive pedestal modelling of this shift indicates a 25% decrease in the attainable pedestal top pressure, which compares well with experimental observations in the gas scan.Since the HFSHD can be mitigated by applying nitrogen seeding, a combined scan in fuelling rate, heating power, and nitrogen seeding is presented. Significant increases in the achievable pedestal top pressure are observed with seeding, in particular at high heating powers, and are correlated with inward shifted density profiles and a reduction of the HFSHD and separatrix density. Interpretive linear stability analysis also confirms the impact of a radially shifted pressure profile on peeling-ballooning stability, with an inward shift allowing access to higher pressure gradients and pedestal widths.

Local electronic structure, work function, and line defect dynamics of ultrathin epitaxial ZnO layers on a Ag(1 1 1) surface

Using combined low-temperature scanning tunneling microscopy and Kelvin probe force microscopy we studied the local electronic structure and work function change of the (0 0 0 1)-oriented epitaxial ZnO layers on a Ag(1 1 1) substrate. Scanning tunneling spectroscopy (STS) revealed that the conduction band minimum monotonically downshifts as the number of the ZnO layers increases up to 4 monolayers (ML). However, it was found by field emission resonance (FER) spectroscopy that the local work function of Ag(1 1 1) slightly decreases for 2 ML thick ZnO but it dramatically changes and drops by about 1.2 eV between 2 and 3 ML, suggesting a structural transformation of the ZnO layer. The spatial variation of the conduction band minimum and the local work function change were visualized at the nanometer scale by mapping the STS and FER intensities. Furthermore, we found that the ZnO layers contained line defects with a few tens of nm long, which can be removed by the injection of a tunneling electron into the conduction band.

Atomic scale analysis of sterical effects in the adsorption of 4,6-dimethyldibenzothiophene on a CoMoS hydrotreating catalyst

The low catalytic hydrodesulfurization (HDS) activity toward sterically hindered sulfur-containing molecules is a main industrial challenge in order to obtain ultra-low sulfur diesel. In this study we report a combined Scanning Tunneling Microscopy (STM) and Density Functional Theory (DFT) investigation of the adsorption of the sterically hindered sulfur-containing molecule 4,6-dimethyldibenzothiophene (4,6-DMDBT) onto a hydrotreating model catalyst for the Co promoted MoS2 (CoMoS) phase. The molecular adsorption occurs exclusively on the Co-promoted S-edge, most predominantly in a precursor-like diffusive physisorption referred to as delocalized π-mode. 4,6-DMDBT adsorption directly in a S-edge sulfur vacancy is observed exclusively in S-edge corner vacancies in an adsorption configuration reflecting a σ-coordination. STM movies reveal dynamic conversion between the σ-mode and an on-top π-adsorption providing a link between different adsorption sites and hence between the hydrogenation and direct desulfurization pathways in HDS. The low overall direct desulfurization activity of 4,6-DMDBT and related molecules is consistent with the low occurrence of S-vacancies on CoMoS S-edges predicted under HDS conditions in this study.

Cell adaptations of Rhodococcus rhodochrous IEGM 66 to betulin biotransformation

The findings of a comprehensive study on R. rhodochrous IEGM 66 and triterpenoid betulin interactions during its biotransformation were reported. In the presence of betulin, rhodococci were shown to form heterogeneous cell aggregates. The enhanced size of the aggregates from 12–15 μm to 25– 35 μm was consistent with the increase in betulin concentration from 0.5 to 3.0 g/L. The confocal laser scanning microscopy indicated a high (80.0%) level of rhodococcal viability during betulin biotransformation regardless of the betulin concentration. Experiments employing the combined confocal laser scanning and atomic force microscopy system confirmed that interactions between actinobacterial cells and betulin occur by direct contact. Transforming activities of the crude cell extracts from R. rhodochrous IEGM 66 were compared, and localization of enzymes catalyzing betulin oxidation to betulone was determined. Additionally the effects of betulin on fatty acid composition of rhodococci and their morphometric and morphofunctional characteristics during biotransformation were studied. Our findings could be used to develop approaches for enhanced betulin bioavailability, thus leading to improved biotransformation efficiency.

The role of electron confinement in Pd films for the oscillatory magnetic anisotropy in an adjacent Co layer

We demonstrate the interplay between quantum well states in Pd and the magnetic anisotropy in Pd/Co/Cu (0 0 1) by combined scanning tunneling spectroscopy (STS) and magneto optical Kerr effect (MOKE) measurements. Low temperature scanning tunneling spectroscopy reveals occupied and unoccupied quantum well states (QWS) in atomically flat Pd films on Co/Cu (0 0 1). These states give rise to sharp peaks in the differential conductance spectra. A quantitative analysis of the spectra reveals the electronic dispersion of the Pd (0 0 1) d-band (-type) along the -X direction. In situ MOKE experiments on Pd/Co/Cu (1, 1, 13) uncover a periodic variation of the in-plane uniaxial magnetic anisotropy as a function of Pd thickness with a period of 6 atomic layers Pd. STS shows that QWS in Pd cross the Fermi level with the same periodicity of 6 atomic layers. Backed by previous theoretical work we ascribe the variation of the magnetic anisotropy in Co to QWS in the Pd overlayer. Our results suggest a novel venue towards tailoring uniaxial magnetic anisotropy of ferromagnetic films by exploiting QWS in an adjacent material with large spin–orbit coupling.

In-Situ Electrochemical Microscopy Techniques (AFM-SECM, sMIM and Liquid SEM) to Study Solid/Liquid Interface

Ever since the invention of the scanning probe and electron microscope, a goal has been to image liquid specimens as easily as in a light microscope, and to measure liquid processes with a good resolution in both spatial and temporal. Direct observation of electrochemical processes is essential to develop electrochemical models, optimize nanostructures, and understand reaction mechanisms. We have developed and improved some in-situtechniques and tested them on electrochemical processes. In an attempt to have improved topography and surface reactivity information, we have designed and fabricated nanometer sized scanning probe tips for combined atomic force microscopy (AFM) and scanning electrochemical microscopy (SECM). We report here the characterization of these tips using an in-house fabricated calibration sample and a model anode. In another approach we have used scanning near-field microwave microscopy (sMIM) for imaging in liquids using ultrathin molecular impermeable membranes separating scanning probes from samples enclosed in environmental cells. We imaged a process of dendritic growth during model electroplating reaction. Due to very small energy of few gigahertz microwaves we demonstrate the advantages of this microscopy for non-destructive artifact-free imaging compared to electron microscopy [1]. Different to TEM in liquids which has been used successfully to study the electrochemical processes very little research has been performed using liquid SEM [2]. We explore this imaging modality and describe here a novel chip [3,4] and cell designs enabling us to study Ag electrodeposition in real time using SEM in liquids. All these techniques are complementary and well suited for in situelectrochemistry. These examples demonstrate the versatility of these techniques and can be extended to other applications such as corrosion, battery and bio-medical research.

Thermal annealing of natural, radiation-damaged pyrochlore

Abstract Radiation damage in minerals is caused by the α-decay of incorporated radionuclides, such as U and Th and their decay products. The effect of thermal annealing (400–1000 K) on radiation-damaged pyrochlores has been investigated by Raman scattering, X-ray powder diffraction (XRD), and combined differential scanning calorimetry/thermogravimetry (DSC/TG). The analysis of three natural radiation-damaged pyrochlore samples from Miass/Russia [6.4 wt% Th, 23.1·1018 α-decay events per gram (dpg)], Panda Hill/Tanzania (1.6 wt% Th, 1.6·1018 dpg), and Blue River/Canada (10.5 wt% U, 115.4·1018 dpg), are compared with a crystalline reference pyrochlore from Schelingen (Germany). The type of structural recovery depends on the initial degree of radiation damage (Panda Hill 28%, Blue River 85% and Miass 100% according to XRD), as the recrystallization temperature increases with increasing degree of amorphization. Raman spectra indicate reordering on the local scale during annealing-induced recrystallization. As Raman modes around 800 cm−1 are sensitive to radiation damage (M. T. Vandenborre, E. Husson, Comparison of the force field in various pyrochlore families. I. The A2B2O7 oxides. J. Solid State Chem. 1983, 50, 362, S. Moll, G. Sattonnay, L. Thomé, J. Jagielski, C. Decorse, P. Simon, I. Monnet, W. J. Weber, Irradiation damage in Gd2Ti2O7 single crystals: Ballistic versus ionization processes. Phys. Rev. 2011, 84, 64115.), the degree of local order was deduced from the ratio of the integrated intensities of the sum of the Raman bands between 605 and 680 cm−1 divided by the sum of the integrated intensities of the bands between 810 and 860 cm−1. The most radiation damaged pyrochlore (Miass) shows an abrupt recovery of both, its short- (Raman) and long-range order (X-ray) between 800 and 850 K, while the weakly damaged pyrochlore (Panda Hill) begins to recover at considerably lower temperatures (near 500 K), extending over a temperature range of ca. 300 K, up to 800 K (Raman). The pyrochlore from Blue River shows in its initial state an amorphous X-ray diffraction pattern superimposed by weak Bragg-maxima that indicates the existence of ordered regions in a damaged matrix. In contrast to the other studied pyrochlores, Raman spectra of the Blue River sample show the appearance of local modes above 560 K between 700 and 800 cm−1 resulting from its high content of U and Ta impurities. DSC measurements confirmed the observed structural recovery upon annealing. While the annealing-induced ordering of Panda Hill begins at a lower temperature (ca. 500 K) the recovery of the highly-damaged pyrochlore from Miass occurs at 800 K. The Blue-River pyrochlore shows a multi-step recovery which is similarly seen by XRD. Thermogravimetry showed a continuous mass loss on heating for all radiation-damaged pyrochlores (Panda Hill ca. 1%, Blue River ca. 1.5%, Miass ca. 2.9%).