Scanning Probe Microscopy Studies Research Articles

Using Coordination Chemistry to Control "Click" Reactions: The Selective Formation of Asymmetrically Ligated Polyoxometalates.

The Cu(I)-catalyzed azide-alkyne cycloaddition reaction between (NBu4)2[V6O13((OCH2)3CCH2N3)2] and 3-ethynylpyridine led to the formation of products capable of forming poorly soluble coordination compounds with transition metal ions such as Cu(I) and Zn(II). The formation of these poorly soluble phases is an important feature that was used to determine the course of reactions, allowing the selective preparation of symmetric bis-pyridyltriazolyl and asymmetric monopyridyltriazolyl derivatives with relatively high yields and high substrate conversions. The asymmetric compound (NBu4)2[V6O13((OCH2)3CCH2-N3C2H-C5H4N)((OCH2)3CCH2N3)] (V6asym) was utilized in the subsequent "click" postfunctionalization reaction with 1,4-diethynylbenzene, resulting in a covalently bound V6asym-V6asym dimer. This dimeric compound was subjected to scanning probe microscopy studies on gold surfaces, which revealed no electronic coupling between the hexavanadate cores within the dimer upon potential-induced switching. This observation indicates that such dimers and higher-order oligomers composed of polyoxometalate-ligand-polyoxometalate bridges can be exploited as active capacitor/memristor units, relevant to increase the data storage capacity of standard memory devices with innovative molecular switching mechanisms.

PREPARATION AND OPTIMIZATION OF CILOSTAZOL NANOEMULSION ORAL LIQUID DOSAGE FORM

Objective: Cilostazol has poor water solubility and low oral bioavailability. Therefore, the formulation of cilostazol as a nanoemulsion may enhance its solubility and improve oral bioavailability. Hence, the aim of this study was to formulate and characterize an oil-in-water (o/w) nanoemulsion of cilostazol as an oral liquid dosage form. Methods: Pseudo-ternary phase diagrams were constructed using the aqueous titration method. Formulations of pseudo-ternary phase plots consisting of oil, various weight ratios of S mix (mixture of surfactant and co-surfactant), and deionized water were made. Different characterization studies, droplet size measurement, polydispersity index, drug content, zeta potential measurement, and in vitro release have been conducted to choose the optimized formula. Results: The characterization studies have demonstrated that the optimized formula is (F-6), consisting of 20 % S mix (3:1), 10% ginger oil, and 70% deionized water. This formula had the following characteristics; droplet size (72.9-110 nm), polydispersity index (0.22), percentage of drug content (99.8%), and in vitro release of cilostazol nanoemulsion was significantly higher (P<0.05) in comparison with other formulations. A Scanning probe microscopy (SPM) study has revealed that the droplet size of F-6 was at the nano-scale. Conclusion: In conclusion, the optimized cilostazol formula (F-6) is a promising formula which may have the capability of improving the oral bioavailability of cilostazol.

Increasing the redox switching capacity of Lindqvist-type hexavanadates by organogold post-functionalisation.

The covalent attachment of organogold(I) moieties to the Lindqvist-type polyoxovanadate results in a measurable charge re-distribution across the formed Au-{V6}-Au linkages. Scanning probe microscopy studies of these hybrid compounds on the Au(111) surface demonstrate the increase in the number of switching states with stepwise increase in molecular conductance, compared with unfunctionalised hexavanadates.

Scanning probe microscopy study of functionalized nanographene

Scanning probe microscopy study of functionalized nanographene

Scanning probe microscopy study of functionalized nanographene

Scanning probe microscopy study of functionalized nanographene

Combined scanning probe microscopy and electron microscopy study of microstructure evolution in copper processed by equal channel angular pressing

Abstract We produced submicrocrystalline Cu using the equal channel angular pressing technique with four passes. The as-deformed samples exhibited a high yield strength > 400 MPa and a poor elongation before failure < 20%. The majority of the grain boundaries after equal channel angular pressing were of the low-angle type. A series of heat treatments in the temperature range 220 – 300 °C was performed and partly recrystallized microstructures with different fractions of recrystallized grains were obtained. The microstructures were analyzed by a combination of transmission electron microscopy, orientation image microscopy, light microscopy and scanning probe microscopy. The increase in ductility in partly recrystallized samples was accompanied by a decrease in the yield strength. It was suggested that to obtain a bulk nanocrystalline material which is both strong and ductile the majority of the grain boundaries should be of the high-angle type. It is shown that the scanning probe microscopy technique allows one to determine the microstructure of partly and fully recrystallized samples and to draw qualitative conclusions about the defects density and their distribution in the sample.

Electrically Tunable Reactivity of Substrate-Supported Cobalt Oxide Nanocrystals.

First-row transition metal oxides are promising materials for catalyzing the oxygen evolution reaction. Surface sensitive techniques provide a unique perspective allowing the study of the structure, adsorption sites, and reactivity of catalysts at the atomic scale, which furnishes rationalization and improves the design of highly efficient catalytic materials. Here, a scanning probe microscopy study complemented by density functional theory on the structural and electronic properties of CoO nanoislands grown on Au(111) is reported. Two distinct phases are observed: The most extended displays a Moiré pattern (α-region), while the less abundant is 1Co:1Au coincidental (β-region). As a result of the surface registry, in the β-region the oxide adlayer is compressed by 9%, increasing the unoccupied local density of states and enhancing the selective water adsorption at low temperature through a cobalt inversion mechanism. Tip-induced voltage pulses irreversibly transform α- into β-regions, thus opening avenues to modify the structure and reactivity of transition metal oxides by external stimuli like electric fields.

Structure and dielectric properties of thin nanocrystalline ZnFe2O4 films

Optically transparent high-quality nanosized crystalline zinc ferrite thin films on different substrates have been synthesized by the decomposition of organic zinc and iron (III) compounds. According to scanning probe microscopy study, the films are 40-50 nm thick and their surface consists of densely spaced uniformly oriented crystallites with morphology depending on the substrate. X-ray diffraction analysis has shown that the films are polycrystalline and ZnFe2O4 has a cubic spinel structure. The dielectric constant lies in the range of 53 ÷ 54. The films are spontaneously polarized with a residual polarization of about 0.59 ÷ 0.69 μC⋅cm−2 , the coercive field is (8 ÷ 12)·104 V/cm.

Application of a long short-term memory for deconvoluting conductance contributions at charged ferroelectric domain walls

Ferroelectric domain walls are promising quasi-2D structures that can be leveraged for miniaturization of electronics components and new mechanisms to control electronic signals at the nanoscale. Despite the significant progress in experiment and theory, however, most investigations on ferroelectric domain walls are still on a fundamental level, and reliable characterization of emergent transport phenomena remains a challenging task. Here, we apply a neural-network-based approach to regularize local I(V)-spectroscopy measurements and improve the information extraction, using data recorded at charged domain walls in hexagonal (Er0.99,Zr0.01)MnO3 as an instructive example. Using a sparse long short-term memory autoencoder, we disentangle competing conductivity signals both spatially and as a function of voltage, facilitating a less biased, unconstrained and more accurate analysis compared to a standard evaluation of conductance maps. The neural-network-based analysis allows us to isolate extrinsic signals that relate to the tip-sample contact and separating them from the intrinsic transport behavior associated with the ferroelectric domain walls in (Er0.99,Zr0.01)MnO3. Our work expands machine-learning-assisted scanning probe microscopy studies into the realm of local conductance measurements, improving the extraction of physical conduction mechanisms and separation of interfering current signals.

Visualization of Functional Components in a Lithium Silicon Titanium Phosphate–Natural Graphite Composite Anode

Here, a multimodal scanning probe microscopy study of a composite anode with a dispersed lithium silicon titanium phosphate (LSTP) lithium ion conductor for all-solid-state batteries is presented. ...

DESIGN AND CHARACTERIZATION OF CANDESARTAN CILEXETIL ORAL NANOEMULSION CONTAINING GARLIC OIL

Objective: This study was designed to prepare and characterize oil in water (o/w) nanoemulsion of candesartan cilexetil for oral administration. Preparation of candesartan cilexetil as nanoemulsion could increase its water solubility and thus could enhance its bioavailability.
 Methods: Aqueous titration method was used to construct the pseudo-ternary phase diagrams of nanoemulsion (NE) consisting of oil, various weight ratios of surfactant and co-surfactant (S mix), and deionized water. Different characterization techniques were conducted on the prepared nanoemulsions to obtain the optimized formula.
 Results: Characterizations of formula NE-4 (consists of 0.16% of candesartan cilexetil, 10% of garlic oil, 35 % of S mix (3:1) and 54.84% of deionized water) revealed the following characteristics: droplet size range (95-139 nm), polydispersity index (0.14), zeta potential value (-41.06 mV) and pH value (6.71), which are suitable for oral administration. Candesartan cilexetil in vitro release from this formula was significantly high (P<0.05) and scanning probe microscopy (SPM) study confirmed that the optimized formula (NE-4) was in nano-scale.
 Conclusion: Nanoemulsion formula 4 (NE-4) of candesartan cilexetil is the optimized formula and it could be a promising formula for improving the water solubility of candesartan cilaxetil.

Correlation of resistance switching and polarization rotation in copper doped zinc oxide (ZnO:Cu) thin films studied by Scanning Probe Microscopy

This paper presents multiple-modes Scanning Probe Microscopy (SPM) studies on characterize the correlation of resistance switching (RS) and polarization rotation (PR) in copper doped ZnO (ZnO:Cu) thin films. Firstly, the bipolar RS behavior is confirmed by conductive Atomic Force Microscopy (c-AFM). The PR with almost 180° phase angle is confirmed by using the Piezoresponse Force Microscopy (PFM) on the same location. In addition, it elucidates that obvious PR behavior can be observed in the sample with increasing Cu concentration by combining Kelvin Probe Force Microscopy (KPFM). Furthermore, it is found that the region with downward polarization has low resistance state (LRS), whereas the region with upward polarization has high resistance state (HRS). Moreover, the Piezoresponse Force Spectroscopy (PFS) and Switching Spectroscopy PFM (SS-PFM) measurements further confirm that the existence of the built-in voltage, Vbuilt-in is largest in the ZnO:Cu (8 at.%) film deposited at the oxygen partial pressure of 2 × 10−4 Torr. The schematic diagrams of energy band diagram with varied built-in field, Ebuilt-in, polarization directions and redistributed charges are presented to explain the correlation between RS and PR behavior.

Probing host-guest interactions in hydroxyapatite intercalated graphene oxide nanocomposite: NMR and scanning probe microscopy studies

The surface structure instability of the nanoscale Hydroxyapatite (HAP) and reduced graphene oxide (rGO) sheets under the dynamic chemical environment capable of forming host-guest complexes has been determined by nuclear magnetic resonance (NMR) spectroscopy and scanning probe microscopy (SPM). From the NMR and SPM studies, we have found that the interaction between the nanoHAP and rGO sheets is occurred through the surface POxH− group of nanoHAP with epoxy carbon of rGO. Complexation of rGO sheets with nanoHAP facilitates electron transfer between them and an enhanced piezo response of 65 ± 2.5 pm/V at the nanoHAP intercalated rGO region.

Engineering the structural, plasmonic, and optical properties of multilayered aluminum-doped zinc oxide metamaterial grown by pulsed laser deposition.

We engineer a tunable multilayered aluminum-doped zinc oxide metamaterial with low-loss and high-carrier concentration using the pulsed laser deposition. The results of the scanning probe microscopy study show excellent surface quality with a root mean square roughness value of 1.88±0.07 nm. The transmission electron microscopy measurements indicate a clear layer-by-layer structure of the multilayered samples. The optical permittivity results, obtained using the ellipsometry approach, show that the hyperbolic dispersion of the dielectric constant [Re (ε‖)>0, Re (ε⊥)<0] is achieved in the near-IR spectral range. The low imaginary part of the optical permittivity Im (ε⊥)=0.003 and Im (ε‖)=0.011 is achieved for the optimized sample at the epsilon-near-zero spectral point [Re (ε⊥)=0 at 1885nm]. The results of the ellipsometry analysis show that the systematic variation of different fabrication conditions, such as the AZO/ZnO ratio, the thickness of an individual layer, the film's total thickness, and the deposition temperatures, allows for tuning the plasma frequency ωp and damping frequency γp of the investigated samples, which is a promising approach for the future precise engineering of linear and nonlinear optical properties of multilayered aluminum-doped zinc oxide metamaterial.

Scanning Probe Microscopy Study of the Negative Electrode Materials for Li-based Secondary Batteries

Scanning Probe Microscopy Study of the Negative Electrode Materials for Li-based Secondary Batteries

A scanning probe microscopy study of nanostructured TiO2/poly(3-hexylthiophene) hybrid heterojunctions for photovoltaic applications.

The nanoscale morphology of photoactive hybrid heterojunctions plays a key role in the performances of hybrid solar cells. In this work, the heterojunctions consist of a nanocolumnar TiO2 surface covalently grafted with a monolayer of poly(3-hexylthiophene) (P3HT) functionalized with carboxylic groups (–COOH). Through a joint analysis of the photovoltaic properties at the nanoscale by photoconductive-AFM (PC-AFM) and surface photovoltage imaging, we investigated the physical mechanisms taking place locally during the photovoltaic process and the correlation to the nanoscale morphology. A down-shift of the vacuum level of the TiO2 surface upon grafting was measured by Kelvin probe force microscopy (KPFM), evidencing the formation of a dipole at the TiO2/P3HT-COOH interface. Upon in situ illumination, a positive photovoltage was observed as a result of the accumulation of photogenerated holes in the P3HT layer. A positive photocurrent was recorded in PC-AFM measurements, whose spatial mapping was interpreted consistently with the corresponding KPFM analysis, offering a correlated analysis of interest from both a theoretical and material design perspective.

Face-on vs. edge-on: tuning the structure of tetrathiafulvalene monolayers with solvent

Molecular orientation and supramolecular structure of tetrathiafulvalene derivative on graphite can be controlled by the change of deposition solvent, as revealed by scanning probe microscopy study.

Synthesis, structural characterization, QSAR and docking studies of a new binuclear nickel (II) complex based on the flexible tetradentate N-donor ligand as a potent antibacterial and anticancer agent

A new nickel (II)complex namely [Ni2(Lt)Cl4] derived from the NiCl2.6H2O and 1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazolyl)propane (Lt) has been synthesized and fully characterized by the single crystal X-ray diffraction, elemental analysis, FT-IR, UV–vis, density functional theory (DFT) calculations, antibacterial and anticancer activities. In the title complex, each of the Ni(II) atoms is tetrahedrally coordinated by two N atoms from one of the chelating bidentate bis(3,5-dimethylpyrazolyl)methane units of the Lt ligand and two Cl as terminal ligands. The neighboring [Ni2(Lt)Cl4] molecules are linked together by the intermolecular CH⋯Cl hydrogen bonds to generate a 1D chain structure. The chains are further stabilized by the intermolecular CH⋯π interactions to form a two-dimensional non-covalent bonded structure. The antibacterial activity of the free Lt ligand and its Ni (II) complex shows that the ability of these compounds to inhibit growth of the tested bacteria increase from the Lt to binuclear nickel (II) complex. Scanning probe microscopy (SPM) study of the treated B. subtilis and E. coli bacteria was implemented to understand the structural changes caused by the interactions between the nickel (II) complex and the target bacteria. The cytotoxicity test of the Lt ligand and its complex was evaluated against the human carcinoma cell line (Caco-2) using the MTT assay. The results indicate that the Lt ligand and its complex display cytotoxicity against Caco-2 with the IC50 values of 36.29μM and 12.97μM, respectively. Therefore, the complex can be nominated as a potential anticancer agent. Molecular docking investigations on the five standard antibiotic, five standard anticancer drugs, free Lt ligand, title complex and twelve receptors were performed by Autodock vina function. The results of docking and DFT calculations are in line with the in vitro data obtained via the antibacterial and anticancer activity of Lt ligand and its made-complex.

Structural variability in Cu(I) and Ag(I) coordination polymers with a flexible dithione ligand: Synthesis, crystal structure, microbiological and theoretical studies

Two new compounds namely [Cu(SCN)(µ-L)]n (1) and {[Ag (µ2-L)](ClO4)}n (2) have been synthesized at room temperature by one-pot reactions between the 1,1-(1,4-butanediyl)bis(1,3-dihydro-3-methyl-1H-imidazole- 2-thione) (L) and appropriate copper(I) and silver(I) salts. These polymers have been characterized by single crystal X-ray diffraction, XRPD, TGA, elemental analysis, infrared spectroscopy, antibacterial activity and scanning probe microscopy studies. In the crystal structure of 1, copper atoms have a distorted trigonal planar geometry with a CuS2N coordination environment. Each of the ligands in the structure of 1 acting as a bidentate S-bridging ligand to form a 1D chain structure. Additionally, the adjacent 1D chains are interconnected by the intermolecular C-H…S interactions to create a 2D network structure. In contrast to 1, in the cationic 3D structure of 2 each of the silver atoms exhibits an AgS4 tetrahedral geometry with 4-membered Ag2S2 rings. In the structure of 2, the flexible ligand adopts two different conformations; gauche-anti-gauche and anti-anti-anti. The antibacterial studies of these polymers showed that polymer 2 is more potent antibacterial agent than 1. Scanning probe microscopy (SPM) study of the treated bacteria was carried out to investigate the structural changes cause by the interactions between the polymers and target bacteria. Theoretical study of polymer 1 investigated by the DFT calculations indicates that observed transitions at 266nm and 302nm in the UV–vis spectrum could be attributed to the π→π* and MLCT transitions, respectively.

Synthesis, structural characterization, antibacterial activity, DNA binding and computational studies of bis(2-methyl-1H-imidazole κN3)silver(I)dichromate(VI)

A new silver complex [Ag(C4H6N2)2]2Cr2O7 (1) derived from Ag2[CrO4] and 2-methylimidazole has been synthesized and fully characterized by Single crystal X-ray diffraction, UV–Vis, FT-IR, elemental analysis, DFT and AIM calculations. The crystal structure of 1 shows that the discrete, ionic compound of [Ag(C4H6N2)2]2Cr2O7 consists of two [Ag(C4H6N2)2]+ cations bridged by a [Cr2O7]2− counter anion. In each of the [Ag(C4H6N2)2]+ complexes, the Ag center is coordinated by two N atoms from two distinct neutral monodentate 2-methylimidazole ligands in an almost linear geometry with AgN distances between 2.068(4) Å and 2.076(4) Å and NAgN bond angles of 179.4(2)° and 173.8(2)°. The NH⋯O and CH⋯ O hydrogen bonds, π⋯π stacking, CH⋯π and Ag⋯O interactions play an important role in the structural stabilization of the complex to generate a three-dimensional framework. The antibacterial activity and molecular docking studies of the free 2-methylimidazole ligand and the title complex show that these compounds have ability to inhibit the growth of the tested bacteria. A scanning probe microscopy (SPM) study of the treated bacteria was carried out to investigate the structural changes caused by the interactions between the complex and target bacteria. The interaction of the complex 1 with the E.coli DNA (E-DNA) has been studied by UV–Vis absorption, competitive DNA-binding studies with ethidium bromide by fluorescence and gel electrophoresis techniques. These experiments indicate that the complex interacts with DNA by intercalative binding.