Tip-enhanced Raman Spectroscopy (TERS) is now well established as a nanoscale chemical imaging method with a spatial resolution of the order of 10 nm. TERS is simlar to SERS, and relies on enhancement of the local electromagnetic field in the vicinity of a metallic plasmonic nanostructure that is rastered over a sample by means of a scanning probe microscope using either AFM or STM feedback. The local enhancement of Raman scattered light is many orders of magnitude, large enough to render monomolecular films spectroscopically visible that would otherwise be optically too thin to be analyzed with conventional vibrational spectroscopy. In this presentation, the principle and experimental realization of TERS will be explained. An important advance concerns the realization of long-lived silver TERS tips that, thanks to the presence of a chemical protection layer, live for many weeks as opposed to the typical lifetime of ≈1 day for bare Ag tips. Applications of TERS to the chemical analysis of 2D polymers [1] and self-assembled monolayers [2] will be discussed.
[1] W. Dai et al., Synthesis of a Two-Dimensional Covalent Organic Monolayer through Dynamic Imine Chemistry at the Air/Water Interface, Angew. Chem. Int. Ed. 55, 213-217 (2016).
[2] W.-I. Lin et al., Tip-Enhanced Raman Spectroscopic Imaging Shows Segregation within Binary Self-Assembled Thiol Monolayers at Ambient Conditions, Anal. Bioanal. Chem. 407, 8197-8204 (2015)
TEM and SEM measurements are commonly used methods for characterization of nanomaterials.
Typically a single sample is applied onto an EM specimen holder or grid. Due to the fact that these grids have to be moved inside a vacuum chamber, the actual sample exchange may take several minutes depending on the EM instrument. Using a new loading technology, utilizing picoliter dispensing to print arrays of up to 100 samples on one EM support, results in a significant increase in sample throughput while decreasing operational costs in EM measurements significantly.
Scanning Probe Microscopy techniques are widely used for analysis of various physical properties of nano-objects and nano-systems. Quantitative measurements of more complex physical properties (thermal conductivity, refractive index, elastic modulus, etc.) are however still very problematic. One way how to deal these measurements is to use model based approach - to use suitable structural model of the sample, computational tool to calculate the instrument response and fit the sample model to the experimental data. This is in fact an approach very similar to many other techniques, e.g. reflectometry or ellipsometry. For SPM it is still challenging approach, as the interactions between probe and sample are complex and hard to solve analytically. With advent of cheap and powerful computational tools, like graphics cards, we can handle the problem numerically as discussed in this contribution, showing examples in the field of optical, thermal and mechanical measurements in SPM.
Last three decades have established the atomic force microscope (AFM) as an indispensable high-resolution tool for analysis of morphology, mechanics, as well as adhesion profiles of specimens ranging from single molecules to complex biological systems, in combination to commercially available optical microscopy.
A number of important research issues in the field of biomedicine, are directly related to the increased antimicrobial resistance of various biofilms to commonly prescribed drugs, as well as, understanding adhesion, as the leading factor for biofilm formation, colony progression, and pathogenesis of microbial agents. The very high sensitivity of novel AFM systems have led to the development and customisation of particular techniques, that enable the study of single-molecule forces and adhesion profiles at the cell/cell or cell/substrate interface.
We will give examples of the application of a new force tool “Quantitative Imaging” (QI™) based on fast force mapping which offers nanotopographical resolution with the opportunity of obtaining mechanical properties from various bacterial strains with pN-resolution. The “entire force distance curve behind every pixel” philosophy enables a full-range user-customised topographic and force spectroscopy analysis, including contact point (“zero-force”) images, Young´s modulus maps, as well as recognition events. The nanoscale mechanical compliance of bacterial walls can therefore be directly correlated to existing/hypothetic models of their structure. We will also discuss the application of novel fast scanning AFMs for the characterisation of dynamic biofilms with high spatiotemporal resolution reaching seconds per frame.
Carbon nanotubes (CNTs) are a popular sample for various nanotechnology studies. However, they are very difficult to synthesize en masse. As a result, researchers have started looking at alternatives with similar properties. One of the candidates to replace CNTs in some nanocomposite materials is cellulose nanowhiskers (CNWs), structures that can be readily produced from plant sources. To determine the feasibility of substituting CNWs for CNTs, it is important to verify the two materials have similar morphologies and nanomechanical properties. One must first establish a baseline for comparison by accurately characterizing CNW properties at nanoscale. To this end, three CNW samples were examined using an atomic force microscope (AFM) with non-contact AFM mode and an AFM-based fast nanomechanical mode. The target properties for evaluation were the samples' topography to determine the nanowhiskers' size and shape and their Young's modulus values. The ensuing AFM measurements yielded topography data showing the nanowhiskers ranging from 100 to 1000 nm in length and 1 to 3 nm in width. Nanomechanical property data acquired with the AFM in fast nanomechanical mode demonstrated the CNW samples had a modulus value of approximately 180 GPa. Not only do these measurements establish a baseline CNW to CNT comparison for topography and a specific nanomechanical property, but they also demonstrate the viability of AFM as an effective tool for dimensional nanometrology and quantitative property measurements of novel nanocomposite components.
Antiferromagnetically ordered magnetic moments alternate their directions between neighboring atomic sites in the crystal, which makes them notoriously difficult to control. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in thin film of a novel antiferromagnetic material CuMnAs. We place this effect in the context of the field of non-volatile solid state memories and demonstrate the complete write/read functionality on a simple lithographically patterned device. Both writing and readout are realized electrically and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.
Unlike natural polymers, most synthetic polymers can not be decomposed by microorganisms, hence the landfill approach becomes inefficient, and other plastics waste management should be found. A study of the biodegradation properties of synthetic polymers has become very important. A modification of nonbiodegradable synthetic polymers with a biodegradable polymer producing environmentally friendly polymers. The main problem in modification of nonbiodegradable synthetic polymers with biodegradable polymers is compatibility between polymers mixtures with different properties. Polypropylene (PP) is a thermoplastic polymer and difficult to be decomposed by microorganisms in environment. The aim of this work is to improve the properties of PP as well as its biodegradability by blending with biodegradable polycaprolactone (PCL). PCL is nontoxic, biodegradable polymer material and can be blended with various synthetic polymers over a wide composition range. The main problem in preparation of PP/PCL polymer blends is compatibility between polymers. In this work is presented results of thermal properties and compatibility of PP and PCL polymer blends reinforced with nano sized titan dioxide (TiO2) particles as well as effect of nTiO2 reinforcement on the thermal properties and compatibility. The neat polymers, PP/PCL and PP/PCL (nTiO2) polymer blends were prepared by melt compounding with a twin screw extruder, the granules of the blends were compression moulding in hydraulic press. The thermal properties of the neat polymers, PP/PCL and PP/PCL/nTiO2 blends are measured using the differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermogravimetry (TGA) techniques.
Residual strain in thin films represents a key factor in manipulating their macroscopic physical properties, such as electrical conductivity in semiconductors, electric polarization in ferroelectric materials, magnetoelectric coupling in multiferroics or the electrooptical effect in birefringent optical materials. Measuring and, in particular, mapping the residual strain in epitaxial films with thicknesses in the range from few nm up to hundreds of nm represents a challenging task for the microstructural characterization methods. High-Resolution Transmission Electron Microscopy is the most suitable method to provide measurable atomic-resolution microstructural data which can be quantitatively processed to reveal local atomic displacements as small as a few picometers. Furthermore, 2D strain maps with a space resolution down to 1 nm or below can be obtained. In our study we investigated epitaxial perovskite thin films (BCZT, PZT and SrRuO3) with a thickness in the range from 5 to 400 nm deposited by pulsed laser deposition. Cross-section specimens for TEM investigations have been prepared by mechanical grinding and ion milling. The HRTEM investigations have been performed on a JEM ARM 200F electron microscope. We used the Geometrical Phase Analysis to measure and map the residual strain in the thin films and to reveal the dependence on the films thickness. By analyzing the strain evolution, our study brings important HRTEM-based information regarding the film growth mechanism as a first step in correlating the microstructure and the macroscopic physical properties to be further used in applications.
The magnetic and electrical properties of doped nanostructured ZnO films are affected by the non-random distribution of dopants/impurities in the film due to segregation at grain boundaries (GBs) or extended defects. Currently used methods for identifying the nature and mapping the spatial distribution of low concentrations (< 1%) of impurities are very complex and laborious. We present here a non-destructive statistically relevant method of quantitative determination of the paramagnetic impurities distribution and segregation at the GBs in nanostructured films, based on electron paramagnetic resonance (EPR) spectroscopy.
From correlated EPR and transmission electron microscopy investigations we determined the localization of trace amounts of Mn2+ ions, present as native impurities in a ZnO film deposited onto r-cut sapphire by RF magnetron sputtering at RT. In the as-deposited ZnO film the Mn2+ ions were all localized in nano-pockets of highly disordered ZnO dispersed between nanocrystalline columns. Further pulse annealing treatments in air up to 600 oC were performed in order to study the dynamics of the Mn2+ ions and crystallization process. Similar investigations on 1% Mn doped ZnO film deposited in identical conditions have shown that less than 10% of the Mn2+ ions are atomically dispersed, localized in disordered ZnO at GBs, while the rest of the Mn2+ ions are agglomerated, forming secondary phases. ACKNOWLEDGEMENTS: Financial support from CNCS-UEFISCDI under the Project PN-II-RU-TE-2014-4-0939 is gratefully acknowledged. REFERENCES: M. Stefan, S.V. Nistor, D. Ghica, Cryst. Growth Des. 13, 350 (2013).; D. Ghica, M. Stefan, C. Ghica, G.E. Stan, ACS Appl. Mater. Interfaces 6, 14231 (2014).
In the last 10 years, researches concerning new methods used for the synthesis of silver nanoparticles (AgNPs) focused especially on green chemistry mainly because these methods are cost effective, eco-friendly and do not involve toxic chemicals. The raw materials used for the green synthesis of AgNPs are either biological microorganisms or alcoholic and/or aqueous plant extracts thus making green chemistry an attractive alternative to conventional chemical routes that often require and produce hazardous chemicals.
This work presents the biosynthesis of AgNPs using aqueous extract of Sea buckthorn (Hippophae rhamnoides L.) and European cornel (Cornus Mas L.), fruits that have different pharmacological effects (e.g.: antimicrobial, antioxidant, platelet aggregation, etc.). The aqueous extracts were obtained from fruits dried under several different conditions: direct sunlight, darkness at room temperature, cold dried at 40C and controlled drying at 500C in an oven. The potential capacity of these two fruits to bioreduce Ag+ to Ag0 was investigated by different spectral techniques (FTIR, UV-Vis, absorption). The size of the biosynthesized AgNPs was determined by diffraction light scattering measurements (DLS) and the AgNPs obtained from S. buckthorn and European cornel aqueous extract were compared to the AgNPs obtained by the sodium citrate chemical method.
In conclusion, this paper describes a new method to prepare AgNPs from eco-friendly aqueous extracts of S. buckthorn and European cornel. The experimental results clearly demonstrate that AgNPs are obtained and that these fruits contain all the natural components (e.g.: carbohydrates, tannins, flavonoides, etc.) able to bioreduce the silver ions.
Polyamide plays an important role in biomedical application such as suture material, coated textile for skin infection, wound dressing, catheters and bone tissue scaffolds. Surface modification of polyamide is very crucial factor to improve its performances by imparting desirable biomaterial properties. This report is focused on the efficient reduction of amide functional groups to secondary amine on Nylon 6 film surface with borane-tetrahydrofuran (BH3-THF) complex, followed by further alkylation. More precisely, we have studied the reaction of benzyl chloride (C6H5CH2Cl) in presence of potassium tert-butoxide (t-BuOK) on the modified Nylon 6 films. Thus, introduction of benzyl group to secondary amine of modified Nylon 6 has been accomplished. This type of transformation is expected to be generally applicable for functionalization of almost any polyamide. By using different alkylation reactions we will be able to tune the surface properties of polymers obtained for almost any applications. We also hope that polymers thus obtained will be biocompatible. The surface modifications were confirmed by both non-spectral methods and spectroscopic as well as microscopic analyses. Water contact angle (WCA) and free surface energy (FSE) measurements indicated the significant change in surface morphology that were established by X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy and atomic force microscopy (AFM). We are firmly convinced of the future prospect for further surface modification of these functionalized nylon 6 films with high potential in the field of biomedical application.