Bias-dependent conductive characteristics of individual GeSi quantum dots studied by conductive atomic force microscopy

The bias-dependent electrical characteristics of individual self-assembled GeSi quantum dots (QDs) are investigated by conductive atomic force microscopy. The results reveal that the conductive characteristics of QDs are strongly influenced by the applied bias. At low (-0.5 to - 2.0 V) and high (-2.5 to - 4.0 V) biases, the current distributions of individual GeSi QDs exhibit ring-like and disc-like characteristics respectively. The current of the QD's central part increases more quickly than that of the other parts as the bias magnitude increases. Histograms of the magnitude of the current on a number of QDs exhibit the same single-peak feature at low biases, and double- or three-peak features at high biases, where additional peaks appear at large-current locations. On the other hand, histograms of the magnitude of the current on the wetting layers exhibit the same single-peak feature for all biases. This indicates the conductive mechanism is significantly different for QDs and wetting layers. While the small-current peak of QDs can be attributed to the Fowler-Nordheim tunneling model at low biases and the Schottky emission model at high biases respectively, the large-current peak(s) may be attributed to the discrete energy levels of QDs. The results suggest the conductive mechanisms of GeSi QDs can be regulated by the applied bias.     

Electron transport through supported biomembranes at the nanoscale by conductive atomic force microscopy

We present a reliable methodology to perform electron transport measurements at the nanoscale on supported biomembranes by conductive atomic force microscopy (C-AFM). It allows measurement of both (a) non-destructive conductive maps and (b) force controlled current-voltage characteristics in wide voltage bias range in a reproducible way. Tests experiments were performed on purple membrane monolayers, a two-dimensional (2D) crystal lattice of the transmembrane protein bacteriorhodopsin. Non-destructive conductive images show uniform conductivity of the membrane with isolated nanometric conduction defects. Current-voltage characteristics under different compression conditions show non-resonant tunneling electron transport properties, with two different conduction regimes as a function of the applied bias, in excellent agreement with theoretical predictions. This methodology opens the possibility for a detailed study of electron transport properties of supported biological membranes, and of soft materials in general.     

Characterization of the oxygen oonosorption effect on a single SnO2 nanowire by using conductive atomic force microscopy

We have verified that SnO2 nano-wire has an n-type semiconductor property and it can be a p-type one when it is exposed to O2. We employed conductive AFM system to measure the I-V curve and resistance of single SnO2 nano-wire which had been synthesized on the Au thin film by a thermal process. To analyze a effect of O2 ionosorption into nano-wire, resistance was measured with various O2 concentration and we observed increment and maintenance of resistance which caused by O2 ionosorption. Also, the O2 ionosorption causes a type transfer of semiconductor and this phenomenon was verified by comparing the Schottky property of nano-wire before and after O2 exposure.     

Characterization of Pt/a-plane GaN Schottky contacts using conductive atomic force microscopy

We investigated the local electrical properties of Pt Schottky contacts to a-plane n-type GaN using conductive atomic force microscopy (C-AFM). Current-voltage characteristics obtained by C-AFM showed rectifying properties, indicating nano-scale Schottky junction formation. Two-dimensional current maps revealed that the surface microstructures of GaN influenced transport properties of the junctions.     

Phyto‐fabricated silver nanoparticles inducing microbial cell death via reactive oxygen species‐mediated membrane damage

Eco‐friendly synthesis of the silver nanoparticles (AgNPs) has a number of advantages like simplicity, biocompatibility, low toxicity in nature over their physical and chemical methods. In the present study, the authors report biosynthesized AgNPs using the root extract of the perennial plant ‘Spiny gourd’ (Momordica dioica) and investigated their anti‐bacterial application with mechanistic approaches. Different biophysical techniques such as UV‐Vis spectroscopy, FTIR, XRD, TEM, SAED, and DLS were employed for AgNPs characterization. The synthesized AgNPs were polydispersed, crystalline in nature, with anionic surface (−22.3 mV), spherical in shape with an average size of 13.2 nm. In addition, the AgNPs were stable in room temperature and in different biological buffers. The anti‐bacterial activities of AgNPs were studied with respect to the pathogens such as Bacillus subtilis, Staphylococcus aureus (Gram‐positive), Pseudomonas aeruginosa, Escherichia coli, Klebsiella planticola (Gram‐negative), and Candida albicans. Also, mechanistic studies of AgNPs such as protein leakage assay, nucleic acid leakage assay, ATP leakage assay, ROS accumulation, determination of biofilm degrading activity, measurement of potassium, showing that the synthesized AgNPs are capable of containing a potential application in the antimicrobial therapeutic agents and the pharmaceutical industry.     

Experimental validation of atomic force microscopy-based cell elasticity measurements

Atomic force microscopy (AFM) is widely used for measuring the elasticity of living cells yielding values ranging from 100 Pa to 100 kPa, much larger than those obtained using bead-tracking microrheology or micropipette aspiration (100-500 Pa). AFM elasticity measurements appear dependent on tip geometry with pyramidal tips yielding elasticities 2-3 fold larger than spherical tips, an effect generally attributed to the larger contact area of spherical tips. In AFM elasticity measurements, experimental force-indentation curves are analyzed using contact mechanics models that infer the tip-cell contact area from the tip geometry and indentation depth. The validity of these assumptions has never been verified. Here we utilize combined AFM-confocal microscopy of epithelial cells expressing a GFP-tagged membrane marker to directly characterize the indentation geometry and measure the indentation depth. Comparison with data derived from AFM force-indentation curves showed that the experimentally measured contact area for spherical tips agrees well with predicted values, whereas for pyramidal tips, the contact area can be grossly underestimated at forces larger than ～0.2 nN leading to a greater than two-fold overestimation of elasticity. These data suggest that a re-examination of absolute cellular elasticities reported in the literature may be necessary and we suggest guidelines for avoiding elasticity measurement artefacts introduced by extraneous cantilever-cell contact.     

Dynamic behaviour of a nanoscale-patterned phospholipid thin film on mica and silicon studied by atomic force microscopy

The temporal evolution of the morphology of nanoscale-patterned phospholipid thin films on mica and silicon surfaces has been investigated with an atomic force microscope (AFM). The AFM images reveal that nanoscale scratch lines on thin films prepared on mica contract with time and eventually form roundish holes. An elevated sample temperature accelerates this morphological evolution. We model such an evolution based on the interplay of the thin-film surface line tension and the friction between the thin film and the substrate. The results show that the temperature-dependent contraction is governed by the ratio of the friction coefficient and the surface line tension. The friction at the lipid/mica interface decreases to a seventh as the sample temperature rises from 18 to 60 °C. This model is supported by experiments on silicon surfaces, on which contraction of the scratch patterns is limited because of an expected greater interfacial friction.     

Surface‐enhanced Raman spectroscopy analysis of mast cell degranulation induced by low‐intensity laser

Mast cell (MC) degranulation is an important step in the healing process. In this study, silver‐nanoparticles‐based surface‐enhanced Raman spectroscopy (SERS) was used to investigate the spectral characteristics of degranulation of MCs activated by low‐intensity laser. The significant spectral changes, such as Raman peak intensities, suggested the concentration variation of some degranulated substances. The Raman intensity ratio of 799–554 cm ^{− 1} could be used as a potential internal indicator for the degranulation degree of MCs. Principal component analysis (PCA) was employed to reduce the high dimension of spectra into a few principal components (PCs) while retaining the most diagnostically significant information for sample differentiation. Using the diagnostically significant PC scores (P  < 0.05), linear discriminate analysis (LDA) was applied to identify different cell degranulation groups with high sensitivity, specificity and accuracy. This exploratory work demonstrates that SERS technique combined with a PCA‐LDA algorithm possesses great potential for developing a label‐free, comprehensive, non‐invasive and accurate method for measuring MC degranulation.Inspec keywords: Raman spectra, silver, surface enhanced Raman scattering, Raman spectroscopy, nanoparticles, cellular biophysics, biological techniques, principal component analysisOther keywords: MCs, principal component analysis, diagnostically significant information, diagnostically significant PC scores, linear discriminate analysis, different cell degranulation groups, PCA‐LDA algorithm possesses great potential, MC degranulation, surface‐enhanced Raman spectroscopy analysis, mast cell degranulation, low‐intensity laser, healing process, silver‐nanoparticles‐based surface‐enhanced Raman spectroscopy, significant spectral changes, Raman peak intensities, concentration variation, degranulated substances, Raman intensity ratio, potential internal indicator, degranulation degree     

Precise control of nanofabrication by atomic force microscopy

With an aim of the precise control of the anodic oxidation process by atomic force microscopy, the technical improvement has been carried out based on the mechanism studies. The accuracy and reliability of the nanofabrication have been improved by the combination of ambient humidity control, improvement of instrumental performance and meniscus lifetime control. In parallel, the mechanism study has been proceeded through the detection of Faradaic current. The in situ Faradaic current detection of the nano-oxidation process can actually work as a sensitive monitor for the nano-oxidation process with a high reliability. From an engineering viewpoint with an eye to practical applications, controllable physical parameters which affect on the product size are enumerated to consider what we should do to raise the precision of nano-oxidation. Then the fast fabrication in a large area by a patchwork method, Faradaic current detection during oxidation-reduction reaction, and nanofabrication by current-control are shown as examples.     

Imaging dielectric properties of Si nanowire oxide with conductive atomic force microscopy complemented with femtosecond laser illumination

In most Si nanowire (NW) applications, Si oxide provides insulation or a medium of controlled electron tunneling. This work revealed both similarities and differences in the dielectric properties of NW oxide compared with that grown on wafers. The interface barrier to electron transit from the semiconductor to the dielectric and the threshold electric field for current flow are quite similar to those in the planar geometry. This is not true for the lowest currents measured which are not uniformly distributed, indicating variations of trap density in the gap of NW oxide.     

Measurement of interfiber friction force for pulp fibers by atomic force microscopy

Interfiber friction in paper exists in fiber suspensions, fiber flocs, and fiber networks. The interfiber friction force is, therefore, important both in papermaking and in the use of paper. The objective of this research is to develop a methodology using atomic force microscopy (AFM) for the direct measurement of the friction force between pulp fibers. Different factors such as AFM scanning velocity, contact area, and fiber surface roughness were investigated. The results show that AFM is an effective tool for measuring micro-scale interfiber friction forces. Both AFM scanning velocity and fiber surface roughness affect the measured results. The coefficient of friction increases, but the initial adhesion force decreases, with increasing fiber surface roughness.     

原位气相聚合法合成制备PTh/PVDF导电复合膜的研究

在低温低压条件下,以FeCl3为氧化剂,通过原位气相聚合法合成制备PTh(聚噻吩)/PVDF(聚偏氟乙烯)导电复合膜,探讨了制备条件对复合膜性能的影响.ATR-IR光谱测试结果证实,该复合膜的光谱图中出现了聚噻吩的特征吸收峰.扫描电镜观察表明,该复合膜的表观形貌随聚合进行而逐步变化.四探针法测试结果显示,该复合膜的电导率为0.1～1.0S·cm-1.滤速法测定结果说明,该复合膜的平均孔径随聚合反应时间增加而逐渐减小.     

Characterization of titanium polycide films by atomic force microscope

Non-destructive methods are required for in-line process control in VLSI circuits. In this study, mean roughness values as obtained from AFM analysis have been used to follow phase transformation of Ti-polycide films formed by annealing Ti films on polysilicon. The results are supported from XRD analysis of the TiSi₂ films.     

Non-contact atomic force microscopy study of atomic manipulation on an insulator surface by nanoindentation

Experimental results on vertical manipulation on an insulator surface using non-contact atomic force microscopy are presented. Cleaved ionic KCl(100) single crystal is used as an insulator surface. With the nanoindentation method used, the vertical manipulation of a single atom in an ionic crystal surface is more difficult than in a semiconductor surface. Therefore, in many cases, more than one surface atom is manipulated while, in rare cases, single-atom manipulation is successfully performed. Lateral manipulation of a vacancy has occasionally succeeded on the KCl(100) surface. We have presumed that the lateral manipulation was induced by pulling.     

Fabrication of conductive human bio‐nanoelectrode from graphene oxide modified with polyvinyl alcohol

It is time for electrodes prepared from graphene oxide (GO) to replace the traditional electrodes. However, GO is an electrically insulating material. However, in this study, a conductive electrode was prepared from GO modification with glycerol (GL) under the esterification reaction at 90°C for 3 h with sulphuric acid as a catalyst under vacuum conditions. Polyvinyl alcohol (PVA) acts as a polymer host. It was mixed with GO and modification was carried out under heating conditions. The mixture of the GO/GL/PVA nanocomposite was rapidly cooled and poured into the electrode mould. Finally, it is placed in a desiccator at room temperature for two days. The characterisation (Fourier transform infrared spectroscopy, X‐ray diffraction, and scanning electron microscopy) proved that the ester bond was formed and a complete distribution of GO/GL into the matrix of PVA was verified. The GO/GL/PVA nanocomposite was tested for electrocardiogram (ECG) electrodes. The biopic instrument was used to compare the behaviour of the GO/GL/PVA plastic electrode and the commercial one. The results indicated that the GO/GL/PVA plastic electrode efficiently detected ECG signals after two months with high conductivity and lower noise than the commercial electrode. The GO/GL/PVA plastic electrode has been reported for the first time in the literature.Inspec keywords: catalysts, scanning electron microscopy, filled polymers, nanofabrication, X‐ray diffraction, moulding, nanocomposites, graphene compounds, Fourier transform infrared spectra, nanomedicine, biomedical electrodes, electrocardiography, electrical conductivity, medical signal detection, bonds (chemical)Other keywords: graphene oxide, polyvinyl alcohol, electrode mould, electrocardiogram electrodes, conductive human bionanoelectrode, electrically insulating material, GO‐GL‐PVA nanocomposite, GO‐GL‐PVA plastic electrode, esterification reaction, sulphuric acid, catalyst, vacuum conditions, polymer host, heating conditions, desiccator, glycerol, Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, ester bond, biopic instrument, ECG signal detection, electrical conductivity, temperature 90.0 degC, time 3.0 hour, temperature 293 K to 298 K, time 2 day, CO