Growth and electrical characterization of type II InAs/GaSb superlattices for midwave infrared detection

Herein, we report a type II InAs/GaSb superlattice structure (SLS) grown on GaSb(1 0 0) substrates by molecular beam epitaxy (MBE) and its electrical characterization for mid-wavelength infrared detection. A GaSb buffer layer was grown under optimized SLS growth conditions, which can decrease the occurrence of defects for similar pyramidal structures. The complications associated with these conditions include oxide desorption of the substrate, growth temperature of the SLS, the V/III ratio during superlattice growth and the shutter sequence. High-resolution X-ray diffraction (HRXRD) shows the sixth satellite peak, and the period of the SLS was 52.9 Å. The atomic force microscopy (AFM) images indicated that the roughness was less than 2.8 nm. High-resolution transmission electron microscopy (HRTEM) images indicated that the SLS contains few structural defects related to interface dislocations or strain relaxation during the growth of the superlattice layer. The photoresponse spectra indicated that the cutoff wavelength was 4.8 μm at 300 K. The SLS photodiode surface was passivated by a zinc sulfide (ZnS) coating after anodic sulfide.     

Spatial alignment evolution of self-assembled In0.4Ga0.6As island arrays grown on GaAs (3 1 1)B surface by atomic hydrogen-assisted molecular beam epitaxy

Self-assembled In_0.4Ga_0.6As island arrays have been grown on (3 1 1)B GaAs substrates by using atomic hydrogen-assisted molecular beam epitaxy (H-MBE). The evolution process of surface morphology with deposition has been analyzed by atomic force microscopy (AFM) and the development of lateral ordering has been highlighted by two-dimensional fast Fourier transformation (2DFFT) analysis of the AFM images. It is revealed that the InGaAs islands are arranged in nearly perfect two-dimensional (2D) square-like lattice with two sides parallel to [0 1 −1] and [−2 3 3] azimuths. Such an alignment of islands is coincident with the anisotropy of bulk elastic modulus of the GaAs (3 1 1)B substrate.     

Observation of intermolecular N–I interaction during the growth of a 4-cyano-4′-iodobiphenyl molecular crystal on GeS(001)

The electronic and atomic structures of 4-cyano-4′-iodobiphenyl (CIB) during the growth of a molecular crystal on a GeS(001) substrate were studied by ultraviolet photoemission spectroscopy (UPS), atomic force microscopy (AFM), and extended X-ray absorption fine structure (EXAFS) spectroscopy. AFM images suggest that the CIB molecule grows as a microcrystal at a nominal thickness of 80 Å. The microcrystal grows with the crystal plane parallel to the surface and isotropic crystal axis orientation. EXAFS analysis suggests that a CIB crystal forms by strong N···I interaction, called halogen bonding. The formation of the intermolecular N···I bond was demonstrated by EXAFS analyses in which the N–I distance was determined to be 3.29 Å. An upward shift of the highest occupied molecular orbital level was observed by UPS and can be attributed to the aggregation of CIB molecules caused by halogen bonding.     

Connection between biomechanics and cytoskeleton structure of lymphocyte and Jurkat cells: An AFM study

The mechanical properties of cells are important for many cellular processes. Here, atomic force microscopy (AFM) and laser scanning confocal microscopy (LSCM) were carried out to characterize lymphocyte and Jurkat cells. The average elastic modulus of lymphocyte is 1.24 ± 0.09 kPa, which is almost twofold higher than that of Jurkat cell (0.51 ± 0.06 kPa). LSCM images of sub-membrane cytoskeleton showed a significant difference in the organization of their F-actin structures. Lymphocyte cells had more and thicker actin bundles than that of Jurkat cells. Lymphocyte and Jurkat cells after adding the F-actin destabilizing agent Cytochalasin-B (Cyt-B) were also investigated by AFM. A decrease in the elastic modulus of lymphocyte from a value of 1.24 ± 0.09 kPa down to 0.34 ± 0.04 kPa for 24 h was observed, and that of Jurkat cell decreased from 0.51 ± 0.06 kPa to 0.23 ± 0.04 kPa. We really believe that this technology will be used for cancer detection and opens a door to study the biophysical properties of signaling domains extending from the cell surface to deeper parts of the cell.     

Properties of Bi2O3 thin films prepared via a modified Pechini route

Thin bismuth oxide films have been prepared by a modified Pechini route on glass substrate and annealed at temperatures ranging between 400 °C and 700 °C using bismuth nitrate as raw material. The thin films were then characterized for structural, surface morphological, optical and electrical properties by means of X-ray diffraction (XRD), Atomic force microscopy (AFM), scanning electron microscopy (SEM), optical absorption and d.c. two-probe, respectively. Structural investigations indicated that as-prepared bismuth oxide films were polycrystalline and multiphase, and annealing temperatures played a key role in the composition and optical properties of these films. AFM and SEM images revealed well defined particles which are highly influenced by annealing temperatures. The optical studies showed a direct band gap which varied with annealing temperatures between 3.63 eV and 3.74 eV. The electrical measurement showed that the electrical resistivity increased with annealing temperatures and the films were typical semiconductors. As catalyst, bismuth oxide films annealed at 550 °C had the best photocatalytic performance for photodegradation of methyl orange.     

Effect of ultrasonic treatment on the morphology of casein particles

In this study, the effect of ultrasonic treatment duration on the morphology of self-assembled casein particles was investigated by atomic force microscopy (AFM), low vacuum scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the case of AFM images, the particle analysis which was carried out by the SPIP program showed that the self-assembled casein particles after being ultrasonically treated for 2 min got smaller in size compared to the casein particles that have not been exposed to any ultrasonic treatment. Surprisingly, however, increasing the ultrasonic time exposure of the particles resulted in an opposite effect where larger particles or aggregates seemed to be present. We show that by comparing the results obtained by AFM, SEM and TEM, the information extracted from the AFM images and analyzed by SPIP program give more detailed insights into particle sizes and morphology at the molecular level compared to SEM and TEM images, respectively.     

Synthesis of nanocrystalline ZnO nanobelts via pyrolytic decomposition of zinc acetate nanobelts and their gas sensing behavior

The pyrolytic decomposition of layered basic zinc acetate (LBZA) nanobelts (NBs) into nanocrystalline ZnO NBs is investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). We also report on the gas sensing response of the resulting ZnO nanomaterial to CO. The LBZA NBs are grown at 65 °C in an aqueous solution of zinc acetate dihydrate. AFM and SEM results show as-grown products possess the characteristic layered structure of the LBZA crystals. XRD and XPS results show that annealing as-grown products at 210 °C in air causes a transformation from zinc acetate to nanocrystalline ZnO NBs via thermal decomposition. The ZnO crystalline domain size increases with temperature from 9.2 nm at 200 °C to 94 nm at 1000 °C, as measured from XRD. SEM shows evidence of sintering at 600 °C. The thickness of the NBs, determined via AFM, ranges from 10 to 50 nm and remains approximately constant with annealing temperature. XPS confirmed the chemical transformation from zinc acetate to ZnO and showed a significant remaining zinc hydroxide component for the ZnO NBs consistent with published results. PL measurements at room temperature show a blue shift in peak emission as the nanobelts change from LBZA to ZnO at 200 °C. Above this transition temperature, the ZnO nanobelts possess strong band edge emission at 390 nm and little broad band emission in the visible region. The AFM and SEM images reveal that the crystallites within the nanobelts orientate in rows along the long axis during annealing. This structure provides a high surface area to volume ratio of aligned nanoparticles which is beneficial for gas sensing applications. Gas sensors fabricated from 400 °C annealed nanobelts showed a response of 1.62 when exposed to 200 ppm of CO in dry air at 400 °C, as defined by the ratio of resistance before and during exposure. This indicates that ZnO nanostructures obtained by thermal decomposition of LBZA NBs could provide a cost effective route to high sensitivity gas sensors.     

Numerical study of the hydrodynamic drag force in atomic force microscopy measurements undertaken in fluids

When atomic force microscopy (AFM) is employed for in vivo study of immersed biological samples, the fluid medium presents additional complexities, not least of which is the hydrodynamic drag force due to viscous friction of the cantilever with the liquid. This force should be considered when interpreting experimental results and any calculated material properties. In this paper, a numerical model is presented to study the influence of the drag force on experimental data obtained from AFM measurements using computational fluid dynamics (CFD) simulation. The model provides quantification of the drag force in AFM measurements of soft specimens in fluids.The numerical predictions were compared with experimental data obtained using AFM with a V-shaped cantilever fitted with a pyramidal tip. Tip velocities ranging from 1.05 to 105 μm/s were employed in water, polyethylene glycol and glycerol with the platform approaching from a distance of 6000 nm. The model was also compared with an existing analytical model. Good agreement was observed between numerical results, experiments and analytical predictions. Accurate predictions were obtained without the need for extrapolation of experimental data. In addition, the model can be employed over the range of tip geometries and velocities typically utilized in AFM measurements.     

Effects of fluoride treatment on phosphoric acid-etching in primary teeth: An AFM observation

The aim of this study was to examine the effect of fluoride application on 37% phosphoric acid-etching by atomic force microscopy (AFM) in primary tooth samples based on a clinical protocol used in a pediatric dental hospital. Enamel samples were prepared from 36 exfoliated and non-carious primary teeth. Primary tooth samples were randomly assigned to one of the four groups based on the timing of acid-etching with 37% phosphoric acid after an acidulated phosphate fluoride (APF) pre-treatment. Group 1 received no fluoride application, Group 2 was pre-treated with fluoride and then received acid-etching 2 weeks later. One week separated the fluoride treatment and the acid-etching in Group 3, while Group 4 received acid-etching immediately after the fluoride treatment. The vestibular enamel surfaces of each primary tooth sample were scanned in air at a resolution of 512 × 512 pixels and a scan speed of 0.8 line/s. On the enamel surfaces of the primary teeth after APF pre-treatment, debris were observed although the teeth were smoother than they were prior to APF. As a result, it was concluded that APF treatment is responsible for decreased primary tooth surface roughness. The enamel surfaces etched for 20 s showed that acid-etching was effective not only in removing scratches and debris, but also for evaluating enamel rod characteristics. Primary tooth enamel surfaces after etching showed minute structures caused by the decreased hydroxyapatite nanoparticle space, compared to those before etching. Also, acid-etching showed significantly increased roughness effects (p < 0.0001, n = 9). Finally, as more time elapsed after APF pre-treatment, the roughness was decreased to a lesser degree (p = 0.005, n = 9). We suggest that primary teeth etching 2 weeks after APF pre-treatment used clinically in pediatric hospitals may be effective to obtain properly etched enamel surfaces.     

In situ SEM,TEM and AFM studies of the antimicrobial activity of lemon grass oil in liquid and vapour phase against Candida albicans

Inhibition of Candida albicans growth was shown by lemon grass oil (LGO) and lemon grass oil vapour (LGO vapour) at 288 μg/ml and 32.7 μg/ml concentration, respectively. The assessment of cell damage by LGO and LGO vapour was done through scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) observations. SEM analysis showed complete rupture of C. albicans cells treated with LGO vapour while in those treated with LGO in broth, only shrinkage was observed. TEM study showed the alterations in morphology upon treatment with LGO while complete degradation of the Candida cells was observed in case of LGO vapour. Further three dimensional morphological changes and roughness of the cells have also been evaluated with AFM after the treatment with LGO & LGO vapour. Roughness (root mean square value) was significantly higher in control C. albicans cells (211.97 nm) than LGO (143 nm) and LGO vapour (5.981 nm) treated cells. The results for the first time demonstrate relatively higher efficacy of LGO vapours for inhibition and cellular damage of C. albicans cells as compared to the LGO in liquid phase. This suggests the potential application of LGO vapour phase against infections caused by C. albicans.     

Quantitative Dixon MRI sequences to relate muscle atrophy and fatty degeneration with range of motion and muscle force in brachial plexus injury

BackgroundAssessment of muscle atrophy and fatty degeneration in brachial plexus injury (BPI) could yield valuable insight into pathophysiology and could be used to predict clinical outcome. The objective of this study was to quantify and relate fat percentage and cross-sectional area (CSA) of the biceps to range of motion and muscle force of traumatic brachial plexus injury (BPI) patients.MethodsT1-weighted TSE sequence and three-point Dixon images of the affected and non-affected biceps brachii were acquired on a 3 Tesla magnetic resonance scanner to determine the fat percentage, total and contractile CSA of 20 adult BPI patients. Regions of interest were drawn by two independent investigators to determine the inter-observer reliability. Paired Students' t-test and multivariate analysis were used to relate fat percentage, total and contractile CSA to active flexion and biceps muscle force.ResultsThe mean fat percentage 12 ± 5.1% of affected biceps was higher than 6 ± 1.0% of the non-affected biceps (p < 0.001). The mean contractile CSA 8.1 ± 5.1 cm² of the affected biceps was lower than 19.4 ± 4.9 cm² of the non-affected biceps (p < 0.001). The inter-observer reliability was excellent (ICC 0.82 to 0.96). The contractile CSA contributed most to the reduction in active flexion and muscle force.ConclusionQuantitative measurement of fat percentage, total and contractile CSA using three-point Dixon sequences provides an excellent reliability and relates with active flexion and muscle force in BPI.     

Mechano-chemical AFM nanolithography of metallic thin films: A statistical analysis

A mechano-chemical atomic force microscope (AFM) nanolithography on a metallic thin film (50 nm in thickness) covered by a spin-coated soft polymeric mask layer (50–60 nm in thickness) has been introduced. The surface stochastic properties of initial grooves mechanically patterned on the mask layer (grooves before chemical wet-etching) and the lithographed patterns on the metallic thin film (the grooves after chemical wet-etching) have been investigated and compared by using the structure factor, power spectral density, and AFM tip deconvolution analyses. The effective shape of cross section of the before and after etching grooves have been determined by using the tip deconvolution surface analysis. The wet-etching process improved the shape of the grooves and also smoothed the surface within them. We have indicated that relaxation of the surface tension of the deposited mask layer after the AFM scribing is independent from surface density of the grooves and also their length scale. Based on the statistical analysis, it was found that increase of the width of the grooves after the wet-etching and also relaxation of surface tension of the mask layer resulted in a down limit in the size of the metallic nanowires made by the combined nanolithography method. An extrapolation of the analyzed statistical data has indicated that, in this method, the minimum obtainable width and length of the metallic nanowires are about 55 nm and 2 μm, respectively.     

Fabrication of bacterial cellulose thin films self-assembled from sonochemically prepared nanofibrils and its characterization

Bacterial cellulose (BC) film formation could be a critical issue in nanotechnology applications such as biomedical or smart materials products. In this research, purified pretreated BC was subjected to high intensity ultrasound (HIUS) and was investigated for the development of BC films. The morphological, structural and thermal properties of the obtained films were studied by using FE-SEM, AFM, FT-IR, XRD, TGA and DSC characterizations. Results showed that the most favorable purification treatment was the 0.01 M NaOH at 70 °C for 2 h under continuous stirring. The most suitable ultrasound operating conditions were found to be, 1 cm distance of ultrasonic probe from the bottom of the beaker, submerged in cold water bath cooling around 12 ± 2 °C. The power (25 W/cm²), time (30 min), BC concentration (0.1% w/w), amplitude (20 μm) and frequency (20 kHz) were maintained constant.     

AFM measurement of atomic-scale Si surface etching by active oxidation

Atomic-scale etching of a clean Si surface by active oxidation with oxygen molecules was examined using ex-situ atomic force microscopy (AFM). The etch rate was directly determined by measuring the etch depth with AFM. A SiO₂ anti-etching mask was used on a H-terminated Si(001)-2 × 1:H surface prepared by low pH HF treatment followed by annealing in H₂. The etch rate under active oxidation conditions was almost proportional to the O₂ pressure, which was consistent with previous reports. The etch rate exhibited a weak temperature dependence with an apparent activation energy of 0.2 eV. A distinct transition of the reaction mode from etching to oxide formation was observed in detail as an abrupt decrease of the etch rate by lowering the temperature near the boundary condition between the etching and oxide formation conditions.     

Synergetic effects of ultrasound and slightly acidic electrolyzed water against Staphylococcus aureus evaluated by flow cytometry and electron microscopy

This study evaluated the synergetic effects of ultrasound and slightly acidic electrolyzed water (SAEW) on the inactivation of Staphylococcus aureus using flow cytometry and electron microscopy. The individual ultrasound treatment for 10 min only resulted in 0.36 log CFU/mL reductions of S. aureus, while the SAEW treatment alone for 10 min resulted in 3.06 log CFU/mL reductions. The log reductions caused by combined treatment were enhanced to 3.68 log CFU/mL, which were greater than the sum of individual treatments. This phenomenon was referred to as synergistic effects. FCM analysis distinguished live and dead cells as well as revealed dynamic changes in the physiological states of S. aureus after different treatments. The combined treatment greatly reduced the number of viable but nonculturable (VBNC) bacteria to 0.07%; in contrast, a single ultrasound treatment for 10 min induced the formation of VBNC cells to 45.75%. Scanning and transmission electron microscopy analysis revealed that greater damage to the appearance and ultrastructure of S. aureus were achieved after combined ultrasound-SAEW treatment compared to either treatment alone. These results indicated that combining ultrasound with SAEW is a promising sterilization technology with potential uses for environmental remediation and food preservation.     

Study on the interactions between anti-cancer drug oxaliplatin and DNA by atomic force microscopy

Oxaliplatin is one of the most important anticancer drugs at present. However, the mechanism of action of oxaliplatin is still controversial. In this study, the interactions between oxaliplatin and a plasmid DNA have been studied so as to reveal the structural basis of its activity. The structural characteristic of pUC19 DNA (2 ng/μL) incubated with 100 μmol/L and 1000 μmol/L of oxaliplatin for the different time on a freshly cleaved highly ordered pyrolytic graphite (HOPG) surface was investigated by atomic force microscopy (AFM). High resolution AFM observation indicated that oxaliplatin can induce pUC19 DNA molecules change from the extended conformation to the entangled structures with many nodes, and finally to the compact particles. The present AFM results provide structural evidence about the interactions between oxaliplatin and circular duplex DNA containing multiple targets.     

LEED and STM studies of the stability of the MoO2(100) surface

Atomic scale images and low energy electron diffraction pattern of a MoO₂(100) single crystal surface are presented, which show different structural modifications depending on surface preparation. A short in-situ heat treatment of the as-grown single crystal results in an atomically ordered surface whose diffraction pattern and STM images are consistent with those expected from the bulk structure. The symmetry of the STM images suggests an oxygen termination of the surface. A significantly longer heat treatment causes a thermodynamically stable (4 × 1) reconstruction which is interpreted to be due to a loss of oxygen chains. The (4 × 1) reconstruction vanishes after Ar-ion-sputtering and subsequent annealing. Additional long sputtering cycles result in a (2 × 1) reconstruction. The observed surface reconstructions can be transformed into each other by heating or sputtering cycles.     

Influence of heat treatment on field emission characteristics of boron nitride thin films

Boron nitride (BN) nanometer thin films are synthesized on Si (1 0 0) substrates by RF reactive magnetron sputtering. Then the film surfaces are treated in the case of the base pressure below 5 × 10⁻⁴ Pa and the temperature of 800 and 1000 °C, respectively. And the films are studied by Fourier transform infrared spectra (FTIR), atomic force microscopic (AFM) and field emission characteristics at different annealing temperature. The results show that the surface heat treatment makes no apparent influence on the surface morphology of the BN films. The transformations of the sample emission characteristics have to do with the surface negative electron affinity (NEA) of the films possibly. The threshold electric fields are lower for BN samples without heat-treating than the treated films, which possibly ascribed to the surface negative electron affinity effect. A threshold field of 8 V/μm and the emission current of 80 μA are obtained. The surface NEA is still presence at the heat treatment temperature of 800 °C and disappeared at temperature of 1000 °C.     

Synthesis of superhydrophobic PTFE-like thin films by self-nanostructuration in a hybrid plasma process

Superhydrophobic poly(tetrafluoro-ethylene) (PTFE) like thin films were grown on silicon wafers using a plasma-based hybrid process consisting on sputtering a carbon target in an Ar/CF₄ atmosphere. The influence of the bias voltage applied to the substrate (V_Bias) as well as of the gas mixture composition (%CF₄) on the chemical composition, the wettability and the morphology of the deposited thin films were evaluated.The chemical composition measured by X-ray Photoelectron Spectroscopy (XPS) has revealed that the F/C atomic ratio is always lower than for conventional PTFE (F/C = 2) and that it decreases when V_Bias increases (from F/C = 1 for V_Bias = ? 100 V to F/C = 0.75 for V_Bias = ? 200 V). This behavior is associated with the preferential sputtering of the fluorine atoms during the plasma-assisted growth of the films. Consecutively, a self-nanostructuration enhanced when increasing V_Bias is observed. As a consequence, the water contact angle (WCA) measurements range from 70° up to 150° depending on (i) the fluorine concentration and (ii) on the magnitude of the nanostructuration. In addition, for the films presenting the highest WCAs, a small hysteresis between the advancing and receding WCAs is observed (< 10°) allowing these films to fulfill completely the requirements of superhydrophobicity. The nanostructuration is probably due to the chemical etching by fluorine atoms of the fluorinated group.In order to get more understanding on the wettability mechanisms of these surfaces, the topography of the films has been evaluated by atomic force microscopy (AFM). The data have revealed, for all films, a dense and regular structure composed by conic objects (A_vH is their average height and A_vD is the average distance between them) for which the dimensions increase with V_Bias. A correlation between A_vH/A_vD, defined as the “morphological ratio”, with the WCA was established. Theoretical evaluations of the WCA using the Wenzel and Cassie equations with, as inputs, the features of the deposited thin film surfaces measured by AFM suggest that the wetting regime is intermediate between these two ideal situations.