Nm In Depth Research Articles

Research on the regulation of the spatial structure of acetylcholinesterase tetramer with high efficiency by AFM

Atomic force microscopy (AFM) was applied for obtaining structural information about acetylcholinesterase (AChE) tetramer (AChE G4) before and after reaction with S-acetylcholine iodide (S-ACh), in the presence or absence of propidium iodide (PI), an inhibitor for peripheral anionic sites (PAS). An iced-bath ultrasound was used to prepare the phospholipid membrane. Ves-fusion technique was applied for incorporating AChE G4 in a lipid layer on mica. Before reaction with substrates, the single AChE G4 particle was ellipsoid in shape with a clear border. It had a smooth surface with a central projection. The four subunits of a single enzyme particle were arranged tightly (no separated subunits being found, with an average size of 89 ± 7 nm in length, 68 ± 9 nm in width, and 6 ± 3 nm in height). After reaction with S-ACh in the absence of PI, the loose arrangement of subunits of AChE G4 was seen, with an average size of 104 ± 7 nm in length, 91 ± 5 nm in width, and 8 ± 2 nm in height. Also there was free-flowing space amongst the four subunits of the AChE G4. This was consistent with the results of the ×-ray diffraction crystallography and molecular dynamics studies. The apparent free space was the central path of AChE G4, changing from small to big, to small, to lateral door appearance, with an average size of 60 ± 5 nm in length and 51 ± 9 nm in width. The size of lateral door was 52 ± 5 nm in width and 32 ± 3 nm in depth on average. In the presence of PI, S-ACh could not cause topological structure changes of AChE G4. AFM verified that the central path might govern the turnover of the enzyme morphologically, and the interactions between PI and S-ACh might gate the creation of a central path and the opening of ACG in monomer; and the combination of S-ACh with peripheral anionic sites is conducive to the opening of ACG while PI can inhibit this action. Resolution at the inframolecular level is favorable in providing substantial information on how the spatial structure is adapted to the high efficiency of AChE molecules.

21201 超臨界二酸化炭素エマルジョンを用いたCu電気めっき法による微細埋込配線技術(OS4-1【機械工学が支援する微細加工技術(1)】)

This paper reports an electroplating method with supercritical carbon dioxide (sc-C02) emulsion, denoted as "Supercritical Nano Plating (SNP)" on hole test element group (TEG), which has an integrated structure of Cu seed layer on TiN barrier layer sputtered on Si substrates. The reaction is carried out in an emulsion of sc-C0_2 in copper-sulfate-based electrolyte with surfactants. It was reported that Ni film obtained by SNP is uniform and without pinhole, because sc-C0_2 has low viscosity and compatibility of hydrogen. Thus, this method is applicable in fine Cu wiring, but dissolution of Cu seed layer in SNP was observed Therefore, Cu particle was added to form a suspension An electroplating method with sc-C0_2 suspension, denoted as Modified SNP (M-SNP) is proposed to inhibit dissolution of Cu seed layer. We applied M-SNP technique into filling of hole TEG with via having 70 nm in diameter and 350 nm in depth, and complete filling of all the holes with electrodeposited copper without any void was obtained while poor gap-filling with voids was observed in conventional plating method. The electrodeposited Cu filled into holes formed a single crystal or had a few twin boundaries parallel to the surface of TEG.

Nano-dot and nano-pit fabrication on a GaAs substrate by a pulse applied AFM

The nano-patterning characteristics of GaAs is investigated using a pulse applied atomic force microscope (AFM). Very short range voltage pulses of micro to nano-seconds’ duration are applied to a conductive diamond-coated silicon (Si) tip in contact mode, to regulate the created feature size. The effects of pulse conditions such as pulse voltage, duration, frequency, offset voltage, anodization time, and applied tip pressure on nano-dot generation are characterized, based on the experiments. An interesting phenomenon, nano-pit creation instead of nano-dot creation, is observed when the applied pulse duration is less than 100 μs. Pulse frequency and offset voltage are also involved in nano-pit generation. The electrical spark discharge between the tip and the GaAs's surface is the most probable cause of the nano-pit creation and its generation mechanism is explained by considering the relevant pulse parameters. Nano-pits over 15 nm in depth are acquired on the GaAs substrate by adjusting the pulse conditions. This research facilitates the fabrication of more complex nano-structures on semiconductor materials since nano-dots and nano-pits could be easily made without any additional post-processes.

Near-surface crystallization of PET

The near-surface crystallization behaviour of poly(ethylene terephthalate) films of various thickness, spin-cast from solution onto silicon substrates, has been studied. In the as-cast state, the films are amorphous, with featureless morphology. A relationship is mapped between the film thickness (in the range 3 nm–700 nm), the isothermal annealing temperature (ambient to 150 °C), and the crystalline morphology. Two distinct morphologies are observed which are associated with surface-specific crystallization and bulk crystallization (producing much rougher film surfaces). The surface crystallization process is associated with a top-surface region (measured to be of about 13 nm in depth) of lower glass transition temperature, where, at temperatures between the surface and bulk crystallization temperatures, only the material in the more-mobile surface region is able to reorganize to form crystals. This phenomenon is observed for films of all the thicknesses studied and it is therefore concluded that this is not specifically a thin-film phenomenon, rather a surface-specific phenomenon possible in material of any thickness.

Nanoscale channels on ectomycorrhizal‐colonized chlorite: Evidence for plant‐driven fungal dissolution

The roots of many trees in temperate and boreal forests are sheathed with ectomycorrhizal fungi (EMF) that extend into the soil, forming intimate contact with soil minerals, from which they absorb nutrient elements required by the plants and, in return, are supported by the organic carbon photosynthesized by the trees. While EMF are strongly implicated in mineral weathering, their effects on mineral surfaces at the nanoscale are less documented. In the present study, we investigated the effects of symbiotic EMF on the topography of a chlorite mineral using atomic force microscopy. A cleaning protocol was successfully applied to remove fungal hyphae without altering the underlying mineral structure and topography. Examination of the exposed chlorite surface showed the presence of primary channels, of the order of a micron in width and up to 50 nm in depth, the morphology of which strongly indicates a fungal‐induced origin. Smaller secondary channels were observed extending from the primary channels and would appear to be involved in their enlargement. The presence of channels is the first nanoscale demonstration of the effects of fungal interaction, fuelled by plant photosynthate, on the topography of a chlorite mineral, and it provides clear evidence of the ability of EMF to enhance mineral dissolution.

Design considerations for ultraviolet-nanoimprint lithography resists

Design considerations for ultraviolet-nanoimprint lithography resists were investigated focusing on the major issues of ink-jetting performance, pattern formability, release property, and dry etching resistance. Regarding ink-jetting performance, small droplet ink-jetting of 0.7 pl was successfully demonstrated by adjusting the resist fluid property to the ink-jet coater and controlling the resist volatilization. Regarding pattern formability, a resist pattern was imprinted from a mold pattern of 28 nm in width and 60 nm in depth without pattern dimension change. It was thought that modulus control of the resist was more important than resist shrinkage in achieving excellent pattern formability. As for release property, resist with fluorine monomer and with nonreactive fluorine antisticking agent were compared. The results indicated that resist design has the capability to both reduce separation force and maintain a clear mold surface. The mold release agent decomposed with an increasing number of imprint shots, but the low release-force resist with nonreactive antisticking agent was able to control degradation of the mold release agent and thus improve release property endurance. Regarding etching resistance, it was found that increasing the ring parameter of resist is essential for high etching resistance, and resulted in improved etched pattern features of the substrate.

Strength enhancement of nano patterns from edge lithography for nanoimprint mold

► SiO 2 nano patterns are fabricated by edge lithography. ► Nano pattern strength is enhanced by small Si step. ► Nano patterns are transferred by thermal nano imprint. ► Polystyrene nano patterns are obtained. ► Si nano trench is successfully fabricated. Although SiO 2 nano-patterns with a high aspect ratio could already be fabricated by edge lithography, the SiO 2 nano-patterns were often not suitable as molds for nano-imprint lithography because they were too fragile. To improve the SiO 2 nano-pattern strength, a small Si step was fabricated around the bottom of the SiO 2 nano-patterns. Such strength enhanced SiO 2 nano-patterns were successfully replicated into both polymethylmethacrylate and polystyrene films on a Si substrate by thermal nano-imprint lithography. Resist patterns 25 nm in width and 430 nm in depth were obtained. The residual layer was removed in an N 2 /O 2 plasma. Si trenches were fabricated using the imprinted polystyrene nano-patterns, and Si nano-trenches 35 nm in width and 285 nm in depth were thereby successfully obtained.

In-situ Observation of Surface Graphitization of Gallium Droplet and Concentration of Carbon in Liquid Gallium

Although carbon has been recognized to be insoluble in gallium, we found that the outermost surface of gallium has unexpectedly high carbon solubility, particularly the limited region of about a few nanometers in depth. Our in-situ transmission electron microscope observations revealed that a graphene layer was precipitated at the surface of a gallium droplet simultaneously with gallium evaporation, and some of the droplets created an internal graphitic layer. On the basis of these experimental data, we evaluated a substantial carbon solubility that seemed to exceed about 50 at. %, but was realized in a very thin surface region of about 4 nm in depth. We believe that this high carbon solubility at the gallium surface is the key mechanism for the catalytic ability of gallium that was observed at the interface between liquid gallium and solid amorphous carbon.

Critical Density of Nanoscale Pits for Suppressing Variability in Leakage Current of a SiC Schottky Barrier Diode

We investigate the influence of SiC surface morphology on increase and variability in reverse leakage current of SiC Schottky barrier diodes using device simulation. It is found that etch pits with only a few tens of nm in depth has a large influence on leakage current and is also shown that leakage current is sensitive to both etch pit shape and density. From these results, we suggest the critical density of nanoscale pit, which is suppressing the variability of leakage current, at various drift layer thickness tdrift and doping concentration Ndrift.

Oxide Ion Transport in Donor‐Doped Pb(ZrxTi1−x)O3: Near‐Surface Diffusion Properties

Oxide ion transport in Pb(ZrxTi1–x)O3 (PZT) was investigated using 18O tracer diffusion and time‐of‐flight secondary ion mass spectrometry analysis. Particularly diffusion in the near‐surface regions (a few 100 nm in depth) is discussed and strong evidence for a space charge layer near the surface is provided. In this layer, an enrichment of oxygen vacancies is found at temperatures up to 600°C, resulting in box‐shaped tracer diffusion profiles. At 650°C, however, the profile shape is modified and reveals a depletion of oxygen vacancies close to the surface. Accordingly, a change in the polarity of the surface charge takes place between 600°C and 650°C. The tracer diffusion profiles are very sensitive to surface modification, caused by etching or annealing at higher temperature, and also depend on the sintering procedure. Moreover, application of an external field during the tracer experiments affected the tracer diffusion at the cathode, while leaving the profile at the anode unperturbed. Quantitative analysis of the profiles was performed by means of numerical calculations based on Gouy‐Chapman or Mott‐Schottky space charge models. Estimates of the oxygen vacancy concentration and ionic transference number of donor‐doped PZT are provided.

Atom probe tomography characterisation of a laser diode structure grown by molecular beam epitaxy

Atom probe tomography (APT) has been used to achieve three-dimensional characterization of a III-nitride laser diode (LD) structure grown by molecular beam epitaxy (MBE). Four APT data sets have been obtained, with fields of view up to 400 nm in depth and 120 nm in diameter. These data sets contain material from the InGaN quantum well (QW) active region, as well as the surrounding p- and n-doped waveguide and cladding layers, enabling comprehensive study of the structure and composition of the LD structure. Two regions of the same sample, with different average indium contents (18% and 16%) in the QW region, were studied. The APT data are shown to provide easy access to the p-type dopant levels, and the composition of a thin AlGaN barrier layer. Next, the distribution of indium within the InGaN QW was analyzed, to assess any possible inhomogeneity of the distribution of indium (“indium clustering”). No evidence for a statistically significant deviation from a random distribution was found, indicating that these MBE-grown InGaN QWs do not require indium clusters for carrier localization. However, the APT data show steps in the QW interfaces, leading to well-width fluctuations, which may act to localize carriers. Additionally, the unexpected presence of a small amount (x = 0.005) of indium in a layer grown intentionally as GaN was revealed. Finally, the same statistical method applied to the QW was used to show that the indium distribution within a thick InGaN waveguide layer in the n-doped region did not show any deviation from randomness.

The roles of RGD and grooved topography in the adhesion, morphology, and differentiation of C2C12 skeletal myoblasts

Both chemical and topographic cues are crucial for the development of skeletal muscle. In this study, the relative roles of both signals in regard to cell adhesion, morphology, and differentiation of C2C12 skeletal myoblasts were investigated. Grooved polystyrene substrates containing grooves with approximately 900 nm in width with 600 nm ridge spans and 665 nm in depth were conjugated with the cell adhesion peptide arginine-glycine-aspartic acid (RGD). RGD conjugation significantly enhanced the adhesion, growth and differentiation of C2C12 cells. On the other hand, anisotropic topography primarily directed the direction and alignment of myoblasts and myotubes. The results in this study provide information regarding the relative roles of chemical and topographic cues in musculoskeletal myogenesis, and are of interest to applications in muscle tissue engineering.

Fabrication of planar nanofluidic channels in thermoplastic polymers by O 2 plasma etching

A simple O2 plasma etching method is developed and first used to fabricate planar nanofluidic channels in thermoplastic polymers. In this process, a copper etching mask with a micron-scale width is made by traditional UV lithography and wet etching on a polymer substrate, then the polymer substrate is etched by O2 plasma in a commonly used plasma cleaner to form the planar nanochannel. Effects of the process parameters of the plasma cleaner on the etching rate are studied. The average etching rate for most thermoplastic polymers used in lab-on-a-chip is about 10 nm/min and the surface roughness is less than 2 nm when radio frequency power and chamber pressure are 60 W and 200 Pa, respectively. To demonstrate this method, a polymethylmethacrylate (PMMA) micro-nanofluidic chip containing nine parallel nanochannels, 100 nm in depth, 5 µm wide and 1 mm long, is fabricated to investigate the ion enrichment of 1 µM fluorescein isothiocyanate (FITC) in 10 mM phosphate buffered saline (PBS) buffer.

Atomic force microscopy in oncocytology

A new atomic force microscopy (AFM) method was used to examine 51 cytology specimens from breast and thyroid tumors and pretumors and 17 uterine cervix scrapes. The authors formulated the main tasks of using AFM in oncocytology: to search for objective criteria for differential diagnosis between intact and cancer cells; to identify viral changes in the squamatous epithelial cells; and to objectify the immunocytochemical reaction of Her-2/neu oncoprotein hyperexpression. The studies have revealed as follows: glandular cancers are characterized by an increased nucleus/cytoplasm height ratio (from 1.8 to 2.5 for breast cancer and from 1.9 to 2.5 for thyroid cancer); the squamatous epithelial cells show an inverse trend (a decrease from 2.96 to 2.08 for keratinizing carcinoma of the cervix uteri); viral squamatous cell lesion appears as a perinuclear groove 200 nm in depth; Her-2/neu oncoprotein hyperexpression corresponds to the increase in cytoplasmic height from 248 to 850 nm.

Theoretical probing of the phenomenon of the formation of the outermost surface layer of a multi-component particle, and the surface chemical composition after the rapid removal of water in spray drying

Spray drying is a primary process for the manufacture of powders, which satisfy a vast array of societal demands in the areas of nutrition, health and medicine. The functionality of a spray-dried product begins with its incorporation into water (wetting followed by dispersion) Therefore, as its surface chemical composition and structure determine its first contact with water (that is, its hydrophilic nature), these are of prime concern. Laboratory studies on this first layer, which is in the order of several nm in depth from the surface, have been extensive but there is still a lack of a fundamental quantitative explanation of it. This has hampered the development of any sort of approach, which would enable industries to predict what the product may be like before conducting costly trials. This current study is an attempt to describe the on-set of solid formation around the outermost layer of a single droplet during the drying process using an innovative ‘conventional’ continuum approach, i.e. diffusion–convection equations, with a few innovative derivations. Though some complexities such as multi-component equations deduced from irreversible thermodynamics, are avoided for simplicity, some comparisons with experimental/industrial results are made. The main feature of this work is that the multi-component effect is combined with the viscosity (at the surface) effect upon the diffusivities of individual components in the solution droplets or suspension droplets. The derivations allow some extended analytical procedures to proceed in order to help make sense of the experimental observations. Comparisons are made against the data published on dairy fluids. This work provides a good basis for a fruitful area of study that will have a positive impact for spray drying industries. In particular, to help this kind of industry to forge ahead into high performing functional particle production, which are becoming increasingly popular.

Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate (a-plane Al2O3)

An energetic condensation technique, cathodic arc discharge deposition, is used to grow epitaxial Niobium (Nb) thin films on a-plane sapphire (hexagonal-closed-packed Al2O3) at moderate substrate heating temperature (<400 °C). The epitaxial Nb(110)/Al2O3(1,1,-2,0) thin films reached a maximum residual resistance ratio (RRR) value 214, despite using a reactor-grade Nb cathode source whose RRR was only 30. The measurements suggest that the film’s density of impurities and structural defects are lower when compared to Nb films produced by other techniques, such as magnetron sputtering, e-beam evaporation or molecular-beam-epitaxy. At lower substrate temperature, textured polycrystalline Nb thin films were created, and the films might have twin symmetry grains with {110} orientations in-plane. The texture was revealed by x-ray diffraction pole figures. The twin symmetry might be caused by a combination effect of the Nb/Al2O3 three-dimensional epitaxial relationship (“3D-Registry” Claassen’s nomenclature) and the “Volmer-Weber” (Island) growth model. However, pole figures obtained by electron backscattering diffraction (EBSD) found no twin symmetry on the thin films’ topmost surface (∼50 nm in depth). The EBSD pole figures showed only one Nb{110} crystal plane orientation. A possible mechanism is suggested to explain the differences between the bulk (XRD) and surface (EBSD) pole figures.

AN ATOMIC FORCE MICROSCOPY STUDY IN THE DETECTION OF HEPATITIS B SURFACE ANTIGEN BY ENZYME-LINKED IMMUNOSORBENT ASSAY

Atomic force microscopy (AFM) was employed to study certain enzyme immunoassay steps for the detection of hepatitis B surface antigen (HBsAg). Physical adsorption of monoclonal antibodies (mAb), blocking of surface active sites free of antibodies by neutral proteins, and capture of HBsAg particles by sensitized surfaces were visualized successively in microplate wells of standard immunological plates from various manufacturers. The previously undescribed details such as “etching holes” up to 20 nm in depth were observed on the surface of plates some companies. The quantitative relationships between the optical density (OD) values obtained by enzyme immunoassay (EIA) and the number of antigen–antibody complexes in AFM were calculated.

Relationship between hardness and dislocation processes in a nanocrystalline metal at the atomic scale

(Received 18 February 2011; revised manuscript received 25 March 2011; published 9 June 2011)By combining atomic force microscopy (AFM) and large-scale molecular dynamics (MD) simulations, weexamineatcomparablescalestheatomisticprocessesgoverningnanohardnessinelectrodepositednanocrystallineNi with a mean grain diameter of 18.6 nm under confined contact deformation. Notably, this mean graindiameter represents the “strongest” size for Ni and other nanocrystalline materials where both crystal slipand grain-boundary deformation processes are intertwined to accommodate plastic flow. Accurate hardnessmeasurements were obtained from shallow nanoindentations, less than 10 nm in depth, using an AFM diamondtip.Weshowevidencethatthecontrollingyieldingmechanisminthepeakofhardnessasafunctionofpenetrationdepth corresponds to the emission of partial dislocations from grain boundaries. However, MD simulations alsoreveal for this grain size that the crystalline interfaces must undergo significant sliding at small penetrationdepths in order to initiate crystal slip. The strong interplay between intergranular and intragranular deformationprocesses found in this model nanocrystalline metal is discussed and shown to considerably reduce the localdependenceofnanohardnessontheinitialmicrostructureatthisscale,unlikepastobservationsofnanoindentationinNielectrodepositswithlargergrainsizes.Thesenewfindingsthereforeconstituteanimportantstepforwardtounderstanding the contribution of nanoscale grain-boundary networks on permanent deformation and hardnessrelevant for nanoscale materials and structures.DOI: 10.1103/PhysRevB.83.224101 PACS number(s): 62

Activation-induced Reorganization in Membrane Nanostructures and Alteration in Adhesion of CD4 + T Lymphocytes Exploited by AFM/LFM

To date, the activation induced reorganization in membrane nanostructures and alteration in membrane adhesion property of CD4 + T lymphocytes largely remain unclear yet even though their immunological functions have been well elucidated. The present work focused on detecting the differences in topography, membrane nanostructures and adhesion/friction behaviors of CD4 + T cells in the absence and presence of stimulus (Phorbol dibutyrate, PDB, plus Ionomycin, ION). The results showed that, due to cell activation in vitro, (a) the formation of pseudopodia, lamellipodia; (b) the appearance of membrane pores with 200∼450 nm in diameter and 70∼110 nm in depth; (c) the formation of nanostructural domains with different adhesion behavior; (d) the loading rate and loading force could affect the measured adhesion force nonlinearly; (e) the dynamic changes in membrane adhesion force, from 348±9.08 pN for resting cells, 827.07±24.61 pN for 24 hours of activation, 372.87±9.26 pN for 48 hours of activation, to 302.45±11.42 pN for 72 hours of activation. This work achieved the biophysical changes of CD4 + T cells with and without stimulation, which would enable us to seek new implications and potential links between cytoarchitectures, membrane adhesion and immunological functions at the single-cell and nanoscale level.

Electronic and optical switching of solution-phase deposited SnSe2 phase change memory material

We report the use of chalcogenidometallate clusters as a solution-processable precursor to SnSe2 for phase change memory applications. This precursor is spin-coated onto substrates and then thermally decomposed into a crystalline SnSe2 film. Laser testing of our SnSe2 films indicate very fast recrystallization times of 20 ns. We also fabricate simple planar SnSe2 electronic switching devices that demonstrate switching between ON and OFF resistance states with resistance ratios varying from 7−76. The simple cell design resulted in poor cycling endurance. To demonstrate the precursor’s applicability to advanced via-geometry memory devices, we use the precursor to create void-free SnSe2 structures inside nanowells of ∼25 nm in diameter and ∼40 nm in depth.