Application of a self-sensing conductive probe for Si device imaging

For the evaluation of two-dimensional carrier profiles in semiconductor devices, we have developed a novel form of probe–sensor combined unit that uses an etched tungsten wire as a conductive probe, and commercially available quartz tuning fork as the force sensor. This unit has a self-sensing capability due to the piezoelectric effect of quartz tuning fork, thus obviating optical setup, and its conductivity is higher and more stable than that of conventional metal-coated Si cantilever. In addition, this probe–sensor combined unit is inexpensive and easy to use, when compared to the well-known optical methods of Si-based cantilever vibration detection system. Our scanning probe microscope using this probe–sensor combined unit is able to mapping the capacitive gradient signal (dC/dZ image) and internal damping of quartz tuning fork oscillation (dissipation image) while scanning the sample surface. In this letter, we show the results of visualization of the p–n junction locus of a Si metal–oxide–semiconductor field effect transistor in both dC/dZ and dissipation images.     

Delineation of a p–n junction using dC/dX imagery produced by shear-mode scanning capacitance microscopy

Using a laterally oscillating all-metallic probe, a scanning capacitance microscope (SCM) has been used to yield an image of the spatial derivative of the local capacitance, dC/dX, where C and X are the local capacitance and the axis of the probe tip locus on the sample surface, respectively. Bias fields, except for the ultra-high-frequency fields used for sensing the capacitance, are not necessary to detect the dC/dX signal, which yields an image delineating clearly the depletion region due to the p–n junction. Simultaneously with the dC/dX image, the new SCM can give images of topography and dC/dV if an alternating field V is applied between the probe and sample. Received: 19 March 2001 / Accepted: 22 March 2001 / Published online: 27 June 2001     

Several types of bilayer smectic liquid crystals with ferroelectric and antiferroelectric properties in binary mixture of dimeric compounds

The mesomorphic behavior and phase structure were examined in the mixture of two kinds of dimeric compounds, alpha,omega-bis(4-alkoxyanilinebenzylidene-4'-carbonyloxy)pentane (mOAM5AMOm), by optical microscopy, X-ray diffraction, polarization switching, and second-harmonic generation measurements. One compound is 4OAM5AMO4 with a short terminal alkyl chain that forms a single-layer smectic phase (SmCAs) with a random mixing of spacer and tail groups. Another compound is 16OAM5AMO16 with a long terminal alkyl chain that forms a chiral, anticlinic, and antiferroelectric bilayer phase (SmCAb) with the bent molecules tilted to the bilayer. By mixing these two compounds, the SmCAs phase of 4OAM5AMO4 is easily destabilized, leading to the wide content region of the bilayer phases. In the bilayer regime, three other smectic phases are newly induced. Two of them are antiferroelectric and ferroelectric phases in which the molecules lie perpendicularly with respect to the layer. The other shows no polar response to an external electric field and behaves like a smectic A. The new appearance of these bilayer phases is discussed as a mixing effect of long and short tail groups.     

Mechanical properties and inhomogeneous nanostructures of dicyandiamide-cured epoxy resins

Dicyandiamide (DICY)-cured epoxy resins are important materials for structural adhesives and matrix resins for fiber reinforced prepregs. The objective of this study was to examine the mechanical and physical properties as well as the gel structures of the cured resins and discuss the relationships among them. Diglycidyl ether of bisphenol-A (DGEBA) oligomers were chosen as the common chemical structure of the epoxy resins. Four kinds of resin mixtures were formulated using the seven types of DGEBA oligomers having different molecular weight distributions. Three resin formulations having bimodal-type molecular weight distributions were designed to have almost identical rubbery plateau values of the storage modulus in dynamic mechanical analyses after curing, means that they had almost equivalent average crosslink density and basic chemical structure. However, the toughness, ductility, and environmental (heat and solvent) resistance of these three formulations were different. Atomic force microscopy revealed the existence of inhomogeneous nanoscale gel structures in these cured resins. The morphological differences in the gel structures in terms of their size, the connectivity, and the relative magnitude of the heterogeneity would cause the difference in several properties of the DICY-cured epoxy resins. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1425–1434, 2007     

An efficient heteropolyacid catalyzed acylation of pyruvate esters to alpha-acyloxyacrylate esters as potential candidate monomers for bio-based polymers

Alpha-acyloxyacrylate esters were efficiently synthesized from pyruvate esters and carboxylic anhydrides under mild conditions. These esters are potential candidate monomers for bio-based polymers with high durability and transparency. Tungsten-based Keggin type heteropolyacids, especially H(3)PW(12)O(40), worked more effectively as catalysts for this reaction than other typical acids.     

Proteome analysis of UV-B-induced anti-apoptotic regulatory factors

Ultraviolet (UV) irradiation is well known to induce apoptosis, a hallmark event of which is the occurrence of sunburn cells in the epidermis. Keratinocytes in which DNA damaged by UV irradiation is not repaired undergo apoptosis as sunburn cells. However, we have previously reported that low-dose UV-B irradiation (approximately 0.1 J/cm2) suppressed the apoptosis induced by cell detachment and serum depletion. Dysregulation of apoptosis is important in tumor progression and malignancy and in promoting resistance to cancer therapy. To develop a better understanding of the antiapoptotic effect of UV irradiation, and to design the effective induction of apoptosis, we tried the proteome analysis of the molecules regulating apoptosis in low-dose UV-B-irradiated NIH3T3 cells, using two-dimensional difference gel electrophoresis (DIGE). Of a total of 3811 protein spots detected, 42 were found to be different between the cells undergoing apoptosis and cells after the irradiation. Of the spots selected, 25 were identified using MALDI-TOF/TOF-MS, some as structural proteins. Although typical apoptosis-related molecules were not detected, possibly because proteins with low molecular weights were difficult to identify in the gel conditions used in this study, some of the proteins were considered to be involved in apoptosis. The DIGE system used in this experiment has advantages (including a high level of statistical confidence) for discovering new functional proteins related to the regulation of apoptosis.     

Study on channel depletion in metal‐oxide‐semiconductor field effect transistor using top‐view imaging through scanning capacitance microscopy

Carrier profiles within the near‐surface channel region of n‐type metal‐oxide‐semiconductor field‐effect transistors (n‐MOSFETs) have been examined using scanning capacitance microscopy (SCM). After the removal of a poly‐Si gate electrode, we were able to assess the qualitative local carrier concentration within specified regions of an n‐MOSFET using static capacitance (dC/dZ) measurement with its bias dependence (dC/dZ–V spectra). We found that the dC/dZ‐signal at the center of the channel region lowers as the gate length is reduced. This result is attributed to the carrier depletion within the channel, which is consistent with the threshold voltage (V_th) characteristics of the device properties. Copyright © 2008 John Wiley & Sons, Ltd.     

Visualization of unsteady shock oscillations in the High-enthalpy flow field around double cones

The presence of an adverse pressure gradient, shock/shock interaction and shock wave/boundary layer interaction often induces flow separation around bodies. However, the effect of dissociated flow on separated flow characteristics, especially at hypersonic speeds, is still not clear, and considerable differences are observed between experiments and numerical simulations. In this investigation, the unsteady separated flow features around double cones are visualized in the Shock Wave Research Center (SWRC) free-piston driven shock tunnel at a nominal Mach Number of 6.99 using multiple optical techniques. The time resolved shock structure oscillations in the flow field around double cones (first cone, semi-apex angle = 25°; second cone, semi-apex angles=50°, 65°, 68° and 70°) have been visualized using a high-speed image converter camera (IMACON) at a nominal stagnation enthalpy of 4.8 MJ/kg. In addition, flow visualization studies around the double cone is also carried out using Schlieren and double exposure holographic interferometry in order to precisely locate the separation point and measure the separation length. The presence of a triple shock structure in front of the second cone and a non-linear unsteady shock structure oscillation in the flow field are the significant results from visualization studies on the 25° /65°, 25° /68° and 25°/70° double cones. On the other hand, the flow field around 25° /50° is relatively steady and Type V shock/shock interaction is observed. Illustrative numerical simulation studies are carried out by solving N-S equations to complement the experiments. The simulated flow features around a double cone agree well qualitatively with experiments.     

An efficient synthesis of 5-silyl-2,3-dihydrofurans via acid-catalyzed ring-enlargement of cyclopropyl silyl ketones and their functionalization

Treatment of cyclopropyl silyl ketones with trimethylsilyl trifluoromethanesulfonate as a strong acid having low nucleophilic counter anion gives the corresponding 5-silyl-2,3-dihydrofuran derivatives, exclusively, regardless of substituents on the cyclopropane ring or silicon atom. The resulting 5-silyl-2,3-dihydrofuran derivatives exhibit both reactivities of the vinylsilane and the cyclic enol ether in the subsequent reaction with electrophilic reagents or Heck type reaction.