Low voltage scanning electron microscopy

The scanning electron microscope (SEM) is usually operated with a beam voltage, V₀, in the range of 10–30 kV, even though many early workers had suggested the use of lower voltages to increase topographic contrast and to reduce specimen charging and beam damage. The chief reason for this contradiction is poor instrumental performance when V₀=1–3 kV, The problems include low source brightness, greater defocusing due to chromatic aberration greater sensitivity to stray fields, and difficulty in collecting the secondary electron signal. Responding to the needs of the semiconductor industry, which uses low V₀ to reduce beam damage, considerable efforts have been made to overcome these problems. The resulting equipment has greatly improved performance at low kV and substantially removes the practical deterrents to operation in this mode. This paper reviews the advantages of low voltage operation, recent progress in instrumentation and describes a prototype instrument designed and built for optimum performance at 1 kV. Other limitations to high resolution topographic imaging such as surface contamination, the de-localized nature of the inelastic scattering event and radiation damage are also discussed.     

The inner ear ultrastructure from the paddlefish (Polyodon spathula) using transmission electron microscopy

The structure of the hair cells on each sensory macula from the inner ear of the paddlefish (Polyodon spathula) was studied using scanning and transmission electron microscopy, revealing the nucleated cell bodies and peripheral nerve fibres of the saccule utricle and lagena. Examination of the structures within the cell body revealed comparable features with those found in the inner ear hair cells from bony fish species, although in P. spathula the afferent cell body is almost twice the size. This is the first time that the inner ear hair cells from an Acipenseriform fish have been studied using transmission microscopy, thus providing benchmark anatomical information in relation to the cellular morphology of the afferent receptors from a ‘healthy’P. spathula ear. Structural information is of assistance in the study of aquatic animal hearing for environmental monitoring purposes, as morphological data can be used to confirm if evidence of raised hearing thresholds from animals exposed to intense anthropogenic noise or other destructive agents (determined using electrophysiological or behavioural techniques) are a direct result of damage to the ultrastructure of the inner ear.     

Experimental investigation and optimization of EDM process parameters for machining of aluminum boron carbide (Al–B4C) composite

This study investigates the effect of electric discharge machining (EDM) process parameters [current, pulse-on time (T_on), pulse-off time (T_off) and electrode material] on material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) during machining of aluminum boron carbide (Al–B₄C) composite. This article also summarizes a brief literature review related to aluminum metal matrix composites (Al-MMCs) based on different process and response parameters, work and tool material along with their sizes, dielectric fluid and different optimization techniques used. The MMC used in the present work is stir casted using 5% (wt) B₄C particles of 50 micron size in Al 6061 metal matrix. Taguchi technique is used for the design of experiments (L₉-orthogonal array), while the experimental results are analyzed using analysis of variance (ANOVA). Response table for average value of MRR, EWR and SR shows that current is the most significant factor for MRR and SR, while electrode material is most important for EWR. ANOVA also confirms similar results. It is also observed that the optimum level of process parameters for maximum MRR is A₃B₁C₃D₃, for minimum EWR is A₁B₂C₃D₁, and for SR is A₁B₃C₃D₃.     

Imaging of immunolabeled membrane receptors in uncoated sem specimens

Epidermal growth factor receptors (EGFR) were labeled with 10 nm immunogold and examined on uncoated specimens of A431 human epidermoid carcinoma cells. A field emission gun and a high-sensitivity YAG ring detector were used to demonstrate the affinity labeling simultaneously in the secondary-electron (SE) and backscattered-electron (BSE) modes with a low accelerating voltage (V_o). At V_o=2kV, the SE and BSE signals were too weak to identify all markers, while at V_o=3–7 kV labeling was observed unambiguously in both the SE and BSE modes with smaller and higher working distances. Increasing the V_o to above 7 kV sometimes provokes instability of the specimens. A V_o of ? 10 kV produces charging artifacts in the SE image, but permits a BSE image of the gold markers providing additional topographic information. In conclusion, immunogold labeling can be used with good results for uncoated specimens.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

On the estimation of particle number

Two methods are proposed for estimating the number of separated particles within a solid structure per unit volume of structure, N_v. Apart from being arranged with independence of any size parameter, no special assumptions upon the size, shape and orientation of the particles are made. The first method is based on the identity N_V = (N_A)_u ? μ_u^?1, where (N_A)_u is the mean number of particle sections per unit area of a plane probe T_u which is uniform random within the structure and perpendicular to a given direction u, whereas μ_u is the mean particle caliper length along u. The second method uses N_V = A_A?V^?1, where A_A is the mean areal fraction of the particles per unit area of section, whereas v is the mean particle volume. The estimation of (N_A)_u, μ_u, and v requires the examination of parallel serial sections above and below T_u. Particle model reconstructions are not needed, however. Previous approaches to the problem are discussed.     

Resistive loss compensation in the power supply system of the toroidal field winding in the TUMAN-3M tokamak

In the tokamak, in which the winding generating the toroidal field with induction B _t is powered from an inductive energy storage, resistive losses are the main factor that causes B _t to decrease during a discharge. Upgrading of the power supply circuit of the toroidal magnetic field winding (TFW) in the TUMAN-3M tokamak is aimed, primarily, at increasing B _t in the injection heating phase and, second, at maintaining B _t quasi-stationarity during the whole tokamak discharge. To do this, an additional two-section capacitive storage commuted by two thyristor switches has been introduced into the available circuit. Either section of the storage is characterized by a charging voltage of 0.25 kV, a capacitance of 4.32 F, and an energy capacity of 135 kJ. The maximum discharge current of the section is 40 kA. The upgraded circuit compensates for the resistive loss in the TFW and ensures thereby a 50% increase in the magnetic field during injection heating relative to the old circuit: B _t = 1.0 T instead of 0.68 T. In this case, the circuit maintains a TFW current of 110 kA with an accuracy of 10% for ∼60 ms.     

Determination of experimental and theoretical kASi factors for a 200-kV analytical electron microscope

The relative sensitivity of an analytical electron microscope and energy-dispersive x-ray detector to x-rays of various elements is investigated through an extensive k_ASi factor study. Elemental standards, primarily National Bureau of Standards multielement research glasses, were dry-ground into submicrometer-sized particles and analyzed at 200 kV accelerating potential. The effect of self-absorption of x-rays by the particle has been corrected for, allowing the experimental k_ASi factors from this study to approximate those that could be obtained from “infinitely thin” specimens. Whenever possible, elemental k-factors were determined by the analysis of many (up to a maximum of nine) different standard materials. Experimental k_ASi factors were calculated for a wide range of K_α, L_α, and M_α x-ray lines. For comparison, theoretical k_ASi factors, employing a variety of ionization cross sections, were computed. Good agreement is obtained between several of the theoretical k-factor models and the experimental results. Mass volatilization of Na and K from the small glass particles during analysis is discussed, as are observations that the grinding and/or dispersing of standard materials in a liquid (such as ethanol) may promote leaching of certain elements from the particle matrix.     

Third-order aberration theory of Wien filters for monochromators and aberration correctors

Third-order aberrations at the first and the second focus planes of double focus Wien filters are derived in terms of the following electric and magnetic field components – dipole: E₁, B₁; quadrupole: E₂, B₂; hexapole: E₃, B₃ and octupole: E₄, B₄. The aberration coefficients are expressed under the second-order geometrical aberration free conditions of E₂ = −(m + 2)E₁/8R, B₂ = −mB₁/8R and E₃R²/E₁ − B₃R²/B₁ = m/16, where m is an arbitrary value common to all equations. Aberration figures under the conditions of zero x- and y-axes values show very small probe size and similar patterns to those obtained using a previous numerical simulation [G. Martínez & K. Tsuno (2004) Ultramicroscopy, 100 , 105–114]. Round beam conditions are obtained when B₃ = 5m²B₁/144R² and (E₄/E₁ − B₄/B₁)R³ = −29m²/1152. In this special case, aberration figures contain only chromatic and aperture aberrations at the second focus. The chromatic aberrations become zero when m = 2 and aperture aberrations become zero when m = 1.101 and 10.899 at the second focus. Negative chromatic aberrations are obtained when m < 2 and negative aperture aberrations for m < 1.101. The Wien filter functions not only as a monochromator but also as a corrector of both chromatic and aperture aberrations. There are two advantages in using a Wien filter aberration corrector. First, there is the simplicity that derives from it being a single component aberration correction system. Secondly, the aberration in the off-axis region varies very little from the on-axis figures. These characteristics make the corrector very easy to operate.     

CsI(Tl)-calorimeter calibration with positive-kaon decay products

The CsI(Tl) calorimeter was calibrated in the KEK-E246 experiment withK _μ2-andK _π2-positivekaon decays. The following calorimeter parameters were obtained: an energy resolution (σ) of 4.1% forE=242.5 MeV, a π⁰ invariant-mass resolution (σ) of 5.6%, and an angular resolution (σ) of 3.1^o.     

Tannin-osmium conductive staining of biological specimens for non-coated scanning electron microscopy

Osmication of biological specimens with a mixture of tannic acid, guanidine hydrochloride, arginine hydrochloride and glycine imparted sufficient electron conductivity to permit SEM observations of non-coated samples. No charging was noted at 25 kV acceleration voltage and 1 × 10^?10 A specimen current in rat kidney specimens. The foot-processes of the glomerular podocytes were clearly visible without metal coating. This tannin-osmium method even allowed block staining and enabled continuous observations during and after dissection in the SEM.     

Radiation damage to lyophilized mineral solutions during electron probe analysis: quantitative study of chlorine loss as a function of beam current-density and sample mass-thickness

The quantitative effects of beam current-density and sample mass-thickness on the loss of chlorine which occurs from lyophilized solutes of micro-droplets of mineral salt solutions irradiated in an electron probe analyser were studied. Results are reported for chlorine loss from lyophilized deposits with mass-thickness varying between 5 and 50 mg mm^?2 for NaCl salts and 5 and 80 mg mm^?2 for KCl salts. Electron accelerating voltage was kept constant at 15 kV. The range of beam current-density (I/S, current/sample surface area) was from 0.1 to 1.5 A mm^?2. Samples were irradiated for 1200 s. The results show that under some conditions there is a period of stable chlorine signal before chlorine loss occurs. This is observed between 0.1 and 1 A mm^?2, for a period which can last several hundred seconds depending on beam current-density and sample mass-thickness. For each value of I/S, however, no stable chlorine signal can be observed for samples whose mass-thickness exceeds a value negatively correlated with I/S. The curves of decrease of characteristic chlorine X-ray signal (expressed as per cent of count rate in the initial counting interval) versus irradiation time can be fitted by the sum of two exponentials with half lives T₁ and T₂. In NaCl, T₁ and T₂ values are highly correlated with I/S but not with mass-thickness. In KCl, T₁ is correlated only with mass-thickness and T₂ only with I/S. Mixing plasma with mineral solutions prevents chlorine loss.     

A method for measuring the surface impedance of superconductors in the temperature range 0.4–120 K

A method and a setup for making precision measurements of the temperature dependences of components of surface impedance Z(T) = R(T) + iX(T) of small superconductor crystals in the temperature range 0.4–120 K have been developed. The setup combines a high-quality-factor resonance system for measuring the microwave response of a sample at a frequency of 28 GHz and a refrigerating unit with the use of evaporation of ³He vapors. Measurements of Z(T) of optimally doped YBa₂Cu₃O_6.93 single crystals in the superconducting and normal states were performed to illustrate the operation of the setup.     

Random sets theory and its applications to stereology

In order to study objects forming a sub-set A of euclidean space, mathematical morphology uses structuring figures B and notes the frequency of events such as ‘B hits A’, ‘B is included into A’ etc. Thus, a probabilistic formalism is associated with this experimental technique and facilitates its interpretation. If A is considered as a closed set, we obtain a random closed-sets theory, closely connected with integral geometry. The functionals T defined by T(K) = P(A ∩ K ≠ Ø) for K compact are characterized as alternating capacities of infinite order. Interesting classes of functionals T are obtained if A is indefinitely divisible or semi-markovian. At last, the mathematical notion of granulometry (size distribution) is studied by using an axiomatic method.     

Immature oocyte quality and maturational competence of porcine cumulus-oocyte complexes subpopulations

Porcine immature oocyte quality (i.e., that of live oocytes at the germinal vesicle stage) was evaluated according to features of the surrounding cumulus, aiming to establish maturational competence of different subpopulations of such cumulus-oocyte complexes. Six subpopulations were identified: A₁ (with a dense cumulus), A₂ (with a translucent cumulus), B₁ (with the corona radiata), B₂ (partly naked oocytes), C (naked oocytes), D (with a dark cumulus). The percent incidence of live oocyte in these subpopulations changed significantly as related to cumulus features, however the occurrence of oocytes in the germinal vesicle stage was lower in class D only. Similar metaphase II rates achieved in A₁, A₂, B₁ and B₂ classes after in vitro maturation suggest that the nucleus may in fact mature in vitro, in spite of the different accompanying cumulus features which are typical of these classes. In contrast, a higher cytoplasmic maturation rate obtained in class A₁ may indicate a stronger dependence of this variable upon cumulus features than that shown by nuclear maturation. When different types of cumulus expansion after in vitro maturation were considered (i.e., fully expanded cumulus, partly expanded cumulus, and partly naked oocyte), no differences were found in the percent of oocytes reaching metaphase II or cytoplasmic maturation. It is concluded that morphological features of the collected porcine cumulus-oocyte complexes (rather than cumulus behavior during culture) may be useful for selection of potentially competent oocytes for in vitro fertilization and embryo production.     

Determining Generation–Recombination Characteristics of a Semiconductor–Dielectric Interface from the Current Kinetics of Surface Minority Carrier Generation

Conditions for the one-to-one characterization of the generation (G _s) and surface recombination (R _s) rates of minority charge carriers (MCCs) in a metal–oxide–semiconductor (MOS) structure (in the case of strong nonequilibrium depletion) by the MCC surface generation current (I(t)) flowing in an external circuit of this structure are revealed. These conditions are the following: (1) the generation current I is independent of the time t (until the structure enters an equilibrium state) and the voltage V _{g 0} corresponding to the initial nonequilibrium depletion and (2) the duration of current steps I(V _{g 0}) = const and, consequently, the equilibrium surface charge increase with increasing V _{g 0}. The observed kinetics of the MCC generation current for the MCCs induced in an n-Si MOS structure at 293 K experimentally confirms the realization of these conditions. The values of the generation and recombination rates G _s = 2.84 × 10¹⁰ cm^–2s^–1 and R _s = 6.82 cm s^–1 obtained from current levels I(V _{g 0}) = const are typical of high-quality Si MOS structure. Additionally measured capacitance–voltage characteristics were used to determine the interface state density at the Si/SiO₂ contact near the middle of the Si gap (N _ss(E) 6.4 × 10¹⁰ cm^–2eV^–1), which allowed the estimation of the effective capture cross section of these states _eff 1.4 × 10^–16 cm².     

Analysis of spatial vapor-phase distribution using the LIF method on multi-component fuel

We analyzed the vapor-phase distribution and behavior of each component in multi-component fuel (MCF). Evaporation characteristic of MCF was researched by laser-induced fluorescent (LIF) method. A pulsed Nd-YAG laser was used as incident light, and an experiment was performed in a constant-volume vessel so that optical measurement could be possible. MCF was injected through electronically controlled common rail injector into the vessel. I-octane (C₈H₁₈), n-dodecane (C₁₂H₂₆) and n-hexadecane (C₁₆H₃₄) were selected to be low boiling point (LO-B.P.), mid boiling point (MI-B.P.) and high boiling point (HI-B.P.) components, respectively, and Fuel A, Fuel B and Fuel C, made by compounding those components at different mass fractions, were used as MCF. Experimentation was performed under the conditions that injection pressures were 42MPa, 72MPa and 112MPa, respectively, ambient gas density was 15kg/m3 and ambient gas temperature was 700K. The spatial vapor-phase distribution, dispersion process of mixture, and vaporphase homogeneity were researched. It was ascertained that the vapor-phase of MCF showed stratified distribution and the dispersion of mixture was improved in proportion to the mass fraction of the LO-B.P. component.     

Development and application of an ultra-precision lathe

This paper deals with the detailed development of an ultraprecision lathe for the purpose of machining magnetic disks. The rotational and feed accuracy and stiffness of the air bearing and the air slide were tested, respectively. A microcutting device using a piezoelectric material was also developed in order to maintain a uniform and precise depth of cut. Experiments machining a magnetic disk were carried out.Nomenclature A [m²] Area of piezoelectric actuator - C _o [mF] Capacitance of PZT - d ₃₃ [m V^–1] Piezoelectric constant - K _f [N V^–1] Equivalent force constant - K _m [N m^–1] Coefficient of force feedback - k _h [N m^–1] Stiffness of hinge - l [m] Length of PZT - M [kg] Mass of PZT system - r [mm] Radius of notch - U [m] Displacement of piezoelectric - ₃ [F m^–1] Dielectric constant of PZT - b [mm] Width of hinge - D _e [N s^–1] Equivalent damping coefficient - F _l [N] External load - K _e [N m^–1] Equivalent stiffness of PZT - k [m² N^–1] Elastic compliance of PZT - L [mm] Distance between hinge holes - M _e [kg] Equivalent mass of PZT - R _o [W] Output impedance of amp. - t [mm] Thickness between hinge holes - V _i [V] Input voltage - [g cm^–3] Density of PZT     

Solute-enriched surface layers and X-ray microanalysis of thin foils of a commercial aluminium alloy

Thin foils of the commercial Al alloy 7075 were subjected to X-ray microanalysis in a Jeol 100 CX TEMSCAN using a modified double-tilting stage. The ratio of the Cu K_x and Al K_x peaks, I_cu/I_Al, was found to decrease rapidly with increasing foil thickness, t, in regions thinner than about 200 nm. This was attributed to the formation of surface layers enriched in Cu during electropolishing, consistent with the findings of other investigators. An equation predicting the variation of I_B/I_A with t in an A-rich alloy in which B (or additional solute elements) is dilute is derived for a sample with surface layers enriched in B. The derivation predicts that I_B/I_A should vary linearly with t^?1, and that the intercept of such a plot should be positive. It is suggested that consistency with this prediction serves as a criterion for true surface enrichment. Our data on Cu obey these predictions, and further analysis indicates that the layers on both surfaces are enriched by a factor of about 5.6. The ratio of the intensities of the Zn K_x and Al K_x X-ray peaks was found to be nearly independent of foil thickness to t?400 nm. This result, combined with additional analysis, indicates that the apparent enrichment observed by other investigators is most likely due to the influence of instrumental factors.     

Discharge coefficient in the combined weir-gate structure

The present study investigated the flow discharge coefficient (C_dt) in the combined rectangular broad crested weir-gate structure. To this end, the effect of the following dimensionless parameters on the C_dt were investigated: the width ratio of the central weir to the width of the total structure (B/B_o), the height ratio of the central weir to the height of the central weir floor (Z/P), the ratio of the gate width to the width of the total structure (b/B_o), the ratio of the gate opening height to the height of the central weir floor (d/P), and the ratio of the head on central weir to the total head behind the structure (h₁/H). The Flow-3D numerical model, artificial intelligence models such as linear multilayer perceptron (MLP), Canfis network (CNN), recurrent network (RNN), modular neural network (MNN), and regression equation, were used to estimate the C_dt. The results indicated that increasing d/P and b/B_o ratios led to a decline in this coefficient. In the case of h₁/H ≤ 0.4, an increase in B/B_o ratio resulted in decreasing the turbulence intensity and C_dt while the impact of enhancing the size of B/B_o was not significant if h₁/H > 0.4. Besides, increasing Z/P ratio caused an increase in resistance against the flow and thus a decline in C_dt. Further, the results of artificial intelligence models and regression equation demonstrated that the MNN model with an RMSE and R² of 0.03 and 0.97, respectively, could have an accurate estimate of the C_dt values.