Scanning Electron Microscope Chamber Research Articles

Nanorobot-Based Handling and Transfer of Individual Silicon Nanowires

Presented is a new experimental implementation for well-directed handling of silicon nanowires with diameters of less than 100 nm and length of up to 10 µm. Handling device is a robotic setup of several centimeters in size and nanometer accuracy, mounted inside a SEM (Scanning Electron Microscopy) chamber. The actual transfer of the nanowires is done by this setup from a production substrate to a different electrode substrate by using an STM (Scanning Tunneling Microscope) tungsten tip as carrier, gas based adhesive bonding, and FIB (Focused Ion Beam) assisted milling. The goal of this series is the placement on the electrodes in order to facilitate further electrical characterization measurements. The presented handling technique for nanoscale objects facilities an accurate picking and placing of individual nanowires on the one hand and a transfer over several centimeters to a complete different substrate on the other hand. Advantages, prospects and limits are investigated particularly with regard to a handling automation for applications.

Size‐Dependent Fracture Mode Transition in Copper Nanowires

In situ uni-axial tensile tests of single-crystalline copper nanowires are performed using a micromechanical device inside a scanning electron microscope chamber. The single-crystalline copper nanowires are synthesized by solvothermal processes, and the growth direction along the wire axis is the <110> orientation as confirmed by transmission electron microscopy (TEM) selected area diffraction (SAD) analysis. The fracture strengths of copper nanowires are found to be much higher than that of bulk copper. More interestingly, both ductile and brittle-like fracture modes are found in the same batch of fabricated nanowires, and the fracture modes appear to be dependent on the diameters of tested nanowires. From the analysis of fracture surfaces, sample morphologies and corresponding stress-strain curves, the competition between deformation and fracture mechanisms controlled by initial defects density and by the probability of dislocation interactions is attributed to this intriguing size-dependent fracture mode transition.

Local sputter etching by micro plasma jet in SEM

A local high pressure micro plasma jet was proposed for micro scale local sputter etching in a vacuum system. A small orifice gas nozzle as an anode was placed in a Scanning Electron Microscope (SEM) chamber to produce the local high gas pressure and supply Argon gas for DC plasma generation at a short gap distance. The characteristics of local sputter etching by the micro plasma jet were studied. At DC power of 1.68 mW, a silicon sputtering rate of approximately 0.01 μm/s was achieved by using an orifice 40 μm in diameter at 2.5 sccm gas flow rate and 100 μm gap distance. The sputtered area was 60 μm in diameter.

&lt;i&gt;I&lt;/i&gt;&lt;i&gt;n Situ&lt;/i&gt; Study of Fracture Process for B-Class Shipbuilding Steel

Crack initiation, propagation and microfracture processes of B-class shipbuilding steel have been investigated by using an in-situ tensile stage installed inside a scanning electron microscope chamber, meanwhile the secondary crack propagation at low temperature brittle fracture has also been studied. It is revealed that micro cracks always nucleated at the notch of specimens due to the stress concentration and then propagate along the interface of ferrite-pearlite. The plastic deformation of polygonal ferrite occurred in the loading process, the cracks propagated as “Z” morphology in the matrix. In the low temperature brittle fracture zone, the secondary crack propagated through the ferrite matrix in the manner of transgranular crack. When the secondary crack propagated to pearlite region, the intragranular crack and transgranular crack were observed in the pearlite region .

Nanomanipulation of biological samples using a compact atomic force microscope under scanning electron microscope observation

We introduce a compact nanomanipulator that can be operated inside the sample chamber of a scanning electron microscope (SEM) for biological sample manipulation. The design of the nanomanipulator is based on that of an atomic force microscope (AFM). A self-sensitive cantilever is used to realize the compact body and thus it is possible to put a pair of the standalone AFM units on the sample stage in the SEM chamber. Using this system, we accomplished nanodissection of biological samples as well as AFM imaging under SEM observation. We then fabricated the surface of a rat renal glomerulus by scan-scratching and succeeded in making a small hole on the wall of a blood capillary. As a result, it was possible to observe the internal structure of the capillary, which had been hidden beneath the surface wall. Furthermore, using two AFM units on the sample stage of the SEM, we successfully dissected the lens fiber cells taken from a rat eye in a multi-probe operation using the two cantilevers. This system is expected to become a very useful tool for micro- and nanometer-scale anatomy and engineering applications.

In-Situ Fracture Observation and Fracture Toughness Analysis of Ni-Mn-Ga-Fe Ferromagnetic Shape Memory Alloys

The fracture property improvement of Ni-Mn-Ga-Fe ferromagnetic shape memory alloys containing ductile γ particles was explained by direct observation of microfracture processes using an in-situ loading stage installed inside a scanning electron microscope (SEM) chamber. The Ni-Mn-Ga-Fe alloys contained a considerable amount of γ particles in β grains after the homogenization treatment at 1073 K to 1373 K (800 °C to 1100 °C). With increasing homogenization temperature, γ particles were coarsened and distributed homogeneously along β grain boundaries as well as inside β grains. According to the in-situ microfracture observation, γ particles effectively acted as blocking sites of crack propagation and provided the stable crack growth, which could be confirmed by the R-curve analysis. The increase in fracture resistance with increasing crack length improved overall fracture properties of the Ni-Mn-Ga-Fe alloys. This improvement could be explained by mechanisms of blocking of crack propagation and crack blunting and bridging.

Numerical Modelling of the Electron Backscattering at the Variable Gas Pressure

The authors prepared a computer programme for simulations of electron flow in various gas conditions. This software combines a commercial programme SIMION 3D v. 7.0, destined for computations of charged particles trajectories in electric and magnetic fields, and the Monte Carlo one written by the authors in the SIMION internal language. The programme takes into consideration the electron scattering in elastic and inelastic collisions, the ionising avalanche and γ processes. This programme was used to investigate the secondary electron backscattering by gas filling the sample chamber of the environmental scanning electron microscope and its influence on the signal to noise ratio S/N and material contrast suppression.

Microstructural evidence of the chemical driving force in eutectic SnPb electromigration

An observation of electromigration behavior in a eutectic SnPb solder with various line lengths was performed using an in-situ scanning electron microscope chamber with a 100 °C, 3 × 10 4 A/cm 2 condition. Edge-drift occurred at the cathode, and hillocks formed at the anode were observed at the eutectic SnPb solder stripe during current stressing. The incubation time for the edge-drift and the edge-drift velocity increased as the line length was increased. This result is discussed along with the void nucleation stage of the solder bump and the electromigration back flux force. The existence of the electromigration product (jL) and its line length dependency are also discussed.

Microtexture development during equibiaxial tensile deformation in monolithic and dual phase steels

Subgrain texture and microstructure evolution in individual ferrite grains in single (so called interstitial-free) and dual phase (DP) steel sheets with various martensitic fractions during stepwise equibiaxial deformation was observed by high resolution electron backscatter diffraction (EBSD) measurement on a special deformation stage positioned inside a scanning electron microscope chamber. The micromechanical effect of hard martensite islands on adjacent ferrite grains in DP steels was analyzed by comparing the microstructural changes in the two steels. The strain partitioning between ferrite and martensite in DP steel, the development of orientation gradients in ferrite grains near martensite islands, and the surface height variation were observed via a combination of high resolution transmission electron microscopy, EBSD, and atomic force microscopy. From these microstructural and geometrical observations the main effect of the hard martensite islands was to shed strain into the adjacent ferrite, thus inducing strain gradients, orientation spread, geometrically necessary dislocations and increased surface height variation.

Field emission from single and few-layer graphene flakes

We report the observation and characterization of field emission current from individual single- and few-layer graphene flakes laid on a flat SiO2/Si substrate. Measurements were performed in a scanning electron microscope chamber equipped with nanoprobes which allowed local measurement of the field emission current. We achieved field emission currents up to 1 μA from the flat part of graphene flakes at applied fields of few hundred volt per micrometer. We found that the emission process is stable over a period of several hours and that it is well described by a Fowler–Nordheim model for currents over five orders of magnitude.

Image instability during the electrical measurement in scanning electron microscope

AbstractDuring electrical measurements in a scanning electron microscope (SEM), secondary electron (SE) images often become dark or the image contrast becomes weaker. We have revealed that this phenomenon originates in the negative charging of the insulating part in an electric circuit. This charging can be caused by stray electrons, even if the insulator is not directly irradiated. The electrostatic field owing to this charge deflects SEs and reduces the intensity of detected electrons. We have demonstrated this effect by observing systematic shifts of the field of view of SE detector, which appears in SE images. This explanation is supported by a calculation of electron trajectories in the electrostatic field in the SEM chamber. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

In Situ Scanning Electron Microscope Observation and Finite Element Method Analysis of Delayed Hydride Cracking Propagation in Zircaloy-2 Fuel Cladding Tubes

Abstract The objective of the present research is to build a modeling method for delayed hydride cracking (DHC) of zirconium alloys. DHC tests were carried out on Zircaloy-2 cladding tubes in the chamber of a scanning electron microscope to directly observe the crack propagation and measure the crack velocity in the radial direction. These in situ observations showed that a sharply tipped crack propagated at a relatively high rate, while the velocity decreased when the crack tip was blunted, supporting the occurrence of intermittent crack propagation that could be expected from the DHC mechanism. V-KI curves or diagrams of crack velocity, V, versus stress intensity factor at a crack tip, KI, were obtained as a function of 0.2 % offset yield stress, hydride orientation, and pre-crack depth. The steady state crack velocity and the threshold stress intensity factor for the onset of the crack propagation tended to increase or decrease, respectively, with an increase in the 0.2 % offset yield stress. Analyses of stress distribution and hydrogen diffusion around a crack tip were made using a finite element computer code. The analyses showed that a strong hydrostatic pressure field was generated concentrically around the crack tip and hydrogen diffused towards the crack tip according to the hydrostatic pressure gradient. The crack velocity was estimated from the calculated hydrogen flux rate assuming the critical hydrogen quantity for the crack propagation. There was good agreement between the experiments and the calculations regarding the crack velocity and its dependency on KI. Calculations showed that the increase in the 0.2 % offset yield stress would accelerate the crack propagation by increasing the hydrostatic pressure at the crack tip.

Permanent magnet finger-size scanning electron microscope columns

This paper presents permanent magnet scanning electron microscope (SEM) designs for both tungsten and field emission guns. Each column makes use of permanent magnet technology and operates at a fixed primary beam voltage. A prototype column operating at a beam voltage of 15kV was made and tested inside the specimen chamber of a conventional SEM. A small electrostatic stigmator unit and dedicated scanning coils were integrated into the column. The scan coils were wound directly around the objective lens iron core in order to reduce its size. Preliminary experimental images of a test grid specimen were obtained through the prototype finger-size column, demonstrating that it is in principle feasible.

Quantitative characterization of microfiltration membranes by 3D reconstruction

Sophisticated characterization methods for porous microfiltration membranes are gaining importance because of the higher complexity of the newest generation of microfiltration membranes. Therefore it is necessary to develop methods that allow a quantitative determination of all the vital parameters such as volume specific surface area, pore diameter and pore length distribution and connectivity across the membrane. 2D images from scanning or transmission electron microscopy are not sufficient for this purpose but a three dimensional (3D) reconstruction of the membranes is required. This paper presents quantitative results from 3D reconstructions of two different microfiltration membranes. Such information can help to improve the filtration properties and to design new morphologies. This investigation was carried out using an ultramicrotome mounted in the specimen chamber of an environmental scanning electron microscope (ESEM). This equipment enables automated serial sectioning and imaging of specimens and thus provides an easy and time-saving way to obtain the stacks of images necessary for the 3D reconstruction of the membrane morphology. The results gained from the 3D models are compared with results from single 2D images.

Grid Method for Microscale Discontinuous Deformation Measurement

The objective of this paper is to explore both grid method and Digital Image Correlation (DIC) technique for microscale and discontinuous displacement measurements, such as those associated with crack tips. First, the principle of the grid method is revisited. The grid method and DIC technique are then applied to computer generated images to calculate the displacement field around crack tips. Finally, the grid method is applied to actual experimental images of fracture tests which are conducted inside a Scanning Electron Microscope (SEM) chamber. A new technique is developed to generate microscale pattern that is suitable for both grid method and DIC technique. The displacement fields calculated from grid method are compared with those from DIC technique to identify the strengths and weaknesses of each technique for the microscale and discontinuous displacement measurements. It has been determined that grid method can obtain data closer to the discontinuity than DIC; however, DIC produces smoother displacement fields at the far field. Using this new pattern generation technique, both grid method and DIC technique can be applied to the fracture test at the microscale to complement with each other to achieve the best experiment results.

Towards high accuracy calibration of electron backscatter diffraction systems

For precise orientation and strain measurements, advanced Electron Backscatter Diffraction (EBSD) techniques require both accurate calibration and reproducible measurement of the system geometry. In many cases the pattern centre (PC) needs to be determined to sub-pixel accuracy. The mechanical insertion/retraction, through the Scanning Electron Microscope (SEM) chamber wall, of the electron sensitive part of modern EBSD detectors also causes alignment and positioning problems and requires frequent monitoring of the PC. Optical alignment and lens distortion issues within the scintillator, lens and charge-coupled device (CCD) camera combination of an EBSD detector need accurate measurement for each individual EBSD system. This paper highlights and quantifies these issues and demonstrates the determination of the pattern centre using a novel shadow-casting technique with a precision of ∼10 μm or ∼1/3 CCD pixel.

Tensile Strength of Spinnable Multiwall Carbon Nanotubes

Individual multi walled Carbon Nanotubes (CNTs) exhibit exceptional strength and stiffness. However, large scale constructs of directly spinnable CNTs (such as yarns) has reached only a few percent of their potential. To improve their performances in such scale, it is important to understand the stress-strain characteristics and failure modes of individual CNTs. This paper reports the experimental tensile strength of spinnable multiwalled carbon nanotubes (MWNT). These experiments were conducted using a nano tensile testing stage inside Scanning Electron Microscope (SEM) chamber. An Atomic Force Microscope (AFM) tip with known force constant was used as a nano manipulator and as s force transducer to measure the desired mechanical properties. Transmission Electron Microscope (TEM) images were used to accurately measure the diameter of CNT samples. The fracture strength was calculated using the determined applied force and the diameter of the CNT. Fracture strength in relations to number of failed walls, pullout (sword/sheath) behaviour and angle of stress are studied. It was found that the tensile strength of the tested spinnable CNTs were at least 20 to 90 Gpa with a mean value of 48 Gpa considering a solid cross sectional area.

Effect of Nitrogen Doping on the Mechanical Properties of Carbon Nanotubes

We report on the usage of a simple microfabricated device that works in conjunction with a quantitative Nanoindenter within a scanning electron microscope (SEM) chamber, for the in situ quantitative tensile testing of individual catalytically grown pristine and nitrogen-doped multiwall carbon nanotubes (MWNTs). The two types of MWNTs were found to possess similar strengths but different load-bearing abilities owing to the differences in their wall structures. Also, stress versus strain curves and fracture surfaces showed that while the pristine MWNTs deform and fail in a brittle fashion, the nitrogen-doped MWNTs deform plastically to varying degrees prior to failure. High resolution transmission electron microscope (TEM) images of the nitrogen-doped MWNT fracture specimens showed the presence of regions of reduced cross-section areas and kinks in close proximity to the fracture surfaces. The presence of nitrogen atoms in the graphitic sheets was assumed to have led to the formation of kinks whose motion induced by straining could have resulted in the plastic deformation of the carbon nanotubes.

Effect of Hardness of Second Phase Particle on Fatigue Crack Growth Behavior of Steels with Hard Second Phase Particle in Soft Ferrite Matrix

K-constant fatigue crack growth (FCG) tests were conducted on low carbon steels with uniformly distributed hard particle with different of pearlite, bainite and martensite in a soft ferrite matrix. The FCG tests by using a single edge cracked tension (SECT) type was performed inside a scanning electron microscope chamber equipped with a servo-hydraulic fatigue machine. During the test, in-situ crack path observation was carried out to identify the crack tip stress shielding phenomena. From the results, influence of hardness of second phase particle on the FCG behavior in Paris regime was systematically investigated. The results revealed that the ferrite-martensite (FM) steel showed significantly higher FCG resistance compared to that of ferrite-pearlite (FP) and ferrite-bainite (FB) steels. The harder second phase particle would be more difficult to be plastically deformed, which would induce higher plastic constrain. This higher plastic constrain may result in significant crack closure effect and stress shielding effect, thereby increasing higher FCG resistance.

Observations of the morphology and sublimation‐induced changes in uncoated snow using scanning electron microscopy

AbstractThe morphology of a fresh‐snow specimen and the sublimation‐induced structural changes in an individual snow crystal were examined using a high‐vacuum scanning electron microscope (SEM) equipped with a cryo system. The snow specimen was collected during a snowfall in Hanover, NH, USA, and was initially maintained at liquid nitrogen temperature in order to prevent any structural changes. Without coating, snow crystals can sublimate in the SEM chamber at a rate that is mainly determined by the temperature of the specimen. After the initial morphology was examined at − 180 °C, sublimation was initiated by slowly increasing the stage temperature, and changes in morphology were recorded by taking images of an individual snow crystal intermittently and recording the temperatures and times. Severe morphological destructions due to sublimation occurred at around − 150 °C. This approach allowed us to closely observe both the initial morphology and the structural changes in snow crystals as they underwent sublimation, a significant process during snow metamorphism. These observations also serve as a reference for temperature selection in the study of uncoated snow with a similar morphology using a high‐vacuum SEM. Copyright © 2010 John Wiley &amp; Sons, Ltd.