Fredrik Östlund

Fracture strength and Young's modulus of ZnO nanowires

The fracture strength of ZnO nanowires vertically grown on sapphire substrates was measured in tensile and bending experiments. Nanowires with diameters between 60 and 310 nm and a typical length of 2 μm were manipulated with an atomic force microscopy tip mounted on a nanomanipulator inside a scanning electron microscope. The fracture strain of (7.7 ± 0.8)% measured in the bending test was found to be close to the theoretical limit of 10% and revealed a strength about twice as high as in the tensile test. From the tensile experiments, the Youngs modulus could be measured to be within 30% of that of bulk ZnO, contrary to the lower values found in the literature.

Plastic deformation of gallium arsenide micropillars under uniaxial compression at room temperature

The authors have experimentally investigated the compressive strength of GaAs pillars with a diameter of 1μm by uniaxial compression tests. The tests were performed at room temperature and, contrary to macroscopic tests, the micropillars were found to exhibit ductile plasticity comparable to that of metal single crystal micropillars. The yield stress was 1.8±0.4GPa and, for one pillar that was more closely examined, a total deformation of 24% was observed. In the diffraction patterns from transmission electron microscopy studies of this pillar, a high density of twins was observed.

Ductile-brittle transition in micropillar compression of GaAs at room temperature

Experiments have been carried out on how compressive failure of <100> axis GaAs micropillars at room temperature is influenced by their diameter. Slip was observed in all micropillars, often on intersecting slip planes. Cracks could nucleate at these intersections and then grow axially in the sample, with bursts of crack growth. However, GaAs micropillars with diameters less than approximately 1 µm did not split, nor was splitting observed where slip occurred on only one plane. The conditions under which such splitting can occur have been estimated by modifying an existing analysis. This predicts a ductile–brittle transition at a micropillar diameter of approximately 1 µm, consistent with experimental observations.

High Spatial Resolution Time-of-Flight Secondary Ion Mass Spectrometry for the Masses: A Novel Orthogonal ToF FIB-SIMS Instrument with In Situ AFM

We describe the design and performance of an orthogonal time-of-flight (TOF) secondary ion mass spectrometer that can be retrofitted to existing focused ion beam (FIB) instruments. In particular, a simple interface has been developed for FIB/SEM instruments from the manufacturer Tescan. Orthogonal extraction to the mass analyser obviates the need to pulse the primary ion beam and does not require the use of monoisotopic gallium to preserve mass resolution. The high-duty cycle and reasonable collection efficiency of the new instrument combined with the high spatial resolution of a gallium liquid metal ion source allow chemical observation of features smaller than 50 nm. We have also demonstrated the integration of a scanning probe microscope (SPM) operated as an atomic force microscope (AFM) within the FIB/SEM-SIMS chamber. This provides roughness information, and will also allow true three dimensional chemical images to be reconstructed from SIMS measurements.

In-situ Testing of Mechanical Properties of Materials

The mechanical properties of small structures, typically with dimensions within the range of a few hundred microns down to several microns or below, cannot simply be extrapolated from the properties of bulk samples. The mechanical properties of small structures, typically with dimensions within the range of a few hundred microns down to several microns or below, cannot simply be extrapolated from the properties of bulk samples. Samples used for bulk mechanical testing usually have dimensions, which are much larger than the micro-structural features, such as grains or particles. Mechanical behavior is controlled by certain fundamental length scales. The mechanical properties of a material will fundamentally change as the sample dimensions become smaller than these fundamental length scales. It is therefore necessary to measure the mechanical properties at a length scale comparable to the feature sizes used in miniature or micro-electromechanical devices.

Chapter 31 – In situ Testing of Mechanical Properties of Materials1

In this chapter, the peculiarities of integrating micro-/nano-materials testing within a scanning electron microscope are addressed. The mostly popular techniques are described, including miniaturized tensile tests, compression tests, and nano-indentation tests. Then the subject of image analysis is addressed and, finally a case study combining the use of compressive and tensile testing methods is presented.