Reduction of electrical damage in specimens prepared using focused ion beam milling for dopant profiling using off-axis electron holography

Mapping of the Electrostatic Potentials in a Fully Processed Led Device with nm-Scale Resolution by In Situ off-Axis Electron Holography

The optoelectronic properties of a fully processed red emitting AlGaInP micro-diode device is measured using standard I-V and luminescence measurements. A thin specimen is then prepared for in situ transmission electron microscopy analysis by focused ion beam milling, then the changes of electrostatic potential as a function of applied forward bias voltage are mapped by off-axis electron holography. We demonstrate that the quantum wells in the diode sit on a potential gradient until the threshold forward bias voltage for light emission is reached; at which point the quantum wells are aligned at the same potential. From simulations, a similar effect for the band structure can be demonstrated, where the quantum wells are aligned at the same energy level, and contain electrons and holes that are available for radiative recombination at this threshold voltage. We demonstrate that off-axis electron holography can be used to directly measure the potential distribution in optoelectronic devices, and is a powerful tool to help better understand their performance and to improve simulations.

A hard x-ray nanoprobe for scanning and projection nanotomography

To fabricate and qualify nanodevices, characterization tools must be developed to provide a large panel of information over spatial scales spanning from the millimeter down to the nanometer. Synchrotron x-ray-based tomography techniques are getting increasing interest since they can provide fully three-dimensional (3D) images of morphology, elemental distribution, and crystallinity of a sample. Here we show that by combining suitable scanning schemes together with high brilliance x-ray nanobeams, such multispectral 3D volumes can be obtained during a single analysis in a very efficient and nondestructive way. We also show that, unlike other techniques, hard x-ray nanotomography allows reconstructing the elemental distribution over a wide range of atomic number and offers truly depth resolution capabilities. The sensitivity, 3D resolution, and complementarity of our approach make hard x-ray nanotomography an essential characterization tool for a large panel of scientific domains.

The use of dual beam ESEM FIB to reveal the internal ultrastructure of hydroxyapatite nanoparticle-sugar-glass composites

Microparticles (MP) spray dried from hydroxyapatite (HA) nanoparticle (NP) sugar suspensions are currently under development as a prolonged release vaccine vehicle. Those with a significant sugar component cannot be sectioned by ultramicrotomy as resins are excluded by the sugar. Focused ion beam (FIB) milling is the only method to prepare thin sections that enables the inspection of the MPs ultrastructure by transmission electron microscopy (TEM). Several methods have been explored and we have found it is simplest to encapsulate MPs in silver dag, sandwiched between gold foils for FIB-milling to enable multiple MPs to be sectioned simultaneously. Spray dried MPs containing 80% sugar have an inter-nanoparticle separation that is comparable with NP size (approximately 50 nm). MPs spray dried with 50% sugar or no sugar are more tightly packed. Nano-porosity in the order of 10 nm exists between NPs. MPs spray dried in the absence of sugar and sectioned by ultramicrotomy or by FIB-milling have comparable nanoscale morphologies. Selected area electron diffraction (SAED) demonstrates that the HA remains (substantially) crystalline following FIB-milling.

Quantitative electron holographic tomography for the 3D characterisation of semiconductor device structures

Electron tomography and electron holography experiments have been combined to investigate the 3D electrostatic potential distribution in semiconductor devices. The experimental procedure for the acquisition and data reconstruction of holographic tilt series of silicon p-n junction specimens is described. A quantitative analysis of the experimental results from specimens of two different thicknesses is presented, revealing the 3D electrostatic potential variations arising from the presence of surfaces and damage generated by focused ion beam (FIB) sample preparation. Close to bulk-like properties are measured in the centre of the tomographic reconstruction of the specimen, revealing higher electrically active dopant concentrations compared to the measurements obtained at the specimen surfaces. A comparison of the experimental results from the different thickness specimens has revealed a 'critical' thickness for this specimen preparation method of 350nm that is required for this device structure to retain 'bulk'-like properties in the centre of the membrane.