Sample preparation for nanoanalytical electron microscopy using the FIB lift-out method and low energy ion milling

Thinning specimens to electron transparency for electron microscopy analysis can be done by conventional (2 - 4 kV) argon ion milling or focused ion beam (FIB) lift-out techniques. Both these methods tend to leave ''mottling'' visible on thin specimen areas, and this is believed to be surface damage caused by ion implantation and amorphisation. A low energy (250 - 500 V) Argon ion polish has been shown to greatly improve specimen quality for crystalline silicon samples. Here we investigate the preparation of technologically important materials for nanoanalysis using conventional and lift-out methods followed by a low energy polish in a GentleMill™ low energy ion mill. We use a low energy, low angle (6 - 8°) ion beam to remove the surface damage from previous processing steps. We assess this method for the preparation of technologically important materials, such as steel, silicon and GaAs. For these materials the ability to create specimens from specific sites, and to be able to image and analyse these specimens with the full resolution and sensitivity of the STEM, allows a significant increase of the power and flexibility of nanoanalytical electron microscopy

Advanced nanoanalysis of a Hf-based high-<i>k</i> dielectric stack prior to activation

Analytical electron microscopy techniques are used to investigate elemental distributions across a high-&lt;i&gt;k&lt;/i&gt; dielectric stack with a metal gate. Electron energy-loss spectroscopy results from a Si(100)/SiO2/HfO2/TiN/a-Si gate stack confirm the presence of an oxide interfacial phase at the TiN/a-Si interface prior to activation of the stack

ELNES investigations of the structure and electronic properties of chromium spinels

A series of spinels have been studied to investigate the influence of the occupation of d orbitals on the energy loss near edge structure (ELNES). In this paper the oxygen K edges from a variety of chromium spinels and magnesium aluminate are presented. Extra fine structure is observed from compounds containing transition metals with partially filled d orbitals. This is assigned to transitions to states created by hybridisation of the oxygen 2p and transition metal 3d orbitals at the bottom of the conduction band

Investigating physical and chemical changes in high-k gate stacks using nanoanalytical electron microscopy

The thermal budget involved in processing high-k gate stacks can cause undesirable physical and chemical changes which limit device performance. The transmission electron microscope and associated analytical techniques provide a way of investigating these changes on a sub-nanometre scale. Using electron energy loss near edge structure (ELNES), information on the local chemistry may be extracted. These techniques are applied to high-k dielectric stacks grown on Si and containing HfO2 and HfSiO layers

SERRS dyes - part 2. Syntheses and evaluation of dyes for multiple labelling for SERRS

The syntheses of a number of azo and azine dyes with various surface attachment groups is described. The dyes use different methods of achieving surface complexing and are evaluated for their suitability as multiple labels for SERRS. The surface complexing agents, 8-hydroxyquinoline, benzotriazole, and pyridine are both shown to form robust layers on the silver surface. The relative intensities of the SERRS signals from each dye were shown to be predictive by considering the molar absorption coefficient at the laser excitation frequency

ELNES as a probe of magnetic order in mixed oxides

A previous study of chromite and ferrite spinels revealed energy-loss near-edge structure (ELNES) in the oxygen K-edge that could not be reproduced in non-spin polarised calculations. Chromite and ferrite spinels typically undergo transitions to long range ordered magnetic structures at temperatures below ~15K. A model in which dynamic magnetic short range order (SRO) persists above the Néel temperature until 100K has been proposed using neutron powder diffraction. In the TEM, the interaction time of the fast electron with the specimen is sufficiently short for dynamic magnetic interactions to influence the observed ELNES at 300K. Here we present new spin polarised calculations performed using the commercially available codes FEFF8.2 and Wien97. The calculated oxygen K-edge ELNES show improved agreement with experiment when magnetic interactions are included in the calculation

Modelling paramagnetism in EELS: a study of magnetic order

Magnetic ordering has been shown to have a significant effect on the shape of the oxygen K-edge energy-loss near edge structure (ELNES) in a series of chromite spinels. However, the ELNES of these materials has only been simulated using a rough approximation of antiferromagnetism - the true nature of the magnetic interactions responsible for the detailed oxygen K-edge shape is still unknown. Chromite spinels typically undergo transitions to long range ordered antiferromagnetic (AFM) structures at temperatures below ~15K. Dynamic short range magnetic order (SRO) has been observed at temperatures up to 150K using neutron powder diffraction (NPD). It is not clear whether long range magnetic order, short range magnetic order or paramagnetic effects are responsible for the characteristic oxygen K-edge ELNES observed at room temperature. Here we discuss the possibility of carrying out paramagnetic simulations using the real space multiple scattering program FEFF8.2, and show preliminary results of paramagnetic simulations of the oxygen K-edge ELNES of magnesium chromite

Understanding and preventing beam damage effects in partially processed high-k gate stacks

Electron beam damage effects on a partially and a fully processed HfO2 gate stack on silicon substrates are investigated, and their origins and prevention are discussed. Growth of silica between the silicon and hafnia layers is observed for the partially processed sample but is not seen for the fully processed wafer. Two sources of oxygen are found to react with the substrate to form silica. One is from the glue used in sample preparation. The oxygen from this source can be prevented from diffusing to the substrate by putting a gold barrier layer between the stack and the glue. The other source seems to come from the amorphous HfO2 layer. Using a cooling rod sufficiently slows the diffusion rate so that growth is no longer observed

Multiple labelled nanoparticles for bio detection

Remote nanoparticle detection is required for the development of in situ biological probes. Here we describe the labelling of silver nanoparticles to produce multiply coded particles which can be detected by surface enhanced resonance Raman scattering (SERRS). There is a potential for thousands of codes to be written and read without the need for spatial resolution of components of the code. The use of these systems in bioanlaysis and in situ detection is discussed

The first SERRS multiplexing from labelled oligonucleotides in a microfluidics lab-on-a-chip

The first simultaneous detection of three dye-labelled oligonucleotides in a microfluidics chip by SERRS is reported