Two high-k gate stacks with the structure Si/SiO2/HfO2/TiN/poly-Si are characterised using nanoanalytical electron microscopy. The effect of two key changes to the processing steps during the fabrication of the stacks is investigated. Electron energy-loss spectroscopy is used to show that the TiN layer has a very similar composition whether it is deposited by PVD or ALD. Spectrum imaging in the electron microscope was used to profile the distribution of elements across the layers in the stack. It was found that when the anneal after HfO2 deposition is carried out in a NH3 atmosphere instead of an O2 atmosphere, there is diffusion of N into the SiO2 and HfO2 layers. There is also significant intermixing of the layers at the interfaces for both wafers.

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.

Hafnia and hafnium silicate thin films and bulk powders were analysed using thermal analysis, X-ray diffraction and transmission electron microscope techniques to improve understanding of the crystallisation mechanism of the dielectric material. It was found that thin films exhibit instability under device processing conditions. Starting precursors greatly affect the crystallisation pathway in the bulk materials. By studying these phenomena a better understanding of the chemistry involved during crystallisation can be gained.

Analytical electron microscopy techniques are used to investigate elemental distributions across a high-k 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. (c) 2007 The Electrochemical Society.

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.

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.

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.

Superconducting thin films of Nd1−xBa2+xCu3O7−δ have been grown on single crystal SrTiO3 substrates by pulsed laser deposition (PLD) using an off-stoichiometric Nd0.97Ba2.03Cu3O6 (Ba-rich NBCO) target. The statistical methods of Experimental design and regression analysis were used to understand and optimise the growth mechanism. The structural properties of both the target and the films were investigated by X-ray diffraction (XRD). The surface morphology of the films was examined by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). Electron probe microanalysis (EPMA) using a scanning electron microscope equipped with wavelength-dispersive X-ray (WDX) spectrometers was used to carry out qualitative and quantitative analysis of both the target and films. Micro-Raman spectroscopy was used to study the oxygen sublattice vibrations of both the target and the films.

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 HfO"2 and HfSiO layers.

EELS and EDX are widely used as complementary analytical techniques in the analytical TEM. Traditionally EELS has been preferred for light element analyses and EDX for heavier element analyses. While EELS and EDX can be performed simultaneously in the TEM, frequently the experimental set-up is such that the conditions are not optimized for EDX and there is a detrimental effect on the quality of EDX data obtained. It would be advantageous if analyses of the heavier elements of interest could also be performed by EELS. We are investigating the ability of EELS to analyse heavy elements in several systems of current importance such as PZT and HfO2 and HfSiO based materials. We have previously shown that the Hf M-edges can be used to map the presence of Hf in a HfO2/HfSiO gate stack deposited by International Sematech [1]. However, it is also possible to use the Hf N-edges to map the Hf signal. Thus it is possible to collect edges from Si, Hf and O in a single spectrum opening up the way to determine the metal to oxide ratio via EELS. Fig 1 shows an EELS spectrum containing the Hf N-edges and O K-edge from HfO2. We have also had some success using the Pb N-edges to study the composition variation in PZT grown by a sol-gel method.

Raman spectroscopy is a form of vibrational spectroscopy that is well suited to the molecular identification of a variety of analytes, including both explosives and biological agents. The technique has been gaining more widespread interest due to improvements in instrumentation, sensitivity, and its ease of use, in comparison to other techniques. In this paper, we describe recent advances in Raman spectroscopy with respect to the detection of high-energy explosives and biological materials. In particular, emphasis is placed on the exploitation of enhancement factors that overcome traditional limitations on sensitivity, namely, surface enhancement and resonance enhancement, functionalization of target analytes, and the use of novel lab-on-a-chip technology.

Silica particles were partially coated with silver, and a suitable chromophore, such that they could be simultaneously trapped within an optical tweezers system, and emit a surface-enhanced resonance Raman scattering (SERRS) response. A standard 1064 nm TEM00 mode laser was used to trap the bead whilst a frequency doubling crystal inserted into the beam gave several microwatts of 532 nm co-linear light to excite the SERRS emission. The con fi guration has clear applications in providing apparatus that can simultaneously manipulate a particle whilst obtaining surface sensitive sensory information.

Superconducting thin films of Ndl-xCaxBa2Cu3O7-delta (x = 0.03 and 0.08) have been grown on single crystal SrTiO3 substrates by pulsed laser deposition. The statistical methods of Experimental Design and regression analysis were used to optimize the film properties and to understand the correlation between the growth parameters and film properties. The orientation of the films was investigated by x-ray diffraction. The surface morphology of the films was examined by atomic force microscopy and scanning tunnelling microscopy. Qualitative and quantitative elemental analyses of the films were carried out using electron probe microanalysis. Micro-Raman spectroscopy was used to study the oxygen sublattice vibrations of the films. The effect of annealing oil the superconducting transition temperature of the patterned films was also studied.

Superconducting thin films of Nd1−xYxBa2Cu3O7−δ have been grown on single crystal SrTiO3 substrates by pulsed laser deposition (PLD) using a (1 − z)(NdBa2Cu3O7)z(YBa2Cu3O7) (z = 0.05 wt%) target. The statistical methods of Experimental Design and regression analysis were used to understand and optimise the growth mechanism. The orientation of the films was investigated by X-ray diffraction (XRD). Their surface morphology was examined by atomic force microscopy (AFM) and scanning tunnelling microscopy (STM). Qualitative and quantitative elemental analysis of the films was done by Electron probe microanalysis (EPMA). Micro-Raman spectroscopy was used to study the oxygen sublattice vibrations of the films.

Surface-enhanced resonance Raman scattering (SERRS) is considerably more efficient than Raman spectroscopy, thereby enabling the detection of single molecules. Strong and short-lived SERRS emissions (<100 ms) from single, partially silver-coated, dye-adsorbed microparticles have been detected within optical tweezers (see picture). Full spectra, recorded from single particles, clearly show that the emission is due to 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.

We demonstrate three-dimensional trapping of micrometer-diameter silica particles, partially coated with silver, within conventional optical tweezers. Although metallic particles are usually repelled from the beam focus by the scattering force, we show that transparent spheres partially coated with silver can be trapped with efficiencies comparable with dielectric particles. The trapping characteristics of these particles are examined as a function of metallic coverage, and the application of these particles to surface-enhanced resonance Raman scattering is investigated.

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.

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

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.