The use of Raman microscopy to determine and localize vitamin E in biological samples

Alpha-tocopherol (aT), the predominant form of vitamin E in mammals, is thought to prevent oxidation of polyunsaturated fatty acids. In the lung, aT is perceived to be accumulated in alveolar type II cells and secreted together with surfactant into the epithelial lining fluid. Conventionally, determination of aT and related compounds requires extraction with organic solvents. This study describes a new method to determine and image the distribution of aT and related compounds within cells and tissue sections using the light-scattering technique of Raman microscopy to enable high spatial as well as spectral resolution. This study compared the nondestructive analysis by Raman microscopy of vitamin E, in particular aT, in biological samples with data obtained using conventional HPLC analysis. Raman spectra were acquired at spatial resolutions of 2-0.8 microm. Multivariate analysis techniques were used for analyses and construction of corresponding maps showing the distribution of aT, alpha-tocopherol quinone (aTQ), and other constituents (hemes, proteins, DNA, and surfactant lipids). A combination of images enabled identification of colocalized constituents (heme/aTQ and aT/surfactant lipids). Our data demonstrate the ability of Raman microscopy to discriminate between different tocopherols and oxidation products in biological specimens without sample destruction. By enabling the visualization of lipid-protein interactions, Raman microscopy offers a novel method of investigating biological characterization of lipid-soluble compounds, including those that may be embedded in biological membranes such as aT.

Germanium MOS Capacitors with Hafnium Dioxide and Silicon Dioxide Dielectrics

Germanium (Ge) does not grow a suitable oxide for MOS devices. The Ge/dielectric interface is of prime importance to the operation of photo-detectors and scaled MOSTs. Therefore there is a requirement for deposited or bonded dielectric materials. MOS capacitors have been formed on germanium substrates with three different dielectric materials. Firstly, a thermally grown and bonded silicon dioxide (SiO2) layer, secondly, SiO2 deposited by atmospheric pressure CVD ‘silox’, and thirdly a hafnium oxide (HfO2) high-k dielectric deposited by atomic layer deposition (ALD). Ge wafers used were p-type 1 0 0 2 O cm. C–V measurements have been made on all three types of capacitors to assess the interface quality. ALD HfO2 and silox both display acceptable C–V characteristics. Threshold voltage and maximum and minimum capacitance values closely match expected values found through calculation. However, the bonded SiO2 has non-ideal C–V characteristics, revealing the presence of a high density of interface states. A H2/N2 post metal anneal has a detrimental effect on C–V characteristics of HfO2 and silox dielectrics, causing a shift in the threshold voltage and rise in the minimum capacitance value. In the case of hafnium dioxide, capacitor properties can be improved by performing a plasma nitridation of the Ge surface prior to dielectric deposition.

Laser annealing of sputtered silicon for wafer-bonding applications

Sputtered silicon is investigated as a bonding layer for transfer of pre-processed silicon layers to various insulating substrates. Although the material appears suitable for low temperature processing, previous work has shown that gas trapped in the pores of the sputtered material is released at temperatures above 350 degrees C and further increases of temperature lead to destruction of any bonded interface. Pre-annealing at 1000 degrees C before bonding drives out gas and/or seals the surface, but for device applications where processing temperatures must be kept below about 300 degrees C, this technique cannot be used. In the current work, we have investigated the effect of excimer laser-annealing to heat the sputtered silicon surface to high temperature whilst minimising heating of the underlying substrate. Temperature profile simulations are presented and the results of RBS, TEM and AFM used to characterise the annealed layers. The results verify that gases are present in the sub-surface layers and suggest that while sealing of the surface is important for suppression of the out-diffusion of gases, immediate surface gas removal may also play a role. The laser-annealing technique appears to be an effective method of treating sputtered silicon, yielding a low roughness surface suitable for wafer bonding, thermal splitting and layer transfer.