The greatest achievement of the excellent National Cardiac Surgery Audit is the engagement of clinicians to ensure accuracy of their data and risk prediction, which takes account of patients’ illnesses and frailties so that difficult cases are done without detriment to the results.1 Mortality and morbidity occur despite our best efforts. Patients understand and accept that …

Metastatic spinal cord compression is thought to affect more than 4000 people each year in the United Kingdom.1 2 Treatment before paralysis is clinically effective and cost effective. Despite the fact that spinal pain is often present for three months and neurological symptoms for two months before paraplegia, almost 50% of patients are unable to walk by the time of diagnosis.1 3 Recognition is difficult as non-specific back pain is common in both the general population and patients with cancer.4 5 In addition, 23% of patients with spinal metastases have no prior cancer diagnosis.1 The added distress and disability caused by paralysis affecting someone already living with cancer cannot be overestimated.6 This article summarises the most recent recommendations from the National Institute for Health and Clinical Excellence (NICE) on how to diagnose and manage patients at risk of or with metastatic spinal cord compression.7 The algorithm outlines the management of patients with suspected metastatic spinal cord compression (figure⇓). Management of patients with suspected metastatic spinal cord compression NICE recommendations are based on systematic reviews of best available evidence. When minimal evidence is available, recommendations are based on the guideline development group’s opinion of what constitutes good practice. Evidence levels for the recommendations are given in italic in square brackets. ### Early recognition and diagnosis

Proton irradiation decreases the doping concentration and increases the ideality factor and series resistance, but has very little effect on the Schottky barrier height in n-Gallium nitride Schottky diodes. 1.0-MeV protons cause greater degradation than 1.8-MeV protons because of their higher nonionizing energy loss. The displacement damage recovers during annealing. Comparison between Schottky diodes and high electron-mobility transistors suggests that the degradation in both types of devices is predominantly due to carrier removal and mobility degradation caused by radiation-induced defect centers in the crystal lattice, with interface disorder playing a relatively insignificant part in overall device degradation.

A conversion from ohmic to rectifying behavior is observed for Au contacts on atomically ordered polar ZnO surfaces following remote, room-temperature oxygen plasma treatment. This transition is accompanied by reduction of the “green” deep level cathodoluminescence emission, suppression of the hydrogen donor-bound exciton photoluminescence and a ∼0.75eV increase in n-type band bending observed via x-ray photoemission. These results demonstrate that the contact type conversion involves more than one mechanism, specifically, removal of the adsorbate-induced accumulation layer plus lowered tunneling due to reduction of near-surface donor density and defect-assisted hopping transport.

1.8 MeV proton radiation-induced degradation in high electron mobility transistors with Si-doped Al/sub x/Ga/sub 1-x/N and thick GaN cap layers is studied up to a fluence of 1/spl times/10/sup 15/ protons/cm/sup 2/. The thick GaN cap layer reduces sheet charge modulation induced by the surface states, as it electrostatically separates the active device layers from the surface, thereby enhancing the device performance. The devices exhibit good tolerance up to 10/sup 14/ protons/cm/sup 2/, with displacement damage being the primary degradation mechanism. Charged defect centers introduced by proton radiation in the active device layers degrade carrier mobility and sheet carrier density. Proton radiation alters the barrier height at the Schottky gate and increases the resistance of the thin film structure.

We have characterized high-electron mobility transistors and corresponding uprocessed material as a function of 1.8 MeV proton fluence. Electrical data shows degradation of the electrical contacts at low fluences (10(11) - 10(14) p(+) /cm(2)) and degradation of the channel properties, for higher fluences. In conjunction with the electrical data, cathodoluminescence and secondary-ion mass spectrometry results suggest mechanisms for the higher fluence degradation.

Depth and laterally-resolved cathodoluminescence spectroscopy (CLS) enable electronic property measurements of III-V nitride heterojunctions and device structures on a nanometer scale and localized to individual micron-scale transistor devices. We have correlated these microscopic electronic properties to the optical and electrical features on a macroscopic scale. Our results for quantum wells, GaN/sapphire growth templates, and AlGaN/GaN high electron mobility transistor (HEMT) devices reveal clear evidence for the effects of morphological change, chemical interdiffusion and resultant defect formation on the microscopic electronic structure. Indeed, for state-of-the-art device structures, they demonstrate clear correlations between the defect features observed optically versus the transport properties measured electrically of the individual transistors. These results show that spatially-resolved spectral features can provide detailed physical explanations for optoelectronic and microelectronic properties observed macroscopically.

Mg‐doped GaN epilayers are analyzed by Raman and low‐energy electron‐excited nanoluminescence (LEEN) spectroscopies before and after oxygen ambient annealing at temperatures from 450 to 550 °C. Annealing as low as 450 °C shows the appearance of a local vibrational mode of the Mg Ga acceptor. Correspondingly, LEEN emission at 2.8 eV increases and that at 3.27 eV decreases after annealing in oxygen ambient. On the other hand, electron beam treatment decreases 2.8 eV emission and increases 3.27 eV emission. These luminescence properties are explained by a donor‐acceptor pairs transition model due to hydrogen‐related deep and shallow donors and Mg Ga acceptor. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The degradation of AlGaN/AlN/GaN high electron mobility transistors due to 1.8-MeV proton irradiation was measured at fluences up,to 3 x 10(15) cm(-1). The devices have much, higher mobility than AlGaN/GaN devices, but they possess similarly high radiation tolerance, exhibiting little degradation at flue ences up to 1 x 10(14) cm(-2). Decreased sheet carrier mobility due to increased carrier scattering and decreased sheet carrier density due to carrier removal are the primary damage mechanisms. The device degradation is observed as a decrease in the maximum transconductance, an increase in-the threshold voltage, and a decrease in the drain saturation current.

We have characterized AlGaN/GaN high-electron-mobility-transistors on sapphire and silicon carbide substrates with electrical and microcathodoluminescence spectral measurements. Quarter wafer-scale comparisons of spectral features in the GaN attributed to donor–acceptor pair (DAP) transitions and yellow luminescence (YL) from deep acceptors show that the specific contact resistance is related to the ratio of the DAP to YL defect emission intensities. This suggests that these defects interact to change the contact resistance locally on the GaN side of the AlGaN/GaN interface. We show that changes in the frequency response of these transistors can be attributed to these defects at the interface.

Both luminescence properties and dissociation kinetics of Mg–H complex for as-grown Mg-doped GaN are simultaneously investigated by low-energy electron-excited nanoluminescence (LEEN) spectroscopy. Ultraviolet luminescence at 3.2–3.3 eV and blue luminescence at 2.8–2.9 eV are observed as predominant LEEN emissions. In-depth profiles of LEEN emission show that the blue luminescence is the predominant emission for highly Mg-doped GaN. Electron-beam exposure less than 50 mC/cm2 produces an increase of the ultraviolet luminescence intensity and reduction of the blue luminescence intensity. These characteristics suggest that the blue luminescence is due to a transition from hydrogen-related deep donor to Mg acceptor and that the ultraviolet luminescence is due to transitions from conduction band and/or shallow hydrogen donor to Mg acceptor. We propose a kinetic model for dissociation reactions of Mg–H complex during electron exposure, and the reaction rate is evaluated to be (3.5±0.3)×10−3 s−1 for electron beams with 3.1×10−5 A/cm2 at 5.0 keV.

Low energy electron-excited nano-luminescence (LEEN) spectroscopy has been used to correlate higher intensities of deep level emissions with higher ohmic contact values on AlGaN/GaN device layers. Deep level defect emissions in the AlGaN layers have also been identified by LEEN as a signature of uncharacteristically high sheet resistances for a given wafer. The spectral features observed locally at the ohmic contact region are compared with direct electrical measurements of the same device structures. Ohmic contacts formed by annealing Ti/Al/Ni/Au at 800 °C for 30 s in nitrogen range from 1.0×10−6 to 1.0×10−4Ωcm2 (0.2–3.9 Ωmm), with average sheet resistance values ranging from 650 to 2275 Ω/□ as Al mole fraction decreases. The depth dependent characterization capacity of LEEN allows the density of defect emissions to be assigned to particular interfaces. For these samples, the deep level emissions found at 2.20 and 2.60–3.15 eV found near the surface of the sample while the defect emissions associated with high sheet resistance are found to be in the AlGaN layer itself. Unprocessed material shows that samples with the lowest amounts of midgap luminescence produce the lowest contact resistance. This information can be used to determine the outcome of device fabrication prior to contact formation.

Yasuo Koide 1, , D. E. Walker, Jr., B. D. White, L. J. Brillson, T. Itoh, R. L. McCreery, Masanori Murakami, S. Kamiyama, H. Amano, and I. Akasaki 1 Department of Electrical Engineering, The Ohio State University, Columbus, Ohio 43210, USA 2 Department of Materials Science and Engineering, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan 3 Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA 4 Department of Materials Science and Engineering, Meijo University, Tempaku-ku, Nagoya, 468-8502, Japan

Microcathodoluminescence (CLS) spectroscopy is used to probe the effect of ionizing radiation on defects inside Al gate oxide structures. Micron-scale Al–SiO2–Si capacitors exposed to 10 keV x-ray irradiation exhibit spatially localized CLS emissions characteristic of multiple deep level traps, including positively charged oxygen-deficient centers and nonbridging oxygen hole centers (NBOHC). Irradiation produces both increases and decreases in their relative emission intensities, depending on spatial location within the oxide. These changes result in a gradient of E′ versus NBOHC defect densities across the oxide thickness between Al and Si interfaces. These results demonstrate that x-ray irradiation-induced deep level traps can be monitored spatially in metal-oxide-semiconductor gate structures, that x-ray irradiation produces separate increases or decreases in E′ versus NBOHC defect densities, and that these changes vary with position within the oxides.

We have used depth-resolved cathodoluminescence spectroscopy to examine AlGaN/GaN modulation-doped field-effect transistors that display degraded source-drain current characteristics after 1.8-MeV proton irradiation, along with bulk heterojunction field-effect transistor material after similar proton irradiation. For both cases, we have observed distinct changes in spectral emission features due to decreased internal electric-field strength and new point defects within different layers of the device structure with nanometer-scale depth resolution. These changes can account for the degraded electrical characteristics.

Ultra-thin SiO2/Si gate dielectric structures exposed to heavy X-ray irradiation exhibit optical emission characteristic of interface traps. Low energy electron-excited luminescence spectroscopy with nanometer-scale depth resolution yields a characteristic spectral energy and excitation depth dependence. Ultra-thin (5 nm) oxide films on Si substrates exposed to 10 keV, 7.6 Mrad(SiO2) [13.7 Mrad (Si)] X-ray irradiation introduces trap densities on the order of 10(11) cm(-2)eV(-1), localized near the intimate SiO2-Si interface. This density is consistent with the trapped oxide and interface charge densities expected based on observed capacitance- voltages shifts of thicker oxides, their corresponding charge densities, and the proportionally smaller charge densities expected for the thinner oxide layers in this study.

Low-energy electron-excited nanoluminescence spectroscopy reveals depth-resolved optical emission associated with traps near the interface between ultrathin SiO2 deposited by plasma-enhanced chemical vapor deposition on plasma-oxidized crystalline Si. These near-interface states exhibit a strong dependence on local chemical bonding changes introduced by thermal/gas processing, layer-specific nitridation, or depth-dependent radiation exposure. The depth-dependent results provide a means to test chemical and structural bond models used to develop advanced dielectric-semiconductor junctions.

Your Committee begs leave to report on the legal limits for butter as follows: We recommend 80 per cent butter fat, 16 per cent moisture and 1.25 per cent casein. No tolerance should be allowed. This limit should be applicable to both salted and unsalted butter. Since it is possible to test for moisture, allowing 1 per cent for casein, the ordinary buttermaker can with a reasonable degree of accuracy determine the per cent of fat in his butter without the necessity of analyzing the same for that purpose. The question of allowing a higher percent of moisture for unsalted than for salted butter has been discussed, but since the butter fat is of intrinsic value, and unsalted butter commands a higher price than salted butter, it is not deemed wise by your Committee to have one standard for salted and another for unsalted butter. Your Committee further begs leave to report that if there is to be a tolerance, the butter fat in the butter should be increased to the extent of the tolerance.