Reversible Formation of 2D Electron Gas at the LaFeO3 /SrTiO3 Interface via Control of Oxygen Vacancies.

A conducting 2D electron gas (2DEG) is formed at the interface between epitaxial LaFeO3 layers >3 unit cells thick and the surface of SrTiO3 single crystals. The 2DEG is exquisitely sensitive to cation intermixing and oxygen nonstoichiometry. It is shown that the latter thus allows the controllable formation of the 2DEG via ionic liquid gating, thereby forming a nonvolatile switch.

Demonstration of electrooptic modulation at 2165nm using a silicon Mach-Zehnder interferometer.

We demonstrate electrooptic modulation at a wavelength of 2165nm, using a free-carrier injection-based silicon Mach-Zehnder modulator. The modulator has a V(π)∙L figure of merit of 0.12V∙mm, and an extinction ratio of -23dB. Optical modulation experiments are performed at bitrates up to 3Gbps. Our results illustrate that optical modulator design methodologies previously developed for telecom-band devices can be successfully applied to produce high-performance devices for a silicon nanophotonic mid-infrared integrated circuit platform.

Ordered nanopillar structured electrodes for depleted bulk heterojunction colloidal quantum dot solar cells.

A bulk heterojunction of ordered titania nanopillars and PbS colloidal quantum dots is developed. By using a pre-patterned template, an ordered titania nanopillar matrix with nearest neighbours 275 nm apart and height of 300 nm is fabricated and subsequently filled in with PbS colloidal quantum dots to form an ordered depleted bulk heterojunction exhibiting power conversion efficiency of 5.6%.

Plasmonic nanohybrid with ultrasmall Ag nanoparticles and fluorescent dyes.

We investigate a hybrid nanocomposite combining fluorescent dyes and ultrasmall (<3 nm) silver nanocrystals in a block copolymer micelle. Although the metal nanoparticles are significantly smaller than the electromagnetic skin depth, we observe a modification of the exciton lifetime and the nonradiative energy transfer among the dyes. This behavior is absent in a control experiment with dyes whose energetic levels are far from the plasmonic resonance, establishing the plasmonic nature of the interaction.

Ultra-violet radiation is responsible for the differences in global epidemiology of chickenpox and the evolution of varicella-zoster virus as man migrated out of Africa.

BACKGROUND: Of the eight human herpes viruses, varicella-zoster virus, which causes chickenpox and zoster, has a unique epidemiology. Primary infection is much less common in children in the tropics compared with temperate areas. This results in increased adult susceptibility causing outbreaks, for example in health-care workers migrating from tropical to temperate countries. The recent demonstration that there are different genotypes of varicella-zoster virus and their geographic segregation into tropical and temperate areas suggests a distinct, yet previously unconsidered climatic factor may be responsible for both the clinical and molecular epidemiological features of this virus infection. PRESENTATION OF THE HYPOTHESIS: Unlike other human herpes viruses, varicella-zoster virus does not require intimate contact for infection to occur indicating that transmission may be interrupted by a geographically restricted climatic factor. The factor with the largest difference between tropical and temperate zones is ultra-violet radiation. This could reduce the infectiousness of chickenpox cases by inactivating virus in vesicles, before or after rupture. This would explain decreased transmissibility in the tropics and why the peak chickenpox incidence in temperate zones occurs during winter and spring, when ultra-violet radiation is at its lowest. The evolution of geographically restricted genotypes is also explained by ultra-violet radiation driving natural selection of different virus genotypes with varying degrees of resistance to inactivation, tropical genotypes being the most resistant. Consequently, temperate viruses should be more sensitive to its effects. This is supported by the observation that temperate genotypes are found in the tropics only in specific circumstances, namely where ultra-violet radiation has either been excluded or significantly reduced in intensity. TESTING THE HYPOTHESIS: The hypothesis is testable by exposing different virus genotypes to ultra-violet radiation and quantifying virus survival by plaque forming units or quantitative mRNA RT-PCR. IMPLICATIONS OF THE HYPOTHESIS: The ancestral varicella-zoster virus, most probably a tropical genotype, co-migrated with man as he left Africa approximately 200,000 years ago. For this virus to have lost the selective advantage of resistance to ultra-violet radiation, the hypothesis would predict that the temperate, ultra-violet sensitive virus should have acquired another selective advantage as an evolutionary trade-off. One obvious advantage could be an increased reactivation rate as zoster to set up more rounds of chickenpox transmission. If this were so, the mechanism responsible for resistance to ultra-violet radiation might also be involved in reactivation and latency. This could then provide the first insight into a genetic correlate of the survival strategy of this virus.

Cryogenic plasmas for controlled processing of nanoporous materials.

Plasma processing at cryogenic temperatures tremendously suppresses the depth penetration of plasma radical species within nanoporous materials. We demonstrate that this confining effect is surprisingly unrelated to changes in the phase diffusivity of radical species gas, but is determined by the increase of the sticking coefficient and the radical recombination and reaction factors, favoring an early irreversible surface adsorption of the plasma radical species.

Microwave-assisted synthesis of monodispersed CdTe nanocrystals.

High quality and monodispersed CdTe nanocrystals with tunable emission spectra ranging from 516 nm to 650 nm were synthesized by a highly reproducible microwave method.

CMOS-integrated high-speed MSM germanium waveguide photodetector.

A compact waveguide-integrated Germanium-on-insulator (GOI) photodetector with 10 +/- 2fF capacitance and operating at 40Gbps is demonstrated. Monolithic integration of thin single-crystalline Ge into front-end CMOS stack was achieved by rapid melt growth during source-drain implant activation anneal.

Increased tunneling magnetoresistance using normally bcc CoFe alloy electrodes made amorphous without glass forming additives.

Using cross-section transmission electron microscopy we show that films of CoFe alloys, sandwiched between two conventional amorphous materials, are amorphous when less than approximately 25-30 A thick. When these amorphous layers are integrated into magnetic tunnel junctions with amorphous alumina tunnel barriers, significantly higher tunneling magnetoresistance is found compared to when these layers are made crystalline (e.g., by heating or by thickening them). We postulate that this is likely due to changes in interfacial bonding at the alumina-CoFe interface. Indeed, x-ray emission spectroscopy shows a significant increase in the Fe, but not the Co, 3d density of states at the Fermi energy for thin amorphous CoFe layers.

The effectiveness of behavioural interventions in the primary prevention of hepatitis C amongst injecting drug users: a randomised controlled trial and lessons learned.

AIM: To develop and evaluate the comparative effectiveness of behavioural interventions of enhanced prevention counselling (EPC) and simple educational counselling (SEC) in reducing hepatitis C viral (HCV) infection in sero-negative injecting drug users (IDU). DESIGN: Randomised controlled trial (RCT) of EPC intervention in comparison with simple educational counselling (SEC). SETTING SPECIALISED: Drug services in London and Surrey, United Kingdom. PARTICIPANTS AND MEASUREMENTS: Ninety five IDUs were recruited and randomised to receive EPC (n = 43) or SEC (n = 52). Subjects were assessed at baseline using the Addiction Severity Index (ASI), the Injecting Risk Questionnaire (IRQ), and Drug Injecting Confidence Questionnaire (DICQ). The primary outcome was measured by the rate of sero-conversion at 6 months and 12 months from baseline and by the ASI, IRQ and DICQ at 6 months from baseline. Hepatitis C testing was undertaken by the innovative test of the dried blood spot (DBS) test which increased the rate of testing by 4 fold compared to routine blood testing. FINDINGS SEVENTY: Eighty two subjects (82%) out of the 95 recruited were followed up at 6 months and 62 (65%) were followed up at 12 months. On the primary outcome measure of the rate of seroconversion, 8 out of 62 patients followed-up at twelve months seroconverted, three in the EPC group and five in the SEC group, indicating incidence rates of 9.1 per 100 person years for the EPC group, 17.2 per 100 person years for the SEC group, and 12.9 per 100 person years for the cohort as a whole. Analysis of the secondary outcome measures on alcohol use, risk behaviour, psychological measures, quality of life, showed no significant differences between the EPC and the SEC groups. However, there were significant changes on a number of measures from baseline values indicating positive change for both groups. CONCLUSION: We were not able to prove the efficacy of EPC in comparison with SEC in the prevention of hepatitis C in IDUs. This was related to low recruitment and retention rates of the participants. Moreover there was a low adherence rate to EPC. The study provided the benefits of developing and introducing behavioural interventions of the EPC and SEC and the DBS screening for Hepatitis C. Moreover the main lessons learnt were that piloting of a new intervention is a crucial first step before conducting pragmatic RCTs of psychological interventions in the field of addiction; that an infrastructure and culture for psychosocial interventions is needed to enable applied research in the service environment, and research funding is needed for enabling the recruitment of dedicated trained therapists for the delivery of these interventions.

Performance of the automated Abbott RealTime HIV-1 assay on a genetically diverse panel of specimens from London: comparison to VERSANT HIV-1 RNA 3.0, AMPLICOR HIV-1 MONITOR v1.5, and LCx HIV RNA Quantitative assays.

Automated RNA extraction and quantitation of HIV-1 by real-time PCR offer potential advantages of efficient sample processing, improved sensitivity, expanded dynamic range and reduced contamination risk. In this study, plasma was collected from 100 HIV-1 infected patients visiting The Courtyard Clinic of St. George's Hospital in London, United Kingdom (UK). Viral loads measured using the automated Abbott RealTime HIV-1 assay (m2000sp sample preparation and m2000rt amplification and detection instruments) were compared to results obtained with Versant HIV-1 RNA 3.0 (bDNA), AMPLICOR HIV-1 MONITOR v1.5 (Monitor v1.5) and LCx HIV RNA Quantitative (LCx HIV) assays. Based on gag p24, pol integrase, and env gp41 sequences, the panel included 26 subtype A, 20 B, 27 C, 10 D, 1 CRF01_AE, 3 CRF02_AG and 13 recombinant viruses. RealTime HIV-1, bDNA, Monitor v1.5 and LCx HIV quantitated 82, 74, 82, and 83% of samples, respectively, with 82, 71, 69 and 80 of the 100 samples measured within the dynamic ranges. Viral loads were highly correlated with 99% of values within 1 log(10) copies/ml between tests. The automated m2000 system and RealTime HIV-1 assay can increase laboratory throughput, enhance overall efficiency and reduce operator-associated errors while providing reliable quantitation of genetically diverse strains of HIV-1.

Enfurvitide prevents vertical transmission of multidrug-resistant HIV-1 in pregnancy but does not cross the placenta.

The use of previously successful antiretroviral regimens in mother-to-child transmission (MTCT) prevention will be increasingly challenged by the rising prevalence of multidrug-resistant (MDR) HIV. We used enfurvitide together with an optimized antiretroviral backbone to prevent the MTCT prevention of MDR HIV in two pregnant women. The measurement of maternal and foetal peripheral blood levels of enfurvitide showed no evidence of transplacental transfer.

Imaging thin films of nanoporous low-k dielectrics: comparison between ultramicrotomy and focused ion beam preparations for transmission electron microscopy.

Ultramicrotomy, the technique of cutting nanometers-thin slices of material using a diamond knife, was applied to prepare transmission electron microscope (TEM) specimens of nanoporous poly(methylsilsesquioxane) (PMSSQ) thin films. This technique was compared to focused ion beam (FIB) cross-section preparation to address possible artifacts resulting from deformation of nanoporous microstructure during the sample preparation. It was found that ultramicrotomy is a successful TEM specimen preparation method for nanoporous PMSSQ thin films when combined with low-energy ion milling as a final step. A thick, sacrificial carbon coating was identified as a method of reducing defects from the FIB process which included film shrinkage and pore deformation.

Oriented mesoporous organosilicate thin films.

Coassemblies of block copolymers and inorganic precursors offer a path to ordered inorganic nanostructures. In thin films, these materials combined with domain alignment provide highly robust nanoscopic templates. We report a simple path to control the morphology, scaling, and orientation of ordered mesopores in organosilicate thin films through the coassembly of a diblock copolymer, poly(styrene-b-ethylene oxide) (PS-b-PEO), and an oligomeric organosilicate precursor that is selectively miscible with PEO. Continuous films containing cylindrical or spherical pores are generated by varying the mixing composition of symmetric PS-b-PEO and an organosilicate precursor. Tuning interfacial energy at both air/film and film/substrate interfaces allows the control of cylindrical pore orientation normal to the supported film surfaces. Our method provides well-ordered mesoporous structures within organosilicate thin films that find broad applications as highly stable nanotemplates.

Dumbbell-like bifunctional Au-Fe3O4 nanoparticles.

Dumbbell-like Au-Fe(3)O(4) nanoparticles are synthesized using decomposition of Fe(CO)(5) on the surface of the Au nanoparticles followed by oxidation in 1-octadecene solvent. The size of the particles is tuned from 2 to 8 nm for Au and 4 nm to 20 nm for Fe(3)O(4). The particles show the characteristic surface plasmon absorption of Au and the magnetic properties of Fe(3)O(4) that are affected by the interactions between Au and Fe(3)O(4). The dumbbell is formed through epitaxial growth of iron oxide on the Au seeds, and the growth can be affected by the polarity of the solvent, as the use of diphenyl ether results in flower-like Au-Fe(3)O(4) nanoparticles.

DNA microarrays for virus detection in cases of central nervous system infection.

A low-density, high-resolution diagnostic DNA microarray comprising 38 gene targets for 13 viral causes of meningitis and encephalitis was constructed. The array has been used for the detection of multiplex PCR-amplified viruses in cerebrospinal fluid (CSF) and non-CSF specimens. A total of 41 clinical specimens were positive for echoviruses (23 samples), herpes simplex virus type 2 (4 samples), varicella-zoster virus (4 samples), human herpesvirus 7 (1 sample), human herpesvirus 6A (1 sample) and 6B (2 samples), Epstein-Barr virus (three samples), polyomavirus JC (1 sample), and cytomegalovirus (2 samples). Probes for herpes simplex virus type 1, polyomavirus BK, and mumps and measles viruses were also included on the array. Three samples were false negative by the microarray assay due to discordant results between the multiplex PCR for all 13 viruses simultaneously and the virus-specific PCR alone. Fifteen CSF specimens were true negative. The clinical sensitivity, specificity, and negative and positive predictive values of the assay were 93, 100, 100, and 83%, respectively, when the results were compared to those of the single-virus PCR, which was used as the "gold standard." The microarray-based virus detection assay is qualitative and provides a single-format diagnostic tool for the detection of panviral CNS infections.

Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers.

Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.

Shape-controlled synthesis and shape-induced texture of MnFe2O4 nanoparticles.

Monodisperse MnFe2O4 nanoparticles with cubelike and polyhedron shapes were synthesized by reaction of Fe(acac)3 and Mn(acac)2 with 1,2-hexadecanediol, oleic acid, and oleylamine. Controlled evaporation of the particle dispersion led to nanoparticle superlattices. The crystal orientation of the particle in the assembly depends on the shape of the particles, with particles in a cubelike shape showing (100) texture and those in the polyhedron shape exhibiting (110) texture.