Design of defect-chemical properties and device performance in memristive systems

Future development of the modern nanoelectronics and its flagships internet of things, artificial intelligence, and neuromorphic computing is largely associated with memristive elements, offering a spectrum of inevitable functionalities, atomic level scalability, and low-power operation. However, their development is limited by significant variability and still phenomenologically orientated materials' design strategy. Here, we highlight the vital importance of materials' purity, demonstrating that even parts-per-million foreign elements substantially change performance. Appropriate choice of chemistry and amount of doping element selectively enhances the desired functionality. Dopant/impurity-dependent structure and charge/potential distribution in the space-charge layers and cell capacitance determine the device kinetics and functions. The relation between chemical composition/purity and switching/neuromorphic performance is experimentally evidenced, providing directions for a rational design of future memristive devices.

Electrically controlled transformation of memristive titanates into mesoporous titanium oxides via incongruent sublimation

Perovskites such as SrTiO3, BaTiO3, and CaTiO3 have become key materials for future energy-efficient memristive data storage and logic applications due to their ability to switch their resistance reversibly upon application of an external voltage. This resistance switching effect is based on the evolution of nanoscale conducting filaments with different stoichiometry and structure than the original oxide. In order to design and optimize memristive devices, a fundamental understanding of the interaction between electrochemical stress, stoichiometry changes and phase transformations is needed. Here, we follow the approach of investigating these effects in a macroscopic model system. We show that by applying a DC voltage under reducing conditions on a perovskite slab it is possible to induce stoichiometry polarization allowing for a controlled decomposition related to incongruent sublimation of the alkaline earth metal starting in the surface region. This way, self-formed mesoporous layers can be generated which are fully depleted by Sr (or Ba, Ca) but consist of titanium oxides including TiO and Ti3O with tens of micrometre thickness. This illustrates that phase transformations can be induced easily by electrochemical driving forces.

Low Temperature Deposition of High-k/Metal Gate Stacks on High-Sn Content (Si)GeSn-Alloys

(Si)GeSn is an emerging group IV alloy system offering new exciting properties, with great potential for low power electronics due to the fundamental direct band gap and prospects as high mobility material. In this Article, we present a systematic study of HfO2/TaN high-k/metal gate stacks on (Si)GeSn ternary alloys and low temperature processes for large scale integration of Sn based alloys. Our investigations indicate that SiGeSn ternaries show enhanced thermal stability compared to GeSn binaries, allowing the use of the existing Si technology. Despite the multielemental interface and large Sn content of up to 14 atom %, the HfO2/(Si)GeSn capacitors show small frequency dispersion and stretch-out. The formed TaN/HfO2/(Si)GeSn capacitors present a low leakage current of 2 × 10(-8) A/cm(2) at -1 V and a high breakdown field of ∼8 MV/cm. For large Sn content SiGeSn/GeSn direct band gap heterostructures, process temperatures below 350 °C are required for integration. We developed an atomic vapor deposition process for TaN metal gate on HfO2 high-k dielectric and validated it by resistivity as well as temperature and frequency dependent capacitance-voltage measurements of capacitors on SiGeSn and GeSn. The densities of interface traps are deduced to be in the low 10(12) cm(-2) eV(-1) range and do not depend on the Sn-concentration. The new processes developed here are compatible with (Si)GeSn integration in large scale applications.

MeV Ion Implantation of Er into LiNbO3

The incorporation of Er into LiNbO3 is of great interest for fabricating waveguide lasers and amplifiers. We compare Er diffusion data with the results of Er implantation, performed at 3.6 MeV energy. Even after annealing for 4h at 1060°C, the resulting Er profiles display very good matching to the optical modes. The results of a theoretical gain estimate are presented.

Non-conventional yeasts as producers of polyhydroxyalkanoates?genetic engineering of Arxula adeninivorans

The non-conventional yeast Arxula adeninivorans was equipped with the genes phbA, phbB and phbC of the polyhydroxyalkanoate (PHA) biosynthetic pathway of Ralstonia eutropha, which encode beta-ketothiolase, NADPH-linked acetoacetyl-CoA reductase and PHA synthase, respectively. Arxula strains transformed solely with the PHA synthase gene (phbC) were able to produce PHA. However, the maximum content of the polymer detected in these strains was just 0.003% poly-3-hydroxybutyrate (PHB) and 0.112% poly-3-hydroxyvalerate (PHV). The expression of all three genes (phbA, phbB, phbC) resulted in small increases in the PHA content of the transgenic Arxula cells. However, under controlled cultivation conditions with minimal medium and ethanol as the carbon source, the recombinant yeast was able to accumulate up to 2.2% PHV and 0.019% PHB. Possible reasons for these differences are discussed.

XRF and SIMS/SNMS analyses of BaxSr1-xTiO3 dielectrics

The development of analytical tools and procedures for process control is a prerequisite for the integration of high permittivity and/or ferroelectric materials in CMOS devices. The thickness and composition of perovskite oxide films were determined by wavelength dispersive X-ray fluorescence analysis (XRF) with special emphasis on the ratio of the group-II elements to the Ti content, and a precision of 0.5% was achieved for a typical film thickness of 20-30 nm. Secondary ion mass spectrometry (SIMS) and sputtered neutrals mass spectrometry (SNMS) was used for depth profiling to determine film homogeneity and elemental interdiffusion at hetero-interfaces. Examples are given for Ba(x)Sr(1-x)TiO(3) and SrTiO(x) thin films which were grown in a prototype MOCVD production tool. No interdiffusion was observed for films grown at 600 degrees C on Pt electrodes in contrast to films grown directly on Si.

Physiology, regulation, and limits of the synthesis of poly(3HB)

The properties of poly(3-hydroxybutyrate) combined with the fact that it can be produced easily by numerous prokaryotes from renewable resources and even from potentially toxic waste products using well-known fermentation processes have generated keen interest in this biopolyester as a substitute for chemo-synthetic petroleum-derived polymers in many applications. However, the high price of poly(3HB) compared with the conventional synthetic materials currently in use has restricted its availability in a wide range of applications. If the economic viability of poly(3HB) production and its competitiveness are to be improved, more must be found out about the phenotypic optimization and the upper limits of bacterial systems as the factory of poly(3HB). In this chapter, two aspects of poly(3HB) are reviewed--poly(3HB) formation as a physiological response to external limitations and overcoming internal bottlenecks, and poly(3HB) as a commercially attractive polyester. From a physiological viewpoint, the ability to synthesize and degrade poly(3HB) is considered an investment in the future and provides organisms with a selective advantage. Poly(3HB) is presented as a strategic survival polymer, and it is shown that growth-associated synthesis is not as rare as reported. The influence of the efficiency and velocity of cell multiplication and product formation, of poly(3HB) content and of productivity on the overall yield, and finally on the economics of the whole process are discussed and evaluated from the technological or consumer's point of view. The specific production rate and poly(3HB) content appear to be more important than the yield coefficients.

TEM and SNMS studies of protective alumina scales on NiCrAlY-alloys

The effect of Si addition on the oxidation behaviour of NiCrAlY alloys in the temperature range 950 bis 1100 degrees C has been investigated. During isothermal oxidation oxide growth rates were practically independent of the Si-content. However during cyclic oxidation Si additions were beneficial. Si additions of 1-2(m)/(0) appeared to shift the onset for spallation to longer times. It was found that Si stabilizes the beta-phase and probably it suppresses the formation of metastable Al(2)O(3) modifications.

Trace and surface analysis of ceramic layers of solid oxide fuel cells by mass spectrometry

For the trace analysis of impurities in thick ceramic layers of a solid oxide fuel cell (SOFC) sensitive solid-state mass spectrometric methods, such as laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and radiofrequency glow discharge mass spectrometry (rf-GDMS) have been developed and used. In order to quantify the analytical results of LA-ICP-MS, the relative sensitivity coefficients of elements in a La(0.6)Sr(0.35)MnO(3) matrix have been determined using synthetic standards. Secondary ion mass spectrometry (SIMS) - as a surface analytical method - has been used to characterize the element distribution and diffusion profiles of matrix elements on the interface of a perovskite/Y-stabilized ZrO(2) layer. The application of different mass spectrometric methods for process control in the preparation of ceramic layers for the SOFC is described.

Comparative studies of MCs + -SIMS and e ? -beam SNMS for quantitative analysis of bulk materials and layered structures

For the quantification of heterostructure depth profiles the knowledge of relative sensitivity factors (RSF) and the influence of matrix effects on the measured profiles is necessary. Matrix dependencies of the measured ion intensities have been investigated for sputtered neutral mass spectrometry (SNMS) and MCs(+)-SIMS. The use of Cs as primary ions for SNMS is advantageous compared to Ar because the depth resolution is improved without changing RSFs determined under Ar bombardment. No significant amount of molecules has been found in the SNMS spectra under Cs bombardment. Using MCs(+)-SIMS the RSFs are matrix dependent. An improvement of depth resolution can be achieved by biasing the sample against the primary ion beam for SNMS due to a reduction of the net energy of the primary ions and a resulting more gracing impact angle.

Quantitative determination of element distributions in silicon based thin film solar cells using SNMS

The determination of elemental distributions in thin film solar cells based on amorphous silicon using electron beam SNMS is possible by quantifying the measured ion intensities. The relative sensitivity factors (RSFs) for all elements measured have to be known. The RSFs have been determined experimentally using implantation and bulk standards with known concentrations of the interesting elements. The measured RSFs have been compared with calculated RSFs. The model used for the calculation of the RSFs takes into account the probability for electron impact ionization and the dwell time of the neutrals inside the postionization region. The comparison between measured and calculated RSF shows, that this model is capable to explain the RSFs for most elements. Differences between calculated and measured values can be explained by the formation of hydride and fluoride molecules (in case of H and F) and influences of the angular distribution of the sputtered neutrals in case of Al. The experimentally determined RSFs have been used for a quantification of depth profiles of the i-, buffer-, p- and front contact layers of a-Si solar cells.

Diabetic patient's compliance with bespoke footwear after healing of neuropathic foot ulcers

OBJECTIVES

To define personal attributes and factors associated with compliance to wearing protective footwear in severely neuropathic diabetic patients with a history of foot ulceration.

DESIGN

Case-control study.

SETTING

Diabetic foot clinic.

SUBJECTS

85 patients regularly attending the foot clinic were assessed after healing of neuropathic foot ulceration.

INTERVENTION

Recommendation of wearing cushioned bespoke shoes instead of normal shoes, prescription of up to 2 pairs of bespoke shoes on request.

MAIN OUTCOME MEASURES

Clinical characteristics and attitudes of compliant patients wearing bespoke shoes (cases) versus non-compliant control patients wearing normal shoes on a random day.

RESULTS

The 51 case patients were significantly older and more often amputated than the 34 controls; they more frequently rated their feets' sickness and their overall health status as less favourable than did controls (p < 0.05). The controls, however, were more often on renal replacement therapy. Although the appearance of bespoke shoes was disliked by all of the patients, and 47% of the cases and 100% of the controls would favour normal shoes for cosmetic reasons, all case patients wore their bespoke shoes according to the physicians recommendation, as compared to 26% of the controls (p < 0.01).

CONCLUSION

Differences in age, perception of foot abnormalities and health status, and other distressing medical conditions (i.e. renal replacement therapy, previous minor amputations) in addition to cosmetic reasons may affect the patients' compliance with bespoke protective footwear.

Outpatient treatment of unilateral diabetic foot ulcers with 'half shoes'

The impact of 'half shoes' in the treatment of neuropathic forefoot ulcers was studied in two groups of diabetic patients, who were treated either by standard treatment alone (retrospective controls, n = 22), or by standard treatment plus 'half shoes' (cases, n = 26). The groups were matched for sex, age, type, and duration of diabetes and ulcer grading. The 'half-shoe' cases' vs controls' median overall healing time was 70 vs 118 days, the median difference being 48 (95% CI: -5 to 82) days (NS). In the case group, hospitalization was required in 1/26 (4%) of patients, vs 9/22 (41%) of the control patients (chi-square, p < 0.01). The home nursing service was required in 23% of the cases vs 18% of the controls (NS). It is concluded that the use of half-shoes, in conjunction with standard treatment provided by a specialized diabetic foot clinic, may reduce the overall healing time and does reduce the hospitalization rate. This has implications for a rational strategy of treating unilateral diabetic neuropathic foot ulcers.

[Skin tests with phytohaemagglutinin (PHA). Correlation with other parameters of cell-mediated immunity (author's transl)]

100 healthy persons were investigated to find out whether there is a correlation between a lymphocyte stimulation (3H-thymidine incorporation in the lymphocyte transformation test) with phytohaemagglutinin, pokeweed mitogen and concanavalin A and the in vivo reactivity to intracutaneous phytohaemagglutinin application (measured as medium diameter of infiltrates). Further we searched for an influence of positive or negative reactivity to the specific antigens trichophytin, candidin and streptokinase-streptodornase. 1. There is a good qualitative correlation in normal persons between in vitro lymphocyte stimulation by phytohaemagglutinin, pokeweed mitogen and concanavalin A and the medium diameter of infiltrates after intracutaneous application of 2 mug phytohaemagglutinin. Using lower doses of phytohaemagglutinin no such correlation could be found. A quantitative correlation between the medium diameter of infiltrates and lymphocyte transformation by phytohaemagglutinin and pokeweed mitogen cannot be demonstrated. For concanavalin A there is a negative correlation significant at the 99% level. 2. In vivo reactivity to phytohaemagglutinin does not differ in persons with negative and positive reactions to the specific antigens. 3. Lymphocyte stimulation by phytohaemagglutinin, pokeweed mitogen and concanavalin A of persons with positive reactions to trichophytin, candidin and streptokinase-streptodornase is significantly greater than in those with negative reactivity. 4. The results indicate in vivo phytohaemagglutinin testing as a good screening method to judge cell-mediated immunocompetence. The general applicability for differentiation of immunodeficient and immunocompetent patients is to be further investigated.