Roadmap on thermoelectricity

The increasing energy demand and the ever more pressing need for clean technologies of energy conversion pose one of the most urgent and complicated issues of our age. Thermoelectricity, namely the direct conversion of waste heat into electricity, is a promising technique based on a long-standing physical phenomenon, which still has not fully developed its potential, mainly due to the low efficiency of the process. In order to improve the thermoelectric performance, a huge effort is being made by physicists, materials scientists and engineers, with the primary aims of better understanding the fundamental issues ruling the improvement of the thermoelectric figure of merit, and finally building the most efficient thermoelectric devices. In this Roadmap an overview is given about the most recent experimental and computational results obtained within the Italian research community on the optimization of composition and morphology of some thermoelectric materials, as well as on the design of thermoelectric and hybrid thermoelectric/photovoltaic devices.

Spinterface Effects in Hybrid La0.7Sr0.3MnO3/SrTiO3/C60/Co Magnetic Tunnel Junctions

Orbital hybridization at the Co/C₆₀ interface been has proved to strongly enhance the magnetic anisotropy of the cobalt layer, promoting such hybrid systems as appealing components for sensing and memory devices. Correspondingly, the same hybridization induces substantial variations in the ability of the Co/C₆₀ interface to support spin-polarized currents and can bring out a spin-filtering effect. The knowledge of the effects at both sides allows for a better and more complete understanding of interfacial physics. In this paper we investigate the Co/C₆₀ bilayer in the role of a spin-polarized electrode in the La_0.7Sr_0.3MnO₃/SrTiO₃/C₆₀/Co configuration, thus substituting the bare Co electrode in the well-known La_0.7Sr_0.3MnO₃/SrTiO₃/Co magnetic tunnel junction. The study revealed that the spin polarization (SP) of the tunneling currents escaping from the Co/C₆₀ electrode is generally negative: i.e., inverted with respect to the expected SP of the Co electrode. The observed sign of the spin polarization was confirmed via DFT calculations by considering the hybridization between cobalt and molecular orbitals.

Enhancing Light Emission in Interface Engineered Spin-OLEDs through Spin-Polarized Injection at High Voltages

The quest for a spin-polarized organic light-emitting diode (spin-OLED) is a common goal in the emerging fields of molecular electronics and spintronics. In this device, two ferromagnetic (FM) electrodes are used to enhance the electroluminescence intensity of the OLED through a magnetic control of the spin polarization of the injected carriers. The major difficulty is that the driving voltage of an OLED device exceeds a few volts, while spin injection in organic materials is only efficient at low voltages. The fabrication of a spin-OLED that uses a conjugated polymer as bipolar spin collector layer and ferromagnetic electrodes is reported here. Through a careful engineering of the organic/inorganic interfaces, it is succeeded in obtaining a light-emitting device showing spin-valve effects at high voltages (up to 14 V). This allows the detection of a magneto-electroluminescence (MEL) enhancement on the order of a 2.4% at 9 V for the antiparallel (AP) configuration of the magnetic electrodes. This observation provides evidence for the long-standing fundamental issue of injecting spins from magnetic electrodes into the frontier levels of a molecular semiconductor. The finding opens the way for the design of multifunctional devices coupling the light and the spin degrees of freedom.

Controlling Magnetoresistance by Oxygen Impurities in Mq3-Based Molecular Spin Valves

The understanding of magnetoresistance (MR) in organic spin valves (OSVs) based on molecular semiconductors is still incomplete after its demonstration more than a decade ago. Although carrier concentration may play an essential role in spin transport in these devices, direct experimental evidence of its importance is lacking. We probed the role of the charge carrier concentration by studying the interplay between MR and multilevel resistive switching in OSVs. The present work demonstrates that all salient features of these devices, particularly the intimate correlation between MR and resistance, can be accounted for by the impurity band model, based on oxygen migration. Finally, we highlight the critical importance of the carrier concentration in determining spin transport and MR in OSVs and the role of interface-mediated oxygen migration in controlling the OSV response.

Oxygen Impurities Link Bistability and Magnetoresistance in Organic Spin Valves

Vertical crossbar devices based on manganite and cobalt injecting electrodes and a metal-quinoline molecular transport layer are known to manifest both magnetoresistance (MR) and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the MR and magnetic modulation of bistability. To explain the device functionality, we identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with the chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrate under voltage application, resulting in a modification of the electronic properties of the organic material and of the oxidation state of the interfacial layer with the ferromagnetic contacts. Variable oxygen doping of the organic molecules represents the key element for correlating bistability and MR, and our measurements provide the first experimental evidence in favor of the impurity-driven model describing the spin transport in organic semiconductors in similar devices.

Quantifying the critical thickness of electron hybridization in spintronics materials

In the rapidly growing field of spintronics, simultaneous control of electronic and magnetic properties is essential, and the perspective of building novel phases is directly linked to the control of tuning parameters, for example, thickness and doping. Looking at the relevant effects in interface-driven spintronics, the reduced symmetry at a surface and interface corresponds to a severe modification of the overlap of electron orbitals, that is, to a change of electron hybridization. Here we report a chemically and magnetically sensitive depth-dependent analysis of two paradigmatic systems, namely La_1−xSr_xMnO₃ and (Ga,Mn)As. Supported by cluster calculations, we find a crossover between surface and bulk in the electron hybridization/correlation and we identify a spectroscopic fingerprint of bulk metallic character and ferromagnetism versus depth. The critical thickness and the gradient of hybridization are measured, setting an intrinsic limit of 3 and 10 unit cells from the surface, respectively, for (Ga,Mn)As and La_1−xSr_xMnO₃, for fully restoring bulk properties.

Surface versus bulk effects in electronic structure of spintronics materials are crucial to their applications but are yet well understood. Here the authors experimentally determine the critical thickness that defines the crossover of electron hybridization between surface and bulk for two prototype spintronics materials.

Seed layer technique for high quality epitaxial manganite films

We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

Multilayered Magnetic Gelatin Membrane Scaffolds

A versatile approach for the design and fabrication of multilayer magnetic scaffolds with tunable magnetic gradients is described. Multilayer magnetic gelatin membrane scaffolds with intrinsic magnetic gradients were designed to encapsulate magnetized bioagents under an externally applied magnetic field for use in magnetic-field-assisted tissue engineering. The temperature of the individual membranes increased up to 43.7 °C under an applied oscillating magnetic field for 70 s by magnetic hyperthermia, enabling the possibility of inducing a thermal gradient inside the final 3D multilayer magnetic scaffolds. On the basis of finite element method simulations, magnetic gelatin membranes with different concentrations of magnetic nanoparticles were assembled into 3D multilayered scaffolds. A magnetic-gradient-controlled distribution of magnetically labeled stem cells was demonstrated in vitro. This magnetic biomaterial-magnetic cell strategy can be expanded to a number of different magnetic biomaterials for various tissue engineering applications.

Selective electrochemical decomposition of outgrowths and nanopatterning in La 0.7 Sr 0.3 MnO3 perovskite thin films

The outgrowth formation in inorganic thin films is a dramatic problem that has limited the technological impact of many techniques and materials. Outgrowths are often themselves part of the films, but are detrimental for vertical junctions since they cause short-circuits or work as defects, compromising the reproducibility and in some cases the operation of the corresponding devices. The problem of outgrowth is particularly relevant in ablation-based methods and in some complex oxides, but is present in a large variety of systems and techniques. Here we propose an efficient local electrochemical method to selectively decompose the outgrowths of conductive oxide thin films by electrochemical decomposition, without altering the properties of the background film. The process is carried out using the same set-up as for local oxidation nanolithography, except for the sign of the voltage bias and it works at the nanoscale both as serial method using a scanning probe and as parallel method using conductive stamps. We demonstrated our process using La_0.7Sr_0.3MnO₃ perovskite as a representative material but in principle it can be extended to many other conductive systems.

Ultrahigh vacuum and low-temperature cleaning of oxide surfaces using a low-concentration ozone beam

We present a novel method of delivering a low-concentration (<15%) ozone beam to an ultra-high vacuum environment for the purpose of cleaning and dosing experimental samples through oxidation processing. The system described is safe, low-cost, and practical and overcomes the limitations of ozone transport in the molecular flow environment of high or ultrahigh vacuum whilst circumventing the use of pure ozone gas which is potentially highly explosive. The effectiveness of this method in removing surface contamination is demonstrated through comparison of high-temperature annealing of a simple oxide (MgO) in ozone and oxygen environments as monitored using quadrupole mass spectroscopy and Auger electron spectroscopy. Additionally, we demonstrate the potential of ozone for obtaining clean complex oxide surfaces without the need for high-temperature annealing which may significantly alter surface structure.

A single-device universal logic gate based on a magnetically enhanced memristor

Memristors are one of the most promising candidates for future information and communications technology (ICT) architectures. Two experimental proofs of concept are presented based on the intermixing of spintronic and memristive effects into a single device, a magnetically enhanced memristor (MEM). By exploiting the interaction between the memristance and the giant magnetoresistance (GMR), a universal implication (IMP) logic gate based on a single MEM device is realized.

An independent evaluation of the Age-Related Eye Disease Study (AREDS) cataract grading system

PURPOSE

To assess intra- and interobserver reproducibility of the Age-Related Eye Disease Study (AREDS) system for grading lens opacities and to provide data on its capacity to reliably detect changes in lens status.

METHODS

Independent and replicate grading of 40 sets of lens photographs (one slit-lamp and two retroillumination photographs) were performed by three experienced observers. Patients were participants in the Collaborative Italian-American Clinical Trial of Nutritional Supplements which is testing the effect of a mineral-multivitamin supplement on age-related cataract (CTNS). Scatterplots and intraclass correlation were used to assess measurement error.

RESULTS

Analysis revealed good intra- and interobserver reproducibility of the system. Greatest intraobserver measurement error showed 100% of pairs within 10% areal difference for cortical cataract, 97.5% within 15% areal difference for posterior subcapsular cataract, and 100% within 1 density unit difference for nuclear opacity. Greatest interobserver measurement error showed 95% of pairs within 10% areal difference for cortical cataract, 97.5% within 15% areal difference for posterior subcapsular cataract, and 97.5% within 1.5 density unit difference for nuclear opacity.

CONCLUSIONS

The AREDS lens opacities grading system appears to be sufficiently reliable to detect changes of at least 10% areal involvement for cortical, 15% areal involvement for posterior subcapsular, and 1.0 units for nuclear opacities. It therefore seems sufficiently sensitive to adequately monitor progression of lens opacities in a longitudinal study of patients with early cataract. Its applicability in a population with advanced or complex mixed opacities must await further testing.

[Effects of partial ventriculectomy on left ventricular mechanical properties, shape, and geometry in patients with dilated cardiomyopathy]

PURPOSE

To investigate the short-term effects of the partial ventriculectomy (resection of lateral wall associated to mitral annuloplasty) on cardiac mechanics, contractility, shape and geometry of the left ventricle (LV).

METHODS

Eleven male patients with severe congestive heart failure due to dilated cardiomyopathy were studied. The mean age was 51 +/- 7 years and the functional class was III (five patients) or IV (six patients) before the surgery. Patients were evaluated before and at 17 +/- 4 days after the surgery by simultaneous LV pressure and echocardiographic data. End-diastolic pressure (EDP-mmHg), wall stress (EDS-g/cm2) and diameter (EDD-cm); endsystolic wall stress (ESS) and diameter (ESD), fractional shortening (FS-%) and maximal elastance (Emax-mmHg/ cm/s); the diastolic slope of the pressure-diameter (Kp-mmHg/cm) and stress-strain (Km-g/cm2) loops; shape (L/ EDD, adimensional, where L is the LV long axis) and geometry (Th/EDD, adimensional, where TH is the LV diastolic thickness) were obtained.

RESULTS

1) The ressected muscle fragments (diamond shape) were 10.8 +/- 1.3 cm in length and 5 +/- 0.6 cm in width; 2) all patients were discharged from hospital (15-29 days) in class I (eight cases), II (two), and III (one); 3) it was observed a decrease in EDP (24.3 +/- 7.7 x 17.5 +/- 3.2, p = 0.016); in EDD (8.0 +/- 0.7 x 7.2 +/- 0.8, p = 0.002); in EDS (57.9 +/- 26.8 x 37.4 +/- 19.2, p = 0.005); in ESS (199 +/- 46.9 x 102.8 +/- 33.1, p = 0.004); in ESD (7.1 +/- 0.7 x 5.7 +/- 0.8, p < 0.001); in Kp (22.3 +/- 15.9 x 11.5 +/- 6.9, p = 0.014); and in K(m) (467.4 +/- 212 x 214.6 +/- 87.4, p = 0.01); and, 4) it was noted an increase in FS (11.5 +/- 1.8 x 19.8 +/- 3.9, p < 0.001); in Emax (13.8 +/- 2.2 x 18.6 +/- 3.2, p < 0.001); and in L/EDD (1.32 +/- 0.1 x 1.47 +/- 0.13, p < 0.007) and Th/Dd (0.11 +/- 0.04 x 0.17 +/- 0.08, p < 0.038).

CONCLUSION

The partial ventriculectomy showed multiple significant beneficial effects in these dilated myopathic hearts.

Location and severity of cortical opacities in different regions of the lens in age-related cataract

PURPOSE

To examine the distribution of cortical opacities across the lens in the Italian-American Natural History Study of Age-Related Cataract and to study the association between an index of sunlight exposure and the location of cortical cataract within the lens.

METHODS

Lens photographs of one eye of 731 persons with cortical opacities (503 with pure and 228 with mixed types of opacity) were included in the analysis. A radial grid superimposed on the photographs was used to assess presence, location, and severity of wedge-shaped cortical opacities.

RESULTS

Both the prevalence and the extent of cortical opacities were highest in the inferior-nasal quadrant and lowest in the superior-nasal quadrant of the lens. In polychotomous logistic regression, persons with the greatest excess areal involvement in the inferior half of the lens were more likely to have high exposure to sunlight, as measured by a sunlight index, than persons with excess involvement in the superior half of the lens (odds ratio, 1.73; 95% confidence interval 1.03, 2.93). Excess areal involvement of the inferior lens also was associated with the pure type of cortical cataract and with the total extent of the opacity.

CONCLUSIONS

Age-related cortical opacities occur more frequently inferiorly than superiorly and, to a lesser extent, nasally than temporally. Possibly higher exposure of these lens segments to sunlight may explain this preferential location of cortical opacities.

[Lipoprotein (a), apolipoproteins and the lipid profile late after heart transplantation]

PURPOSE--To evaluate if the levels of lipoprotein (a) [Lp(a)], apolipoproteins (apo) A1, B and the lipid profile (LP) differ among heart transplantation (HT) patients, with coronary artery disease (CAD) and patients without CAD (NL) and if LP discriminates patients with graft vascular disease (GVD). METHODS--A hundred and seventy patients separated in 3 groups: I) HT [n = 43 46 +/- 15 years, 24 months (median) after transplantation], of these 28 were submitted to serial angiography after the first year of transplantation subgroups with GVD (n = 9) and without GVD (NGVD) (n = 19); II) CAD (n = 72, 48 +/- 6 years); III) NL (n = 45, 50 +/- 6 years). RESULTS--HT presented higher apo A1 levels than CAD and NL (1.5 +/- 0.5 vs 1.2 +/- 0.05 vs 1.1 +/- 0.06 g/l p < 0.05 respectively). Apo B was higher on CAD than in HT and NL (1.5 +/- 0.05 vs 1.2 +/- 0.07 vs 1.3 +/- 0.09 g/l p < 0.05). Lp (a) presented a trend to higher levels in HT and CAD than in NL [25(2-97), 24(1-130) and 15 (1-100) mg/dl, p = 0.05)]. However, when individually evaluated against NL Lp(a) levels were higher in HT and CAD (p = 0.019 and 0.03 respectively). LP did not differ between GVD and NGVD. CONCLUSION--Increased Lp(a) levels after transplantation might be related to the high prevalence of GVD. The LP did not discriminate GVD.

Influence of type and severity of pure forms of age-related cataract on visual acuity and contrast sensitivity. Italian American Cataract Study Group

PURPOSE

To compare the relationship between logMAR visual acuity (VA) and cataract severity and between contrast sensitivity (CS) and cataract severity in pure types of age-related lens opacities.

METHODS

Analysis included patients followed in the ongoing Italian-American Study of the Natural History of Age-Related Cataract. Lens opacities were classified and graded according to the Lens Opacities Classification System II (LOCS II). Visual acuity was measured with the Early Treatment Diabetic Retinopathy Study Chart. Contrast sensitivity was measured with the Pelli-Robson chart.

RESULTS

Data from 1,076 eyes were used for the analysis (366 clear lenses; 550, 124, and 36 eyes with cortical, nuclear and posterior subcapsular cataract, respectively). In age-adjusted analyses, increasing severity of all three cataract types was associated with progressively higher logMAR VA, which translates into poorer acuity, and lower CS scores. For both VA and CS, the effect of increasing severity was greatest for nuclear and least for cortical opacities. After adjusting for age and VA, CS scores were no longer associated with cataract type and severity, with the exception of advanced cortical opacities.

CONCLUSIONS

Increased cataract severity, as determined by LOCS II grading, is strongly associated with both VA and CS scores. Contrast sensitivity scores obtained from testing at low spatial frequency do not seem to offer additional information over standard VA testing in early cortical and posterior subcapsular opacities nor in nuclear cataracts.

The effect of cataract severity and morphology on the reliability of the Lens Opacities Classification System II (LOCS II)

Data collected from 3646 eyes in the Italian-American Natural History Study of Age-Related Cataract were used to investigate whether the reliability of the Lens Opacities Classification System II (LOCS II) by the severity of the opacity that is being graded or is influenced by the presence and severity of coexisting opacities. Reliability was assessed by comparing the slit-lamp gradings of two clinical examiners (346 eyes) and the gradings performed at the slit lamp with gradings of photographs (3646 eyes). The severity of cortical and nuclear opacities did not affect the reproducibility of slit-lamp gradings, but clinical grading of posterior subcapsular opacities became more reliable as the severity of the posterior subcapsular opacities increased. More advanced coexisting opacities decreased the agreement in the slit-lamp diagnosis of nuclear, but not cortical or posterior subcapsular, opacities. Comparisons of clinical and photographic gradings showed very good to excellent agreement for nuclear and cortical opacities, regardless of the severity of the specific opacity or the severity of the coexisting opacities. Agreement in diagnosing posterior subcapsular opacities was decreased in eyes with milder posterior subcapsular opacities and in eyes with more severe coexisting nuclear and/or cortical opacities. The effect of the severity of the opacity being graded and the severity of coexisting opacities on the reliability of the LOCS II must be considered in studies that use the system to classify and grade cataracts.