Ultrathin ferroic HfO2-ZrO2 superlattice gate stack for advanced transistors.

With the scaling of lateral dimensions in advanced transistors, an increased gate capacitance is desirable both to retain the control of the gate electrode over the channel and to reduce the operating voltage1. This led to a fundamental change in the gate stack in 2008, the incorporation of high-dielectric-constant HfO2 (ref. 2), which remains the material of choice to date. Here we report HfO2-ZrO2 superlattice heterostructures as a gate stack, stabilized with mixed ferroelectric-antiferroelectric order, directly integrated onto Si transistors, and scaled down to approximately 20 ångströms, the same gate oxide thickness required for high-performance transistors. The overall equivalent oxide thickness in metal-oxide-semiconductor capacitors is equivalent to an effective SiO2 thickness of approximately 6.5 ångströms. Such a low effective oxide thickness and the resulting large capacitance cannot be achieved in conventional HfO2-based high-dielectric-constant gate stacks without scavenging the interfacial SiO2, which has adverse effects on the electron transport and gate leakage current3. Accordingly, our gate stacks, which do not require such scavenging, provide substantially lower leakage current and no mobility degradation. This work demonstrates that ultrathin ferroic HfO2-ZrO2 multilayers, stabilized with competing ferroelectric-antiferroelectric order in the two-nanometre-thickness regime, provide a path towards advanced gate oxide stacks in electronic devices beyond conventional HfO2-based high-dielectric-constant materials.

Publisher Correction: Enhanced ferroelectricity in ultrathin films grown directly on silicon.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Enhanced ferroelectricity in ultrathin films grown directly on silicon.

Ultrathin ferroelectric materials could potentially enable low-power perovskite ferroelectric tetragonality logic and nonvolatile memories1,2. As ferroelectric materials are made thinner, however, the ferroelectricity is usually suppressed. Size effects in ferroelectrics have been thoroughly investigated in perovskite oxides-the archetypal ferroelectric system3. Perovskites, however, have so far proved unsuitable for thickness scaling and integration with modern semiconductor processes4. Here we report ferroelectricity in ultrathin doped hafnium oxide (HfO2), a fluorite-structure oxide grown by atomic layer deposition on silicon. We demonstrate the persistence of inversion symmetry breaking and spontaneous, switchable polarization down to a thickness of one nanometre. Our results indicate not only the absence of a ferroelectric critical thickness but also enhanced polar distortions as film thickness is reduced, unlike in perovskite ferroelectrics. This approach to enhancing ferroelectricity in ultrathin layers could provide a route towards polarization-driven memories and ferroelectric-based advanced transistors. This work shifts the search for the fundamental limits of ferroelectricity to simpler transition-metal oxide systems-that is, from perovskite-derived complex oxides to fluorite-structure binary oxides-in which 'reverse' size effects counterintuitively stabilize polar symmetry in the ultrathin regime.

Twistable Origami and Kirigami: from Structure-Guided Smartness to Mechanical Energy Storage.

For achieving active shape transformable materials and structures, smart materials with shape memory effects along with deliberate structure design are generally used as the critical parameters in realizing structure transformation. Beyond such conventional approaches, here a novel structure-guided multimaterial three-dimensional (3D) printing strategy based on twistable origami structures is demonstrated to realize dynamic smart shape transformation. By thermally or photothermally triggering the prestored energy in the twisted structures, the 3D-printed integrated origami structures based on Miura and square-twist origami structures coupled with modifying by kirigami approaches are enabled to present a variable multistep transformable feature as well as a manipulatable stimulus-response behavior. Such shape transformation configuration allows the integrated origami and kirigami structures for constructing smart structures in delivering dynamic multifunction. More importantly, the shape transformation mechanism also suggests a unique capability in mechanical energy storage and release, promising a novel prototype of mechanical actuators. Implication of the results offers a great platform to construct smart and active structures using structure-guided strategies.

Photocatalysis and Hydrogen Evolution of Al- and Zn-Doped TiO2 Nanotubes Fabricated by Atomic Layer Deposition.

Highly homogeneous Al- and Zn-doped TiO2 nanotubes were fabricated by atomic layer deposition (ALD) via nanolaminated stacks of binary layers of TiO2/Al2O3 and TiO2/ZnO, respectively. The bilayers were alternately deposited on the polycarbonate (PC) membrane template by ALD with various cyclic sequences. The nanotubes in a length of 20 µm and a diameter of 220 nm were obtained after removal of the PC membrane by annealing at 450 °C. The effects of doping composition on the photocatalytic and photoelectrochemical (PEC) activities were investigated. Increasing the Al doping reduced the photocatalytic activity of TiO2 due to formation of charge recombination sites and reduction of hydroxide radicals. In contrast, there was an optimal range of Zn doping to get enhanced photocatalytic activity and higher PEC efficiency. With a doping ratio of 0.01, the hydrogen production rate from water splitting was 6 times higher than that of commercial P25 TiO2. The energy-band diagram of Zn-doped TiO2 determined by ultraviolet photoelectron spectroscopy revealed shift up of the Fermi level to provide more electrons to the conduction band. The photoinduced trapped electrons and holes were detected in Zn-doped TiO2 by in situ electron paramagnetic resonance spectroscopy, which revealed that Ti3+ sites on the surface and surface oxygen vacancies played a key role in promoting the photocatalytic process.

Fabrication of TiO2 on porous g-C3N4 by ALD for improved solar-driven hydrogen evolution.

Porous graphitic carbon nitride (P-g-C3N4) thin sheets were fabricated by a one-step calcination of a mixture of urea, melamine, and ammonia chloride at 550 °C. P-g-C3N4 showed 48% higher photocatalytic H2 production from methanol aqueous solution than conventional urea-derived graphitic carbon nitride (g-C3N4) because the existence of numerous pores reduces the recombination rate of charge carriers. In order to further enhance the photocatalytic activity, TiO2 was uniformly deposited on P-g-C3N4 by 60-300 cycles of atomic layer deposition (ALD) to form the TiO2@P-g-C3N4 composite. They exhibited much higher photocatalytic hydrogen production rates than both TiO2 and P-g-C3N4. Among all composites, the sample deposited with 180 ALD cycles of TiO2 showed the highest H2 production because of optimal diffusion length for electrons and holes. It also performed better than the sample of g-C3N4 deposited with 180 cycles of TiO2.

Constructing Repairable Meta-Structures of Ultra-Broad-Band Electromagnetic Absorption from Three-Dimensional Printed Patterned Shells.

Ultra-broad-band electromagnetic absorption materials and structures are increasingly attractive for their critical role in competing with the advanced broad-band electromagnetic detection systems. Mechanically soft and weak wax-based materials composites are known to be insufficient to serve in practical electromagnetic absorption applications. To break through such barriers, here we developed an innovative strategy to enable the wax-based composites to be robust and repairable meta-structures by employing a three-dimensional (3D) printed polymeric patterned shell. Because of the integrated merits from both the dielectric loss wax-based composites and mechanically robust 3D printed shells, the as-fabricated meta-structures enable bear mechanical collision and compression, coupled with ultra-broad-band absorption (7-40 and 75-110 GHz, reflection loss  smaller than -10 dB) approaching state-of-the-art electromagnetic absorption materials. With the assistance of experiment and simulation methods, the design advantages and mechanism of employing such 3D printed shells for substantially promoting the electromagnetic absorption performance have been demonstrated. Therefore, such universal strategy that could be widely extended to other categories of wax-based composites highlights a smart stage on which high-performance practical multifunction meta-structures with ultra-broad-band electromagnetic absorption could be envisaged.

Giant barocaloric effect in hexagonal Ni2In-type Mn-Co-Ge-In compounds around room temperature.

The most widespread cooling techniques based on gas compression/expansion encounter environmental problems. Thus, tremendous effort has been dedicated to develop alternative cooling technique and search for solid state materials that show large caloric effects. An application of pressure to a material can cause a change in temperature, which is called the barocaloric effect. Here we report the giant barocaloric effect in a hexagonal Ni2In-type MnCoGe0.99In0.01 compound involving magnetostructural transformation, Tmstr, which is accompanied with a big difference in the internal energy due to a great negative lattice expansion(ΔV/V ~ 3.9%). High resolution neutron diffraction experiments reveal that the hydrostatic pressure can push the Tmstr to a lower temperature at a rate of 7.7 K/kbar, resulting in a giant barocaloric effect. The entropy change under a moderate pressure of 3 kbar reaches 52 J kg(-1) K(-1), which exceeds that of most materials, including the reported giant magnetocaloric effect driven by 5 T magnetic field that is available only by superconducting magnets.

AgSCF3-Mediated Trifluoromethylthiolation/Radical Cascade Cyclization of 1,6-Enynes.

A AgSCF3-mediated radical cascade cyclization/trifluoromethylthiolation of 1,6-enynes triggered by a C-C triple bond is developed. This protocol also provides another opportunity to construct a valuable trifluoromethylthio-substituted polycyclic fluorene system through the formations of one C-SCF3 bond and two C-C bonds in a single step.

Pre-treatment metabolic tumor volume and total lesion glycolysis are useful prognostic factors for esophageal squamous cell cancer patients.

OBJECTIVES: To study application of the maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) with 18F-FDG PET/CT for predicting prognosis of esophageal squamous cell cancer (ESC) patients. METHODS: Eighty-six patients with ESC staged from I to IV were prospectively enrolled. Cisplatin-based chemoradiotherapy (CCRT) or palliative chemoradiotherapy were the main treatment methods and none received surgery. 18F-FDG PET/CT scans were performed before the treatment. SUVmax, MTV, and TLG were measured for the primary esophageal lesion and regional lymph nodes. Receiver operating characteristic curves (ROCs) were generated to calculate the P value of the predictive ability and the optimal threshold. RESULTS: MTV and TLG proved to be good indexes in the prediction of outcome for the ESC patients. An MTV value of 15.6 ml and a TLG value of 183.5 were optimal threshold to predict the overall survival (OS). The areas under the curve (AUC) for MTV and TLG were 0.74 and 0.70, respectively. Kaplan-Meier analysis showed an MTV less than 15.6 ml and a TLG less than 183.5 to indicate good media survival time (p value <0.05). In the stage III-IV patient group, MTV could better predict the OS (P < 0.001), with a sensitivity and specificity of 0.80 and 0.67, respectively. CONCLUSIONS: Pre-treatment MTV and TLG are useful prognostic factors in non- surgical ESC.

Factors contributing to de qi in acupuncture randomized clinical trials.

De qi is a core concept of acupuncture and is necessary to produce therapeutic effect. In 2010, de qi has been received as a term in the official extension of the CONSORT Statement. However, there are few articles that discuss which factors have influences on obtaining de qi in clinical trials. This paper aims to explore these factors and give advice on trial design in order to optimize de qi in acupuncture RCTs.

[Serial (18)F-FDG PET-CT imaging during radiotherapy for nasopharyngeal carcinoma: a prospective clinical study].

OBJECTIVE: The primary aim of this prospective study was to use serial (18)F-FDG PET-CT imaging to evaluate the trend of the tumor's maximum standardized uptake value (SUVmax) during radiotherapy (RT) for patients with nasopharyngeal carcinoma (NPC), and to explore the possibility of early evaluation of the tumor bio-metabolic response during radiotherapy. METHODS: Sixty patients with biopsy-proven primary NPC were prospectively enrolled into the study. All patients underwent four (18)F-FDG PET-CT scans: one initial scan before RT/cisplatin based concurrent chemoradiotherapy, at the point of 50 Gy during RT, the end of RT, and one month after RT, respectively. Tumor (18)F-FDG uptake was analyzed according to the World Health Organization pathological type. RESULTS: There was a significant difference (P < 0.001) of the mean of SUVmax of the primary site among pretreatment (11.20 ± 5.37) and posttreatment at the dose of 50 Gy (3.50 ± 1.59), at the end of RT (3.05 ± 1.56) and one month after RT (2.52 ± 1.46). There was also a significant difference (P < 0.001) of the mean of SUVmax of neck node site. However, there was a significant difference of the SUVmax between histological WHO type IIb and type IIa in the primary site (P = 0.046) [(67 ± 19)% reduction at dose 50 Gy for type IIb vs. (55 ± 24)% for type IIa] but not in the lymph nodes. CONCLUSIONS: Early PET scan during or right after RT instead of conventional 3 months interval after RT is indicated to evaluate the tumor response and to develop individualized adaptive radiotherapy in NPC. Our next study will attempt to demonstrate the results based on long-term follow-up data.

A Rasch-based validation of the Hooper Visual Organization Test in Chinese-speaking children.

The aim of this study was to examine the validation of the Hooper Visual Organization Test (HVOT) for use in children by testing for item fit, unidimensionality, item hierarchy, reliability, and screening capacity. A modified scoring system was devised for the HVOT so that children received some credit for being able to describe the function of objects. The HVOT was administered to 630 typically developing school-aged children and 210 children with Down syndrome matched for age and education. Rasch analysis and receiver operating characteristic curve were applied. Rasch analysis of data from typically developing children showed that twelve items were candidates for deletion due to poor fit to the Rasch model, violation of normality and age-related item bias. Removing these items resulted in a shortened version with 18 items that forms a reliable and strong unidimensional, hierarchical scale. The items were well targeted to the ability level of the children tested. Area under the curve for HVOT-18 was 0.84, indicating very good ability to identify visual integration deficit in children with Down syndrome. The 18-item HVOT can be summed to produce an overall index of visual synthetic ability. Subsequent work is needed to validate its use in other childhood disabilities.

Design, synthesis and structure-activity relationship studies of 6-phenyl-4,5-dihydro-3(2H)-pyridazinone derivatives as cardiotonic agents.

Based on our previous study, a variety of 12 novel 6-phenyl-4,5-dihydro-3(2H)-pyridazinone derivatives were synthesized. The structures attributed to the compounds were elucidated using IR, 1H-NMR and mass spectra. The cardiotonic activities of these compounds were assessed by Straub's perfusion method and a clear cardiotonic effect was shown for compounds 1c (2,3-dichloro-N-(4-(4-methyl-6-oxo-1,4,5,6-tetrahydro-pyridazin-3-yl)phenyl) benzamide), 1d (4-amino-3-methyl-N-(4-(4-methyl-6-oxo-1,4,5,6-tetrahydropyridazin-3-yl) phenyl)benzamide), 2a (3-methyl-4-nitro-N-(4-(6-oxo-1,4,5,6-tetrahydro-pyridazin-3-yl)phenyl)benzamide) and 2d (4-amino-3-methyl -N-(4-(6-oxo-1,4,5,6-tetrahydropyridazin-3-yl)phenyl) benzamide) when compared to another 3(2H)-pyridazinone derivative, levosimendan (CAS 141505-33-1). The structure-activity relationships of the compounds were studied using the rough sets theory.

Synthesis and bioactivity of 6-phenyl-4,5-dihydro-3(2H)-pyridazinone derivatives.

A series of 6-phenyl-4,5-dihydro-3(2H)-pyridazinone derivatives was prepared and examined for cardiotonic activity The structures of these new pyridazinone derivatives were confirmed by IR, 1H-NMR and mass spectrum. The cardiotonic activities of these compounds were studied on isolated perfused toad heart and compared with the activity of levosimendan (CAS 141505-33-1). Compound 5a emerged as the mostinteresting compound in this series with potential cardiotonic activity.

Synthesis and bioactivity of aripiprazole derivatives.

Ten aripirazole (CAS 129722-12-9) derivatives were prepared and examined for dopamine receptor antagonist activity. The structures of these newly synthesized compounds were confirmed by their elemental analyses and by IR, 1H-NMR and mass spectra. It was demonstrated that all the new compounds have dopamine receptor antagonist activity to a certain extent. Three compounds showed more potent activity than aripiprazole.

Molecular epidemiology and control of nosocomial methicillin-resistant Staphylococcus aureus infection in a teaching hospital.

BACKGROUND AND PURPOSE: Nosocomial methicillin-resistant Staphylococcus aureus (MRSA) infection is difficult to control. Due to a dramatic increase in the nosocomial MRSA infection rate at our hospital from 2000 to 2001, this study was conducted to identify the source of these infections and the effectiveness of control measures. METHODS: 179 healthcare workers (HCWs) were screened for carriage of MRSA. Starting in April 2001, all patients with MRSA infection or colonization were put in strict contact and cohort isolation. The bacterial isolates of HCW carriers and patients with MRSA infection from April 2001 to September 2001 were subjected to antimicrobial susceptibility testing by disk-diffusion method and molecular typing by pulsed-field gel electrophoresis (PFGE). RESULTS: Fifteen HCWs were found to be carriers of MRSA. They were all given topical mupirocin treatment. After these interventions, the nosocomial MRSA infection rate decreased from 1.23 to 0.53 per 1000 patient-days. All 61 MRSA isolates available for antimicrobial susceptibility testing and molecular typing were multidrug resistant. PFGE study revealed 2 predominant types, type C and type Y, comprising 36 and 12 isolates, respectively. CONCLUSIONS: The current study demonstrates the importance of measures to control nosocomial MRSA infections in hospitals that already have a high incidence of endemic MRSA infection. Elimination of carriage by healthcare workers, and strict contact and cohort isolation are the main effective measures.