Wafer-scale graphene-ferroelectric HfO2/Ge-HfO2/HfO2 transistors acting as three-terminal memristors.

In this paper we report a set of experiments at the wafer level regarding field-effect transistors with a graphene monolayer channel transferred on the ferroelectric HfO2/Ge-HfO2/HfO2 three-layer structure. This kind of transistor has a switching ratio of 103 between on and off states due to the bandgap in graphene induced by the ferroelectric structure. Both top and back gates effectively control the carriers' charge flow in graphene. The transistor acts as a three-terminal memristor, termed a memtransistor, with applications in neuromorphic computation.

Efficacy of annealing and fabrication parameters on photo-response of SiGe in TiO2 matrix.

SiGe nanoparticles dispersed in a dielectric matrix exhibit properties different from those of bulk and have shown great potential in devices for application in advanced optoelectronics. Annealing is a common fabrication step used to increase crystallinity and to form nanoparticles in such a system. A frequent downside of such annealing treatment is the formation of insulating SiO2 layer at the matrix/SiGe interface, degrading the optical properties of the structure. An annealing process that could bypass this downside would therefore be of great interest. In this work, a short-time furnace annealing of a SiGe/TiO2 system is applied to obtain SiGe nanoparticles without formation of the undesired SiO2 layer between the dielectric matrix (TiO2) and SiGe. The structures were prepared by depositing alternate layers of TiO2 and SiGe films, using direct-current magnetron sputtering technique. A wide range spectral response with a response-threshold up to ∼1300 nm was obtained, accompanied with an increase in photo-response of more than two-orders of magnitude. Scanning electron microscopy, transmission electron microscopy, energy-dispersive x-ray spectroscopy and grazing incidence x-ray diffraction were used to analyze the morphological changes in respective structures. Photoconductive properties were studied by measuring photocurrent spectra using applied dc-voltages at various temperatures.

Orthorhombic HfO2 with embedded Ge nanoparticles in nonvolatile memories used for the detection of ionizing radiation.

Trilayer memory capacitors of control HfO2/floating gate of Ge nanoparticles in HfO2/tunnel HfO2/Si substrate deposited by magnetron sputtering and subsequently annealed are investigated for the first time for applications in radiation dosimetry. In the floating gate (FG), amorphous Ge nanoparticles (NPs) are arranged in two rows inside the HfO2 matrix. The HfO2 matrix is formed of orthorhombic/tetragonal nanocrystals (NCs). The adjacent thin films to the FG are also formed of orthorhombic/tetragonal HfO2 NCs. This phase is formed during annealing, in samples with thick control HfO2, in the presence of Ge, being induced by the stress. In the rest of the control oxide, HfO2 NCs are monoclinic. Orthorhombic HfO2 has ferroelectric properties and therefore enhances the memory window produced by charge storage in Ge NPs to above 6 V. The high sensitivity of 0.8 mV Gy-1 to α particle irradiation from a 241Am source was measured by monitoring the flatband potential during radiation exposure after electrical writing of the memory.

Single layer of Ge quantum dots in HfO2 for floating gate memory capacitors.

High performance trilayer memory capacitors with a floating gate of a single layer of Ge quantum dots (QDs) in HfO2 were fabricated using magnetron sputtering followed by rapid thermal annealing (RTA). The layer sequence of the capacitors is gate HfO 2/floating gate of single layer of Ge QDs in HfO 2/tunnel HfO 2/p-Si wafers. Both Ge and HfO2 are nanostructured by RTA at moderate temperatures of 600-700 °C. By nanostructuring at 600 °C, the formation of a single layer of well separated Ge QDs with diameters of 2-3 nm at a density of 4-5 × 1015 m-2 is achieved in the floating gate (intermediate layer). The Ge QDs inside the intermediate layer are arranged in a single layer and are separated from each other by HfO2 nanocrystals (NCs) about 8 nm in diameter with a tetragonal/orthorhombic structure. The Ge QDs in the single layer are located at the crossing of the HfO2 NCs boundaries. In the intermediate layer, besides Ge QDs, a part of the Ge atoms is segregated by RTA at the HfO2 NCs boundaries, while another part of the Ge atoms is present inside the HfO2 lattice stabilizing the tetragonal/orthorhombic structure. The fabricated capacitors show a memory window of 3.8 ± 0.5 V and a capacitance-time characteristic with 14% capacitance decay in the first 3000-4000 s followed by a very slow capacitance decrease extrapolated to 50% after 10 years. This high performance is mainly due to the floating gate of a single layer of well separated Ge QDs in HfO2, distanced from the Si substrate by the tunnel oxide layer with a precise thickness.

Rolling dopant and strain in Y-doped BiFeO3 epitaxial thin films for photoelectrochemical water splitting.

We report significant photoelectrochemical activity of Y-doped BiFeO3 (Y-BFO) epitaxial thin films deposited on Nb:SrTiO3 substrates. The Y-BFO photoanodes exhibit a strong dependence of the photocurrent values on the thickness of the films, and implicitly on the induced epitaxial strain. The peculiar crystalline structure of the Y-BFO thin films and the structural changes after the PEC experiments have been revealed by high resolution X-ray diffraction and transmission electron microscopy investigations. The crystalline coherence breaking due to the small ionic radius Y-addition was analyzed using Willliamson-Hall approach on the 2θ-ω scans of the symmetric (00 l) reflections and confirmed by high resolution TEM (HR-TEM) analysis. In the thinnest sample the lateral coherence length (L∥) is preserved on larger nanoregions/nanodomains. For higher thickness values L∥ is decreasing while domains tilt angles (αtilt) is increasing. The photocurrent value obtained for the thinnest sample was as high as Jph = 0.72 mA/cm2, at 1.4 V(vs. RHE). The potentiostatic scans of the Y-BFO photoanodes show the stability of photoresponse, irrespective of the film's thickness. There is no clear cathodic photocurrent observation for the Y-BFO thin films confirming the n-type semiconductor behavior of the Y-BFO photoelectrodes.

Dense Ge nanocrystals embedded in TiO2 with exponentially increased photoconduction by field effect.

Si and Ge nanocrystals in oxides are of a large interest for photo-effect applications due to the fine-tuning of the optical bandgap by quantum confinement in nanocrystals. In this work, dense Ge nanocrystals suitable for enhanced photoconduction were fabricated from 60% Ge in TiO2 amorphous layers by low temperature rapid thermal annealing at 550 °C. An exponential increase of the photocurrent with the applied voltage was observed in coplanar structure of Ge nanocrystals composite films deposited on oxidized Si wafers. The behaviour was explained by field effect control of the Fermi level at the Ge nanocrystals-TiO2 layer/substrate interfaces. The blue-shift of the absorption gap from bulk Ge value to 1.14 eV was evidenced in both photocurrent spectra and optical reflection-transmission experiments, in good agreement with quantum confinement induced bandgap broadening in Ge nanocrystal with sizes of about 5 nm as found from HRTEM and XRD investigations. A nonmonotonic spectral dependence of the refractive index is associated to the Ge nanocrystals formation. The nanocrystal morphology is also in good agreement with the Coulomb gap hopping mechanism of T-1/2 -type explaining the temperature dependence of the dark conduction.

Joining Chemical Pressure and Epitaxial Strain to Yield Y-doped BiFeO3 Thin Films with High Dielectric Response.

BiFeO3 is one of the most promising multiferroic materials but undergoes two major drawbacks: low dielectric susceptibility and high dielectric loss. Here we report high in-plane dielectric permittivity (ε' ∼2500) and low dielectric loss (tan δ < 0.01) obtained on Bi0.95Y0.05FeO3 films epitaxially grown on SrTiO3 (001) by pulsed laser deposition. High resolution transmission electron microscopy and geometric phase analysis evidenced nanostripe domains with alternating compressive/tensile strain and slight lattice rotations. Nanoscale mixed phase/domain ensembles are commonly found in different complex materials with giant dielectric/electromechanical (ferroelectric/ relaxors) or magnetoresistance (manganites) response. Our work brings insight into the joined role of chemical pressure and epitaxial strain on the appearance of nanoscale stripe structure which creates conditions for easy reorientation and high dielectric response, and could be of more general relevance for the field of materials science where engineered materials with huge response to external stimuli are a highly priced target.

Human atheromatous plaque extracts induce tissue factor activity (TFa) in monocytes and also express constitutive TFa.

Tissue factor activity (TFa) is a major activator of the coagulation cascade and may play a role in atheroma-induced thrombosis. Monocyte-macrophages (MO-MF) generate considerable quantities of TFa when stimulated by a variety of inducers. To test the hypothesis that MO could be induced by atheromatous plaque to generate TFa, plaque extracts obtained from patients with obstructive atheromatous disease were used. These extracts were also assayed for constitutive TFa. The constitutive activity was variable from extract to extract but could be very high, up to 250 U TFa. The TFa induced in MO could be also very high, up to 200 U (i.e. 1/5 of the TFa of full strength rabbit brain thromboplastin). These findings point to a major role for MO-MF TFa in the induction or thrombosis by atheromatous plaque.

Hemodialysis access placement with preoperative noninvasive vascular mapping: comparison between patients with and without diabetes.

We retrospectively analyzed data on preoperative vascular mapping in 195 consecutive patients to investigate the common belief that patients with diabetes are poor candidates to have an arteriovenous fistula placed as dialysis access because they lack suitable blood vessels. There was no difference in venous diameter, arterial diameter, and arterial peak systolic velocity measurements between patients with and without diabetes. Patients with diabetes had a greater prevalence of vascular calcifications and greater cuff measurements of systolic segmental arterial pressure. In 140 of 195 patients, subsequent vascular access surgery had been performed in our institution, and 127 of these patients were on hemodialysis therapy at the end of the study period. There was no difference in the prevalence of fistula placement (66% versus 60%; chi-square = 2.6; df = 2; P = 0.28, not significant [NS]) and percentage of functioning fistulae between patients with and without diabetes (67% versus 62%; chi-square = 0.27; df = 1; P = 0.61, NS). The percentage of patients dialyzed through a temporary catheter was equal in patients with and without diabetes (18%). In summary, patients with diabetes seem to be as good candidates for arteriovenous fistula placement as patients without diabetes. Additional studies are required to determine the long-term outcome of fistulae in patients with diabetes.

Gold-induced colitis: a case report and review of the literature.

A case of severe colitis requiring subtotal colectomy following administration of 35 mg Solganal b for intractable arthritis is described. Abdominal pain and watery diarrhea developed six weeks after the last dose of gold. Colonoscopy revealed mucosal edema and ulceration of the entire colon. Supportive measures failed and the patient required subtotal colectomy. Review of the literature revealed 29 cases, ranging in severity from limited ileal involvement to fulminant panenteritis. Most of the patients responded to intravenous fluids, steroids, and antibiotics, but four required surgery. The case described is notable for the delay in appearance of abdominal symptoms following the cessation of gold therapy. The mechanism of injury is unknown. Abdominal complaints in a patient who has received gold therapy, especially parenteral, merit strict attention, even if occurring several weeks after the final dose, and the diagnosis of gold colitis should be entertained.

Regional procurement and export of hepatic allografts for transplantation.

A team dedicated to hepatic procurement exclusively for export to distant centers was established at The Mount Sinai Hospital in New York. Between January 1987 and March 1988, 20 livers were retrieved and sent to five institutions in the U.S. and Canada for implantation. These procedures were carried out in concert with local cardiac and renal procurement teams; 12 hearts and 34 kidneys were used from these 20 donors. Functional results of both the livers and the other organs were in line with nationally reported standards. The multi-organ procurement procedure was streamlined as a result of the coordination which developed between the teams. Savings in time and travel expense by skilled personnel were realized; in five cases no alternative hepatic procurement team was available. With the ability to preserve livers for increasingly long periods, this type of program will assume greater importance in the future.

Treatment of "swing point stenoses" in hemodialysis arteriovenous fistulae.

AIM: This is a retrospective study of percutaneous transluminal balloon angioplasty (PTA) efficacy for treatment of surgical vein mobilization site ("swing point") stenoses in hemodialysis arteriovenous fistulae (AVF) that fail to mature or are poorly functioning. METHOD: Between February 1, 1999, and February 28, 2001, 65 non-maturing or poorly functioning AVF were studied in 63 consecutive hemodialysis patients (30 male, 33 female, aged 26-92 years). All AVF underwent contrast angiography to study the inflow artery, AVF, outflow and central veins. PTA of stenotic sites was performed to initiate or restore AVF function. RESULTS: Seventy-eight venous and 2 arterial stenoses were found and treated with PTA in the 65 AVF. All PTA were technically successful. A total of 55 stenoses were identified in the vein at the site of surgical mobilization ("swing point"). Additionally, 19 cephalic and 4 central venous stenoses were found. During the study, 13 AVF underwent repeat PTA at the "swing point". Of the 65 AVF treated, 50 were being successfully used as an access site, 4 AVF were lost during follow-up (34-688 days; mean: 258 days) and 8 patients died within the study period. The duration of functional patency of the treated AVF was 39-660 days (mean: 280 days). CONCLUSION: Non-maturing or poorly functioning AVF frequently have stenoses in the outflow vein at the original site of surgical vein mobilization. These "swing point stenoses" are amenable to PTA, which is a safe and effective treatment for prolonging AVF patency and function.

Obese and non-obese hemodialysis patients have a similar prevalence of functioning arteriovenous fistula using pre-operative vein mapping.

AIMS: The arteriovenous fistula (AVF) is the preferred hemodialysis access. Subset analyses of both the HEMO and DOPPS studies have shown that obese hemodialysis patients have a lower prevalence of functioning AVF. Doppler ultrasound may increase the prevalence of functioning AVF in obese subjects. PATIENTS AND METHODS: The effect of pre-operative vein mapping employed between 10/01/98 and 12/08/00 on the prevalence of functioning AVF in a single university hemodialysis program was studied. Preoperative ultrasound was performed to study venous and arterial systems on both arms. RESULTS: There were 50 obese patients, defined as bodymass index (BMI) > or = 27 kg/m2, and 130 patients with a lower BMI. The groups were similar in mean age and diabetes prevalence. The obese group had statistically significantly more females 34/50 versus 61/130 with p = 0.01. There was no statistically significant difference between the vein mapping parameters studied in the two BMI groups, including mean mid-forearm cephalic vein diameter, distal radial artery peak systolic velocity and subclavian vein patency. No obese patient required venography. There was no significant difference between the number of functioning AVF in both groups (22/50 obese, 48/130 lower BMI, p = 0.24). CONCLUSIONS: Pre-operative vein mapping is associated with a similar prevalence of functioning AVF in obese and lower BMI patients. Pre-operative ultrasound screening is a useful tool to promote AVF placement in obese patients.

Management of thrombophlebitis in the prepartum period. A case report.

The case of a 30-year-old female who presented with acute onset of ileofemoral thrombophlebitis during the 37th week of pregnancy is presented. Treatment with intravenous infusion of heparin was initiated on the day of admission. The following day, the patient went into active labor. Heparin was stopped, and a Greenfield filter was placed in the suprarenal inferior vena cava. Six hours later, the patient had a normal vaginal delivery. Fifteen hours after delivery, heparin was restarted. The patient was discharged eight days later on therapeutic levels of Coumadin. Anticoagulation was maintained for six months and at one year she was asymptomatic.

Transcutaneous oxygen tension in subjects with tetraplegia with and without pressure ulcers: a preliminary report.

This study compared transcutaneous oxygen tension (TcpO2) in subjects with paraplegia and pressure ulcers (PU), those with paraplegia and no pressure ulcer (NPU), and ambulatory controls. TcpO2 was measured using a surface-electrode monitoring system, recorded at 1-min intervals for 5 min and averaged. Mean TcpO2 was significantly lower in the PU than the NPU and control groups (23.53+/-1.83 vs. 58.93+/-2.53 and 79.70+/-6.77 mmHg, respectively, p<0.05). In a PU subgroup (n=4) mean TcpO2 of the pressure ulcer and nonpressure ulcer sides (trochanter or ischium) were significantly different (21.05+/-2.98 vs. 67.65+/-2.11 mmHg, respectively, p<0.001). Additionally, the NPU group demonstrated significantly lower TcpO2 than the controls. PUs had a greater reduction in TcpO2 levels relative to controls than NPUs. No association was found between TcpO2 and duration of injury, completeness of lesion, or smoking history. Thus, TcpO2 may be an effective method to identify individuals who are susceptible to pressure ulcers. The further attenuation of TcpO2 observed in the PU group may be useful to help predict whether ulcers will heal with local care or will require additional treatment.

Vascular screening prior to placement of tunnelled and cuffed hemodialysis catheters.

PURPOSE: To demonstrate the importance of venous vascular screening before the placement of tunneled and cuffed hemodialysis catheters in patients requiring hemodialysis prior to placement and/or maturation of an arteriovenous fistula (AVF) or graft (AVG). METHODS: Between October 1998 and March 2000, all patients requiring hemodialysis access placement were prospectively evaluated with duplex ultrasound for status of upper extremity vessels and central veins prior to selection of a permanent access site. When interim tunneled and cuffed hemodialysis catheters were required, they were placed on the side contralateral to proposed AVF/AVG placement. No catheters were placed without initial vascular screening. The study group was compared to historical controls during a similar period (April 1997 through September 1998) when no vascular screening was performed. RESULTS: During the study period, 234 screening duplex ultrasound examinations were performed in 244 patients. Ten patients required no screening prior to access site placement. Overall, 353 catheters were placed, 243 (69%) on the right side and 110 (31%) on the left side. During the control period, 394 catheters were placed in 255 patients, 306 (78%) right-sided and 88 (22%) left-sided. The increase in left-sided catheters with ultrasound screening and careful planning for future access sites was significant (p<0.01). CONCLUSION: Vascular-screening-directed catheter placement significantly alters the side of catheter placement when compared to a management protocol without prior screening. Such screening helps identify the side of permanent access placement, while directing interim catheters to the contralateral side such that central veins may be preserved for permanent access.

In vitro toxicity evaluation of Ti(4+)-stabilized γ-Bi2O3 sillenites.

We report results regarding the in vitro toxicology of γ-Bi2O3 represented by its isomorphous phase Bi12TiO20 (γ-BTO). The γ-BTO microparticles were synthesized by two methods: coprecipitation from a bismuth nitrate-tetrabutyl titanate solution and solid state reaction of Bi2O3 and TiO2 oxides. The structural and morphological characteristics of the obtained materials were determined using X-ray diffraction (XRD), selected area electron diffraction (SAED), transmission (TEM) and scanning (SEM) electron microscopy. The elemental composition was investigated using energy dispersive spectrometry (EDS). The cytotoxicity and oxidative/nitrosative stress (intracellular reactive oxygen species (ROS) and nitric oxide (NO) release) induced by the studied microparticles in HepG2, SH-SY5Y and 3T3-L1 cell cultures were determined using the MTT, DCF-DA (2',7'-dichlorfluorescein-diacetate) and Griess methods respectively. Depending on the cell type and γ-BTO concentration, results showed only weak cytotoxic effects after 24h of γ-BTO exposure and cell proliferation effects for longer treatment times. Only reduced NO release increases (corresponding to high γ-BTO concentrations) were detected in case of SH-SY5Y and 3T3-L1 cells. The intracellular ROS production (higher for HepG2 cells) appeared inversely proportional to the γ-BTO concentration. The obtained results indicated a promising in vitro biocompatibility of γ-BTO and encourage further studies regarding its potential for biomedical applications.

Value of drug-eluting stents after failed percutaneous transluminal angioplasty in the infrapopliteal vessels for the treatment of critical limb ischemia: favorable mid-term patency and limb salvage results.

AIM: The endovascular treatment of infrapopliteal arterial disease in the setting of critical limb ischemia (CLI) is increasing in use. In patients in whom percutaneous transluminal angioplasty (PTA) resulted in suboptimal angiographic results, flow limiting dissection or re-coil is thought to limit clinical success. This single-center experience examines the angiographic and clinical results when Drug-Eluting Stents (DES) were placed in a large cohort of patients with CLI after immediate infrapopliteal PTA failure. METHODS: A retrospective review of a prospectively collected single-center endovascular database was performed. Sixty-seven Rutherford grade 4, 5, and 6 patients were treated between October 2005 and February 2010 with PTA because lack of an acceptable autologous vein for bypass-grafting or severe medical comorbidities precluded them from surgical bypass. The study cohort had suboptimal angiographic results immediately after PTA that was subsequently treated with DES. Patients were then placed on clopidogrel and aspirin indefinitely. Angiographic, clinical, and the results of noninvasive vascular examinations were collected. RESULTS: In total, 123 stents (94 sirolimus, 27 everolimus, 2 paclitaxel) were placed in 67 patients to treat a total of 84 angiographic lesions. Simultaneous femoral-popliteal intervention was performed in 66% of the patients while 45% of the treated lesions were total occlusions. Lesion length ranged from 17 mm-142 mm (mean 50 mm). Initial technical success was 100%, with all 84 lesions being treated successfully with less than 10% stenosis after stent implantation. Mean follow-up was 20 months (1-42 months) with 6, 12, and 24-month primary patency rates of 90%, 86%, and 72% respectively. Freedom from major amputation was 91.1% (61/67) with all six amputations occurring in the Rutherford grade 6 group (6/11). Overall mortality rate was 19% (13/67) with one death occurring within 30 days. CONCLUSION: The use of drug-eluting stents following suboptimal PTA for the treatment of infrapopliteal arterial disease in this cohort of patients with CLI produced high primary patency and limb salvage rates supporting the efficacy of this treatment strategy.

Common iliac artery pseudoaneurysm following inguinal hernia repair--a case report and literature review.

The authors report a patient presented with a ruptured infected iliac artery pseudoaneurysm 2 weeks after ipsilateral inguinal hernia repair. Pseudoaneurysms that occur because of infection develop rapidly and mandate ligation of the affected artery and extraanatomic bypass. Noninfected pseudoaneurysms are usually discovered incidentally and may be managed with either endovascular or standard surgical techniques. A percutaneously placed aortic occlusion balloon may prevent exsanguination, when used as an adjunct to surgical repair in cases of ruptured pseudoaneurysm.