Bayesian optimization of hydrogen plasma treatment in silicon quantum dot multilayer and application to solar cells.

Silicon quantum dot multilayer (Si-QDML) is a promising material for a light absorber of all silicon tandem solar cells due to tunable bandgap energy in a wide range depending on the silicon quantum dot (Si-QD) size, which is possible to overcome the Shockley-Queisser limit. Since solar cell performance is degenerated by carrier recombination through dangling bonds (DBs) in Si-QDML, hydrogen termination of DBs is crucial. Hydrogen plasma treatment (HPT) is one of the methods to introduce hydrogen into Si-QDML. However, HPT has a large number of process parameters. In this study, we employed Bayesian optimization (BO) for the efficient survey of HPT process parameters. Photosensitivity (PS) was adopted as the indicator to be maximized in BO. PS (σp/σd) was calculated as the ratio of photoconductivity (σp) and dark conductivity (σd) of Si-QDML, which allowed the evaluation of important electrical characteristics in solar cells easily without fabricating process-intensive devices. 40-period layers for Si-QDML were prepared by plasma-enhanced chemical vapor deposition method and post-annealing onto quartz substrates. Ten samples were prepared by HPT under random conditions as initial data for BO. By repeating calculations and experiments, the PS was successfully improved from 22.7 to 347.2 with a small number of experiments. In addition, Si-QD solar cells were fabricated with optimized HPT process parameters; open-circuit voltage (VOC) and fill factor (FF) values of 689 mV and 0.67, respectively, were achieved. These values are the highest for this type of device, which were achieved through an unprecedented attempt to combine HPT and BO. These results prove that BO is effective in accelerating the optimization of practical process parameters in a multidimensional parameter space, even for novel indicators such as PS.

Fabrication of light trapping structures specialized for near-infrared light by nanoimprinting for the application to thin crystalline silicon solar cells.

Vehicle-integrated photovoltaics (VIPV) are gaining attention to realize a decarbonized society in the future, and the specifications for solar cells used in VIPV are predicated on a low cost, high efficiency, and the ability to be applied to curved surfaces. One way to meet these requirements is to make the silicon substrate thinner. However, thinner substrates result in lower near-infrared light absorption and lower efficiency. To increase light absorption, light trapping structures (LTSs) can be implemented. However, conventional alkali etched pyramid textures are not specialized for near-infrared light and are insufficient to improve near-infrared light absorption. Therefore, in this study, as an alternative to alkaline etching, we employed a nanoimprinting method that can easily fabricate submicron-sized LTSs on solar cells over a large area. In addition, as a master mold fabrication method with submicron-sized patterns, silica colloidal lithography was adopted. As a result, by controlling silica coverage, diameter of silica particles (D), and etching time (tet), the density, height, and size of LTSs could be controlled. At the silica coverage of 40%, D = 800 nm, and tet = 5 min, the reduction of reflectance below 65% at 1100 nm and the theoretical short-circuit current gain of 1.55 mA/cm2 was achieved.

Epitaxial growth of SiGe films by annealing Al-Ge alloyed pastes on Si substrate.

A simple, low-cost, and non-vacuum epitaxial growth method to realize large-area semiconductors on crystalline silicon will become the game-changer for various applications. For example, we can expect the disruptive effect on the cost of large-scale III-V multi-junction solar cells if we could replace the high-cost germanium substrate with silicon-germanium (SiGe) on Si. For SiGe epitaxial growth, we attempted to develop a process using original Al-Ge pastes for screen printing and subsequent annealing. We compare two pastes including Al-Ge alloyed pastes with compositional uniformity in each particle and Al-Ge mixed pastes. We revealed that Al-Ge alloyed paste could form flatter SiGe film with much less residual pastes, supported by in-situ observations. The uniform and sufficient dissolution of the alloyed paste is responsible for these and led to higher average Ge-composition by annealing at 500 °C. The composition in SiGe was vertically graded up to ~ 90% at the topmost surface. These results show that printing and firing of Al-Ge alloyed paste on Si is the desirable, simple, and high-speed process for epitaxial growth of SiGe, which could be potentially used as the lattice-matched virtual substrate with III-V semiconductors.

A Wireless Sensor Network for Growth Environment Measurement and Multi-Band Optical Sensing to Diagnose Tree Vigor.

We have tried to develop the guidance system for farmers to cultivate using various phenological indices. As the sensing part of this system, we deployed a new Wireless Sensor Network (WSN). This system uses the 920 MHz radio wave based on the Wireless Smart Utility Network that enables long-range wireless communication. In addition, the data acquired by the WSN were standardized for the advanced web service interoperability. By using these standardized data, we can create a web service that offers various kinds of phenological indices as secondary information to the farmers in the field. We have also established the field management system using thermal image, fluorescent and X-ray fluorescent methods, which enable the nondestructive, chemical-free, simple, and rapid measurement of fruits or trees. We can get the information about the transpiration of plants through a thermal image. The fluorescence sensor gives us information, such as nitrate balance index (NBI), that shows the nitrate balance inside the leaf, chlorophyll content, flavonol content and anthocyanin content. These methods allow one to quickly check the health of trees and find ways to improve the tree vigor of weak ones. Furthermore, the fluorescent x-ray sensor has the possibility to quantify the loss of minerals necessary for fruit growth.

Graphene growth on a Pt(111) substrate by surface segregation and precipitation.

We report on the fabrication of a sizable graphene sheet on a carbon-doped Pt(111) substrate through surface segregation and precipitation. Scanning Auger electron spectroscopy (AES) reveals that the graphene covered more than 98% of the substrate surface. Our graphene consists of single-layer graphene across the substrate with fractions of several micrometer wide bi- and tri-layer graphene islands. We also show that the number of graphene layers can be precisely determined by analyzing AES data. While Raman spectroscopy is usually used to study graphene on SiO2, we show that AES is a powerful tool to characterize graphene grown on metal substrates.

Transport of deposited atoms throughout strain-mediated self-assembly.

Using enriched isotopes, we developed a method to elucidate the long-standing issue of Ge transport governing the strain-driven self-assembly. Here 76Ge was employed to form the 2D metastable layer on a Si(001) surface, while the 3D transition and growth were completed by additional evaporation of 70Ge. This isotope tracing combined with the analysis of the Ge-Ge LO phonon enables the tracking of the origin of Ge atoms and their flow towards the growing islands. This atomic transport was quantified based on the quasiharmonic approximation of Ge-Ge vibrations and described using a rate equation model.

Unique synthesis of few-layer graphene films on carbon-doped Pt(83)Rh(17) surfaces.

We report a unique synthesis of single- and few-layer graphene films on carbon-doped Pt(83)Rh(17) surfaces by surface segregation and precipitation. The ultrathin graphene films were characterized by atomic force microscopy, Auger electron spectroscopy, and micro-Raman spectroscopy measurements, providing evidence of graphene film thickness and structural quality. The G and 2D band intensity images from micro-Raman spectroscopy measurements confirm that the graphene films with different coverage have very limited defects. Additionally, the 2D band peak can be well-fitted by a single Lozentian peak, indicating that graphene films are characteristic of single layer graphene. Graphene film thickness can be determined by analysis of Auger spectra, indicating that graphene films after 850 degrees C annealing mainly consist of monolayer graphene. By precise adjustment of annealing temperature, graphene film thickness and area size can be controlled and uniform large-area single-layer and double-layer graphene can be achieved.

PSF1, a DNA replication factor expressed widely in stem and progenitor cells, drives tumorigenic and metastatic properties.

PSF1 (partner of sld five 1) is an evolutionarily conserved DNA replication factor implicated in DNA replication in lower species that is strongly expressed in a wide range of normal stem cell populations and progenitor cell populations. Because stem and progenitor cells possess high proliferative capacity, we hypothesized that PSF1 may play an important role in tumor growth. To begin to investigate PSF1 function in cancer cells, we cloned the mouse PSF1 promoter and generated lung and colon carcinoma cells that stably express a PSF1 promoter-reporter gene. Reporter expression in cells correlated with endogenous PSF1 mRNA expression. In a tumor cell xenograft model, high levels of reporter expression correlated with high proliferative activity, serial transplantation potential, and metastatic capability. Notably, cancer cells expressing reporter levels localized to perivascular regions in tumors and displayed expression signatures related to embryonic stem cells. RNAi-mediated silencing of endogenous PSF1 inhibited cancer cell growth by disrupting DNA synthesis and chromosomal segregation. These findings implicate PSF1 in tumorigenesis and offer initial evidence of its potential as a theranostic target.

Hemorrhagic shock and encephalopathy syndrome--the markers for an early HSES diagnosis.

BACKGROUND: The hemorrhagic shock and encephalopathy syndrome (HSES) is a devastating disease that affects young children. The outcomes of HSES patients are often fatal or manifesting severe neurological sequelae. We reviewed the markers for an early diagnosis of HSES. METHODS: We examined the clinical, biological and radiological findings of 8 patients (4 months to 9 years old) who met the HSES criteria. RESULTS: Although cerebral edema, disseminated intravascular coagulopathy (DIC), and multiple organ failure were seen in all 8 cases during their clinical courses, brain computed tomography (CT) scans showed normal or only slight edema in 5 patients upon admission. All 8 patients had normal platelet counts, and none were in shock. However, they all had severe metabolic acidosis, which persisted even after 3 hours (median base excess (BE), -7.6 mmol/L). And at 6 hours after admission (BE, -5.7 mmol/L) they required mechanical ventilation. Within 12 hours after admission, fluid resuscitation and vasopressor infusion for hypotension was required. Seven of the patients had elevated liver enzymes and creatine kinase (CK) upon admission. Twenty-four hours after admission, all 8 patients needed vasopressor infusion to maintain blood pressure. CONCLUSION: CT scan, platelet count, hemoglobin level and renal function upon admission are not useful for an early diagnosis of HSES. However, the elevated liver enzymes and CK upon admission, hypotension in the early stage after admission with refractory acid-base disturbance to fluid resuscitation and vasopressor infusion are useful markers for an early HSES diagnosis and helpful to indicate starting intensive neurological treatment.

Effect of 2-methoxyestradiol, buthionine sulfoximine and hydrogen peroxide on the viability of renal carcinoma cell lines (ACHN and ACVB).

2-Methoxyestradiol (2-ME), an endogenous metabolite of 17beta-estradiol, induces the intracellular accumulation of superoxide anion (O2*-) and buthionine sulfoximine (BSO) is an inhibitor of glutathione (GSH) synthesis. We have examined the combination anticancer effect of 2-ME and BSO accompanied with hydrogen peroxide (H2O2). 2-ME inhibited cell growth in renal carcinoma cell lines (ACHN and ACVB) accompanied by an increase in the intracellular contents of GSH. The combination of 2-ME, BSO and H2O2 showed a significant antiproliferation effect in both ACHN and ACVB. The intracellular levels of reactive oxygen species (ROS) with a combination with 2-ME and H2O2 in ACHN and ACVB pretreated with BSO were markedly increased, which may have contributed to the potential antiproliferative action.

Optimal method of coronary endarterectomy for diffusely diseased coronary arteries.

BACKGROUND: Although several techniques for coronary artery bypass grafting have been introduced that incorporate coronary endarterectomy (CE), there is little information about late patency among the various CE methods. To clarify the quality of CE, we assessed clinical and angiographic results of our experience with this procedure on 127 patients who had diffusely diseased coronary arteries. METHODS: Between January 1994 and December 2002, 127 patients underwent coronary artery bypass grafting with CE. Sixty-eight patients undergoing CE with long arteriotomies and on-lay patch bypass grafting (group O) were compared with 59 patients undergoing CE with the conventional pull-out method (group P). RESULTS: Thirty-day mortality was 2.9% in group O and 6.8% in group P. The early angiographic results of 115 patients revealed a patency rate of 92.1% (grade A: 79.4%) in group O and 88.6% (grade A: 68.6%) in group P. Actuarial survival at 5 years was 90.7% in group O and 74.0% in group P (p = 0.1). Angiograms performed on 78 patients after a mean period of 21 +/- 16 months showed a patency rate of 89.1% (grade A:76.1%) in group O and 81.0% (grade A: 38.1%) in group P (grade A: p < 0.001). CONCLUSIONS: The midterm angiographic results of CE with long arteriotomies and on-lay patch bypass grafting were better than the results obtained with the conventional pull-out method. This procedure was found to be safe and effective for complete revascularization in patients with a severely and diffusely diseased coronary artery.

Persistent left superior vena cava draining to left atrium with normal coronary sinus.

In embryology, a persistent connection of the left superior vena cava to the left atrium rarely coexists with a coronary sinus. We herein report an unusual case of persistent left superior vena cava terminating in a left atrium with normal coronary sinus, which was revealed at the time of permanent pacemaker implantation after a second operation for recurrent left atrioventricular valve regurgitation. Because this anomaly had gone undiagnosed at the first operation, we were unable to diagnose it prior to the second operation, because the preoperative coronary angiogram clearly demonstrated a coronary sinus that was not dilated. We would have repaired the anomaly using a patch or other procedure had it been diagnosed before the second operation in order to prevent cyanosis or brain complications secondary to right-to-left shunting. One should always be on guard for this rare condition.

Pseudoaneurysm of the dorsalis pedis artery causing neurological deficit.

Pseudoaneurysm of the dorsalis pedis artery is very rare. This case report describes a 71-year-old man with an idiopathic aneurysm of the dorsalis pedis artery that caused neurological deficit. Surgical resection was performed and his symptoms improved.

Extensive thoracoabdominal aortic aneurysm repair using deep hypothermic bypass and circulatory arrest.

We sought to evaluate the safety and usefulness of deep hypothermic cardiopulmonary bypass with intervals of circulatory arrest for extensive thoracoabdominal aortic aneurysms. Between March 1994 and December 2002, 17 patients with Crawford type I and II were reviewed retrospectively. The patients were divided into two groups: group H (hypothermic circulatory arrest, n = 8) and group N (normothermic cardiopulmonary bypass, n = 9). In group H, in-hospital mortality was 12.5%, and that in group N was 11.1%. Operation times were similar between the two groups though the cardiopulmonary bypass time was significantly shorter in group N than in group H (p < 0.05). Postoperative paraplegia occurred in 1 patient of group N. Postoperative renal dysfunction occurred in none of group H except in 1 preoperative dialysis case, whilst it occurred in 6 patients of group N. Postoperative creatinine levels were significantly higher in group N than in group H. Three cases in group H required tracheostomy. Our experience with hypothermic cardiopulmonary bypass and circulatory arrest for diffuse type thoracoabdominal aortic aneurysm confirms the safety and efficacy of this technique. Although respiratory complications remain a problem, the technique is considered to be effective for renal protection.

Complete revascularization in patients with severe left ventricular dysfunction.

OBJECTIVE: This study evaluates whether patients with coronary artery disease and severely depressed left ventricular ejection fraction (LVEF) benefit from complete revascularization by multivessel coronary artery bypass. METHODS: From April 1994 to May 2002, 42 patients who underwent coronary artery bypass grafting (CABG) at our institution had impaired left ventricular (LV) function [an ejection fraction (EF) of 30% or less]. The average preoperative LVEF was 23.8%. The mean number of grafts was 4.6. Complete revascularization by multivessel bypass grafting was the goal for all patients. RESULTS: Thirty days mortality was 0 and hospital mortality was 2.4%. The mean graft patency rate for 35 (83%) patients at one month was 98.8%. The mean postoperative LVEF improved significantly, from 23.8% to 35.2% (p<0.05), and the New York Heart Association (NYHA) classification was improved in most patients. The Kaplan-Meier estimate of survival at 5 years was 83.1%, and that of the cardiac event-free rate at 5 years was 77.5%. CONCLUSION: For patients with poor LV function, complete surgical revascularization by multivessel bypass grafting can be performed safely, with satisfactory hospital mortality and long-term results.