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Esophageal Lymphoepithelioma-Like Carcinoma with Unique Daisy-Like Appearance

Olmez, Sehmus; Can, Alper; Yavuz, Alpaslan; İliklerden, Umit Haluk; Bulut, Gulay
Fonte: The Korean Society of Gastrointestinal Endoscopy Publicador: The Korean Society of Gastrointestinal Endoscopy
Tipo: Text
Português
Due to differences in prognosis and management, it is important to subclassify esophageal carcinoma. Esophageal lymphoepithelioma-like carcinoma (LELC) is extremely rare, with only a few cases reported to date. Review of the literature revealed case reports describing lesions with similar histology. We present a 69-year-old man with a giant pedunculated-polypoid lesion of the esophagus shrinking the lumen. Endoscopic excision of the tumor was performed and final histopathological diagnosis was confirmed to be LELC. In contrast to a previous case with a more aggressive course and a recurrent lesion, our patient died of his disease within 8 months of diagnosis. Here we discuss the endoscopic and radiologic findings of the case and a review of the literature.

Delayed Pneumoperitoneum and Acute Pulmonary Edema Secondary to Acute Gastric Dilatation

Ahn, Jae Yun; Kim, Jong Kun
Fonte: The Korean Society of Gastrointestinal Endoscopy Publicador: The Korean Society of Gastrointestinal Endoscopy
Tipo: Text
Português
Pneumoperitoneum caused by acute gastric dilatation (AGD) is a very rare complication. We report a case of pneumoperitoneum and acute pulmonary edema caused by AGD in a patient with Parkinson’s disease. A 78-year-old woman presented with pneumonia and AGD. We inserted a nasogastric tube and administered empirical antibiotics. We performed an endoscopy, and perforation or necrosis of the stomach and pyloric stenosis were not observed. Thirty-six hours after admission, the patient suddenly developed dyspnea and shock, and eventually died. We suspected the cause of death was pneumoperitoneum and acute pulmonary edema caused by AGD during the conservative treatment period. Immunocompromised patients with chronic illness require close observation even if they do not show any symptoms suggestive of complications. Even if the initial endoscopic or abdominal radiologic findings do not show gastric necrosis or perforation, follow-up with endoscopy is essential to recognize complications of AGD early.

Endoscopic Submucosal Dissection for Recurrent or Residual Superficial Esophageal Cancer after Chemoradiotherapy: Two Cases

Hwang, Changhyeok; Youn, Young Hoon; Choi, Sung-eun; Jung, Young Hak; Park, Hae Yeul; Park, Jae Jun; Kim, Jie Hyun; Park, Hyojin
Fonte: The Korean Society of Gastrointestinal Endoscopy Publicador: The Korean Society of Gastrointestinal Endoscopy
Tipo: Text
Português
We report two cases of endoscopic submucosal dissection (ESD) for recurrent or residual esophageal squamous cell carcinoma (ESCC) lesions after chemoradiotherapy for advanced esophageal cancer. Case 1 involved a 64-year-old man who had previously undergone chemoradiotherapy for advanced ESCC and achieved a complete response (CR) for 22 months, until metachronous recurrent superficial ESCC was detected on follow-up esophagogastroduodenoscopy (EGD). We performed ESD and found no evidence of recurrence for 24 months. Case 2 involved a 59-year-old man who had previously undergone chemoradiotherapy for advanced ESCC. He responded favorably to treatment, and most of the tumor had disappeared on follow-up EGD 4 months later. However, there were two residual superficial esophageal lugol-voiding lesions. We performed ESD, and he had a CR for 32 months thereafter. ESD can be considered a viable treatment option for recurrent or residual superficial ESCC after chemoradiotherapy for advanced esophageal cancer.

The Past, Present, and Future of Image-Enhanced Endoscopy

Jang, Jae-Young
Fonte: The Korean Society of Gastrointestinal Endoscopy Publicador: The Korean Society of Gastrointestinal Endoscopy
Tipo: Text
Português
Despite the remarkable progress recently made to enhance the resolution of white-light endoscopy, detection, and diagnosis of premalignant lesions, such as adenomas and subtle early-stage cancers, remains a great challenge. As for example, although chromoendoscopy, such as endoscopy using indigo carmine, is useful for the early diagnosis of subtle lesions, the technique presents various disadvantages ranging from the time required for spray application of the dye and suctioning of excess dye to the increased difficulty in identifying lesions in the presence of severe inflammation and obstruction of visual field due to the pooling of solution in depressed-type lesions. To overcome these diagnostic problems associated with chromoendoscopy, research has focused on the development of endoscopes based on new optical technologies. Several types of image-enhanced endoscopy methods have recently been presented. In particular, image-enhanced endoscopy has emerged as a new paradigm for the diagnosis of gastrointestinal disorders. Image-enhanced endoscopes provide high-contrast images of lesions by means of optical or electronic technologies, including the contrast enhancement of the mucosal surface and of blood vessels. Chromoendoscopy, narrow-band imaging...

Albumin adsorption on CoCrMo alloy surfaces

Yan, Yu; Yang, Hongjuan; Su, Yanjing; Qiao, Lijie
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
Proteins can adsorb on the surface of artificial joints immediately after being implanted. Although research studying protein adsorption on medical material surfaces has been carried out, the mechanism of the proteins’ adsorption which affects the corrosion behaviour of such materials still lacks in situ observation at the micro level. The adsorption of bovine serum albumin (BSA) on CoCrMo alloy surfaces was studied in situ by AFM and SKPFM as a function of pH and the charge of CoCrMo alloy surfaces. Results showed that when the specimens were uncharged, hydrophobic interaction could govern the process of the adsorption rather than electrostatic interaction, and BSA molecules tended to adsorb on the surfaces forming a monolayer in the side-on model. Results also showed that adsorbed BSA molecules could promote the corrosion process for CoCrMo alloys. When the surface was positively charged, the electrostatic interaction played a leading role in the adsorption process. The maximum adsorption occurred at the isoelectric point (pH 4.7) of BSA.

Identification of a highly efficient stationary phase promoter in Bacillus subtilis

Yu, Xiaoxia; Xu, Jiangtao; Liu, Xiaoqing; Chu, Xiaoyu; Wang, Ping; Tian, Jian; Wu, Ningfeng; Fan, Yunliu
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
A promoter that enabled high-level expression of the target gene during the stationary phase in the absence of an inducer would facilitate the efficient production of heterogeneous proteins at a low cost. In this study, a genome-scale microarray-based approach was employed to identify promoters that induced high-level expression of the target genes in Bacillus subtilis from the late log phase to the stationary phase without an inducer. Eleven candidate promoters were selected based on B. subtilis microarray data and the quantitative PCR analysis. Among the selected promoters, Pylb exhibited the highest activity with the reporter bgaB during the stationary phase. Compared with P43 (a commonly used constitutive promoter), promoter Pylb could express two reporter genes (egfp and mApple), and the expression levels of EGFP and RFP were 7.8- and 11.3-fold higher than that of P43, respectively. This finding was verified by overexpression of the genes encoding pullulanase and organophosphorus hydrolase, the activities of which were 7.4- and 2.3-fold higher, respectively, when driven by Pylb compared with P43. Therefore, our results suggest that the Pylb promoter could be used to overexpress target genes without an inducer; this method could facilitate the identification and evaluation of attractive promoters in the genome.

Immobilization of myoglobin on Au nanoparticle-decorated carbon nanotube/polytyramine composite as a mediator-free H2O2 and nitrite biosensor

Vilian, A. T. Ezhil; Veeramani, Vediyappan; Chen, Shen-Ming; Madhu, Rajesh; Kwak, Cheol Hwan; Huh, Yun Suk; Han, Young-Kyu
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
A novel composite film was designed for use as a highly selective mediator-free amperometric biosensor, and a method was created for accomplishing direct electrochemistry of myoglobin on a multi-walled carbon nanotube and tyramine-modified composite decorated with Au nanoparticles on a glassy carbon electrode. The ultraviolet-visible and electrochemical impedance spectroscopy results showed that myoglobin retained its native conformation in the interaction with Au-PTy-f-MWCNT. The surface coverage of Mb-heme-Fe(II)/(III) immobilized on Au-PTy-f-MWCNT and the heterogeneous electron-transfer rate constant were 2.12 × 10−9 mol cm−2 and 4.86 s−1, respectively, indicating a higher loading capacity of the nanocomposite for direct electron transfer of Mb onto the electrode surface. The proposed Mb/Au-PTy-f-MWCNT biofilm exhibited excellent electrocatalytic behavior toward the reduction of H2O2 and the oxidation of nitrite with linear ranges of 2 to 5000 μM and 1 to 8000 μM and lower detection limits of 0.01 μM and 0.002 μM, respectively. An apparent Michaelis-Menten constant of 0.12 mM indicated that the Mb immobilized on the Au-PTy-f-MWCNT film retained its native activity. This biosensor can be successfully applied to detect H2O2 and nitrite in disinfectant cream...

Hypericin-photodynamic therapy induces human umbilical vein endothelial cell apoptosis

Zhang, Qian; Li, Zhuo-heng; Li, Yuan-yuan; Shi, San-jun; Zhou, Shi-wen; Fu, Yuan-yuan; Zhang, Qing; Yang, Xue; Fu, Ruo-qiu; Lu, Lai-chun
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
The conventional photosensitizers used in photodynamic therapy (PDT), such as haematoporphyrin (HP), have not yet reached satisfactory therapeutic effects on port-wine stains (PWSs), due largely to the long-term dark toxicity. Previously we have showed that hypericin exhibited potent photocytotoxic effects on Roman chicken cockscomb model of PWSs. However, the molecular mechanism of hypericin-mediated photocytotoxicity remains unclear. In this study, we employed human umbilical vein endothelial cells (HUVECs) to investigate the hypericin-photolytic mechanism. Our study showed that hypericin-PDT induced reactive oxygen species (ROS), resulting in cell killings and an activation of the inflammatory response. Importantly, we have also discovered that photoactivated hypericin induced apoptosis by activating the mitochondrial caspase pathway and inhibiting the activation of the vascular endothelial growth factor-A (VEGF-A)-mediated PI3K/Akt pathway. Notably, we found that hypericin exhibited a more potent photocytotoxic effect than HP, and largely addressed the inconvenience issue associated with the use of HP. Thereby, hypericin may be a better alternative to HP in treating PWSs.

Fully epitaxial C1b-type NiMnSb half-Heusler alloy films for current-perpendicular-to-plane giant magnetoresistance devices with a Ag spacer

Wen, Zhenchao; Kubota, Takahide; Yamamoto, Tatsuya; Takanashi, Koki
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
Remarkable magnetic and spin-dependent transport properties arise from well-designed spintronic materials and heterostructures. Half-metallic Heusler alloys with high spin polarization exhibit properties that are particularly advantageous for the development of high-performance spintronic devices. Here, we report fully (001)-epitaxial growth of a high-quality half-metallic NiMnSb half-Heusler alloy films, and their application to current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with Ag spacer layers. Fully (001)-oriented NiMnSb epitaxial films with very flat surface and high magnetization were prepared on Cr/Ag-buffered MgO(001) single crystalline substrates by changing the substrate temperature. Epitaxial CPP-GMR devices using the NiMnSb films and a Ag spacer were fabricated, and room-temperature (RT) CPP-GMR ratios for the C1b-type half-Heusler alloy were determined for the first time. A CPP-GMR ratio of 8% (21%) at RT (4.2 K) was achieved in the fully epitaxial NiMnSb/Ag/NiMnSb structures. Furthermore, negative anisotropic magnetoresistance (AMR) ratio and small discrepancy of the AMR amplitudes between RT and 10 K were observed in a single epitaxial NiMnSb film, indicating robust bulk half metallicity against thermal fluctuation in the half-Heusler compound. The modest CPP-GMR ratios could be attributed to interface effects between NiMnSb and Ag. This work provides a pathway for engineering a new class of ordered alloy materials with particular emphasis on spintronics.

A protein polymerization cascade mediates toxicity of non-pathological human huntingtin in yeast

Serpionov, Genrikh V.; Alexandrov, Alexander I.; Antonenko, Yuri N.; Ter-Avanesyan, Michael D.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
Several neurodegenerative amyloidoses, including Huntington disease, are caused by expansion of polyglutamine (polyQ) stretches in otherwise unrelated proteins. In a yeast model, an N-terminal fragment of mutant huntingtin with a stretch of 103 glutamine residues aggregates and causes toxicity, while its non-toxic wild type variant with a sequence of 25 glutamines (Htt25Q) does not aggregate. Here, we observed that non-toxic polymers of various proteins with glutamine-rich domains could seed polymerization of Htt25Q, which caused toxicity by seeding polymerization of the glutamine/asparagine-rich Sup35 protein thus depleting the soluble pools of this protein and its interacting partner, Sup45. Importantly, only polymers of Htt25Q, but not of the initial benign polymers, induced Sup35 polymerization, indicating an intermediary role of Htt25Q in cross-seeding Sup35 polymerization. These data provide a novel insight into interactions between amyloidogenic proteins and suggest a possible role for these interactions in the pathogenesis of Huntington and other polyQ diseases.

Radionuclide Gas Transport through Nuclear Explosion-Generated Fracture Networks

Jordan, Amy B.; Stauffer, Philip H.; Knight, Earl E.; Rougier, Esteban; Anderson, Dale N.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
Underground nuclear weapon testing produces radionuclide gases which may seep to the surface. Barometric pumping of gas through explosion-fractured rock is investigated using a new sequentially-coupled hydrodynamic rock damage/gas transport model. Fracture networks are produced for two rock types (granite and tuff) and three depths of burial. The fracture networks are integrated into a flow and transport numerical model driven by surface pressure signals of differing amplitude and variability. There are major differences between predictions using a realistic fracture network and prior results that used a simplified geometry. Matrix porosity and maximum fracture aperture have the greatest impact on gas breakthrough time and window of opportunity for detection, with different effects between granite and tuff simulations highlighting the importance of accurately simulating the fracture network. In particular, maximum fracture aperture has an opposite effect on tuff and granite, due to different damage patterns and their effect on the barometric pumping process. From stochastic simulations using randomly generated hydrogeologic parameters, normalized detection curves are presented to show differences in optimal sampling time for granite and tuff simulations. Seasonal and location-based effects on breakthrough...

Functional tooth restoration utilising split germs through re-regionalisation of the tooth-forming field

Yamamoto, Naomi; Oshima, Masamitsu; Tanaka, Chie; Ogawa, Miho; Nakajima, Kei; Ishida, Kentaro; Moriyama, Keiji; Tsuji, Takashi
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
The tooth is an ectodermal organ that arises from a tooth germ under the regulation of reciprocal epithelial-mesenchymal interactions. Tooth morphogenesis occurs in the tooth-forming field as a result of reaction-diffusion waves of specific gene expression patterns. Here, we developed a novel mechanical ligation method for splitting tooth germs to artificially regulate the molecules that control tooth morphology. The split tooth germs successfully developed into multiple correct teeth through the re-regionalisation of the tooth-forming field, which is regulated by reaction-diffusion waves in response to mechanical force. Furthermore, split teeth erupted into the oral cavity and restored physiological tooth function, including mastication, periodontal ligament function and responsiveness to noxious stimuli. Thus, this study presents a novel tooth regenerative technology based on split tooth germs and the re-regionalisation of the tooth-forming field by artificial mechanical force.

Synthesis of heavy hydrocarbons at the core-mantle boundary

Belonoshko, Anatoly B.; Lukinov, Timofiy; Rosengren, Anders; Bryk, Taras; Litasov, Konstantin D.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
The synthesis of complex organic molecules with C-C bonds is possible under conditions of reduced activity of oxygen. We have found performing ab initio molecular dynamics simulations of the C-O-H-Fe system that such conditions exist at the core-mantle boundary (CMB). H2O and CO2 delivered to the CMB by subducting slabs provide a source for hydrogen and carbon. The mixture of H2O and CO2 subjected to high pressure (130 GPa) and temperature (4000 to 4500 K) does not lead to synthesis of complex hydrocarbons. However, when Fe is added to the system, C-C bonds emerge. It means that oil might be a more abundant mineral than previously thought.

Heterogeneous distribution of dye-labelled biomineralizaiton proteins in calcite crystals

Liu, Chuang; Xie, Liping; Zhang, Rongqing
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
Biominerals are highly ordered crystals mediated by organic matters especially proteins in organisms. However, how specific proteins are distributed inside biominerals are not well understood. In the present study, we use fluorescein isothiocyanate (FITC) to label extracted proteins from the shells of bivalve Pinctada fucata. By confocal laser scanning microscopy (CLSM), we observe a heterogeneous distribution of dye-labelled proteins inside synthetic calcite at the microscale. Proteins from the prismatic calcite layers accumulate at the edge of crystals while proteins from the nacreous aragonite layers accumulate at the center of crystals. Raman and X-ray powder diffraction show that both the proteins cannot alter the crystal phase. Scanning electron microscope demonstrates both proteins are able to affect the crystal morphology. This study may provide a direct approach for the visualization of protein distributions in crystals by small-molecule dye-labelled proteins as the additives in the crystallization process and improve our understanding of intracrystalline proteins distribution in biogenic calcites.

TALEN-mediated homologous recombination in Daphnia magna

Nakanishi, Takashi; Kato, Yasuhiko; Matsuura, Tomoaki; Watanabe, Hajime
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
Transcription Activator-Like Effector Nucleases (TALENs) offer versatile tools to engineer endogenous genomic loci in various organisms. We established a homologous recombination (HR)-based knock-in using TALEN in the crustacean Daphnia magna, a model for ecological and toxicological genomics. We constructed TALENs and designed the 67 bp donor insert targeting a point deletion in the eyeless mutant that shows eye deformities. Co-injection of the TALEN mRNA with donor DNA into eggs led to the precise integration of the donor insert in the germ line, which recovered eye deformities in offspring. The frequency of HR events in the germ line was 2% by using both plasmid and single strand oligo DNA with 1.5 kb and 80 nt homology to the target. Deficiency of ligase 4 involved in non-homologous end joining repair did not increase the HR efficiency. Our data represent efficient HR-based knock-in by TALENs in D. magna, which is a promising tool to understand Daphnia gene functions.

The aglycone of ginsenoside Rg3 enables glucagon-like peptide-1 secretion in enteroendocrine cells and alleviates hyperglycemia in type 2 diabetic mice

Kim, Ki-Suk; Jung Yang, Hea; Lee, In-Seung; Kim, Kang-Hoon; Park, Jiyoung; Jeong, Hyeon-Soo; Kim, Yoomi; Seok Ahn, Kwang; Na, Yun-Cheol; Jang, Hyeung-Jin
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
Ginsenosides can be classified on the basis of the skeleton of their aglycones. Here, we hypothesized that the sugar moieties attached to the dammarane backbone enable binding of the ginsenosides to the sweet taste receptor, eliciting glucagon-like peptide-1 (GLP-1) secretion in the enteroendocrine L cells. Using the human enteroendocrine NCI-H716 cells, we demonstrated that 15 ginsenosides stimulate GLP-1 secretion according to the position of their sugar moieties. Through a pharmacological approach and RNA interference technique to inhibit the cellular signal cascade and using the Gαgust−/− mice, we elucidated that GLP-1 secreting effect of Rg3 mediated by the sweet taste receptor mediated the signaling pathway. Rg3, a ginsenoside metabolite that transformed the structure through a steaming process, showed the strongest GLP-1 secreting effects in NCI-H716 cells and also showed an anti-hyperglycemic effect on a type 2 diabetic mouse model through increased plasma GLP-1 and plasma insulin levels during an oral glucose tolerance test. Our study reveals a novel mechanism where the sugar moieties of ginsenosides Rg3 stimulates GLP-1 secretion in enteroendocrine L cells through a sweet taste receptor-mediated signal transduction pathway and thus has an anti-hyperglycemic effect on the type 2 diabetic mouse model.

Autophagic degradation of aquaporin-2 is an early event in hypokalemia-induced nephrogenic diabetes insipidus

Khositseth, Sookkasem; Uawithya, Panapat; Somparn, Poorichaya; Charngkaew, Komgrid; Thippamom, Nattakan; Hoffert, Jason D.; Saeed, Fahad; Michael Payne, D.; Chen, Shu-Hui; Fenton, Robert A.; Pisitkun, Trairak
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
Hypokalemia (low serum potassium level) is a common electrolyte imbalance that can cause a defect in urinary concentrating ability, i.e., nephrogenic diabetes insipidus (NDI), but the molecular mechanism is unknown. We employed proteomic analysis of inner medullary collecting ducts (IMCD) from rats fed with a potassium-free diet for 1 day. IMCD protein quantification was performed by mass spectrometry using a label-free methodology. A total of 131 proteins, including the water channel AQP2, exhibited significant changes in abundance, most of which were decreased. Bioinformatic analysis revealed that many of the down-regulated proteins were associated with the biological processes of generation of precursor metabolites and energy, actin cytoskeleton organization, and cell-cell adhesion. Targeted LC-MS/MS and immunoblotting studies further confirmed the down regulation of 18 selected proteins. Electron microscopy showed autophagosomes/autophagolysosomes in the IMCD cells of rats deprived of potassium for only 1 day. An increased number of autophagosomes was also confirmed by immunofluorescence, demonstrating co-localization of LC3 and Lamp1 with AQP2 and several other down-regulated proteins in IMCD cells. AQP2 was also detected in autophagosomes in IMCD cells of potassium-deprived rats by immunogold electron microscopy. Thus...

Classical ROS-dependent and early/rapid ROS-independent release of Neutrophil Extracellular Traps triggered by Leishmania parasites

Rochael, Natalia C.; Guimarães-Costa, Anderson B.; Nascimento, Michelle T. C.; DeSouza-Vieira, Thiago S.; Oliveira, Matheus P.; Garcia e Souza, Luiz F.; Oliveira, Marcus F.; Saraiva, Elvira M.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
Neutrophil extracellular traps (NETs) extruded from neutrophils upon activation are composed of chromatin associated with cytosolic and granular proteins, which ensnare and kill microorganisms. This microbicidal mechanism named classical netosis has been shown to dependent on reactive oxygen species (ROS) generation by NADPH oxidase and also chromatin decondensation dependent upon the enzymes (PAD4), neutrophil elastase (NE) and myeloperoxidase (MPO). NET release also occurs through an early/rapid ROS-independent mechanism, named early/rapid vital netosis. Here we analyze the role of ROS, NE, MPO and PAD4 in the netosis stimulated by Leishmania amazonensis promastigotes in human neutrophils. We demonstrate that promastigotes induce a classical netosis, dependent on the cellular redox imbalance, as well as by a chloroamidine sensitive and elastase activity mechanism. Additionally, Leishmania also induces the early/rapid NET release occurring only 10 minutes after neutrophil-parasite interaction. We demonstrate here, that this early/rapid mechanism is dependent on elastase activity, but independent of ROS generation and chloroamidine. A better understanding of both mechanisms of NET release, and the NETs effects on the host immune system modulation...

Physical Modeling of Gate-Controlled Schottky Barrier Lowering of Metal-Graphene Contacts in Top-Gated Graphene Field-Effect Transistors

Mao, Ling-Feng; Ning, Huansheng; Huo, Zong-Liang; Wang, Jin-Yan
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
A new physical model of the gate controlled Schottky barrier height (SBH) lowering in top-gated graphene field-effect transistors (GFETs) under saturation bias condition is proposed based on the energy conservation equation with the balance assumption. The theoretical prediction of the SBH lowering agrees well with the experimental data reported in literatures. The reduction of the SBH increases with the increasing of gate voltage and relative dielectric constant of the gate oxide, while it decreases with the increasing of oxide thickness, channel length and acceptor density. The magnitude of the reduction is slightly enhanced under high drain voltage. Moreover, it is found that the gate oxide materials with large relative dielectric constant (>20) have a significant effect on the gate controlled SBH lowering, implying that the energy relaxation of channel electrons should be taken into account for modeling SBH in GFETs.

Nature of low-frequency noise in homogeneous semiconductors

Palenskis, Vilius; Maknys, Kęstutis
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Text
Publicado em 17/12/2015 Português
This report deals with a 1/f noise in homogeneous classical semiconductor samples on the base of silicon. We perform detail calculations of resistance fluctuations of the silicon sample due to both a) the charge carrier number changes due to their capture–emission processes, and b) due to screening effect of those negative charged centers, and show that proportionality of noise level to square mobility appears as a presentation parameter, but not due to mobility fluctuations. The obtained calculation results explain well the observed experimental results of 1/f noise in Si, Ge, GaAs and exclude the mobility fluctuations as the nature of 1/f noise in these materials and their devices. It is also shown how from the experimental 1/f noise results to find the effective number of defects responsible for this noise in the measured frequency range.