Charge transfer and trapping as origin of a double dip in the transfer characteristics of graphene based field-effect transistors

We discuss the origin of an additional dip other than the charge neutrality point observed in transfer characteristics of graphene-based field-effect transistors. The double-dip is proved to arise from charge transfer between graphene and metal electrodes, while charge storage at the graphene/SiO2 interface enhances it. Considering different Fermi energy from the neutrality point along the channel and partial charge pinning at the contacts, we propose a model which explains all features in gate voltage loops.Comment: 14 pages, 5 figure

Fabrication of graphene based devices and study of their electrical and optical properties

2011 - 2012This work is dedicated to investigate the unique and excellent electrical and optical properties of graphene, through the fabrication and experimental study of several graphene based devices. Particular attention is paid to the details of all stages of the fabrication process which might have an effect on the properties of the final product. It also describes the characterization of graphene transistor structures, as well as experimental studies of charge transport. I focused part of my research on optoelectronics and plasmonics of nanomaterials, in particular, I carried on a research that matched graphene and Plasmonics, the goal was to assess how the plasmonic response of metallic nanoparticles is modified by the presence of a graphene substrate, with results that could be very attractive as a starting point for the future optoelectronics applications. This is how the thesis is planned: in the Chapter 2 I present a brief theoretical overview on the structural, electronic and optical properties of graphene. In Chapter 3, I present the methods used for sample preparation, investigation of graphene flakes and the measurement setup. In particular, the identification of graphene is a very delicate step and involves the use of multiple techniques that complement each other. It is extremely difficult to find small graphene crystallites in the “haystack” of millions of thicker graphitic flakes. Thus, the identification is made by combining two or more of the following techniques: optical microscopy, Raman spectroscopy, SEM and the calculation of the contrast to give raise the best visibility. The next, Chapter 4, is dedicated to the study of graphene based devices and their related features. First, I fabricated 2D graphene FETs (GFETs) and explored several device designs to analyze transfer characteristic, mobility, and the influence of the contacts on the overall conductance. The contacts between graphene and metal electrodes can significantly affect the electronic transport and limit or impede the full exploitation of the graphene intrinsic properties. In this context I investigated the contact resistance on mono- and bi-layer graphene sheets by fabricating structures suitable for transfer length method measurements with Ni and Ti metals. We also observed anomalies in GFET transfer characteristics, namely double dips, and here I present a work in which the origin of double dips in the transfer characteristics of GFET devices is explained. In Chapter 5, I performed the characterization of Field Emission properties of several mono and bi layer graphene samples. I report the observation and characterization of field emission current from individual single- and few-layer graphene flakes laid on a flat SiO2/Si substrate. Measurements were performed in a scanning electron microscope chamber equipped with nanoprobes which allowed local measurement of the field emission current finding that the emission process is stable over a period of several hours and that it is well described by a Fowler–Nordheim model for currents over five orders of magnitude. In the last Chapter 6, I present an exploration of the potential that electromagnetic surface waves known as surface plasmons may have in building both photonic elements and a new photonics technology based on nanostructured metals. I report results from an investigation into the plasmonic properties of metallic nanoparticles supported by substrates made of graphene, in order to extract information of its optical properties. In summary: the main accomplishments of this work are to: a) The Set-up of a routine procedure to identify graphene samples and make their morphological characterization. b) The fabrication of graphene based electronic devices, like graphene field effect transistors and non-volatile memories. c) The Study of the influence of different metal contact on the overall conductance, and the investigation of anomalies in GFET. d) The investigation of quantum tunneling phenomenon in graphene. e) The investigation of graphene as a substrate for plasmonics particles. These results will be presented in due course. [edited by Author]XI n.s

Transfer characteristics and contact resistance in Ni- and Ti-contacted graphene-based field-effect transistors

We produced graphene-based field-effect transistors by contacting mono- and bi-layer graphene by sputtering Ni or Ti as metal electrodes. We performed electrical characterization of the devices by measuring their transfer and output characteristics. We clearly observed the presence of a double-dip feature in the conductance curve for Ni-contacted transistors, and we explain it in terms of charge transfer and graphene doping under the metal contacts. We also studied the contact resistance between the graphene and the metal electrodes with larger values of ~30 kΩμm2 recorded for Ti contacts. Importantly, we prove that the contact resistance is modulated by the back-gate voltage

The role of free endosomal epitopes in the mechanisms of amelioration and flares of rheumatoid arthritis-associated conditions: pregnancy and infective hepatitis

Abstract Background It is known that rheumatoid symptoms improve in pregnancy and in patients who develop infective jaundice. The mechanism of amelioration might involve the direct interaction of free endosomal self-epitopes that are released by the cells of the involved organ with antigen binding sites on the membranes of anti-idiotypic cells, resulting in possible suppressive effects. Methods Immune responses of peripheral blood mononuclear cells (PBMCs) to longstanding synovial fluid (SFMC or primary ultrafiltrate) and to the endosomal extracts enriched with self-epitope-receptor microcomplexes (MICs) were investigated. The MICs (secondary ultrafiltrate) were prepared from PBMCs that were previously cultured with SFMC ultrafiltrates and had therefore been in contact with large number of self-epitopes. Results Addition of primary ultrafiltrate to PBMCs elicited significant expansion of regulatory T cells (CTLA-4+CD4+CD25+), and reduction of CD69+CD4+CD25+ cells. In contrast, secondary ultrafiltrate, which contains the microcomplexes, produced an inflammatory response, with CD69+ cells increasing to 47% of CD4+CD25+ cells. This opposite response indicated that, in all likelihood, the response of mononuclear cells to secondary ultrafiltrate in culture involved a subset of CD4+ T cells other than those of the primary ultrafiltrate. Conclusions Free endosomal epitopes, released from the maternal-fetal interface and necrotic areas of diseased liver, inducing expansion of regulatory T cells, provided a type of endogenous, autonomic immunotherapy. The post-partum flare-up of the disease could be due to the sudden interruption of endogenous immunotherapy at delivery and to the inflammatory response to microcomplexes that are recognized by autoreactive T cells

Field emission from graphene flakes

We report the observation and characterization of field emission current from individual single- and few-layer graphene flakes laid on a flat SiO2 / Si substrate. Measurements were performed in a scanning electron microscope chamber equipped with nanoprobes which allowed local measurement of the field emission current. We achieved field emission currents up to 1μA from the flat part of graphene flakes at applied fields of few hundred volt per micrometer. We found that the emission process is stable over a period of several hours and that it is well described by a Fowler–Nordheim model for currents over five orders of magnitude

Effect of back-gate on contact resistance and on channel conductance in graphene-based field-effect transistors

We study the contact resistance and the transfer characteristics of back-gated field effect transistors of mono- and bi-layer graphene. We measure specific contact resistivity of ~ 7 k Ω μm2 and ~ 30k Ω μm2 for Ni and Ti, respectively. We show that the contact resistance is a significant contributor to the total source-to-drain resistance and it is modulated by the back-gate voltage. We measure transfer characteristics showing a double dip feature that we explain as the effect of doping due to charge transfer from the contacts causing minimum density of states for graphene under the contacts and in the channel at different gate voltage

MOESM1 of Vaccination with endosomal unknown epitopes produces therapeutic response in rheumatoid arthritis patients and modulates adjuvant arthritis of rats

Additional file 1. RIASSUNTO

Should we exclude patients with peritoneal carcinosis of colorectal origin and high PCI from CRS + HIPEC?

International guidelines exclude from surgery patients with peritoneal carcinosis of colorectal origin and a peritoneal cancer index (PCI) ≥ 16. This study aims to analyze the outcomes of patients with colorectal peritoneal carcinosis and PCI greater or equal to 16 treated with cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) (CRS + HIPEC). We retrospectively performed a multicenter observational study involving three Italian institutions, namely the IRCCS Policlinico San Matteo in Pavia, the M. Bufalini Hospital in Cesena, and the ASST Papa Giovanni XXIII Hospital in Bergamo. The study included all patients undergoing CRS + HIPEC for peritoneal carcinosis from colorectal origin from November 2011 to June 2022. The study included 71 patients: 56 with PCI < 16 and 15 with PCI ≥ 16. Patients with higher PCI had longer operative times and a statistically significant higher rate of not complete cytoreduction, with a Completeness of Cytoreduction score (CC) 1 (microscopical disease) of 30.8% (p = 0.004). The 2-year OS was 81% for PCI < 16 and 37% for PCI ≥ 16 (p < 0.001). The 2-years DFS was 29% for PCI < 16 and 0% for PCI ≥ 16 (p < 0.001). The 2-year peritoneal DFS for patients with PCI < 16 was 48%, and for patients with PCI ≥ 16 was 57% (p = 0.783). CRS and HIPEC provide reasonable local disease control for patients with carcinosis of colorectal origin and PCI ≥ 16. Such results form the basis for new studies to reassess the exclusion of these patients, as set out in the current guidelines, from CRS and HIPEC. This therapy, combined with new therapeutical strategies, i.e., pressurized intraperitoneal aerosol chemotherapy (PIPAC), could offer reasonable local control of the disease, preventing local complications. As a result, it increases the patient’s chances of receiving chemotherapy to improve the systemic control of the disease