Handling Geometric Features in Nanoscale Characterization of Charge Injection and Transport in thin Dielectric Films

International audienceDue to miniaturization and attractiveness of nanosized and/or nanostructured dielectric layers, characterization at the local scale of charge injection and transport phenomena comes to the fore. To that end the electric modes derived from Atomic Force Microscopy (AFM) are more and more frequently used. In this study, the influence of AFM tip-plane system configuration on the electric field distribution is investigated for homogeneous and heterogeneous (nanostructured) thin dielectric layers. The experimental and computing results reveal that the radial component of the electric field conveys the charge lateral spreading whereas the axial component of the electric field governs the amount of injected charges. The electric field distribution is slightly influenced by the heterogeneity of the material. Moreover, the interpretation of the current measurements requires consideration of the entire electric field distribution and not only the computed field at the contact point

Methodology for extraction of space charge density profiles at nanoscale from Kelvin probe force microscopy measurements

International audienceTo understand the physical phenomena occurring at metal/dielectric interfaces, determination of the charge density profile at nanoscale is crucial. To deal with this issue, charges were injected applying a DC voltage on lateral Al-electrodes embedded in a SiN x thin dielectric layer. The surface potential induced by the injected charges was probed by Kelvin probe force microscopy (KPFM). It was found that the KPFM frequency mode is a better adapted method to probe accurately the charge profile. To extract the charge density profile from the surface potential two numerical approaches based on the solution to Poisson's equation for electrostatics were investigated: the second derivative model method, already reported in the literature, and a new 2D method based on the finite element method (FEM). Results highlight that the FEM is more robust to noise or artifacts in the case of a non-flat initial surface potential. Moreover, according to theoretical study the FEM appears to be a good candidate for determining charge density in dielectric films with thicknesses in the range from 10 nm to 10 μm. By applying this method, the charge density profile was determined at nanoscale, highlighting that the charge cloud remains close to the interface

Characterization of the Electrical Behaviour of Thin Dielectric Films at Nanoscale using Methods Derived from Atomic Force Microscopy: Application to Plasma Deposited AgNPs-Based Nanocomposites

International audienceRecent advances in the development of micro-and nano-devices call for applications of thin nanocomposite dielectric films (thickness less than few tens of nanometers) with tuneable electrical properties. For optimization purposes, their behaviour under electrical stress needs to be probed at relevant scale, i.e. nanoscale. To that end electrical modes derived from Atomic Force Microscopy (AFM) appear the best methods due to their nanoscale resolution and non-destructive nature which permits in-situ characterization. The potentialities of electrical modes derived from AFM are presented in this work. The samples under study consist of plasma processed thin dielectric silica layers with embedded silver nanoparticles (AgNPs). Charge injection at local scale, performed by using AFM tip, is investigated by Kelvin Probe Force Microscopy (KPFM). Modulation of the local permittivity induced by the presence of AgNPs is assessed by Electrostatic Force Microscopy (EFM)

Charges injection investigation at metal/dielectric interfaces by Kelvin Probe Force Microscopy

International audienceCharges injection at metal/dielectric interface and their motion in silicon nitride layer is investigated using samples with embedded lateral electrodes and surface potential measurement by Kelvin Probe Force Microscopy (KPFM). Bipolar charge injection was evidenced using this method. From surface potential profile, charge density distribution is extracted by using Poisson's equation. The evolution of the charge density profile with polarization bias and depolarization time was also investigated

Charge injection phenomena at the metal/dielectric interface investigated by Kelvin probe force microscopy

International audienceThe understanding of charge injection mechanism at metal/dielectric interface is crucial in many applications. A direct probe of such phenomenon requires a charge measurement method whose spatial resolution is compatible with the characteristic scale of phenomena occurring after injection, like charge trapping, and with the geometry of samples under investigation. In this paper, charge injection at metal/dielectric interface and their motion in silicon nitride layer under tunable electric field are probed at nanoscale using a technique derived from Atomic Force Microscopy. This was achieved by realizing embedded lateral electrode structures and using surface potential measurement by Kelvin Probe Force Microscopy (KPFM) to provide voltage, field and charge profiles close to the metal/dielectric interface during and after biasing the electrodes. The influence of electric field enhancement at the interface due to the electrode geometry was accounted for. Electron and hole mobility was estimated from surface potential profiles obtained under polarization. Charge dynamic was investigated during depolarization steps

Modelling COVID‑19 Severity In the Republic of Ireland Using Patient Co‑morbidities, Socioeconomic Profle and Geographic Location, February to November 2020

Understanding patient progression from symptomatic COVID-19 infection to a severe outcome represents an important tool for improved diagnoses, surveillance, and triage. A series of models have been developed and validated to elucidate hospitalization, admission to an intensive care unit (ICU) and mortality in patients from the Republic of Ireland. This retrospective cohort study of patients with laboratory-confirmed symptomatic COVID-19 infection included data extracted from national COVID-19 surveillance forms (i.e., age, gender, underlying health conditions, occupation) and geographically-referenced potential predictors (i.e., urban/rural classification, socio-economic profile). Generalised linear models and recursive partitioning and regression trees were used to elucidate COVID-19 progression. The incidence of symptomatic infection over the study-period was 0.96% (n= 47,265), of whom 3781 (8%) required hospitalisation, 615 (1.3%) were admitted to ICU and 1326 (2.8%) died. Models demonstrated an increasingly efficacious ft for predicting hospitalization [AUC 0.816 (95% CI 0.809, 0.822)], admission to ICU [AUC 0.885 (95% CI 0.88 0.89)] and death [AUC of 0.955 (95% CI 0.951 0.959)]. Severe obesity (BMI ≥ 40) was identified as a risk factor across all prognostic models; severely obese patients were substantially more likely to receive ICU treatment [OR 19.630] or die [OR 10.802]. Rural living was associated with an increased risk of hospitalization (OR 1.200 (95% CI 1.143–1.261)]. Urban living was associated with ICU admission [OR 1.533 (95% CI 1.606–1.682)]. Models provide approaches for predicting COVID-19 prognoses, allowing for evidence-based decision making pertaining to targeted non-pharmaceutical interventions, risk-based vaccination priorities and improved patient triage

Study of required conditions to limit the dielectric charging phenomenon when measuring the electron emission yield from thin dielectric layers

International audienceThe electron emission yield of materials is an important quantity to be determined in various fields of physics. Among them, dielectric materials have a strong ability to retain charges and remain charged when submitted to electrical field, in particular when irradiated by electron beam. Without the use of specific measurement methodology, experimental investigation of dielectric materials may lead to an inaccurate measurement of the total electron emission yield (TEEY). This paper shows that a particular attention should be paid to the pulse duration of the incident electron beam and to hysteresis effects induced by charge trapping

Barrier effect to charge injection in polyethylene by silver nanoparticles containing plasma polymer composites investigated by conductivity measurements

International audienceMain challenge in the development of HVDC polymeric insulation is to avoid the accumulation of space charge under electrical and/or thermal stresses which can significantly reduce the component reliability. Injection mitigation in low density polyethylene (LDPE) films by plasma processed silver nanoparticles (AgNPs) containing plasma polymer composites was recently reported through space charge measurements. The barrier effect has been assigned to the creation of permanent deep traps by introducing silver nanoparticles near the polyethylene surface. To substantiate the above findings, current measurements realized on composite layers and on polyethylene films with and without silver nanoparticles have been carried out. It is shown that in the presence of AgNPs in organosilicon layer, polarization/depolarization currents are one order of magnitude lower, transient currents decay faster and are not sensitive to multiple polarization. This can be understood if the AgNPs in the layer are acting as deep traps mitigating further injection with the result to decrease the apparent conductivity of the layer and to increase its breakdown strength. Similar trend is observed in polyethylene tailored by composite layer. These results strengthen the interpretation of the barrier effect based on space charge stabilized by deep traps formed by the AgNPs

On the secondary electron emission phenomenon when originating from very thin layers

International audienceThe secondary electron emission phenomenon lays down the principle of operation of many physical devices and processes. Although it is fairly well described in the case of irradiation of metals there is still lack of information on the secondary electron emission when originating from dielectrics. In this work we report on the secondary electron emission resulting from very thin layers. It is found that for dielectric SiO 2 layers of less than 100 nm of thickness a departure from the general behaviour occurs for incident primary electrons with energy of around 1 keV. The departure in the electron emission yield heavily depends on the layer thickness. The case of nanostructured layers-dielectric matrices containing metal nanoparticles is also considered in the study

Interface properties in dielectrics: A cross-section analysis by atomic force microscopy

International audienceEven if interfaces are more and more investigated their properties remain partially unknown, especially as regards their electronic properties. This is mainly related to the lack of characterization at relevant scale. In this context, electrical modes derivate from Atomic Force Microscopy appear well adapted. In this paper, a method to probe space charge at nanoscale is proposed. This method is based on surface potential measurement by Kelvin Probe Force Microscopy (KPFM) and post-processing technique based either on numerical derivation or Finite Element Method. Through these methods, densities of interface charges and injected charges were determined at different metal/dielectric interfaces