How do electronic carriers cross Si-bound alkyl monolayers?

Electron transport through Si-C bound alkyl chains, sandwiched between n-Si and Hg, is characterized by two distinct types of barriers, each dominating in a different voltage range. At low voltage, current depends strongly on temperature but not on molecular length, suggesting transport by thermionic emission over a barrier in the Si. At higher voltage, the current decreases exponentially with molecular length, suggesting tunneling through the molecules. The tunnel barrier is estimated, from transport and photoemission data, to be ~1.5 eV with a 0.25me effective mass.Comment: 13 pages, 3 figure

Self Assembly of Nano Metric Metallic Particles for Realization of Photonic and Electronic Nano Transistors

In this paper, we present the self assembly procedure as well as experimental results of a novel method for constructing well defined arrangements of self assembly metallic nano particles into sophisticated nano structures. The self assembly concept is based on focused ion beam (FIB) technology, where metallic nano particles are self assembled due to implantation of positive gallium ions into the insulating material (e.g., silica as in silicon on insulator wafers) that acts as intermediary layer between the substrate and the negatively charge metallic nanoparticles

Implementation of PIXE for classification, discrimination, and identification of vehicle window glass samples: the way to database building (Metadata RADIATE TA Proposal 20002190-ST)

Proposal title "Implementation of PIXE for classification, discrimination, and identification of vehicle window glass samples: the way to database building". Measurements carried out at the external beam set-up for cultural heritage of the INFN LABEC accelerator laboratory), from 2 till 3 and from 9 till 11 December 2020 and on 20 September 2021. Hands-off mode. Glass is a material frequently present at the scene of such events as car accidents, burglaries, assaults, and criminal offenses. Glass as physical evidence could provide valuable information to assist criminal investigations. One of the problems of forensic glass analysis is the comparison problem. The other task related to glass analysis, and frequently addressed, is a determination of the category of a glass fragment, for example, was the fragment from a window, or some glass container such as a bottle? This process is also called a classification problem and becomes especially important when there may be no control sample to compare with one found at the scene of a crime. Characterization of glass fragments is normally accomplished by measuring the physical and optical properties of density and refractive index (RI). However further discrimination, such as identification of a suspected source of origin, has become more difficult as the range of RI has narrowed within glass subtypes because of advances in glass manufacturing technology. Moreover, the main requirement for the chosen method should be non-destructive leaving the material available for re-use. The motivation of the project is to develop the algorithm for glass fragments classification and discrimination using a combination of refractive index (RI) data and elemental analysis using ion beam analysis (IBA) methods and particularly, PIXE and PIGE 48 glass samples from 13 vehicles (different models, and production years) were analyzed by PIXE and PIGE techniques to determine minor and trace elements concentration for identifying unknown car glass fragments. The samples from car windows were provided by the Israeli police force. The measurements were carried out using an extracted proton beam of 3.0 MeV and two Silicon Drift Detectors for PIXE (one small area SDD for elements from Na to Ca, and one large area SDD for elements from Ti and above), one HPGe detector for PIGE and one SI PIN diode for RBS. The use of an external beam set-up has the advantage of allowing the easy positioning of the small irregular glass fragments, possibly avoiding errors in the analysis due to the positioning of the samples on fixed geometry sample holders in in-vacuum scattering chambers. Every sample includes several small fragments (appr. 3 x 3 mm); a fragment from each sample has been selected randomly for each kind of sample. Three measurements were done for each fragment (on the two external smooth surfaces and one - on the rupture surface). Glass reference standards (NIST 1412, 620 and 610) were analysed frequently as well for quality assurance purposes

Modification of Parylene film-coated glass with TiO2 nanoparticles and its photocatalytic properties

A titania film was deposited on Parylene-coated glass by a one-step, ultrasound-assisted procedure. The TiO2 nanoparticles formed during the sonochemical hydrolysis of Ti(i-OPr)4 were thrown to the surface and strongly attached to the Parylene substrate. By using different solvents (water, ethanol or their mixture) and reagent concentrations, the thickness, uniformity and crystallinity of the deposited layer were regulated. PVP was used to stabilize the highly homogeneous distribution of TiO2 nanocrystals on the Parylene surface. The morphology and structure of the coated films were characterized by physical and chemical methods such as: X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), and optical spectroscopy. The photocatalytic activity of the titania-modified Parylene film in the photo discoloration of methylene blue was demonstrated. The experimental results revealed a correlation between the uniformity of the nanostructured anatase titania film and its photocatalytic properties

Trace Elements in Tears: Comparison of Rural and Urban Populations Using Particle Induced X-ray Emission

We aimed to evaluate the types and concentrations of trace elements in tears of individuals living in urban and rural environments using particle induced X-ray emission (PIXE) and the possible association with exposure to air pollution and suggest a novel method for tear-based biomonitoring studies. This cross-sectional pilot study comprised 42 healthy subjects, 28 living in a rural area and 14 in an industrial city. Tears were collected with Schirmer paper and characterized by PIXE. Trace element concentrations from both eyes were averaged together with environmental pollution data. Main outcome measures were between-group differences in types and concentrations of trace elements in tears and comparison to environmental data. The rural group included 12/28 men, mean age 45.2 ± 14.8 years. The urban group consisted of 11/14 men of mean age 27 ± 5.9 years. Six rural and all urban were active smokers. Air pollution data showed more toxic elements in the rural environment. On PIXE analysis, chlorine, sodium, and potassium were found in similar concentrations in all samples. Normalizing to chlorine yielded higher values of aluminum, iron, copper, and titanium in the rural group; aluminum was found only in the rural group. The higher levels of certain trace elements in the rural group may, in part, be a consequence of exposure to specific environmental conditions. No direct association was found with air pollution data. PIXE is useful to analyze trace elements in tears, which might serve as a marker for individual exposure to environmental pollutants in biomonitoring studies

One-Step Synthesis of N‑Doped Graphene Quantum Dots from Chitosan as a Sole Precursor Using Chemical Vapor Deposition

We present a simple, environment-friendly, and fast synthesis of nitrogen-doped graphene quantum dots (N-GQDs) on copper foil by chemical vapor deposition using exclusively chitosan, a cheap and nontoxic biopolymer, as a carbon and nitrogen precursor. We characterized the synthesized N-doped graphene quantum dots using Raman spectroscopy, XPS, AFM, HRTEM, and HRSEM and found them to be in the range 10–15 nm in diameter and 2–5 nm-thick with 4.2% of maximum nitrogen content. The proposed growth mechanism process includes three key steps: (1) decomposition of chitosan into nitrogen-containing compounds, (2) adsorption of reactive species (HCN) on the copper surface, and (3) nucleation to form N-doped graphene quantum dots. The synthesized N-GQDs exhibit photoluminescence (PL) emission in the visible band region, thus making them suitable for applications in nano-optoelectronics

High Rate of Hydrogen Incorporation in Vertically Aligned Carbon Nanotubes during Initial Stages of Growth Quantified by Elastic Recoil Detection

We quantified the amount of hydrogen in as-grown vertically aligned multiwall CNTs at different stages of growth using elastic recoil detection analysis (ERDA). We suggest that hydrogen is associated with atomic defects and/or amorphous carbon impurities formed at earlier deposition stages. We found that the highest amount of hydrogen (2.3 wt %) was incorporated during the initial growth stage (15–20 s). Our results show a decrease of hydrogen content with increasing deposition time and/or with decreasing growth rate, which points to dynamical self-annealing of hydrogen-saturated defects. Consequently, the decrease of hydrogen-related defects leads to a higher quality of MWCNTs, which can be easily detected by ERDA. This research provides new insight into the nanotube growth mechanism and provides a new characterization approach for quantifying hydrogen-saturated atomic defects in MWCNTs

Toward Developing Techniques─Agnostic Machine Learning Classification Models for Forensically Relevant Glass Fragments

Glass fragments found in crime scenes may constitute important forensic evidence when properly analyzed, for example, to determine their origin. This analysis could be greatly helped by having a large and diverse database of glass fragments and by using it for constructing reliable machine learning (ML)-based glass classification models. Ideally, the samples that make up this database should be analyzed by a single accurate and standardized analytical technique. However, due to differences in equipment across laboratories, this is not feasible. With this in mind, in this work, we investigated if and how measurement performed at different laboratories on the same set of glass fragments could be combined in the context of ML. First, we demonstrated that elemental analysis methods such as particle-induced X-ray emission (PIXE), laser ablation induct i v e l y coupled plasma mass spectrometry (LA-ICP-MS), scanning electron microscopy with energy-dispersive X-ray spectrometry (SEM-EDS), particle-induced Gamma-ray emission (PIGE), instrumental neutron activation analysis (INAA), and prompt Gamma-ray neutron activation analysis (PGAA) could each produce lab-specific ML-based classification models. Next, we determined rules for the successf u l combinations of data from different laboratories and techniques and demonstrated that when followed, they give rise to improved models, and conversely, poor combinations wi l l lead to poor-performing models. Thus, the combination of PIXE and LA-ICP-MS improves the performances by similar to 10-15%, while combining PGAA with other techniques provides poorer performances in comparison with the lab-specific models. Finally, we demonstrated that the poor performances of the SEM-EDS technique, sti l l in use by law enforcement agencies, could be greatly improved by replacing SEM-EDS measurements for Fe and Ca by PIX E measurements for these elements. These findings suggest a process whereby forensic laboratories using different elemental analysis techniques could upload their data into a unified database and get reliable classification based on lab-agnostic models. This in tur n brings us closer to a more exhaustive extraction of information from glass fragment evidence and furthermore may form the basis for international-wide collaboration between law enforcement agencies.Peer reviewe