Chemically specific identification of carbon in XPS imaging using Multivariate Auger Feature Imaging (MAFI)

Until now, a difficult prospect in XPS imaging has been the identification of similar chemical states of carbon. With the advent of novel nano-carbons such as nanotubes and graphene, the ability to easily and unambiguously identify materials of varying sp2/sp3 nature in XPS spectra and images is becoming increasingly important. We present herein methods for the identification of such species in XPS images by shifting focus from the traditionally analysed C1s region to the X-ray induced carbon Auger feature. By extracting the D-Parameter from XPS data, we have generated what we refer to as "D-Parameter Images", that clearly identify regions of different carbon hybridisation in an image of a graphite flake mounted on carbon tape, and areas of reduced graphene oxide (GO) in a laser-scribed GO film. This method is then enhanced by multivariate analysis, a technique we call "Multivariate Auger Feature Imaging", where the distinction between varying sp2 carbon content on a surface is improved

Laser modification of graphene oxide layers

The effect of linearly polarized laser irradiation with various energy densities was successfully used for reduction of graphene oxide (GO). The ion beam analytical methods (RBS, ERDA) were used to follow the elemental composition which is expected as the consequence of GO reduction. The chemical composition analysis was accompanied by structural study showing changed functionalities in the irradiated GO foils using spectroscopy techniques including XPS, FTIR and Raman spectroscopy. The AFM was employed to identify the surface morphology and electric properties evolution were subsequently studied using standard two point method measurement. The used analytical methods report on reduction of irradiated graphene oxide on the surface and the decrease of surface resistivity as a growing function of the laser beam energy density

Raman investigation of laser-induced structural defects of graphite oxide films

Since the beginning of intensive studies on graphene and graphitic materials, Raman spectroscopy has always been used as a characterisation technique. This is due to two main reasons: the non-destructive nature of this experimental technique and its ability to distinguish between the plethora of existing carbon materials. One of the most challenging research activities concerns the production of graphene microcircuits. To address this issue, a possible strategy is to directly reduce and pattern graphite oxide (GO) film by laser irradiation. The objective of this study is to evaluate the laser irradiation-induced structural changes on thin GO films by using Micro-Raman spectroscopy. We used as a source a Nd:YAG laser (1064 nm) and different laser fluences: 15 J/cm2, 7.5 J/cm2 and 5 J/cm2. We have analyzed the modifications of the main Raman contributions of these graphitic materials: the D band (defect induced band), the G band (band due to sp2 hybridized carbon atoms) and the 2D band (D band overtone). In particular, we found out that our figure of merit (FOM) parameters, i.e. the intensity ratio ID/IG (for the D band and G band) and I2D/IG (for the 2D band and G band), change with the laser fluences, revealing a different effect induced by the laser irradiation. The best results are found in the sample irradiated with 5 J/cm2, suggesting that higher fluences do not lead to better results

Grafeno sluoksnių formavimas ir modifikavimas, panaudojant lazerio spinduliuotę

In this thesis research results on application of laser irradiation for forming and modification of graphene layers are presented. Graphite oxide (GO) films on polycarbonate substrate were prepared using Hummers-Offeman method. Composition of films differed by thickness, additives and their concentration. Picosecond laser irradiation was applied to form heat conductive graphene channels. Laser power, beam scanning speed and atmosphere gases was varied during the experiments. Raman spectroscopy was applied for graphene identification. Spectroscopy measurements showed that reduction level of GO to graphene depends on various factors: applied optical power, scanning speed, concentration of GO additives (Congo Red) and ambient atmosphere. Forming of heat conductive channels was also confirmed by drop of resistance in treated films and thermo-vision measurements. Temperature dynamics of GO film after picosecond laser pulse was modeled. The results of modelling together with Raman spectroscopy measurements confirmed that optimal laser power for GO reduction is 50 mW at 100 kHz pulse repetition rate. Graphene/chitosan composite film on ITO contact was modified with picosecond laser irradiation. Raman spectroscopy showed, that laser treatment increase the disorder in composite film. EIS spectra measurements confirmed that rise of capacitance occurs in samples after laser treatment. The capacitance of modified electrodes is proportional to average power of applied laser irradiation

Formation and Modification of Graphene Layers Using Laser Irradiation

In this thesis research results on application of laser irradiation for forming and modification of graphene layers are presented. Graphite oxide (GO) films on polycarbonate substrate were prepared using Hummers-Offeman method. Composition of films differed by thickness, additives and their concentration. Picosecond laser irradiation was applied to form heat conductive graphene channels. Laser power, beam scanning speed and atmosphere gases was varied during the experiments. Raman spectroscopy was applied for graphene identification. Spectroscopy measurements showed that reduction level of GO to graphene depends on various factors: applied optical power, scanning speed, concentration of GO additives (Congo Red) and ambient atmosphere. Forming of heat conductive channels was also confirmed by drop of resistance in treated films and thermo-vision measurements. Temperature dynamics of GO film after picosecond laser pulse was modeled. The results of modelling together with Raman spectroscopy measurements confirmed that optimal laser power for GO reduction is 50 mW at 100 kHz pulse repetition rate. Graphene/chitosan composite film on ITO contact was modified with picosecond laser irradiation. Raman spectroscopy showed, that laser treatment increase the disorder in composite film. EIS spectra measurements confirmed that rise of capacitance occurs in samples after laser treatment. The capacitance of modified electrodes is proportional to average power of applied laser irradiation

Substrate Impact on the Structure and Electrocatalyst Properties of Molybdenum Disulfide for HER from Water

It is expected that utilization of molybdenum disulfide (MoS2)-based nanostructured electrocatalysts might replace the Pt-group electrodes most effectively applied for hydrogen evolution reaction from water. Therefore, in the past two decades, various approaches have been reported for fabrication of nanostructured MoS2-based catalysts, but their applications in practice are still missing due to lower activity and stability. We envisaged that the knowledge about the peculiarities of MoS2 nanoplatelets attachment to various conductive substrates by hydrothermal processing could be helpful for fabrication of more active and stable working electrodes. Therefore, in this study, the hydrothermal syntheses at the Mo, Ti, Al, anodized Ti, and hydrothermally designed titanium suboxide substrates were performed; the electrodes obtained were characterized; and hydrogen evolution reaction (HER) activity was tested. In this way, MoS2-based HER catalyst possessing a surprising stability and a low Tafel slope was designed via attachment of nanoplatelet-shaped MoS2 species to the nanotube-shaped anatase-TiO2 surface

A Sensor for Electrochemical pH Monitoring Based on Laser-Induced Graphene Modified with Polyfolate

A laser-induced graphene (LIG) modified with chitosan (Chit) and conducting polymer polyfolate (PFA) was used as a base to develop a flat and flexible pH sensor. LIGs were formed using two different irradiation wavelengths of 355 nm and 532 nm. Depending on the wavelengths, the obtained electrodes were named LIG355 and LIG532. Microscopic imaging revealed that the bare LIG electrode surface had rough structures after laser treatment giving hydrophilic properties, and that PFA forms fibre-like structures on Chit coated LIG. Electrochemical investigation with the redox probe demonstrated that diffusion is a limiting process at the bare and modified LIG electrodes. A capacitive behaviour was observed from electrochemical impedance spectra at bare electrodes, showing a rather rough interface at LIG355 but a microporous one at LIG532. The developed flat and flexible electrode was sensitive to pH in the region from 6.0 to 9.0. In the studied pH range, the sensitivity was 27.86 ± 0.81 for PFA/Chit/LIG355 and 30.32 ± 0.50 mV/pH for PFA/Chit/LIG532 with moderate stability for a period of more than two months

Laser-Assisted Selective Fabrication of Copper Traces on Polymers by Electroplating

The selective deposition of metals on dielectric materials is widely used in the electronic industry, making electro-conductive connections between circuit elements. We report a new low-cost laser-assisted method for the selective deposition of copper tracks on polymer surfaces by electroplating. The technique uses a laser for the selective modification of the polymer surface. The electrical conductivity of some polymers could be increased due to laser irradiation. Polyimide samples were treated using nanosecond and picosecond lasers working at a 1064 nm wavelength. An electro-conductive graphene-like layer was formed on the polymer surface after the laser treatment with selected parameters, and the copper layer thickness of 5–20 µm was deposited on the modified surface by electroplating. The selective laser-assisted electroplating technology allows the fabrication of copper tracks on complex shape dielectric materials. The technology could be used in the manufacturing of molded interconnect devices (MID)