Ultra-short pulsed laser ablation of highly oriented pyrolytic graphite

Local anodic oxidation (LAO) has been performed on highly oriented pyrolytic graphite (HOPG) and few layer graphene (FLG) using contact-mode (CM) atomic force microscopy (AFM) in a controlled humidity chamber. Different types of LAO patterns, namely, protrusion and trench features were observed for different tip speeds under similar conditions of LAO patterning, in both CM and noncontact-mode (NCM) AFM images. Observed LAO patterns show a variation in their dimensions over time. This paper carries out a study performed on the observed changes in dimensions of LAO patterns made on HOPG and FLG over several days, pointing to the dynamics of these LAO patterns. The stability of the LAO patterns on HOPG is compared with that for FLG. LAO patterns on HOPG show a widening and reduction in depth over a day. LAO patterns on FLG show, in contrast, a random variation in the lateral dimension “width” and stabilization in the vertical dimension “depth” over several days.

Morphology and topography of perovskite solar cell films ablated and scribed with short and ultrashort laser pulses

Sustainable process for functional group introduction onto HOPG by exposing [rad]OH and 1O2 using a radical vapor reactor (RVR) without any chemical reagents

Microdrilling based on laser ablation has been widely applied for manufacturing micro-/nanofeatures on different materials as a noncontact thermal removal approach. It has the advantages of high aspect ratio manufacturing capability and reduced surface damage. However, laser ablation is a complicated process that is challenging to model. In this paper, a standardized modeling procedure was demonstrated to predict the area and depth of laser ablation based on experimental study and simulation validation. A case study was conducted where microdrilling of high-density polyethylene (HDPE) was investigated using a 1064 nm nanosecond pulsed laser. Blind microholes were fabricated on the HDPE samples by ablating under different laser powers and numbers of pulses. Gain factors were defined and determined by the experimental data. A quantitative area-depth approximation model was formulated based on the gain factors. A comparison of the measured and the simulated results of microholes presented average 96.5% accuracy for the area and 85.7% for the depth. This research provided a simple but effective approach to predict dimensions of microholes on various substrates using laser ablation under different laser powers and the numbers of pulses, which could pave the way for development and modeling of laser ablation on polymers.

Numerical and experimental investigation on pulsed nanosecond laser ablation processing of aluminum alloy

Pulsed laser ablation is a well-known technique used for thin film deposition, extending from oxydes to hard and wear resistant Diamond-Line Carbon (DLC) films. Most of the previous studies devoted to DLC thin films elaboration have used pulsed duration in the nanosecond range. The present study concerns femtosecond (10 -15 s range) laser ablation of a graphite target for the elaboration of Diamond-Like Carbon. Compared to conventional nanosecond laser ablation, femtosecond laser pulses allow the production of high energy (up to a few keV) ions in the plasma, which may strongly affect the structure and properties of the deposited films. DLC films have been deposited under vacuum onto (100) p-type silicon substrates at room temperature, by ablating graphite targets with femtosecond laser pulses. The nature and properties of the film have been characterized by various techniques, including Raman, XPS and AFM. Discussion will be focused on the comparison between present results obtained using femtosecond laser pulses, with previously published results related to DLC films deposited using nanosecond laser pulses. Especially, Raman spectra of DLC films obtained by nanosecond laser ablation always show the two well-known D and G bands (located respectively at around 1350 cm -1 and 1550 cm -1 ), whereas some DLC films obtained when using femtosecond laser pulses exhibit an intense peak at 1140 cm -1 , which may be attributed to nanocrystalline diamond.

Atomic force microscopy of DNA self-assembled on a highly oriented pyrolytic graphite electrode surface

Pulsed laser ablation (PLA) is a unique method used to obtainatoms, ions, and small molecules from solid targets because ofits high-energy output, the ability to adjust the power of thelaser, and the purity of the final product.1,2 Most experiments onpulsed laser-solid interaction have been carried out in vacuum(10−4 Pa)3 or in a low pressure background gas,4 aiming at thin film fabrication and cluster formation.1 One of the advantages ofthe PLA method is that stoichiometric thin films can be preparedwith the same composition as the target materials. In addition,metals, semiconductors, and ceramics with high melting point canbe obtained at lower temperatures. However, this method has somedisadvantages, such as the size of the granules on the surface ofthin films is not even, big particles exist in the surface, and ahigh vacuum environment raises the preparation cost. Also, it isdifficult to obtain a thin film with big area using the PLA method.Some researchers have attempted to produce new materials by PLAin a static liquid medium. Figure 11.1 shows a typical schematicdiagram of the experimental apparatus of PLA in static liquid.5Mafune´ and coworkers prepared small silver, gold, and platinumclusters by laser ablation of ametal plate in the aqueous solution of asurfactant, where the clusters are encapsulated by the surfactant. Atthe same time, they also researched the influence of the preparationconditions, such as the concentration of the surfactant and thepower of laser ablation, on the stability of the nanoparticles in thesolution.5−8 Yang and coworkers prepared nanocrystalline diamond and cubic C3N4 by laser ablation of a graphite target in acetonesolution and ammonia solution, respectively.9,10,11 Iwabuchi et al.12prepared nanosized titania particles by PLA of a rutile single-crystaltarget in water. Compagnini et al.13 reported PLA of gold andsilver in several liquids (mainly water, ethanol, and chloroform).They observed the formation of metal sols by laser ablation inwater and ethanol and the formation of chloride compound solsby laser ablation in chloroform. This revealed that the chemicalstate of the formed nanoparticles depends mainly on the chemicalreactivity of the liquid. Liang et al.14 synthesized ultrafine SnO2−x nanocrystals by PLA of a tin metal plate in aqueous solutions ofsodium dodecyl sulfate and in pure water. Yeh and coworkers15also prepared aluminum hydroxides by laser ablation of an Al rodimmersed in water solvent. During aging, bayerite, gibbsite, andboehmite particles were formed simultaneously.

Pulsed laser ablation in liquid (PLAL) was used to synthesise indium oxide (In2O3) nanocolloidal suspension. Colloidal In2O3 nanoparticles (NPs) are synthesised by pulsed laser ablation of high-purity indium target in distilled water with various laser fluences at room temperature. UV–vis absorption and transmission electron microscopy were conducted to determine the bandgap, size, distribution and shape of the NPs. The optical properties, size and the morphology of the synthesised In2O3 were influenced strongly by laser fluence and wavelength. Laser ablation of indium in water produced spherical In2O3 NPs with an average size of 30 nm and their distribution was nearly Gaussian type.

The basic interaction mechanism of pulsed laser ablation of tissue reveals a complexity of parameters, such as the optical properties of the tissue and the technical characteristics of the laser beam. The role of the laser wavelength, the pulse duration, the energy fluence, etc. as well as the implications on the beam delivery means, the ablated surface modifications and the diagnostic techniques employed are under investigation. For example, it was experimentally verified that when using mid-infrared lasers with pulse durations in the ns range, the photothermal mechanism involved exhibits strong absorption restricting the residual thermal damage to a relatively small zone. On the other hand the ablation of tissue with ultrashort, picosecond and femtosecond, visible and near-infrared laser pulses has been investigated as an alternative, as the energy threshold for ablation biological tissue, depends approximately on the square root of the pulse duration. However the pulse length shortening creates problems to the fibers or the waveguides ends, due to the very high laser power densities involved. Conventional and advanced microscopy, scanning electron microscopy--SEM and atomic force microscopy--AFM, were used to study the surface and ends alterations of the delivery system involved and the surface alterations of the soft or the hard tissue target in pulsed laser ablation. Finally differentiation between the normal and the pathological tissue was achieved by employing the laser induced fluorescence--LIF diagnostic technique in a long term effort to develop a computer aided system, which will facilitate the automated, real-time characterization of healthy or atherosclerotic plaques in a less invasive laser ablation clinical procedure.

Scanning probe microscopy (SPM) can be successfully used in biological investigations1. Scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) are two main SPM techniques and they are capable of imaging biological objects at molecular level under in situ conditions. With this advantage, STM and AFM are applied to study not only the topographical structures of bio-samples in their natural environment, but also their electrochemical properties at liquid-solid interfaces. The electrochemical properties of biomolecules are usually studied by integral electrochemical methods, like cyclic voltammetry. The degree of surface coverage, the surface orientation of enzymes and the activity of a single enzyme remain a question of dispute, however, electrochemical SPM techniques can bring clarification. Electrochemical scanning tunnelling microscopy (EC-STM) and electrochemical atomic force microscopy (EC-AFM) provide visual topological information of biomolecules adsorbed on the electrode surface at single-molecular level. Some experimental issues, such as the requirement of the sample being conductive, potential damage to samples caused by the tunnelling current or tip-sample force, may limit their application. Scanning electrochemical potential microscopy (SECPM), a technique that measures the surface potential distribution at zero current, can be a promising alternative. SECPM shares most of the hardware setup with EC-STM except for the current amplifier being substituted by a potentiometer. It is easy to switch between SECPM and EC-STM to compare the topographical profile of the same area by mapping electron density and surface potential2. In our study, SPM techniques are used to study various biological objects, from nanometer-sized DNA and redox proteins to micrometer-sized bacteria spores. Since high-resolution images of DNA origami nanostructures can be achieved by using AFM3, we use both EC-AFM and SECPM techniques to investigate the morphology and potential-dependent adsorption behaviour of DNA scaffold and origamis4 on the modified HOPG surface. We found DNA scaffold can adsorb on HOPG in a certain potential range, and the adsorption structure changes with the applied electrochemical potential. Horseradish peroxidase (HRP), a redox enzyme, was studied using both, EC-STM and SECPM under in situ conditions5. HRP molecules were adsorbed on highly oriented pyrolytic graphite (HOPG) surfaces and imaged in phosphate buffered saline. We found that SECPM shows a better resolution than EC-STM in imaging this biomolecule. SECPM is also capable of measuring the surface charge distribution of the adsorbed biomolecules at the electrochemical interfaces. AFM in liquid was used to investigate the morphology and cellular process of Streptomycetes venezuelae both the wild type and the mutant6. To immobilize the bacteria on the surface for imaging, we use SiC patterned by photolithography with hole arrays (1.5×1.5×0.6 µm) to trap the bacteria and then measure under the physiological condition. The designed hole arrays trap the bacteria without causing any denaturation and due to the high electronic conductivity, they can serve as the working electrode under electrochemical conditions for EC-AFM and SECPM studies. EC-AFM was applied to image the morphology of the bacterial spore under different potential, and we found the morphology of the spore didn’t change in the wide potential window. (1) Choi, E.; Kim, A.; Son, H.; Pyo, S. G. J. Nanosci. Nanotechnol. 2014, 14 (1), 924. (2) Herpich, M.; Friedl, J.; Stimming, U. In Surface Science Tools for Nanomaterials Characterization; Springer Berlin Heidelberg: Berlin, Heidelberg, 2015; pp 1–67. (3) Bald, I.; Keller, A. Molecules 2014, 19 (9), 13803. (4) Kozyra, J.; Ceccarelli, A.; Torelli, E.; Lopiccolo, A.; Gu, J.-Y.; Fellermann, H.; Stimming, U.; Krasnogor, N. ACS Synth. Biol. 2017, 6 (7), 1140. (5) Baier, C.; Stimming, U. Angew. Chem. Int. Ed. Engl. 2009, 48 (30), 5542. (6) Santos-Beneit, F.; Gu, J.-Y.; Stimming, U.; Errington, J. Heliyon. Accepted

Controlling the self-assembly and nanoarchitectures of metal complexes at the molecular scale is essential for the development of new functional materials and devices. Since two-dimensional (2D) sheets consisting of metal complexes can be designed and controlled with various bonding modes, geometric structures, and chemical functions, they have been studied using various approaches by selecting metal ions and organic ligands. Trinuclear metal clusters contain three metal ions in one complex and are expected to be building blocks for the formation of 2D sheets of metal complexes by selecting their shape and axial ligands. In this study, a trinuclear cluster of ruthenium ions, Ru3O(EtCOO)6(CO)(THF)2:1, was used as the core to form nanostructures on highly oriented pyrolytic graphite (HOPG) substrates via axial ligand exchange with 1,4-Di (4-pyridyl) benzene:2 and 4,4’-di(4-pyridyl) biphenyl: 3. The adlayer structures and electrochemical properties of the nanoarchitectures were investigated by atomic force microscopy (AFM) and cyclic voltammetry (CV). In the experimental procedure, powders of 1, 2, and 3 were dissolved in methanol (MeOH) and tetrahydrofuran (THF), respectively, and a 0.78 µM solution was prepared. A predetermined amount of this was cast on HOPG, dried to form a thin film, and the thin film was observed in air using AFM. Next, equal amounts of 1 and 2 and 1 and 3 solutions were mixed in each solvent, and after heating a water bath at 60°C for 1 h, thin films were prepared in the same manner and observed by AFM. Ultraviolet–visible (UV-vis) absorption spectra and electrochemical measurements by CV were performed before and after heating the mixed solutions. First, in the AFM image of the thin film prepared by casting the MeOH mixture of 1 and 2, two stripe-like domains with different heights were observed, which matched the heights of the structures obtained in the AFM images of the single-domain formation of 1 and 2. In addition, no new absorption peaks were observed in the UV-vis absorption spectrum after mixing the solution; it was inferred that 1and 2 did not exchange ligands. However, when the mixed solution was heated in a water bath for 1 h, a few striped domains were observed, and a new ring-like structure was formed. The CV results also supported the change in the AFM images and absorption spectra after heating the solution. Before heating the mixed solution, a small redox peak was observed around 0.8 V, whereas after the warm bath, a large redox peak was observed around 0.6 V. A dramatic change in the magnitude of the current density was observed, indicating a significant improvement in conductivity. These results suggest that heating the mixed solution replaced THF ligand 1 with 2, forming a cyclic structure consisting of 1 and 2. When the same experiment was carried out in THF solution, a different structure was observed from that of the methanol solution, and a one-dimensional (1D) molecular wire structure was formed after heating the water bath. The absorption spectra and CV results also supported that ligand exchange occurred in the 1D wire structure, revealing the solvent dependence of the nanoarchitecture. When 3 was used as the axial ligand, larger structures were formed compared to 2, and one-dimensional wire structures of several micrometers were observed in the THF solution after the warm bath. Larger current densities and peak separations are also observed in the voltammograms. Thus, the length dependence of the organic ligand for the nanoarchitecture formation on the HOPG surface was demonstrated. Figure 1

Two-phase zirconium boride thin film obtained by ultra-short pulsed laser ablation of a ZrB12 target

Mono- and multilayers of a novel amphiphilic hexapyridinium cation with six eicosyl chains (3) are spread at the air/water interface as well as on highly ordered pyrolytic graphite (HOPG). On water, the monolayer of 3 is investigated by recording surface pressure/area and surface potential/area isotherms, and by Brewster angle microscopy (BAM). Self-organized tubular micelles with an internal edge-on orientation of molecules form at the air/water interface at low surface pressure whereas multilayers are present at high surface pressure, after a phase transition. Packing motifs suggesting a tubular arrangement of the constituting molecules were gleaned from atomic force microscopy (AFM) investigations of Langmuir-Blodgett (LB) monolayers being transferred on HOPG at different surface pressures. These LB film structures are compared to the self-assembled monolayer (SAM) of 3 formed via adsorption from a supersaturated solution, which is studied by scanning tunnelling microscopy (STM). On HOPG the SAM of 3 consists of nanorods with a highly ordered edge-on packing of the aromatic rings and an arrangement of alkyl chains which resembles the packing of molecules at the air/water interface at low surface pressure. Additional details of the molecular packing were gleaned from single-crystal X-ray structure analysis of the hexapyridinium model compound 2b, which possesses methyl instead of eicosyl residues.

A new single source approach was developed to synthesize Pd-Co nanoparticles using a bimetallic compound,[Et3NH]2[CoPd2(μ-4-I-3,5-Me2pz)4Cl4] (CoPd2), as a molecular precursor to obtain dispersed catalyst on highly ordered pyrolytic graphite (HOPG) surface, in view of preparing oxygen reduction catalysts for low temperature fuel cells. X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques were employed to characterize the nanostructure formations and to determine the composition and morphology of the complex on the HOPG. Results of high resolution XPS analysis (HR-XPS) revealed the binding energies corresponding to the atomic constituents of the precursor. When the precursor solution was placed on the surface of the HOPG, the bimetallic complex assumes a tubular structure and it appears that the surface of the HOPG offers a ground for the self-organization of nanostructural formations.