Copper Metal Surface Research Articles

MXene-based eutectic salt hydrate phase change material for efficient thermal features, corrosion resistance & photo-thermal energy conversion

Salt hydrate phase change materials (PCMs) possess low thermal conductivity, degree of supercooling, lack of corrosion resistance and poor photo thermal conversion ability. To overcome these challenges, a two dimensional, chemically stable, optically & thermally efficient MXene@eutectic salt hydrate composite PCM is developed for effective harnessing of solar energy and thermal energy storage (TES) applications. Low temperature eutectic salt hydrate PCM with phase transition temperature of 27.6 °C and 216 J/g melting enthalpy is developed using sodium sulphate decahydrate (SSD) and sodium phosphate dibasic dodecahydrate (SPDD) based on Schrader equation. Advanced 2D layered material, MXene (Ti3C2) is synthesised from MAX phase (Ti3AlC2). Furthermore, MXene based PCM nanocomposite is developed with binary eutectic PCM of SSD/SPDD at different weight fractions through two step technique. Developed nanocomposite PCM exhibits better chemical stability, high optical absorbance of (1.1), low transmissibility (10.2 %), reliable thermal conductivity (0.621 W/m⋅K), improved melting enthalpy (161.2 J/g) and considerable cycle stability. The optical absorbance and thermal conductivity demonstrated a superior photo-thermal conversion capability and thermal networks for the developed MXene based composite sample at 0.9 wt% of MXene. The above properties are experimentally inferred by evaluating the developed MXene@ eutectic salt hydrate and base eutectic PCM under the solar simulator. The interfacial attraction between the two dimensional MXene nano flakes and the developed eutectic PCM ensures a promising ability to trap solar energy effectively for thermal regulation in a sustainable direction. Subsequently, the effect of MXene with SSD/SPDD in regard to the issue of corrosion is explored for copper and aluminium metal surface.

Adhesives Based on Poly(glycidyl methacrylate‐co‐butyl acrylate) with Controlled Structure: Curing Behavior and Adhesion Properties on Metal Substrates

AbstractThe adhesion properties of poly(glycidyl methacrylate (GMA)‐co‐butyl acrylate (BA)) statistical copolymers, synthesized by atom transfer radical polymerization (ATRP), are investigated employing three different curing agents or hardeners, such as diethanolamine (DEA), dicyandiamide (DICY), and 2‐cyanoacetamide (2‐CA) on copper, iron, brass, aluminum, and titanium metal surfaces. This work describes the treatment of the different surfaces, establishes the optimal curing conditions from differential scanning calorimetry (DSC) analysis of these novel adhesive systems, and evaluates the results of the single‐lap shear test for metal joints. Thus, by dynamic DSC measurements of the mixtures, a low curing temperature of 90 °C is defined when DEA is used as a curative; while systems based on DICY and 2‐CA require temperatures of 150 °C and 160 °C, respectively. In addition, the curing process of this controlled acrylic copolymer with DICY exhibits a singular behavior, possibly due to the curing reaction mechanism, where multiple epoxy‐amine ring‐opening polyaddition reactions take place between DICY's active hydrogens and epoxy groups of poly(GMA‐co‐BA). This latter curing system shows the highest adhesion features with lap‐shear strength at room temperature of 15.5 MPa, using copper as metallic substrate; however, the best results are obtained using 2‐CA as curing agent with aluminum and iron.

CO electroreduction on single-atom copper.

Electroreduction of carbon dioxide (CO2) or carbon monoxide (CO) toward C2+ hydrocarbons such as ethylene, ethanol, acetate and propanol represents a promising approach toward carbon-negative electrosynthesis of chemicals. Fundamental understanding of the carbon─carbon (C-C) coupling mechanisms in these electrocatalytic processes is the key to the design and development of electrochemical systems at high energy and carbon conversion efficiencies. Here, we report the investigation of CO electreduction on single-atom copper (Cu) electrocatalysts. Atomically dispersed Cu is coordinated on a carbon nitride substrate to form high-density copper─nitrogen moieties. Chemisorption, electrocatalytic, and computational studies are combined to probe the catalytic mechanisms. Unlike the Langmuir-Hinshelwood mechanism known for copper metal surfaces, the confinement of CO adsorption on the single-copper-atom sites enables an Eley-Rideal type of C-C coupling between adsorbed (*CO) and gaseous [CO(g)] carbon moxide molecules. The isolated Cu sites also selectively stabilize the key reaction intermediates determining the bifurcation of reaction pathways toward different C2+ products.

Non-contact detection of a naturally formed oxide layer on copper metal surface using terahertz time-domain spectroscopy

We demonstrate the use of the terahertz time-domain spectroscopy (THz-TDS) as a complementary tool in detecting the naturally formed oxide (NFO) layer on a copper metal surface. The THz emission from Cu-metal sheets having NFO were compared with Cu-sheets that were rapidly oxidized between temperatures ranges from 100 °C to 500 °C for 2 h. Raman spectroscopy and scanning electron microscopy were initially utilized as standard techniques for characterizing the oxide layer. However, the two performed standard techniques could not provide distinguishable results between the NFO and the thin oxide layer grown at temperatures below 200 °C. The THz-TDS provides clear results for non-destructive detection of the NFO on the Cu-surface. Excitation-power dependence and magnetic field dependence measurements revealed that the dominant THz emission mechanism is diffusion for CuxO formed below 300 °C and drift for thicker oxides grown at temperatures greater than 400 °C. The carrier diffusion and carrier drift mechanism are also dependent on the absorption efficiency and structural properties of the oxide layer that was formed. No THz radiation mechanism originating form nonlinear optical process was observed.

Femtosecond laser and oscillation induced large-scale periodic micro/nanostructures on copper surfaces

Femtosecond laser micro-nano machining has become an important field for novel material and/or structure fabrications. In this paper, we propose a new and efficient laser micro-nano fabrication technique on the metal surface, in which, a femtosecond laser combined with the ultralow frequency periodic oscillation of a two-phase stepping motor was used to fabricate a large-scale 20 μm period micro/nanostructures on the copper metal surface by line scanning. The copper foils fabricated by this femtosecond laser show excellent superhydrophobic properties. Subsequently, we use femtosecond laser Z-shaped line scanning, combined with a two-phase stepping motor with ultralow frequency periodic oscillation, works on copper foil fabricate a micropores structure with a period span of 20 μm. In addition, we simulated the butterfly wing superhydro-phobic micro/nanostructures on copper plates and fabricatedsuperhydrophobic copper surfaces. This technique lays a solid foundation for the practical application of femtosecond laser lithography and is expected to be extended to other materials for new device applications.

K X-ray Emission for Slow Oxygen Ions Approaching a Copper Metal Surface

We report on the K X-ray emission for 9–140 keV oxygen ions with initial charge states from 3 to 7 approaching a copper surface. The peak center of the measured X-ray spectrum slightly shifts towards higher energies with the increasing of the initial charge state of the incident ions. For the collisions of oxygen ions with no K-vacancies (q = 3–6), the X-ray yield per incident ion increases gradually with the projectile’s kinetic energy, while for the O7+ ions (with a K-vacancy) it is nearly independent of the energy. The K-shell ionization cross-sections for the oxygen ions with no K-vacancies obtained from the experiments are well consistent with the calculations of the binary encounter approximation model when the collision energy is larger than 30 keV, whereas they are several times larger than the theoretical values at collision energies of less than 30 keV.

Spectroscopic imaging of photoexcited states at a polycrystalline copper metal surface via two-photon photoelectron emission microscopy

The local photoexcited surface states of a polycrystalline-copper (Cu) substrate were observed via two-photon photoelectron emission microscopy (2P-PEEM) using a femtosecond laser. The 2P-PEEM results revealed local distributions of the photoexcited electrons, strongly depending on the crystal domains. With the energy-filtered images, the local 2P-photoemission spectra were selectively obtained for (111)- and (110)/(100)-crystal domains. Furthermore, the 2P-PEEM could visualize propagating Cu surface plasmon polaritons with wavevector of 7.61 × 106 m−1. These results indicate that the 2P-PEEM technique is a promising tool for studying the distribution of nonequivalent photoexcited surface states for various inhomogeneous functional nanomaterials.

Microscopic Structure and Binding Mechanism of the Corrosion-Protective Film of Oleylpropanediamine on Copper in Hot Water

The structure of the film formed by oleylpropanediamine (OLDA) on the copper (Cu) metal surface in water at 150 °C was investigated by combining quantitative NMR and surface characterization methods. We succeeded in quantifying the amount of film formation by precisely determining all mass balances in the systems examined. 2D IR microscopic mapping showed that the film thickness is uneven in the horizontal direction with a length scale of ∼100 μm and hundreds of OLDA layers. This film thickness was also confirmed by AFM. The analysis of the C–H stretching vibrational frequency disclosed that the alkyl chains are highly ordered in the layers close to the Cu surface and are conformationally disordered in the layers distant from the Cu surface in the thicker portion of the film. Combining XPS measurements using argon gas cluster ion beam etching with the ICP-AES analysis, we revealed that the key to multiple layering is the formation of a coordination complex of the unprotonated amino groups of OLDA with Cu that presumably results in polymer chain-like network structures. Contact angle measurements at different OLDA concentrations and treatment times showed that the water repellency of the film originated from the thick layering of OLDA molecules with disordered hydrophobic chains.

ELECTROCHEMICAL, DFT AND MULTISCALE SIMULATION STUDIES ON SELF-ASSEMBLED FILMS OF 2-AMINO-4-METHYL-PYRIDINE INHIBITOR FOR COPPER METAL CORROSION PROTECTION IN 3.5% NaCl MEDIUM

Copper metal and its alloys are the most used in the industries because it holds excellent conductivity and natural corrosion protectiveness against air/moisture. However, copper undergoes degradation in presence of aggressive 3.5% NaCl. Protective coating is one of the practical methods to safeguard copper metal. In this study, 2-amino-4-methyl-pyridine (AMP) was coated as self-assembled monolayer method (SAM) with different immersion periods (12 h/24 h) and investigated the corrosion potential against 3.5% NaCl medium. Chemical composition of AMP/SAM/Cu was characterized using Fourier-transform infrared (FT-IR) spectroscopy and morphological analysis using atomic force microscopy (AFM) techniques. AMP’s corrosion inhibition potential were evaluated via electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDS) analyses. Quantum chemical calculations and molecular dynamics (MD) simulations explained the stronger adsorption of AMP over copper metal surface via self-assembly method. The corrosion analysis revealed that AMP’s SAM formation (24 h immersion) enhances the corrosion protection of Cu metal, which is mainly due to the uniform thin adhesive compact layer formation and blocks incoming corrosive chloride ions. EIS investigation evident that AMP forms an adhesive layer over the copper surface and prevents the diffusion of aggressive corrosive medium, while PP studies revealed that AMP acts via the mixed mode of corrosion inhibition mechanism. AMP’s significant inhibition efficiency 90% was confirmed via PP analysis. AFM analysis enabled the morphology image of AMP’s shielding over Cu surface and the molecular modeling investigation supported well for the Cu–N (from AMP) bond formation.

A method validation for the hemoglobin chemical reagent test strip with the addition of ethylenediaminetetraacetic acid to increase the selectivity of this presumptive test for residual blood

Tetramethylbenzidine based chemical reagent test strips are often used in forensic science as a presumptive test for blood. These tests are designed as urinalysis test strips and include brands such as Combur®, HENSOTest®, Hemastix®, MultiStix® and Chemstrip®. They are used because they are simple to apply, stable, temperature tolerant and cost effective. The addition of a chelating agent, ethylenediaminetetraacetic acid increases the selectivity of this presumptive test for blood. This is a method validation for the hemoglobin chemical reagent test strip with EDTA. A range of substances, metal compounds, chemical solutions, blood and mixtures were tested in this method validation. The chelation with EDTA successfully prevented non-blood (false) positive results from all the substances tested and consistently produced a positive result for blood on a variety of surfaces. This study has shown that this method is capable of discriminating a blood stain on copper metal surfaces and eliminate the positive results generated by clean-up solutions such as hydrogen peroxide, which usually produce a positive result for most other presumptive tests for blood. This modified method is a simple, effective and reliable test for blood stains. A variety of variations were evaluated in this study. The simplest method of application was spraying the surface of the stain with a 0.5 M EDTA solution and testing the surface of the stain, and only requires a spray bottle of 0.5 M EDTA and the chemical reagent test strip. This spray approach is rugged and can be applied to horizontal, vertical and underside surfaces and requires little additional training. Overall, this study provides the forensic science community with an improved method more easily used, stored, transported and selective for blood, than luminol and safer than TMB.

Robust bulk micro-nano hierarchical copper structures possessing exceptional bactericidal efficacy

Conventional copper (Cu) metal surfaces are well recognized for their bactericidal properties. However, their slow bacteria-killing potency has historically excluded them as a rapid bactericidal material. We report the development of a robust bulk superhydrophilic micro-nano hierarchical Cu structure that possesses exceptional bactericidal efficacy. It resulted in a 4.41 log10 reduction (>99.99%) of the deadly Staphylococcus aureus (S. aureus) bacteria within 2 min vs. a 1.49 log10 reduction (96.75%) after 240 min on common Cu surfaces. The adhered cells exhibited extensive blebbing, loss of structural integrity and leakage of vital intracellular material, demonstrating the rapid efficacy of the micro-nano Cu structure in destructing bacteria membrane integrity. The mechanism was attributed to the synergistic degradation of the cell envelope through enhanced release and therefore uptake of the cytotoxic Cu ions and the adhesion-driven mechanical strain due to its rapid ultimate superhydrophilicity (contact angle drops to 0° in 0.18 s). The scalable fabrication of this micro-nano Cu structure was enabled by integrating bespoke precursor alloy design with microstructure preconditioning for dealloying and demonstrated on 2000 mm2 Cu surfaces. This development paves the way to the practical exploitation of Cu as a low-cost antibiotic-free fast bactericidal material.

3-Mercaptopropanoic Acid-Doped Chitosan/Hybrid-Based Multilayer Sol-Gel Coatings for Cu Protection in 3.5% NaCl Solution.

In this work, biopolymer based sol-gel was synthesized by doping 3-mercaptopropanoic acid (MPA) with chitosan and a hybrid of 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TEOS). Prepared MPA/hybrid-doped chitosan was applied toa copper (Cu) metal surface by the self-assembly technique to protect the Cu metal from corrosion in a 3.5% NaCl solution. The structure, mechanism and morphology of the modified electrodes were examined using Fourier transform infra-red (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), and atomic force microscopy (AFM). The decrease in surface roughness for Hy/chitosan/MPA-coated Cu indicates the formation of a dense layer on Cu metal confirmed by AFM. The corrosion protection evaluation of sol-gel coated electrodes was analyzed using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies (PDS) in a 3.5% NaCl medium. The MPA/hybrid-doped chitosan sol-gel coated Cu metal showed the greatest resistance to corrosionthanother sol-gel modified electrodes. The MPA-doped-chitosan/Hy sol-gel coating protected the Cu metal by an anodic dissolution process and improved its corrosion protection to 99.9%.

A Mathematical Model for Localized Corrosion of Copper Under a Droplet

The Nuclear Waste Management Organization (NWMO) is responsible for the implementation of Adaptive Phased Management (APM), the federally-approved plan for the safe long-term management of Canada’s used nuclear fuel.1 Under the APM plan, used nuclear fuel will ultimately be placed within a deep geological repository in a suitable host rock formation. Part of evaluating the long-term performance and safety of the repository system is understanding the behavior of the copper coated container with respect to localized corrosion. The Canadian Deep Geological Repository (DGR) system does not lend itself to passivation of the copper surface, owing to the nature of copper and the environment, so conventional pitting corrosion is not expected. However, the system will transition from dry to wet conditions, and there is a possibility that deliquescent species may be present on the container surface, which may produce different localized environments, and as a result, localized corrosion damage.A 2-D axisymmetric time-dependent model for localized corrosion is being developed using the concept of an Evans droplet,2 in which the metal is covered by a drop of electrolyte. The model considers the aerobic, unsaturated conditions likely to be found at early times in a deep geological repository.3 In the present work, sodium chloride was chosen as the supporting electrolyte and the concentration of oxygen in the solution at the droplet boundary was assumed to be in equilibrium with the oxygen in the surrounding air. The electrochemical reactions proposed for the copper metal surface include oxygen (O2) reduction and copper dissolution through a sequence of steps in which copper chloride is an adsorbed intermediate that reacts in a second chemical step to form cuprous chloride (CuCl2 -). The model accounts for the homogeneous oxidation of cuprous chloride to form cupric ion (Cu2+), and Cu2+ introduced a cathodic reaction to form CuCl2 -. Hydrolysis of both Cu(I) and Cu(II) to form precipitates is also considered in the current model.The mathematical model is developed using the finite-element method (COMSOL Multiphysics). The mathematical approach is similar to that developed by Chang et al.4 for corrosion of iron under a droplet or under a deposit. The model includes coupled, nonlinear, diffusion equations for ionic species, which include the contribution of migration, local electroneutrality, homogeneous reactions, and formation of precipitates. One of the unique approaches taken in this work is that the anodic and cathodic regions are not predefined but are rather determined by values of local concentration and potential from the simulation results. While in its preliminary stages, the model shows a time-dependent radial distribution of anodic and cathodic current, fractional coverage of the CuCl adsorbed intermediate, and dissolved oxygen concentration.References NWMO, “Choosing a Way Forward. The Future Management of Canada’s Used Nuclear Fuel. Final Study,” Nuclear Waste Management Organization, Toronto, Ontario, 2005.U. R. Evans, The Corrosion of Metals, E. Arnold & Company, London, 1926.F. King, M. Kolar, P. Maak, “Reactive-transport model for the prediction of the uniform corrosion behavior of copper used fuel containers,” Journal of Nuclear Materials 379 (2008) 133-141.Y.-C. Chang, R. Woollam, and M. E. Orazem, "Mathematical Models for Under-Deposit Corrosion: 1. Aerated Media,'' Journal of The Electrochemical Society, 161 (2014), C321-C329. AcknowledgementThis work was supported by the Nuclear Waste Management Organization, Canada, under project 2000904.

Surface Characterization of High-Purity Copper Electropolishing and Electrodeposition Treatments in an Ionic Liquid

High purity (>99.9% composition) copper metal specimens were used in electropolishing treatments with an acid-free ionic liquid electrolyte prepared from quaternary ammonium salts as a green polishing solution. A prominent ionic liquid composed of ethylene glycol (HOCH2CH2OH) and choline chloride (HOC2H4N(CH3)3 +Cl−), sometimes abbreviated as 2EG:1VB4, has been used in other studies to successfully electropolish various metal alloys, but has only been used in limited capacity to polish pure rare earth metals (1-5), like copper, the focus of this study. Voltammetry and chronoamperometry tests were conducted to determine the optimum conditions for electrochemical polishing, while Atomic Force Microscopy (AFM) revealed nanoscale effectiveness of the ionic liquid relative to an industry standard acid polishing treatment of 1 Mol Phosphoric Acid (H3PO4). Surface morphology comparisons summarized electrochemical polishing efficiency of these relative treatments by providing root mean square roughness prior to and post-electrochemical polishing.Electropolishing using the ionic liquid revealed a mirror finish >10 times smoother than the same copper metal surface prior to electropolishing. This transition manifested in a marked change in root mean squared roughness from 167.15 nm to 14.744 nm and resulted in a mass loss of 0.0535 g for an electropolishing rate of 59.444 µg/s when subjected to a 900 second treatment with an average voltage of 1.5 V. By comparison, the phosphoric acid electropolishing treatment yielded an improvement in root mean squared roughness of 85.019 nm, resulted in a mass loss of 0.067 g for a higher electropolishing rate of 74.444 µg/s when subjected to the same treatment conditions. However, the it can be noted that while the elctropolishing rate via the acid solutionis greater, there are extreme peaks and troughs etched on the smoothed surface due to pitting at low current densities (Figure 1). Hydrogen contamination can be observed to affect the overall root mean square average of the region, which may be remedied via a relatively costly degassing treatment at temperatures up to 800 deg C to achieve more comparable results to the ionic liquid solution.After these electropolishing pretreatments, the resulting copper surfaces were subsequently electroplated during a 1 hour treatment at 2 V with an 2EG:1VB4 ionic liquid solution that had previously been used to electropolish high-purity niobium metal. A thin film of niobium metal coated the polished copper during electrodeposition resulting in an average mass gain of 0.002 g, and a root mean squared roughness of increase of -2.101 nm for the ionic liquid pretreated sample, compared to the -2.417 nm resulting roughness from the phosphoric acid pretreatment.As a result, pretreatments revealed a cheaper, recyclable, and environmentally-friendly approach to electopolishing pure copper was demonstrated to be more effective than an acidic industry standard electrolyte. Additionally, electrodeposition of niobium metals on each pretreatment sample provides a reasonably cost-effective method to combine the electroconductivity benefits of copper and ferroelasticity attributes of niobium metals. References Derek Lofis and Tarek M Abdel-Fattah, International Journal of Minerals, Metallurgy and Materials, 26(5), 649–656 (2019)Derek Lofts and Tarek M. Abdel-Fattah, Colloids and Surfaces A: Physicochemical and Engineering Aspects, 511C, 113-119 (2016)Tarek M. Abdel-Fattah, Derek Loftis and Anil Mahapatro, Nanoscience and Nanotechnology, 5(2), 36-44 (2015)Tarek M. Abdel-Fattah, Derek Loftis and Anil Mahapatro, Journal of Surfaces and Interfaces of Materials, 3, 67-74 (2015)Tarek M. Abdel-Fattah, Derek Loftis and Anil Mahapatro, Journal of Biomedical Nanotechnology, 7(6) 794-800 (2011) Figure 1

Capture of femtosecond plasmon excitation on transient nonequilibrium states of the metal surface

This paper utilizes the time dependent orientation change of the laser-induced periodic subwavelength structures to capture the nonequilibrium states on copper metal surface.

Bee pollen extract as an eco-friendly corrosion inhibitor for pure copper in hydrochloric acid

Herein, bee pollen extract (BPE) was assessed for its performance as a green inhibitor of copper corrosion in acidic media. Gas chromatography mass spectrometry was used to identify the major components of BPE. Multiscale testing techniques, i.e. weight assessment, potentiodynamic polarisation tests, and electrochemical impedance spectroscopy, were employed to explore the corrosion properties of pure copper specimens in 1 M HCl with 0–7 g/L BPE. The adsorption of BPE on the copper surface fitted a Langmuir-type isotherm. BPE behaves as a mixed-type inhibitor that effectively decreases the corrosion of pure copper metal surfaces in 1 M HCl. Increasing the concentration of BPE increases its inhibition efficiency; at 7 g/L BPE, a high inhibition efficiency of 94.5% was attained. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and scanning electron microscopy were employed to analyse the copper surface. The inhibitive properties of BPE on pure copper corrosion are attributed to the adsorption of antioxidants and phenolic compounds on the copper surface. This study provides insight into the efficiency of BPE as a potential corrosion inhibitor of copper in acidic environments.

The effect of DTPA on calcium carbonate scale deposition on copper and aluminium surfaces

Calcium carbonate (CaCO3) scale inhibition by Diethylenetriaminepentaacetic acid (DTPA) on copper and aluminium metal surfaces was studied at 60 and 100 °C. The samples were characterized using X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results revealed a novel pot like morphology for calcite which was resulted from the transformation of dumbbell morphology. The pot like morphology exposed the possibility of hollow structures for other polymorphs and is resulted from the breaking apart of the dumbbell structures at the middle, followed by fluffing of the separated parts.

Simulation of Wetting and Interfacial Behavior of Quaternary Ammonium and Phosphonium Ionic Liquid Nanodroplets Over Face-Centered Cubic Metal Surfaces.

We studied the behavior of quaternary ammonium- and phosphonium-based ([N2225][NTf2] and [P2225][NTf2]) ionic liquid (IL) nanodroplets on copper (Cu) and platinum (Pt) metal surfaces using classical molecular dynamics simulations. Solid-liquid interactions were underpinned by studying the dynamic spreading, contact angle, time-dependent binding energies, mean-square displacements, number and charge density profiles, and orientational distribution of these two IL nanodroplets. In particular, the role and importance of different crystallographic facets of face-centered cubic metal surface [Cu(100), Cu(111), Pt(100), and Pt(111)] were investigated. The results indicate a vast variety of properties that are dictated highly by the structure of different crystallographic facets of the metal substrate. The nature of the facet (e.g., the atomic arrangement symmetry, the extent of closed packed, and the unit cell size) leads to an extended scale spreading of the ILs on the surface with the (111) index but not with the (100) index, while the nature of metals itself plays a role.

Above-threshold multiphoton photoemission from noble metal surfaces

Exciting solids with intense femtosecond laser pulses prompts electrons of the interrogated material to respond in a highly nonlinear manner, as is evident in the emission of high-order harmonic radiation and photoelectrons with kinetic energies well above that of the driving photons. Such high-field interactions can be resolved, for example, in above-threshold multiphoton photoemission (ATP) spectroscopy. In this work, we interrogate the nonlinear photoelectric responses of the pristine copper, silver, and gold noble metal surfaces in (111) and (100) crystal orientations in the perturbative regime. Using multiphoton photoemission spectroscopy (mPP) excited by finely tuned optical fields, we characterize enhancement of the mPP and ATP yields from (111) surfaces in selected ${k}_{||}$-momentum ranges when the occupied Shockley surface (SS) states are (near-)resonantly coupled by multiphoton transitions to image potential (IP) intermediate states in the excitation process. The ATP signal from the IP states of (111) surfaces is largely defined by their formation through polarization of SS electrons; this observation is contrasted with ATP experiments from the Ag(100) surface, for which the SS becomes an unoccupied resonance and the IP states can only be excited from bands with significantly more bulk character. In addition, based on the optical power and nonlinear order-dependent mPP spectra, we provide evidence for ATP being a one-step, rather than a sequential process, as previously postulated.

Comparison of scanning Kelvin probe with SEM/EPMA techniques for fingermark recovery from metallic surfaces

Most traditional techniques to recover latent fingermarks from metallic surfaces do not consider the metal surface properties and instead focus on the fingermark chemistry. The scanning Kelvin probe (SKP) technique is a non-contact, non-destructive method, used under ambient conditions, which can be utilised to recover latent prints from metallic surfaces and does not require any enhancement techniques or prevent subsequent forensic analysis. Where a fingermark ridge contacted the metal, the contact potential difference (CPD) contrast between the background surface and the fingermark contact area was 10–50mV.Measurements were performed on the untreated brass, nickel-coated brass and copper metal surfaces and compared to traditional forensic enhancement techniques such as Vacuum Metal Deposition (VMD) using Au–Zn and Au–Ag. Using VMD, the CPD change ranged from 0 to 150mV between the dissimilar metal surfaces affected by the fingermark. In general, SKP worked best without additional enhancement techniques.Scanning Electron Microscope (SEM) scans were used to identify the fingermark contact areas through a sodium, chlorine and oxygen electron probe micro-analyzer (EPMA). The fingermark was observed in the backscattered electron image as the carbon deposits scattered the electrons less than the surrounding metal surface. The fingermark is shown clearly in a Cathodoluminescence scan on the copper sample as it blocks the photon emission at band gap (2.17eV) from the underlying copper oxide (Cu2O) surface. For the first time, SEM, EPMA and Cathodoluminescence techniques were compared to SKP data.Visible and latent fingermarks were tested with latent, eccrinous fingermarks more easily imaged by SKP. Results obtained were very encouraging and suggest that the scanning Kelvin probe technique, which does not need vacuum, could have a place as a first stage analysis tool in serious crime investigation.