Time-resolved spatial distributions of individual components of electroactive films during potentiodynamic electrodeposition

Of the attributes that determine the performance of electroactive film-based devices, the least well quantified and understood is the spatial distribution of the component species. This is critical since it dictates the transport rates of all the mobile species (electrons, counterions, solvent, analyte, and reactant) and the film mechanical properties (as exploited in actuator devices). One of the few techniques able to provide individual species population profiles in situ is specular neutron reflectivity (NR). Historically, this information is obtained at the cost of poor time resolution (hours). Here we show how NR measurements with event mode data acquisition enable both spatial and temporal resolution; the latter can be selected postexperiment and varied during the transient. We profile individual species at “buried” interfaces under dynamic electrochemical conditions during polypyrrole electrodeposition and Cu deposition/dissolution. In the case of polypyrrole, the film is homogeneous throughout growth; there is no evidence of dendrite formation followed by solvent (water) displacement. Correlation of NR-derived film thickness and coulometric assay allows calculation of the solvent volume fraction, ϕS = 0.48. In the case of Cu in a deep eutectic solvent, the complexing nature of the medium results in time-dependent metal speciation: mechanistically, dissolution does not simply follow the deposition pathway in reverse

Real-time in situ dynamic sub-surface imaging of multi-component electrodeposited films using event mode neutron reflectivity

Exquisite control of the electrodeposition of metal films and coatings is critical to a number of high technology and manufacturing industries, delivering functionality as diverse as anti- corrosion and anti-wear coatings, electronic device interconnects and energy storage. The frequent involvement of more than one metal motivates the capability to control, maintain and monitor spatial disposition of the component metals, whether as multilayers, alloys or composites. Here we investigate the deposition, evolution and dissolution of single and two- component metal layers involving Ag, Cu, and Sn on Au substrates immersed in the deep eutectic solvent (DES) Ethaline. During galvanostatically controlled stripping of the metals from two-component systems the potential signature in simultaneous thickness electrochemical potential (STEP) measurements provides identification of the dissolving metal; coulometric assay of deposition efficiency is an additional outcome. When combined with quartz crystal microbalance (QCM) frequency responses, the mass change:charge ratio provides oxidation state data; this is significant for Cu in the high chloride environment provided by Ethaline. The spatial distribution (solvent penetration and external roughness) of multiple components in bilayer systems is provided by specular neutron reflectivity (NR). Significantly, the use of recently established event mode capability shortens the observational timescale of the NR measurements by an order of magnitude, permitting dynamic in situ observations on practically useful timescales. Ag,Cu bilayers of both spatial configurations give identical STEP signatures indicating that, despite the extremely low layer porosity, thermodynamic constraints (rather than spatial accessibility) dictate reactivity; thus, surprisingly, Cu dissolves first in both instances. Sn penetrates the Au electrode on the timescale of deposition; this can be prevented by interposing a layer of either Ag or Cu

Electrochemical deposition of silver and copper from a deep eutectic solvent studied using time-resolved neutron reflectivity

Here, we describe new developments in the study of electrodeposition processes with time-resolved dynamic neutron reflectivity (NR) methods to achieve insights into the differences between growth of metal films using a range of electrochemical control functions. We show that the temporal resolution has increased from 1 to 2 h per data set (in our previous studies) to approximately 8 min. We have studied the electrochemical deposition of copper and silver as thin-film metals onto a gold electrode substrate from a deep eutectic solvent using potentiodynamic (PD), potentiostatic (PS) and galvanostatic (GS) electrochemical control functions. In particular, we have utilised novel developments in neutron reflectivity methods to acquire real-time data for the growing metal films. Event mode capture of neutron scattering events, as a function of momentum transfer vector, Q, during electrochemical growth has enabled time-resolved measurement of the neutron reflectivity, R(Q), profiles of the growing metal films. Subsequent fitting and iterative optimisation of the R(Q,t) data reveals the thickness, roughness and relative density (spatially resolved solvent content) of the metal film during growth. These data show that the different electrochemical growth methodologies exhibit different trends in thickness, roughness and solvation. Silver films show an increasing roughness trend with time but these trends are largely independent of growth method. In contrast, the roughness of copper films, grown under similar conditions, shows a strong dependency on growth method with PS methods producing smoothest films. These conclusions are confirmed by ex-situ AFM measurements. The fitted NR data show that the Cu and Ag films contain between 5 and 10% volume fraction solvent. Furthermore, we have explored different NR data fitting methodologies in order to process the large numbers of data sets produced. Gratifyingly, the different methodologies and starting conditions yield a very consistent picture of metal film growth

Microscopy in forensic science

This chapter examines the use of electron microscopy, atomic force microscopy and other analytical techniques in forensic investigation and research. These tools can be used to enhance examination of human remains and trace evidence to improve understanding of cause of death, victim identification or post mortem interval.A police-designed scenario is used to highlight trace evidence such as glass, gun shot residue and paint. The validity of forensic techniques is discussed, with reference to international standards, repeatability, and false convictions. Ballistic evidence is used to highlight the complexities in evidence interpretation, including manufacturing variability, environmental effects and likelihood ratios.The use of scanning electron microscopy (SEM), atomic force microscopy (AFM) and other techniques in the development of forensic research is showcased, with particular examples from the field of fingerprints. Examples include improvements in the development of fingermarks from difficult surfaces, interaction of evidence types, and added intelligence from the crime scene, such as forensic timeline or gender of perpetrator

Detection of fingermarks - applicability to metallic surfaces: A literature review

There are many different fingermark visualization techniques available, and the choice of methodology employed may be dependent on the surface type. This comprehensive review of the scientific literature evaluates the methodologies of fingermark enhancement methods that are applicable to metallic surfaces; optical, physical, chemical, and physicochemical methods are critically discussed. Methods that are currently used and those that have the potential to reduce the cost and time required to process evidence and increase the recovery rates are considered and are assessed against the Centre for Applied Science and Technology (CAST) and the International Fingerprint Research Group (IFRG) guidelines. The use of chemical imaging techniques in particular has increased the potential to recover fingermarks of sufficient quality for identification purposes. Presently, there appears to be a lack of detailed research pertaining to validation and thorough casework studies for fingermark enhancement techniques. Further studies incorporating these guidelines are recommende

Characterizing electroactive polymer films : from fundamentals to fingerprints

Visualisation of latent fingerprints present on metallic surfaces has been demonstrated by means of spatially selective deposition of conducting copolymers. This novel technique utilises the inhibition of electrochemical processes on areas that have been masked by the fingerprint. This results in electropolymerisation between the ridges, generating a negative image of the fingerprint. The efficiency of recovery in forensically challenging scenarios of the copolymers was compared with the corresponding homopolymers. An extension of this electrochromic enhancement to include fluorescence has been developed using a novel synthetic pathway aiming to create more free volume to aid the inclusion of bulky fluorophore moieties. The unique selectivity of neutron reflectivity (NR), with isotopic contrast variation, permitted the diagnosis of chemical and structural changes within the depth profile of the polymer during the incorporation of the fluorophore moieties. The properties of conducting polymer films are determined by film composition and structure which, this thesis will show, can lead to different routes to electroneutrality maintenance during electrochemically controlled redox switching (doping/undoping). NR was used to quantify the diverse permeation characteristics of conventional solvents and ionic liquids into an electroactive copolymer. It revealed how the availabilities of these mechanisms are dictated by anion and cation sources and sinks in the film and liquid phases where molecular solvent is/is not present. In multi-layered systems, the nature of the polymer/polymer interface is central to the rectifying (segregated) or capacitive (interdiffused) characteristics of the films, such that the spatial distribution of the different polymer components determines the optical and electronic properties of the films. These properties are important for the potential applications of these multi-component systems in energy storage. NR was used to probe the extent of segregation and solvation properties of multi-layer films and revealed the order the components are deposited has a great effect on the final film properties

Electrochromic enhancement of latent fingerprints by poly(3,4-ethylenedioxythiophene)

Spatially selective electrodeposition of poly-3,4-ethylenedioxythiophene (PEDOT) thin films on metallic surfaces is shown to be an effective means of visualizing latent fingerprints. The technique exploits the fingerprint deposit as an insulating mask, such that electrochemical processes (here, polymer deposition) may only take place on deposit-free areas of the surface between the ridges of the fingerprint deposit; the end result is a negative image of the fingermark. Use of a surfactant (sodium dodecylsulphate, SDS) to solubilise the EDOT monomer allows the use of an aqueous electrolyte. Electrochemical (coulometric) data provide a total assay of deposited material, yielding spatially averaged film thicknesses, which are commensurate with substantive filling of the trenches between fingerprint deposit ridges, but not overfilling to the extent that the ridge detail is covered. This is confirmed by optical microscopy and AFM images, which show continuous polymer deposition within the trenches and good definition at the ridge edges. Stainless steel substrates treated in this manner and transferred to background electrolyte (aqueous sulphuric acid) showed enhanced fingerprints when the contrast between the polymer background and fingerprint deposit was optimised using the electrochromic properties of the PEDOT films. The facility of the method to reveal fingerprints of various ages and subjected to plausible environmental histories was demonstrated. Comparison of this enhancement methodology with commonly used fingerprint enhancement methods (dusting with powder, application of wet powder suspensions and cyanoacrylate fuming) showed promising performance in selected scenarios of practical interest