Polymer Surface Analysis: The Leadership and Contributions of David Briggs

David Briggs was a surface analysis pioneer. Starting in 1970 and continuing throughout his career, Dave used his expertise, vision and ability to quickly master new surface analysis methods and solve important industrial problems. It certainly helped that he was an outstanding fund raiser in both industrial and academic settings, which ensured he always had an impressive array of the latest, most advanced surface analysis instrumentation at his disposal. He insisted on doing surface analysis correctly and through his publications, databases and books he provided the community with the needed guidelines and methods to do so. In the 1970s Dave's research was largely focused on x-ray photoelectron spectroscopy (XPS, also known as electron spectroscopy for chemical analysis (ESCA)) characterization of polymers and catalysts. He added secondary ion mass spectrometry (SIMS) to his instrumentation arsenal in the 1980s and provided many of the key, pioneering publications that described how to use this method to characterize polymer surfaces. He also did some of the first surface analysis imaging experiments in the 1980s. In the 1990s he continued his XPS and SIMS research on polymers and advanced the surface analysis community's ability to properly interpret surface analysis data through data bases and advanced data processing methods. Dave continued to publish polymer and catalysis surface analysis papers in the 2000s, but also expanded his surface analysis studies to several other topics.

Chemical Imaging of Human Fingermark by X-ray Photoelectron Spectroscopy (XPS)

X-ray photoelectron spectroscopy (XPS) is a widely used technique to characterize the surface chemistry of materials. It plays a crucial role in accessing qualitative and quantitative information and in detecting the presence of chemical functional groups on the surface of any material. The forensic methods available to detect and identify elements and organic/inorganic compounds are often destructive, so evidence cannot be re-analyzed. However, XPS allows rapid analysis of samples without damaging them. Recently, an increasing number of forensic researchers have begun to study certain chemical information on fingermarks. In this study, the authors aimed to present the applicability and power of XPS imaging in fingermark analysis which can also provide specific information about the fingermark chemical composition. Herein, monochromated X-ray (Al Kα) spot size was fixed at 50 μm. XPS mapping resulted in the acquisition of spectra at each pixel, in an array of 41 × 30 pixels with a step size of 50 μm. Then, a simple discussion has been made about how the scanned surface spectrum and basic snapshot spectra are used to identify different components at a fingertip of a scanned surface area (~3 mm² ). Hence, a fingermark pattern contaminated with caffeine, TiO₂ , and Pb/PbO deposited on the silicon wafer can be chemically mapped and visualized by XPS using principal component analysis (PCA). Thus, the present study showed the possible applicability of XPS for the identification of illicit drugs of abuse, gunshot residue, and skin care products on latent fingermark by mimicking a crime scene evidence.

Development of Latent Fingerprints via Aryldiazonium Tetrachloroaurate Salts on Copper Surfaces: An XPS Study

Surface studies of developed fingerprints have aided in the elimination of criminal cases before moving to the court. The combination of X-ray photoelectron spectroscopy (XPS) with the aryldiazonium gold(III), 4-O₂NC₆H₄N₂⁺AuCl₄^-, surface modifier has been shown to be a novel approach in latent fingerprint detection and development for the quantification of film elements. The robust gold-aryl film was developed on the reducing chemicals excreted in the sebaceous fingerprints without the need for external stimuli and at a lesser extent after contacting the free metal surface. The concurrent reduction of the diazonium functional group and gold(III) from [AuCl₄]^- developed a robust gold-aryl film, which showed increasing gold(0) quantity in the time range of 30-120 min over copper coins and model flat sheets. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) support the presence of reduced gold on the top of the latent fingerprints and the presence of CuO resulting from the reaction of the diazonium salt with copper metal. This research combines the quantification of deposits using XPS, a surface-sensitive technique for chemical analysis, in addition to surface imaging.

Infrared spectroscopy and spectroscopic imaging in forensic science

Infrared spectroscopy and spectroscopic imaging, are robust, label free and inherently non-destructive methods with a high chemical specificity and sensitivity that are frequently employed in forensic science research and practices. This review aims to discuss the applications and recent developments of these methodologies in this field. Furthermore, the use of recently emerged Fourier transform infrared (FT-IR) spectroscopic imaging in transmission, external reflection and Attenuated Total Reflection (ATR) modes are summarised with relevance and potential for forensic science applications. This spectroscopic imaging approach provides the opportunity to obtain the chemical composition of fingermarks and information about possible contaminants deposited at a crime scene. Research that demonstrates the great potential of these techniques for analysis of fingerprint residues, explosive materials and counterfeit drugs will be reviewed. The implications of this research for the examination of different materials are considered, along with an outlook of possible future research avenues for the application of vibrational spectroscopic methods to the analysis of forensic samples.

Surface Analysis of Nanocomplexes by X-ray Photoelectron Spectroscopy (XPS)

Self-assembled nanocomplexes composed of individual molecules that spontaneously connect via noncovalent interactions have recently emerged as versatile alternatives to conventional controlled drug delivery systems because of their unique bioinspired properties (responsiveness, dynamics, etc.). Characterization of such nanocomplexes typically includes their size distribution, surface charge, morphology, drug entrapment efficiency, and verification of the coexistence of labeled components within the nanocomplexes using a colocalization study. Less common is the direct examination of the molecular interactions between the different components in the coassembled nanocomplex, especially in nanocomplexes composed of hygroscopic components, because convenient methods are still lacking. Here, we present a detailed experimental protocol for determining the surface composition and the chemical bonds by X-ray photoelectron spectroscopy (XPS) after drying the deposit hygroscopic sample overnight under UHV. We applied this method to investigate the surface chemistry of binary Ca²⁺-siRNA nanocomplexes and ternary nanocomplexes of hyaluronan-sulfate (HAS)-Ca²⁺-siRNA, deposited on a wafer. Notably, we showed that the protocol can be implemented to study the surface composition and interactions of the deposited nanocomplexes with a traditional XPS instrument, and it requires only a relatively small amount of the nanocomplex suspension.

Application of X-ray Photoelectron Spectroscopy (XPS) for the Surface Characterization of Gunshot Residue (GSR)

Gunshot residue (GSR) is typically found on the hands or clothing of persons who have been in the environment of a discharging firearm, but it may also be found on objects in the vicinity of the discharge. Computer-controlled scanning electron microscopy (CCSEM) is the method preferred by the forensic community for the automated analysis of GSR. GSR samples are therefore typically collected from a crime suspect's hands and/or clothing using SEM sample stubs coated with a conductive adhesive. The three major components in modern firearm cartridge primers are lead styphanate (initiator), antimony sulfide (fuel), and barium nitrate (oxidizer). GSR consists of the products of combustion of these primer materials. Large populations of particles in the size range of ~1–10 μm are rapidly screened by energy-dispersive X-ray spectroscopy (EDS) for the presence of combinations of Pb, Sb, and Ba. When combinations of these three elements are detected, the particles are flagged as potential GSR particulate. Flagged particles with significant Pb/Sb/Ba compositions are subsequently relocated for a live identification and a positive confirmation of GSR. Positive particles are classified as being either “characteristic of GSR” (that is, all three key elements are present) or “consistent with GSR” (that is, any two of the key elements are present) based on the particle composition and morphology. Classification is based on the presence of the constituent elements and is not dependant on the element amounts. If a particle does not meet the proper compositional or morphological criteria, it is rejected as GSR. However, CCSEM generally does not provide information regarding the population of particles much less than 1 μm or the surface chemistry of the GSR particles. This article examines the fine fraction of GSR particles with high-resolution electron microscopy and complements the microscopy data with surface chemistry information from X-ray photoelectron spectroscopy (XPS).