Mark S. Anderson

Controls on development and diversity of Early Archean stromatolites

The ≈3,450-million-year-old Strelley Pool Formation in Western Australia contains a reef-like assembly of laminated sedimentary accretion structures (stromatolites) that have macroscale characteristics suggestive of biological influence. However, direct microscale evidence of biology—namely, organic microbial remains or biosedimentary fabrics—has to date eluded discovery in the extensively-recrystallized rocks. Recently-identified outcrops with relatively good textural preservation record microscale evidence of primary sedimentary processes, including some that indicate probable microbial mat formation. Furthermore, we find relict fabrics and organic layers that covary with stromatolite morphology, linking morphologic diversity to changes in sedimentation, seafloor mineral precipitation, and inferred microbial mat development. Thus, the most direct and compelling signatures of life in the Strelley Pool Formation are those observed at the microscopic scale. By examining spatiotemporal changes in microscale characteristics it is possible not only to recognize the presence of probable microbial mats during stromatolite development, but also to infer aspects of the biological inputs to stromatolite morphogenesis. The persistence of an inferred biological signal through changing environmental circumstances and stromatolite types indicates that benthic microbial populations adapted to shifting environmental conditions in early oceans.

Microstructural investigations of light-emitting porous Si layers

The structural and morphological characteristics of visible‐light‐emitting porous Si layers produced by anodic and stain etching of single‐crystal Si substrates are compared using transmission electron microscopy and atomic force microscopy (AFM). AFM of conventionally anodized, laterally anodized and stain‐etched Si layers show that the layers have a fractal‐type surface morphology. The anodized layers are rougher than the stain‐etched films. At higher magnification 10 nm sized hillocks are visible on the surface. Transmission electron diffraction patterns indicate an amorphous structure with no evidence for the presence of crystalline Si in the near‐surface regions of the porous Si layers.

Enhanced infrared absorption with dielectric nanoparticles

Enhanced infrared absorption is demonstrated for anthracene coating polar dielectric nanoparticles of silicon carbide and aluminum oxide. An enhancement factor greater than 100 was measured near the surface of silicon carbide particles. This is the result of the enhanced optical fields at the surface of the particles when illuminated at the surface phonon resonance frequencies. This phonon resonance effect is analogous to plasmon resonance that is the basis of surface enhanced infrared absorption and surface enhanced Raman scattering. The results have implications for near-field microscopy, the characterization of nano-optical devices, and chemical sensing. In addition, the methodology used for surface phonon analysis of particles is useful for simulating comet and interstellar dust spectra.

A Raman-atomic force microscope for apertureless-near-field spectroscopy and optical trapping

An instrument that combines the analytical power of Raman spectroscopy with the spatial resolution of the Atomic Force Microscope (AFM) is presented. This instrument is capable of resolving 50 nm scale spectral features or better by using surface enhanced Raman scattering at the AFM tip. The localized spectrochemical information allows the interpretation of the concurrently acquired friction or phase contrast AFM images. This instrument has a unique combination of features including side illumination of the tip–sample interface that permits opaque samples. As a result of precise focusing of a laser at the AFM tip–sample interface this instrument is also capable of laser beam profiling and studying optical trapping at the probe tip. Applications of this versatile instrument include chemical analysis of nanometer scale phenomena, chemical separation, and the potential for targeted single molecule spectroscopy.

Surface enhanced infrared absorption by coupling phonon and plasma resonance

A gold and silicon carbide particle matrix is presented that concentrates light to its surface using a combination of phonon and plasmon resonance mechanisms. The enhanced infrared absorption spectrum of absorbed molecules is used to probe the coupled phonon and plasmon surface resonances. Sensitive molecular detection is achieved by measuring the enhanced infrared absorption or the frequency shift in the surface modes of the coated matrix. This work demonstrates that hybrid polariton resonance structures using metallic and polar dielectric materials are feasible for applications in near-field microscopy, nano-optical devices, and trace chemical sensing.

Biosignature Detection at an Arctic Analog to Europa

The compelling evidence for an ocean beneath the ice shell of Europa makes it a high priority for astrobiological investigations. Future missions to the icy surface of this moon will query the plausibly sulfur-rich materials for potential indications of the presence of life carried to the surface by mobile ice or partial melt. However, the potential for generation and preservation of biosignatures under cold, sulfur-rich conditions has not previously been investigated, as there have not been suitable environments on Earth to study. Here, we describe the characterization of a range of biosignatures within potentially analogous sulfur deposits from the surface of an Arctic glacier at Borup Fiord Pass to evaluate whether evidence for microbial activities is produced and preserved within these deposits. Optical and electron microscopy revealed microorganisms and extracellular materials. Elemental sulfur (S⁰), the dominant mineralogy within field samples, is present as rhombic and needle-shaped mineral grains and spherical mineral aggregates, commonly observed in association with extracellular polymeric substances. Orthorhombic α-sulfur represents the stable form of S⁰, whereas the monoclinic (needle-shaped) γ-sulfur form rosickyite is metastable and has previously been associated with sulfide-oxidizing microbial communities. Scanning transmission electron microscopy showed mineral deposition on cellular and extracellular materials in the form of submicron-sized, needle-shaped crystals. X-ray diffraction measurements supply supporting evidence for the presence of a minor component of rosickyite. Infrared spectroscopy revealed parts-per-million level organics in the Borup sulfur deposits and organic functional groups diagnostic of biomolecules such as proteins and fatty acids. Organic components are below the detection limit for Raman spectra, which were dominated by sulfur peaks. These combined investigations indicate that sulfur mineral deposits may contain identifiable biosignatures that can be stabilized and preserved under low-temperature conditions. Borup Fiord Pass represents a useful testing ground for instruments and techniques relevant to future astrobiological exploration at Europa.

Infrared Spectroscopy with an Atomic Force Microscope

An atomic force microscope (AFM) has been used to measure the modulated photothermal displacement of a surface, thus acting as a local detector. This was demonstrated with Fourier transform infrared (FT-IR) and filter spectrometers focused on various samples. Similarly, surface layers were removed by an AFM and analyzed by the photothermal deformation of the coated cantilever. This work shows that the AFM can function as both an infrared detector and a precise surface separation device for spectroscopic analysis. The AFM combined with an FT-IR has the potential to enhance the sensitivity, selectivity, and spatial resolution of infrared spectroscopy.

Nonplasmonic surface enhanced Raman spectroscopy using silica microspheres

Surface enhanced Raman spectroscopy is presented using a nonplasmonic mechanism based on whispering gallery modes in silica microspheres. Sensitive Raman analysis of molecular films is demonstrated by using 5–10 μm sized silica spheres. The advantages of this nonplasmonic approach are the active substrate is chemically inert, thermally stable, and relatively simple to fabricate. Applications include trace organic analysis particularly for in situ planetary instruments that require robust sensors with consistent response.

In situ cleaning of instruments for the sensitive detection of organics on Mars

A method is presented for in situ cleaning of spacecraft instruments that analyze planetary soil and rock. We have found that vibrating hardware, used to facilitate powder transport, was also effective at removing contamination. Surfaces can be cleaned below monolayer levels using vibrating surfaces in the presence of mineral powder. Both organic and particulate contamination is efficiently removed. Fine grained regolith from the planetary surface or an organic free reference material may serve as the powder used for cleaning. We present both analytical and experimental results for the contamination transfer fraction and the conditions required to clean the hardware prior to sensitive chemical analysis.

Vacuum ultraviolet radiation/atomic oxygen synergism in fluorinated ethylene propylene Teflon erosion

A micrographic investigation is reported of samples of the fluorinated ethylene propylene (FEP) Teflon thermal-blanketing materials recovered from the Long-Duration Exposure Facility (LDEF) satellite. The samples are taken from the trailing edge and row 8 which correspond to exposures to vacuum UV (VUV) and VUV + atomic O, respectively. Data are taken from SEM and IR-spectra observations, and the LDEF leading-edge FEP shows a high degree of erosion, roughening, and sharp peaks angled in the direction of the flow of atomic O. The trailing edge sample influenced primarily by VUV shows a hard brittle layer and some cracked mosaic patterns. Comparisons to a reference sample suggest that the brittle layer is related to exposure to VUV and is removed by atomic-O impingement. Polymers that are stable to VUV radiation appear to be more stable in terms of atomic oxygen.