Category Archives: 2015 – Summer Research

Samples & Spectra

One of the most important and groundbreaking applications of Raman spectroscopy is detecting materials associated with signs of life and organic chemistry. Gypsum, a sulfate mineral found on Mars, is closely associated with water and has been known to harbor fossil life on Earth. Apatite is made of calcium phosphates, and phosphates can be evidence of life because they are part of the backbone of DNA. Scientists believe that the first life on Earth may have been formed near volcanic seeps in seawater, a sulfur-rich environment. Calcite is also important to life because L- and D-amino acids are known to adsorb to this mineral.

Below we compare the results from our instruments (blue) to the data published on the RRUFF online database (red).

The solubility of apatite, a group of calcium phosphate minerals, controls the solubility of phosphorous and thus affects whether or not abiogenesis, the creation of living organisms from non-living matter, is possible on planets such as Mars. The higher the concentration of phosphorous, the higher chance of abiogenesis occurring. Raman spectroscopy is also an important technique for this mineral because the v1 PO4 band has a very distinct peak between 957 and 962 cm-1 that makes it easily identifiable.
Some calcites, or calcium carbonates, are associated with recent biological life and after thermal processing behave spectroscopically differently than those of abiotic origin. Raman spectroscopy could easily  identify calcites with recent biological activity, suggesting a recent presence of both life and water. Though different calcites have different spectra, they are generally characterised by the 288 and 309 cm-1 peaks. Our instrument was able to identify this peak as well as one of the carbonate Raman bands at 1081 cm-1.
Large concentrations of gyspum have been found on Mars, especially near the North Polar Cap. On Earth, this mineral made of calcium sulfates has been found to harbor and preserve microbial and fossil life. Scientists are investigating whether this calcium sulfate is also associated with water. The (SO4)4- modes lie between 400 and 1150 cm-1, which our instrument was able to identify. If the mineral were to contain traces of water, there would be additional peaks around 2000 to 3000 cm-1.
Spectroscopy has revealed a significant presence of sulfur compounds on the surface of mars, as well as a strong correlation between sulfur and water. Many Mg-, Ca- and Fe3+-sulfates are found on the surface in different hydration states, hosting much of the planet’s hydrogen. Sulfur has not yet been identified on the surface of Mars, but because of its strong Raman cross-section, our instrument would be able to easily detect low levels of sulfur.

The Instrument

This summer research project greatly expanded upon the work done previously by Brett Berger in his Senior Thesis (see work here). In Berger’s device, however, the current increased exponentially with the input voltage, making the laser quite unstable. This summer’s group came up with an op-amp circuit design that would be controlled by a potentiometer and provided a linear relationship between the current and voltage. After weeks of testing, the team found that though the current was stable, the temperature and power output of the laser greatly fluctuated with time, also making the laser unstable. This also posed a potential threat to the laser and/or sample, as they may overheat and be damaged. In the future, the lab hopes to design a temperature-control circuit that will not greatly cut down on the power output of the laser. Below is a diagram of the circuit implemented:

 

 

In order to make the instrument adaptable, the team also made changes to the instrument itself. A new stage was designed to hold a cuvette for liquid samples, a slide for solid samples, and a power meter to measure the laser power output. The team also stationed the spectrometer inside a box with the inside painted black in order to minimize background noise in the spectra and to absorb any laser light that may bounce and reflect. Below is a photograph of the adapted instrument:

Naming of the Lab

Meet the summer research students of 2015! Yvonne Ban is a physics major of the class of 2017, interested in astrophysics. Viviana Bermudez is a prospective engineering major of the class of 2018. During the first few days of research, they came up with an official name for the HMC Astrobiology lab: Extraterrestrial Vehicle Instrumentation Lab, a.k.a. EVIL.