Abstract

Raman spectroscopy has been used extensively on meteoritic samples since it is a nondestructive tool that provides information about their structure and mineralogical composition, which can give important clues about planet formation. However, the power of the excitation laser used in this technique can alter the properties of the samples due to thermal effects. In this undergraduate research work, the laser-induced thermal effects produced on the carbonaceous chondritic meteorite Northwest Africa 6603 were studied in detail by analyzing the low- and high-resolution Raman spectra parameters of the minerals found in the inclusions and matrix of this sample as a function of the excitation power. Olivine (forsterite), graphitic carbon, pyroxene (enstatite), hematite and gehlenite were the minerals identified in the studied regions. The Raman parameters of these minerals were affected by the laser power to a greater or lesser extent, indicating an increase in structural disorder. In general, the alterations observed were permanent (reverse changes were not observed). These thermal effects were correlated with the topography of the irradiated regions by analyzing their changes using optical microscopy. The micrographs of a few regions showed changes on their topography after irradiating the regions with the maximum applied power (e.g., more depressed areas). These findings exhibited strong evidence of the thermal effects induced by the laser power on the materials found in this fragment, which must be considered to avoid alterations of the physical and chemical properties of the meteoritic samples. In addition, this work presents the first study done on the mineralogical composition of Northwest Africa 6603 using Raman spectroscopy. Furthermore, from an educational standpoint, this project exposed the involved undergraduate physics students to numerous research steps (e.g., experiment preparation, data acquisition/analysis, and manuscript preparation) which provided them with a broad spectrum of valuable scientific and technical tools for their future careers.

摘要

拉曼光谱已广泛用于陨石样品，因为它是一种非破坏性工具，可以提供有关其结构和矿物成分的信息，从而提供有关行星形成的重要线索。然而，由于热效应，该技术中使用的激发激光的功率会改变样品的特性。在这项本科生研究工作中，通过分析在该样品的包裹体和基质中发现的矿物的低分辨率和高分辨率拉曼光谱参数，详细研究了碳质球粒陨石 Northwest Africa 6603 产生的激光诱导热效应：激励功率的函数。橄榄石（镁橄榄石）、石墨碳、辉石（顽辉石）、赤铁矿和钙黄长石是在研究区域发现的矿物。这些矿物的拉曼参数或多或少受到激光功率的影响，表明结构紊乱程度增加。一般来说，观察到的改变是永久性的（没有观察到反向变化）。通过使用光学显微镜分析它们的变化，这些热效应与受照射区域的地形相关。一些区域的显微照片显示在用最大施加功率照射区域后它们的形貌发生变化（例如，更凹陷的区域）。这些发现展示了激光功率对该碎片中发现的材料产生热效应的有力证据，必须考虑到这一点，以避免改变陨石样品的物理和化学性质。此外，这项工作介绍了使用拉曼光谱对西北非洲 6603 的矿物成分进行的第一项研究。此外，从教育的角度来看，该项目让参与的本科物理学生接触到许多研究步骤（例如，实验准备、数据采集/分析和手稿准备），为他们的未来提供了广泛的有价值的科学和技术工具事业。