Introducing Students to Raman Spectroscopy as a Research Tool

We describe an experiment designed as an upper level physics laboratory that introduces students to Raman Scattering of electronic materials and research methodology. This experiment is an effective approach in demonstrating the relationship between the Raman intensity of the scattered light from crystals and symmetry dependent Raman selection rules. In our measurements we alter the angle between the crystal axis and the polarization of the incident laser beam by sample rotation. The three dimensional plot of the intensity profile versus the theoretical model is used to distinguish between various crystal plans of the same electronic material. This experiment combines knowledge regarding properties of materials with optical characterization. It is suitable as an upper level physics laboratory or for introducing new graduate student to use Raman spectroscopy as a research tool

Micro-Raman Measurements and Depth Profiling of SiC Article

Recent progress in growth of high quality 4H- SiC and 6H-SiC polytypes materials may lead to new applications for SiC as high power, high temperature, and high frequency devices that can tolerate harsh environments. Nondestructive techniques that could be used in analyzing various layers of such materials after growth or after exposure to harsh environment could be used in investigation of induced defects or structural damages. We have utilized micro-Raman scattering to investigate the depth profiling of Nitrogen doped 4H-SiC samples. Heavily N-doped 4H-SiC epilayers grown on low doped 4H-SiC substrates were examined. Each SiC sample was placed on micro-positioning translational stage in order to accurately control the focal plane of the laser beam within the sample by adjusting normal distance of the microscope objective with respect to the SiC wafer. We were able to clearly distinguish the epilayer from the SiC substrate. Strong phonon peaks and distinct coupled plasmon-LO phonon modes from the N-doped epilayer were used in this depth profiling analysis. A scattering efficiency model describing the optimal focusing condition for backscattering from a translucent sample was developed. The experimental results of depth profiling and our model for optimal backscattering condition will be presented and discussed

Intensity analysis of polarized Raman spectra for off axis single crystal silicon

In this work we demonstrate that polarized backscattered Raman spectroscopy can be used for identifying the crystallographic orientation of silicon cut off axis. The orientation of the crystal is defined by two angles one defined between the (0 0 1) crystal axis and the lab z-axis and the other as the angle of rotation of the crystallographic x-y plane about the crystal’s z-axes. Theoretical Raman intensity profiles are generated by rotating wafers of different geometry about the lab z-axis in the backscattered configuration. This changes the polarization of the incident light with respect to the crystallographic axes. The impact of the off axis Si on the Raman intensity profile were investigated to identified specific signatures in the Raman spectra that are most effective in determining the degree of off axis cut for single crystal Si. The results show excellent agreement with experimental outcomes

Materials processing and spectroscopic characterization of 4H-SiC

The effect of chemical-mechanical polishing and high temperature furnace annealing on nitrogen-doped crystalline 4H-SiC was investigated using spectroscopic and microscopic techniques. SiC wafers were processed by Chemical-Mechanical Polishing (CMP) and high temperature furnace annealing up to 1600C. The X-ray Photon Spectroscopy (XPS) results indicate that annealing at the higher temperatures varies the surface chemical composition of the samples. The non-bridging oxygen content increases with annealing temperature. This suggests that the oxycarbide content may be increasing with temperature, a fact that could affect the free carrier concentration. Preliminary experiments suggest that the forbidden Raman mode is visible at temperatures around 1200C and indicating more out of plane stress. Preliminary experiments also suggest that the transverse optic phonon mode shows a slight shift indicating in plane stress at the same temperature. The environmental scanning electron microscope (ESEM) was used to image the defects on the sample surfaces. The chemical composition of the bulk and specifically that of the defects were also determined using Energy Dispersive x-ray Spectroscopy (EDS). The defects on the unannealed CMP samples were mostly confined to the surface. SEM micrographs obtained by backscattered electrons did not indicate defects propagating into the sample. The samples annealed at 1000C and 1200C showed an increase in oxygen content in the bulk. Higher temperatures of annealing introduced defects that were carbon rich. However, for 1400C only a single silicon rich defect was observed. The carbon rich defects were found to increase with annealing temperature and grow out of the surface of the samples. Lines were found to appear on the samples at 1200 C although the chemical composition did not appear to vary. These lines increased in length for samples annealed at 1400 C. The Raman results correlate with surface structural variations at this temperature. This investigation concludes that the optimal furnace annealing temperature for an argon atmosphere could be below 1200oC

Introducing Raman Spectroscopy Of Crystalline Solids In The Undergraduate Curriculum

We describe an experiment designed as an upper level physics laboratory that introduces students to Raman Scattering of electronic materials and research methodology. This experiment is an effective approach in demonstrating the relationship between the Raman intensity of the scattered light from crystals and symmetry dependent Raman selection rules. In our measurements we alter the angle between the crystal axis and the polarization of the incident laser beam by Si (100) sample rotation. The three dimensional plot of the intensity profile versus the theoretical model is used to distinguish differences between various crystal planes of the same electronic sample. This experiment will combine optical analysis with materials aspects of electronic materials

Growth Of (100) Oriented Diamond Thin Films On Ball Structure Diamond-Like Particles

The morphology of typical CVD diamond thin films has been shown to be controlled by the concentration of methane during deposition. For example, for CH4 concentrations c \u3c 0.4% the (111) faces dominate, while at 0.4% \u3c c \u3c 1.2% (100) faces dominate. Here we showed that the (100) oriented diamond films can be grown on top of the microcrystalline ball-like particles under suitable conditions. These (100) oriented diamond films are grown under the condition of 1.5% methane in hydrogen, substrate temperature of 680 °C-750 °C, and pressure of 30–80 Torr. The bombardment of the diamond thin films by ions in the plasma is believed to be an important factor for the formation of (100) oriented films on top of the ball-like particles. SEM, Raman, and x-ray techniques were used to characterize the deposited (100) oriented diamond thin films. © 1992, Materials Research Society. All rights reserved

Microscopic and Spectroscopic Characterization of Chemo-Mechanically Polished, Furnace-Annealed, Nitrogen-Doped 4H:SiC

The effect of chemical–mechanical polishing and high-temperature furnace annealing at temperatures ranging from 1000 °C to 1600 °C on nitrogen-doped crystalline 4H:SiC was investigated. Techniques used to characterize the samples included environmental scanning electron microscopy (ESEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy. The ESEM micrographs and EDS data indicated that there were structural defects on the unannealed sample that did not propagate into the sample or vary in composition from the bulk. The sample annealed at 1000 °C showed oxygen-rich and carbon-depleted surface defects. Annealing at temperatures above 1200 °C introduced defects that grew out of the sample surface. These were carbon and oxygen rich, but depleted in silicon. This supported the XPS data, which showed an increase in the surface C bonding with annealing temperatures above 1200 °C. The XPS data also suggested that the oxycarbide content may be increasing on annealing above 1200 °C. Raman micro-probe data from the defects on the sample annealed at 1200 °C showed the maximum shift in the transverse optical phonon mode at 776 cm-1, indicating that the beginning of carbon out-diffusion may be accompanied with structural changes. Optimal annealing temperatures are thus below 1200 °C

Investigation of magnetite nanoparticles using Raman scattering and electron microscopy

The thriving physics program at Kettering University has experienced a three-fold increase in the number of physics majors since 2002. Our unique physics program requires students alternate between on-campus academic terms and off-campus co-op work terms on a three months rotation format to complete their degree in 4.5 years that includes summer as either school or co-op term. Students complete a minimum of five terms (∼ 15 months) of cooperative work terms, and two terms (∼ 6 months) of senior thesis work. The IP of the thesis work done at a co-op site belongs to the company. This has attracted co-op sponsors for our program by removing the IP concerns. The cooperative and experiential education part of our program is required for graduation, without any credits assigned to it. At the end of every co-op term students\u27 work performance is evaluated by their co-op supervisor, which should match expected performance standards. In addition to co-op and thesis, our programs include a senior capstone design project course, concentrations within physics (Acoustics, Optics, and Materials), a required technical sequence outside physics, as well as entrepreneurship across curriculum. The success of our student securing the highest paid jobs for undergraduate physics majors in the nation plus their success in graduate studies are the main ``Pull Factors\u27\u27 that has lead to three fold increase the physics majors since 2002

Investigation of Magnetite Nanoparticles Using Raman Scattering and Electron Microscopy

The thriving physics program at Kettering University has experienced a three-fold increase in the number of physics majors since 2002. Our unique physics program requires students alternate between on-campus academic terms and off-campus co-op work terms on a three months rotation format to complete their degree in 4.5 years that includes summer as either school or co-op term. Students complete a minimum of five terms (∼ 15 months) of cooperative work terms, and two terms (∼ 6 months) of senior thesis work. The IP of the thesis work done at a co-op site belongs to the company. This has attracted co-op sponsors for our program by removing the IP concerns. The cooperative and experiential education part of our program is required for graduation, without any credits assigned to it. At the end of every co-op term students\u27 work performance is evaluated by their co-op supervisor, which should match expected performance standards. In addition to co-op and thesis, our programs include a senior capstone design project course, concentrations within physics (Acoustics, Optics, and Materials), a required technical sequence outside physics, as well as entrepreneurship across curriculum. The success of our student securing the highest paid jobs for undergraduate physics majors in the nation plus their success in graduate studies are the main ``Pull Factors\u27\u27 that has lead to three fold increase the physics majors since 2002

Chemical-Mechanical Polishing and Rapid Thermal Annealing of SiC: Raman Spectroscopy and ESCA (XPS) Studies

The effects of Chem-Mechanical Polishing (CMP) and Rapid Thermal Annealing (RTA) on n-type 4H:SiC samples doped with nitrogen were investigated using Raman scattering and X-ray Phtoelectron Spectroscopy (XPS a.k.a. ESCA) measurements. A comparison of the Raman spectra from Mechanically Polished (MP) SiC annealed at 600°C and 800°C displays a frequency shift in the coupled plasmon LO-phonon mode. Since the coupled mode frequency is a direct measure of the free carrier concentration, this observation may suggest the removal of polishing induced carrier traps with increasing annealing temperature. The CMP samples did not show this frequency shift, thereby indicating that such polishing traps were not created in that process. The Si-peak observed in the XPS spectra of the unannealed CMP sample indicates primarily a Si-C bonding, while that for the MP sample is more complex, indicating other bonds beside Si-C. Drastic changes in O, C, Si surface content were observed for annealing between 1000°C and 1100°C. The peaks in the XPS spectra associated with the chemical environment for C, O, and N are complex and may be explained as silicon oxycarbide type structures near the surface or possibly around the interface of the SiC substrate with a thin surface oxide layer