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Raman Spectroscopy

Raman spectroscopy probes vibrational modes in materials through inelastic light scattering. Raman provides information about crystal structure, bonding, stress, and chemical composition in a non-destructive manner.

Overview

This schema package defines:

  • RamanMeasurement - Raman measurements with laser conditions, spectral data, and peak analysis

Raman measurements extend BaseMeasurement, providing:

  • Links to measured samples and instrument
  • Laser excitation parameters (wavelength, power, spot size)
  • Spectrometer configuration (grating, detector, filters)
  • Raman spectra (intensity vs. Raman shift)
  • Peak positions, widths, and assignments

Typical Usage

  1. Select samples: Reference samples to analyze
  2. Set laser: Wavelength (visible or NIR), power, spot size, polarization
  3. Configure spectrometer: Grating, spectral range, integration time
  4. Measure spectrum: Raman intensity vs. wavenumber shift (cm⁻¹)
  5. Identify peaks: Assign vibrational modes to chemical bonds/structures
  6. Analysis: Peak positions (bonding), widths (disorder), intensities (concentrations)

What Raman Tells You

  • Crystal structure: Characteristic mode fingerprints for each phase
  • Phase identification: Distinguish polymorphs and crystal structures
  • Bonding environment: Bond types from mode frequencies
  • Stress/strain: Peak shifts from lattice distortion
  • Crystallinity: Peak widths indicate disorder
  • Composition: For alloys/solutions, mode shifts track composition
  • Defects: Disorder-induced modes

Common Raman Applications

  • Material identification: Quick phase ID (complementary to XRD)
  • Carbon materials: Graphene layers, disorder (D/G ratio)
  • Semiconductors: Phonon modes, strain, doping
  • Oxides/ceramics: Phase purity, oxygen vacancies
  • Stress mapping: Spatially-resolved strain analysis

Key Parameters

  • Laser wavelength: Visible (532, 633 nm) or NIR (785 nm)
  • Shorter wavelength: Better scattering, may cause heating/damage
  • Longer wavelength: Reduced fluorescence background
  • Laser power: Signal vs. sample heating trade-off
  • Spot size: Spatial resolution vs. signal
  • Polarization: Access to specific modes in oriented samples
  • Temperature: In-situ measurements possible

Raman vs. Other Techniques

  • Raman vs. XRD: Raman works on amorphous materials, small volumes, gives bonding info
  • Raman vs. XPS: Raman is non-destructive, less surface-sensitive, faster
  • Raman vs. FTIR: Complementary selection rules (Raman: polarizability; FTIR: dipole moment)
  • Measured samples: Samples from any synthesis method
  • Instrument: DTUInstrument (Raman spectrometer with laser)
  • Complementary: XRD for crystal structure, XPS for composition
  • Analysis: Jupyter Analysis for peak fitting, deconvolution, stress analysis

Schema Documentation

RamanResult

description: Single Raman spectrum result at a specific spatial position. Stores spectral data (intensity vs Raman shift) along with metadata about the measurement position and associated optical image. Inherits from MappingResult to get standardized position handling and naming.

Note: Laser wavelength, accumulation count, and exposure time are stored at the RamanMeasurement level as they are common to all measurement points.

inherits from: nomad_measurements.mapping.schema.MappingResult

properties:

name type
intensity float64 The Raman intensity at each wavenumber
shape=['*']
raman_shift float64 The Raman shift values in 1/cm
shape=['*'], unit=1 / centimeter
optical_image str

normalization:

Normalize the Raman result metadata.

Calls parent MappingResult normalizer to generate the result name from position coordinates (e.g., "Stage x = 2.0 mm, y = 5.0 mm").

RamanMeasurement

description: Main schema for Raman mapping measurements. Top-level section for a complete Raman mapping measurement, containing multiple individual spectra (results), metadata, sample references, and auto-generated visualizations. Implements NOMAD Schema interface for ELN integration.

inherits from: nomad_dtu_nanolab_plugin.schema_packages.basesections.DtuNanolabMeasurement, nomad.datamodel.metainfo.plot.PlotSection, nomad.datamodel.data.EntryData

properties:

name type
raman_data_file str Data file containing the Raman spectra. The expected format is Renishaw WDF mapping file.
accumulation_count int Number of accumulations for each measurement point. Common to all spectra in the mapping.
exposure_time float64 Total exposure time per accumulation point. Common to all spectra in the mapping.
unit=second
laser_wavelength float64 The wavelength of the laser used in the Raman measurement. Common to all spectra in the mapping.
unit=nanometer
laser_power_percent float64 Laser power as a percentage of maximum power (0-100%). Common to all spectra in the mapping.
objective_magnification float64 Objective lens magnification (e.g., 20 for 20x, 50 for 50x, 100 for 100x). Common to all spectra in the mapping.
optical_image_grid str Optical image of the measurement grid.
results RamanResult The result of the measurement.
sub-section, repeats
sample_alignment nomad_measurements.mapping.schema.RectangularSampleAlignment The alignment of the sample.
sub-section

normalization:

Main normalization pipeline for Raman measurements.

Executed automatically when entry is saved in NOMAD. Orchestrates the complete data processing workflow from raw WDF file to searchable, visualized results.

Processing Pipeline: 1. Set default location if not provided 2. Link measurement to sample based on filename pattern 3. Parse WDF file and extract all data (read_raman_data) 4. Call parent normalizers for standard metadata 5. Generate interactive plots if results exist (plot) 6. Add intensity map to figures