Metadata structure¶

The BaseSignal class stores metadata in the metadata attribute that has a tree structure. By convention, the nodes labels are capitalized and the leaves are not capitalized.

When a leaf contains a quantity that is not dimensionless, the units can be given in an extra leaf with the same label followed by the “_units” suffix.

The metadata structure is represented in the following tree diagram. The default units are given in parentheses. Details about the leaves can be found in the following sections of this chapter.

├── Acquisition_instrument
│   ├── SEM
│   │   ├── Detector
│   │   │   └── EDS
│   │   │       ├── azimuth_angle (º)
│   │   │       ├── elevation_angle (º)
│   │   │       ├── energy_resolution_MnKa (eV)
│   │   │       ├── live_time (s)
│   │   │       └── real_time (s)
│   │   ├── beam_current (nA)
│   │   ├── beam_energy (keV)
│   │   ├── convergence_angle (mrad)
│   │   ├── microscope
│   │   └── tilt_stage (º)
│   └── TEM
│       ├── Detector
│       │   ├── EDS
│       │   │   ├── azimuth_angle (º)
│       │   │   ├── elevation_angle (º)
│       │   │   ├── energy_resolution_MnKa (eV)
│       │   │   ├── live_time (s)
│       │   │   └── real_time (s)
│       │   └── EELS
│       │       ├── collection_angle (mrad)
│       │       ├── dwell_time (s)
│       │       ├── exposure (s)
│       │       └── spectrometer
│       ├── acquisition_mode
│       ├── beam_current (nA)
│       ├── beam_energy (keV)
│       ├── convergence_angle (mrad)
│       ├── microscope
│       └── tilt_stage (º)
├── General
│   ├── date
│   ├── original_filename
│   ├── time
│   └── title
├── Sample
│   ├── description
│   ├── elements
│   ├── thickness
│   └── xray_lines
└── Signal
    ├── Noise_properties
    │   ├── Variance_linear_model
    │   │   ├── correlation_factor
    │   │   ├── gain_factor
    │   │   ├── gain_offset
    │   │   └── parameters_estimation_method
    │   └── variance
    ├── binned
    ├── record_by
    ├── signal_type
    └── signal_origin

General¶

title

type: Str

A title for the signal, e.g. “Sample overview”

original_filename

type: Str

If the signal was loaded from a file this key stores the name of the original file.

time

type: datetime.time

The acquistion or creation time.

date

type: datetime.time

The acquistion or creation date.

Acquisition_instrument¶

TEM¶

Contain information relevant to transmission electron microscope signals.

microscope

type: Str

The microscope model, e.g. VG 501

acquisition_mode

type: Str

Either ‘TEM’ or ‘STEM’

convergence_angle

type: Float

The beam convergence semi-angle in mrad.

beam_energy

type: Float

The energy of the electron beam in keV

beam_current

type: Float

The beam current in nA.

dwell_time

type: Float

The dwell time in seconds. This is relevant for STEM acquisition

exposure

type: Float

The exposure time in seconds. This is relevant for TEM acquistion.

tilt_stage

type: Float

The tilt of the stage in degree.

SEM¶

Contain information relevant to scanning electron microscope signals.

microscope

type: Str

The microscope model, e.g. VG 501

convergence_angle

type: Float

The beam convergence semi-angle in mrad.

beam_energy

type: Float

The energy of the electron beam in keV

beam_current

type: Float

The beam current in nA.

tilt_stage

type: Float

The tilt of the stage in degree.

Detector¶

All instruments can contain a “Detector” node with information about the detector used to acquire the signal. EDX and EELS detectors should follow the following strcture:

EELS¶

This node stores parameters relevant to electron energy loss spectroscopy signals.

spectrometer

type: Str

The spectrometer model, e.g. Gatan 666

collection_angle

type: Float

The collection semi-angle in mrad.

dwell_time

type: Float

The dwell time in seconds. This is relevant for STEM acquisition

exposure

type: Float

The exposure time in seconds. This is relevant for TEM acquistion.

EDS¶

This node stores parameters relevant to electron X-ray energy dispersive spectroscopy data.

azimuth_angle

type: Float

The azimuth angle of the detector in degree. If the azimuth is zero, the detector is perpendicular to the tilt axis.

elevation_angle

type: Float

The elevation angle of the detector in degree. The detector is perpendicular to the surface with an angle of 90.

energy_resolution_MnKa

type: Float

The full width at half maximum (FWHM) of the manganese K alpha (Mn Ka) peak in eV. This value is used as a first approximation of the energy resolution of the detector.

real_time

type: Float

The time spent to record the spectrum in second.

live_time

type: Float

The time spent to record the spectrum in second, compensated for the dead time of the detector.

Sample¶

description

type: Str

A brief description of the sample

elements

type: list

A list of the symbols of the elements composing the sample, e.g. [‘B’, ‘N’] for a sample composed of Boron and Nitrogen.

xray_lines

type: list

A list of the symbols of the X-ray lines to be used for processing, e.g. [‘Al_Ka’, ‘Ni_Lb’] for the K alpha line of Aluminum and the L beta line of Nickel.

thickness

type: Float

The thickness of the sample in m.

Signal¶

signal_type

type: Str

A term that describes the signal type, e.g. EDS, PES... This information can be used by HyperSpy to load the file as a specific signal class and therefore the naming should be standarised. Currently HyperSpy provides special signal class for photoemission spectroscopy, electron energy loss spectroscopy and energy dispersive spectroscopy. The signal_type in these cases should be respectively PES, EELS and EDS_TEM (EDS_SEM).

signal_origin

type: Str

Either ‘simulation’ or ‘experiment’.

record_by

type: Str

One of ‘spectrum’ or ‘image’. It describes how the data is stored in memory. If ‘spectrum’ the spectral data is stored in the faster index.

Noise_properties¶

variance

type: float or Signal instance.

The variance of the data. It can be a float when the noise is Gaussian or a BaseSignal instance if the noise is heteroscedastic, in which case it must have the same dimensions as data.

Variance_linear_model¶

In some cases the variance can be calculated from the data using a simple linear model: variance = (gain_factor * data + gain_offset) * correlation_factor.

gain_factor: type: Float
gain_offset: type: Float
correlation_factor: type: Float
parameters_estimation_method: type: Str

_Internal_parameters¶

This node is “private” and therefore is not displayed when printing the metadata attribute. For example, an “energy” leaf should be accompanied by an “energy_units” leaf.

Stacking_history¶

Generated when using stack(). Used by split(), to retrieve the former list of signal.

step_sizes

type: list of int

Step sizes used that can be used in split.

axis

type: int

The axis index in axes manager on which the dataset were stacked.

Folding¶

Constains parameters that related to the folding/unfolding of signals.