*Scatter*is a software for the analysis of small-angle X-ray (SAXS) and neutron scattering (SANS) curves and patterns of nano- and mesoscopically structured materials such as surfactant, lipid and polymeric micelles and vesicles, lyotropic phases, block copolymers, core/shell-nanoparticles, nanocomposites and mesoporous materials. It in particular can model and fit 2-dimensional scattering patterns and allows the automated, non-interactive analysis of large series of data files.

**Model Structures **

Analysis is possible by linearized presentations (linear/logarithmic, Guinier, Zimm, Holtzer, Kratky, Porod) and by fitting calculated scattering curves and patterns of models to the experimental data. Form factors for the most common geometrical and polymeric structures such as spheres, cylinders, disks, uni- and multilamellar vesicles, Kratky-Porod chains and excluded volume chains are provided. The calculations take into account size distributions (Schulz-Zimm-type) and orientational distributions (Gaussian, Exponential, Onsager, Maier-Saupe), as well as particles with core/shell-structures. Structure factors are available for ordered arrays of these objects including lamellae, cylinders packed in hexagonal (P6/mm), square (P4/mm) or centered rectangular arrays (cmm), spheres arranged on simple cubic (Pm3m), body-centered cubic (Im3m), face-centered cubic (Fm3m), hexagonal (P6/mmc), body-centered tetragonal (I4/mm) or randomly stacked close-packed arrays, and ordered bicontinuous cubic arrays, i.e. gyroid (G-surface, Ia3d), double diamond (D-surface, Pn3m) and the plumbers nightmare (Im3m). Also liquid-like (Percus-Yevick) and fractal structures can be described. Statistical deviations of the objects from their ideal lattice site are described by the Debye-Waller factor. Finite domain sizes and correlation lengths are taken into account by a corresponding peak width. Available peak shapes are Gaussian, Lorentzian, modified Lorentzian I and II, pseudo-Voigt, Pearson VII, and a generalized gamma function which in the limits of a continuous parameter becomes a Gaussian or Lorentzian. It is possible to analyze GISAXS and GISANS patterns of hexagonal arrays of spheres and cylinders.

Scatter uses a downhill Simplex algorithm followed by a Levenberg-Marquardt (LM) algorithm to fit the data to model calculations. This allows the determination of the errors of the fitted parameters from the covariance matrix.

**Data Formats **

Scatter can analyze 1-dimensional data (scattering curves) and 2-dimensional data (scattering patterns). Input data formats for 1-dimensional data are columnar ASCII, one data set per file, in EXCEL format (*.csv), GIFT-format (*.pri; O. Glatter), Fit2D-format (*.chi; A. Hammersley), ESRF-format (*.out, ID02 beamline) or Bruker AXS-format (*.uxd). The primary output data format is columnar ASCII spreadsheet in EXCEL, comma delimited data format (*.csv) which can be imported in many graphics software packages. For the analysis of 1-dimensional data Scatter provides tools for binning and identification of the lattice type.

Input formats for 2-dimensional data are EDF (ESRF/Klora format; *.edf), BSL/OTOKO (EMBL format), raw and T-files output by ILL D11 SANS beamline, AIDA (*.pcb) used by image plate detectors, spreadsheet (ASCII) generated by the program Fit2D (*.spr), *.img format as used at the ALS (Berkeley Lab), *.tif as used by the MAR-CCD detector, as well as some common formats like Bitmap (*.bmp), 8-bit and 16-bit TIFF (*.tif), and *.png. Many other data formats can be read by Fit2D and exported as a spreadsheet files (*.spr), which can be imported into Scatter.

**2D-Tools**

For the analysis of 2-dimensional data Scatter provides tools for beam centering and calibration, azimuthal sector averaging, zooming, lattice identification, peak indexing, real space visualization, and the display and storage of the intensity along predefined lines and circles. It is the only software available that is able to model and fit 2-dimensional scattering patterns. It considers the occurrence of twinned structures and anisotropic peak shapes. The spatial orientation of objects and unit cells can be fixed or rotated around arbitrary axis for calculation.

**Data Series**

Scatter is able to automatically load, view and non-interactively fit large series of data files (> 10000) for the analysis of large amounts of data. The fitted parameters together with their fit errors are stored in a file that can be imported into standard graphics programs (Origin, Sigma Plot, Excel).

**Licensing**

The compiled version for Windows is freely available for non-commercial use, license-free and is provided as-is without any warranty regarding reliability, accuracy and fitness for purpose. It is accompanied by a manual and two example files.