+++
title = "2D structures"
weight = 10
+++

## 2D structures (surface particles)

Particles deposited on or suspended from a surface or interface. The structure
defines how scattering from multiple particles combines.

For dilute distributions, particles scatter independently. For ordered or
partially ordered systems, the structure also describes spatial correlations.

### Positioning: deposit vs suspend

2D structures can be positioned in two ways:

- **Deposit**: The bottom of particles is placed at the layer's bottom
  interface. Use `deposit2D` or `addDeposit2D`. Appropriate for particles
  sitting on a substrate.
- **Suspend**: The top of particles is placed at the layer's top interface.
  Use `suspend2D` or `addSuspend2D`. Appropriate for particles hanging from
  below an interface, such as holes or inclusions embedded in a substrate.

For other vertical positions, translate the particle before constructing the
2D structure.

### Disordered particles

For uncorrelated particles on a surface:

```python
structure = ba.Dilute2D(density, particle)
layer.deposit2D(structure)
```

### Ordered structures

For particles with spatial correlations, use structured layouts:

```python
structure = ba.Crystal2D(particle, lattice)
layer.deposit2D(structure)
```

Structure types include:

- **1D/2D crystal**: particles at periodic positions
- **Paracrystal**: short-range order with cumulative disorder

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