Controllable synthesis of two-dimensional metal nanoparticle arrays with oriented size and number density gradients

Two dimensional metal nanoparticle arrays with a size gradient (see figure) are generated by shadow deposition of a finely-collimated low energy cluster beam under an oblique incident configuration. The length of the gradient region is tunable from hundreds of nanometers to several micrometers, by adjusting the incident angle of the cluster beam. The size of the nanoparticles changes by about one order of magnitude across the gradient region.