Methods of creating porous materials, such as silicon, are described. In some embodiments, plasma sheath modification is used to create ion beams of various incidence angles. These ion beams may, in some cases, form a focused ion beam. The wide range of incidence angles allows the material to be deposited amorphously. The porosity and pore size can be varied by changing various process parameters. In other embodiments, porous oxides can be created by adding oxygen to previously created layers of porous material.