Dielectric spheres arranged in the diamond lattice was the first photonic crystal showing a complete photonic band gap [1]. This photonic crystal was found by placing extra spheres (red) in the face-centered-cubic lattice (green). For dielectric spheres with refractive index n=3.6 in air background, a maximum dw/w=15% gap was obtained at dielectric volume fraction f=0.37. For air spheres in a dielectric background a maximum 29% gap was found at air volume fraction f=0.81. However, the results for dielectric spheres have been recalculated [2,3,4] and the gap at dielectric volume fraction f=0.34 (where the dielectric spheres touch each other and form a self-sustained structure) is only 3.5%.

A possible method to build spheres in the diamond lattice is the robot-aided micromanipulation of micro-spheres [5,6]. The method involves the construction of a bcc lattice by stacking inorganic (e.g. silicon) and organic (e.g. latex) spheres along the (001) or (111) cubic directions. The stacking sequence along the (001) vertical direction is shown in Fig. 2 (a-e). The spheres are in equilibrium because they are located at minimum energy locations. Red and green spheres are silicon spheres while brown spheres are latex spheres. Once the bcc lattice is constructed (Fig. 2 e), the latex (brown) spheres are removed to leave a diamond structure of silicon spheres (see Fig.2 f).

The selective removing of spheres can be achieved because the latex spheres are chemically different from the silicon spheres.

Even though a diamond lattice of silicon spheres is obtained, the silicon volume fraction f=0.34 is not suitable to have a large photonic band gap. Larger spheres are needed since dielectric (n=3.6) spheres  in the diamond lattice possess a large complete gap for dielectric volume fraction f~0.43. In this regard, some processes to increase the dielectric volume fraction have been proposed [5,6].  

The experimental realization of the robot-aided micromanipulation of micro-spheres is shown below.