Currently, aluminum plasmonics face technical challenges for the manufacture of reproducible structures by simple and low-cost techniques. In this work, we used a direct current (DC) sputtering system to grow a set of quasi-spherical aluminum nanoparticles with diameters below 10 nm. Our particles are uniformly distributed over the surface of quartz and nitrocellulose substrates. We review in detail the methodology for the determination of adequate deposition parameters to allow great reproducibility in different production runs. Likewise, we carry out an exhaustive nanostructural characterization by means of scanning and transmission electron microscopy. The latter allowed us to identify that our depositions are nanoparticle monolayers with thicknesses equal to the average particle diameter. Finally, by means of absorbance spectra we identify the presence of a very well-defined plasmonic resonance at 186 nm that is associated with the dipolar mode in particles smaller than 10 nm. Due to the sharpness of their plasmonic resonances as well as their great manufacturing simplicity and high reproducibility, our aluminum nanoparticles could be used as optical sensors.