Investigation of abrasive wear at the nanometer-length scale is presented on single crystalline (001) and amorphous silicon. Experiments were performed using nanoindentation and nanoscratch approaches. Surface characterization was carried out using an atomic force microscope. Results show that both materials behave quite differently from each other during indentation and scratch. Specifically, amorphous silicon is proven to be more unstable during scratching than single crystal silicon. The comparison of in situ and ex situ normal displacement was made. Evidence was found on the hysteretic and viscoplastic behavior of amorphous silicon in nanoscratch that is also seen in indentation. Furthermore, it is found that this material is unstable under stress within small scales. Indications of phase transformation, (reverse) densification, and transition of elastic-plastic deformation are seen. These observations, enabled on silicon using an in situ and nanometer length scale process, are fundamentally different from the understanding of conventional abrasive wear.