We fabricated Al2O3 dielectrics on highly ordered pyrolytic graphite(HOPG)by atomic layer deposition(ALD)and studied the effects of growth temperature and cycles on the growth behaviors.It is found that Al2O3 preferentially grows along the step edges and promote the formation of nanowires at the initial stage.Al2O3 nanowires can exist after 100 ALD cycles at 50,150,and 200℃,but discontinuous Al2O3 thin films rather than nanowires are evidenced at 100℃.Moreover,the Al2O3 layers tend to evolve into continuous thin films with increasing ALD cycles.It suggests a transformation of growth behavior from three-dimensional mode to two-dimensional mode with increasing ALD cycles.The transformation rate and the lateral growth rate are dependent on the growth temperatures.Raman spectra indicate that HOPG maintains undamaged and greatly reserves its original properties after the film deposition.The results are of great significance to the fabrication of high-quality dielectric layers on graphene as well as the related devices.