## 1 Introduction  
Sapphire has many special characteristics such as high hardness, great thermal stability, good light transmission, excellent electrical insulation and chemical inertness [1]. It is widely used in mechanics, optics, electronics, light emitting diodes (LEDs) industry and other fields [2]. In recent years, LEDs have attracted great attention due to their environmental friendliness, longer life span and high energy efficiency while comparing to traditional lighting sources [3]. In LED manufacturing processes, sapphire is the predominant material used as substrates for gallium and indium nitride films [4]. The surface of sapphire is known to play a critical role in determining the crystal quality of the grown GaN epilayer by metal-organic chemical vapor deposition (MOCVD) [5; 6]. When growing thin film on sapphire substrates with a poor surface quality, the film tends to grow preferentially in scratches. The morphology and size of the scratch will be completely reproduced on the film surface, which will lead to poor connections between thin film layers. Therefore, surface quality is an important parameter that influences the performance of the devices.  
Chemical mechanical polishing (CMP) has been widely and effectively applied to a variety of materials in the last two decades, including semiconductors wafers, crystals, glasses, special metals, plastics and computer disks [7; 8]. CMP is becoming popular due to its advantages over other surface finishing techniques, advantages such as little or no surface and subsurface damages, and elimination of surface defects [9; 10; 11]. Sapphire is no exception. CMP is normally used as the last processing step for sapphire substrate polishing. However, sapphire substrates are noted for their physical properties of wear and corrosion resistance, and in many cases the efficiency of CMP processes are low [12]. Fine surface machining and polishing of sapphire substrates may exceed 80% of the total production cost. In CMP processing, the polishing slurry distribution on the sapphire surface is uneven and the slurry tends to quickly leave the processing area due to the centrifugal force, resulting in uneven surface and polishing slurry waste. Statistics [13] show that in the process of mass processing of sapphire substrates, the proportion of rupture and edge collapse is high, accounting for 6% of all yield losses, and the surface of the polished sapphire substrates have slight scratches. Therefore, developing a highly efficient and high precision sapphire substrate polishing method has become extremely urgent.  
Dielectrophoresis (DEP) has been proven to manipulate micro particles [14], and successfully applied in many fields. [PERSON] used DEP to trap and separate yeast cells from a mixed suspension with PS microspheres and achieved a high capture rate and separation efficiency [15]. [PERSON] demonstrated the design, fabrication and testing of a label-free continuous manipulation and separation micro-device of particles/biological cells suspended on a medium based on conventional DEP [16]. [PERSON] indirectly removed heavy metal ions in water by using DEP to control and separate rare earth oxides [17]. [PERSON] studied applications of DEP-based lab-on-a-chip devices in pharmaceutical sciences and biomedicine [18]. [PERSON] used DEP to fabricate atomic force microscope probes [19].  
In this study, the authors apply a non-uniform electric field to produce a DEP effect on polishing slurry consisting of abrasive particles in the polishing area of the traditional polishing machine. Under DEP force, slurry was compelled to stay with the polishing pad for a longer time to improve the distribution of slurry between the polishing pad and the sapphire substrate [20]. The principle of dielectrophoresis polishing (DEPP) will be explained and a set of experiments for comparison will be carried out. Finally, the summary of this study will be presented.