MgO的湿法清洁

Preparation and cleaning of the substrate is the first and most important step before thin film  deposition. Substrate preparation starts from cutting and polishing of single crystal to very complex  structures achieved by lithography techniques with purposes such as the removal of contaminants and native oxide layers. Many different processes are used to prepare and clean the substrate. In most cases, combinations of different techniques are used.

The contact angle measurement was measured using CAM 200 optical contact angle meter  (KSV Instruments Ltd., Helsinki, Finland). A droplet of approximately 5-7 L was deposited on the  surface using a syringe. The contact angles were computed based on the images of droplet on the MgO  surface. For each sample a minimum of four different readings were recorded. A typical error in  readings was ∼2°.

Figure 1 shows photographs of the side view of the water droplet deposited on the surface of  MgO(001) substrate for the five different wet-cleaning treatments used in the present paper. The asreceived sample (labelled REF) had a hydrophobic surface with a contact angle of 80. The cleaning  with the organic solvent only (fig1-b, c and d) did not improve the wettability of the surface, yielding an even higher contact angle of 96 for the AI sample. The use of a detergent clearly decreased the contact angle to a minimum of 15 for the D sample and 32 for the DAE sample. The surface of MgO  cleaned using a detergent was found to be hydrophilic. This change of wettability of the surface  showed that contaminants (particles, oil, wax, hydroxides, carbonates …) present on the as-received  substrate (REF) was removed after a wet-cleaning process using a detergent. Wettability of the  substrate is an important aspect for the chemical solution coating using spin /dip-coating or spraying of a film with homogeneous thickness. A hydrophilic surface is preferred for a good spread of the resin on  the substrate, therefore a detergent step may be necessary to improve the deposition by solution on  MgO(001).

The surface of the AI sample had less contaminants than the REF sample (figure 2-b). Cleaning  by acetone following by isopropanol removed the contaminants responsible for the peak for Mg2s at  high binding energy but the relative ratio of oxide/contaminants remains approximately the same as  before the cleaning (figure 2-g). The same observation was made on the O1s peak with the absence of  the component at 529.2 eV and another component at 533.0 eV which may issue from the left over of  the solvent and corresponding to C-O-H or C-O-C.

Fig1

This paper studied the effect of different wet-cleaning processes on MgO(001) substrate  monitored at different stage in thin film deposition. The surface chemistry of the substrate was checked after the different wet-cleaning processes, after in-situ annealing at 700C for 2 h and after ScN thin  film deposition with the study of the interface.