## 3 Results and Discussion  
### Introduction of HMDS for QD Improvement  
For the first approach to improve the material properties of QDs itself, the following two steps proceeded. The first step is to coat the QDs with HMDS, and the second step is to expose the HMDS-coated QDs under atmospheric conditions. The result of this process is the growth of the SiOx on the surface of QDs as shown in Figure 1a. HMDS is widely used in cleaning processes that oxidize around impurities on the semiconductor wafer surface with chemical stability and then remove them through etch [22; 23]. With this in mind, it is intended to improve the properties by oxidation on the surface of QDs. In this work, we further expect the additional benefits from this simple process such that the thickness growth of the SiOx is self-limited and effectively passivate the defects located on the surface of QDs without deteriorating the intrinsic properties including the color-purity of QDs as we will discuss later in this work. For instance, the SiO(CH\({}_{3}\))\({}_{3}\) layer is known to be formed via the substitution reaction between ammonium in the HMDS chemicals and oxygen in the air as shown in Figure 1a. The growth of the SiO(CH\({}_{3}\))\({}_{3}\) layer on the CdSe/ZnS core-shell QDs surface is a self-limited process. Figure 1b represents the data of the high resolution-transmission electron microscopy (HR-TEM) measurement, and clearly shows the lattice of CdSe/ZnS core-shell QDs regardless of the coating with (W) and without (W/O) HMDS. It is, however, difficult to distinguish the existence of the nonstoichiometric oxide layer (i.e., SiOx) from the samples treated with HMDS in Figure 1b. We, in fact, expected this result because the Si-O-(CH\({}_{3}\))\({}_{3}\) layer can be formed only when the HMDS chemicals and oxygen in the air were simultaneously supplied. Figure 1: _Cont._  
Figure 1: Improvement of the quantum dot light emitting diodes (QD-LED) characteristics by adding a simple step to the conventional fabrication process: (**a**) a schematic for the surface reaction of the quantum dot (QDs) with hexamethyldisilazane (HMDS) and the formation of SiO bond as a consequence, (**b**) high resolution-transmission electron microscopy (HR-TEM) results for both without (W/O) and with (W) an HMDS treatment process. No clear evidence for the formation of the SiO bonds both in W/O HMDS (left) and in W HMDS (right) samples. (**c**) colored energy dispersive X-ray spectroscopy (EDX) results for both without (W/O) and with (W) the HMDS treatment process. Note the clear shape of Si elements only in W HMDS (right) samples. (**d**) X-ray photoelectron spectroscopy (XPS) results of O 1s and Si 2p obtained from the samples without (W/O) and with (W) an HMDS treatment process. Once the SiO(CH\({}_{3}\))\({}_{3}\) layer was formed on the CdSe/ZnS core-shell QDs surface, the substitution reaction between ammonium in the HMDS chemicals and oxygen in the air was limited. The growth of SiO(CH\({}_{3}\))\({}_{3}\) layer with consequently the SiO bonds on the surface of the CdSe/ZnS core-shell QDs is the self-limited process, causing the non-distinguishable HR-TEM results in Figure 1b. Another method of determining the presence of the SiO(CH\({}_{3}\))\({}_{3}\) layer (i.e., SiO bonds) is to determine the presence of oxygen and silicon on the QD surface using the EDX component mapping method. Regardless of coating the CdSe/ZnS QDs with HMDS, the elements of Cd, Se, Zn, and S were clearly observed in the EDX results shown in Figure 1c as expected. The element of Si, however, demonstrates the roles of the HMDS coating: the samples coated with HMDS show the Si pattern of evenly dispersed QDs. It is, however, practically impossible to distinguish the form of QDs in the case of the samples measured without the HMDS treatment. It is also interesting to notice that the HMDS-coated QDs were well dispersed because the hydrophobic interface was created by the CH\({}_{3}\) groups in the SiO(CH\({}_{3}\))\({}_{3}\) layer.