In this work, we studied the impact of the plasmonic heating generated by Au NPs on the surrounding photocatalyst support, specifically, TiO2 (Degussa P25) NP thin film. We investigated phase transition and melting of TiO2 NP thin film and surface evaporation of Au under different laser powers on and off the plasmonic resonance. The temperature of Au and TiO2 NPs was compared with the calculated temperature using the established theoretical model by considering self-heating and collective heating. The temperature was also directly measured using Raman spectroscopy. The results raised questions about the high transient temperature that the Au and TiO2 experienced in the photocatalytic reactions. showing g) Au NPs and h) Ti element of the P25 (TiO2). Labels: R: Rutile, A: Anatase, and Au: Gold P25 film, consisting of anatase and rutile TiO2 NPs, was used as a support to test the effects of plasmonic heating in this study. The sample preparation and characterization are described in the Methods section. After the Au NPs decorated the P25 film, the white P25 sample turned darker red (Figure ). The LSPR absorption of the Au nanoparticle was at 533 nm (Figure ); thus, the reflection of a rich red color was observed. The 532 nm wavelength laser source was chosen for maximum resonance absorption in the plasmonic heating study. The size of the Au NPs was around 25-30 nm (Figure ). The average size of the P25 NPs was around 27 nm, measured from the TEM images. XRD patterns (Figure ) of P25 and P25-Au thin films match the characteristic patterns of P25 and FCC gold NPs. The P25 was a mixer of anatase nanocrystals (~80%), rutile nanocrystals (15%), and a small amount of amorphous TiO2 49 ; thus, anatase and rutile peaks were observed in the XRD. The crystal structure of the TiO2 NPs was measured using Raman spectroscopy. The Raman spectra of the P25 and the rutile phase of TiO2 (Figure ) matched the reference spectra from previous reports. The Raman spectrum of P25 exhibits a combination of anatase and rutile peaks (Figure black curve). The peaks of the anatase vibrational spectrum can be observed at 143 cm -1 (Eg mode), 195 cm -1 (Eg mode), 396 cm -1 (B1g mode), 517 cm -1 (A1g mode), and 638 cm -1 (Eg mode), and the rutile Eg mode of 446 cm -1 as shown in the insertion.