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X-ray photoelectron spectroscopy, reflection-absorption infrared spectroscopy, and temperature-programmed reaction/desorption have been employed to investigate the adsorption and reaction pathways of CH2=CHCOOH and CH3CHFCOOH on Cu(100) and oxygen-precovered Cu(100) [O/Cu(100)]. In the case of CH2=CHCOOH on O/Cu(100), CH2=CHCOO is the surface intermediate detected between 110 K and 400 K. CH2=CHCOO is adsorbed vertically and can change adsorption sites at a higher temperature. The propenoate (acrylate) decomposes at higher temperatures (>500 K), with formation of >C=C=O (ketenylidene) surface species and gaseous products. On Cu(100), CH2=CHCOOH is adsorbed in dimer form and can dissociate to generate CH2=CHCOO and CH3CHCOO intermediates on the surface. The CH3CHCOO continuously recombines with the H from deprotonation of CH2=CHCOOH, resulting in the formation CH3CH2COO. The co-existing CH2=CHCOO and CH3CH2COO further decompose at ∼550 K to evolve reaction products, but without >C=C=O being detected. On O/Cu(100), CH3CHFCOOH readily deprotonates to form CH3CHFCOO at 120 K. This intermediate reacts on the surface at ∼460 K to evolve gaseous products, also producing CH2=CHCOO. In the case of Cu(100), deprotonation of CH3CHFCOOH occurs at ∼250 K, forming CH3CHFCOO. Without oxygen on the surface, this intermediate decomposes into HF and CH2=CHCOO at ∼455 K.

The temperature-dependent ammonia gas sensing performance of an interesting indium tin oxide (ITO) based device with an underlying Au-nanodot layer (ITO-Au) is studied and demonstrated. The studied ITO-Au device exhibits good ammonia gas sensing performance and widespread ammonia gas concentration regime. The optimal operation temperature of the studied ITO-Au device is 150°C. The studied ITO-Au device exhibits the benefit of improved sensing performance and extremely low ammonia gas concentration detecting ability. For example, under introduced 1000 ppm and 175 ppb NH3/air gases, the studied ITO-Au device demonstrates remarkable sensitivity ratios of 1786% and 98%, respectively, at 150°C. The related transient responses are also studied. The enhanced sensing performance of the studied ITO-Au device is primarily caused by the presented rougher surface which gives to the increased effective adsorption area. Experimentally, the studied ITO-Au device reveals advantages of simple structure, ease of fabrication, high sensing response, extremely low ammonia gas detecting limit, and low temperature operation capability.