Ostblom Mattias, Ekeroth Johan, Konradsson Peter, Liedberg Bo
Division of Molecular Physics, Department of Physics, Chemistry, and Biology, Linköping University, SE-581 83 Linköping, Sweden.
J Phys Chem B. 2006 Feb 2;110(4):1695-700. doi: 10.1021/jp055169j.
This paper reports on the structure and desorption dynamics of thin D2O ice overlayers (0.2-10 monolayers) deposited on serine- and serinephosphate- (with H+, Na+, Ca2+ counterions) terminated self-assembled monolayers (SAMs). The D2O ice overlayers are deposited on the SAMs at approximately 85 K in ultrahigh vacuum and characterized with infrared reflection absorption spectroscopy (IRAS). Reflection absorption (RA) spectra obtained at sub-monolayer D2O coverage reveal that surface modes, e.g. free dangling OD stretch, dominate on the serine SAM surface, whereas vibrational modes characteristic for bulk ice are more prominent on the serinephosphate SAMs. Temperature programmed desorption mass spectrometry (TPD-MS) and TPD-IRAS are subsequently used to investigate the energetics and the structural transitions occurring in the ice overlayer during temperature ramping. D2O ice (approximately 2.5 monolayers) on the serine SAMs undergoes a gradual change from an amorphous- to a crystalline-like phase upon increasing the substrate temperature. This transition is not as pronounced on the serine phosphate SAM most likely because of reduced mobility due to strong pinning to the surface. We show also that the energy of desorption for a sub-monolayer of D2O ice on serinephosphate SAM surfaces with a Na+ and Ca2+ counterions is equally high or even exceeds previously reported values for analogous high-energy SAMs.
本文报道了沉积在以丝氨酸和丝氨酸磷酸盐（带有H⁺、Na⁺、Ca²⁺抗衡离子）为终端的自组装单分子层（SAMs）上的薄重水（D₂O）冰覆盖层（0.2 - 10个单分子层）的结构和解吸动力学。D₂O冰覆盖层在超高真空下于约85 K沉积在SAMs上，并用红外反射吸收光谱（IRAS）进行表征。在亚单分子层D₂O覆盖度下获得的反射吸收（RA）光谱表明，表面模式，如自由悬空的OD拉伸模式，在丝氨酸SAM表面占主导，而大块冰的特征振动模式在丝氨酸磷酸盐SAMs上更为突出。随后使用程序升温脱附质谱（TPD-MS）和TPD-IRAS来研究在升温过程中冰覆盖层中发生的能量学和结构转变。丝氨酸SAMs上的D₂O冰（约2.5个单分子层）在提高衬底温度时经历从非晶态到类晶态的逐渐变化。这种转变在丝氨酸磷酸盐SAM上不太明显，最可能的原因是由于与表面的强固定作用导致迁移率降低。我们还表明，带有Na⁺和Ca²⁺抗衡离子的丝氨酸磷酸盐SAM表面上亚单分子层D₂O冰的脱附能量同样很高，甚至超过了先前报道的类似高能SAMs的值。
