γ-Fe single crystal thin film growing process at room temperature and its surface chemistry

分子束外延(MBE)形成的超薄膜的异质结构被广泛研究，因为这类人造系统是创新多相催化和微电子制造工艺的候选之一。众所周知，体相Fe在1183K以下具有体心立方(Bcc)结构，而在单晶铜(Fcc)衬底上即使在室温下也可以用分子束外延(MBE)获得面心立方(Fcc)Fe薄膜。原位观察这类物种在fcc-Fe薄膜上的原子或分子行为，对其表面化学方面是很有意义的。用红外反射吸收光谱(IRRAS)研究了一氧化碳(CO)在铜(100)和铜(111)表面不同厚度的fcc-Fe膜上的吸附和解吸行为。结果表明，CO分子最初吸附在铜(100)表面的桥位，然后随着覆盖度的增加吸附在顶位。对于CO的饱和吸附，p…随着沉积铁厚度的增加，表面碳氧拉伸带的位置和宽度也发生变化，进而改变表面结构。面心立方Fe(100)面上CO物种分布较为尖锐，饱和覆盖度为2038 cm^~(-1)~(-1)。当厚度大于10ML时，由面心立方到体心立方的相变使能带变宽。CO在1-3ML膜上的吸附在2104 cm~(-1)~(-1)~gt~(-1)处产生了一个附加带，明显高于CO在清洁的Cu(100)表面上的C-O拉伸带，这代表了Fe的影响。对于Cu(111)衬底上1-4ML的面心立方Fe薄膜，RHEED图像显示面心立方Fe(111)表面在90K时的饱和CO拉伸带位于2000 cm^&lt；-1&gt；在4ML和8ML之间观察到了CO吸附引起的两个吸收带(2032和2000 cm^&lt；-1&gt；)，这一区域的RHEED图像清楚地显示了fcc(111)和bcc(110)表面的混合相。在薄膜表面转变为体心立方结构的8ML以上，该带仅位于2032 cm^~(-1)&gt；较少

Hetero-structures of ultra-thin films formed by molecular beam epitaxy (MBE) have been widely investigated since such man-made systems are one candidate for innovating heterogeneous catalysis and microelectronics fabrication processes. It is well known that bulk Fe has a body-centered-cubic (bcc) structure below 1183 K. In contrast, face-centered-cubic (fcc) Fe thin films can be obtained on single crystal Cu (fcc) substrates by MBE even at room temperature. In situ survey of atomic or molecular behavior of such species on fcc-Fe film is quite interesting for its surface chemistry aspects. We have investigated in this research project that adsorption and desorption behavior of carbon monoxide (CO) on the various thick fcc-Fe films on Cu(100) and Cu(111) using IR reflection absorption spectroscopy (IRRAS).It was shown that, on the Cu(100) substrate, CO molecules initially adsorbed on bridge sites and adsorbed on on-top sites with increasing coverage. For saturated adsorption of CO, the p … More osition and width of the on-top C-O stretch band were found to change with deposited Fe thickness and in turn the surface structures. The on-top CO species at the fcc Fe(100) surface is sharp and located at 2038 cm^<-1> at saturated coverage. At the thickness above 10 ML the band is broadened by the phase transition from fcc to bcc. It was also found that CO adsorption on the 1-3 ML films gave an additional band at 2104 cm^<-1> which is remarkably higher than the C-O stretch band of CO adsorbed on the clean Cu(100) surface, representative of the influence of Fe. For fcc Fe films of 1-4 ML on the Cu(111) substrate, where RHEED images suggest fcc Fe(111) surface the saturated CO stretch band at 90K was centered at 2000 cm^<-1>. Between 4 and 8 ML the two absorption (2032 and 2000 cm^<-1>) bands due to adsorbed CO were observed; RHEED images in this region clearly show the mixed phase of fcc (111) and bcc (110) surfaces. Above 8 ML at which the film surface transformed to the bcc structure, the band was located only at 2032 cm^<-1>. Less