Electronically patterning through one-dimensional nanostripes with high density of states on single-crystalline Al2O3 domain

Abstract

Self-assembled one-dimensional nanostripes on the single-crystalline Al2O3 domains are found to be the nucleation sites of nanoparticles through an enhanced density of states observed by the scanning tunneling microscopy and spectroscopy. Bias-dependent topographic images and the conductivity spectra indicate that these nanostripes have both enhanced occupied and unoccupied states within the oxide bandgap. These more metallic nanostripes have stronger electronically trapping ability than the oxide domain, which can be used as a one-dimensional electronically self-patterned template for the guided growth of nanostructures.

The formation of double-row oxide stripes during the initial oxidation of NiAl(100)

“…It can be seen that the stripe spacing is about 3 nm and the stripe height is about 1.2 Å . These observations are consistent with the earlier studies under the similar oxidation condition, and more details can be found from the results by Hsu et al 18 The stripe spacing of 3 nm is much larger than that (i.e., stripe spacing of 6 Å ) for oxide stripes formed by first oxidizing the NiAl(100) at room temperature followed by vacuum annealing at 750 C. In addition, the double-row stripes observed here from the room-temperature oxidation followed by annealing at 750 C are surrounded by clean surface areas, instead of oxide domains that Hsu et al 18 observed from the oxidation at the high temperature. This is further supported by the LEED pattern as shown in Fig.…”

“…The height of the double-row stripes is measured to be about 0.8 Å , which is close to the one observed on the oxide formed with 1 L oxygen exposure. It should be noted that the measured heights of the oxide stripes can vary with the bias voltage, 18,20 but it is also found that the height is largely independent of the bias measured in our experiments ranging from À0.5 V to À1.0 V. The double-row stripes are formed from the high-temperature annealing at 750 C under vacuum, which suggests that these fine stripes represent an ordered and stable oxide phase. The formation of oxide stripes was also observed by oxidizing a clean NiAl(100) surface directly at a high temperature, but their structure features are found to be different from the results described above.…”

“…The structures of these oxides have been determined by electron energy loss spectroscopy, low energy electron diffraction (LEED), scanning tunneling microscopy (STM), and low energy electron microscopy (LEEM). [11][12][13][14][15][16][17][18][19][20] Blum et al 12,13 showed that oxide stripes can form along h001i and h010i directions of the NiAl(100) surface and the stripes have a mean width of about 27 Å and a height of 3 Å or larger. Maurice et al 15 observed high resolution STM images on the oxides grown on NiAl(100) that are in agreement with the surface structure of the h-Al 2 O 3 phase.…”

“…The spacing between the two rows is about 6 Å , and the height of these stripes is only about 0.8-1.0 Å , which is much smaller than what has been reported in the literature. 12,18 Furthermore, the spacing between two double-row stripes varies and can be as small as 22 Å , which is about the spacing for another double-row stripe to grow in between. All the evidence suggests that the observed double-row stripe structure is the basic building unit of the ordered oxide phase for the growth of the bulk-oxide-like (2 Â 1) superstructure of the h-Al 2 O 3 film on NiAl(100).…”

The Crystallization of Amorphous Aluminum Oxide Thin Films Grown on NiAl(100)

“…Aluminum oxide thin films have important applications in microelectronics, protective coatings, and catalysis. In particular, the formation of aluminum oxide on NiAl substrates has been studied extensively owing to its important applications in harsh environments ranging from high‐temperature materials in propulsion systems and gas turbine engines to ambient‐temperature reactions, such as surface catalysts and electronic metallization . The aluminum oxides on NiAl(100) were typically formed by directly oxidizing a clean NiAl(100) surface at a high temperature (typically around 727°C or above) or by exposing a clean NiAl(100) surface to oxygen gas at room temperature followed by annealing at a high temperature, both of which would result in fully‐ or partially crystallized oxides .…”