Abstract
The physical investigation of surfaces and their properties crucially depends on their quality. Such investigations are commonly performed in an ultra-high vacuum environment. Thereby, the transfer of samples among different setups and under ambient conditions is desirable. The usage of a capping layer for the protection of surfaces against contaminations during long-time storage and transfer, and the subsequent temperature-controlled decapping is an established approach. However, a residual-free removal of the capping layer may present a challenge. Here, we systematically investigate the decapping process of a tellurium protected topological insulator Bi2Te3. We give evidence for the material segregation from the contaminated capping layer surface to the substrates. Therefore, a simple, temperature controlled decapping is not sufficient. We demonstrate that near perfect surfaces can be reliably obtained even after long-time storage through a combination of an initial argon ion sputtering process and a following heating for decapping. This approach is suitable for dedicated analysis systems as well as for industrial applications, large throughput of samples of arbitrary shapes, and is easily implemented in existing setups.
Highlights
Using capping layers is a common approach to protect surfaces for handling in a reactive environment and in industrial processes, for example, to prevent corrosion.1 In conventional devices, where device properties are not affected by the immediate interface, i.e., beyond the nm scale, the material choice for the capping layer is uncritical and the capping layer prevents aging due to environmental exposure
Samples are introduced without prior treatment into the ultra-high vacuum (UHV) system and first degassed in situ at low temperatures of ∼400 K to remove the residual water film from the storage under ambient conditions
For Bi2Te3, tellurium is an ideal choice as a leak-proof capping layer
Summary
Using capping layers is a common approach to protect surfaces for handling in a reactive environment and in industrial processes, for example, to prevent corrosion. In conventional devices, where device properties are not affected by the immediate interface, i.e., beyond the nm scale, the material choice for the capping layer is uncritical and the capping layer prevents aging due to environmental exposure. The systematic investigation of bulk doping of patterned and multiple devices excludes the usage of cleaved materials but heavily relies on a continuous supply of freshly prepared thin films by established methods, such as MOCVD, CVD, and MBE.25 This is equivalently relevant in industrial applications with high sample throughput and complicates in the research environment the transfer of samples among different experimental setups and groups. Samples are removed from the UHV environment, cut into pieces, and mounted on sample holders for usage in different setups (in total ∼60 min under ambient conditions). After PES and XPS measurements, samples are stored without protective capping layer in rough vacuum (∼0.1 mbar to 0.3 mbar) for one to seven days for additional post-characterization by ex situ atomic force microscopy (AFM). Voltages V refer to the voltage applied to the sample, i.e., positive voltages refer to tunneling into unoccupied states
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