Abstract
The use of conventional doping methods requires consideration of not only the energy connection with the base material but also the limits of the type and doping range of the dopant. The scope of the physico-chemical change must be determined from the properties of the base material, and when this limit is exceeded, a large energy barrier must be formed between the base material and the dopant as in a heterojunction. Thus, starting from a different viewpoint, we introduce a so-called metallization of surface reduction method, which easily overcomes the disadvantages of existing methods while having the effect of doping the base material. Such new synthetic techniques enable sequential energy arrangements–gradients from the surface to the centre of the material–so that free energy transfer effects can be obtained as per the energies in the semiconducting band, eliminating the energy discontinuity of the heterojunction.
Highlights
Even within a single material, the surface must physically and chemically differ from the interior due to its structural characteristic of being directly in contact with another medium
As the reduction reaction from the surface proceeds, the existing base material (SnO2) can act as a frame so that crystals can be formed without surface amorphousness, and sequential arrangement (i.e., SnO2-SnOx-Sn) from ceramic SnO2 to metal Sn becomes possible
In order to investigate the difference between the samples in the two conditions that are not distinguished in the SnO2 NW state, Fig. 2 indicates (1) the carrier concentration, Hall mobility, and resistivity values of SnO2 thin films before and after MW irradiation for different durations (1, 3, 5, and 8 min; Fig. 2a), (2) the point energy-dispersive X-ray (EDX) analysis corresponding to MW irradiation at different times (1, 3, 5, and 8 min) in SnO2 NWs (Fig. 2b–e, respectively), and (3) the interplanar spacings in the high-resolution TEM (HRTEM) of SnO2 NW with 5 min of MW irradiation (Fig. 2f)
Summary
Jae Hoon Bang[1], Myung Sik Choi[1], Han Gil Na1, Wansik Oum[1], Sun-Woo Choi[2], Sang Sub Kim[3], Hyoun Woo Kim1,4 & Changhyun Jin 1,4. Given sufficient energy, this energy will gradually change the material, starting at the surface and gradually penetrating into the core, causing a continuous gradation effect of Sn (surface)–SnOx (between surface and core) –SnO2 (core) (Fig. 4b) This effect can generate a final Sn-rich state at the surface from the initial SnO2-rich state, with an excess of electron carriers remaining due to a stoichiometric imbalance originating from the oxygen vacancies at the surface. The much lower initial resistance (i.e., approximately 100 Ω) after 5 min of energy irradiation means that the reduction efficiency was most prominent for this irradiation duration, suggesting that metallization was the most active for this experimental condition This metallization of surface reduction technique differs from existing methods in its capacity to modify from the surface, creating the gradation effect, which is analogous to a continuous energy transition in an energy band. It will be possible to switch to a material suitable for the needs up to a desired area in a much simpler manner, while overcoming the disadvantages of the current doping technique
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