Electrochemical impedance spectroscopy, photoelectron spectroscopy, and Kelvin probe measurements on various TiO₂ single-crystal surfaces show that the position of the Fermi level and the conduction band minimum depend significantly on the sample environment (vacuum, air, water vapor, and aqueous or aprotic electrolyte solutions). In most cases, the conduction-band minimum increases in the series: anatase < rutile < brookite. The offset between anatase and rutile indicates a type II staggered alignment if the environment is vacuum, air, water vapor, or aprotic electrolyte solution, but a type IV aligned configuration is found in an aqueous electrolyte solution. The photoelectron spectra in water vapor reveal a strong upshift of the conduction band, which is nearly reversible in the early stages of water/titania interactions. Our results rationalize various earlier contradictions and highlight the need for proper analytical techniques and experimental conditions for investigation of the band energetics, which is relevant to practical applications of titania materials.

中文翻译：

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TiO ₂（锐钛矿，金红石和板钛矿）单晶的功函数：环境的影响

在各种TiO ₂上的电化学阻抗谱，光电子谱和开尔文探针测量单晶表面显示费米能级和导带最小值的位置在很大程度上取决于样品环境（真空，空气，水蒸气以及水或非质子电解质溶液）。在大多数情况下，导带最小值按系列增加：锐钛矿<金红石<板钛矿。如果环境是真空，空气，水蒸气或非质子电解质溶液，锐钛矿和金红石之间的偏移表示II型交错排列，但是在水性电解质溶液中发现IV型排列配置。水蒸气中的光电子光谱揭示了导带的强烈上移，这在水/二氧化钛相互作用的早期几乎是可逆的。