A spectroscopic-imaging scanning tunneling microscope in vector magnetic field.

Cryogenic scanning tunneling microscopy and spectroscopy (STM/STS) performed in a high vector magnetic field provide unique possibilities for imaging surface magnetic structures and anisotropic superconductivity and exploring spin physics in quantum materials with atomic precision. Here, we describe the design, construction, and performance of a low-temperature, ultra-high-vacuum (UHV) spectroscopic-imaging STM equipped with a vector magnet capable of applying a field of up to 3 T in any direction with respect to the sample surface. The STM head is housed in a fully bakeable UHV compatible cryogenic insert and is operational over variable temperatures ranging from ∼300 down to 1.5 K. The insert can be easily upgraded using our home-designed 3He refrigerator. In addition to layered compounds, which can be cleaved at a temperature of either ∼300, ∼77, or ∼4.2 K to expose an atomically flat surface, thin films can also be studied by directly transferring using a UHV suitcase from our oxide thin-film laboratory. Samples can be treated further with a heater and a liquid helium/nitrogen cooling stage on a three-axis manipulator. The STM tips can be treated in vacuo by e-beam bombardment and ion sputtering. We demonstrate the successful operation of the STM with varying the magnetic field direction. Our facility provides a way to study materials in which magnetic anisotropy is a key factor in determining the electronic properties such as in topological semimetals and superconductors.

Engineering of electron-selective contact for perovskite solar cells with efficiency exceeding 15%.

The past 5 years have witnessed the rise of highly efficient organometal halide perovskite-based solar cells. In conventional perovskite solar cells, compact n-type metal oxide film is always required as a blocking layer on the transparent conducting oxide (TCO) substrate for efficient electron-selective contact. In this work, an interface engineering approach is demonstrated to avoid the deposition of compact n-type metal oxide blocking film. Alkali salt solution was used to modify the TCO surface to achieve the optimized interface energy level alignment, resulting in efficient electron-selective contact. A remarkable power conversion efficiency of 15.1% was achieved under AM 1.5 G 100 mW · cm(-2) irradiation without the use of compact n-type metal oxide blocking layers.