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The optically levitated particles have been driven to rotate at an ultra-high speed of GHz, and the gyroscopic application of these levitated particles to measure angular motion have long been explored. However, this gyroscope has not been proven either theoretically or experimentally. Here, a rotor gyroscope based on optically levitated high-speed rotating particles is proposed. In vacuum, an ellipsoidal vaterite particle with 3.58 $\mu$m average diameter is driven to rotate at MHz, and the optical axis orientation of the particle is measured by the particle rotational signal. The external inputted angular velocity makes the optical axis deviate from the initial position, which changes the frequency and amplitude of the rotational signal. The inputted angular velocity is hence detected by the rotational signal, and the angular rate bias instability of the prototype is measured to be $0.08^o/s$. It is the smallest rotor gyroscope in the world, and the bias instability can be further improved up to $10^{-9o}/h$ theoretically by cooling the motion and increasing the angular moment of the levitated particle. Our work opens a new application paradigm of the levitated optomechanical systems and possibly bring the rotor gyroscope to the quantum realm.

The junctions formed between gate contact and III-nitride are crucial components of GaN-based electronics and optoelectronics. In this work, solution-processed inorganic Ti3C2Tx MXene films were spray coated on the AlGaN/GaN epitaxial wafer as the gate contact. The workfounction of MXene films was effectively enhanced by partial oxidization process, and accordingly, the gate leakage current and off-state drain current were significantly suppressed. The van der Waals heterojunction between MXene films and III-nitride without direct chemical bonding retained the pristine atomically flat native oxides of III-nitride, record high Ion/Ioff current ratio of 1013, and near ideal subthreshold swing of 61 mV/dec was achieved in the Schottky-Type gate GaN HEMTs. In addition, the MXene gate GaN HEMTs display superior electron mobility and transcoductance, high uniformity with 20 measured transistors. The unprecedented performance can be correlated to the damage-free interface between MXene and III-nitride, negligible atomic diffusion of MXene into the semiconductor layer, and excellent adhesion between MXene and III-nitride. This work provides an alternative method to create contact not only in GaN HEMTs but also in other electronic and optoelectronic devices which uniquely features cost-effective, non-vacuum, high deposition rate, and damage-free properties.