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In this Letter, an enhancement mode (E-mode) β-Ga2O3 metal-oxide-semiconductor field-effect transistor (MOSFET) with quasi-two-dimensional channel was reported, and the channel mobility of 147.5 cm2/(V·s) is achieved. Low damage etching technology and low Ohmic contact resistance technology are introduced. As a result, the E-mode transistor demonstrates a maximum drain to source current (ID) of 230.5 mA/mm, a peak transconductance (Gm) of 54.2 mS/mm, a current gain cut-off frequency (fT) of 18 GHz, and a power gain cut-off frequency (fMAX) of 42 GHz. Additionally, a positive threshold voltage (VT) of 1.65 V, a breakdown voltage (VBK) of 420 V, and a specific on-resistance (RON,SP) of 1.24 mΩ·cm2 are achieved. Moreover, a fMAX × VBK of 17.64 THz·V and a fT × VBK of 7.56 THz·V are found to be a close value so far to the theoretical limit of β-Ga2O3. This device leads to excellent radio frequency (RF) characteristics, which paved the way for future millimeter-wave RF power electronics applications with β-Ga2O3 MOSFET. [ABSTRACT FROM AUTHOR]

A composite contrast agent, a nanoemulsion bead with assembled gold nanospheres at the interface, is proposed to improve the specific contrast of photoacoustic molecular imaging. A phase transition in the bead's core is induced by absorption of a nanosecond laser pulse with a fairly low laser fluence (~3.5 mJ/cm2), creating a transient microbubble through dramatically enhanced thermal expansion. This generates nonlinear photoacoustic signals with more than 10 times larger amplitude compared to that of a linear agent with the same optical absorption. By applying a differential scheme similar to ultrasound pulse inversion, more than 40 dB contrast enhancement is demonstrated with suppression of background signals. [ABSTRACT FROM AUTHOR]