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In this Letter, low-temperature (400 °C) chemical vapor deposition-grown boron nitride (BN) was investigated as the gate dielectric for AlGaN/GaN metal–insulator–semiconductor high electron mobility transistors (MISHEMTs) on a Si substrate. Comprehensive characterizations using x-ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, atomic force microscope, high-resolution transmission electron microscopy, and time-of-flight secondary ion mass spectrometry were conducted to analyze the deposited BN dielectric. Compared with conventional Schottky-gate HEMTs, the MISHEMTs exhibited significantly enhanced performance with 3 orders of magnitude lower reverse gate leakage current, a lower off-state current of 1 × 10−7 mA/mm, a higher on/off current ratio of 108, and lower on-resistance of 5.40 Ω mm. The frequency-dependent conductance measurement was performed to analyze the BN/HEMT interface, unveiling a low interface trap state density (Dit) on the order of 5 × 1011–6 × 1011 cm−2 eV−1. This work shows the effectiveness of low-temperature BN dielectrics and their potential for advancing GaN MISHEMTs toward high-performance power and RF electronics applications. [ABSTRACT FROM AUTHOR]

Surface morphology, in addition to hydrophobic and electrostatic effects, can alter how proteins interact with solid surfaces. Understanding the heterogeneous dynamics of protein adsorption on surfaces with varying roughness is experimentally challenging. In this work, we use single-molecule fluorescence microscopy to study the adsorption of α-lactalbumin protein on the glass substrate covered with a self-assembled monolayer (SAM) with varying surface concentrations. Two distinct interaction mechanisms are observed: localized adsorption/desorption and continuous-time random walk (CTRW). We investigate the origin of these two populations by simultaneous single-molecule imaging of substrates with both bare glass and SAM-covered regions. SAM-covered areas of substrates are found to promote CTRW, whereas glass surfaces promote localized motion. Contact angle measurements and atomic force microscopy imaging show that increasing SAM concentration results in both increasing hydrophobicity and surface roughness. These properties lead to two opposing effects: increasing hydrophobicity promotes longer protein flights, but increasing surface roughness suppresses protein dynamics resulting in shorter residence times. Our studies suggest that controlling hydrophobicity and roughness, in addition to electrostatics, as independent parameters could provide a means to tune desirable or undesirable protein interactions with surfaces. [ABSTRACT FROM AUTHOR]

Analysis of human hair using time-of-flight secondary ion mass spectrometry (ToF-SIMS) is particularly challenging because of the high transverse curvature of the hair fiber and the presence of the cuticle scales on its surface, which hampers mass spectrometric imaging. Delayed extraction of the secondary ions combined with a simple planar sectioning of the hair has been used to limit the image artifacts encountered with hair samples, giving access to the desired level of information. In this study, the entire structure of human hair was characterized using ToF-SIMS with longitudinal sectioning. Thus, the authors have examined the inner structure of the hair fiber and obtained chemical information from various regions of the hair. Atomic force microscopy (AFM) was also used to characterize the variation in surface properties that are dependent on the presence of different cosmetic residues on the hair surface. By subjecting a hair with an unknown cosmetic residue to AFM observation combined with principal component analysis of a ToF-SIMS image, the authors were able to identify the type of cosmetic present and to correlate its spectrometric signature with that of the original hair styling product. These results demonstrate the potential of their methodology for the investigation of human hair specimens and for the development of hair styling products in the cosmetic industry. [ABSTRACT FROM AUTHOR]