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We investigate the chemistry and kinetics of the surface functionalization of InAs with hemin aimed at demonstrating novel hemin-functionalized InAs planar resistors or molecularly controlled resistors (MOCSERs) with subparts per billion sensitivity to NO at 300 K. The high performance is a result of the strong coupling of the intrinsic surface-confined two-dimensional electron gas (2DEG) at the InAs surface with the surface-attached hemin molecules and their selective interactions with NO. The presence of the surface 2DEG in InAs is highly advantageous for sensing and obviates the need for high surface area to volume geometries conferred by nanowire structures. The chemistry and kinetics of surface attachment processes are investigated using X-ray photoelectron spectroscopy, atomic force microscopy, and spectroscopic ellipsometry, showing that the covalent attachment of hemin to both In and As sites modifies the band-bending of the InAs. In addition, the selective, reversible electronic interaction between hemin and NO molecules increases the InAs resistance, reducing the NO during the interaction. In addition to presenting the sensor performance characteristics, a chemical model based on the electron transfer from the 2DEG of InAs to the iron center of hemin, which reduces Fe(III) to the higher NO affinity Fe(II) state, is proposed.

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The integration of oxides with semiconductors is important for the technological advancement of the next generation electronics. Concomitant ferroelectric and antiferromagnetic (AF) behavior is demonstrated in single crystal BiFeO3 (BFO) films grown on 20 nm SrTiO3 (STO) virtual substrates on Si(100) using molecular beam epitaxy (MBE). STO thin films are grown in an oxide MBE chamber by co-deposition of Sr, Ti, and molecular O2. Careful control of the O2 during nucleation produced commensurate growth of STO on Si. The sequence of the steps allows for the suppression of an amorphous SiO2 layer. This STO(20 nm)/Si structure was used as a virtual substrate for MBE deposition of BFO on Si without breaking vacuum. BFO was deposited using Fe and O2 plasma with an overpressure of Bi flux, the growth rate was controlled by the incoming Fe flux. The reflection high energy electron diffraction image shows a 2-D growth front with a 6-fold surface reconstruction under optimized O2 pressure of 5 × 10−8 mbar. Cross-sectional transmission electron microscopy (TEM) confirms the high crystallinity of the films and shows sharp, atomically flat interfaces. The selected area diffraction pattern (SADP) reveals that BFO grows in a distorted rhombohedral crystal structure. X-ray diffraction does not show formation of second phases and is consistent with the TEM and SADP results. The BFO films show AF behavior with a Neel temperature that exceeds 350 K, as expected (TN = 673 K) and with a residual ferromagnetic behavior that decreases with film thickness and is consistent with the G-type AF due to the canted spins. The saturation magnetization per unit volume for a 40 nm thick film was 180 emu/cm3 at an in-plane magnetic field of 8 kOe. The ferroelectric behavior of the films was verified using piezoresponse force microscopy.

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