The electron g factor in an InAs-inserted-channel In 0.53 Ga 0.47 As/In 0.52 Al 0.48 As heterostructure is studied by measuring the angle dependence of magnetotransport properties. The gate voltage dependence of the g factor is obtained from the coincidence method. The g-factor values are surprisingly smaller than the g-factor value of bulk InAs, and close to the bare g-factor value of In 0.53 Ga 0.47 As. A large change in the g factor is observed by applying the gate voltage. The gate voltage dependence is not simply explained by the energy dependence of the g factor. © 2003 American Institute of Physics. ͓DOI: 10.1063/1.1631082͔The electron g factor is of fundamental importance for the electronic band structure in semiconductors as well as for spin-related devices. Recently, much attention was focused on the g-factor engineering for processing of quantum information based on the electron spin degree of freedom.1 The gate controlled g factor has been demonstrated in GaAs/ AlGaAs systems by time-resolved Kerr rotation measurements 2 and by the electron spin resonance, 3 since a carrier wave-function penetrates into the barrier material with a different g factor from that of the quantum well resulting in a different contribution to the g factor.The coincidence method, 4 where the tilt angle dependence of Shubnikov-de Haas ͑SdH͒ oscillations is measured, has often been used to deduce the g factor in twodimensional electron gas ͑2DEG͒, e.g., in an InAs-AlSb quantum well, 5 an InAs-GaSb superlattice, 6 an InAs-GaSb quantum well, 7 and an InGaAs/InAlAs quantum well. As layers are lattice matched to InP, while the 4-nm-InAs-inserted layer is not matched and strained. It has been reported that the mobility is highest when the thickness of InAs is 4 nm and starts to decrease above the thickness of 5 nm InAs since the thickness of 4 nm InAs is less than the critical thickness.9 Shown in Fig. 1͑a͒ is the potential profile and squared wavefunction obtained by a self-consistent Poisson-Schrödinger calculation.A 20ϫ80 m 2 Hall bar sample was made by the typical photolithography technique. The gate electrode was deposited on top of the 100-nm-thick Al 2 O 3 insulating layer that covers the entire area of the Hall bar. All transport measurements were performed in a 3 He cryostat equipped with a 9 T superconducting magnet, where the magnetic field was applied at a tilt angle from perpendicular to the heterointerface. Figure 1͑b͒ shows a gray-scale plot of R xx (B,V g ) data presenting a Landau fan diagram, where the magnetic field B is applied perpendicular to the 2DEG plane. In this figure, is the filling factor and is determined by comparing with Hall resistance R xy (V g ). The carrier concentration N s and the electron mobility were changed from 8.3ϫ1011 cm Ϫ2 and 66 000 cm 2 /Vs at V g ϭϪ5 V to 1.9ϫ10 12 cm Ϫ2 and 119 000 cm 2 /Vs at V g ϭ5 V. The effective mass was m*ϭ0.041m 0 at V g ϭϪ3 V and m*ϭ0.044m 0 at V g ϭ3 V as determined from the temperature dependence of the SdH-oscillation amplitude. Here, m 0 is the free-el...

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Despite the recent advances in electrochemical water splitting, developing cost-effective and highly efficient electrocatalysts for oxygen evolution reaction (OER) still remains a substantial challenge. H e r e i n , t w o -d i m e n s i o n a l c o b a l t p h o s p h a t e h y d r o x i d e s (Co 5 (PO 4 ) 2 (OH) 4 ) nanosheets, a unique stacking-disordered phosphate-based inorganic material, are successfully prepared via a facile and scalable method for the first time to serve as a superior and robust electrocatalyst for water oxidation. On the basis of the detailed characterization (e.g., X-ray absorption near-edge structure and X-ray photoelectron spectroscopy), the obtained nanosheets consist of special zigzag CoO 6 octahedral chains along with intrinsic lattice distortion and excellent hydrophilicity, in which these factors contribute to the highly efficient performance of prepared electrocatalysts for OER. Specifically, Co 5 (PO 4 ) 2 (OH) 4 deposited on glassy carbon electrode (loading amount ≈0.553 mg cm −2 ) can exhibit an unprecedented overpotential of 254 mV to drive a current density of 10 mA cm −2 with a small Tafel slope of 57 mV dec −1 in alkaline electrolytes, which outperforms the ones of CO 3 (PO 4 ) 2 (370 mV) and Co(OH) 2 (360 mV) as well as other advanced catalysts. Evidently, this work has opened a new pathway to the rational design of promising metal phosphate hydroxides toward the efficient electrochemical energy conversion. KEYWORDS: Co 5 (PO 4 ) 2 (OH) 4 , nanosheet, lattice distortion, electrocatalyst, oxygen evolution reaction

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