No abstract

The decomposition processes of alkali or alkaline earth carbonates with a large excess of carbon, and the reverse Boudouard reaction given by over metal carbonates, were compared. The carbonates of CO 2 /C ] 2CO Li`, Na`, K`, Cs`, Sr2`and Ba2`generated CO exclusively by an intermolecular redox reaction given byThe reverse Boudouard reaction over these metal carbonates at 700 ¡C proceeded CO 3 2~] C ] 2CO ] O2~. at a steady rate until just before the carbon was completely consumed, and in the cases of Li`, Sr2`and Ba2`, the rates agreed with the initial rates of the intermolecular redox reaction. On the other hand, the rates over the carbonates of Na`, K`and Cs`, the oxides of which undergo a disproportionation reaction to produce gas-phase metal and liquid-phase metal peroxide, were much higher than the initial rates of the intermolecular redox reaction. This discrepancy can be explained by the presence of a catalytic process on the metal-covered surface of the silica wool that was used for preventing the highly basic gas-phase metals from escaping.

We observe variation in the resistively-detected nuclear magnetic resonance (RDNMR) lineshapes in quantum Hall breakdown. The breakdown is locally occurred in a gate-defined quantum point contact (QPC) region. Of particular interest is the observation of a dispersive lineshape occured when the bulk 2D electron gas (2DEG) is set to ν b = 2 and the QPC filling factor to the vicinity of νQPC = 1, strikingly resemble the dispersive lineshape observed on a 2D quantum Hall state. This previously unobserved lineshape in a QPC points to simultaneous occurrence of two hyperfinemediated spin flip-flop processes within the QPC. Those events give rise to two different sets of nuclei polarized in the opposite direction and positioned at a separate region with different degree of electronic spin polarization.Recent advent in NMR technique through a resistive detection (RDNMR) has made it possible to study various spin physics in a 2D quantum Hall system [1][2][3][4][5][6][7], and a quasi-1D channel [8,9]. Despite the success achieved, a certain aspect related to the origin of the RDNMR lineshape variations noted experimentally in continuous wave (cw) mode is still poorly understood. One of them involved the puzzling observation of a dispersive lineshape in the quantum Hall state, a resistance dip followed by a resistance peak resonance line with increasing radio frequency [10]. It is first reported by Desrat et al [11] in the vicinity of ν b = 1 and has been confirmed in a number of follow-up papers [7,[12][13][14][15][16][17]. Similar dispersive like lineshape has been observed as well in the vicinity of ν b = 2/9[18], ν b = 2/3, ν b = 1/3 [19], and at ν b = 2 Landau level crossing [20]. A number of appealing explanations has been put forward, but none of them provides a comprehensive explanation. Part of the reason why it still is difficult to unravel its physical origin is that we do not have a mature level of understanding about manybody 2D electronic states at the first Landau level yet, let alone their coupling to the nuclear spin. Thus, it would be highly desirable to study the lineshape variations in a platform where one can avoid such complexity.In this Rapid Communication, we resort to a quasione dimensional system in a gate-defined quantum point contact (QPC) to study various possible lineshapes including the dispersive lineshape noted experimentally in cw mode. Unlike on the 2D system, the mechanism for generation and resistive detection of nuclear spin polarization is tractable, allowing conveniently a direct interpretation of the observed lineshapes.Generation and detection of nuclear spin polarization are achieved by setting the filling factor in the bulk 2DEG to ν b = 2 and ν QPC = 1 in the QPC[21-30]. Fig. 1(a)-(b) schematically displays how the nuclear polarization affects the transmission probability through the potential barrier of the QPC. For ν QPC < 1 (the down-spin channel T ↓ does not affect the transport), the up-spin channel T ↑ sees an increase(decrease) in the barrier potential in the presence of p...

The spin polarization (P) of high-density InSb two-dimensional electron systems (2DESs) has been measured using both parallel and tilted magnetic fields. P is found to exhibit a superlinear increase with the total field B. This P-B nonlinearity results in a difference in spin susceptibility between its real value χ s and χ gm ∝ m * g * (m * and g * are the effective mass and g factor, respectively) as routinely used in experiments. We demonstrate that such a P-B nonlinearity originates from the linearly P-dependent g * due to the exchange coupling of electrons rather than from the electron correlation as predicted for the low-density 2DES. 71.27.+a, 73.43.Qt Direct experimental evidence of the P-B nonlinearity has so far been reported in low-density GaAs 2DESs with a relatively large r s ~ 5.6 at P < 0.5 [11], where the correlation energy is believed to determine the P-B nonlinearity [11,12]. We here, however, present a similar nonlinear P-B dependence via a high-density InSb 2DES with a small r s ~ 0.2. The large g * (over 39 in magnitude) of the InSb 2DES makes the P = 1 state achievable at easily accessible fields and the magnetization curve (P vs. its corresponding field B p ) observable over a wide range of P from 0.07 to 1. P is found to be superlinear in B p , which is analogous to the findings in Ref. 11. This P-B nonlinearity is fit well by a simple empirical equation. Note that χ gm calculated by this equation can also be used to fit the non-monotonic n 2D -χ gm data in Ref. 11. However, the P-B nonlinearity in the high-density specimen does not arise from the electron correlation because of the small r s . Further experiments demonstrate that this P-B nonlinearity is attributed to a linear P dependence of g * . PACS: Samples and methodsUnless otherwise noted, the employed InSb 2DES in a Hall bar (80 μm ×30 μm) is confined to a 30 nm wide InSb quantum well (QW) with δ-doped Al 0.09 In 0.91 Sb barriers on each side of the well [15].The parallel and tilted-field measurements were performed at 200 mK in a dilution refrigerator with an in situ rotator. The tilt angle θ between B and the sample normal (inset, figure 1(a)) was determined from the Hall resistance with an accuracy of at least 0.1 ○ . A low-frequency AC lock-in technique (13.3 Hz, 3 nA) was used to measure the longitudinal resistance R xx . Magnetotransport measurements gave n 2D = 1.83 × 10 15 m -2 and an electron mobility of μ = 14.3 m 2 /Vs in this sample. Experimental results and discussionAs shown in the inset of figure 1(b), the energy space between Landau levels (LLs) with spin-up (↑) and spin-down (↓) electrons is enhanced with increasing the tilted angle. Because the cyclotron energy (where is the reduced Planck's constant h, * / m eB E perp C

The thermal dehydration and decomposition of the oxalates of Mg(II), Ca(II), Sr(II), Ba(II), Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and Zn(II) were investigated by means of TG, DTA, DSC, EGA, X-ray powder diffraction analysis, and reflectance and infrared spectroscopies. In general, the temperature at which the oxalates were dehydrated increased with 1/r, where r denotes the radius of metal ion. The heats of dehydration (ΔHH2O) of the alkaline earth metal oxalates increased with 1/r, but those of transition metal oxalates decreased as 1/r increased. By considering the decomposition products, the reactions of anhydrous oxalates were classified into three groups and the relations between the decomposition temperatures and 1/r were discussed for each group.

We report magnetotransport measurements of a gated InSb quantum well (QW) with high quality Al 2 O 3 dielectrics (40 nm thick) grown by atomic layer deposition. The magnetoresistance data demonstrate a parallel conduction channel in the sample at zero gate voltage (V g ). A good interface between Al 2 O 3 and the top InSb layer ensures that the parallel channel is depleted at negative V g and the density of twodimensional electrons in the QW is tuned by V g with a large ratio of 6.5 × 10 14 m -2 V -1 but saturates at large negative V g . These findings are closely related to layer structures of the QW as suggested by self-consistent Schrödinger-Poisson simulation and two-carrier model.

The thermal decomposition reactions of MC4H4O4 (M : Mg(II), Co(II), Ni(II), Cu(II), Zn(II), and Pb(II)) in nitrogen or helium were investigated by means of TG-DTA, X-ray diffraction measurements, gas chromatography, and combustion analysis for carbon. The decomposition residues of the Mg and Zn salts were composed of the corresponding metal oxides and some carbon, while those of the Co, Ni, Cu, and Pb salts were composed of the corresponding metals and some carbon. H2, O2, CO, CO2, H2O, CH4, C2H2, C2H4, HCOOCH3, HCOOC2H5, CH3COOC2H5, C2H5COOC2H5, and (CH2CO)2O were identified as the gaseous decomposition products; the compositions of the gaseous mixtures varied a great deal with the metals. Possible reaction mechanisms were discussed mainly on the basis of the decomposition products.

We report on the demonstration of the resistively detected nuclear magnetic resonance (RDNMR) of a single InSb two-dimensional electron gas (2DEG) at elevated temperatures up to 4 K. The RDNMR signal of 115 In in the simplest pseudospin quantum Hall ferromagnet triggered by a large direct current shows a peak-dip line shape, where the nuclear relaxation time T 1 at the peak and the dip is different but almost temperature independent. The large Zeeman, cyclotron, and exchange energy scales of the InSb 2DEG contribute to the persistence of the RDNMR signal at high temperatures.