Cyclotron Resonance Measurements Research Articles

On the Gas-Phase Reactivity of Complexed OH+ with Halogenated Alkanes

OH(+) is an extraordinarily strong oxidant. Complexed forms (L--OH(+)), such as H(2)OOH(+), H(3)NOH(+), or iron-porphyrin-OH(+) are the anticipated oxidants in many chemical reactions. While these molecules are typically not stable in solution, their isolation can be achieved in the gas phase. We report a systematic survey of the influence on L on the reactivity of L--OH(+) towards alkanes and halogenated alkanes, showing the tremendous influence of L on the reactivity of L--OH(+). With the help of with quantum chemical calculations, detailed mechanistic insights on these very general reactions are gained. The gas-phase pseudo-first-order reaction rates of H(2)OOH(+), H(3)NOH(+), and protonated 4-picoline-N-oxide towards isobutane and different halogenated alkanes C(n)H(2n+1)Cl (n=1-4), HCF(3), CF(4), and CF(2)Cl(2) have been determined by means of Fourier transform ion cyclotron resonance measurements. Reaction rates for H(2)OOH(+) are generally fast (7.2x10(-10)-3.0x10(-9) cm(3) mol(-1) s(-1)) and only in the cases HCF(3) and CF(4) no reactivity is observed. In contrast to this H(3)NOH(+) only reacts with tC(4)H(9)Cl (k(obs)=9.2x10(-10)), while 4-CH(3)-C(5)H(4)N-OH(+) is completely unreactive. While H(2)OOH(+) oxidizes alkanes by an initial hydride abstraction upon formation of a carbocation, it reacts with halogenated alkanes at the chlorine atom. Two mechanistic scenarios, namely oxidation at the halogen atom or proton transfer are found. Accurate proton affinities for HOOH, NH(2)OH, a series of alkanes C(n)H(2n+2) (n=1-4), and halogenated alkanes C(n)H(2n+1)Cl (n=1-4), HCF(3), CF(4), and CF(2)Cl(2), were calculated by using the G3 method and are in excellent agreement with experimental values, where available. The G3 enthalpies of reaction are also consistent with the observed products. The tendency for oxidation of alkanes by hydride abstraction is expressed in terms of G3 hydride affinities of the corresponding cationic products C(n)H(2n+1) (+) (n=1-4) and C(n)H(2n)Cl(+) (n=1-4). The hypersurface for the reaction of H(2)OOH(+) with CH(3)Cl and C(2)H(5)Cl was calculated at the B3 LYP, MP2, and G3(m*) level, underlining the three mechanistic scenarios in which the reaction is either induced by oxidation at the hydrogen or the halogen atom, or by proton transfer.

Magnetotransport in high-g-factor low-density two-dimensional electron systems confined inIn0.75Ga0.25As∕In0.75Al0.25Asquantum wells

We report magneto-transport measurements on high-mobility two-dimensional electron systems (2DESs) confined in In_0.75Ga_0.25As/In_0.75Al_0.25As single quantum wells. Several quantum Hall states are observed in a wide range of temperatures and electron densities, the latter controlled by a gate voltage down to values of 1.10^11 cm^-2. A tilted-field configuration is used to induce Landau level crossings and magnetic transitions between quantum Hall states with different spin polarizations. A large filling factor dependent effective electronic g-factor is determined by the coincidence method and cyclotron resonance measurements. From these measurements the change in exchange-correlation energy at the magnetic transition is deduced. These results demonstrate the impact of many-body effects in tilted-field magneto-transport of high-mobility 2DESs confined in In_0.75Ga_0.25As/In_0.75Al_0.25As quantum wells. The large tunability of electron density and effective g-factor, in addition, make this material system a promising candidate for the observation of a large variety of spin-related phenomena.

Cyclotron resonance measurements of the high-quality single crystal GdSb

Cyclotron resonance (CR) measurements on single crystals of GdSb have been performed in the frequency range from 50 to 110 GHz . By using the high-quality crystal with the residual resistivity ratio of about 500, two CR absorption lines are observed at low temperatures for B||[0 0 1] . The effective mass values are estimated to be 0.26 m 0 and 0.50 m 0, respectively.

Charge coupled cyclotron motion of electrons and holes in InGaAsN epitaxial layers

ABSTRACTTime resolved cyclotron resonance measurements are used to investigate more in further detail the effective mass of electrons and holes in InGaAsN epitaxial layers. The In and N content in the alloy are adjusted to yield the latticematching of the epilayers (200 nm thick) to GaAs. A continuous increase of the effective mass of electron and an increase of the resonance associated with holes is observed. Through the evolution of the imaginary part of conductivity as a function of the elapsed time we show that this observation is a coupled cyclotron resonance that may have maxima in the real part of conductivity but should not be necessarily correlated with the “increase” of the effective mass.

Electronic parameters and electronic structures in modulation-doped highly strained In xGa 1− xAs/In yAl 1− yAs coupled double quantum wells

Electronic parameters of a two-dimensional electron gas (2DEG) in modulation-doped highly strained In x Ga 1− x As/In y Al 1− y As coupled double quantum wells were investigated by performing Shubnikov–de Haas (S–dH), Van der Pauw Hall-effect, and cyclotron resonance measurements. The S–dH measurements and the fast Fourier transformation results for the S–dH at 1.5 K indicated the electron occupation of two subbands in the quantum well. The electron effective masses of the 2DEG were determined from the cyclotron resonance measurements, and satisfied qualitatively the nonparabolicity effects in the quantum wells. The electronic subband structures were calculated by using a self-consistent method.

Strain effects, electronic parameters, and electronic structures in modulation-doped InxGa1−xAs/InyAl1−yAs coupled step-rectangular quantum wells

The electronic parameters of a two-dimensional electron gas (2DEG) in unique modulation-doped InxGa1−xAs/InyAl1−yAs coupled step-rectangular quantum wells were investigated by using the Shubnikov–de Haas (SdH)–Van der Pauw Hall effect and cyclotron resonance measurements. The SdH measurements and the fast Fourier transformation results for the SdH data at 1.5 K indicated electron occupation of two subbands in the quantum well. The electron effective masses of the 2DEG were determined from the cyclotron resonance measurements, and their values qualitatively demonstrated the nonparabolicity effects of the conduction band on the 2DEGs in the quantum wells. The electronic subband energies, the energy wave functions, and the Fermi energies were calculated by using a self-consistent method taking into account exchange-correlation effects, together with strain and nonparabolicity effects. These results can help in understanding potential applications of unique InxGa1−xAs/InyAl1−yAs coupled step-rectangular quantum wells in high-speed electronic and long-wavelength optoelectronic devices.

Cyclotron Resonance and Magnetic Resonance in GdSb

Cyclotron resonance (CR) and magnetic resonance measurements on single crystals of GdSb have been performed at temperatures between 1.4 K and 30 K in the frequency range from 50 to 110 GHz. By using a high-quality crystal with the residual resistivity ratio of about 500, two CR absorption lines are observed at low temperatures for B ∥[001] in addition to an antiferromagnetic resonance. The effective mass values are estimated to be 0.26 m 0 and 0.50 m 0 , respectively, which are reasonably consistent with the results of dHvA measurements. On the other hand, in the case of a low grade crystal, a magnetic resonance of Gd impurities is observed. The absorption line of the impurities shows broadening and g -shift at low temperatures.

Cyclotron resonance experiments on rare-earth monopnictides

Cyclotron resonance (CR) measurements on high-quality single crystals ofrare-earth monopnictides have been performed in the frequency range from 50 to190 GHz. We have successfully observed CR signals for a strongly correlatedelectron system, CeSb, as well as other rare-earth monopnictides, LaSb and PrSb.We have also observed Doppler-shifted CR including nonlinear behaviour in thefrequency–field diagrams.

Large splitting of the cyclotron-resonance line inAlxGa1−xN/GaNheterostructures

Cyclotron-resonance (CR) measurements on two-dimensional (2D) electrons in AlGaN/GaN heterojunctions reveal large splittings (up to 2 meV) of the CR line for all investigated densities, $n_{2D}$, from 1 to $4\times 10^{12}cm^{-2}$ over wide ranges of magnetic field. The features resemble a level anti-crossing and imply a strong interaction with an unknown excitation of the solid. The critical energy of the splitting varies from 5 to 12 meV and as $\sqrt{n_{2D}}$. The phenomenon resembles data from AlGaAs/GaAs whose origin remains unresolved. It highlights a lack of basic understanding of a very elementary resonance in solids.

Transport properties in asymmetric InAs/AlSb/GaSb electron-hole hybridized systems

Transport properties in asymmetric InAs/GaSb and InAs/AlSb/GaSb heterostructures sandwiched by AlGaSb layers were studied. For the InAs/GaSb structures, partially compensated quantum Hall effects arising from the electron-hole hybridization were observed. By changing the thickness of each layer, the energy positions of the conduction band and the valence band can be controlled independently. In InAs/AlSb/GaSb structures, we tried to control the hybridization strength by varying the AlSb barrier thickness. Magnetoresistance measurements, in which the magnetic field was applied perpendicular and parallel to the surface, and cyclotron resonance (CR) measurements show that there is a clear transition from the electron-hole-hybridized system to the electron-hole-independent system. The transition point appeared at around the 2-nm-barrier thickness in all experiments, suggesting a dominant role of the overlap of electron and hole wave functions. According to the absorption peak shapes in the CR measurements, the hybridized system can be further classified as strongly hybridized or weakly hybridized. Only in the weakly hybridized system was the Shubnikov--de Haas--like oscillation due to the short-range scattering by the hole potential observed in the electron CR absorption peak.

Cyclotron Resonance in PrSb

Cyclotron resonance (CR) measurements on a single crystal of PrSb have been performed at temperatures between 1.5 K and 20 K in the frequency range from 50 to 110 GHz. Three CR absorption lines are observed at low temperatures. For magnetic fields parallel to the [001] direction, the determined effective masses are 0.25 m 0 , 0.3 m 0 , and 0.53 m 0 , respectively. In addition to “normal” CR, we have observed Doppler-shifted cyclotron resonance which shows nonlinear behavior on the frequency–field diagram.

Doppler-shifted cyclotron resonance with Alfven waves in LaSb

Abstract Cyclotron resonance (CR) measurements on a single crystal of LaSb have been performed in the frequency range from 50 to 190 GHz. In addition to “normal” CR, we have observed anomalous absorption lines which show nonlinear behavior on the frequency-field diagram. The nonlinear behavior is explained by Doppler-shifted cyclotron resonance with Alfven waves.

Research in Super-High Pulsed Magnetic Fields at the Megagauss Laboratory of the University of Tokyo

We present in this paper a brief review of the facilities of the Megagauss Laboratory (MGL) of the University of Tokyo, and an overview of the highlights of solid state physics in megagauss fields at MGL. The Megagauss Laboratory has a long history since the first prototype was established in 1972 in order to pursue new phenomena which may occur in the extreme high magnetic field limit. Since then, it has achieved successful development in the last three decades, and very recently in 1999, it was enlarged and renewed at the Kashiwa new campus. At the MGL, pulsed high magnetic fields are produced by three different techniques: electromagnetic flux compression (EMFC), the single-turn coil (STC) technique, and non-destructive long pulse magnets. The highest magnetic fields of 622 T has been obtained by EMFC. By the STC technique, very high fields exceeding 300 T have been obtained depending on the coil bore, in two systems with horizontal and vertical coil axes. These fields are applied in many different kinds of experiments, such as optical spectroscopy, cyclotron and electron spin resonance, magnetization and transport measurements. Non-destructive long pulse fields up to nearly 70 T from wire-wound coils are also available.

Observation of Doppler-shifted cyclotron resonance in LaSb

Cyclotron resonance (CR) measurements on a single crystal of LaSb have been performed at temperatures between 1.6 and 40 K in the frequency range from 50 to 190 GHz. In addition to ``normal'' CR, we have observed two anomalous absorption lines that show nonlinear behavior on the frequency-field diagram. The nonlinear behavior is explained by the Doppler-shifted cyclotron resonance coupled with a magnetoplasma wave (Alfven wave) propagating in the quite high-quality single crystal of LaSb.

Cyclotron Resonance in CeSb

Cyclotron resonance (CR) measurements on a single crystal of CeSb have been performed at temperatures between 1.6 K and 10 K in the frequency range from 50 to 110 GHz. We have successfully observed several CR absorption lines at low temperatures. For magnetic fields in the [001] direction, the determined effective masses are between 0.3 and 1.5 m 0 .

Determination of Cyclotron Effective Masses on LaSb

Cyclotron resonance (CR) measurements on a single crystal of LaSb have been performed in the temperature range from 1.6 K to 40 K in the frequency range from 50 to 190 GHz. We have observed three C...

Interface Magnetopolaron in III-V Nitride Single Heterostructures

Polaronic corrections due to the electron-interface-phonon interaction in AIN/GaN single heterostructures are calculated within the improved Wigner-Brillouin perturbation theory using a dielectric continuum approach for the optical phonons, and a simplified triangular quantum well potential model for the conduction band electrons. The renormalization of the GaN electron effective mass is particularly investigated in order to be compared with cyclotron resonance measurements.

Observation of cyclotron resonance on LaBi

Cyclotron resonance (CR) measurements on a single crystal of LaBi have been performed in the frequency range from 50 to 190 GHz. Two CR absorption lines are observed for B∥[1 0 0], which correspond to effective masses m CR * of 0.33 m 0 and 0.65 m 0.

Electronic property variations due to an embedded potential barrier layer in modulation-doped step quantum wells

Electronic property variations of a two-dimensional electron gas (2DEG) in modulation-doped step quantum wells due to an embedded potential barrier were studied by performing Shubnikov–de Haas (SdH), Van der Pauw–Hall-effect, and cyclotron resonance measurements on two kinds of InxGa1−xAs/InyAl1−yAs step quantum wells which were one without and the other with an embedded barrier. The fast Fourier transformation results for the SdH data at 1.5 K indicated the electron occupation of two subbands in both step quantum wells. The total electron carrier density and the mobility of the 2DEG in the step quantum well with an embedded barrier were smaller than those in the quantum well without an embedded barrier. The electron effective masses were determined from the slopes of the main peak absorption energies as functions of the magnetic field, and satisfied qualitatively the nonparabolicity effects in both quantum wells. The electronic subband energies, the wave functions, and the Fermi energies were calculated by using a self-consistent method taking into account exchange-correlation effects together with strain and nonparabolicity effects. These present results indicate that the electronic parameters in modulation-doped InxGa1−xAs/InyAl1−yAs step quantum wells are significantly affected by an embedded barrier.

Observation of cyclotron resonance in rare-earth monopnictides microwave region

We have directly determined the cyclotron effective masses of RX (R=La,Gd, X=As,Sb,Bi) by means of cyclotron resonance measurements at the frequency range between 56 and 190 GHz in the temperature range from 50 to 0.5 K. In addition to normal cyclotron resonance, two anomalous absorption lines are observed for the high-quality single crystal of LaSb, which shows quadratic behavior on the frequency–field diagram.