摘要:

The doping of a manganese site with various M elementsM=Fe3+,Al3+,Ga3+,Ti4+,Sn4+,andMg2+was studied in insulating charge ordered manganitePr0.6Ca0.4MnO3that exhibits a canted CE-type magnetic structure. Whatever M, the charge ordering disappears for lowxlevels(x⩾0.02)in doped manganitePr0.6Ca0.4Mn1−xMxO3.But the most important feature deals with the fact that a transition to a ferromagnetic metallic state is induced forM=Fe3+,Al3+,Ga3+,andMg2+in spite of the small size of the interpolated cation (Pr,Ca). In contrast, doping with a tetravalent cation does not drastically modify the magnetic and transport properties of the phase. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365929

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Solid state reactions between thin films of titanium and amorphous silicon (a-Si) were studied using differential scanning calorimetry. Multilayered diffusion couples were heated from just above room temperature to 900 K while monitoring the heat flow from the sample during the reaction. From analysis of our data we have calculated the enthalpy of formation to be&Dgr;Hf=−62±5kJ/mol for the reaction,a-Si+Ti→C49−TiSi2and have subsequently estimated the heat evolved during the reactionc-Si+Ti→C54−TiSi2as&Dgr;Hf=−56±5kJ/mol. Based upon this estimate, we find the enthalpy as determined from thin film samples for this system agrees with previous studies which made use of bulk sampling techniques. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365930

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

An x-ray study of electric fields on the incommensurate phase transition inZrTiO4ceramic was performed in order to obtain information concerning the nature of the competing forces that give rise to structural instability at a general wave vector. It was found that an increase in dc electric field increases the normal incommensurate phase transition temperature[(dTi/dEi)≅+1.7 °C cm/kV].The electric field dependence of the incommensurate to commensurate transition was also investigated [(dTc/dEc)≅+1.5 °C cm/kV].©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365931

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Photoluminescence (PL) and photoluminescence excitation (PLE) measurements were carried out to investigate the interband transitions inCdxZn1−xTe/ZnTeasymmetric step quantum wells which consist of a deepCd0.1Zn0.9Tewell and a shallowCd0.18Zn0.82Tewell bound by two thick ZnTe barriers. The results for the PL data at 20 K showed clearly the excitonic transition from the first electronic state to the first heavy-hole state(E1–HH1),and the PLE data showed the excitonic transition from the second electronic state to the first heavy-hole state(E2–HH1),which in this case is forbidden by the selection rules in contrast to the square-quantum-well case, together with the(E1–HH1)transition. The electronic subband energies and the wave functions in the step quantum wells were calculated, taking into account the strain effects by an envelope-function approximation and the calculated values of the interband transitions were in reasonable agreement with those obtained from the PL and the PLE measurements. These results indicate thatCdxZn1−xTe/ZnTestep quantum wells hold promise for potential applications such as new types of modulators and quantum-well infrared photodetectors in the blue-green region of the spectrum. ©1997 American Institute of Physics. 

ISSN:0021-8979    

DOI:10.1063/1.365932

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

AlGaAs antidot arrays with about107antidots are produced by single-shot interference processing with a pulsed high-power Nd:YAG laser system. We apply magnetotransport experiments and atomic force microscopy (AFM) to explore the electronic and geometric properties of the arrays. The size of the antidot arrays are 3 mm×3 mm and the period varies from 400 to 1000 nm. The dots are elliptic or circular and have diameters ranging from 255 to 690 nm. The magnetotransport experiments are performed at 1.5 K in van der Pauw contact configuration. The laser structuring leaves the two dimensional electron density nearly unchanged but decreases the mobility by a factor of about 30. Several maxima are detected in the low magnetic field magnetoresistivity which are discussed based on the geometric data determined by AFM. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365933

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A novel form birefringence effect associated with periodic corrugations in semiconductor/oxide interfaces of large-index-step high contrast Bragg mirrors of vertical microcavities is discussed in this communication. A simple model is proposed in which the corrugations have a square-wave profile with alternating refraction index whose period is much smaller than the cavity mode wavelength. This new effect has potential use in polarization controlled emission of vertical cavity surface emitting lasers. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.365934

出版商:AIP    

年代:1997

数据来源: AIP