摘要:

Secondary ion mass spectrometry correlated with ionic implantations has allowed us to determine oxygen bulk concentration in scandium diphthalocyanine thin films. This concentration, around 2×1020atom cm−3, increases by a factor 20–25 in implanted areas. This oxygen enhancement is observed for oxygen implantation but as well for xenon, caesium, or iodine implantation, and therefore is not dependent on the nature of the implanted atoms. The oxygen concentration saturates in the damaged region but its quantity depends on the energy loss and on the fluence;thelarger the damaged layer,thelarger the region where the enhancment takes place. The phenomenon will be tentatively related to the creation of free radicals induced by bond breaking occurring during the implantation process.But, other explanationsincludingmore severe degradations of the molecular material cannot be dismissed.

ISSN:0021-8979    

DOI:10.1063/1.347095

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effect of hydrogen removal by ion irradiation on the first‐ and second‐order resonant Raman scattering ofa‐C:H are reported. We have measured the absolute first‐order Raman intensity versus ion‐irradiation dose and found a monotonic decrease in the absolute intensity with increasing ion dose. In addition, second‐order Raman scattering also exhibited some resonance enhancement. The consequences of these results are discussed, particularly the important role of hydrogen in determining the vibrational properties ofa‐C:H films.

ISSN:0021-8979    

DOI:10.1063/1.347096

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The range distributions of10B+and11B+ions implanted into silicon have been studied by secondary ion mass spectrometry. Implantation energies in the range of 50 to 250 keV were used. An isotope effect on the boron profiles is clearly resolved for the energies above ∼100 keV. Projected range and parallel straggling values extracted from the measured profiles are compared with calculated values obtained from Monte Carlo simulations and from numerical computations applying Boltzmann’s transport equation. A good agreement is found, and also the computed values reveal a clear isotope dependence. This effect is attributed to a larger electronic stopping cross sectionSefor the10B+ions than for the11B+ions at a given energy in the range whereSeis roughly proportional to the ion velocity. 5

ISSN:0021-8979    

DOI:10.1063/1.347097

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Polarized absorption spectra of 13 nematic liquid crystals (LCs) with various conjugations and structures were measured in the spectral range from 185 to 400 nm. These absorption bands represent all the &pgr;→&pgr;* electronic transitions of these LCs. Resonance wavelength, absorption coefficient, and dichroic ratio of each band were characterized. The contribution of each band to LC birefringence is briefly discussed. Some structural effects on the LC absorption are illustrated. These absorption spectra will also serve as valuable data bases for further theoretical calculations on the band structure of LC molecules.

ISSN:0021-8979    

DOI:10.1063/1.347073

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effects of chemical etching in KI solution, heating, and vacuum exposures of HgI2were individually studied by low‐temperature photoluminescence (PL) spectroscopy. Each of these processing steps is important in the manufacturing of mercuric iodide detectors and may be responsible for the incorporation of carrier traps both in the near‐surface region and in the bulk. The results of etching experiments showed that the near‐surface region has a different defect structure than the bulk, which appears to result from iodine deficiency. Bulk heating at 100 °C also modifies the defect structure of the crystal. Vacuum exposure has an effect similar to chemical etching, but it does not cause significant degradation of the stoichiometry for recently KI‐etched specimens. These studies suggest that some features in the PL spectra of HgI2are associated with stoichiometry of the specimens.

ISSN:0021-8979    

DOI:10.1063/1.347074

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Semiconducting &bgr;‐FeSi2films grown on (100)‐oriented Si and on (11¯02)‐sapphire substrates are investigated by x‐ray diffraction, Nomarski optical microscopy, stress, and surface roughness measurements. As a result of an exothermic, nucleation controlled reaction, we observe a characteristic ring‐shaped surface pattern of the silicide. Surface roughness and stress in &bgr;‐FeSi2are less pronounced for films grown at lower temperatures and cooling rates. Sapphire substrates result in smoother surfaces than Si due to the match of the thermal expansion coefficient of sapphire to the silicides.

ISSN:0021-8979    

DOI:10.1063/1.347159

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Growth behavior of epitaxial layers of GaAs on(111)Aplane has been studied for atmospheric pressure organometallic vapor‐phase epitaxy.The arsine partial pressure and the growth temperature are the most influential factors for the surface morphology of the epitaxial layers on (111)Aplanes. A smooth surface morphology is obtained only under limited growth conditions and a higher AsH3partial pressure is needed to obtain the mirror surface as the substrate temperature increases. This region is found to spread to higher values of arsine pressure by introducing the predeposition process of thin homoepitaxial layers at the most favorable deposition condition.

ISSN:0021-8979    

DOI:10.1063/1.347076

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

Using the carbonization process, single‐crystalline SiC films were grown at substrate temperature (Tsub) in the range of 750–1050 °C by the gas‐source molecular‐beam epitaxial method. This process was performed by using C2H4gas and a special growth method in which the temperature was raised at a predetermined rate (RT) during growth. To realize the growth of single‐crystalline carbonized films, it was found that a C2H4gas pressurePC2H4=8×10−5Torr and rising rateRT=25–25/3 °C/min were necessary. After the carbonization process, essential growth of SiC films using SiHCl3and C2H4gases in the range of gas pressure ratiosPSiHCl3/PC2H4= (1)/(3) –5 (PSiHCl3=1–5×10−5Torr) atTsub=1000 °C was performed. In these all experimental ranges, single‐crystalline 3C‐SiC films could be grown.

ISSN:0021-8979    

DOI:10.1063/1.347099

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

The effects of misfit strain on physical properties (lattice parameters, photoluminescence, and electron mobility) are discussed for In1−xGaxP epilayers with a constant thickness of around 0.75 &mgr;m grown by metalorganic molecular‐beam epitaxy on GaAs(001) substrates. The elastic accommodation of misfit strain is observed in the analysis of lattice parameters and energy‐band‐gap shift. Tensile strain is relaxed more easily than the compressive strain. Theoretical predictions of critical thickness for elastic‐strain accommodation and of energy‐band‐gap shift agree well with experimental results. The energy‐band‐gap shift and electron mobility are relatively insensitive to dislocations generated by relaxation of the misfit strain.

ISSN:0021-8979    

DOI:10.1063/1.347100

出版商:AIP    

年代:1990

数据来源: AIP

摘要:

X‐ray diffraction from the (110) thin edges is proposed to analyze the ZnTe‐ZnSe strained‐layer superlattices grown on GaAs(001) substrates. Strained lattice spacings parallel to the interfaces and the critical layer thickness of coherent growth can be determined directly by this technique. In spite of the large (7%) lattice mismatch between ZnTe and ZnSe layers, the experimental results show that the ZnTe‐ZnSe superlattices have been prepared coherently by hot wall epitaxy and the critical thickness is about 10 A˚. The strained lattice spacings determined by x‐ray [440] diffraction, together with those of Raman scattering measurement, agree very well with the theoretical results. The residual strain in ZnTe/GaAs(001) was also estimated to be about 5×10−4(biaxial tensile) by x‐ray diffraction, where the main cause is found to be the difference of thermal expansion between ZnTe films and GaAs substrates.

ISSN:0021-8979    

DOI:10.1063/1.347101

出版商:AIP    

年代:1990

数据来源: AIP