摘要:

The use of a stable glow discharge for the synthesis of carbon nanotubes is reported. Bundles of buckytubes are synthesized with remarkably large diameters (up to 200 &mgr;m). The bundles are evenly spaced, parallel, and occupy the entire central region of the deposited rod. High resolution electron microscopy (HREM) images of the deposited rod produced by the glow discharge revealed higher yield and improved quality buckytubes as compared to those produced by an arc discharge. The behavior of the two deposition modes (glow and arc) has been compared and their effects on the formation of buckytubes are discussed. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114045

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report a novel method for fullerene formation during diamond synthesis via a hot filament, chemical vapor deposition (CVD) procedure. The fullerenes occur in the soot that forms as a by‐product on the edges and rear surface of the substrate holder, where the temperature does not favor diamond deposition. Mass spectrometry of the soot shows a peak having a mass to charge ratio corresponding to C60. From typical concentrations of gaseous species in the diamond‐growing CVD chamber, we conclude that hydrocarbon species such as CH3or C2H2may be the precursors for the fullerene in the CVD chamber. The atomic hydrogen in the gaseous species is believed to play an important role in removing the hydrogen from hydrocarbon to form the all‐carbon fullerene. Our observations also suggest that fullerenes produced in the CVD diamond growth chamber play a role in diamond nucleation on foreign substrates. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114046

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

Analytic solutions have been found for a system of nonlinear integro‐differential equations describing compositional changes and sputtering of materials under ion bombardment in planar geometry. These solutions refer to the stationary (high‐fluence) limit and were found by adopting feasible expressions for intermediate quantities from which both input and output can be derived. Explicit examples include sputtering, collisional mixing, and relaxation, but the method allows inclusion of a wider variety of effects. ©1995 American Institute of Physics.Multicomponent materials like alloys, compounds, and isotopic mixtures undergo composition changes under ion bombardment as a result of preferential sputtering and Gibbsian segregation at the surface, ion implantation and mixing in the region penetrated by the incident beam, and defect‐assisted processes that may affect a wider region. A theoretical scheme describing compositional changes in planar geometry was presented many years ago. Its ingredients were (i) a relocation operator accounting for atomic mixing and preferential sputtering, and (ii) a relaxation term ensuring stability of the target as well as adjustment of the depth scale such that the target surface is located at depthx=0 at any time. The scheme has been expanded recently such as to allow inclusion of all athermal and thermal processes leading to compositional changes. The essence is a set of nonlinear integro‐differential equations of the form

ISSN:0003-6951    

DOI:10.1063/1.114047

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The charge transfer between the &dgr;‐doped region and channel of an AlxGa1−xAs/InyGa1−yAs pseudomorphic high electron mobility transistor (p‐HEMT) is explored theoretically. The model is based on a self‐consistent solution of thek⋅pHamiltonian and Poisson equation and explicitly accounts for surface states. It is shown that heavily doping the &dgr; layer does not guarantee a large amount of electrons in the channel. At higher doping, an increasing number of electrons are retained in the &dgr;‐layer, reducing the charge‐transfer ratio. It is further shown that charge transfer is drastically reduced when the cap layer is recessed to form the gate. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114048

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We studied confinement effects in CdTe quantum dots by means of photoluminescence excitation spectroscopy. We show that by changing the detection energy we can resolve the spectrum of quantum dots of different sizes inside their much broader size distribution in CdTe‐doped glass. The spectra obtained show several well‐resolved lines. There is excellent agreement between the photoluminescence excitation spectra peak energies and calculations of the confined energy transitions based on a modified multiband envelope function model. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114049

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We report the molecular beam epitaxy growth of (Al) GaAsSb/AlAsSb Bragg reflectors around the 1.55 &mgr;m wavelength region. Mirrors with 96% reflectivity have been achieved by using ten pairs of quarter wavelength layers. This demonstrates the capability of the (Al) GaAsSb/AlAsSb system to achieve efficient Bragg mirrors lattice matched to InP substrates. ©1995 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.114050

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We present a study of photo‐ and electroluminescence of SiGe dots buried in Si and compare them with structures containing smooth SiGe layers. The SiGe dot structures were fabricated by low‐pressure chemical vapor deposition using the Stranski–Krastanov growth mode (island growth). We show that the localization of excitons in the dots leads to an increase of the luminescence efficiency at low excitation compared to smooth SiGe layers (e.g., quantum wells). At higher excitation the efficiency decreases which is attributed to nonradiative Auger recombination processes in the dots. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114051

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We use the tunneling microscope to measure the surface lattice spacing of Ge islands grown on Si(111) as a function of their height. It changes in three stages: (I) (0–50 layers tall) Rapid relaxation from near the bulk Si value, at the end of which the lattice spacing atop some of the islands exceeds that of bulk Ge. (II) (50–80 layers) Rapid decrease in surface lattice spacing, to nearly 2% below the bulk Ge value. (III) (≳80 layers) Gradual relaxation to the bulk value. Additional observations of dislocations and analysis of island widths are used to explain this behavior. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114052

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

We propose anti‐phase direct bonding and report on the first demonstration of its application to device fabrication. Cross‐sectional observation by high‐resolution transmission electron microscope showed that InP and GaAs wafers bonded at the atomic level and the misfit dislocations were localized at the bonding interface. Then InP‐based 1.55 &mgr;m wavelength lasers were fabricated on GaAs. The performance of the lasers was approximately equal to that of the lasers formed by in‐phase direct bonding. Moreover, stable operation was possible for more than 1000 h at 50 °C. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114053

出版商:AIP    

年代:1995

数据来源: AIP

摘要:

The minority charge‐carrier lifetime of undoped GaInP2has been investigated in disordered–ordered–disordered GaInP2double heterostructures. It is found that minority charge carriers can be confined to the ordered GaInP2if the growth is performed on a (100) 6° off towards [111¯] substrate. Minority charge‐carrier lifetimes of 1.2±0.35 &mgr;s are measured. These high lifetimes are the result of the extremely low interface recombination velocity of the disordered–ordered GaInP2interface. ©1995 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.114054

出版商:AIP    

年代:1995

数据来源: AIP