摘要:

Composites with a bulk metallic glass matrix were synthesized and characterized. This was made possible by the recent development of bulk metallic glasses that exhibit high resistance to crystallization in the undercooled liquid state. In this letter, experimental methods for processing metallic glass composites are introduced. Three different bulk metallic glass forming alloys were used as the matrix materials. Both ceramics and metals were introduced as reinforcement into the metallic glass. The metallic glass matrix remained amorphous after adding up to a 30 vol&percent; fraction of particles or short wires. X-ray diffraction patterns of the composites show only peaks from the second phase particles superimposed on the broad diffuse maxima from the amorphous phase. Optical micrographs reveal uniformly distributed particles in the matrix. The glass transition of the amorphous matrix and the crystallization behavior of the composites were studied by calorimetric methods. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120512

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report that a rapid drop of pressure applied to a melt whose crystallization point is a decreasing function of the pressure may, if the temperature, the initial pressure, and the final pressure are appropriately chosen, be equivalent to a rapid thermal quenching. In particular, it may lead to the formation of metastable crystalline or glassy phases bulk materials. The method might be useful to simulate adiabatic decompressions subsequent to shocks such as meteorite impacts. The relation between the undercooling rate(&ngr;c)obtained by rapid decompression and the rate of pressure release(&ngr;p)is given by&ngr;c=k&ngr;p,wherekis the drop rate of the melting point with pressure. This method is evaluated for the Al–Ge system. The solidification products are either stable or metastable crystalline compounds, depending on the rate at which the pressure is released. Our experimental results indicate that quenching with rapid decompression is an effective method to generate high undercooling rates exceeding105 Ks−1.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120542

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Carbon nitride(CNx)thin films have been deposited using a hybrid system combining pulsed laser deposition of graphite with the surface-wave discharge atomic nitrogen source (3&percent;N2in Ar). Using this system, an experiment is designed to study the influence of the atomic nitrogen flux on the composition of theCNxthin films at various laser intensities. The nitrogen percentage in the thin films is positively correlated with the N atom flux impinging on the substrate surface but it is counter-productive to use excessively high values of laser intensities on the graphite target. For a laser intensity of6×108 W/cm2,the nitrogen percentage increases with the N atom flux and saturates at only about 16 at. &percent;. On the other hand, a maximum nitrogen percentage of 30 at. &percent; is obtained at the much lower laser intensity of5×107 W/cm2.©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120513

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on a high sensitivity of GaN–AlN–GaN semiconductor–insulator–semiconductor structures grown on sapphire to an applied strain. The measured static gauge factor (GF) is almost twice as large as the GF forn-type SiC films. We link the observed magnitude and sign of the gauge factor to the crystalline structure of the GaN and AlN films and to their piezoelectric constants. We show that even higher sensitivity can be achieved if the material and interface quality is improved. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120514

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have developed a process for making thick, stress-free, amorphous-tetrahedrally bonded carbon(a-tC)films with hardness and stiffness near that of diamond. Using pulsed-laser deposition, thina-tCfilms (0.1–0.2 &mgr;m) were deposited at room temperature. The intrinsic stress in these films (6–8 GPa) was relieved by a short (2 min) anneal at 600 °C. Raman and electron energy-loss spectra from single-layer annealed specimens show only subtle changes from as-grown films. Subsequent deposition and annealing steps were used to build up thick layers. Films up to 1.2 &mgr;m thick have been grown that are adherent to the substrate and have low residual compressive stress(<0.2 GPa).The values of hardness and modulus determined directly from an Oliver–Pharr analysis of nanoindentation experimental data were 80.2 and 552 GPa, respectively. We used finite-element modeling of the experimental nanoindentation curves to separate the “intrinsic” film response from the measured substrate/film response. We found a hardness of 88 GPa and Young’s modulus of 1100 GPa. From these fits, a lower bound on the compressive yield stress of diamond(∼100 GPa)was determined. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120515

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We measured the photoluminescence spectra of very thin and partially strainedSi1−xGex(0.2⩽x⩽0.5)layers grown on silicon substrates with varying degrees of strain relaxation. We observed photoluminescence lines, so-calledDlines, which arise from dislocations in theSi1−xGex/Sialloys. Surprisingly, we observed noDlines originating from theSi1−xGexlayers. We identify the origin of theDlines as the penetrated dislocations in the Si substrates extending from the SiGe/Si interface with the assistance of transmission electron microscopy. We discuss possible mechanisms of the dominance of luminescence from the dislocations in the Si substrates over those in the SiGe layers. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120516

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

To study the conditions for substitutional incorporation of carbon into Si layers, we grew pseudomorphic Si1−yCy/Si superlattices with absolute carbon concentrations between 0.3&percent; and 2&percent; and growth temperatures varying between 400 and 650 °C. We employed a novel technique to derive the amount of substitutional carbon, which is based on comparative x-ray rocking analyses of Si1−yCy/Si superlattices grown with constant and step-graded temperature profiles. At growth rates around 1 Å/s, we find complete substitutional incorporation of carbon up to growth temperatures of 550 °C and carbon concentrations of about 1&percent;. At higher growth temperatures and/or higher carbon concentrations, the percentage of substitutional carbon drops significantly, concomitant with a thus far unnoticed morphological transition to island growth. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120517

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We investigate the morphology of porous layers obtained by electrochemical anodization of (100)-orientedn-type GaP substrates before and after a preliminary 5-MeVKr+implantation. Apart from favoring the observation of a surface-related phonon in the frequency gap between the bulk optical phonons, ion implantation appears to be an effective means of controlling the morphology of porous GaP, irrespective of initial substrate material features. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120518

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The reaction of atomic hydrogen with a growing amorphous hydrogenated silicon film plays a crucial role in determining the final material properties: hydrogen saturates dangling bonds in the film and thereby lowers the defect density, and it is assumed that hydrogen is inserted into strained bonds of the silicon network thereby reducing the local disorder. The latter reaction can be inferred indirectly since the total hydrogen uptake exceeds the decrease in the defect density. This letter presents the first direct experimental evidence fromin situinfrared spectroscopy for the insertion of hydrogen into strained Si–Si bonds. This reaction becomes visible during the addition of atomic hydrogen to an as-grown film by the appearance of a characteristic SiH vibrational mode at 2033cm−1, indicating a different embedding Si matrix compared to the standard SiH bulk vibration at 2000 cm−1. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120544

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Dissociation and solid phase epitaxial regrowth of GaAs in Ti/Ge/Ni/GaAs were investigated using the transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS) of x-rays with spatial resolution approaching 2 nm. A ternaryNi2.4GaAsphase,∼130 nmthick, was formed by 300 °Cin situanneals of 65 nm Ni film on GaAs. After thisin situanneal, films of 30 nm Ge and 20 nm Ti were deposited in sequence. The EDS analysis showed thatNi2.4GaAstransformed into Ni–As and Ni–Ga binaries after annealing at 500 °C for 5 min, while∼30 nmof GaAs regrew by solid phase epitaxial regrowth from decomposition of the binary phases. High spatial resolution microanalysis allowed detection of∼1×1020 cm−3Ge in the regrown GaAs. This confirms that Ge is incorporated into GaAs during regrowth for ohmic contact formation. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120519

出版商:AIP    

年代:1997

数据来源: AIP