摘要:

We report on the implementation of epitaxial liftoff in magnetic garnets. Deep-ion implantation is used to create a buried sacrificial layer in single-crystal yttrium iron garnet (YIG) and bismuth-substituted YIG epilayers grown on gadolinium gallium garnet. The damage generated by the implantation induces a large etch selectivity between the sacrificial layer and the rest of the garnet. 10-&mgr;m-thick films of excellent quality are lifted off and bonded to silicon and GaAs substrates. No noticeable degradation in magnetic coercivity due to domain pinning is observed. Stress-induced microfracturing in the thin oxide layers is also addressed. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120192

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A film of well-oriented carbon nanotubes was produced by sublimation decomposition of silicon carbide at 1700 °C by using YAG laser heating in a transmission electron microscope (TEM). The processes of SiC decomposition and the formation of carbon nanotubes were observed successively by high-resolution electron microscopy (HREM). Carbon nanotubes were mostly oriented along the [111] direction on the (111) surface plane of &bgr;-SiC single crystal. The interface between them was observed by HREM. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120158

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A simple relationship between the initial unloading slope, the contact area, and the elastic modulus is derived for indentation in elastic-plastic solids by an indenter with an arbitrary axisymmetric smooth profile. Although the same expression was known to hold for elastic solids, the new derivation shows that it is also true for elastic-plastic solids with or without work hardening and residual stress. These results should provide a sound basis for the use of the relationship for mechanical property determination using indentation techniques. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120159

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The growth of diamond films synthesized by the hot filament chemical vapor deposition method has been studied by scanning tunneling microscopy (STM). The smooth (100) faces of micron-sized diamond crystallites were found to exhibit pyramidal shaped architecture at the nano level. The STM data for chemical vapor deposited diamond is analyzed in the light of recently developed dynamical scaling approach. The value of the scaling exponent&agr;≅0.85signifies a growth primarily driven by the transport of reacting species on the surface rather than molecular diffusion in gas phase. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120160

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We present a technique to control the length of carbon nanotubes. Individual carbon nanotubes can be locally cut by applying a voltage pulse to the tip of a scanning tunneling microscope (STM). Topographic imaging and STM spectroscopy are subsequently used to investigate the result. The electronic properties of a nanotube can be strongly changed by reducing the size. Current-voltage curves obtained by STM spectroscopy on a 30 nm short tube created from a longer nanotube show a stepwise increase of the current, which is attributed to quantum size effects. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120161

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Pulsed-force-mode atomic force microscopy (PFM-AFM) using a cantilever with aSi3N4tip was applied to map charge distribution on a sample surface in water. In order to confirm the applicability of the present PFM, we prepared a patterned sample by vapor deposition of Al on a quartz plate covered with silica beads, followed by oxidation of Al withO2and removal of the beads with ultrasonication. The two different areas ofAl2O3andSiO2had different isoelectric points and bore positive and negative charge, respectively, atpH 8.6. The lateral resolution of the present method was found to be ca. 30 nm. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120162

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

The polarity is found to be a key parameter for the growth of high quality epitaxial GaN films on sapphire (00.1) substrates. A model is suggested which may consistently explain the observed influence of the process parameters on the polar orientation of the epitaxial film. A simple etching technique is proposed for quick distinction of the film polarity. The assignment of the etching behavior to the proper crystal structure is achieved by an analysis of the respective two-dimensional photoelectron diffraction patterns. ©1997 American Institute of Physics. 

ISSN:0003-6951    

DOI:10.1063/1.120163

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Organometallic vapor phase lateral epitaxy and coalescence of GaN layers originating from GaN stripes deposited within 3-&mgr;m-wide windows spaced 3 &mgr;m apart and contained inSiO2masks on GaN/AlN/6H–SiC(0001) substrates are reported. The extent and microstructural characteristics of the lateral overgrowth were a strong function of stripe orientation. A high density of threading dislocations, originating from the interface of the underlying GaN with the AlN buffer layer, were contained in the GaN grown in the window regions. The overgrowth regions, by contrast, contained a very low density of dislocations. The coalesced layers had a rms surface roughness of 0.25 nm. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120164

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Results of a photoluminescence (PL) and photoluminescence excitation (PLE) study of Er implanted GaN are presented. Upon optical excitation at 325 and 488 nm, we observed strong 1.54 &mgr;mEr3+ PLwhich remained temperature stable from 15 to 550 K. At 550 K, the integrated PL intensity decreased by∼10&percent;for above gap excitation(&lgr;ex=325 nm)and∼50&percent;for below gap excitation(&lgr;ex=488 nm)relative to its value at 15 K. The excellent temperature stability makes GaN:Er very attractive for high temperature optoelectronic device applications. PLE measurements were conducted to gain insight into theEr3+excitation mechanisms in the GaN host. The PLE results show thatEr3+can be excited continuously over a broad wavelength region spanning from 425 to 680 nm. In addition, sharp PLE features were observed at approximately 495, 525, 553, 651, and 980 nm. The PLE spectrum suggests that optically activeEr3+ions can be excited either through carrier-mediated processes involving defects in the host or through resonant pumping intoEr3+4fenergy levels. With respect to these two excitation schemes, distinctEr3+ PLproperties were observed for resonant and off-resonantEr3+excitation indicating the presence of different subsets ofEr3+ions in GaN. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120165

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We report on radioluminescence (RL) studies of the wide band gap semiconductors GaP and GaInAsP exposed to tritium gas. All samples were prepared by liquid phase epitaxy. RL tests were performed as a function of tritium pressure, sample temperature, and time, enabling the limiting factors for developing high efficiency visible RL sources to be identified. The studies were complemented by photoluminescence (PL) and cathodoluminescence (CL) measurements. Reduction of surface recombination velocity was shown to be essential for obtaining low threshold CL response and improved PL efficiency. This factor resulted in tritium-activated RL visible to the naked eye. With appropriate materials optimization, these structures should be suitable for developing high efficiency RL devices. ©1997 American Institute of Physics.

ISSN:0003-6951    

DOI:10.1063/1.120166

出版商:AIP    

年代:1997

数据来源: AIP