摘要:

Energetic ion beam irradiation of diamondlike carbon thin films induces a decrease of 4–5 orders of magnitude in the resistivity of the films from their as‐grown value of 107&OHgr; cm. The initial decrease in resistivity with increasing ion dose is due to the loss of hydrogen from the films with a concomitant decrease in the optical band gap. Heating the films during the irradiation greatly accelerates the rate of hydrogen loss as a function of dose. Once the hydrogen removal is complete, further irradiation increases the film conductivity by inducing the growth of microcrystallites of graphite.

ISSN:0003-6951    

DOI:10.1063/1.97452

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Explosive crystallization of Cu implanted amorphous silicon during irradiation by a 32‐ns FWHM ruby laser pulse has been studied using time‐resolved reflectivity measurements and Rutherford backscattering spectrometry. From interferences in the reflectivity, the position and the velocity of the self‐propagating melt have been deduced as a function of time. A maximum average velocity of 13±2 m/s has been obtained. The reflectivity behavior indicates the presence of crystalline nuclei in the melt.

ISSN:0003-6951    

DOI:10.1063/1.97453

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Amorphous Fe‐Zr powders have been prepared by mechanical alloying in a powder mill. The samples are characterized by x‐ray diffraction, differential scanning calorimetry, and saturation magnetization measurements. The glass forming range reaches from 30 to 78 at. % Fe being much wider than for melt‐spun samples. Eutectic concentrations do not play any role. The results are compared with the glass forming ability predicted by free‐enthalpy diagram calculations based on the Miedema model [A. R. Miedema, Philips Tech. Rev.36, 217 (1976)]. Amorphization by mechanical alloying seems to be a metastable equilibrium process neglecting intermetallic phases. Rather high crystallization temperatures are found in the concentration range which is not accessible by melt spinning.

ISSN:0003-6951    

DOI:10.1063/1.97454

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

In tunneling microscopy a potential barrier separates a pointed tip from the sample to be investigated. In this letter we show that atomic resolution can be achieved in special cases where the gap spacing has been reduced to the point where the potential barrier may have completely collapsed. In this example the tip may be said to be touching the sample. The forces between the tip and sample are then strongly repulsive and the possibility exists for studying tribology on an atomic scale.

ISSN:0003-6951    

DOI:10.1063/1.97403

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Aluminum implantation into (100) Si has been studied here by transmission electron microscopy (TEM), secondary ion mass spectrometry, and spreading resistance methods. For the implantation conditions (2×1015cm−2, 200 keV, room temperature) used in our experiments a buried amorphous layer is created from 50 to 300 nm below the surface. During N2annealing at 600–1000 °C, two discrete layers of dislocations at (110 and 330 nm) bounding a band of precipitates (>1011cm−2) were created, accompanied by a pronounced redistribution of Al in the implanted region. Three Al peaks at depths corresponding to the defect layers observed by TEM appeared. The positions and number of the peaks remained almost unaffected as a function of annealing temperature. High resolution TEM showed that the band of precipitate contained oriented Al particles and that these particles also nucleated on dislocations. The stability of the Al peak and associated low electrical activity (<10%) has been explained by taking into account the formation of Al precipitates and their interaction with the oxygen in the surrounding regions.

ISSN:0003-6951    

DOI:10.1063/1.97404

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

A scanning tunneling microscope (STM) operating in an electrochemical cell was used to observe Ag films that had been electrodeposited on a graphite substrate. Before Ag deposition and after stripping the deposited Ag, the atomic features of the graphite substrate were observed. The observed STM images are consistent with an island film growth mechanism. This initial study demonstrates that STM studies of electrochemical processes occurring at electrodes in solution are now possible.

ISSN:0003-6951    

DOI:10.1063/1.97405

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Samples of polymethylmethacrylate have been irradiated with laser pulses of 266 nm wavelength along with the wavelengths generated via hydrogen‐shifted stimulated Raman scattering. A quadrupole mass spectrometer monitors in real time the photoablation products produced during the irradiation. At wavelengths of 266 nm and above, the products are dominated by monomer, CO2, and CO. At wavelengths below 266 nm, a dramatic change of ablation products is observed, with methyl formate appearing as a major photochemical product.

ISSN:0003-6951    

DOI:10.1063/1.97406

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Microcrystalline SiNx:H films were prepared by rf glow discharge of SiH4‐B2H6‐N2‐H2mixtures with the gas volume ratio of B2H6/SiH4=4.5×10−3. The volume fraction of the crystalline phase and the crystallite size decrease with an increase in N contentx, and the films were amorphous atxabove 0.2. The dark conductivity &sgr;ddecreases and the optical gapEgincreases withx. The gap‐state density is lowest atxnear 0.2, where &sgr;d∼10−2–10−3/&OHgr; cm (the activation energy is 0.1 eV) andEg∼1.9 eV. These electrical properties are improved as compared with those for B‐doped amorphous SiNx:H.

ISSN:0003-6951    

DOI:10.1063/1.97407

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Atomic hydrogen in silicon‐implanted GaAs samples is studied by photoluminescence. The near‐band‐gap luminescence of GaAs samples subjected to a hydrogen plasma reveals the neutralization effect of the shallow donors. The photoluminescence intensity increases after hydrogen plasma treatment. However, the donor‐related luminescence is drastically reduced, indicating a smaller shallow donor concentration. After a thermal anneal (400 °C, 15 min), the original intensities of donor‐related lines are restored. We confirm the model of an electrically inactive hydrogen‐donor complex and rule out compensating defects created by the plasma treatment.

ISSN:0003-6951    

DOI:10.1063/1.97408

出版商:AIP    

年代:1986

数据来源: AIP

摘要:

Photoluminescence spectra of Mg‐doped GaAs grown by molecular beam epitaxy (MBE) are for the first time reported. Mg was introduced during MBE growth by using a synergic reaction of Mg3As2. Two near‐band‐edge emissions,gand [g‐g], were observed below bound exciton emissions which were originally obtained in Mg+ion‐implanted GaAs. It is explicitly demonstrated that there is no essential difference of photoluminescence spectra between Mg+ion‐implanted GaAs and the present material. These results conclusively indicate that the above two emissions are definitively related with the acceptor levels and exclusively not associated with crystalline defects produced by ion implantation. It is additionally presented that [g‐g] is principally established also in Mg‐doped GaAs prepared by liquid phase epitaxy, where [g‐g] is significantly suppressed due to the unintentional incorporation of Si donor atoms. For moderately Mg‐doped GaAs prepared by MBE a new fine emission with a doublet structure, temporarily denoted byAX, is obtained 5 meV below (A0, X) a bound exciton emission at neutral acceptors.

ISSN:0003-6951    

DOI:10.1063/1.97628

出版商:AIP    

年代:1986

数据来源: AIP