Silicon CCDs have limited sensitivity to particles and photons with short penetration depth, due to the surface depletion caused by the inherent positive charge in the native oxide. Because of surface depletion, internally-generated electrons are trapped near the irradiated surface and therefore cannot be transported to the detection circuitry. This deleterious surface potential can be eliminated by low-temperature molecular beam epitaxial (MBE) growth of a delta-doped layer on the Si surface. This effect has been demonstrated through achievement of 100% internal quantum efficiency for UV photons detected with delta-doped CCDs.

In this paper, we will discuss the modification of the band bending near the CCD surface by low-temperature MBE and report the application of delta-doped CCDs to low-energy electron detection. We show that modification of the surface can greatly improve sensitivity to low-energy electrons. Measurements comparing the response of delta-doped CCDs with untreated CCDs were made in the 50 eV-1.5 keV energy range. For electrons with energies below 300 eV, the signal from untreated CCDs was below the detection limit for our apparatus, and data are presented only for the response of delta-doped CCDs at these energies. The effects of multiple electron hole pair (EHP) production and backscattering on the observed signals are discussed.

Be diffusivity data in the bulk metallic glass forming alloys Zr41.2Ti13.8Cu12.5Ni10Be22.5 and Zr46.7Ti8.3Cu7.5Ni10Be27.5 are reported for temperatures between 530K and 710K, extending up to 80K into the supercooled liquid states of the alloys. At the glass transition temperature, Tg, a change in temperature dependence of the data is observed in both alloys, and above Tg the diffusivity increases faster with temperature than below. The data in the supercooled liquid can be described by a modified Arrhenius expression containing the communal entropy of the supercooled liquid and based on a diffusion mechanism suggested earlier. The comparison with viscosity data in the supercooled liquid state of Zr46.7Ti8.3Cu7.5Ni10Be27.5 reveals a breakdown of the Stokes- Einstein relation, whereas D(T) and η(T) follow a relation close to van den Beu-kel's. The breakdown of the Stokes- Einstein relation indicates a cooperative diffusion mechanism in the supercooled liquid state of the ZrTiCuNiBe alloys.

We report systematic studies of the dc transport properties in proton-irradiated Y-Ba-Cu-O single crystals. We find that the onset of vortex dissipation in moderately irradiated samples is associated with the occurrence of a second-order vortex-solid melting transition. In addition, the decreasing zero-field transition temperature and increasing critical current density with the increasing defects reveal the effects of disorder on reducing the electron mean-free-path and on increasing the pinning density.

A modified version of the multiple-interaction code SPUT2 has been used to simulate impacts of 63-atom Cu clusters on six–layer Cu targets. Simulations were carried out with cutoff times of 100 and 500 fs for an incident cluster energy of 63 keV (1 keV/atom). Significant enhancements were observed in the maximum potential and kinetic energies achieved in the early phase of the collision cascade. Some hard collisions yielded atoms with potential energies as high as 925 eV (in the CM frame). This is almost twice the energy allowed in an isolated two-body collision. The number of hard collisions per time-step vs potential energy is well-fitted with a decaying exponential, allowing extrapolation to higher energies. These results together with similar results for Al clusters impacting Au targets suggest that non-linear collisional effects cannot explain the high D–D fusion rates seen in Beuhler, Friedlander, and Friedman's recent experiment [l].

An experimental study of lattice disordering, the crystalline-to-amorphous (c-a) phase transition, and substrate temperature effects in MeV-ion-implanted III-V compound semiconductor crystals is presented. A comparison has been made between the GaAs and InP systems, which have been implanted with 2 MeV oxygen ions at either room temperature (RT) or near liquid nitrogen temperature (LT). A strong in situ dynamic annealing has been found in the RT implanted GaAs, and the LT implanted GaAs exhibits heterogeneous (at the end-of-range of the ions) and homogeneous (at the subsurface region) c-a phase transitions. In InP crystals, in situ annealing is much less pronounced in RT implantation, and dose-dependent damage nucleation and layer-by-layer amorphization take place. LT implantation results in lattice disordering and phase transition with a critical dose at least one order lower than that for GaAs. The mechanisms and kinetics of lattice disordering by ion irradiation are also discussed.

MeV oxygen ion implantation in GaAs/AlGaAs has been shown to provide a simple and very promising technique for quantum well laser fabrication. A l0μm stripe single quantum well (SQW) graded-index separation confinement heterostructure (GRINSCH) laser made in this way has achieved high performance with high quantum differential efficiency, low threshold current and good electrical isolation characteristics. MeV oxygen ion implantation with optimum thermal annealing produces a deep buried electrical isolation layer in n-type GaAs and reduces optical absorption in GaAs/AlGaAs quantum well structures. Ion implantation stimulated compositional disordering as well as implanted oxygen-related deep level traps may be considered as important effects for electrical and optical modification of interfaces in GaAs and AIGaAs.

Since the discovery in 1981 that the electronic excitation produced by MeV ions can enhance thin film adhesion to a substrate, there have been many investigations to determine the origin of the effect and to apply it to problems of technological interest. As we approach the seventh anniversary of its discovery, I shall use this opportunity to review our progress toward these goals. In general, we have discovered that although the electronic excitation provided by the incident beam is responsible for the improvement in adhesion, it is certain that there are quite a number of separate effects involved. These have been shown to include: surface cracking of the substrate; the breakup of contaminant or oxide layers on the substrate by the beam; and the relaxation of surface strain in the substrate. The recent use of a variety of new techniques seems to offer the hope that we are beginning to make progress in untangling these phenomena.

A comprehensive study of MeV-15N-ion-implanted InP by a variety of analytical techniques has revealed the physical processes involved in MeV ion implantation into III-V compound semiconductors as well as the influence of post-implantation annealing. It provides a coherent picture of implant distribution, structural transition, crystalline damage, and lattice strain in InP crystals induced by ion implantation and thermal annealing. The experimental results from the different measurements are summarized in this report. Mechanisms of amorphization by implantation and recrystallization through annealing in MeV-ion-implanted InP are proposed and discussed in light of the results obtained.

We report on the use of 20 MeV C14+ ion beams for pre-irradiation of Si, SiO2 and Al2O3 surfaces with resulting alterations in the adhesion of subsequently deposited Au and Ag thin films. The effect does not follow the same pattern for Au and Ag films, nor is there a simple correlation to the previously observed adhesion effect induced by ion irradiation after film deposition. Possible mechanisms, both for pre-irradiation and post-irradiation effects, are discussed, as is the importance of chemical structures with respect to interfacial bond strength.

We have studied the formation of buried oxide in MeV oxygen implanted Si. A continuous oxide layer is formed in the samples implanted with 2x1018/cm2 oxygen and annealed at 1300° C. The microstructures are studied by cross-sectional transmission electron microscopy and high resolution electron microscopy. Chemical information was obtained by electron energy loss spectroscopy. The effects of implantation temperature are studied. Implantation at a low substrate temperature leads to a well-defined buried SiO2 layer, inhibits the formation of oxide precipitates in the silicon, and reduces silicon inclusions in the SiO2.

We studied the lattice strain induced in the MeV ion bombarded InP crystals and the annealing behaviors of lattice strain, Raman line shift, and linewidth. The lattice spacing for the planes parallel to the surface decreases as a result of irradiation, and amounts to a strain of −0.061% for (100) face, −0.056% for (110) face, and −0.050% for (111) face for 15 MeV Cl bombarded samples to a dose of 1.25E15 ions/cm2. The negative lattice strain, Raman line shift, and line width completely recover at 450°C, and show a major recovery stage at 250°C – 350°C.

Multiple interaction computer simulations have been used to determine the properties of collision cascades in liquid In targets induced by normally incident 5 keV Ar+ ions. Below the first atomic layer the cascade becomes Thompson-like relatively quickly. However, within the first atomic layer the angular distribution of moving atoms became forward peaked by 150 fs and remained so until,∼300 fs. Energy and angle resolved (EARN) spectra were calculated for the ejected atoms. The peak of the energy distribution shifted to lower energies at larger ejection angles, and the angular distributions became broader for lower energy particles. Both results agree with recent experimental data, and with a simple model proposed bg Garrison. Our results suggest that the detailed structure of the surface layer is very important in the sputtering process.

The sputtering of In and Ga atoms from a “liquid” target composedof gallium coveredby a surface monolayer of indium by incident 5 keV Ar+ ions was simulated using the multiple interaction molecular dynamics technique. Yields, energy distributions, and angular distributions of sputtered atoms were obtained at a temperature above the melting point for the eutectic alloy. Similar information was obtained for a pure gallium and a pure indium target. Our results for layer yield ratios and angular distributions are in good qualitative agreement with Dumke's experimental data for the Ar+, In-Ga system. Absolute yields, however, were found to be sensitive to the detailed nature of the two-body potentials used to describe the atom-atom interactions.

We have explored the origin of the ion-induced conductivity in polymer films and the distinction between low energy ion-implantation and high-energy ion irradiation. In experiments involving irradiation of polymer and carbon films with ions of energy from 200 keV to 25 MeV we have established that with both low and high energy ions the polymers undergo carbonization. However, the saturation resistivity obtained with low energy implantation is four to six orders of magnitude larger than those obtained by high energy ion irradiation. In experiments on irradiation of carbon films low energy ions caused a two orders of magnitude increase in the resistivity while high energy ion caused a two orders of magnitude decrease. This implies that the structure of the carbonized polymer is different for the low and the high energy ion irradiation. While in the former case there may be no crystalline order in the films; in the latter case, a microcrystalline graphitic structure is obtained (with four orders of magnitude larger conductivity than in the former case). The formation of graphitic crystalline order with increasing high energy ion dose was verified by electron energy loss spectroscopy. This is an interesting example of crystallization induced by electronic excitation alone with no macroscopic thermal effect.

Thin gold films over GaAs wafers with different dopants (Cr, Si, Te, and Zn) were used to study the role of he substrate electronic properties in the electrical contact and adhesion modification induced by MeV/nucleon heavy ion bombardment. The enhanced adhesion was studied using a scratch test; the results show very different modifications of adhesion depending on the bulk electronic properties of the substrate. The sample with a Cr compensation doped substrate showed enhancement in adhesion for beam doses as low as 1012 ions/cm2, but Si and Te doped (n–type) substrates showed a sudden enhancement in adhesion for doses around 1014 ions/cm2. Samples with Si and Te doped substrates were used to sudy the bombarding ion dE/dx dependence of the induced adhesion for 19F and 35C1 ions with electronic stopping power ranging from 161 eV/Å to 506 eV/Å. In this range the dose threshold fgfjhe ops! of induced adhesion has a power law dependence, D = D0(dE/dx)− (1.90 ± 1.0)

MeV ion irradiation effects on semiconductor crystals, GaAs(100) and Si (111) and on an insulating crystal CaF2 (111) have been studied by the x-ray rocking curve technique using a double crystal x-ray diffractometer. The results on GaAs are particularly interesting. The strain developed by ion irradiation in the surface layers of GaAs (100) saturates to a certain level after a high dose irradiation (typically 1015/cm2), resulting in a uniform lattice spacing about 0.4% larger than the original spacing of the lattice planes parallel to the surface. The layer of uniform strain corresponds in depth to the region where electronic energy loss is dominant over nuclear collision energy loss. The saturated strain level is the same for both p-type and n-type GaAs. In the early stages of irradiation, the strain induced in the surface is shown to be proportional to the nuclear stopping power at the surface and is independent of electronic stopping power. The strain saturation phenomenon in GaAs is discussed in terms of point defect saturation in the surface layer.

An isochronal (15 min.) annealing was done on the Cr-doped GaAs at temperatures between 200° C and 700° C. The intensity in the diffraction peak from the surface strained layer jumps at 200° C < T ≤ 300° C. The strain decreases gradually with temperature, approaching zero at T ≤ 500° C.

The strain saturation phenomenon does not occur in the irradiated Si. The strain induced in Si is generally very low (less than 0.06%) and is interpreted to be mostly in the layers adjacent to the maximum nuclear stopping region, with zero strain in the surface layer. The data on CaF2 have been analysed with a kinematical x-ray diffraction theory to get quantitative strain and damage depth profiles for several different doses.

We have shown that the irradiation of a wide variety of thin film-substrate combinations with MeV/amu ions leads to greatly enhanced adhesion. The systems studied include metal films on dielectric, semiconductor, and metal substrates. For metal coatings on semiconductors the electrical contact which is originally diode-like becomes ohmic. Metal films on metal or polymeric substrates generally require the lowest dose irradiations. For Au on Ta the threshold dose to achieve a constant level of adhesion (“Scotch Tape” test) is consistent with a model of the process in which the dose threshold varies with the electronic excitation part of the energy loss in the material as (dE/dx + Q)−2 . The value of Q obtained corresponds to an exothermic reaction due to the increased binding that liberates ˜70 eV at the interface. This model and a variant of it based on the production of K-shell vacancies in low Z elements in the target will be discussed.

We have found that irradiation of a variety of thin film–substrate combinations by heavy ion beams at energies of mega-electronvolts per atomic mass unit will produce a remarkable enhancement in the adherence of the film. For example, gold films can be firmly attached to soft materials such as Teflon using a 1 MeV beam of protons (1014 cm−2) or helium ions (1013 cm−2) and to harder materials such as silicon (1015 cm−2), quartz (2×1015 cm−2) and tungsten (2×1014 cm−2) with 0.5 MeV a.m.u.−1 beams of fluorine or chlorine ions. In the case of metal films on semiconductors a low resistance contact results. The mixed layer at the interface is observed to be quite thin (approximately 50 Å or less); for silver on silicon electron diffraction and imaging studies of the interface region reveal the presence of crystalline silver compounds.