A critical regime has been identified for ion implanted silicon where onlyslight changes in temperature can dramatically affect the levels of residualdamage. In this regime decreases of only 5° C aie sufficient to induce acrystalline-to-amorphous transformation in material which only exhibited thebuild-up of extended defects at higher temperatures. Traditional Models ofdamage accumulation and amorphization have proven inapplicable to thisregime which exists whenever dynamic defect annealing and damage productionare closely balanced. Irradiating ion flux, Mass and fluence have all beenshown to influence the temperature—which varies over a range of 300° C forion species ranging from C to Xe—at which the anomalous behaviour occurs.The influence of ion fluence suggests that complex defect accumulation playsan important role in amorphization. Results are presented which furthersuggest that the process is nucleation limited in this critical regime.

We present an investigation on the amorphization process of crystallinesilicon induced by ion beam bombardment by simulating the insertion ofself-interstitials at different temperatures. The simulation is carried outby tight-binding molecular dynamics which allows for a detailedcharacterization of the chemical bonding and electronic properties of theirradiated samples. The irradiation process consists of two steps: (i)insertion of defects at a constant rate; (ii) annealing of the sample andobservation of its structural properties. Thanks to the large size of thesimulation cell (up to 276 atoms) we can characterize the amorphous networkboth on the short-range and Medium-range length scale. Electronic propertiesare investigated as well and their evolution is monitored during theinsertion process. Finally, we present a thorough comparison of thestructural properties of the irradiated sample with amorphous silicon asobtained by rapid quench from the Melt.

We present a study of laser pulse induced crystallization and amorphizationin SbxSc1−x films. The time required to reach stableamorphous state after the pulse increases with exciting pulse length andbecomes constant when stationary temperature field is approached by the endof the pulse. The time dependence of the excited spot's local temperature isdeduced directly from amorphization threshold intensity dependence on thepulse length and is used to calculate the cooling times after theamorphizing pulse. Two photocrystallization regimes are distinguisheddepending on whether the melting starts before or after the end ofcrystallization, the condition depending on crystallization tendency forgiven composition x. The occurrence of melting limits the maximum opticalcontrast during photocrystallization. The results show that thecrystallization tendency of SbxSei-x rises with x and has a local maximumbetween x = 0.5 and x = 0.7.

Single crystals of Ca2La8(SiO4)6O2,with 1% Nd substituted for La, were irradiated with 0.8 MeV Ne+and 1.5 MeV Kr+ ions over the temperature range from 15 K to 773K. The irradiations were carried out using the HVEM-Tandem Facility atArgonne National Laboratory. The structural changes and the ion fluence forcomplete amorphization were determined by in situtransmission electron Microscopy. The ion fluence for complete amorphizationincreased with temperature in two stages associated with defect annealingprocesses. The critical temperature for amorphization increased from -360 Kfor 0.8 MeV Ne+ to -710 K for 1.5 MeV Kr+. During in situ annealing studies, irradiation-enhancedrecrystallization was observed at 923 K. Spatially-resolved fluorescencespectra of the Nd ion excited with 488.0 nm laser excitation showed markedline-broadening toward the center of the amorphous regions. InitialMeasurements indicate the subtle shifts of the 9I9/2groundstate energy levels can be measured by pumping directly into theexcited state 4F3/2 Manifold suggesting that the linebroadening observed originates from a distribution of geometricallydistorted Nd sites.

We have studied MeV ion beam induced phase transformation inphenolformaldehyde cured at 170°C by both Raman Microprobe spectroscopy and in situ resistance measurement of the irradiated area.Samples were irradiated using various doses of protons, alphas and nitrogenbeams. Irradiated volumes in each sample were tested in situ for enhanced electrical conductivity and later on by RamanMicroprobe spectroscopy. The results have shown changes in the resistance asmuch as seven orders of magnitude by alpha particles, six orders by nitrogenbombardment and three orders by hydrogen. Raman Microprobe spectroscopy ofthe darkened phase shows development of the D- and G-lines which arecharacteristic of the production of a carbonized resin. These spectraindicate that maximum carbonization was caused by the nitrogen beam.

The activation strain tensor describes the effect of nonhydrostatic stresseson atomic or interfacial Mobilities. It has been measured for solid phaseepitaxial growth of crystalline Si (001) into amorphous Si. The activationstrain concept is explained and some subtle points are discussed.Implications for proposed mechanisms of solid phase epitaxy are reviewed,and new implications for combined bulk and interfacial control arepresented. Questions raised during the oral presentation are answered.

A comparison of strain relief in SiGe alloy layers during high temperatureannealing and solid phase epitaxial crystallisation (SPEC) has shown thatlayers which are thermodynamically stable are also fully strained followingSPEC, whereas metastable layers that relax at high temperatures also relaxduring SPEC. This is illustrated by the fact that a uniform SiGe layer withx=0.085 is stable during annealing at 1100°C for 60 sec and is fullystrained following SPEC. In contrast, a uniform layer with x=0.17, which wasfully strained as-grown by molecular beam epitaxy (MBE), is shown to relaxduring high temperature annealing and during SPEC.

A depth dependent SPEC velocity is observed for metastable layers, with adecrease in velocity as the alloy layer begins to crystallise and anincrease in velocity as strain relaxation proceeds.

This study investigates the stability of Metastable Si1-yCy/Si heterostructures during rapid thermalannealing (RTA) over a temperature range of 1000 – 1150° C Heterostructuresof Si1-yCy/Si and Si1-x-yGexCy/Si (x=0.077, y ≤ .0014)were formed by solid phase epitaxy from C implanted, preamorphizedsubstrates using a 30 Minute 700° C anneal in N2. The occupancyof C in substitution lattice sites was monitored by Fourier TransformInfrared Absorption spectroscopy. The layer strain was monitored by rockingcurve x-ray diffraction and the structural changes in the layers weredetermined using plan-view and X-sectional transmission electron Microscopy(TEM). For anneals of 1150° C or above, all the substitutional C was lostfrom the Si lattice after 30 seconds. TEM verified that the strainrelaxation was the result of C precipitating into highly aligned βSiCparticles rather than by the formation of extended defects. No nucleationbarrier was observed for the loss of substitutional C Preliminary resultswill also be discussed for Si1-x-yGexCy/Siheterostructures where there is the additional factor of the competitionbetween strain energy and the chemical driving forces.

Carbon was substitutionally incorporated into silicon using ion implantationand solid phase epitaxy (SPE) to regenerate a high quality crystallinesubstrate. Carbon was implanted into Si (100) substrates using a singleimplant of 25 keV ai doses ranging from 1.75 × 1015 to 1.05 × 1016/cm2. After carbon implantation half of thesubstrates were amorphized using a silicon implant. All of the wafers weresubjected to a 700°C anneal in N2 ambient for 30 Minutes toinduce SPE regrowth of the implanted regions. FTIR, SIMS, RBS, and TEM wereused to characterize the samples. Results indicate that carbon wassubstitutionally incorporated into the silicon lattice, but that some carbondid precipitate to form silicon carbide. Post-amorphization improvedregrowth of implanted regions in lower dose implanted wafers. ElectricalMeasurements on diode structures indicate that the band gap was reduced forcarbon incorporation at these concentrations.

At the high growth rates accessible during pulsed-laser induced melting andsolidification and explosive crystallization, crystal growth kinetics aredominated not by equilibrium thermodynamics, but by the atomistic mechanismsby which crystallization proceeds. These Mechanisms can be probed by testingthe predictions of solute trapping models based on various crystal/Meltinterface structures against Measurements. We have measured the dependenceof solute trapping of several group III, IV, and V elements in silicon onboth interface orientation and crystallization speed. The Aperiodic StepwiseGrowth Model of Goldman and Aziz accurately fits both the velocity andorientation dependence of the solute trapping observed in these systems. Thesuccess of the model implies a ledge structure for the crystal/Meltinterface and a step-flow mechanism for crystal growth. In addition, we haveobserved an empirical inverse correlation between the two free parameters(“diffusive speeds”) in this model and the equilibrium solute partitioncoefficient of a system. This correlation may be used to estimate values ofthe diffusive speeds for other systems in which solute trapping has not beenor cannot be Measured.

A pseudomorphic Ge0.12Si0.88 film 265 nm thick grownon a Si (100) substrate by molecular beam epitaxy was implanted at roomtemperature with a dose of 1.5 × 1015 cm2 of 100 keV Pions. The projected range of the ions is about 125 nm, which is well withinthe film thickness. Only the top portion of the Ge0.12Si0.88 layer was amorphized by theimplantation. Both implanted and non-implanted samples were subsequentlyannealed in vacuum for 30 Minutes from 400 °C to 800 °C. Values of electronHall sheet mobility and concentration in the implanted Ge0.12Si0.88 epilayer were measured afterannealing. The solid phase epitaxial regrowth is complete at 550 °C, wherethe implanted phosphorus reaches - 100 % activation. The regrown Ge0.12Si0.88 layer exhibits inferior crystallinequality to that of the virgin sample and is relaxed, but the non-implantedportion of the film remains pseudomorphic at 550 °C. When annealed at 800°C, the strain in the whole epilayer relaxes. The sheet electron mobilityvalues measured at room temperature in the regrown samples (Tann≥ 550 °C) are about 20% less than those of pure Si.

Solid-phase epitaxial growth (SPEG) of amorphous GeSi alloy layers has beenexamined. It is shown that fully strained depth dependent GeSi alloy layerscan be produced by multiple ion-implantation and SPEG for implant dosesbelow critical values. For doses above these critical values strainrelaxation is shown to occur during SPEG at a well defined depth, and to becorrelated with a reduction in the SPEG velocity caused by roughening orfaceting of the crystalline/amorphous interface. The velocity reduction isshown to be a reliable indicator of strain relaxation. Both the criticaldose and the depth at which strain relaxation occurs are shown to be inexcellent agreement with equilibrium critical thickness theory.

The solid-phase epitaxy (SPE) process of Ar+-ion bombarded Si(001) surfaces and recovery of crystallinity by thermal annealing arestudied “in situ” by using a scanning tunneling Microscope (STM).As-bombarded surfaces consist of grains of 0.63–1.6 nm in diameter. Thegrains gradually coalesce and form clusters of 2–3.6 nm in diameter atannealing temperature of 245° C (2×1) and (1×2) reconstructed regionssurrounded by amorphous regions are partially observed on the surface byprolonged annealing, which suggests the onset of SPE. Successive observationreveals that the smoothing of the surface occurs layer by layer. Asannealing temperature is raised up to 445 °C, the amorphous layerepitaxially crystallizes up to the topmost surface, and (2×1) reconstructedsurface with Monatomic-height steps is observed. The smoothing of thesurface structures and the formation of nucleation of Si islands areobserved during annealing at 500 °C.

Strained solid phase epitaxial (SPE) regrowth of amorphous Ge xSi1-x on Si (100) substrates was studied using time-resolved reflectivity(TRR). Films of CVD-grown Ge0.13Si0.87 on Si wereamorphized by Si ion implantation, and subsequently regrown at temperaturesbetween 550°C and 610°. Information on regrowth dynamics and interfaceroughness evolution was obtained by accurately modeling the complicated TRRdata for Ge xSi1-x regrowth using a Moving, statistically roughening interface. The SPEregrowth rate slowed as the interface crossed into the Ge xSi1-x layer and the originally planar interface roughened, as confirmed bytransmission electron Microscopy. A Minimum in the regrowth velocity wasobserved after regrowing approximately 60 nm into the Ge xSi1-x layer; the SPE rate subsequently increased to a final,thickness-dependent velocity that was still below that for pure Si. Uponentering the Ge xSi1-x layer, the interface roughened quickly to a 15–20 nm amplitude,increasing only slightly more during the remainder of regrowth. The degreeof roughening and velocity reduction was found to be dependent on the annealtemperature. In contrast, samples with low Ge concentrations (< 3 at.%)prepared by ion implantation exhibited minimal interface roughening andessentially identical SPE velocities as pure Si.

Discovery several decades ago that long-chain molecules crystallize byfolding prompted vigorous basic research on structure-property relations inbulk semicrystalline polymers with expectation of insights that, parallelingexperience in metal physics, would lead to better materials for technology.However, complexity of the crystallization process and difficulty inexploring morphology in adequate detail were both underestimated. Importantaspects of behavior were recognized but improved polymeric materials haveresulted more from exploratory engineering with composites and blends thanfrom basic research on homopolymers. A summary of this research is presentedwith emphasis upon developments key to present status; also upon the trulyformidable challenges that remain, Most readily accessible questions forresearch being of limited technological significance.

A series of semicrystalline diblock copolymers of poly (ethylene) / poly(ethylene-propylene) (E/EP) were subjected to high levels of plane straincompression using a channel die. Deformations were imposed both below andabove the melting point of the E block. The crystallographic andmorphological textures were examined using wide-angle x-ray diffraction polefigure analysis and two dimensional small-angle x-ray scattering. Thelattice unit cell orientation of the crystallized E chains with respect tothe lamellar superstructure was determined, as well as the lamellarorientation relative to the specimen boundaries. When the diblocks aretextured above the E block melting point at various compression ratios, thelamellae orient perpendicular to the plane of shear, while texturing below Tm causes the lamellae to orient parallel to the plane ofshear. The orientation of the crystallized E chains was perpendicular to thelamellar normal, irrespective of the texturing temperature. The variousshear-induced lamellar morphologies have potential applications in gastransport control to develop membranes for use in gas separations or asbarrier Materials.

Binary polymer blends in which one or both components crystallize have beenconsidered. These May be miscible or immiscible in the amorphous state, andphase separation may occur along with crystallization. The rates of thesetwo processes vary differently with temperature, so the consequentmorphology and properties depend upon the temperature history. For Miscibleblends, the glass transition temperature depends upon composition. Thisaffects diffusion so that crystallization kinetics varies as compositionchanges. If only one component crystallizes and the other is rejected, thisrejected component diffuses away from the growing crystalline regions in amanner dependent upon the interaction between components.

These phenomena are studied using a variety of techniques such ascalorimetry, x-ray diffraction and scattering, and small-angle light andneutron scattering for a number of polymer systems.

Blends of poly (ethylene terephthalate), or PET, and polycarbonate (PC) overa range of compositions were studied in isothermal crystallizations from themelt using differential scanning calorimetry (DSC). Both crystallizationrate and degree of crystallinity of PET depend on blend composition. Theglass transition temperature, Tg, of PET and PC in blends andpure polymer were also measured by DSC. Elevation of the Tg ofPET and depression of the Tg of PC are observed upon blending. Incooling scans, dynamic crystallization from the melt was observed. In PET/PCblends with high PC content, a novel dual-peak crystallization of PET wasobserved. The effects of thermal history on crystallization kinetics anddegree of crystallinity were also determined in isothermal crystallizationstudies. For Melt processing times between 1 and 30 Min and for processingtemperatures between 280 and 300 °C, Melt processing temperature was seen tohave a stronger effect than processing time.

Crystalline Morphologies of poly (e-caprolactone) (PCL) and deuteratedpolycarbonate (PC) blends in both the semicrystalline/amorphous state andsemicrystalline/semicrystalline state were probed by small-angle neutron andX-ray scattering (SANS and SAXS). Due to the different contrast between thephases for neutrons and X-rays, SANS exhibited a monotonie drop in intensitywith increasing scattering angle while SAXS showed lamellar (peak)scattering.

Crystal- and amorphous-phase thickness were determined from the correlationfunction calculated from SAXS. This correlation function analysis suggesteda transition from interlamellar exclusion to interlamellar incorporation ofamorphous PCL in the PC lamellae. A two-correlation length model provided anexcellent fit for the SANS data over the entire composition range. ThisModel not only reproduced the shape but also the absolute magnitude of thescattering profiles. The long range correlation length (∼102 Å)and the short range correlation length (∼ 10 Å) derived from this model wereinferred to be associated with the crystalline PC domains and the localclusters found in the amorphous phase, respectively.

Binary blends of a semicrystalline polymer, poly (butylene terephthalate),PBT, with an amorphous polymer, polyarylate, PAr, were studied for a widerange of compositions. SMall angle x-ray scattering, thermal and mechanicalanalyses were conducted to determine the location of the uncrystallizablePAr relative to the crystal lamellae of PBT, for blends crystallized byheating from the quenched state. Comparison of experimental and calculatedlong periods indicates that interlamellar PAr placement becomes lessprobable as the PAr composition increases. When PBT crystallizes in theseblends, Most PAr is rejected from the regions near the crystal surfaces whenPAr fraction exceeds about 0.40.