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Amorphous surface layers in Ti-implanted Fe

Description: Implanting Ti into high-purity Fe results in an amorphous surface layer which is composed of not only Fe and Ti, but also C. Implantations were carried out at room temperature over the energy range 90 to 190 keV and fluence range 1 to 2 x 10/sup 16/ at/cm/sup 2/. The Ti-implanted Fe system has been characterized using transmission electron microscopy (TEM), ion backscattering and channeling analysis, and (d,p) nuclear reaction analysis. The amorphous layer was observed to form at the surface and grow inward with increasing Ti fluence. For an implant of 1 x 10/sup 17/ Ti/cm/sup 2/ at 180 keV the layer thickness was 150 A, while the measured range of the implanted Ti was approx. 550 A. This difference is due to the incorporation of C into the amorphous alloy by C being deposited on the surface during implantation and subsequently diffusing into the solid. Our results indicate that C is an essential constituent of the amorphous phase for Ti concentrations less than or equal to 10 at. %. For the 1 x 10/sup 17/ Ti/cm/sup 2/ implant, the concentration of C in the amorphous phase was approx. 25 at. %, while that of Ti was only approx. 3 at. %. A higher fluence implant of 2 x 10/sup 17/ Ti/cm/sup 2/ produced an amorphous layer with a lower C concentration of approx. 10 at. % and a Ti concentration of approx. 20 at. %.
Date: January 1, 1979
Creator: Knapp, J.A.; Follstaedt, D.M. & Picraux, S.T.
Partner: UNT Libraries Government Documents Department

Mechanical properties of high strength aluminum alloys formed by pulsed laser deposition

Description: Very high-strength alloys of A1(O) have been formed using a pulsed laser deposition (PLD) system to deposit from alternating targets of A1 and A1{sub 2}O{sub 3}. Ion beam analysis and transmission electron microscopy show that the deposited material is uniform in composition with up to 33 at. % O and has a highly refined microstructure consisting of a fine, uniform dispersion of {approximately}1 nm diameter {gamma}-A1{sub 2}O{sub 3} precipitates. Ultra-low-load indentation testing combined with finite-element modeling is used to determine the mechanical properties of the layers. Yield stresses as high as 5.1 GPa have been measured in these materials, greatly exceeding the strengths of aerospace Al alloys (-0.5 GPa) and even high strength steels. The key to the properties of these materials is the dispersion of small, hard precipitates spaced only a few Burgers vectors apart; dislocations are apparently unable to cut through and must bow around them.
Date: December 31, 1995
Creator: Knapp, J.A. & Follstaedt, D.M.
Partner: UNT Libraries Government Documents Department

Formation of cavities in Si and their chemisorption of metals

Description: Nanometer-size cavities formed in Si by He{sup +} implantation and annealing are examined with cross-section TEM. During annealing at 700 C or above, He degasses from the specimens, leaving uhv cavities with reactive Si bonds on their walls. Cavity microstructures have been characterized in detail for an implanted fluence of 1 {times} 10{sup 17} He/cm{sup 2}: cavity volume remains approximately constant (0.75 lattice sites/He) for anneals from 700 to {approximately}1000 C, while surface area (3 to 7 times the wafer area) decreases with temperature as the cavities coarsen. The cavities are found to getter up to {approximately}1 monolayer of Cu or Au from solution in Si without second-phase formation, thus identifying the trapping mechanism as chemisorption on the cavity walls.
Date: December 31, 1994
Creator: Follstaedt, D.M. & Myers, S.M.
Partner: UNT Libraries Government Documents Department

Sb interactions with TaC precipitates and Cu in ion-implanted. cap alpha. -Fe

Description: The interactions of Sb with the other species implanted into Fe to form Fe-Ta-C-Sb and Fe-Cu-Sb alloys have been examined with transmission electron microscopy and Rutherford backscattering following annealing at 873/sup 0/K. Trapping of Sb at TaC precipitates is observed in the former alloy just as was previously observed in Fe-Ti-C-Sb. In Fe-Cu-Sb, Sb interactions are governed by the atomic ratio of Sb to Cu. For ratios between 0.2 to 0.4, the compound ..beta..-Cu/sub 3/Sb was observed to form. For Sb to Cu ratios approx.< 0.1, fcc Cu precipitates were observed. In addition to the expected Sb dissolution in Cu, Sb trapping by Cu precipitates is also observed. The binding enthalpy of Sb at both TaC and Cu precipitates with respect to a solution site in the bcc Fe is the same as observed for TiC, approx. 0.4 eV. The constancy of the binding enthalpy at such chemically dissimilar precipitates supports the hypothesis that the trapping is due to the structural discontinuity of the precipitate-host interface. The observed Sb trapping at precipitates is of potential significance for the control of temper embrittlement in bcc steels.
Date: January 1, 1980
Creator: Follstaedt, D. M. & Myers, S. M.
Partner: UNT Libraries Government Documents Department

Trapping site location for Sb in Fe-Ti-Sb-C alloys

Description: The lattice location of Sb trapped at TiC precipitates in Fe has been determined. Channeling analysis of ion-backscattering and ion-induced characteristic x-ray yields from Fe and Sb showed a substitutionality of greater than or equal to 50% for trapped Sb relative to the Fe lattice for ion beams incident along Fe (100), (110), and (111). In contrast, Ti x-ray yields showed channeling through the oriented TiC precipitates only along Fe (100). We conclude that Sb is trapped at interfacial Fe sites adjacent to TiC precipitates, rather than within the TiC.
Date: January 1, 1980
Creator: Knapp, J. A. & Follstaedt, D. M.
Partner: UNT Libraries Government Documents Department

Precipitation in ion-implanted Al during electron beam pulsed annealing

Description: TEM and ion channeling were used to examine the microstructure of Al implanted with Zn or Sb following pulsed electron beam annealing with deposited energies of 0.7 to 1.6 J/cm/sup 2/. The Zn-implanted samples show a high density of dislocations in the near surface region. Zn precipitation is not seen in the electron diffraction patterns. For Sb, randomly oriented AlSb precipitates are observed, and precipitation is inferred to have occurred in molten Al. This is accounted for with the Al-Sb binary phase diagram.
Date: January 1, 1979
Creator: Follstaedt, D.M.; Picraux, S.T. & Wampler, W.R.
Partner: UNT Libraries Government Documents Department

Microstructures of Si surface layers implanted with Cu

Description: Microstructures of Si ion-implanted with Cu have been characterized by TEM after annealing. For 1.2 at.%, the Cu is trapped at planar defects, but for 10 at.%, {eta}-Cu{sub 3}Si forms and Cu diffuses at its equilibrium solubility. These observations allow proper evaluation of the binding energies of Cu to previously formed internal cavities (2.2 eV) and {eta}-Cu{sub 3}Si (1.7 eV). The 10 at.% Cu layer promotes oxidation of Si catalyzed by {eta}-Cu{sub 3}Si. The microstructures also indicate that Si implanted with {approximately}2 at.% Cu reforms epitaxially with embedded defects after 8 hr at 700C, but for {approximately}10 at.% Cu, epitaxy is not recovered after 6 hours at 600C.
Date: December 31, 1993
Creator: Follstaedt, D. M. & Myers, S. M.
Partner: UNT Libraries Government Documents Department

Microstructure of GaN Grown on (111) Si by MOCVD

Description: Gallium nitride was grown on (111) Si by MOCVD by depositing an AIN buffer at 108O"C and then GaN at 1060 {degrees}C. The 2.2pm layer cracked along {1-100} planes upon cooling to room temperature, but remained adherent. We were able to examine the microstructure of material between cracks with TEM. The character and arrangement of dislocation are much like those of GaN grown on Al{sub 2}O{sub 3}: -2/3 pure edge and - 1/3 mixed (edge + screw), arranged in boundaries around domains of GaN that are slightly disoriented with respect to neighboring material. The 30 nm AIN buffer is continuous, indicating that AIN wets the Si, in contrast to GaN on Al{sub 2}O{sub 3}.
Date: December 17, 1998
Creator: Fleming, J.G.; Follstaedt, D.M.; Han, J. & Provencio, P.
Partner: UNT Libraries Government Documents Department

Microstructure and interfacial properties of laterally oxidized Al{sub x}Ga{sub 1{minus}x}As

Description: Oxidation of high Al content Al{sub x}Ga{sub 1-x}As has received much attention due to its use in oxide-aperture, vertical-cavity surface emitting lasers (VCSELs) and for passivating AlAs against environmental degradation. We have recently identified the spinel, gamma phase of Al{sub 2}O{sub 3} in layers laterally oxidized in steam at 450 C for x=0.98 & 0.92 and have seen evidence for an amorphous precursor to the gamma phase. At the interface with the unoxidized Al{sub x}Ga{sub 1-x}As, an {approximately}17nm amorphous phase remains which could account for the excellent electrical properties of oxide-confined VCSELs and help reduce stress concentrations at the oxide terminus.
Date: December 31, 1996
Creator: Twesten, R.D.; Follstaedt, D.M. & Choquette, K.D.
Partner: UNT Libraries Government Documents Department

Evaluating mechanical properties of thin layers using nanoindentation and finite-element modeling: Implanted metals and deposited layers

Description: We present a methodology based on finite-element modeling of nanoindentation data to extract reliable and accurate mechanical properties from thin, hard films and surface-modified layers on softer substrates. The method deduces the yield stress, Young`s modulus, and hardness from indentations as deep as 50% of the layer thickness.
Date: December 31, 1996
Creator: Knapp, J.A.; Follstaedt, D.M. & Barbour, J.C.
Partner: UNT Libraries Government Documents Department

Interfaces in InAsSb/InGaAs strained-layer superlattices grown by MOCVD for use in infrared emitters

Description: The authors have prepared InAsSb/InGaAs strained-layer superlattices (SLSs) using metal-organic chemical vapor deposition (MOCVD). X-ray diffraction was used to determine lattice matching as well as composition and structure of the SLS`s. The presence of an InGaAsSb interface layer was indicated by x-ray diffraction for samples grown under non-optimized conditions. Interfacial layers were also identified with transmission electron microscopy (TEM). Two types of interfaces were observed by TEM. The different contrasts observed by TEM could be due to a difference in composition at the interfaces. The width of the x-ray peaks can be explained by a variation of the layer thickness.
Date: February 1, 1995
Creator: Biefeld, R.M.; Follstaedt, D.M.; Kurtz, S.R. & Baucom, K.C.
Partner: UNT Libraries Government Documents Department

Finite-element modeling of nanoindentation for determining the mechanical properties of implanted layers and thin films

Description: The mechanical properties of implanted layers and thin films on dissimilar substrates are difficult to accurately determine. Nanoindentation of the layer provides information, but detailed numerical modeling is required in order to separate the properties of the layer from those of the substrate. We describe here the procedures we have developed to accomplish this modeling with the commercially available finite-element code ABAQUS. Using these techniques, we are able to extract from nanoindentation testing the yield stress, Young`s modulus, and hardness of the layer material, with an absolute accuracy of at least 20%. The procedure is applicable to layers as thin as 50 nm on essentially any substrate, hard or soft. We have used it for materials ranging from ion-implanted layers to thin films of metals and dielectrics formed using plasma-deposition methods. An example is given of 0-implanted Al, a thin, hard layer on a soft substrate.
Date: October 1, 1996
Creator: Knapp, J.A.; Follstaedt, D.M.; Barbour, J.C. & Myers, S.M.
Partner: UNT Libraries Government Documents Department

Gettering of transition metals by cavities in silicon formed by helium ion implantation

Description: We have recently completed studies which quantitatively characterize the ability of nanometer-size cavities formed by He ion implantation to getter detrimental metal impurities in Si. Cavity microstructures formed in Si by ion implantation of He and subsequent annealing have been found to capture metal impurities by two mechanisms: (1) chemisorption on internal walls at low concentrations and (2) silicide precipitation at concentrations exceeding the solid solubility. Experiments utilizing ion-beam analysis, cross-sectional transmission electron microscopy, and secondary ion mass spectrometry were performed to quantitatively characterize the gettering effects and to determine the free energies associated with the chemisorbed metal atoms as a function of temperature. Mathematical models utilizing these results have been developed to predict gettering behavior.
Date: September 1, 1996
Creator: Petersen, G.A.; Myers, S.M. & Follstaedt, D.M.
Partner: UNT Libraries Government Documents Department

Interaction of cavities with misfit dislocations in SiGe/Si heterostructures

Description: Consequences of the strong, short-range attractive interaction between cavities and misfit dislocations are examined in SiGe/Si heterostructures. When He is implanted at the SiGe/Si interface, either in situ during epitaxial growth or by post-growth treatment, cavities form and locate on the misfit dislocation cores. The misfit dislocations are no longer straight lines extending over several microns, but form a network with jogs and intersections at the cavities. The He-implanted cavity layer enhances thermal relaxation of the strained alloy and may increase the achievable degree of relaxation by lowering dislocation energies.
Date: September 1, 1996
Creator: Follstaedt, D.M.; Myers, S.M.; Floro, J.A. & Lee, S.R.
Partner: UNT Libraries Government Documents Department

Cavity formation and impurity gettering in He-implanted Si

Description: Cavity microstructures formed in Si after ion implantation of He and annealing at 700 C or above are examined with cross-section transmission electron microscopy. A threshold concentration of 1.6 at.% He is identified to form cavities that survive such anneals. The cavities coarsen with a constant volume of 15 nm{sup 3}/nm{sup 2} (per wafer surface area), corresponding to {approximately}0.75 lattice sites per implanted He atom. The internal area of the cavities is 3--7 times that of the wafer surface area for fluences of 1 {times} 10{sup 17} He/cm{sup 2}. Transition metal atoms (Cu, Ni, Co, Fe, Au) are shown to be strongly trapped (1.5--2.2 eV) on the cavity walls by chemisorption. Whereas Cu, Au and Ni are bound more strongly to the cavity sites than to their respective precipitated phases, Co and Fe are more strongly bound to their silicides; nonetheless, appreciable trapping of Co and Fe does occur in equilibrium with the silicides. Cavity trapping appears to be an effective gettering mechanism at low impurity levels, as needed to meet future microelectronics device requirements.
Date: December 31, 1994
Creator: Follstaedt, D.M.; Myers, S.M.; Petersen, G.A. & Medernach, J.W.
Partner: UNT Libraries Government Documents Department

Microstructure and interface properties of laterally oxidized Al{sub x}Ga{sub 1{minus}x}As

Description: The selective and passivating nature of the oxidation of high Al content AlGaAs has been used to create high-performance vertical-cavity surface emitting lasers (VCSELs). This is accomplished by using the fact the Ga content of a AlGaAs film will drastically affect its oxidation rate, allowing the strategic placement of high Al content layers in the structure; these are then oxidized to form current-confining and optical-mode-defining apertures. Here, the microstructure and interface properties of Al{sub x}Ga{sub 1{minus}x}As materials that have been laterally oxidized in wet N{sub 2} for several compositions (x = 0.80, 0.82...1.00) and temperatures (360 C to 450 C) have been studied. The microstructure is found to be relatively insensitive to composition and oxidation temperature. The oxidation forms an amorphous solid solution (Al{sub x}Ga{sub 1{minus}x}){sub 2}O{sub 3} that transforms to polycrystalline, {gamma}-(Al{sub x}Ga{sub 1{minus}x}){sub 2}O{sub 3} is formed via post oxidation annealing of the oxide. The level of hydrogen present in the oxidized layers is 1.1 {times} 10{sup 21} cm{sup {minus}3}, which is too low for the amorphous phase observed to be a hydroxide rather than an oxide. The amount of As in the layer is reduced to <2 atm%, and no As precipitates are observed. The (Al{sub x}Ga{sub 1{minus}x}){sub 2}O{sub 3}/GaAs interface is abrupt, but prolonged oxidation will cause the GaAs to oxidize at the internal interfaces. The reaction front between the oxidized and the unoxidized Al{sub x}Ga{sub 1{minus}x}As has a 10 to 20nm-wide amorphous zone that shows a different contrast than the remainder of the amorphous oxide and is stable under electron irradiation.
Date: December 31, 1996
Creator: Twesten, R.D.; Follstaedt, D.M. & Choquette, K.D.
Partner: UNT Libraries Government Documents Department

Segregation gettering by implantation-formed cavities and B-Si precipitates in silicon

Description: The authors show that Fe, Co, Cu, and Au in Si undergo strong segregation gettering to cavities and B-Si precipitates formed by He or B ion implantation and annealing. The respective mechanisms are argued to be chemisorption on the cavity walls and occupation of solution sites within the disordered, B-rich, B-Si phase. The strengths of the reactions are evaluated, enabling prediction of gettering performance.
Date: January 1, 1998
Creator: Myers, S.M.; Petersen, G.A. & Follstaedt, D.M.
Partner: UNT Libraries Government Documents Department

Final report on LDRD Project: Quantum confinement and light emission in silicon nanostructures

Description: Electrochemically formed porous silicon (PS) was reported in 1991 to exhibit visible photoluminescence. This discovery could lead to the use of integrated silicon-based optoelectronic devices. This LDRD addressed two general goals for optical emission from Si: (1) investigate the mechanisms responsible for light emission, and (2) tailor the microstructure and composition of the Si to obtain photoemission suitable for working devices. PS formation, composition, morphology, and microstructure have been under investigation at Sandia for the past ten years for applications in silicon-on-insulator microelectronics, micromachining, and chemical sensors. The authors used this expertise to form luminescent PS at a variety of wavelengths and have used analytical techniques such as in situ Raman and X-ray reflectivity to investigate the luminescence mechanism and quantify the properties of the porous silicon layer. Further, their experience with ion implantation in Si lead to an investigation into alternate methods of producing Si nanostructures that visibly luminesce.
Date: February 1, 1995
Creator: Guilinger, T.R.; Kelly, M.J. & Follstaedt, D.M.
Partner: UNT Libraries Government Documents Department

Extreme Precipitation Strengthening in Ion-Implanted Nickel

Description: Precipitation strengthening of nickel was investigated using ion-implantation alloying and nanoindentation testing for particle separations in the nanometer range and volume fractions extending above 10O/O. Ion implantation of either oxygen alone or oxygen plus aluminum at room temperature was shown to produce substantial strengthening in the ion-treated layer, with yield strengths near 5 GPa in both cases. After annealing to 550"C the oxygen-alone layer loses much of the benefit, with its yield strength reduced to 1.2 GP~ but the dual ion-implanted layer retains a substantially enhanced yield strength of over 4 GPa. Examination by transmission electron f microscopy showed very fine dispersions of 1-5 nm diameter NiO and y-A1203 precipitates in the implanted layers before annealing. The heat treatment at 550"C induced ripening of the NiO particles to sizes ranging from 7 to 20 nm, whereas the more stable ~-A1203 precipitates were little changed. The extreme strengthening we observe is in semiquantitative agreement with predictions based on the application of dispersion-hardening theory to these microstructure.
Date: May 3, 1999
Creator: Follstaedt, D.M.; Knapp, J.A.; Myers, S.M. & Petersen, G.A.
Partner: UNT Libraries Government Documents Department

Strong segregation gettering of transition metals by implantation-formed cavities and boron-silicide precipitates in silicon

Description: We have mechanistically and quantitatively characterized the binding of transition-metal impurities in Si to cavities formed by He implantation and to B-Si precipitates resulting from B implantation. Both sinks are inferred to act by the segregation of metal atoms to pre-existing low-energy sites, namely surface chemisorption sites in the case of cavities and bulk solution sites in the case of the B-Si phase. These gettering processes exhibit large binding energies, and they are predicted to remain active for arbitrarily small initial impurity concentrations as a result of the segregation mechanisms. Both appear promising for gettering in Si devices.
Date: June 1, 1996
Creator: Myers, S.M.; Petersen, G.A.; Follstaedt, D.M. & Headley, T.J.
Partner: UNT Libraries Government Documents Department

Cavity nucleation and evolution in He-implanted Si and GaAs

Description: The criteria for forming stable cavities by He{sup +} implantation and annealing are examined for Si and GaAs. In Si, implanting at room temperature requires a minimum of 1.6 at. % He to form a continuous layer of cavities after annealing at 700{degrees}C. The cavities are located at dislocations and planar defects. Implanting peak He concentrations just above this threshold produces narrow layers of cavities at the projected range. In GaAs, room-temperature implantation followed by annealing results in exfoliation of the surface layer. Cavities were formed instead by implanting Ar followed by overlapping He, both at 400{degrees}C, with additional annealing at 400{degrees}C to outgas the He. This method forms 1.5--3.5 nm cavities that are often on [111] planar defects.
Date: December 1, 1995
Creator: Follstaedt, D.M.; Myers, S.M.; Petersen, G.A. & Barbour, J.C.
Partner: UNT Libraries Government Documents Department

The growth of InAsSb/InGaAs strained-layer superlattices by metal-organic chemical vapor deposition

Description: We have grown InAs{sub l-x}Sb{sub x}/In{sub 1-y}Ga{sub y}As strained-layer superlattice (SLS) semiconductors lattice matched to InAs using a variety of conditions by metal-organic chemical vapor deposition. The V/III ratio was varied from 2.5 to 10 at 475 C, at pressures of 200 to 660 torr and growth rates of 3 {minus} 5 {angstrom}/s and layer thicknesses ranging from 55 to 152 {angstrom}. Composition of InAsSb ternary can be predicted from the input gas molar flow rates using a thermodynamic model. At lower temperatures, the thermodynamic model must be modified to take account of the incomplete decomposition of arsine and trimethylantimony. Diodes have been prepared using Zn as the p-type dopant and undoped SLS as the n-type material. The diode was found to emit at 3.56 {mu}m. These layers have been characterized by optical microscopy, SIMS, x-ray diffraction, and transmission electron diffraction. The optical properties of these SLS`s were determined by infrared photoluminescence and absorption measurements.
Date: December 31, 1993
Creator: Biefeld, R. M.; Baucom, K. C.; Kurtz, S. R. & Follstaedt, D. M.
Partner: UNT Libraries Government Documents Department

ECR plasma-assisted deposition of Al{sub 2}O{sub 3} and dispersion-strengthened AlO{sub 2}

Description: Electron cyclotron resonance (ECR) O{sub 2} plasmas, in conjunction with electron-beam evaporation of Al, were used to grow thick AlO{sub x} films were varying but controlled composition and microstructure. The ion energy was varied from 30 to 190 eV, and growth temperatures varied from 35{degrees}C to 400{degrees}C. The ECR-film compositions were varied from AlO{sub 0.1} to Al{sub 2}O{sub 3} by controlling the plasma parameters and Al deposition rate. The Al-rich alloys exhibited a fine-grain (10-100 nm) fcc Al microstructure with {gamma}-Al{sub 2}O{sub 3} precipitates ({approximately}1 nm), similar to that found in the gigapascal-strength O-implanted Al. The measured hardness of the ECR Al-O alloys ({approximately}3 GPa) was also similar to the ion-implanted alloys which implies that the yield strength of the ECR material is {approximately}1 GPa. Moreover, the Al-O alloys retain much of the elasticity of the Al metal matrix. As-deposited stoichiometric Al{sub 2}O{sub 3} samples grown with an applied bias of -140 to -160 V at 400{degrees}C were fine-grain polycrystalline {gamma}-Al{sub 2}O{sub 3}. The amorphous films crystallized into the {gamma}-Al{sub 2}O{sub 3} phase upon vacuum annealing to 800{degrees}C.
Date: March 1, 1995
Creator: Barbour, J. C.; Follstaedt, D. M. & Myers, S. M.
Partner: UNT Libraries Government Documents Department

Binding of copper and nickel to cavities in silicon formed by helium ion implantation

Description: Cavities formed in Si by He ion implantation and annealing are shown to be strong traps for Cu and Ni impurities. Experiments utilizing ion-beam analysis and transmission electron microscopy indicate that Cu is trapped at the internal surfaces of cavities up to {approximately}1 monolayer coverage with a binding energy of 2.2{plus_minus}0.2 eV relative to solution. This is greater than the heat of solution from the precipitated Cu{sub 3}Si phase, determined to be 1.7 eV in agreement with earlier work. Copper at cavity-wall sites is reversibly replaced by H during heating in H{sub 2} gas, indicating the relative stability of the two surface terminations. Initial results for Ni impurities indicate that trapping at cavities is again energetically preferred to silicide formation. The saturation coverage of Ni on the internal surfaces, however, is an order of magnitude smaller for Ni than Cu, consistent with published studies of external-surface adsorption. These results suggest that cavity trapping may getter metallic impurities in Si more effectively than methods based on silicide precipitation.
Date: December 1, 1993
Creator: Myers, S. M.; Follstaedt, D. M. & Bishop, D. M.
Partner: UNT Libraries Government Documents Department