Au Grains Research Articles

Dependence of fiber texture on composition in metal-insulator Au–SiO2 composite thin films

The authors show that the evolution of metal fiber texture in phase segregated metal-insulator composite thin films depends strongly on the composition. Using x-ray diffraction pole figures, they measured the strength of the Au (111) fiber texture as a function of composition in the phase segregated Au–SiO2 system, codeposited by magnetron sputtering at room temperature. They find that for very low SiO2 volume fractions, less than 5%, Au has low resistivity and a strong (111) fiber texture similar to that of pure Au. For higher SiO2 volume fractions, up to 30%, the strength of the Au fiber texture decreases more rapidly with increasing SiO2 volume fraction than can be attributed to the decreasing Au volume fraction. They propose that the rapid decrease in Au (111) fiber texture strength is consistent with Zener pinning of Au grains by second-phase SiO2 particles. For SiO2 volume fractions greater than 30%, the Au fiber texture is lost as the Au phase becomes disrupted, the films become insulating, and the microstructure changes to randomly oriented Au islands within an insulating matrix of SiO2.

Atomic Force Microscopy Study of the Kinetic Roughening in Nanostructured Gold Films on SiO2.

Dynamic scaling behavior has been observed during the room-temperature growth of sputtered Au films on SiO2using the atomic force microscopy technique. By the analyses of the dependence of the roughness, σ, of the surface roughness power,P(f), and of the correlation length,ξ, on the film thickness,h, the roughness exponent,α = 0.9 ± 0.1, the growth exponent,β = 0.3 ± 0.1, and the dynamic scaling exponent,z = 3.0 ± 0.1 were independently obtained. These values suggest that the sputtering deposition of Au on SiO2at room temperature belongs to a conservative growth process in which the Au grain boundary diffusion plays a dominant role.

고분자전해질 연료전지용 바이폴라 플레이트의 다층 코팅의 증착

The surface region of commercial stainless steel 304 and 316 plates has been modified through deposition of the multi-layered coatings composed of titanium film (0.1 ㎛) and gold film (1-2 ㎛) by an electron beam evaporation method. XRD patterns of the stainless steel plates deposited with conductive metal films showed the peaks of the external gold film and the stainless steel substrate. Surface microstructural morphologies of the stainless steel bipolar plates modified with multi-layered coatings were observed by AFM and FE-SEM images. The stainless steel plates modified with 0.1 ㎛ titanium film and 1 ㎛ gold film showed microstructure of grains of under 100 ㎚ diameter. The external surface of the stainless steel plates deposited with 0.1 ㎛ titanium film and 2 ㎛ gold film represented somewhat grain growth of Au grains in FE-SEM image. The electrical resistance and water contact angle of the stainless steel bipolar plates modified with multi-layered coatings were examined with the thickness of the gold film.

Assessment of Bacterial Communities in Auriferous and Non-Auriferous Soils Using Genetic and Functional Fingerprinting

Understanding the microbial processes affecting the mobility of Au is important in the development of biogeochemical models describing the formation of secondary anomalies and Au grains in soils and deeper regolith materials. This study characterizes bacterial activity in auriferous soils that is linked to the microbially mediated solubilization of Au, as a result of production and consumption of free amino acids, which can form stable complexes with Au. Through the application of 16S rDNA fingerprinting and community level physiological profiling (CLPP), concurrently with Au mobility data, microcosm experiments have demonstrated the role that mobile Au plays in determining the structure and function of bacterial communities in auriferous soils. The bacterial community of auriferous soils displayed genetic differences compared to non-auriferous (background) soils associated with the appearance of Methylocella sp., Arthrobacter sp. and Bacillus sp., as well as functional differences in the utilization of D-Cellobiose, L-Serine, L-Phenylalanine, L-Arginine and N-Acetyl-D-Glucosamine. These results suggest that soil bacterial communities are linked to biogeochemical Au cycling, and that microbial fingerprinting analyses may be used as a screening tool in Au exploration to differentiate auriferous from background terrains.

Laterization and its control to gold occurrence in Laowanchang gold deposit, Guizhou Province, Southwest of China

Laowanchang gold deposit, located in Qinglong County, Guizhou Province, Southwest China, is the first-discovered laterite type gold deposit in Guizhou Province. Although most scholars are inclined to agree that ore-forming substance was closely correlated with “Dachangceng layer”, it still remained controversial. Former researchers did not find existences of visible Au grains in limonite, clay minerals or pyrite under SEM observation; therefore, they considered Au occurrence mainly as micro-disseminated form. In this study, mineral composition, chemical components and chemical index of alteration of laterites indicated that three chemical weathering processes, including argillaceous, bauxitic and ferric process can be observed in Laowanchang laterization. Geochemically, such laterization can be attributed to early laterization stage. Components of K 2O, Na 2O, and CaO were highly leached during weathering indicating a strong chemical alteration. Concentrations of ore-forming elements (Au, As and Sb) varied greatly along laterite profiles. Concentrations of Au were usually in the range of 40 × 10 − 9 –4551 × 10 − 9 ; As in 0.1–0.9% with the highest value of 1.8%; Sb < 0.1%. Concentrations of Au, As and Sb in laterites were obviously higher than in silicalites of Dachanceng layer. During laterization, enrichment of Au and As were obviously related with enrichment of Fe. Au and As enriched in relatively reductive locations, while Sb in the relatively oxidized circumstances. Rare earth element (REE) contents were higher in laterite profiles with LREE/HREE ratios usually less than 10. REE had very similar distribution patterns in laterites, significantly differing from those of Dachanceng layer. Features of trace element pairs (including large ionic lithophile elements and incompatible elements) and ore-forming element pairs diagramed great differently between laterites and Dachanceng layer. These phenomena supported that laterites would not directly be developed from Dachanceng layer rocks, but mainly be related with Quaternary sediments. Ore-forming substances of Laowanchang gold deposit also connected less with Dachanceng layer. Au occurrences in laterites varied under TEM-EDX observations. Gold existed either as granular natural gold, or adsorbed by goethite and As-bearing goethite, or by siliceous matter and quartz, sometimes by illites. Reduction of Au 3+ to Au 0+ by Fe 2+ played an important role in enrichment of Au during laterization.

The structure and growth process of Au/Si(1 1 1) analyzed by high-resolution ion scattering coupled with photoelectron spectroscopy

We analyzed both the elemental depth profile and chemical bonds of Au/p-Si(1 1 1)-7 × 7 grown at room temperature by medium energy ion scattering combined with photoelectron spectroscopy using synchrotron-radiation-light. It is found unambiguously that Au deposition grows some Au-rich silicide phases for Au coverage above 0.31 ML (1 ML = 0.78 × 10 15 atoms/cm 2). At an Au coverage of 5.2 ML, the surface comprises a stable Au 3Si 2 (1.5 × 10 15 atoms/cm 2: ∼2 atomic layers) layer on top and an underlying metallic Au layer which contains Si atoms diffused in the boundaries of fine Au grains. Indeed, we observed two components for Au 4f (Au–silicide and metallic) and three components for Si 2p spectra (bulk, Au–silicide, and incorporated in an Au layer). Further Au deposition increases thickness of the underlying Au layer without changing the thickness of the Au 3Si 2 layer on top. Total number of Si atoms consumed to form the Au 3Si 2 layer and contained in the underlying Au layer coincides with the number of Si atoms making the 7 × 7 reconstruction. The present study reveals clearly the dynamic process happening at the Au/Si(1 1 1) interface.

Exploration using till geochemistry and heavy minerals in the ribbed moraine area of southern Finnish Lapland

The geochemistry of different till size fractions and studies of heavy minerals have been used in mineral exploration in the ribbed moraine terrain in southern Finnish Lapland. The Peräpohja Schist Belt and layered intrusions along its southern margin have known potential for economic Au, Co, Cu, Fe, Zn, U and PGE mineralization. In till, high element concentrations related to mineralization in the local bedrock preferentially occur in the near-surface (less than 2 to 3 m depth) of ribbed moraine ridges. The ridges formed subglacially by gouging of local bedrock, which favoured the deposition of rock material derived from the local bedrock surface into till on the surficial part of ridges. The short distance of glacial transport (&lt;500 m) is indicated by clast angularity, the abundance of locally derived boulders in the upper till and at the surface, and by the preservation of euhedral pyrite and chalcopyrite crystals and native Au grains in the heavy mineral concentrates. Detailed studies show that ribbed moraine ridge tops can be used for mineral exploration because they are more likely to be composed of local bedrock than are the sediments comprising the ridge core.

Electrodeposition of Single-Crystal Cubes of Lead Telluride on Polycrystalline Gold Substrate

Single-crystal cubes of lead telluride (PbTe with NaCl structure) were electrodeposited on polycrystalline gold substrates. Electron and X-ray diffraction patterns and high-resolution TEM confirm that the single-crystal PbTe cubes were grown with their {100} planes parallel to the surface of the gold seed layer. The PbTe cubes might have nucleated on the {100} faces of individual Au grains on the basis of lattice mismatch calculation, followed by the lateral growth of new layers on the nuclei along the 〈110〉 directions from the four edges of the PbTe cubes. The enlargement of the PbTe single crystals occurred through lateral growth, which led to the development of relatively large single-crystal cubes on polycrystalline Au seed layers having a smaller grain size.

Odd characteristics of Au film on pentacene

Anomalies of Au film formed on the pentacene surface are investigated as a counterpart of pentacene/Au structure. The Au film is found to contain pentacene derivatives originated from the pentacene layers, and it is composed of grains of various sizes formed as the Au thickness increases. The authors suggest that it is this abundance of peculiarities of the Au film that accounts for the attenuated density of states in the valence band. Deformation of Au grains is accompanied by the lift of the pentacene layers, which, in turn, brings about the device failure.

STM/STS investigations of titanium oxide nanostructures on au substrate

Au substrate was prepared by Au evaporation on Si(111) surface. Au surface was composed of Au grains with typical diameter of about 50 nm with atomically flat terraces. TiO 2 nanostructures were created by electron gun evaporation of Ti while simultaneous dosing of high purity O 2 gas. The pressure of oxygen was kept at 5 · 10 − 8 mbar and controlled by means of residual gas analyzer (RGA). Scanning tunneling microscopy (STM) images showed that TiO 2 nanocrystallites had grown between Au grains in cavities between them. This may suggest that such spots are preferred TiO 2 nucleation sites. I– V curves measured above Au showed metallic properties while those measured above TiO 2 exhibit energy gap characteristics for semiconducting material.

Study of Gold Thin Films Evaporated on Polyethylene Naphthalate Films toward the Fabrication of Quantum Cross Devices

AbstractMolecular electronics devices continue to be pursued as a technology that offers the prospect of scaling device dimensions down to a few nanometers and also promote a practical introduction for high-density memory applications. One of several molecular devices is a cross-bar memory device fabricated by nanoimprint lithography process, which has achieved the production of 30-nm half-pitch patterning. However, today's production procedures such as nanoimprint lithography, optical lithography, and electron-beam lithography, do not allow for the resolution to achieve sub-10-nm line-width structures. Recently we have proposed a double nano-“baumkuchen” (DNB) structure, composed of two thin slices of alternating metal/insulator nano-“baumkuchen” as a lithography-free nano-structure fabrication technology. The DNB has potential application in a high-density memory device, the cross point of which can scale down to ultimately a few nanometers feature sizes because the pattering resolution is determined by the metal-deposition rate, ranging from 0.01 nm/s to the order of 0.1 nm/s. One element of the DNB structure is called a quantum cross (QC) device that consists of two metal nano-ribbons having edge-to-edge configuration. In the area of edge-to-edge QC devices there has been no experimental reports, meanwhile face-to-face devices such as cross-bar devices and spin tunneling devices, have been widely studied both theoretically and experimentally. In our present work, as the first experimental attempt toward the fabrication of QC devices, we have studied gold thin films evaporated on polyethylene naphtalate (PEN) organic films, which can be a candidate of metal/insulator part used for QC devices, by using the atomic force microscope (AFM). Au thin films were thermally evaporated on PEN films in the high vacuum chamber including the film-rolled-up system. The Au thickness was measured by a mechanical method using the stylus surface profiler and an optical method using the diode pumped solid state (DPSS) green laser. Surface morphologies of Au thin films on PEN films were analyzed by the AFM at room temperature. As the thickness of Au films evaporated on PEN films decreases from 20 nm to 5 nm, the AFM surface roughness is reduced from 4.8 nm down to 1.5 nm in the scanning area of 500~500 nm2. The Au grain size is 28.0-4.6 nm for 5-nm-thick Au films and 45.8-5.8 nm for 10-nm-thick Au films, respectively. As a result of the scaling investigation of the surface roughness, the surface roughness of 5-nm-thick Au films is 0.22 nm, corresponding to one atomic size, in the scanning scale of 5 nm. These experimental results indicate that Au thin films on PEN films are suitable as a candidate of metal/insulator(organic films) hybrid materials used for QC devices, and may open up a noble research field to clarify the electric characterization of QC devices using a few atoms or molecules leading to high-density memories.

Bioaccumulation and secondary gold nugget formation

Experimental evidence suggests that microorganisms are important in the cycling of Au (1). Recent microcosm studies with auriferous soils from Australian mine sites have shown that the resident microbiota are capable of solubilising up to 80 wt.% of the Au contained in these soils (1). A number of common soil bacteria, actinomycetes, archaea, and fungi have been shown to precipitate Au(I/III)-complexes under a wide range of experimental conditions (2). Morphological evidence for the occurrence of micrometre sized bacterioform structures on secondary Au grains has been reported in earlier studies (3). However, neither the biological origin of these structures nor associated organisms or processes have been identified. Gold grains for this study were obtained from the auriferous soils overlying mineralisation at the Tomakin Parkand the Hit or Miss Gold Mine in moderate New South Wales and tropical Queensland, respectively. The grains were 200 to 2200 μm in diameter and generally showed little sign of physical transport. Analyses of gold grain digests that amounted to an average fineness of 99.2% established their secondary origin. Scanning electron microscopy (SEM) revealed bacterioform on untreated grains from both sites. The presence of active bacterial biofilms on the surface of Au grains was confirmed using confocal stereo laser microscopy (CSLM) combined with nucleic acid staining. Isolation, amplification and separation of 16S ribosomal DNA from these biofilms and identification of the organisms present using DNA sequence analysis showed that unique, sitespecific bacterial communities are associated with these Au grains that differ from those dominating the surrounding soil. 16S ribosomal DNA clones bearing 99 % similarity to a known metallophilic bacterium are present on all 16S rDNA positive grains from both locations. The ability of this metallophilic bacterium to accumulate AuCl4 complexes was tested under in-vitro conditions, and biologically active cells typically accumulated twice as much Au as lysed cell preparations. These results indicate that bacteria that are associated with Au grains may be able to actively reduce AuCl4 and accumulate metallic Au, and thus contribute to the authigenic formation of secondary Au nuggets in the regolith.

Microchemical characterisation of natural gold and artefact gold as a tool for provenancing prehistoric gold artefacts: A case study in Ireland

The importance of Au to ancient societies has encouraged many archaeologists to search for the sources exploited in antiquity. These projects generally involve detailed studies of artefacts and comparison of their chemical characteristics with those reported for natural Au. However, descriptions of natural Au are frequently inadequate for provenancing studies, and the compositional variability of the material is not widely recognised. The present study describes a new approach to gold provenancing using the technique of microchemical characterisation in which populations of gold grains are classified according to the alloy compositions and the assemblages of microinclusions of other minerals. This technique, originally developed to identify sources of alluvial gold during Au exploration, has proved applicable to provenancing studies in four main areas. Firstly, microchemical characterisation of artefacts grouped according to archaeological criteria can indicate the number of sources exploited in relation to time and artefact taxonomy. Secondly, knowledge of the total variation in chemical characteristics of natural Au from a particular region provides an excellent database for provenancing and reduces the need for exhaustive sampling. Thirdly, it is possible to predict how Au alloys were modified during fabrication as a consequence of assimilation of mineral inclusions. Finally, identification of inclusion phases in artefact Au can provide information on metallurgical practices. These principles have been applied to the search for the source of Au used for the unique traditions of prehistoric Irish metalworking. Studies of 180 Irish Au artefacts belonging to four major metalworking traditions dating from the Early Bronze Age (2400 BC) to the Iron Age, (150 BC) show that each group exhibits distinctive Ag and Cu contents. Parallel studies of 2267 natural Au grains from 58 alluvial localities and four bedrock localities throughout Ireland reveal a broad pattern of alloy compositions consistent with style of mineralisation and host geology. The ranges of Ag contents of Early Bronze Age and Middle Bronze Age artefacts suggests that the Au source lies within Lower Palaeozoic sedimentary rocks of the Southern Uplands Terrane and significantly, that the same source (or sources) were used in both periods. A different source of relatively Ag-rich Au (most probably at Croagh Patrick, Co. Mayo), was exploited in the Late Bronze Age. Iron Age artefacts have Ag contents higher than natural Irish Au. Evidence for evolution of metallurgical practice during the Bronze Age is provided by the increasing Cu content of the gold alloys (to levels far in excess of natural gold) and the nature of inclusions in artefacts of different ages. Elevated Sn in Cu-rich alloys suggests deliberate or accidental alloying with bronze. This approach has provided the first clear indication that only a few individual indigenous Irish sources of Au were used during the Bronze Age and that their relative importance changed over time. Future archaeological investigations may adopt a geographical focus that was not previously possible.

Gaseous transport and deposition of gold in magmatic fluid: evidence from the active Kudryavy volcano, Kurile Islands

The distribution of gold in high-temperature fumarole gases of the Kudryavy volcano (Kurile Islands) was measured for gas, gas condensate, natural fumarolic sublimates, and precipitates in silica tubes from vents with outlet temperatures ranging from 380 to 870°C. Gold abundance in condensates ranges from 0.3 to 2.4 ppb, which is significantly lower than the abundances of transition metals. Gold contents in zoned precipitates from silica tubes increase gradually with a decrease in temperature to a maximum of 8 ppm in the oxychloride zone at a temperature of approximately 300°C. Total Au content in moderate-temperature sulfide and oxychloride zones is mainly a result of Au inclusions in the abundant Fe–Cu and Zn sulfide minerals as determined by instrumental neutron activation analysis. Most Au occurs as a Cu–Au–Ag triple alloy. Single grains of native gold and binary Au–Ag alloys were also identified among sublimates, but aggregates and crystals of Cu–Au–Ag alloy were found in all fumarolic fields, both in silica tube precipitates and in natural fumarolic crusts. Although the Au triple alloy is homogeneous on the scale of microns and has a composition close to (Cu,Ni,Zn)3(Au,Ag)2, transmission electron microscopy (TEM) shows that these alloy solid solutions consist of monocrystal domains of Au–Ag, Au–Cu, and possibly Cu2O. Gold occurs in oxide assemblages due to the decomposition of its halogenide complexes under high-temperature conditions (650–870°C). In lower temperature zones (<650°C), Au behavior is related to sulfur compounds whose evolution is strongly controlled by redox state. Other minerals that formed from gas transport and precipitation at Kudryavy volcano include garnet, aegirine, diopside, magnetite, anhydrite, molybdenite, multivalent molybdenum oxides (molybdite, tugarinovite, and ilsemannite), powellite, scheelite, wolframite, Na–K chlorides, pyrrhotite, wurtzite, greenockite, pyrite, galena, cubanite, rare native metals (including Fe, Cr, Mo, Sn, Ag, and Al), Cu–Zn–Fe–In sulfides, In-bearing Pb–Bi sulfosalts, cannizzarite, rheniite, cadmoindite, and kudriavite. Although most of these minerals are fine-grained, they are strongly idiomorphic with textures such as gas channels and lamellar, banded, skeletal, and dendrite-like crystals, characteristic of precipitation from a gas phase. The identified textures and mineral assemblages at Kudryavy volcano can be used to interpret geochemical origins of both ancient and modern ore deposits, particularly gold-rich porphyry and related epithermal systems.

Spatial resolution of ballistic electron emission microscopy measured on metal/quantum-well Schottky contacts

Au Schottky contacts on cleaved AlGaAs∕GaAs∕AlGaAs quantum wells (QWs) were used as precise nanometer-scale apertures to quantify the spatial resolution of ballistic electron emission microscopy (BEEM). Both the amplitude and width of the measured average BEEM current profiles showed systematic dependencies on the QW width and Au film thickness, indicating surprisingly large BEEM resolutions of ∼12, ∼16, and ∼22nm for Au film thicknesses of 4, 7, and 15nm, respectively, but roughly independent of Au grain size. These measurements are consistent with theoretical models that include multiple hot-electron scattering at interfaces and in the bulk of the metal film.

Effects of Ca on grain boundary cohesion in Au ballbonding wire

Measurements of the tensile properties of Ca doped Au ballbonding wires show that Ca significantly increases the strength of Au and improves ductility. The strengthening mechanism is poorly understood but the limited solubility of Ca in Au and the large atomic misfit factor precludes solid solution strengthening and there is insufficient Ca present for conventional precipitation hardening to be effective. However, Ca segregation would be a possible mechanism. The effects of Ca segregation are investigated by calculating the cohesive strength of a Ca-containing Au grain boundary relative to a free surface using a first-principles calculation within the framework of density functional theory. The simulation results support the theory that the tensile strength and ductility increase with Ca doping may be due to enhanced Au grain boundary cohesion.

Annealing enhanced hydrogen absorption in nanocrystalline Pd∕Au sensing films

The enhanced hydrogen absorption and sensitivity of nanocrystalline Pd(60at.%)∕Au(40at.%) thin films were realized through the development of a thermal annealing process and a determination of its underlying enhancement mechanism. 20-nm-thick films were deposited by magnetron sputtering and then annealed at temperatures ranging from 100 to 400 °C. Optical reflectance and x-ray diffraction (XRD) analyses were utilized to investigate the H2 response and microstructure characteristics of the as-deposited and annealed films as a function of the annealing temperature. The as-deposited films exhibited a consistently low H absorption, evidenced by a small reflectance-signal change at even a 4% H2 concentration, while displaying a 5-second response time. The combined stress and composition analyses by XRD indicate that the as-deposited film is under a compressive stress of ∼560MPa and has an unexpectedly low Pd (40%) content in the ∼7-nm nanocrystallites, in contrast to the overall film Pd concentration (60%), with Pd enrichment occurring in the disordered grain boundary. The low H absorption characteristics can be overcome by a thermal annealing process, and it was determined that a 200 °C annealing temperature was most desirable. The annealing process resulted in a 4× to 6× enhancement of the signal change, with a minimal effect on the response time. The annealing also stabilized the microstructure, allowing for enhanced sensing stability, reliability, and durability. The underlying mechanism for hydrogen absorption enhancement is comprised of three heat-promoted events within the film microstructure: grain growth, a reduction of the internal compressive stress, and atomic intermixing of Pd from its enrichment and disordered state at the grain boundary into the Pd∕Au grain lattice.

Substrate structure dependence of the growth modes of p-quaterphenyl thin films on gold

The variably oriented crystallite surfaces of a recrystallized polycrystalline gold sample served as substrates for the investigation of the structure dependence of p-quaterphenyl (4P) thin film growth. The films were prepared in ultrahigh vacuum by organic molecular beam evaporation. Optical microscopy, scanning electron microscopy, combined with laterally resolved electron backscatter diffraction and scanning tunnelling microscopy have been applied to determine the correlation between the substrate surface structure and 4P film morphology. Crystallite surfaces consisting of (110) terraces favour highly anisotropic needle-like 4P growth with the needle orientation normal to the Au 〈11¯0〉 directions. Atomic steps on vicinal planes with narrow terraces (< 2 nm) can also induce anisotropy in the 4P thin film growth, in particular elongated 4P islands normal to the step direction. In contrast to that, a nearly isotropic distribution of the needle orientations is observed on Au grains terminated by highly symmetric (111) or (100) crystal planes. Additionally, patches of continuous 4P layers can be found on these surfaces. There is strong evidence that the 4P molecules within the needle-like crystallites are oriented parallel to the Au surface, whereas for the continuous layers the 4P molecules are oriented nearly upright on the surface.

Measurement and interpretation of the mid-infrared properties of single crystal and polycrystalline gold

The contribution of electron–phonon scattering and grain boundary scattering to the mid-IR ( λ = 3.392 μm) properties of Au has been assessed by examining both bulk, single crystal samples—Au(1 1 1) and Au(1 1 0)—and thin film, polycrystalline Au samples at 300 K and 100 K by means of surface plasmon polariton excitation. The investigation constitutes a stringent test for the in-vacuo Otto-configuration prism coupler used to perform the measurements, illustrating its strengths and limitations. Analysis of the optical response is guided by a physically based interpretation of the Drude model. Relative to the reference case of single crystal Au at 100 K ( ε = −568 + i 17.5), raising the temperature to 300 K causes increased electron–phonon scattering that accounts for a reduction of ∼40 nm in the electron mean free path. Comparison of a polycrystalline sample to the reference case determines a mean free path due to grain boundary scattering of ∼17 nm, corresponding to about half the mean grain size as determined from atomic force microscopy and indicating a high reflectance coefficient for the Au grain boundaries. An analysis combining consideration of grain boundary scattering and the inclusion of a small percentage of voids in the polycrystalline film by means of an effective medium model indicates a value for the grain boundary reflection coefficient in the range 0.55–0.71.

Nanocrystals formation and fractal microstructural assessment in Au/Ge bilayer films upon annealing

Nanocrystals formation and fractal microstructural assessment in Au/Ge bilayer films upon annealing have been investigated by transmission electron microscopy and high-resolution transmission electron microscopy observations. Experimental results indicated that the microstructure of the metal Au film plays an important role in metal-induced crystallization for Au/Ge bilayer films upon annealing. Synchronously, the crystallization processes of amorphous Ge accompanied by the formation of Ge fractal clusters, which were composed of Ge nanocrystals. We found that the grain boundaries of polycrystalline Au film were the initial nucleation sites of Ge nanocrystals. High-resolution transmission electron microscopy observations showed successive nucleation of amorphous Ge at Au grain boundaries near fractal tips. The crystallization process was suggested to be diffusion controlled and a random successive nucleation and growth mechanism.