bluuebunny/crossref_metadata_2025 huggingface dataset:
High Rate Deposition of Stable Hydrogenated Amorphous Silicon in Transition from Amorphous to Microcrystalline Silicon
Authors: Hou Guofu , Geng Xinhua , Zhang Xiaodan , Zhao Ying , Xue Junming , Ren Huizhi , Sun Jian , Zhang Dekun , Xu Yueqin
Published: June 2019

High rate deposition of high quality and stable hydrogenated amorphous silicon (a-Si:H) films were performed near the threshold of amorphous to microcrystalline phase transition using a very high frequency plasma enhanced chemical vapor deposition (VHF-PECVD) method. The effect of hydrogen dilution on optic-electronic and structural properties of these films was investigated by Fourier-transform infrared (FTIR) spectroscopy, Raman scattering and constant photocurrent method (CPM). Experiment showed that although the phase transition was much influenced by hydrogen dilution, it also strongly depended on substrate temperature, working pressure and plasma power. With optimized condition high quality and high stable a-Si:H films, which exhibit σph/σd of 4.4×106 and deposition rate of 28.8Å/s, have been obtained.
Silicides for the 65 nm Technology Node
Authors: Besser Paul R. , Chan Simon , Paton Eric , Kammler Thorsten , Brown David , King Paul , Pressley Laura
Published: June 2019

At the 65 nm node, silicide faces formidable challenges. Co is the current process of record for most integrated circuit manufacturers and thus becomes baseline silicide for 65 nm. However, Ni is the likely replacement. Both silicides are challenged to meet the requirements at the 65 nm node. This manuscript reviews the current CoSi2challenges (dopant interactions, Ge interactions, linewidth extendibility, impurity effects, agglomeration issues, etc). Ni consumes less Si but has its own challenges, including issues with contact leakage and thermal budget, excessive diffusion and oxidation, interactions with dopant and impurities. Both silicides have formation and stability issues in the presence of Ge. Additions of Ge increase the temperature at which a low resistance CoSi2is formed due to film segregation into CoSi2and Ge-rich Si-Ge grains. With Ni, additions of Ge decrease the temperature at which NiSi converts to a NiSi2, lead to agglomeration at a lower temperature and lead to germanosilicide formation.
Enhancement of Copper Wetting via Surfactant-Based Post-Treatment of Ultra-Thin Atomic Layer Deposited Tantalum Nitride Liners
Authors: Straten Oscar van der , Zhu Yu , Dunn Kathleen , Kaloyeros Alain
Published: June 2019

The influence of surfactant-based liner post-treatment on the wetting and nucleation characteristics of ultra-thin copper (Cu) films has been examined, employing ultra-thin atomic layer deposited (ALD) tantalum nitride (TaNx) as liner material. This surfactant-based posttreatment consists of in-situ exposure of the liner to a metal-organic source containing a low surface free energy metal (Sn) surfactant, which is a potential candidate for enhancing the wetting of Cu on liner surfaces and subsequently suppressing island-type growth of Cu, due to both the high atomic volume and low surface free energy of the surfactant relative to Cu. A methodology involving thermally-enhanced de-wetting of Cu, promoted by annealing Cu/liner stacks in a forming gas (95% Ar, 5% H2) ambient under several applied thermal budgets (annealing at 350°C for 30 minutes, and at 600°C for 4, 12, and 48 hrs, respectively), was utilized to both elucidate and quantify the wetting properties of Cu on liners, via detailed analyses of the surface morphology of annealed stacks by atomic force microscopy (AFM) and scanning electron microscopy (SEM). By comparing stacks containing ALD TaNx liners to those that contain post-treated ALD TaNx liners, this method allowed an evaluation of the effectiveness of surfactant-based liner surface post-treatments in inhibiting Cu de-wetting.
The Integration of Plasma Enhanced Atomic Layer Deposition (PEALD) of Tantalum-Based Thin Films for Copper Diffusion Barrier Applications
Authors: Cheng Degang , Eisenbraun Eric T.
Published: June 2019

A plasma-enhanced atomic layer deposition (PEALD) process for the growth of tantalumbased compounds is employed in integration studies for advanced copper metallization on a 200- mm wafer cluster tool platform. This process employs terbutylimido tris(diethylamido)tantalum (TBTDET) as precursor and hydrogen plasma as the reducing agent at a temperature of 250°C. Auger electron spectrometry, X-ray photoelectron spectrometry, and X-ray diffraction analyses indicate that the deposited films are carbide rich, and possess electrical resistivity as low as 250νΔcm, significantly lower than that of tantalum nitride deposited by conventional ALD or CVD using TBTDET and ammonia. PEALD Ta(C)N also possesses a strong resistance to oxidation, and possesses diffusion barrier properties superior to those of thermally grown TaN.
Characterization of Atomic Layer DepositedWNxCy Thin Film as a Diffusion Barrier for CopperMetallization
Authors: Kim Soo-Hyun , Oh Su Suk , Kim Hyun-Mi , Kang Dae-Hwan , Kim Ki-Bum , Li Wei-Min , Haukka Suvi , Tuominen Marko
Published: June 2019

The film properties of WNxCy films deposited by atomic layer deposition (ALD) using WF6, NH3, and triethylboron source gases were characterized as diffusion barrier for Cu metallization. It is noted that the as-deposited film shows an extremely low resistivity of about 350 μΔ-cm with a film density of 15.37 g/cm3. The film composition measured from Rutherford backscattering spectrometry shows W, C, and N of approximately 48, 32, and 20 at.%, respectively. Transmission electron microscopy analyses show that the as-deposited film is composed of face-centered-cubic phase with a lattice parameter similar to both β-WC1-x and β-W2N with an equiaxed microstructure. The barrier property of this ALD-WNxCy film at a nominal thickness of 12 nm deposited between Cu and Si fails only after annealing at 700°C for 30 minutes while the sputter-deposited Ta (12 nm) and ALD-TiN (20 nm) fail at 650 and 600°C, respectively. It is thought that the superior diffusion barrier performance of ALD-WNxCyfilm is the consequence of both nanocrystalline equiaxed grain structure and the formation of high density film.
Grain Boundary Characteristics and Stress-induced Damage Morphologies in Sputtered and Electroplated Copper Films
Authors: Park Hyun , Hwang Soo-Jung , Oh Kyu Hwan , Joo Young-Chang
Published: June 2019

Various Cu films were fabricated using sputtering and electroplating with and without additive, and their surface damages after annealing were investigated. After annealing at 435°C, the difference between damage morphologies of the films was observed. In some films stressinduced grooves along the grain boundaries were observed, while in the others voids at the grain boundary triple junctions were observed. It was also observed that the stress-induced groove was formed along the high energy grain boundaries. To explain the morphological difference of surface damages, a simple parameter considering the contributions of grain structures and grain boundary characteristics to surface and grain boundary diffusions is suggested. The effective grain boundary area, which is a function of grain size, film thickness and the fraction of high energy grain boundaries, played a key role in the morphological difference.
Comparison of the Time-Dependent Physical Processes in the Electromigration of Deep Submicron Copper and Aluminum Interconnects
Authors: Zhang G. , Tan C. M. , Gan Z. H. , Prasad K. , Zhang D. H.
Published: June 2019

Electromigration (EM) is a major reliability issue in VLSI. Many physical processes are involved simultaneously in an EM process, namely atom migration due to electron wind force, thermal migration due to temperature gradient, stress migration due to stress gradient, and surface migration (just when free surface is available) due to surface tension. In this work, the intrinsic EM damages of Al and Cu, that is without the effect from the surrounding materials, was investigated and compared based on the finite element analysis (FEA). The FEA results show that, in the intrinsic Al EM damage, electron wind force induced flux divergence is always the main cause of void growth; however, in the intrinsic Cu EM damage, dominant flux divergence varies with time, with the final dominant flux divergence due to electron wind force. It is also found that current density and temperature gradient are the most important factors affecting flux divergence. These simulation predictions agree with experimental observation and theoretical analysis.
Anisotropic Plasma ChemicalVapor Deposition of Copper Films in Trenches
Authors: Takenaka Kosuke , Onishi Masao , Takenshita Manabu , Kinoshita Toshio , Koga Kazunori , Shiratani Masaharu , Watanabe Yukio
Published: June 2019

An ion-assisted chemical vapor deposition method by which Cu is deposited preferentially from the bottom of trenches (anisotropic CVD) has been proposed in order to fill small via holes and trenches. By using Ar + H2 + C2H5OH[Cu(hfac)2] discharges with a ratio H2 / (H2 + Ar) = 83%, Cu is filled preferentially from the bottom of trenches without deposition on the sidewall and top surfaces. The deposition rate on the bottom surface of trenches is experimentally found to increase with decreasing its width.
Afm Studies of Deformation and Interfacial Sliding in Interconnect Structures in Microelectronic Devices
Authors: Park C. , Dutta I. , Peterson K.A. , Vella J.
Published: June 2019

Back-end interconnect structures (BEIS) of micro-electronic devices are susceptible to several deformation phenomena during thermal excursions, because of large differences in thermal expansion coefficients (CTE) between Si, interlayer dielectric (ILD) and metal lines. Here we use atomic force microscopy (AFM) to study plastic deformation and interfacial sliding of Cu interconnect lines on embedded in a low K dielectric (LKD). Following thermal cycling, changes were observed in both inplane Cu line dimensions, as well as out-of plane step height between Cu and LKD in single layer structures. The results of AFM measurements following both ex-situ and in-situ thermal cycling presented. A shear-lag based model is utilized to simulate the thermal cycling response, and rationalize the observed interfacial sliding behavior. Results of in-situ AFM experiments to observe the deformation of Cu-low K interconnect structures under far-field (i.e., package-level) stresses are also presented.
High-Frequency Heterodyne Force Microscopy Investigations Of Copper Interconnects
Authors: Zheng Yuegui , Geer Robert
Published: June 2019

A nondestructive methodology for characterizing Cu interconnects in integrated circuits (ICs) has long been sought and has motivated significant efforts regarding metrology tool development. Here, we present investigations of high-frequency heterodyne force microscopy (HFM) to investigate the acoustic response of damascene-processed Cu interconnects in a silicon oxide dielectric. HFM is a phase-resolved mechanical imaging technique that can, in principle, measure acoustic phase variations with nanometer spatial resolution. HFM measurements at carrier frequencies of 10.8 MHz and 72.5 MHz reveal phase differences of 0.5°-0.7° and 3.5°-4.5°, respectively, between the SiO2 and Cu regions of the IC test structure. Such phase differences are consistent with expected variations due to acoustic propagation time differentials between the Cu and SiO2 regions. Coupled with detailed mechanical measurements of the Cu and SiO2 regions this data may be used to extract spatial maps of acoustic phase delay and investigate subsurface features of similar IC test structures.
Dielectric GlueWafer Bonding For 3D ICs
Authors: Kwon Y. , Jinda A. , McMahon J.J. , Lu J.Q. , Gutmann R.J. , Cale T.S.
Published: June 2019

A process to bond 200 mm wafers for wafer-level three-dimensional integrated circuit (3D-IC) applications is discussed. Four-point bending is used to quantify the bonding strength and identify the weak interface. Using benzocylcobutene (BCB) glue, the bonding strength depends on (1) glue thickness, (2) glue film preparation, and (3) materials and structures on the wafer(s). A seamless BCB-to-BCB bond interface provides the highest bonding strength compared to other interfaces in these structures (> 34 J/m2). Mechanical and electrical properties of a wafer with copper interconnect structures are preserved after wafer bonding and wafer thinning, confirming the potential of the bonding process for 3D ICs.
Plasma Hydrogenation – A New Method of Reducing the k Value of the Low k Polyimide Film
Authors: Kuo Yue , Chung Taewoo , Nominanda Helinda
Published: June 2019

A new method of lowering the dielectric constant (k) of a low k polyimide thin film by plasma hydrogenation has been studied. The influence of the plasma process to the material properties, such as the composition, binding energies, and bond types, and dielectric characters, such as k and leakage current, were investigated. The result showed that after hydrogenation, the film's chemical and physical structures were changed. The film's k value could be lowered to 2.3 or less and the leakage current was only slightly increased. The mechanism of the process, which is responsible for the film's material and electrical property changes, is discussed. This is an effective method in preparing dielectrics with very low k values, which is critical for the success of the multilevel interconnection structure.
Indentation Fracture Toughness Measurements of Low Dielectric Constant Materials
Authors: Morris Dylan J. , Cook Robert F.
Published: June 2019

The physics and mechanics of a fracture toughness measurement technique for low-k films are described. It has been observed experimentally that it is possible to generate reproducible stable cracks at indentation sites in thin low-k films using cube-corner indentation. The fracture response depends on the film thickness and follows no simple scaling laws. The physics of a model that takes into account the stress fields from indentation and film stress, with particular attention paid to the Poisson's ratio of the film, are described. The model is able to predict the changes in observables when the film thickness is changed, which allows one to estimate film toughness independent of the configuration of the material.
Controlled Growth of Single-Walled Carbon Nanotubes from a Line Patterned Mesoporous Silica Template
Authors: Huang Limin , Wind Shalom J. , O'Brien Stephen P.
Published: June 2019

Carbon nanotubes (CNTs) with controlled orientation and diameter (1-4 nm) were grown from thermally stable, highly ordered mesoporous SiO2 thin films by methane chemical vapor deposition (CVD). Controlled incorporation of Fe precursor into pore channels of the mesoporous SiO2 by a sol-gel process results in a nanostructure catalytically active for CNT growth and stable to typical CVD temperatures. Growth of CNTs starts within the mesoporous SiO2, whose pore direction and pore dimension play an important role in the orientation and diameter of the CNTs at the early stage of the growth. Lateral growth results in a parallel assembly of CNTs with controlled tube dimension from a line-micropatterned mesoporous SiO2 film fabricated by soft-lithography.
Processing of Transparent Polymer Nanotube Composites via Heat, UV Radiation and Ionizing (gamma) Radiation using Ultrasonication and Solvent Dissolution
Authors: Clayton L. M. , Muisener P. A. O'Rourke , Harmon J. P. , Sikder A. K. , Kumar A. , Cassell A. M. , Cinke M. , Meyyappan M.
Published: June 2019

Poly (methyl methacrylate)/single walled carbon nanotube (PMMA/SWNT) composites were polymerized in the presence of carbon nanotubes via three methods: heat, uv radiation and ionizing radiation (gamma). Samples were solvent processed and cast into films. Thin films with varying degrees of transparency resulted from these composites. Differential Scanning Calorimetry (DSC) characterized glass transition temperatures. Ultraviolet-visible spectroscopy (UV-VIS) quantified the transparency of composites. The dielectric constant (ε') was obtained from Dielectric Analysis (DEA) and correlated to the refractive index values using Maxwell's Relationship. Scanning Electron Microscopy (SEM) provided images of the polymer- nanotube composite.
Incorporation of Multi Wall Carbon Nanotubes into Glass-Surfaces via Laser-Treatment
Authors: Seeger T. , Fuente G. de la , Maser W.K. , Benito A.M. , Righi A. , Sauvajol J.L. , Martínez M. T.
Published: June 2019

Carbon nanotubes (CNT) are interesting candidates for the reinforcement in robust composites and for conducting fillers in polymers due to their fascinating electronic and mechanical properties. For the first time, we report the incorporation of multi walled carbon nanotubes (MWNTs) into silica-glass surfaces by means of partial surface-melting caused by a continuous wave Nd:YAG laser. MWNTs were detected being well incorporated in the silica-surface. The composites are characterized using scanning electron microscopy (SEM) and Raman-spectroscopy. A model for the composite-formation is proposed based on heatabsorption by MWNTs and a partial melting of the silica-surface.
Growth of Multi Walled CNX Nanotubes: The Role of Synthesis Methods
Authors: Castignolles M. , Loiseau A. , Enouz S. , Bernier P. , Glerup M.
Published: June 2019

Multi walled nitrogen doped nanotubes were synthesized using two different methods. The growth mechanism and nitrogen concentration of the nanotubes synthesized by both methods are discussed and studied. The morphology and nitrogen concentration of the nanotubes are seen to strongly depend on the synthesis methods. The results are based on detailed high resolution transmission electron microscopy (HRTEM) data coupled with electron energy loss spectroscopy (EELS).
Largest Band Gap of All Single Walled Carbon Nanotubes
Authors: Cabria I. , Mintmire J. W. , White C. T.
Published: June 2019

Single walled carbon nanotubes, SWNTs, are either semiconducting, metallic, or quasimetallic. Early theoretical work based on tight-binding models predicted that the band gap of semiconducting carbon nanotubes should increase with decreasing radius and this picture was later confirmed by experiment. However, local-density functional calculations indicate that these models are not accurate for narrow carbon nanotubes, where the effects of curvature can convert nanotubes expected to be semiconductors to metals. This raises the question, what is the largest semiconducting band gap possible in a SWNT? We present results from first-principles calculations for a range of carbon nanotubes with radii between 0.15 and 1 nm. These results indicate that the (4,3) carbon nanotube has the largest band gap of all SWNTs.
Understanding Noncovalent Absorption and Packing of 1-Pyrene Butanoic Acid Succinimidyl Ester on Single Walled Carbon Nanotubes
Authors: Han Si-Ping , Cagin Tahir , Goddard William A.
Published: June 2019

Single walled carbon nanotubes (SWNT) have unique properties that give them strong potential for applications in high performance sensors and molecular electronics.1 One problem relevant to such technological applications is the functionalization of SWNT sidewalls. Recent experiments at Stanford have shown that 1-pyrene butanoic acid succinimidyl ester (PBSE) shows promise for non-covalent absorption onto SWNT sidewalls. We have conducted studies aimed at understanding the structural arrangement and packing of PBSE on the SWNT sidewall.
Formation and Transistor Behavior of Carbon Nanotube T-junctions
Authors: Chiu Po-Wen , Benoit Jean-Michel , Graupner Ralf , Dettlaff Ursula , Roth Siegmar
Published: June 2019

We present the formation of intermolecular nanotube junctions and investigations of their transistor behavior. T-shape junctions were formed by coupling chemically functionalized nanotubes with molecular linkers. An end-to-side or end-to-end heterojunction can be formed by reacting chloride terminated nanotubes with aliphatic diamine. The chemically modified nanotube mats were characterized by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The incorporation of functional groups into nanotubes are first identified by XPS. The carbon binding energy shifts due to the doping effect by attached functional groups. This also leads to a pronounced shift of tangential vibration modes in Raman spectra. To investigate the electrical transport, functionalized nanotubes were deposited on Si substrates, and metal contacts were applied on top of the selected T-shape junctions. The bar of the “T” is used as a transistor channel and the leg of the “T” is used as a gate. In this configuration, the active area is confined to a few nanometers in all three dimensions and gain values of 100 and above are obtained.
Investigation of the Surface Stress in SiC Nanocrystals by In-situ High Pressure Powder Diffraction Technique
Authors: Palosz B. , Stel'makh S. , Grzanka E. , Gierlotka S. , Zhao Y. , Palosz W.
Published: June 2019

The properties of nanocrystals were studied by in-situ high-pressure powder diffraction technique using our methodology of the structural analysis, the “apparent lattice parameter” (alp) concept. The experiments were performed for nanocrystalline SiC and diamond powders using synchrotron and neutron sources and hydrostatic or isostatic pressure. Elastic properties of the samples were examined based on the measurements of the lattice parameters and of the reflection width, as well as of interatomic distances. The results show a dual nature of the properties (compressibilities) of the powders indicating a complex, core-shell structure of the grains.
Creep Behaviour of a Crystallized Si-B-C-N Ceramic Obtained from the Polymeric Precursor T2-1(B[C2H4Si(CH3)NH]3)n
Authors: Kumar N.V. Ravi , Zimmermann André , Aldinger Fritz
Published: June 2019

The boron modified poly(vinyl)silazane polymer precursor with the chemical composition (B[C2H4Si(CH3)NH]3)n was milled and sieved. The polymer particles from different size fractions were compacted using a graphite die in a uni-axial warm pressing machine at a pressure of 48 MPa and in the temperature range 250°C to 330°C. The green bodies were pyrolysed in an argon atmosphere at a temperature of 1300°C when the organic polymer converts into an inorganic amorphous Si-B-C-N ceramic. These amorphous ceramics were annealed under various conditions of temperature, nitrogen overpressure and holding time in order to crystallize them and to produce nano-crystalline microstructures. Compression creep experiments were carried out in atmospheric ambience at loads varying from 5 – 100 MPa and in the temperature range 1350°C – 1500°C to investigate the high temperature deformation behaviour of the crystalline material. The interest is to understand the mechanisms of deformation in these nanocrystalline Si-B-C-N ceramics at elevated temperatures and to compare the results with that of amorphous ceramics. The investigation also includes the determination of viscosity of the material at high temperatures.
Strength of Ultrananocrystalline Diamond Thin films – Identification of Weibull Parameters
Authors: Peng B. , Espinosa H.D. , Moldovan N. , Xiao X. , Auciello O. , Carlisle J.A. , Gruen D.M. , Divan R.S. , Mancini D.C. , Gerbi J.E. , Birrell J.
Published: June 2019

The fracture strength of ultrananocrystalline diamond (UNCD) thin films, grown by microwaveplasma- enhanced chemical-vapor deposition (PECVD), was measured using the membrane deflection experiment (MDE) developed by Espinosa and coworkers. The data show that UNCD fracture strength appears to follow a Weibull distribution. Furthermore, we show that the Weibull parameters are highly dependent on the seeding process used in the growth of the films. When seeding was performed with micron-size diamond particles, using mechanical polishing of the substrate, the stress, resulting in a probability of failure of 67%, was found to be 1.74 GPa, and the Weibull modulus was 5.74. By contrast, when seeding was performed with nano-size diamond particles, using ultrasonic agitation, the stress, resulting in a probability of failure of 67%, increased to 4.13 GPa and the Weibull modulus was 10.76. The investigation highlights the role of microfabrication defects on material properties and reliability, as a function of seeding technique, when identical PECVD chemistry is employed. The parameters identified in this study are expected to aid the designer of MEMS/NEMS devices employing UNCD films.
Decoupling of the Chemical and Mechanical Surface Contributions in a Force Curve Measurement with AFM
Authors: Noel Olivier , Brogly Maurice , Castelein Gilles , Schultz Jacques
Published: June 2019

Atomic Force Microscope (AFM) was used to perform surface force measurements in contact mode to investigate surface properties of model systems at the nanoscale. Model systems were considered and compared. The first one was related to systems of controlled chemical surface properties with identical mechanical properties (chemically modified silicon substrates with hydroxyl, amine, methyl and ester functional groups). The second one deals with model polymer networks (Cross-linked polydimethylsiloxane or PDMS) of controlled mechanical properties and identical surface chemistry. The third system consists in a model polymer network, whose surface is chemically controlled with the same groups as before with silicon substrates. The results show that the viscoelastic contribution is dominating in the adhesion force measurement. Finally, we propose a relationship (derived from the Gent and Schultz's one), which expresses the AFM adhesion force as a function of mechanical energy dissipated in the contact and the surface properties of the material.
Surface Mechanical Property Determination of Soft Materials Through an AFM Nanoindentation Experiment
Authors: Noel Olivier , Brogly Maurice , Castelein Gilles , Schultz Jacques
Published: June 2019

In this paper, we have studied the capability of the AFM to perform nanoindentation experiments. We mainly focused on the importance of a rigorous experimental procedure to get quantitative and reproducible data with the Atomic Force Microscopy (AFM). Systematic calibration procedure of AFM measurements, as well as a complete description of the mechanical behavior of the soft material is necessary before producing reliable quantitative data. In particular, the influences of the creep and of the strain rate have been studied. Then, this technique was used to probe model cross-linked polydimethylsiloxane (PDMS) and to extract their surface mechanical properties at the nanoscale. Young modulus of each sample was calculated by comparing different contact mechanics theories (Hertz and JKR theories and a power law expression). In conclusion, the contact mechanics relationships have to be redefined and adapted to soft materials. In particular, it appears necessary to consider the specific mechanical contribution of the polymers.
Analysis of the Elastic Modulus of a Thin Polymer Film
Authors: Roche S. , Bec S. , Loubet J.L.
Published: June 2019

This paper discusses the interaction between mechanical properties of a thin layer and those of its substrate. The underlined questions are: how the substrate's mechanical properties affect those of the film; how the layer's thickness affects its mechanical properties. Nanoindentation tests were performed on polymer films of different thicknesses deposited onto a silica substrate. The mechanical response of such a system is known to be a composite response (film+substrate). Our aim is to understand the elastic behavior of the film inside this structure.

Model was used to estimate the elastic modulus of the film from the global measured value. For thin and “compliant” polymer layers deposited on “hard” substrates, an increase of the film elastic modulus was observed along indentation. We attribute this increase to the “anvil effect”: the bulk elastic modulus increases with the hydrostatic pressure which results from the compression of the film. In conclusion, one first interpretation is proposed to understand specific behavior of thin soft polymer layers on rigid substrates.
Increasing Initial Yield Stress at Small Length Scales
Authors: Spary I. , Bushby A.J. , Jennett N.M. , Pharr G.M.
Published: June 2019

Plasticity size effects are well known in a wide variety of situations where either the material microstructure or a strain gradient exist at small length scales. Several theories have been developed to describe changes in the work hardening behaviour under these conditions but none that predict a change in the initial yield stress. Careful studies by Chaudhri et al and Pharr et al have unambiguously demonstrated plasticity size effects in ductile metals. In those experiments indentation stress-strain curves were generated using spherical indenters with radii ranging from a few micrometres to several hundred micrometres and these were compared to data from conventional compression tests. Large radius indenters produced a single indentation stress-strain curve independent of indenter radius with a power law hardening coefficient equivalent to that in the compression tests. However, the indentation stress-strain curves appeared at progressively higher pressures for smaller radius indenters. In this paper we model those experiments using finite element analysis methods. By inputting the uniaxial stress-strain data to the model (effectively, using von Mises criterion) the indentation stress-strain curves for the macro size indenters are reproduced. However, the model shows no length scale dependence for any size of indenter. We show that by off-setting the compression stress-strain curve by increasing the initial yield stress and inputting this data to the model, the indentation behaviour of the smaller radius indenters can be modelled. The increase in yield stress with decreasing indenter radius is demonstrated for Cu, Wand Ir and is shown to be consistent with the initiation of yielding over a finite volume.
Molecular-Dynamics Modelling of the Tensile Deformation of Helical Nanowires
Authors: Shintani K. , Kameoka S.
Published: June 2019

Deformations of Au nanowires of helical structures under enforced elongation are addressed by the molecular-dynamics simulation. The embedded-atom method potential is employed for calculating the interaction between Au atoms. Model nanowires of the two kinds of helicities are prepared. Before elongation, a model nanowire is equilibrated at a specified temperature. Then, the Au atoms at one end of the nanowire are translationally moved in the axial direction. The simulation results show that a model nanowire can be elongated to form a single-atom chain of Au atoms under some circumstances.
Mechanical and Structural Properties of TiC and TiCN Thin Films Grown by RF Sputtering
Authors: Mani A. , Aubert P. , Khodja H. , Houdy P.
Published: June 2019

TiC and TiCN thin films were deposited by RF sputtering from a TiC target. For TiC thin films, the various sputtering pressure were carried out in order to observe the influence of this parameter on structural and mechanical properties. The experimental results show that a pressure of 1 Pa is necessary to obtain stoichiometric films with <111> texture. Lower pressures induce the formation of distorted titanium carbide, while RBS spectra show that the Ti/C ratio is constant for all these samples. Both the compressive stress and the hardness exhibited a maximum value for the lowest pressures. For TiCN thin films, the composition and the hardness were investigated as function of the N2 partial pressure (PN2 = 3% to 70%).
Dual Tribological Behavior of a Nanolayered Ceramic: Ti3SiC2
Authors: Souchet Alexandra , Fontaine Julien , Belin Michel , Mogne Thierry Le , Loubet Jean-Luc , Barsoum Michel W.
Published: June 2019

The MAX phases are new, thermodynamically stable, nanolayered ternary carbides and nitrides. These materials have a big potential in tribological applications due to their structure, similar to graphite or molybdenum disulfide. For example, the friction coefficients of the basal planes of Ti3SiC2 have been shown to exhibit very low (<; 5 × 10-3) friction coefficients. The aim of this study is to better understand the tribological behavior of polycrystalline Ti3SiC2 against stainless steel. Experiments were conducted on a ball-on-flat tribometer (∼ 25°C and ∼ 30% relative humidity) that simultaneously measures friction coefficients and electrical contact resistance. Different stainless steel ball diameters and normal loads were used and resulted in contact pressures between 0.35 and 1.25 GPa. Two different tribological behaviors were observed, both with relatively low friction coefficients for ceramics. The first behavior, referred to as type I, is characterized by low friction coefficients (≍ 0.15); low wear and a transfer film containing titanium and carbon formed on the ball. The other behavior, type II, is characterized by friction coefficients that starts at ≍ 0.15, and then increases to about 0.4. At the end of the experiment, the ball is worn, and compacted wear debris containing iron can be found on the plane. The two behaviors seem to be independent of contact pressure, but are rather sensitive to normal applied load. The transition between these two regimes will be discussed.
Atomistic Simulation of Flow Stress and Dislocation-Interface Interaction in Thin Metal Films
Authors: Ege E. S. , Shen Y.-L.
Published: June 2019

This study focuses on the atomistics of interface-mediated plasticity in thin metallic films. Molecular statics simulations are carried out to model the tensile stress-strain response of the free-standing and substrate-bonded films. In the free-standing film dislocation glide readily occurs, inducing slip steps at both surfaces of the film. The existence of an interface with the substrate constrains the dislocation motion in the film and restricts the slip steps to only the free surface. The propensity of film plasticity is dictated by the capability of atoms to slide along the interface. The flow stress of the film can be correlated with the dislocation activities obtained from the simulation. The propensity of spreading of relatively energetic atoms associated with the dislocation near the interface is also discussed.
The Behavior of Copper Nanoparticle Chain Aggregates Under Strain – A Molecular Dynamics Approach
Authors: Dalis Adamos S. , Friedlander Sheldon K.
Published: June 2019

Nanoparticle chain aggregates (NCA) serve as reinforcing fillers that are combined with molecular polymers to produce nano-composite materials, e.g. carbon black in rubber. The reinforcing mechanism due to the incorporation of nanoparticle aggregates is not well understood. Molecular dynamics (MD) computer simulations are employed to investigate the behavior of nanoparticle chain aggregates under strain. The interaction potential used is that of Cu obtained with the embedded atom method (EAM). Three single-crystal Cu nanoparticles are placed in contact in two different configurations (linear and kinked) and the structures are initially relaxed with MD steps for 300 ps. We observe plastic deformation during the sintering process for very small particles (∼2.5 nm in diameter) at temperatures as low as 300 K. The relaxed configurations are then strained to the breaking point at strain rates in the order of 1 m/s. We identify mechanisms of strain accommodation that lead to nanoparticle plastic deformation and eventually fracture. The linear and the kinked configurations break at strains of 0.263 and 0.344 respectively, while the maximum stress is close to 4 GPa (strain rate: 0.625 m/s). Both structures fail at the low-angle grain boundaries developed during the sintering process, while the higher strain for fracture for the kinked configuration is associated with interface sliding not observed in the linear case.
Structure of Dislocation Cores in GaAs
Authors: Beckman S. P. , Chrzan D. C.
Published: June 2019

The atomic scale structures of the partial dislocation cores in GaAs are explored using ab initio electronic structure total energy techniques. The structure of the 30° partial dislocations are expected to be period doubled along the core. The structure of the 90° partial dislocations remains more uncertain, and here, an effort is made to predict which of two proposed reconstruction, double period or single period, is more stable. The relative energies of the two core structures are found to be equal, within the accuracy of the present calculations. It is suggested that at temperature, both core reconstructions will be present.
3D simulation of the dislocation dynamics in polycrystalline metal thin films
Authors: Blanckenhagen B. Von , Arzt E. , Gumbsch P.
Published: June 2019

The plastic deformation of polycrystalline fcc metal thin .lms with thicknesses of 1 μm and less is investigated by simulating the dynamics of discrete dislocations in a representative columnar grain. The simulations are based on the assumption that dislocation sources or multiplication sites are rare and that sources have to operate several times to generate appreciable plastic deformation. This model is thoroughly tested by calculating the response of randomly distributed dislocation sources to an applied stress and comparing the results with experimental data. Stress–strain curves, the influence of boundary conditions, dislocation densities, work hardening rates and their dependence on the film thickness as well as the dependence on grain orientation are studied. The agreement between simulation and experiment is good and many aspects of thin film plasticity can be understood with the assumption that small-scale plastic deformation is source controlled rather than mobility controlled.
Features of Semiconductors during Nanoindentation
Authors: Richter Asta , Wolf Bodo , Smith Roger , Günther Margita
Published: June 2019

Si and InSb were subject to depth sensing multi-cycling nanoindentation. The load-depthcurves exhibited hysteresis loops which are explained in terms of pressure induced phase transformations. In order to study the impact of crystal distortions on phase transformation, the specimens were subject to boron implantation (ion energy 180 keV) of different implantation doses (1014 to 1017 ions/cm2) and indented without annealing. In InSb, the hysteresis loops disappeared after implantation of 1016 ions/cm2, and for Si with its stronger bonds, a dose of 3*1016/cm2 is required for the same effect. Indentation cycling with constant maximum load results in a sudden disappearance of the hysteresis loop after a small gradual loop area reduction during the first initial cycles.
Dislocation patterning in fatigued silicon single crystals
Authors: Legros M. , Ferry O. , Feiereisen J.-P. , Jacques A. , George A.
Published: June 2019

Tension compression fatigue tests and subsequent TEM observations were conducted on single crystalline silicon in a temperature and strain rate domain where lattice friction is still effective: 800-900°C and 1.5 to 6x10-4s-1. Samples oriented for single slip conditions were cyclically loaded under plastic strain amplitude control. For amplitudes ranging from 6x10-4 to 10-2, cyclic stress-strain curves exhibit two different stages of hardening and pass through a maximum before saturation is reached. TEM observations suggest that strain localization takes place near the maximum cyclic stress and beyond. Before mechanical saturation, edge dislocation dipoles sit mainly in thick rectilinear walls. Once the maximum stress is reached, these thick walls “condense” in much thinner walls that seem to carry out the imposed deformation while other regions become inactive. In this case, the dislocation structure anneals out and a loop structure is created from the dipolar walls.
Effects of Grain Boundary Constraint on the Constitutive Response of Tantalum Bicrystals
Authors: Ziegler A. , Campbell G. H. , Kumar M. , Stölken J. S.
Published: June 2019

The role of grain boundary constraint in strain localization, slip system activation, slip transmission, and the concomitant constitutive response was examined performing a series of uniaxial compression tests on tantalum bicrystals. Tantalum single crystals were diffusion bonded to form a (011) twist boundary and compressed along the [011] direction. The resulting threedimensional deformation was analyzed via volume reconstruction. With this technique, both the effective states of stress and strain over the cross-sectional area could be measured as a function of distance from the twist boundary, revealing a highly constrained grain boundary region. Post-test metallurgical characterization was performed using Electron Back-Scattered-Diffraction (EBSD) maps. The results, a spatial distribution of slip patterning and mapping of crystal rotation around the twist-boundary, were analyzed and compared to the known behavior of the individual single crystals. A rather large area near the grain boundary revealed no crystal rotation. Instead, patterns of alternating crystal rotation similar to single crystal experiments were found to be some distance away (~1mm) from the immediate grain boundary region, indicating the large length scale of the rotation free region.
Application of a Modified Jogged-Screw Model for Creep of Titanium Aluminides: Evaluation Of The Key Substructural Parameters
Authors: Karthikeyan Subramanian , Moon Junho , Viswanathan Gopal B. , Mills Michael J.
Published: June 2019

A modification of the jogged-screw model has been adopted recently by the authors to explain observations of 1/2[110]-type jogged-screw dislocations in equiaxed Ti-48Al under creep conditions. The aim of this study has been to verify and validate the parameters and functional dependencies that have been assumed in this previous work. The original solution has been reformulated to take into account the finite length of the moving jog. This is a better approximation of the tall jog. The substructural model parameters have been further investigated in light of the Finite Length Moving Line (FLML) source approximation. The original model assumes that the critical jog height (beyond which the jog is not dragged) is inversely proportional to the applied stress. By accounting for the fact that there are three competing mechanisms (jog dragging, dipole dragging, dipole bypass) possible, we can arrive at a modified critical jog height. The critical jog height was found to be more strongly stress dependent than assumed previously. The original model assumes the jog spacing to be invariant over the stress range. However, dynamic simulation using a line tension model has shown that the jog spacing is inversely proportional to the applied stress. This has also been confirmed by TEM measurements of jog spacings over a range of stresses. Taylor's expression assumed previously to provide the dependence of dislocation density on the applied stress, has now been confirmed by actual dislocation density measurements. Combining all of these parameters and dependencies, derived both from experiment and theory, leads to an excellent prediction of creep rates and stress exponents. The further application of this model to other materials, and the important role of atomistic and dislocation dynamics simulations in its continued development is also discussed.
The Stability of Icosahedral Cd-Yb
Authors: Krauss Günter , Deloudi Sofia , Steiner Andrea , Steurer Walter , Ross Amy R. , Lograsso Thomas A.
Published: June 2019

The stability of single-crystalline icosahedral Cd-Yb was investigated using X-ray diffraction methods in the temperature range 20 K ≤ T ≤ 900 K at ambient pressure and from ambient temperature to 873 K at about 9 GPa. Single-crystals remain stable at low temperatures and in the investigated HP-HT-regime. At high temperatures and ambient pressure, the quasicrystal decomposes. The application of mechanical stress at low temperatures yields to the same decomposition, the formation of Cd. A reaction of icosahedral Cd-Yb with traces of oxygen or water causing the decomposition seems reasonable, but a low-temperature instability of this binary quasi-crystal cannot be ruled out totally.
Effects of Ga- and In-doping on the Thermoelectric Properties in Ba-Ge Clathrate Compounds
Authors: Okamoto Norihiko L. , Inui Haruyuki
Published: June 2019

The crystal structures and thermoelectric properties of Ba-Ge type-I clathrate compounds (Ba8GaXGe46-X and Ba8Ga16-YInYGe30) have been investigated as a function of Ga and In contents. Ba8GaXGe46-X alloys have a crystal structure that contains an ordered arrangement of Ge vacancies, forming a superstructure based on the normal type-I structure until X reaches 3, whereas they have the normal type-I structure when X exceeds 3. The dimensionless thermoelectric figure of merit (ZT) increases with the increase in the Ga content, exhibiting the highest value of 0.49 for Ba8Ga16Ge30. The power factor for Ba8Ga10In6Ge30 is 1.5 times that for Ba8Ga16Ge30 so that the In containing alloy exhibits a ZT value as high as 1.03 at 700°C.
Urbach Edge, Disorder, and Absorption On-set in a-Si:H
Authors: Cody G. D.
Published: June 2019

This paper presents a brief review of the research that began in the early '80s, continued through the '90s, and produced a “standard model” for the optical absorption edge of amorphous silicon. The research began as a response to the invention of a-Si:H solar cells by Carlson and Wronski at RCA laboratories in 1976, and the subsequent worldwide interest in the optical characterization of a-Si:H thin films. The immediate need was soon met, but the research continued as an effort to understand the physics of the optical absorption edge in a-Si:H, as well as to understand the differences between, and similarities to, the indirect optical absorption edge of c-Si. In this paper, we highlight the successes of this standard model, and briefly cover its experimental and theoretical development over the last 25 years. We summarize its current status, and suggest some experimental and theoretical opportunities for, and challenges to, what may now be called a standard model for the optical absorption edge of both a-Si:H and a-Ge:H.