bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and Characterization of the First 1:2 Ordered Perovskite Ruthenate
Authors: Rijssenbeek Job , Malo Sylvie , Saito Takashi , Caignaert Vincent , Azuma Masaki , Takano Mikio , Poeppelmeier Kenneth R.
Published: June 2019

Perovskite-like mixed metal ruthenates are of interest owing to their varied electronic and magnetic properties, which are heavily dependent on the ordering of the transition metals. We report the synthesis and structural characterization of the first 1:2 ordered perovskite ruthenate, Sr3CaRu2O9. The structure was determined from a combination of powder X-ray, electron and neutron diffraction data and is characterized by a 1:2 ordering of Ca2+ and Ru5+ over the sixcoordinate B-sites of the perovskite lattice. Sr3CaRu2O9 is the first example of this structure-type to include a majority metal with d electrons (Ru(V), d3). The relationship of this material to the K2NiF4-type Sr1.5Ca0.5RuO4 (i.e., Sr3CaRu2O8) highlights the dramatic effects of the ruthenium valence on the resultant structure. Remarkably, these two structures can be quantitatively interconverted by the appropriate choice of reaction temperature and atmosphere.
Improvement in Ferroelectric Properties of Sol-Gel Derived SrBi2Ta2O9 thin films with seeding layers
Authors: Leu Ching-Chich , Chien Chao-Hsin , Yang Ming-Jui , Yang Ming-Che , Huang Tiao-Yuan , Lin Hung-Tao , Hu Chen-Ti
Published: June 2019

The effects of a seeding layer, which was deposited on Pt/TiO2/SiO2/Si substrates using magnetron sputtering, on the characteristics of sol-gel-deposited strontium-bismuth-tantalate (SBT) thin films are investigated. The seeding layer serves as nucleation sites so homogeneous crystalline SBT films of bismuth-layered structure (BLS) with fine grains are successfully obtained by 750°C rapid thermal annealing in O2 ambient. The remanent polarization (2Pr) improves from 12.1 to 18.8 μC/cm2 with the addition of the seeding layer. In addition, the seeding layer also results in a lower nucleation temperature, allowing the use of 700°C annealing for 10 min to grow SBT films that are fully crystallized with BLS phase and shows good ferroelectric properties. Finally, crystallinity and microstructures of SBT films are found to be strongly dependent on the thickness of the seeding layer. Optimum Ta-seeded SBT thin film crystallized at 700°C for 10min depicts a higher 2Pr value (12.9 μC/cm2 (@5V) than that of the un-seeded films crystallized at 750°C for 1min.
Enhanced polarization in strained BaTiO3 from first principles
Authors: Neaton J. B. , Hsueh C.-L. , Rabe K. M.
Published: June 2019

The structure, polarization, and zone-center phonons of bulk tetragonal BaTiO3 under compressive epitaxial stress are calculated using density functional theory within the local density approximation. The polarization, computed using the Berry-phase formalism, increases with increasing tetragonality and is found to be enhanced by nearly 70% for the largest compressive misfit strain considered (-2.28%). The results are expected to be useful for the analysis of coherent epitaxial BaTiO3 thin films and heterostructures grown on perovskite substrates having a smaller lattice constant, such as SrTiO3.
Misfit Strain Driven Phase Transformations in Epitaxial Barium Strontium Titanate Films
Authors: Ban Z.-G. , Alpay S. P.
Published: June 2019

We develop phase diagrams for single domain epitaxial barium strontium titanate films on cubic substrates as a function of the misfit strain based on a Landau-Devonshire phenomenological model similar to the one developed by Pertsev et al. [Phys. Rev. Lett. 80, 1988 (1998)]. Unusual ferroelectric phases that are not possible in single crystals and bulk ceramics are demonstrated in epitaxially constrained BST films. The misfit strain is correlated with the film thickness quantitatively by taking into account the formation of misfit dislocations that relieve epitaxial stresses during deposition. Theoretical estimation of the dielectric constant of (001) Ba0.7Sr0.3TiO3 and Ba0.6Sr0.4TiO3 films grown on Si, MgO, LaAlO3, and SrTiO3 substrates as a function of film thickness is provided. It is shown that the selection of the substrate and the film thickness can be chosen as design parameters to manipulate the internal stress level in the film to achieve enhanced dielectric response.
Theoretical Prediction and Experimental Confirmation of Charge Transfer Vibronic Excitons and Their Phase in ABO3 Perovskite Crystals
Authors: Eglitis R. I. , Vikhnin V. S. , Kotomin E. A. , Kapphan S. E. , Borstel G.
Published: June 2019

The current theoretical and experimental knowledge of new polaronic-type excitons in ferroelectric oxides - charge transfer vibronic excitons (CTVE) is discussed. It is shown that quantum chemical Hartree-Fock-type calculations using a semiempirical Intermediate Neglect of Differential Overlap (INDO) method (modified for ionic/partly ionic solids) as well as photoluminescence studies in ferroelectric oxygen-octahedral perovskites confirm the CTVE existence. Our INDO calculations for KTaO3 and KNbO3 have demonstrated that the triplet exciton is a triad centre containing one active O atom and two Ta atoms sitting on the opposite sites from this O atom. The total energy of a system is lowered by the combination of Coulomb attraction between electron and hole and the vibronic effect in this charge transfer vibronic exciton. It is shown by means of our INDO calculations that polaronic-type CTVE in ferroelectric oxides could lead to the formation of a new crystalline phase. The ground state energy of this phase consisting of strongly correlated CTVEs lies within an optical gap of a pure crystal, and is characterized by a strong tetragonal lattice distortion, as well as by the ferroelectric ordering.
Elastic Properties of Calcium Oxide Perovskites
Authors: Ross Nancy L. , Angel Ross J. , Kung Jennifer , Chaplin Tracey D.
Published: June 2019

The equations of state and axial moduli of the CaBO3 perovskites (B=Zr,Sn,Ti,Ge) and CaFeO2.5 with the brownmillerite structure have been determined using high-pressure, singlecrystal X-ray diffraction. The bulk modulus-specific volume relationship for the Ca-perovskites is nonlinear, with CaSnO3 and CaZrO3 displaying anomalous stiffening (higher bulk moduli) than previously reported and predicted [1,2]. The axial moduli of the a- and c-axes decrease steadily by ∼30% from the least-distorted of the Pbnm perovskites, CaGeO3, to the most distorted, CaZrO3, while the b-axis shows little change. The net result is a threefold increase in the anisotropy of the axial moduli of CaSnO3 and CaZrO3 (∼21%) relative to CaGeO3 and CaTiO3 (∼4-8%). The bulk modulus of CaFeO2.5 falls significantly below the trend for the stoichiometric perovskites. The introduction of 1/6 vacancies on the oxygen positions softens the perovskite structure by 25%.
Coupling of Lattice Dynamics to Spin Transitions in La1-xSrxCoO3
Authors: Louca Despina , Sarrao J. L.
Published: June 2019

La1-xSrxCoO3 is distinct because of its unique spin transitions subjecting the system to variable spin-lattice coupling. Pair density function analysis provided strong evidence for local lattice distortions associated with a Jahn-Teller active mode that is directly correlated to the change in the magnetic/conductive states of this system. The presence of Jahn-Teller distortions also serves as an indication for the intermediate spin configuration. Measurements of the dynamic structure function, S(Q, ω), showed that several phonon peaks fluctuate with carrier density and temperature. Such changes were not seen in an otherwise identical structure, LaAlO3. These phonon peaks are quite unusual and are most likely due to localized modes that appear to be dispersionless.
Formation Enthalpies of Tetravalent Lanthanide Perovskites by High Temperature Oxide Melt Solution Calorimetry
Authors: Ushakov S. V. , Cheng J. , Navrotsky A. , Wu J. R. , Haile S. M.
Published: June 2019

High-temperature oxide melt solution calorimetry was used to measure formation enthalpies for several compositions of perovskites of nominal stoichiometry BaPrO3 and BaCeO3. Samples were synthesized from chemical solution methods followed by calcination at 1100-1300°C. PrO2 was synthesized by oxidation of Pr6O11 in an oxygen flow at 280°C. The samples were characterized by microprobe, thermogravimetric and differential thermal analyses. Cell parameters were refined by the Rietveld method. Barium excess in the samples with respect to ideal stoichiometry was detected. Drop solution enthalpies were measured in a Calvet type twin microcalorimeter, using 3Na2O·4MoO3 solvent at 702°C. Preliminary values of the formation enthalpy of BaPrO3 and BaCeO3 from oxides were -70 ±10 kJ/mol and -51 ±10 kJ/mol, respectively. They fall on the normal trend of energetics versus Goldschmidt tolerance factor and do not show any special stabilization of BaPrO3 relative to other MLnO3 perovskites.
Nb polarization in Ferroelectric Perovskites KNbO3 and (PbZn1/3Nb2/3O3)0.88-(PbTiO3)0.12
Authors: Mamontov E. , Dmowski W. , Egami T.
Published: June 2019

XANES measurements have demonstrated that Nb polarization in (PbZn1/3Nb2/3O3)0.88-(PbTiO3)0.12 is small compared to that in KNbO3. This finding disproves the view of Nb5+ as invariably ferroelectrically active cation, and demonstrates that its polarizability depends on the Asite cations. Our results do not support conventional view of relaxor behavior in Pb(B'1/3Nb2/3)O3 ferroelectrics as a consequence of disruption of the connectivity of polarizable Nb5+ ions by their non-polarizable B' counterparts. Instead, they speak in favor of scenario in which relaxor behavior is caused by randomness of the local direction of Pb polarization due to chemical disorder on the B-sites of the perovskite structure.
From Ferroelectric to Quantum Paraelectric: KTa1-xNbxO3 (KTN), a Model System
Authors: Samara George A.
Published: June 2019

The ABO3 perovskite oxides constitute an important family of technologically important ferroelectrics whose relatively simple chemical and crystallographic structures have contributed significantly to our understanding of ferroelectricity. They readily undergo structural phase transitions involving both polar and non-polar distortions from the ideal cubic lattice. This paper focuses on the mixed perovskite system KTa1-xNbxO3, or KTN, which has turned out to be a model system. While the end members KTaO3 and KNbO3 might be expected to be similar, in reality they exhibit very different properties. Their mixed crystals, which can be grown over the whole composition range, exhibit a rich set of phenomena whose study has added greatly to our current understanding of the phase transitions and dielectric properties of these materials. Included among these phenomena are soft mode response, ferroelectric (FE)-to-relaxor (R) crossover, quantum mechanical suppression of the transition, the appearance of a quantum paraelectric state and relaxational effects associated with dipolar impurities. Each of these phenomena is discussed briefly and illustrated. Some emphasis is on the unique role of pressure in elucidating the physics involved.
Surface Potential Mapping of Patterned Self-Assembled Monolayers by Scanning Probe Microscopy
Authors: Getty R. Ross , Alvarez Rodolfo , Bonnell Dawn A. , Sharp Kenneth G. , Percec Simona , Hietpas Paula B.
Published: June 2019

Surface potentials of a number of patterned conducting and insulating self-assembled monolayers (SAMs) were measured by scanning surface potential microscopy (SSPM) as part of a study in molecular electronics. Differences in surface potential were measured for insulating and conducting molecule SAMs on gold. The SAMs were patterned by microcontact printing. High contrast patterns were observed by surface potential even when little imaging was possible in standard AFM modes. Surface potential differences of a few mV to 500 mV were observed under ambient conditions between adjacent SAMs of different compositions or between SAMs and the unmodified substrate.
Electron Holographic Nano-Characterization of Gold Catalyst at Interface
Authors: Ichikawa S. , Akita T. , Okumura M. , Haruta M. , Tanaka K.
Published: June 2019

The catalytic properties of nanostructured gold catalyst are known to depend on the size of the gold particles and to be activated when the size decreases to a few nanometers. We investigated the size dependence of the three-dimensional nanostructure on the mean inner potential of gold catalysts supported on titanium oxide using electron holography and high-resolution electron microscopy (HREM). The contact angle of the gold particles on the titanium oxide tended to be over 90° for gold particles with a size of over 5 nm, and below 90° for a size of below 2 nm. This decreasing change in the contact angle (morphology) acts to increase the perimeter and hence the area of the interface between the gold and titanium oxide support, which is considered to be an active site for CO oxidation. The mean inner potential of the gold particles also changed as their size decreased. The value of the inner potential of gold, which is approximately 25 V in bulk state, rose to over 40 V when the size of the gold particles was less than 2 nm. This phenomenon indicates the existence of a charge transfer at the interface between gold and titanium oxide. The 3-D structure change and the inner potential change should be attributed to the specific electronic structure at the interface, owing to both the “nano size effect” and the “hetero-interface effect.”
Mechanical Behaviour of Nanocrystalline Copper Related to Grain-boundary Structure
Authors: Champion Y. , Langlois P. , Guérin-Mailly S. , Langlois C. , Hÿtch M. J.
Published: June 2019

Understanding the mechanical behaviour of metallic nanostructures is a key issue for their development. On the one hand, knowledge of the plastic behaviour at various temperatures is essential to control the synthesis, forming, and machining of such materials. Equally, a clear understanding of atomic and mesoscopic mechanisms, involving defects and their interactions, is essential for the control of ageing and functional properties. Regarding plastic deformation at room temperature, there is now evidence for unusual behaviour in nanostructured metals. In addition to high resistance and ductility, tensile testing reveals peculiar elasto-plastic deformation. Such behaviour was initially attributed to grain-boundary sliding. However, intergranular areas (including triple junctions) may possess special properties compared to their microcrystalline counterparts. For example, low activation energies have been measured for grain-boundary diffusion and it has been observed that grain-boundaries may act as dislocation sources and nucleation sites for deformation twinning.

In this paper, we report on analysis on bulk copper nanostructures. Grain-boundaries are studied, by cross-correlating information from mechanical tensile testing and structural analysis, including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Macroscopic bulk specimens (with grain size of about 80 nm) are prepared by powder metallurgy techniques, modified to fit to the special properties of nanocrystalline powders. Processing includes coldisostatic pressing, sintering and differential extrusion. The powders used (grain size of 40 nm) are synthesised by evaporation and cryo-condensation of a metallic vapour within liquid nitrogen. Results on mechanical testing and structural analysis will be reported. Emphasis will be placed on the structure of grain-boundaries (type of grain-boundary, grain-boundary thickness) studied by TEM and high resolution TEM image analysed using the geometric phase technique. The nanostructure was revealed to be consist in agglomerate of nano-size grains separated by low angle grain-boundaries. Agglomerates are themselves separerated by general high angle boundaries. These observations will then be related to the unusual mechanical true stress-true strain curves of the metallic nanostructures.
Design of Transition Metal Oxide and Hybrid Mesoporous Materials
Authors: Sanchez Clément , Crepaldi Eduardo L. , Bouchara Anne , Cagnol Florence , Grosso David , Soler-Illia Galo J. de A. A.
Published: June 2019

Mesostructured transition metal (Ti, Zr, V, Al and Ce-Zr) oxide-based hybrid thin films, templated by poly(ethylene oxide)-based surfactants or block copolymers, have been prepared reproducibly, displaying 2D-hexagonal (p6m) or 2D-centred rectangular (c2m) structure. By carefully adjusting the variables involved it is possible to combine both high organisation and excellent optical quality. TiO2 and ZrO2-based materials show thermal stability up to 400-550°C. The elimination of the template can be conducted efficiently and gives rise to high surface area mesoporous films. For the other metal oxide hybrids the inorganic framework is much more fragile, and requires a precise sequence of post-treatments to be stabilised. In addition, original and homogeneous macrotextures shaped with coral-like, helical or macroporous sieves morphologies have been obtained following a nanotectonic approach based on the template-directed assembly by poly-γ-benzyl-L-glutamate (PBLG) of organically functionalised CeO2 crystalline nanoparticles.
Growth of Carbon Nanotubes with Controlled Morphologies
Authors: Dong Lifeng , Jiao Jun , Mosher Catherine L. , Foxley Sean
Published: June 2019

The alignment, orientation and morphologies of multi-walled carbon nanotubes (MWNTs) can be tailored by controlling catalyst deposition on porous silicon substrates. During the growth of MWNTs, H2 promoted the growth of carbon nanotubes and prevented the formation of amorphous carbon particles. With the introduction of H2, the average diameter of MWNTs decreased from 130 nm to 15 nm, and the average growth rate of nanotubes increased from 50 nm/s to 145 nm/s. The use of CH4 as the carbon source resulted in single-walled carbon nanotubes (SWNTs) with an average diameter of 2 nm, and the use of C2H2 as the carbon source resulted in MWNTs with an average diameter of 15 nm.
Structural Analyses and Magnetic Properties of Multiple-Structure Multilayered Co/Au Films
Authors: Koiwai Rimika , Kobayashi Masanobu , Maeno Yoshinori
Published: June 2019

In the interfaces of multilayered Co/Au and Co/Pd films, there were some interesting changes with annealing. For profile fittings, which is a comparison between measured peaks of X-ray diffraction and calculated peaks of the extended 3-step model profile fittings, the mixed layers between Co layers and noble metal layers were decreased in Co/Au films while increased in Co/Pd films. These results are based on the difference that Co-Au is a eutectic system while Co-Pd is an isomorphous system. This time, as new research, we fabricated multiple-structure multilayered Co/Au films (MSM Co/Au films). Magnetic properties and structural analyses were carried out with a vibrating sample magnetometer (VSM), X-ray diffraction (XRD), and extended 3-step model profile fittings. MSM Co/Au films have two periodic thicknesses. MSM Co/Au films showed the same perpendicular magnetization as Co/Au and Co/Pd films, which is dependent on the Co layer thickness. Perpendicular magnetization showed the maximum value after 1 h-annealing at 473 K. It was well confirmed that the mixed layers decreased at this annealing condition with the extended 3-step model profile fittings.
Evaluation of the Chemical-mechanical Planarization (CMP) Performance of Silicon Nitride and Silicon Carbide as Hard Mask Materials for Cu-based Interconnect Technology
Authors: Tseng Wei-Tsu , Lee Jia , Das Sanjit , Fitzsimmons John , Biery Glenn , Barth Edward , Goldblatt Ronald
Published: June 2019

Hydrogenated silicon nitride, hydrogenated silicon carbide, and their intermediates were chemo-mechanically polished. Results showed that, within the material set examined, harder materials also have higher CMP removal rates. In addition, CMP rates for multilayer stacks did not follow those for single layers. Polish mechanisms were proposed to explain these phenomena.
Engineering the Interaction Forces to Optimize CMP Performance
Authors: Basim G. B. , Vakarelski I. , Singh P. , Moudgil B. M.
Published: June 2019

The main objective of Chemical Mechanical Polishing (CMP) process is to planarize the metal or dielectric layers deposited on the wafer surfaces in microelectronics device manufacturing. In CMP, slurries containing submicrometer size particles and chemicals are used to achieve planarization. An effective polishing requires an optimal material removal rate with minimal surface deformation. Therefore, it is important to control the particle-substrate interactions that are responsible for the material removal and the particle-particle interactions, which control the slurry stability and consequently the defect density. This paper discusses the impact of interaction forces on polishing, and underlines the scientific guidelines to formulate consistently high performing CMP slurries.
Material Structure of Microcrystalline Silicon Deposited with an Expanding Thermal Plasma
Authors: Smit C. , Williamson D.L. , Sanden M.C.M. van de , Swaaij R.A.C.M.M. van
Published: June 2019

Expanding thermal plasma CVD (ETP CVD) has been used to deposit thin microcrystalline silicon films. In this study we varied the position at which the silane is injected in the expanding hydrogen plasma: relatively far from the substrate and close to the plasma source, giving a long interaction time of the plasma with the silane, and close to the substrate, resulting in a short interaction time. The material structure is studied extensively. The crystalline fractions as obtained from Raman spectroscopy as well as from X-ray diffraction (XRD) vary from 0 to 67%. The average particle sizes vary from 6 to 17 nm as estimated from the (111) XRD peak using the Scherrer formula. Small angle X-ray scattering (SAXS) and flotation density measurements indicate void volume fractions of about 4 to 6%. When the samples are tilted the SAXS signal is lower than for the untilted case, indicating elongated objects parallel to the growth direction in the films. We show that the material properties are influenced by the position of silane injection in the reactor, indicating a change in the plasma chemistry.
Prediction of the Interface Response Functions for Amorphous and Crystalline Phases of Silicon and Germanium
Authors: Albenze Erik J. , Matejik Laura A. , Fynan Nick F. , Clancy Paulette
Published: June 2019

Interface response functions that govern the solidification kinetics of amorphous and crystalline phases of Si and Ge have been determined for reparameterized versions of the Stillinger-Weber (SW) potential. The strength of the three-body term in the SW potential and the energy scaling parameter were modified to obtain agreement with the experimental melting temperatures of both the amorphous and crystalline phases. These modified models were used to produce predictions of the interface response function for both Si and Ge that adequately fit the few known experimental data.
Size Distribution Of Embedded Nano-Crystallites In Polymorphous Silicon Studied By Raman Spectroscopy And Photoluminescence
Authors: Tripathi V. , Mohapatra Y. N. , Suendo V. , Cabarrocas P. Roca i
Published: June 2019

Polymorphous Silicon (pm-Si:H) deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD) has emerged as an alternative material to amorphous silicon (a-Si:H). Deposition parameters of pm-Si:H are such that small crystallites get embedded in a relaxed amorphous silicon matrix, thus improving the optical and electrical properties. We study the size of crystallites and degree of order in pm-Si:H using Raman and photoluminescence (PL) spectra of pm-Si:H and a-Si:H. Raman Spectra of a variety of hydrogenated nanostructured silicon (pmSi:H) and amorphous Silicon (a-Si:H) samples grown at different pressures were analyzed. Deconvolution of observed multiple peaks in photoluminescence spectra and fitting to Gaussian size distribution also yields particle size to be in the range of 2.3 to 3.5nm in agreement with Transmission Electron Microscopy and Raman results.
Low-temperature Growth of Poly-Si and SiGe Thin Films by Reactive Thermal CVD and Fabrication of High Mobility TFTs over 50 cm2/Vs
Authors: Hanna Jun-Ichi , Shimizu Kousaku
Published: June 2019

We have established a new thermal CVD technique, Reactive Thermal CVD, for polycrystalline silicon (poly-Si) and silicon germanium (poly-SiGe) thin films aiming at thin film transistors (TFTs) applications, in which a low substrate temperature of 450°C enables us to use glass substrates. This technique achieved high crystallinity at very early stage of the film growth, resulting no amorphous incubation layer on the substrate surface. We fabricated bottom and top gate n-and p-channel TFTs with these of 200 nm thick films on SiO2/Si wafers and glass substrates, respectively: the high field effect mobilities as high as 55 cm2/Vs and 25 cm2/Vs were achieved in the bottom-gate and top-gate TFTs, respectively. Here, we discuss the technical requirements in the low-temperature CVD technique for the large-area poly-Si thin films and how they can be achieved in the reactive thermal CVD.
Leakage Current Behavior in Common I-Layer A-SI:H P-I-N Photodiode Arrays
Authors: Theil Jeremy A.
Published: June 2019

Hydrogenated amorphous silicon photodiode arrays form the basis of monolithic three-dimensional integrated circuit sensor technology. In these arrays, the intrinsic a-Si:H layer covers the entire area to maximize light collection. One technique by which the pixel diode is defined, is to pattern the bottom contact layer independently of the intrinsic layer. One of the most important characteristics of any diode array, however, is that the dark-state reverse bias leakage currents must be as low as possible to minimize diode noise. This study examines the leakage currents associated with the pixelated array. These structures are unique in that the edge of the diode is defined by the local electric field between diodes, rather than the physical surface of an a-Si:H film. The effect of the diode edge has been found to induce a field-dependent component to the reverse bias leakage current. For example, diodes with 5500Å i-layer, have a junction leakage of 14 to 20 pA/cm2, at 5.0 x 104 V/cm, while the pixel edge-dependent current component can be as high as 30 pA/cm2. In addition, it will be shown that the i-layer thickness and junction doping plays a key role in determining the behavior of the leakage currents.
Enhanced Blue Sensitivity in ITO/a-SiNx:H/a-Si:H MIS Photodetectors
Authors: Tao S. , Vygranenko Y. , Nathan A.
Published: June 2019

We report an ITO/a-SiNx:H/a-Si:H MIS photodetector with improved performance in terms of its dark current, stability, and spectral response in the blue region. The a-Si:H and a-SiNx:H thin film layers were deposited by plasma-enhanced chemical vapor deposition (PECVD) on a glass substrate with patterned Mo back contact. The ITO was polycrystalline with a wide band gap (>3.75 eV) and was deposited at room temperature by magnetron sputtering. SIMS (Secondary Ion Mass Spectrometer) measurements show that an ultra thin a-SiNx:H film (a few nm) can effectively block the diffusion of oxygen from the ITO to the a-Si:H. In addition, the insulator layer provides a barrier for electrons, which serves to reduce the dark current. This is in contrast to the ITO/a-Si:H Schottky photodiode whose electrical and optical performance is impaired by the large defect density at the interface due to impurity diffusion from the ITO layer. At a reverse bias of 1 V, the dark current density of the MIS photodetector is as low as 4 nA/cm2. Photoresponse measurements show a dramatically enhanced sensitivity in the UV/blue spectral region. A high quantum efficiency (∼80%) is achieved at a wavelength of 440 nm, which can be attributed to reduction of both optical and recombination loses by virtue of the highly transparent polycrystalline ITO and the low defect density at the a-SiNx:H/a-Si:H interface.
Hydrogenated Microcrystalline Silicon Single-Junction and Multi-Junction Solar Cells
Authors: Yan Baojie , Yue Guozhen , Yang Jeffrey , Banerjee Arindam , Guha Subhendu
Published: June 2019

This paper summarizes our recent studies of hydrogenated microcrystalline silicon (μc-Si:H) solar cells as a potential substitute for hydrogenated silicon germanium alloy (a-SiGe:H) bottom cells in multi-junction structures. Conventional radio frequency (RF) glow discharge is used to deposit hydrogenated amorphous silicon (a-Si:H) and μc-Si:H at low rates (∼ 1 Å/s), searching for the highest efficiency. We have achieved an initial active-area efficiency of 13.0% and stable efficiency of 11.2% using an a-Si:H/μc-Si:H double-junction structure. Modified very high frequency (MVHF) glow discharge is used to deposit a-Si:H and μc-Si:H at high rates (∼ 3-10 Å/s) for comparison with our a-Si:H/a-SiGe:H/a-SiGe:H triple-junction production technology. The deposition time for the μc-Si:H intrinsic (i) layer in the bottom cell should be less than 30 minutes in order to be acceptable for mass production. To date, an initial active-area efficiency of 12.3% has been achieved with the bottom cell deposited in 50 minutes. By increasing the deposition rate and reducing the bottom cell thickness, we have achieved an initial active-area efficiency of 11.4% with the bottom cellilayer deposited in 30 minutes. The cell stabilized to 10.4% after prolonged light soaking. We will address issues related to μc-Si:H material, solar cell design, solar cell analysis, and stability.
Femtosecond Far-Infrared Studies of Carrier Dynamics in Hydrogenated Amorphous Silicon and Silicon-Germanium Alloys
Authors: Nampoothiri A. V. V. , Nelson B. P. , Dexheimer S. L.
Published: June 2019

We present femtosecond time-resolved studies of the photoexcited carrier response in the far-infrared spectral range in PECVD a-Si:H and a-SiGe:H thin films. The experiments are carried out using an optical pump / terahertz (THz) probe technique, in which a femtosecond pump pulse excites carriers in the sample and a time-delayed probe pulse measures the resulting change in the far-infrared optical properties as a function of time delay following the excitation. These measurements are sensitive to carrier processes at low energy, corresponding to a range of approximately 1 - 10 meV, a key energy scale in these materials. We find that the observed photoexcited carrier dynamics are consistent with trapping of carriers into band tail states on a picosecond time scale.
The Reliability of Measurements on Electron Energy Distribution Function in Silane rf Glow Discharges
Authors: Lin Kuixun , Lin Xuanying , Chi Linfei , Yu Chuying , Yu Yunpeng , Liu Shi
Published: June 2019

Electron energy distribution function (EEDF) is directly proportional to the second derivative of the probeI-Vcharacteristics. Because of an amplifying effect of unavoidable noises in the experimental probeI-Vcurves on the derivation process, the experimentalI-Vcurves should be smoothed before performing the numerical derivation. This article investigates the effect of adjustable factors used in the smoothing process on the deduced second derivative of theI-Vcurves, and an optimum group of the adjustable factors is selected to make the rms deviation of the smoothedI-Vcurves from the measured ones less than 1 %. A simple differentiation circuit is designed and used to measure the EEDF parameter straightforwardly. It is the first time, so far as we know, to measure the EEDF parameters simultaneously by means of both numerical and circuit derivative methods under the same discharge conditions and on the same discharge equipment. The deviation between two groups of mean electron energy (E) and electron density (ne) obtained by the above different methods is within about 7 %. This apparently improves the reliability of the measurements on the EEDF parameters.
Microcrystalline (Si,Ge):H Solar Cells
Authors: Zhu Jianhua , Dalal Vikram L.
Published: June 2019

We report on the growth and properties of microcrystalline Si:H and (Si,Ge):H solar cells on stainless steel substrates. The solar cells were grown using a remote, low pressure ECR plasma system. In order to crystallize (Si,Ge), much higher hydrogen dilution (∼40:1) had to be used compared to the case for mc-Si:H, where a dilution of 10:1 was adequate for crystallization. The solar cell structure was of the p+nn+ type, with light entering the p+ layer. It was found that it was advantageous to use a thin a-Si:H buffer layer at the back of the cells in order to reduce shunt density and improve the performance of the cells. A graded gap buffer layer was used at the p+n interface so as to improve the open-circuit voltage and fill factor. The open circuit voltage and fill factor decreased as the Ge content increased. Quantum efficiency measurements indicated that the device was indeed microcrystalline and followed the absorption characteristics of crystalline ( Si,Ge). As the Ge content increased, quantum efficiency in the infrared increased. X-ray measurements of films indicated grain sizes of ∼ 10nm. EDAX measurements were used to measure the Ge content in the films and devices. Capacitance measurements at low frequencies ( ~100 Hz and 1 kHz) indicated that the base layer was indeed behaving as a crystalline material, with classical C(V) curves. The defect density varied between 1x1016 to 2x1017/cm3, with higher defects indicated as the Ge concentration increased.
Impact of Low k Dielectrics on Electromigration Reliability for Cu Interconnects
Authors: Ho Paul S. , Lee Ki-Don , Ogawa Ennis T. , Yoon Sean , Lu Xia
Published: June 2019

Multi-link statistical test structures were used to study the effect of low k dielectrics on EM reliability of Cu interconnects. Experiments were performed on dual-damascene Cu interconnects integrated with oxide, CVD low k, porous MSQ, and organic polymer ILD. The EM activation energy for Cu structures was found to be between 0.8 and 1.0 eV, indicating mass transport is dominated by diffusion at the Cu/SiNx cap-layer interface, independent of ILD. Compared with oxide, the decrease in lifetime and (jL)c observed for low-k structures can be attributed to less dielectric confinement in the low k structures. An effective modulus B obtained by finite element analysis was used to account for the dielectric confinement effect on EM. For all the ILDs studied, (jL)c showed no temperature dependence.
Characterization of Electroplated Copper Films with Laser-Generated Surface Acoustic Waves
Authors: Maznev A.A. , Gostein M. , Brongersma S.H.
Published: June 2019

Elastic properties of electroplated copper films fabricated under different plating and annealing conditions have been characterized with laser-generated surface acoustic waves. For acoustic wavelengths longer than the characteristic copper grain size, the effective elastic modulus of copper was found to be unaffected by variations of the plating current as well as by the grain size variation due to different annealing temperatures. Consequently, copper thickness measurements with surface acoustic waves have been found to be more stable with respect to process variations than electrical sheet resistance measurements. For short acoustic wavelengths (∼ 2 νm), grain growth results in a significant increase of acoustic attenuation and a shift in the measured velocity. This finding opens an opportunity for copper structure monitoring by surface wave-based optoacoustic metrology.
Enhanced adhesion of Cu film on a low-k material by using Ti glue layer, B dopant and N2 plasma treatment
Authors: Ko Y.K. , Lee S. , Yang H.J. , Shim C. , Jung D. , Lee J.G.
Published: June 2019

Adhesion property of Cu film on a low-k material was investigated. The low-k films deposited using a mixture of hexamethyldisilane(HMDS) and para-xylene had a dielectric constant as low as 2.7 and thermal stability up to 400°C. In this work, Ti glue layer, boron dopant, and N2 plasma treatment were applied to improve adhesion between Cu and the low-k films. Adhesion property was significantly enhanced by N2 plasma-treatment on the low-k film and boron dopant in Cu film. This enhanced adhesion was attributed to the formation of new binding states between Ti and the plasma-treated surface of the low-k film and to the diffusion of B from Cu to Ti and low-k films. Cu(B)/Ti/low-k film annealed at 350°C withstood an applied load of about 23 N during the scratch test.
Dual Damascene Process for FatWires in Copper/FSG Technology
Authors: Gambino J. , Stamper T. , Trombley H. , Luce S. , Allen F. , Weinstein C. , Reuter B. , Dunbar M. , Samek V. , McLaughlin P. , Kane T.
Published: June 2019

A trench-first dual damascene process has been developed for fat wires (1.26 μm pitch, 1.1 μm thickness) in a 0.18 μm CMOS process with copper/fluorosilicate glass (FSG) interconnect technology. The process window for the patterning of vias in such deep trenches depends on the trench depth and on the line width of the trench, with the worse case being an intermediate line width (lines that are 3X the via diameter). Compared to a single damascene process, the dual damascene process has comparable yield and reliability, with lower via resistance and lower cost.
Development of porous SiLK™ Semiconductor Dielectric Resin for the 65 nm and 45 nm Nodes
Authors: Strittmatter R. J. , Hahnfeld J. L. , Silvis H. C. , Stokich T. M. , Perry J. D. , Ouellette K. B. , Niu Q. J. , Godschalx J. P. , Kalantar T. H. , Mubarekyan E. , Hefner R. E. , Lyons J. W. , Dominowski J. M. , Buske G. R.
Published: June 2019

Porous SiLK resin is an ultra-low-k interlayer dielectric (ILD) material designed to meet the needs of the 65 nm technology node and beyond. In early 2002, the porous SiLK resin formulation was defined and scaled up, facilitating the tight monitoring and control of key properties, including pore size distribution, over several lots of material. The film processing kinetics are now well understood and a wide process window exists which ensures optimum pore morphology and pore size distribution. Thermal cycling of films demonstrates no effect on pore morphology or dielectric constant. The material has been designed to minimize the impact of CTE mismatch at high temperature, which challenged the integration of some previous generations of SiLK and porous SiLK dielectric resins. The discrete, closed-cell pore geometry is well characterized and enables the extendibility of process module development from SiLK resin technology to porous SiLK resin. Concurrent with the scale up efforts, advancements in minimizing both cure time and temperature simultaneously, as well as significant improvements in pore size and pore size distribution, have been achieved. The cure and porogen burn out time has been reduced by 50% or greater, and the temperature has been reduced to 370°C. The pore size has been reduced by ∼35%, and the pore size distribution has been narrowed by ∼40%. These advancements have resulted in the introduction of porous SiLK T resin, with a dielectric constant of k = 2.4 and a recommended cure temperature of 370°C, and the introduction of porous SiLK U resin, with a mean pore diameter of ∼5 nm and a dielectric constant of k = 2.2.
Characterization of Boron Carbo-Nitride Films Deposited By Low Temperature Chemical Vapor Deposition
Authors: Engbrecht E. R. , Cilino C. J. , Junker K. H. , Sun Y.M , White J. M. , Ekerdt J. G.
Published: June 2019

This study reports low temperature chemical vapor deposition of amorphous boron carbonitride films on SiO2 using a dimethylamine borane complex at temperatures ranging from 360 to 500°C and with varying NH3 flow at 360°C. The dielectric constant, k, of the films ranged from 4.11 to 4.83, and increased with temperature while the addition of nitrogen using NH3 decreased k. The index of refraction changed correspondingly with k, ranging from 1.826 to 2.226. Higher substrate temperature caused nitrogen and carbon content to increase with additional bonding to boron. The addition of ammonia increased the N:B ratio to as high as 0.64 and reduced k to 4.11. The higher nitrogen incorporation displaced both boron and carbon in the film, leaving boron bonded primarily to nitrogen and other boron atoms. These films were amorphous with smooth surfaces of RMS roughness ranging from 0.30 nm to 0.53 nm.
Spectrum of Defect States in Porous Organic Low-k Dielectric Films, Annealed in Argon and Nitrogen
Authors: Ligatchev V. , Wong T.K.S. , Goh T.K. , Suzhu Yu Rusli
Published: June 2019

Defect spectrum N(E) of porous organic dielectric (POD) films is studied with capacitance deep-level-transient-spectroscopy (C-DLTS) in the energy range up to 0.7 eV below conduction band bottom Ec. The POD films were prepared by spin coating onto 200mm p-type (1 – 10 Δcm) single-side polished silicon substrates followed by baking at 325°C on a hot plate and curing at 425°C in furnace. The film thickness is in the 5000 – 6000 Å range. The ‘sandwich’ -type NiCr/POD/p-Si/NiCr test structures showed both rectifying DC current-voltage characteristics and linear 1/C2 vs. DC reverse bias voltage. These confirm the applicability of the C-DLTS technique for defect spectrum deconvolution and the n-type conductivity of the studied films. Isochronal annealing (30 min in argon or 60 min in nitrogen) has been performed over the temperature range 300°C - 650°C. The N(E) distribution is only slightly affected by annealing in argon. However, the distribution depends strongly on the annealing temperature in nitrogen ambient. A strong N(E) peak at Ec – E = 0.55 – 0.60 eV is detected in all samples annealed in argon but this peak is practically absent in samples annealed in nitrogen at Ta < 480°C. On the other hand, two new peaks at Ec – E = 0.12 and 0.20 eV appear in the N(E) spectrum of the samples annealed in nitrogen at Ta = 650°C. The different features of the defect spectrum are attributed to different interactions of argon and nitrogen with dangling carbon bonds on the intra-pore surfaces.
Flame Synthesis of Carbon Nanotubes
Authors: Height Murray J. , Howard Jack B. , Tester Jefferson W.
Published: June 2019

Flames offer a potential for the synthesis of carbon nanotubes in large quantities at modest costs. This study aims to examine the conditions for carbon nanotube formation in premixed flames and to characterize the morphology of solid carbon deposits and their primary formation mechanisms in the combustion environment. Single walled nanotubes have been observed in the post-flame region of a premixed acetylene/oxygen/argon flame operated at 50 Torr (6.7 kPa) with iron pentacarbonyl vapor used as a source of metallic catalyst. A thermophoretic sampling method and transmission electron microscopy were used to characterize the solid material present in the flame at various heights above burner (HAB), giving resolution of formation dynamics within the flame system. Catalyst particle formation and growth are observed in the immediate post-flame region, 10 to 40 mm HAB, with coagulation leading to typical particle sizes on the order of 5 to 10 nm. Nanotubes were observed to be present after 40 mm HAB (∼34 milliseconds) with nanotube inception occurring as early as 30mm HAB (∼25 ms). Between 40 and 70 mm HAB (∼30 ms), nanotubes are observed to form and coalesce into clusters. Based on the rapid appearance of nanotubes in this region, it appears that once initiated, the nanotube growth occurs quite rapidly, on the order of 10 νm/s. A nanotube formation ‘envelope’ is evident with a formation limited to fuel equivalence ratios between a lower limit of 1.5 and an upper limit of 1.9. A continuum of morphologies ranging from relatively clean clusters of nanotubes to amorphous material is observed between the lower and upper limits. We suggest that the diversity of morphologies is due to competition between carbon precipitation pathways. High resolution TEM revealed the nanotubes to be primarily single walled. Raman spectroscopy confirmed the presence of single wall nanotubes and indicated a broad range of diameters and differences in chirality to plasma-arc generated material.
Structural Characteristics of Carbon Nanorods and Nanotubes Grown Using Electron Cyclotron Resonance Chemical Vapor Deposition
Authors: Woo Y. S. , Han I. T. , Park Y. J. , Kim H. J. , Jung J. E. , Lee N. S. , Jeon D. Y. , Kim J. M.
Published: June 2019

Vertically aligned carbon nanorods and multi walled carbon nanotubes (MWNTs) were synthesized by electron cyclotron resonance chemical vapor deposition (ECR-CVD) on Ni- coated glass substrates with the RF-self biasing of –100 and –200 V, respectively. High-resolution transmission electron microscopy indicated that the distance between adjacent graphene layers of carbon nanorods is much larger than that of well-graphitized MWNTs. In electron-energy-loss spectra, the energy of π+σ plasmon peak for the carbon nanorod shifts towards lower value of 23.8 eV, by comparison with the well-graphitized MWNT at 25.5 eV. In addition, the π palsmon peak at 6 eV is clearly defined for the well-graphitized MWNT, but not seen for the carbon nanorod. X-ray photoelectron spectroscopy also showed that the delocalization of π electrons gets more pronounced with the structural evolvement from the carbon nanorod to the well-graphitized MWNT. Therefore, it is suggested that ionic bombardment can provide sufficient internal energy for dehydrogenation from hydrocarbon molecules, and thus, well-graphitized MWNTs could be grown even at low temperatures.
NMR studies of alkali intercalted carbon nanotubes
Authors: Schmid M. , Goze-Bac C. , Mehring M. , Roth S. , Bernier P.
Published: June 2019

Lithium intercalted carbon nanotubes have attracted considerable interest as perspective components for energy storage devices. We performed 13C Nuclear Magnetic Resonance spin lattice relaxation measurements in a temperature range from 4 K up to 300 on alkali intercalated Single Walled Carbon Nanotubes in order to investigate the modifications of the electronic properties. The density of states at the Fermi level were determined for pristine, lithium and cesium intercalated carbon nanotubes and are discussed in terms of intercalation and charge transfer effects.
Soldering of Carbon Nanotube Bridges using Electron Beam Deposited Gold
Authors: Dohn Søren , Mølhave Kristian , Madsen Dorte Nørgaard , Mateiu Ramona , Bøggild Peter , Rasmussen Anne Marie , Brorson Michael , Jacobsen Claus J.H.
Published: June 2019

We have formed suspended bridges of carbon nanotubes between microcantilevers using electron beam dissociation of metal-organic vapours. By electron beam exposure of a surface in the presence of gold-carbon molecules emitted inside an environmental scanning electron microscope, we are able to form tips and other freestanding nanostructures of high metallic content. Suspended bridges made entirely of this material exhibit resistances less than 50 times that of pure gold, and consist of dense metallic cores surrounded by a crust of nanoparticles. We used standard microfabrication techniques to produce silicon chips with multiple microcantilevers extending over the edge. Individual multiwalled carbon nanotubes grown catalyticcally by chemical vapour deposition, were positioned across two cantilevers using in-situ nanomanipulation tools. Drawing a cross-shaped gold-carbon bond on each end of the carbon nanotube consistently resulted in electrical contact with resistances in the range 1-90 Ω and linear current-voltage characteristics. We found that soldering bonds having a line width down to 10-15 nm form connections and last for days in ambient conditions.