bluuebunny/crossref_metadata_2025 huggingface dataset:
Creating Nanoporosity by Selective Extraction of Porogens Using Supercritical Carbon Dioxide/Cosolvent Processes
Authors: Lahlouh B. , Rajagopalan T. , Lubguban J. A. , Biswas N. , Gangopadhyaya S. , Sun J. , Huang D. , Simon S. L. , Kim H. C. , Volksen W. , Miller R. D.
Published: June 2019

This work presents a novel approach using supercritical carbon dioxide (SCCO2) to selectively extract poly(propylene glycol) (PPG) porogen from a poly(methylsilsesquioxane) (PMSSQ) matrix, which results in the formation of nanopores. Nanoporous thin films were prepared by spin-casting a solution containing appropriate quantities of PPG porogen and PMSSQ dissolved in PM acetate. The as-spun films were thermally cured at temperatures well below the thermal degradation temperature of the organic polymer to form a cross-linked organic/inorganic polymer hybrid. By selectively removing the CO2 soluble PPG porogen, open and closed pore structures are possible depending upon the porogen load and its distribution in the matrix before extraction. In the present work, two different loadings of PPG namely 25 wt.% and 55 wt.% were used. Both static SCCO2 and pulsed SCCO2/cosolvent treatments were used for PPG extraction. The initial results indicate that the pulsed SCCO2/cosolovent treatment was more efficient. Fourier transform infrared spectroscopy (FTIR) and refractive index measurements further corroborate the successful extraction of the porogens at relatively low temperatures (2000C). For the pure PMSSQ film, the k value is 3.1, whereas it is 1.46 and 2.27 for the open and closed pore compositions respectively after the static SCCO2 extraction and 430°C subsequent annealing. The reduction in the k-value is attributed to the formation of nanopores. The pore structure was verified from transmission electron microscopy (TEM), and from small-angle x-ray scattering (SAXS) measurements, the pore size was determined to be 1-3 nm for these films.
Environmental Effects on Subcritical Delamination of Dielectric and Metal Films from Organosilicate Glass (OSG) Thin Films
Authors: Lin Y. , Vlassak J.J. , Tsui T.Y. , McKerrow A.J.
Published: June 2019

Subcritical delamination of dielectric and metal films from organosilicate glass (OSG) thin films was studied in controlled ambient with different levels of relative humidity and in aqueous environments of varying pH. The material systems studied include OSG/SiO2, OSG/TaN and OSG/SiNx. For both sets of experiments, subcritical crack growth in OSG is found to be described by a model originally developed for soda-lime silicate glass. The threshold energy release rate for water molecule-assisted cracking varies linearly with the natural logarithm of water partial pressure. In aqueous environments, the threshold value decreases linearly with increasing pH in accordance with a simple model. The slope of crack growth rate curve also decreases with increasing pH.
Characterization of Nanoporous Low-k Thin Films by Contrast Match SANS
Authors: Hedden Ronald C. , Bauer Barry J. , Lee Hae-Jeong
Published: June 2019

Small-angle neutron scattering (SANS) contrast variation is used to characterize matrix properties and pore size in nanoporous low-dielectric constant (low-k) thin films. Using a vapor adsorption technique, SANS measurements are used to identify a “contrast match” solvent mixture containing the hydrogen– and deuterium-containing versions of a probe solvent. The contrast match solvent is subsequently used to conduct SANS porosimetry experiments. With information from specular X-ray reflectivity and ion scattering, the technique is useful for estimating the mass density of the matrix (wall) material and the pore size distribution. To illustrate the technique, a porous methylsilsesquioxane (MSQ) spin-on dielectric is characterized.
Novel Process Methodology for Uniformly Cutting Nanotubes
Authors: Lustig Steven R. , Boyes Edward D. , French Roger H. , Gierke Timothy D. , Harmer Mark A. , Hietpas Paula B. , Jagota Anand , Mitchell Greg P. , Onoa G. Bibiana , Sams Kerry D.
Published: June 2019

We present a novel process methodology for the controlled cutting of nanotubes and other nanostructures to well-controlled lengths and sizes. The continuing increase in complexity of electronic devices, coupled with decreasing size of individual elements, are placing more stringent demands on the resolution and accuracy of fabrication patterns. The ability to fabricate on a nanometer scale guarantees a continuation in miniaturization of functional devices. Particularly interesting is the application of nanotubes' chemical and electronic properties which vary with their dimensions and structure. One realization of this process includes the use of photolithography or electron beam lithography to place protective resist patterns over the nanostructures to be cut. Those sections which are not covered by the resist pattern are removed by reactive ion etching. This is a scaleable process which permits the simultaneous cutting of many nanostructures and ensembles of nanostructures. The lengths, shapes or length distributions can be predicted from theory and thus specified for a given application requirement. Nanostructures which can be cut in this process include nanotubes, nanofibers and nanoplanes. Large scale production of nanostructures with uniform length or specific size-distribution can be used in electronic applications such as field-emission transistors, optoelectronic elements, single electron devices and sensors.
Advances in Cnx Nanotube Growth
Authors: Liu J. , Czerw R. , Webster S. , Carroll D.L. , Park J. H. , Park Y. W. , Terrones M.
Published: June 2019

Carbon nanotubes containing substitutionally “doped” nitrogen were synthesized using injection chemical vapor deposition methods. X-ray photoelectron spectroscopy comparisons between materials grown with different nitrogen sources suggest that the nitrogen content of the nanotubes has little correlation with the total nitrogen content of the “dopant” gas. Tunneling microscopy and spectroscopy do, however, confirm that drastic distortions occur within the graphene lattice as the nitrogen is substituted. Further, donor states are clearly identifiable within the density of electronic states.
The Effects of Catalyst Grain Sizes on the Diameter of MPECVD Grown Patterned Carbon Nanotubes
Authors: Wang S. G. , Zhang Qing , Zhong G. F. , Yoon S. F. , Ahn J. , Yang D. J.
Published: June 2019

The electronic structure and properties of carbon nanotubes (CNTs) strongly depend on their diameter and chirality. The well controlled CNTs diameter is becoming one of the challenges for their applications in microelectronics. In this paper, the patterned CNTs were produced by microwave plasma enhanced chemical vapor deposition technique using a metal catalyst of nickel. The correlation between the CNT diameter and the grain sizes of the nickel catalyst was examined. The experimental results show that nickel films converted to nickel particles when they were heated up. The diameter of CNTs increases with increasing grain sizes of the nickel particles, indicating that the CNT diameter can be controlled by controlling the grain sizes of the nickel catalyst.
Electronic Device Fabricated From Polyaniline / Single walled Carbon Nanotubes Composite
Authors: Ramamurthy P.C. , Malshe A.M. , Harrell W.R. , Gregory R.V. , McGuire K. , Rao A.M.
Published: June 2019

Composites of high molecular weight polyaniline and single walled carbon nanotubes are investigated for applications to electronic devices. Electrical characteristics of devices fabricated using this composite show an order magnitude higher current level than those measured in the neat polyaniline devices. Composite materials and devices with various weight percentages of single walled carbon nanotubes were also fabricated. Current-voltage (I-V) characteristics of these devices indicate a significant increase in current with an increase in carbon nanotube concentration in the composite. Analysis of the forward I-V characteristics of these composite devices on a log-log scale shows two power law regions. In the lower voltage range, the exponent is 1, which is consistent with ohmic conduction, while in the higher voltage range, the exponent is between 1.1 and 1.5, which is consistent with space-charge-limited conduction.
Self-Assembly Fabrication of High Performance Carbon Nanotubes Based FETs
Authors: Valentin Emmanuel , Auvray Stephane , Filoramo Arianna , Ribayrol Aline , Goffman Marcelo , Capes Laurence , Bourgoin Jean-Philippe , Patillon Jean-Noel
Published: June 2019

We describe the realization of high quality self-assembled single wall carbon nanotube field effect transistors (CNTFET). A method using self-assembled monolayers (SAMs) is used to obtain high yield selective deposition placement of single wall carbon nanotubes (SWNTs) on predefined regions of a substrate. This is achieved with individual or small bundles of SWNTs and with high densities suitable for fabrication of integrated devices. We show that such positioned SWNTs can be electrically contacted to realize high performance transistors, which very well compare with state-of-the-art CNTFETs. We therefore validate the self-assembly approach to reliably fabricate efficient carbon nanotube based devices.
Fabrication of Carbon Nanotube Triode Using Helicon Plasma Cvd with Electroplated Nico Catalyst
Authors: Muroyama Masakazu , Kimura Kazuto , Yagi Takao , Saito Ichiro
Published: June 2019

A carbon nanotube triode using Helicon Plasma-enhanced CVD with electroplated NiCo catalyst has been successfully fabricated. Isolated NiCo based metal catalyst was deposited at the bottom of the cathode wells by electroplating methods to control the density of carbon nanotubes and also reduce the activation energy of its growth. Helicon Plasma-enhanced CVD (HPECVD) has been used to deposit nanotubes at 400°C. Vertically aligned carbon nanotubes were then grown selectively on the electroplated Ni catalyst. Field emission measurements were performed with a triode structure. At a cathode to anode gap of 1.1mm, the turn on voltage for the gate was 170V.
High Concentration Aqueous Mixtures of Single Walled Nanotubes
Authors: Grunlan Jaime C. , Bannon Michael V.
Published: June 2019

Gum arabic (GA) and polyvinylpyrrolidone (PVP) were used to stabilize relatively high concentration mixtures of single walled carbon nanotubes (SWNTs) in water. Viscosity and electrical conductivity data, along with electron microscopy, suggest that PVP interacts much more strongly with nanotubes than GA does. This strong PVP-SWNT relationship results in better dispersion of the nanotubes, resulting in lower electrical conductivity, but may enhance mechanical behavior in polymer-matrix composites.
Fracture Toughness of Nanocrystalline L12 (Al+X at.%Mn)3 Ti Prepared by Mechanical Alloying and Consolidated by SPS
Authors: Jang Hee Sup , Kang Chang Won , Kim Young-Seok , Kim Seon-Jin
Published: June 2019

The effects of ternary element addition of manganese on microstructure and mechanical properties of nanocrystalline L12 (Al+X at.%Mn)3Ti (X=0 - 12) fabricated by mechanical alloying and spark plasma sintering (SPS) were investigated. The SPS method was used to consolidate nanocrystalline L12 (Al+X at.%Mn)3Ti with the pressure of 50 MPa. The heating rate was 100°C /min. The final sintering temperature was determined from the observation of the shrinkage of the specimen. In binary Al3Ti, the final sintering temperature was 864°C. The sintering temperature was reduced down to 658°C with increasing Mn concentration. After SPS, the L12 structure was maintained in the specimens which contained Mn concentration of 8- 12 at.%. The microhardness test, grain size measurements, and fracture toughness test were conducted as a function of Mn concentration. In order to investigate the effect of the grain size on the microhardness and fracture toughness of the (Al+8 at.%Mn)3Ti, heat treatments were performed in a vacuum furnace ( 10-3 torr ). With increasing heat treatment temperature, the microhardness decreased due to the formation and growth of Al4C3, Al2O3, and TiC, while fracture toughness increased. The fracture toughness of 4.12 MPa m1/2 was attained for the (Al+8 at.%Mn)3Ti specimen and it was the highest value among the specimens after 1h heat treatment at 1100°C. The grain sizes were about 60 nm and 100 nm after 1 h heat treatment at 900°C and 1100°C, respectively.
Indentation Techniques for the Study of Deformation Across Grain Boundaries
Authors: Nibur K. A. , Bahr D. F.
Published: June 2019

The mechanism by which deformation is transferred across grain boundaries and ways in which boundaries of different misorientations impact this process has been studied using indentation testing. This information could be useful in designing texture of nanocrystalline materials to maximize their mechanical properties for specific applications. Atomic force microscopy (AFM) and orientation imaging microscopy (OIM) has been combined to identify slip systems activated around indentations. When indentations are placed near grain boundaries, slip steps can be imaged on both sides of the boundary and the associated slip systems of each grain can be determined. Dislocation pile ups have been observed around indentations near boundaries which do not share a common slip direction with the active slip planes of either grain, and slip steps have been seen to traverse boundaries when these shared slip directions are present.
Nanoindentation of Amorphous and Nanostructured Polymers
Authors: Maner Kyle C. , Begley Matthew R. , Utz Marcel
Published: June 2019

We present a detailed nanoindentation study of micron-scale thin films of polystyrene (PS), poly(phenylene oxide) (PPO), poly(methyl methacrylate) (PMMA), a metal-centered PMMA-Ruthenium block copolymer, and a PS-poly(ethylene-propylene) (PS-PEP) block copolymer with lamellar morphology. The results show that size-dependence is most readily noticeable for the lamellar PS-PEP film, indicating that the nanoidentation approach has sufficient sensitivity to capture scale dependence on scales in the range of tens of nanometers. The less pronounced scale-dependence (or lack thereof) in the other films is discussed in the context of identifying the physical length-scale of elementary processes of plastic deformation. The results indicate that the upper limit on the size of plastic shear zones in amorphous polymers is approximately 1200-9600 nm3 (i.e. a sphere with a diameter in the range of 20-40 nm).
Energetics of Dislocation Nucleation under a Nanoindenter
Authors: Zhang Chuanli , Xu Guanshui
Published: June 2019

Dislocation nucleation under an idealized nanoindenter is analyzed based on the Peierls-Nabarro dislocation model. The variational boundary integral method is used to obtain the dislocation profiles that correspond to the shear displacements between the adjacent atomic layers along the slip plane. The critical condition for dislocation nucleation at absolute zero and the activation energies required to thermally activate dislocations from their stable to unstable saddle point configurations are determined. By treating the surface as part of an infinite crack embedded in the infinite medium, a rather straightforward approach is adopted to account for the surface effect. The emission of multiple dislocations from the surface of a film-substrate system is also studied. The size effects of the indenter width and film thickness are characterized by the typical load-displacement relation.
Microstructure and Mechanical Properties of Nanolayered TiN/Cu Thin Films
Authors: Tse Y.Y. , Abadias G. , Michel A. , Tromas C. , Jaouen M.
Published: June 2019

Structural and mechanical properties of nanoscale TiN/Cu multilayers grown by dual ion beam sputtering with bilayer periods (A) ranging from 2.5 to 50 nm were studied. Both low-angle and high-angle X-ray diffraction (XRD) experiments have been employed to globally characterize the multilayers structure. The microstructure of the multilayers has been scrutinized by high resolution transmission electron microscopy (HRTEM). The effects of interface and bilayer thickness on hardness were investigated by depth-sensing nanoindentation technique. A small hardness increase with decreasing periodicity of the multilayers has been observed. The relationship between the hc/T ratio (hc is the contact depth and T is the total film thickness) and the hardness is established. The correlation between the microstructure and hardness is discussed.
A Mechanical Study of W and W2N Single Layers, and W2N/W Multilayers
Authors: Maillé L. , Sant C. , Aubert P. , Garnier P.
Published: June 2019

The microstructure of W, W2N single layers and W2N/W multilayers are related to their mechanical properties. We study the hardness of multilayers as function of the period thickness. Two partial pressures of nitride (PN2 = 10 % and 50 %) for W2N deposition are investigated. For the single layers, the hardness value increases with the nitrogen partial pressure. The hardness of W2N/W multilayers using PN2 = 50% for W2N deposition increases when the layer spacing decreased. A hardness value of 19.5 GPa is reached for a multilayer with PN2 = 50% and, close to 20 GPa with PN2 = 10% for all the period studied.
Dislocation patterning and recovery under single slip: modelling micromechanisms from observations
Authors: Veyssière Patrick , Chiu Yu-Lung , Grégori Fabienne
Published: June 2019

The paper focuses on the formation and on the role of prismatic loops during deformation. The analysis is restricted to non-diffusive processes in fcc-related crystals. Double cross-slip and cross-slip dipolar annihilation yield strings of loops such that one loop extremity is aligned in the screw direction with the extremity of its nearest neighbour. Reactions between prismatic loops and mobile dislocations are at the origin of a number of microstructural reactions including recovery, dislocation entanglements and patterning in single slip, dislocation multiplication and there is indication that they may nucleate twins.
Single Crystal Deformation Experiments for Validation of Dislocation Dynamics Simulations
Authors: Lassila David H. , LeBlanc Mary M. , Rhee Moono
Published: June 2019

A new experimental apparatus has been developed for performing compression deformation experiments on high-purity Mo single crystals. These experiments provide data that can validate 3-D dislocation dynamics (DD) simulations. The experiments are performed under conditions that allow unconstrained deformation; thus, a relatively uniform state of axial stress is maintained during deformation. In the following sections, we describe the new experimental apparatus and our results from experiments performed at ambient temperature at a strain rate of s–1. Validation criteria based on the Mo experiments may include comparing the stress-strain response using 3-D strain information, the predicted slip-system yield, and work-hardening behavior.
Metallic Island Coalescence: Molecular Dynamics Simulations of Boundary Formation and Tensile Strain in Polycrystalline Thin Films
Authors: Takahashi Andrew R. , Thompson Carl V. , Carter W. Craig
Published: June 2019

Island coalescence during the early stages of polycrystalline film formation is thought to lead to the large values of tensile stress observed in experiments. Continuum models have been developed which are in semi-quantitative agreement with in-situ experimental observations of stress evolution during coalescence. However, the size of coalescing particles is in the nanometer range, so that atomistic treatments might be expected to more accurately reveal the mechanisms leading to coalescence stresses. We have performed molecular dynamics (MD) computational experiments in which small metallic clusters both in free space and on weakly bound substrates are allowed to coalesce. These atomistic simulations complement the finite element modeling (FEM) and analytical work on the tensile strains developed during grain boundary formation by coalescence. Additionally, the atomistic simulations implicitly capture the effects of anisotropy and special orientations. The MD simulations also provide atomic-level detail of the boundary structure that is absent in continuum models. We have focused on simulations of Ag as a high mobility material at and above room temperature and have begun studying Ni as a material that can behave either as a high or low mobility material depending on the deposition temperature(i.e. Ni has a higher activation energy for adatom motion than Ag.). We find that for small islands, the initial boundary formation occurs in times on the order of nanoseconds. For nanometer-sized clusters in free space and on traction-free substrates, the cluster can undergo large rotations prior to boundary formation. The simulated boundary heights fit well with both a FEM model and an analytical model. Work is ongoing to further quantify the results of the simulations and relate the atomistic forces and positions to the stress state. We are pursuing methods for including the effects of traction at the interface, both through continuum and discrete methods.
Grain Rotations during Tensile Deformation of Columnar Tantalum
Authors: El-Dasher B.S. , Adams B. L. , Rollett A. D.
Published: June 2019

We report on tensile tests performed on thin sheet samples of tantalum that have a nearcolumnar structure. By annealing sheet of approximately 1 mm thickness at high temperatures, a columnar structure is generated with grain boundaries nearly perpendicular to the flat surfaces. The purpose of the experiments is to investigate the mechanical behavior in terms of crystal plasticity in a geometry that is readily amenable to both experimental characterization and computer simulation. Automated electron backscatter diffraction (EBSD) has been used to obtain orientation maps both before and after deformation. For the small strains used in this study (<10%), the grains deform rather uniformly with little evidence of cell formation. Analysis of the lattice rotations shows considerable scatter in the rotation axis and demonstrates significant disagreement with polycrystal plasticity calculations.
Aerosol Deposition Method (ADM) for Nano-Crystal Ceramics Coating Without Firing
Authors: Akedo Jun , Lebedev Maxim , Iwata Atsushi , Ogiso Hisato , Nakano Shizuka
Published: June 2019

Aerosol deposition method (ADM) for shock-consolidation of fine ceramics powder to form dense and hard layers is reported. Submicron ceramic particles were accelerated by gas flow in the nozzle up to velocity of several hundred m/s. During interaction with substrate, these particles formed thick (10 ∼ 100 μm), dense, uniform and hard ceramics layers. Experiments were fulfilled at room temperature. The results of fabrications, microstructure and mechanical properties of oxides (Al2O3; (Ni,Zn)Fe2O3; Pb(Zr0.52,Ti0.48)O3 and non-oxide (AlN; MgB2) materials are presented. Every layer has polycrystalline structure with nano-meter order scale.
Non-Stick and Scratch Resistant Sol-Gel Coating for Aluminum
Authors: Wu Linda Y.L. , Nemeth Sandor
Published: June 2019

PTFE-based coatings have been widely used, for example, on aluminum molds for molding of polyolefin packaging materials for its non-stick property. However, these coatings do not meet the users' scratch resistance and durability requirements. This paper describes a preliminary study on the synthesis and characterization of a PTFE/sol-gel composite coating material which combines the required non-stick and low friction properties of PTFE filler with the high scratch resistance and durability of a silica-based sol-gel matrix. The non-stick and low friction properties were achieved by using both the PTFE filler and the lubricious compound resulting from the reaction of a solvent with siloxane. The high scratch resistance was attributed to the enhanced adhesion to the electro-chemically pre-treated surface and the optimized silica and alumina filler contents in the sol-gel material. FE-SEM/EDX, FTIR, contact angle goniometry, scratch testing and a pin-on-disc tribometry were used to evaluate the coating properties.
Surface Analysis of the Environmental Corrosion of Zinalco (Zn-22Al-2Cu) Alloy
Authors: Guerrero-Penalv R. , Farías M.H. , Cota-Araiza L.
Published: June 2019

The surface of a set of zinalco (Zn-22Al-2Cu) samples was prepared by mechanical polishing (MP) and by electropolishing (EP). Samples were subjected to environmental corrosion during 56 days and studied by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Differences in relative atomic concentration ratio of Al/Zn in oxides of the surface layer were obtained and they are related to the bulk microstructure. A different corrosion behavior is observed between MP and EP samples and it is explained in terms of surface composition and morphology. The initial growth of corrosion products was observed in EP samples and a corrosion model is proposed. The surface of both types of samples can be modified by lowenergy argon ion bombardment.
The Effect of Ag Addition on the Corrosion of Zn-22wt%Al Alloys
Authors: M. Flores , L. Huerta , S. R. Casolco , S. Muhl , G. Torres-Villaseñor , J.A. Luna
Published: June 2019

A new Zn–Al-Ag alloy (ZINAG) with mechanical superplastic properties has been developed. In this work four of the Zn–22wt%Al eutectoid alloy doped with between 0.5 to 4.24 wt% Ag have been studied. The superplastic behavior can be explained as a consequence of the fine grain distribution induced during the deformation process. Here the corrosion resistance of these alloys was studied by means of potentiodynamic polarization and measurements of the temporal evolution of the corrosion potential, in a 0.5 M NaCl solution. The corrosion products in the sample surface were analyzed by Rutherford Backscattering Spectrometry (RBS), X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES). It was found that the corroded surface had lost more Zn than Al. The surface was examined by SEM and it was seen that the corrosion products adhered to the surface cracks. It was found that the alloy with 2.12 wt% concentration of Ag had the best corrosion resistance in the electrolyte used, but no clear tendency with the Ag concentration was found.
Photo-Induced Corrosion in Microelectronic Devices Containing Dissimilar Metals.
Authors: Belisle C. , Westergard L. , Florence D. , Haskett T. , Scott G. , Greenwood B. , Prasad J. , Engle M.
Published: June 2019

Various metals with different galvanic potentials are used to fabricate the microelectronic circuits. One of the most commonly used processes during integrated circuit manufacturing is the tungsten via fill. To obtain maximum interconnect density with low via resistance requires that metal-via overlap is essentially zero. Zero overlap with litho variations and thus misalignment may result in unlanded vias. Since the vias are used to connect various metal levels, a large number of these cases may occur causing device failures and thus yield loss. To study this problem a variety of test structures were studied and a new mechanism of corrosion was found. The tungsten corrosion observed in these structures was found to be photo-induced. In this paper we will discuss the mechanism of photoinduced galvanic corrosion that occurs between the aluminum and tungsten metal layers during microelectronic manufacturing.
Real time in-situ stress evolution investigation of highly textured electrodeposited bismuth thin films
Authors: Fan Donglei , Zhu Frank Q. , Shao Ingrid X. , Searson P. C. , Cammarata R. C.
Published: June 2019

Bismuth, a semi-metal with very long mean free path and large magnetoresistance (MR) effect, is a novel candidate material for thin film spintronic devices. Electrochemical deposition followed by a post-deposition anneal has resulted in highly textured bismuth films as characterized by x-ray diffractometry and pole figure measurements. A highly sensitive, real time in-situ stress measurement system was designed and employed to study stress generation during bismuth film growth. Bismuth films displayed a monotonically increasing compressive stress during deposition. The magnitude of the compressive stress decreased with the deposition rate in the range 1.5 Å/sec to 50 Å/sec.
Low Substrate Temperature Deposition of Crystalline SiC using HWCVD
Authors: Klein S. , Carius R. , Houben L. , Finger F.
Published: June 2019

Microcrystalline silicon carbide (μc-SiC) was prepared at substrate temperatures between 300°C and 450°C using Hot Wire Chemical Vapour Deposition (HWCVD). The SiC films were deposited from monomethylsilane (MMS) diluted in hydrogen on glass and crystalline silicon substrates. The influence of the hydrogen dilution on the deposition rate and the structural and the optoelectronic properties was investigated. Infrared and Raman spectroscopy and transmission electron microscopy (TEM) were applied to study the structural properties. Highly crystalline material with large columnar grains was obtained at high hydrogen dilutions. The optical absorption below the band gap is high and the dark conductivities are far above the values expected for intrinsic SiC. At lower hydrogen dilution, less crystalline or amorphous Si1-xCx is growing, showing broader IR- and Raman peaks, lower dark conductivity and higher absorption above the band gap energy. An extended nucleation zone with large structural disorder was observed even for highly crystalline material.
Improved Stability of Hydrogenated Amorphous Silicon Solar Cells Fabricated by Triode-Plasma CVD
Authors: Sonobe H. , Sato A. , Fujibayashi T. , Shimizu S. , Matsui T. , Matsuda A. , Kondo M.
Published: June 2019

We have employed a triode-type plasma CVD system to fabricate highly stabilized hydrogenated amorphous silicon (a-Si:H) solar cells. The p-i-n type solar cells were fabricated on a textured SnO2/glass substrate (ASAHI VU type). By applying a triode system, the Si-H2 bond density in the film decreased to about one third (from 1.7 at.% for conventional parallel-plate-electrode to 0.6 at.% for a triode configuration), and correspondingly the degradation ratio decreased from 13 % to 10 %. We have achieved the degradation ratio of 5 % by optimizing the player deposition conditions. In case of a triode system, there were minor effects of higher hydrogen dilution in the stabilized efficiency. We have experimented the effects of the substrate temperature for a higher stabilized efficiency. Further improvement in solar efficiency has been made by applying antireflection layers to air/glass and TCO/p interfaces. As a result, we have achieved the stabilized efficiency of 9.22 % (Jsc = 15.9 mA/cm2, Voc = 0.863 V, FF = 0.672) with a degradation ratio of 7.8 %. We have also employed the triode-deposited a-Si:H solar cell to a tandem type solar cell with a structure of a-Si:H/hydrogenated microcrystalline silicon (μc-Si:H). We have achieved the stabilized efficiency of 10.9 % (Jsc = 12.0 mA/cm2, Voc = 1.31 V, FF = 0.691) with a degradation ratio of 7.3 %.
Correlation between Powder in the Plasma and Stability of High Rate Deposited a-Si:H
Authors: Yue Guozhen , Ganguly Gautam , Yan Baojie , Yang Jeffrey , Guha Subhendu
Published: June 2019

Hydrogenated amorphous silicon (a-Si:H) solar cells incorporating high deposition rate (8-10Å/s) intrinsic layers were deposited using modified very high frequency (MVHF) plasma. We have monitored the light scattered from powder generated in the plasma using an Ar-laser and a silicon photodiode. This simple, non-invasive technique allows us to make measurements on the same reactor used to make the solar cells. First, we have varied the total flow rate and observed a maximum in the scattered light intensity from powder in the plasma during the deposition of the intrinsic layer, and correlated this with the degradation, as well as the stabilized performance of the solar cells. Then, we have studied the effects of varying the deposition temperature and/or the addition of germane to the gas mixture on the scattered light intensity due to powder in the plasma.
Application of Spectroscopic Ellipsometry and Infrared Spectroscopy for the Real-Time Control and Characterization of a-Si:H Growth in a-Si:H/c-Si Heterojunction Solar Cells
Authors: Fujiwara Hiroyuki , Kondo Michio
Published: June 2019

We have demonstrated real-time process control of a-Si:H growth in an a-Si:H/c-Si heterojunction solar cell by spectroscopic ellipsometry (SE). Accurate thickness control of a-Si:H p-i layers with a precision better than ± Å has been realized by this technique. From real-time attenuated total reflection spectroscopy (ATR), we find the formation of a porous interface layer with a maximum SiH2-hydrogen content of 27 at.% at the a-Si:H/c-Si interface, although a rather high conversion efficiency of 14.6 % has been obtained in the solar cell. We found that an optimum i-layer thickness for the a-Si:H/c-Si solar cells is consistent with the thickness at which the a-Si:H i-layer growth reaches a steady state after the H-rich interface-layer formation. We have applied SE further to determine the dielectric functions of In2O3:Sn and ZnO:Ga with different carrier concentrations. From the dielectric function analysis, the effective mass m is extracted. We find linear increases in m as the carrier concentration of In2O3:Sn and ZnO:Ga increases. The validity of our analyses has been confirmed from excellent agreement between carrier concentrations determined by SE and Hall measurements. The construction of the optical database further enabled us to calculate a reflectance spectrum of the a-Si:H/c-Si solar cell accurately.
Novel in situ and real-time optical probes to detect (surface) defect states of a-Si:H
Authors: Kessels W.M.M. , Aarts I.M.P. , Gielis J.J.H. , Hoefnagels J.P.M. , van de Sanden M.C.M.
Published: June 2019

This paper describes two novel optical diagnostics that were recently introduced to the field of Si-based thin films, in particular for probing defect states present in the bulk and at the surface of a-Si:H films. It is expected that these diagnostics, when applied in situ or real time during film growth, can provide new insights into the a-Si:H film properties as well as into the fundamental surface processes during growth. The first method is cavity ringdown spectroscopy (CRDS). From ex situ measurements on a-Si:H thin films, it is shown that this method is very powerful for measuring absolute defect-related absorptions at subgap energies without the need for a calibration procedure, even for films as thin as 4 nm. It is also shown that the method can be used for measuring rare-earth dopants – here Er3+ in silicon-rich oxide – to the extent that issues about absorption cross-sections can be resolved by using thin samples instead of waveguides. Furthermore, the in situ application of the method for thin films is discussed by presenting the evanescent-wave cavity ringdown (EW-CRDS) technique. The second method is spectroscopic second harmonic generation (SHG). It has been found that this non-linear optical technique yields a photon energy dependent signal for as-deposited a-Si:H films and that this signal has a contribution from a-Si:H surface states. From a comparison with c-Si surface science studies, the possible origin of the signal from surface Si dangling bonds and strained Si-Si bonds is discussed. The application of SHG during real-time film growth is also presented.
Computer Modelling of Non-Equilibrium Multiple-Trapping and Hopping Transport in Amorphous Semiconductors
Authors: Main C. , Marshall J. M. , Reynolds S. , Rose M.J. , Brüggemann R.
Published: June 2019

In this paper we demonstrate a simple computational procedure for the simulation of transport in a disordered semiconductor in which both multi-trapping and hopping processes are occurring simultaneously. We base the simulation on earlier work on hopping transport, which used a Monte-Carlo method. Using the same model concepts, we now employ a stochastic matrix approach to speed computation, and include also multi-trapping transitions between localised and extended states. We use the simulation to study the relative contributions of extended state conduction (with multi-trapping) and hopping conduction (via localised states) to transient photocurrents, for various distributions of localised gap states, and as a function of temperature. The implications of our findings for the interpretation of transient photocurrents are examined.
Real Time Monitoring of the Crystallization of Hydrogenated Amorphous Silicon
Authors: Stradins Paul , Young David , Branz Howard M. , Page Matthew , Wang Qi
Published: June 2019

In-situ real-time optical reflectance spectroscopy is applied to investigate structural changes as hydrogenated amorphous silicon (a-Si:H) loses H and crystallizes at elevated temperature. The interference fringe spectrum (cutoff energy and amplitude) mainly characterize changes in the bulk, while the the crystal Si (c-Si) direct-transition ultra-violet reflectance signatures reveal the presence of any crystalline phase at the surface. Effusion of atomic hydrogen is monitored by a decrease of the interference fringe cutoff energy and is thermally activated with about 1.7 eV. In a-Si:H on glass, optical reflectance spectra are consistent with 2.8 eV activated homogeneous nucleation and growth of a small grain (˜ 100 nm) polycrystalline phase. In contrast, a-Si:H on c-Si crystallizes by solid phase epitaxy with very different spectral kinetics. Our measurements reveal the temperature-time window for thermal crystallization of a-Si:H for photovoltaic device applications, and highlight the versatility of the in-situ spectral reflectance monitoring.
Electrolyte-Gate a-Si:H Thin Film Transistors
Authors: Gonçalves Dina I. , Prazeres Duarte M. , Chu Virginia , Conde João P.
Published: June 2019

This paper presents the fabrication and characterization of electrolyte-gate (EG) hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs). In these devices, the metal gate is replaced by a Pt electrode immersed in an electrolyte. The source-drain current of these devices is modulated by the voltage applied through the Pt electrode. Device characteristics are compared with structurally equivalent top-gate a-Si:H TFTs. The EG devices show higher mobility and smaller subthreshold slope than their counterparts with metal gate and work in a narrower voltage range. EG-TFTs show chemical sensitivity, illustrated by a voltage shift in the transfer curve as a consequence of pH variation. The sensitivity of the devices to pH is different depending on whether the top layer in contact with the electrolyte is SiO2 or SiNx.
Dependence of Microcrystalline Silicon Growth on Ion Flux at the Substrate Surface in a Saddle Field PECVD
Authors: Johnson Erik , Kherani Nazir P. , Zukotynski Stefan
Published: June 2019

The Saddle-Field Glow Discharge PECVD system emulates RF-like excitation using a semi-transparent anode and a DC power supply. It has been used to deposit high quality amorphous and microcrystalline hydrogenated silicon thin films in the past. The growth of microcrystalline material is particularly sensitive to the conditions under which it is produced. Significant levels of microcrystallinity are only produced under conditions of higher pressure and electrical isolation of the substrate surface from the grounded substrate holder. We present results of a study on the relationship between substrate electrical potential and microcrystalline growth, as quantified by Raman scattering spectroscopy, at growth pressures near the minimum required for microcrystalline growth.
Improved optical loss characteristics of PECVD silicon oxynitride films using low frequency plasma
Authors: Naskara S. , Bower C.A. , Wolter S.D. , Stonera B.R. , Glass J.T.
Published: June 2019

With the continued growth of photonics, silicon oxynitride (SiOxNy) is becoming a popular material for optoelectronic applications owing to its large tunable refractive index. However, with the increase in refractive index, these films tend to show poor optical transmission characteristics. In this research we have investigated the influence of growth conditions on the loss characteristics of PECVD SiOxNy films. The films are grown at 350 °C substrate temperature and 1 Torr pressure with silane (SiH4) and nitrous oxide (N2O) precursor gases. The precursor flow rate and power input to the system are varied as the two primary parameters. It is observed that films grown at 100 kHz plasma frequency proved to be more transmissive than films grown at 13.56 MHz plasma frequency. Elastic recoil detection analysis results showed the hydrogen content is less in the low frequency films than the high frequency films, which is believed to be the reason for the low loss behavior. The details of these analysis results are discussed below.
Gate Oxide Integrity for Polysilicon Thin-film Transistors: A Comparative Study for ELC, MILC, and SPC Crystallized Active Polysilicon Layer
Authors: Choi D. C. , Choi B. D. , Jung J. Y. , Park H. H. , Seo J. W. , Lee K. Y. , Chung H. K.
Published: June 2019

In this paper, we present the results of Plasma Enhanced Chemical Vapor Deposition gate oxide (SiO2) integrity on ELC (excimer laser crystallized), MILC (metal induced lateral crystallized) and SPC (solid phase crystallized) polysilicon films. We observed that gate oxide strength of poly Si TFT strongly depends on the crystallization method for the active silicon layer. In the case of ELC films, asperities on the silicon surface reduce the SiO2 breakdown field significantly. The metallic contaminants in MILC films are responsible for a deleterious impact on gate oxide integrity. Among the three cases, the SiO2 breakdown field was the highest for the SPC silicon films. The breakdown fields at the 50% failure points in Weibull plots for the ELC, MILC and SPC cases were 5.1MV/cm, 6.2MV/cm, 8.1MV/cm, respectively. We conclude that the roughness and metallic contamination of the poly Si films are the main factors that cause en-hanced breakdown of SiO2 films.
The Hysteresis Analysis of Hydrogenated Amorphous Silicon Thin Film Transistors for an Active Matrix Organic Light Emitting Diode
Authors: Lee Jae-Hoon , You Bong-Hyun , Shin Kwang-Sub , Han Min-Koo
Published: June 2019

An experimental scheme for validating the cause of the hysteresis phenomenon in hydrogenated amorphous silicon thin film transistor (a-Si:H TFT) is reported. The different gate starting voltage to the desired gate voltage has been considered to prove an effect of filling an acceptor-like or donor-like state in the interface. The integration time of the semiconductor parameter analyzer (HP4156B) has also been controlled to investigate the effect between the detrapping rate and hysteresis. The experimental results show that the previous data voltage in the (n-1)th frame affects the OLED current in the (n)th frame.
Low Hydrogen Concentration Silicon Nitride as a Gate Dielectric of TFTs for Flexible Display Application
Authors: Park Joong Hyun , Kim Chang Yeon , Shin Kwang Sub , Park Sang Geun , Han Min Koo
Published: June 2019

We have proposed low hydrogen concentration (CH) silicon nitride (SiNX) as a dielectric for flexible display application. The fabrication temperature on plastic substrate is limited below Tg (glass transition temperature, typically 130˜180 °C) and it was reported that CH in thin film is strongly depends on fabrication temperature. As the fabrication temperature is decreasing, hydrogen concentration is increasing. SiNX deposited in ultra low temperature (< 150 °C) has high CH which is porous, low density. Our experimental results using SiH4, He, N2 gas mixture shows that in the SiNX CH is less than 15 at.%. Breakdown voltage of proposed SiNX dielectric is 5 MV/cm. In the wet etch rate test using a nitride etching solution, He dilution is more dense than NH3 dilution. This process approach is useful for flexible display application.
High Efficiency Solar Cells with Intrinsic Microcrystalline Silicon Absorbers Deposited at High Rates by VHF-PECVD
Authors: Mai Yaohua , Klein Stefan , Carius Reinhard , Geng Xinhua , Finger Friedhelm
Published: June 2019

Intrinsic microcrystalline silicon (μc-Si:H ) was prepared at high deposition rates (RD) by very high frequency plasma-enhanced chemical vapor deposition (PECVD) working at high-pressure high-power (hphP). The material has similar electrical and optical properties as μc-Si:H material deposited at low rates by low-pressure low-power PECVD, apart from a more pronounced structure in-homogeneity along the growth axis for material deposited on glass substrates. With optimized deposition conditions high efficiency solar cells can be grown with deposition rates of up to 15 Å/s without deterioration of the performance as a function of RD. A high conversion efficiency of 9.8 % was obtained for a single junction μc-Si:H p-i-n solar cell at a deposition rate of RD = 11 Å/s.
Structural and Electronic Properties of Hydrogenated Nanocrystalline Silicon Films Made with Hydrogen Dilution Profiling Technique
Authors: Wang Keda , Han Daxing , Williamson D. L. , Huie Brittany , Weinberg-Wolf J. R. , Yan Baojie , Yang Jeffrey , Guha Subhendu
Published: June 2019

We used X-ray diffraction (XRD), Raman scattering and photoluminescence (PL) spectroscopy to characterize structural and electronic properties of nc-Si:H films made with different hydrogen dilution ratios and hydrogen dilution profiling with continuously reduced hydrogen dilution during the deposition. The XRD results show that the crystalline volume fraction (fc) is in the range of 60-70% with grain size of 22-26 nm for the nc-Si:H films studied. Comparing the sample made using hydrogen dilution profiling to that with constant hydrogen dilution, the hydrogen dilution profiling promotes the (220) preferential orientation due to a very high hydrogen dilution in the initial growth. The Raman results show that the fc is in the range of 60-90%, depending on the sample and excitation wavelength. For the samples with constant hydrogen dilution, the fc measured by Raman increases along the growth direction. The hydrogen dilution profiling reverses this trend, which affirms that the hydrogen profiling controls the nanocrystalline structure evolution along the growth direction. The PL results show only one peak around 0.8-0.9 eV for the samples made with constant hydrogen dilution, but an additional peak at 1.4 eV appears in the sample made with the hydrogen dilution profiling.
Conductance Fluctuations in Amorphous Silicon Nanoparticles
Authors: Belich T. J. , Shen Z. , Blackwell C. , Campbell S. A. , Kakalios J.
Published: June 2019

Hydrogenated amorphous silicon nanoparticles with an average diameter of 150 nm have been synthesized by high-density plasma chemical vapor deposition. The particles are deposited onto a conducting substrate and are then surrounded by an insulating matrix, electrically isolating the particles. Electrical contact is made to the top of each nanoparticle; the current-voltage characteristics of the nanoparticles indicate that transport is space-charge limited through the a-Si:H. The spectral density of the current fluctuations in the a-Si:H nanoparticles is well described by a 1/f frequency dependence for frequency f. However, the octave separation dependence of the correlation coefficients of the noise power for the nanoparticles are very well described by an ensemble of fluctuators whose amplitudes are independently modulated in parallel, rather than the serial kinetics typically observed in bulk a-Si:H.
Transport and Meyer-Neldel Rule in Microcrystalline Silicon Films
Authors: Reynolds Steve , Smirnov Vlad , Finger Friedhelm , Main Charlie , Carius Reinhard
Published: June 2019

Changes in the electrical conductivity of thin (< 300 nm) silicon films following prolonged exposure to atmosphere, are reported. Both reversible (by annealing at 150 °C under vacuum) and irreversible (annealing-resistant) effects are found to occur, which are larger in thinner films. The conductivity prefactor and thermal activation energy obey the Meyer-Neldel rule, although detailed behaviour depends on film thickness and microstructure. Irreversible changes may result from oxidation of thinner, more porous films, with water and/or oxygen adsorption and desorption responsible for reversible changes. The need to identify and account for these effects when discussing and formulating transport mechanisms in these materials is underlined.