bluuebunny/crossref_metadata_2025 huggingface dataset:
Imaging Supported Interfacial Layers – Factors that Influence Interface Organization and Dynamics
Authors: Blanchard Gary J , Setiawan Iwan
Published: February 2020

Supported interfacial structures are centrally important to a variety of electrochemical and chemical sensing applications. Lipid bilayer structures have received widespread attention not only because of their potential utility in creating biomimetic devices but also because of their inherent complexity and sensitivity to their environment. Understanding the factors that influence organization and dynamics in such systems could be of immediate relevance to the chemical sensing and biological communities. Our specific interest lies in the formation of interfaces that could be used to host transmembrane proteins for sensing applications. Knowledge of the relationships between bilayer composition and morphology, as well as the influence of overlayer constituents, is a necessary first step in the creation of useful supported bilayer interfaces. We have constructed model bilayer structures containing phosphocholine, sphingomyelin and cholesterol supported on mica, and have examined the organization of and dynamics within these phase-segregated structures using time-resolved fluorescence lifetime and anisotropy imaging. Our results show that these supported bilayer structures cannot be explained simply in the context of phase segregation of cholesterol and phosphocholine domains, and that the organization of these bilayers depends sensitively on the constituents present in liquid overlayers. Our image and dynamic data provide a useful starting point for the construction of biomimetic bilayer structures capable of housing biomolecules for sensing applications.
Triplet Exciton Production and Lifetimes in Single-Wall Carbon Nanotubes
Authors: Hertel Tobias , Spaeth Florian , Kraus Hannes , Sperlich Andreas , Dyakonov Vladimir
Published: February 2020

Despite a broad body of spectroscopic work on the photophysics of singlet excitons in SWNTs, triplet states and triplet–triplet interactions have mostly remained elusive. Here we report on the first spin sensitive study of triplet excitons in (6,5) SWNTs giving triplet lifetimes and the quantum yield of triplet exciton production using optically detected magnetic resonance (ODMR) [1]. SWNT samples were fabricated from aqueous suspensions and PFO-BPy dispersed CoMoCAT SWNTs. Triplet lifetimes of (30±10) µs were obtained from the modulation frequency dependence of ODMR signals at small excitation intensities. The yield of triplet exciton production of (5±2)% is determined using the intensity dependence of triplet-triplet annihilation, a process that competes with triplet decay as well as with non-radiative singlet decay. The results imply that steady state triplet concentrations in SWNTs are about 5 orders of magnitude higher than those of singlet excitons.

[1] D. Stich, F. Späth, H. Kraus, A. Sperlich, V. Dyakonov and T. Hertel, Nature Photonics, in press (DOI: 10.1038/NPHOTON.2013.316)
Improved CNT-Si Heterojunction Solar Cell with Structured Single-Walled Carbon Nanotubes
Authors: Maruyama Shigeo , Cui Kehang , Chiba Takaaki , Reynaud Olivier , Fujii Shunjiro , Nasibulin Albert , Chiashi Shohei , Kataura Hiromichi , Kauppinen Esko
Published: February 2020

Single-walled carbon nanotubes (SWNTs) with outstanding electronic, optical, mechanical, and thermal properties are expected to be the most promising materials for next-generation energy devices as well as optical and electronic devices. However, the structure controlled assembly of SWNTs for various devices is still challenging. In this study, we discuss two different SWNT assemblies for SWNT-Si heterojuction solar cells.

We proposed a water vapor treatment to build up SWNTs to a self-assembled micro-honeycomb network for the application of solar cells [1]. The micro-honeycomb network consists of vertical aggregated SWNT walls and a buckypaper bottom (quasi 2 dimentional random network). This hierarchical structure exhibits lower sheet resistance and higher optical transmittance compared with the buckypaper. The heterojunction solar cell was fabricated by dry depositing the SWNT film to the 3 mm by 3 mm n-type silicon substrate. The pristine SWNT-Si heterojunction solar cell shows a record-high fill factor of 72 % as well as a power conversion efficiency (PCE) of 6 % without tuning the diameter or height of original vertically aligned SWNTs [2]. The PCE remains stable for months in ambient condition. A PCE exceeding 10 % is achieved in the dry state after dilute nitric acid treatment.

On the other hand, heterojucntion solar cells using highly transparent-conductive SWNT films from controlled bundle-diameter and long bundle length [3] are also promising. Here, SWNTs were synthesized by the thermal decomposition of ferrocene vapor in a carbon monoxide atmosphere, with the average diameter of approx. 2 nm. The SWNT films showed a sheet resistance of 117 Ω/sq. at the transmittance of 91 % over the AM1.5G spectrum. Our preliminary test result shows the PCE of 10.12 %, with short-circuit current, open-circuit voltage and fill factor of 30.9 mA/cm2, 540 mV and 60 %, respectively.

Both types of solar cells are stable after months, which is attributed to the high-purity pristine SWNTs. The updated performance of these solar cells and the detailed mechanism will be discussed.

References:

[1] K. Cui, T. Chiba, S. Omiya, T. Thurakitseree, P. Zhao, S. Fujii, H. Kataura, E. Einarsson, S. Chiashi, S. Maruyama, J. Phys. Chem. Lett., (2013), 4, 2571.

[2] Y. Murakami, S. Chiashi, Y. Miyauchi, M. Hu, M. Ogura, T. Okubo, S. Maruyama, Chem. Phys. Lett., (2004), 385, 298.

[3] A. G. Nasibulin, A. Kaskela, K. Mustonen, A. S. Anisimov, V. Ruiz, S. Kivistö, S. Rackauskas, M. Y. Timmermans, M. Pudas, B. Aitchison, M. Kauppinen, D. P. Brown, O. G. Okhotnikov, E. I. Kauppinen, ACS Nano, (2011), 5, 3214.
Carbon Single Wall Nanotubes As a Low-Barrier, Copper-Free Back Contact to CdTe Solar Cells
Authors: Phillips Adam B. , Khanal Rajendra R. , Song Zhaoning , Zartman Rosa M. , DeWitt Jonathan L. , Stone Jon M. , Roland Paul J. , Plotnikov Victor V. , Carter Chad W. , Stayancho John M. , Ellingson Randall J. , Compaan Alvin D. , Heben Michael J.
Published: February 2020

With a 1.45 eV band gap, a high absorption coefficient, and proven low-cost, high-volume manufacturing, CdTe-based photovoltaic (PV) technology accounted for more than 7% of the 100 GW of solar power generating capacity that was installed worldwide by the end of 2012. Copper doping of CdTe assists in forming back contacts to CdTe, but Cu is known to diffuse through the device and produce junction-shunting pathways. Because of the detrimental effects of Cu, several material systems have been investigated for use as the back contact for Cu-free CdTe devices. If long-term degradation of the photovoltaic performance could be eliminated, the levelized cost of electricity would be subtantially reduced without, in this case, significant changes in the device architecture or manufacturing process flow.

Here, we discuss results1 that demonstrate that carbon single-wall nanotube (SWNTs) films can make a high-performance electrical back contact to CdTe solar cells without the use of Cu. Back contacts formed with SWNT films showed improved open circuit voltage in comparison to cells fabricated with standard Au/Cu back contacts and, once overcoated with a thin metal layer, the solar-to-electric conversion efficiency was higher as well. The results are understood by considering that individual SWNTs within the film extend through the film’s thickness and make barrier-less contacts to individual CdTe grains in the active layer of the device.

This work was supported by the U.S. Department of Energy under Award Number DE-SC0006349 and by faculty start-up funds from the University of Toledo, and was conducted in collaboration with the Wright Center for Photovoltaics Innovations and Commercialization (http://www.utoledo.edu/research/pvic/)

(1) Phillips, et al., Nano Lett., 2013, 13 (11), pp 5224–5232
Direct Measurements of In-plane Thermal and Electrical Transport in P-type Single-walled Carbon Nanotube Thin Films
Authors: Avery Azure D. , Mistry Kevin S. , Zink Barry L. , Olsen Michele , Parilla Philip A. , Ferguson Andrew , Blackburn Jeffrey L.
Published: February 2020

In order to optimize next-generation thermoelectrics for use in converting waste heat into useable energy, the close correlation between the thermal conductivity, electrical conductivity, and Seebeck coefficient or thermopower in these materials must be decoupled. As promising alternatives to traditional inorganic semiconductor materials, nanocomposites constructed of conducting polymers with organic inclusions such as single-walled carbon nanotubes (SWCNTs) offer simple fabrication techniques, reduced cost, and low toxicity. They also offer the possibility of decoupling the thermal and electrical transport pathways which would enable more efficient organic composites for thermoelectric conversion. However, in order to develop high-performance organic thermoelectric devices, it is necessary to develop a detailed fundamental understanding of the factors governing directionally dependent thermal and electrical transport through these materials in reduced geometries such as thin films. In this talk, we describe our suspended membrane technique for directly measuring the in-plane thermal and electrical transport through thin films and present results for several different thin film samples. We present our approach to developing p-type materials with tunable transport behavior, by fabricating composites consisting of SWCNTs dispersed in a polymer matrix. Finally, we discuss fabrication and post-fabrication treatments of the SWCNT thin films and the benefits offered by nanostructuring these architectures to optimize the thermoelectric dimensionless figure-of-merit, ZT.
High Surface Area Graphene-Based Materials for Electrochemical Energy Storage
Authors: Kim TaeYoung , Ruoff Rodney S.
Published: February 2020

We present an overview of work in the Ruoff group on graphene-based and graphene-derived materials in energy storage systems (EES).

With high electrical conductivity and surface area, graphene-based materials are being intensively studied as electrode material or support material in ultracapacitors and batteries. Graphene-based materials with different physicochemical properties have been studied including chemically reduced graphene oxide,[1] thermally reduced graphene oxide,[2] microwave exfoliated graphite oxide (MEGO),[3] and activated microwave-expanded graphite oxide (‘a-MEGO’).[4]

Our recent work based on a highly porous graphene-derived carbon material showed that extremely high specific surface area can be obtained by an activation process, which allows for extensive formation of an electrochemical double layer (EDL) and a high gravimetric capacitance in a symmetric ultracapacitor. In addition, activated graphene-based materials showed significantly improved performance in terms of energy density approaching that of conventional lead-acid batteries.[4, 5]

Other studies of highly porous graphene-derived materials in EES including Li-ion capacitors and Li-S batteries will also be presented, along with current efforts in our group on graphene-based and graphene–derived materials for electrical energy storage.

REFERENCES

1. Stoller, M.D., et al., Graphene-Based Ultracapacitors. Nano Letters, 2008. 8(10): p. 3498-3502.

2. Zhu, Y.W., et al., Exfoliation of Graphite Oxide in Propylene Carbonate and Thermal Reduction of the Resulting Graphene Oxide Platelets. ACS Nano, 2010. 4(2): p. 1227-1233.

3. Zhu, Y.W., et al., Microwave assisted exfoliation and reduction of graphite oxide for ultracapacitors. Carbon, 2010. 48(7): p. 2118-2122.

4. Zhu, Y.W., et al., Carbon-Based Supercapacitors Produced by Activation of Graphene. Science, 2011. 332(6037): p. 1537-1541.

5. Kim, T., et al., Activated graphene-based carbons as supercapacitor electrodes with macro- and mesopores. ACS Nano, 2013. 7(8): p. 6899-905.
Carbon Nanotube Enhanced Lithium Ion Batteries
Authors: Landi Brian J. , Forney Michael W. , Ganter Matthew J. , Staub Jason , Dzara Michael J.
Published: February 2020

Lithium ion battery electrode designs employing carbon nanotubes (CNTs) have recently demonstrated increased battery energy and power densities through use as a conductive additive or a current collector replacement. CNTs as conductive additives can enhance the loading (thickness and areal capacity) of composite coatings, rate capability, and thermal stability of electrodes with traditional active materials. Anodes consisting of germanium nanoparticles (Ge-NP) and single wall carbon nanotube (SWCNT) additives have recently demonstrated active material specific capacities ~3x greater than traditional graphitic anodes. Rate performance is dramatically improved with SWCNT conductive additives, which is necessary for Li+ extraction rates above C/5 at increased areal capacities. In addition, free-standing CNT electrodes provide a lightweight, conductive structure to effectively support high capacity anode active materials like Si and Ge. The electrode extraction capacities of Si-CNT anodes are shown to exceed 1000 mAh/g. Since nanostructured anodes exhibit large irreversible first cycle capacity loss, Stabilized Lithium Metal Powder has been effectively used to pre-lithiate both Si-CNT and Ge NP anodes. Thus, application of these pre-lithiated anodes can allow for the intended capacity to be realized in full batteries when paired with a traditional cathode. An example of Si-CNT anodes paired with NCA cathodes has shown successful capacity matching, has achieved over 1500 cycles, and demonstrated the potential for a cell energy density of 300 Wh/kg.
Oxygen Reduction Reaction Activity of Aerosol Jet Printed Layers of Graphite and Graphene
Authors: Farjami Elaheh , Rottmayer Michael , Deiner L. Jay
Published: February 2020

Graphene and graphene-based materials have shown great promise in a broad range of applications including electrochemical sensors, supercapacitors, and lithium ion batteries. However, practical realization of the potential utility of graphene requires development of low cost, high volume methods of material synthesis and manufacturing-ready methods of device fabrication. This work aims to address the second challenge by demonstrating the use of aerosol jet printing for the fabrication of catalytically active electrodes.

Graphene and graphite were formulated into high concentration inks (10mg/mL). These inks were aerosol jet printed to create micron scale layers (2 – 10 microns). The catalytic activity of the aerosol jet printed electrodes was evaluated in oxygen saturated basic solution. It was found that the oxygen reduction reaction activity of the aerosol jet printed graphene electrode was ~ 5 times higher times than the activity of the same material when drop cast. Electrochemical impedance spectroscopy showed that the activity difference correlated with a large decrease in the charge transfer resistance of aerosol jet printed graphene as opposed to drop cast graphene. Further, the activity of the aerosol jet printed graphene electrode was ~ 3 times greater than the activity of the aerosol jet printed graphite. In contrast, the drop cast materials did not show a measurable difference in performance. These results indicate that aerosol jet printing is a viable way to deposit micron scale layers of graphene and related materials. In addition, the activity of the graphene electrode is strongly dependent on the deposition method, with aerosol jet deposited electrodes showing a strong performance improvement over their drop cast counterparts.
Invited Presentation: In Situ Nanomechanics of Electrode Failure in Lithium-Ion Batteries
Authors: Zhu Ting
Published: February 2020

Lithium-ion batteries revolutionize portable electronics and are key to next-generation electric vehicles. However, they often suffer from the electrochemically induced mechanical degradation in high-capacity electrodes, resulting in capacity fade and short cycle life. Using a unique nanobattery cell inside a transmission electron microscope, we made in situ observations of reaction, deformation and fracture in individual nanowire and nanoparticle electrodes. A wide range of novel phenomena were discovered, including the size dependent fracture in silicon nanoparticles, anisotropic swelling in silicon nanowires, two-phase lithiation in amorphous silicon, nanoporosity formation in germanium nanowires, and cracking in the coating of tin oxide nanowires. We further developed the continuum and atomistic models to reveal the mechanistic origin of stress generation and mechanical failure in these high-capacity electrode materials. The results provide insights into the microstructural evolution and degradation in nanoscale building blocks of battery electrodes, and have broad implications for designing the durable electrodes in high performance lithium-ion batteries.
Invited Presentation: Probing Local Ionic Dynamics in Functional Oxides: From Nanometer to Atomic Scales
Authors: Kalinin Sergei V.
Published: February 2020

Vacancy-mediated electrochemical reactions in oxides underpin multiple applications ranging from electroresistive non-volatile memory and neuromorphic logic devices memories, to chemical sensors and electrochemical gas pumps, to energy conversion systems such as fuel cells. Understanding the functionality in these systems requires probing reversible (oxygen reduction/evolution reaction) and irreversible (cathode degradation and activation, formation of conductive filaments) electrochemical processes. In this talk, I summarize recent advances in probing and controlling these transformations locally on nanometer level using scanning probe microscopy. The localized tip concentrates the electric field in the nanometer scale volume of material, inducing local transition. Measured simultaneously electromechanical response (piezoresponse) or current (conductive AFM) provides the information on the bias-induced changes in material. Here, I illustrate how these methods can be extended to study local electrochemical transformations, including vacancy dynamics in oxides such as titanates, La
x
Sr1-x
CoO3, and Y
x
Zr1-x
O2. The formation of electromechanical hysteresis loops and their bias-, temperature- and environment dependences provide insight into local electrochemical mechanisms and can be directly linked to the defect chemistry. In materials such as lanthanum-strontium cobaltite, mapping both reversible vacancy motion and vacancy ordering and static deformation is possible, and can be corroborated by post mortemSTEM/EELS studies. In ceria, a broad gamut of electrochemical behaviors is observed as a function of temperature and humidity. The possible strategies for elucidation of origins of ionic motion at the electroactive interfaces in oxides using high-resolution electron microscopy and combined ex-situ and in-situ STEM-SPM studies are discussed. In the second part of the talk, probing electrochemical phenomena on in-situ grown surfaces with atomic resolution is illustrated.

Research supported (SVK) by the U.S. Department of Energy, Basic Energy Sciences, Materials Sciences and Engineering Division and partially performed at the Center for Nanophase Materials Sciences, a DOE-BES user facility.
Reversible Chemical and Electrochemical Dehydrogenation/Hydrogenation of Primary Alcohols Catalyzed By Iridium Complexes
Authors: Bonitatibus Peter , Doherty Mark , Rainka Matthew , Peters Andrea , Siclovan Oltea , Simone Davide , Soloveichik Grigorii
Published: February 2020

Development of efficient electrocatalysts for both dehydrogenation and hydrogenation of organic fuels is critical to the realization of regenerative liquid fuel cells (RLFCs). Alcohols are convenient fuels currently utilized in direct alcohol fuel cells (DAFCs) and are capable of undergoing reversible partial dehydrogenation without CO2 emission in a RLFC.1 An Ir-diaminodiolefin complex, [Ir(trop2DACH)][OTf] (trop2DACH = N,N’-bis(5H-dibenzo[a,d]cyclohepten-5-yl)-1,2-diaminocyclohexane) (1) was proposed by Grützmacher et al.2 as a catalyst for alcohol oxidation with benzoquinone. Previously we demonstrated that 1 also catalyzes chemical dehydrogenation of 4-methoxybenzyl alcohol to p-anisaldehyde with one-electron oxidants in the presence of a base as well as electrochemical dehydrogenation at a low applied potential with high selectivity and Faradaic efficiency.3 In this presentation we report both chemical and electrochemical dehydrogenation of primary alcohols and hydrogenation of the corresponding aldehydes using 1 or an analogous iridium complex [Ir(trop2DAD)]OTf (trop2DAD = N,N’-bis(5H-dibenzo[a,d]cycloheptene-5-yl)-1,4-diazabuta-1,3-diene) (2) as a single homogeneous catalyst. In the chemical processes the same acid/conjugate base pair (substituted phenols/phenolates) is used with an appropriate one electron reductant (e.g. cobaltocene) for hydrogenation or oxidant (e.g. ferrocene) for dehydrogenation. In the electrochemical processes 1 and 2 catalyze dehydrogenation and hydrogenation with high faradaic efficiency and excellent selectivity though hydrogenation produced smaller yields. Further details on the effects of the base, solvent and electrolysis conditions on chemical and electrochemical catalysis will be provided.

This work is supported as part of the Center for Electrocatalysis, Transport Phenomena, and Materials (CETM) for Innovative Energy Storage, an Energy Frontier Research Center (EFRC) funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001055.

1. Kariya, N. F., Fukuoka, A.; Ichikawa, M., Phys. Chem. Chem. Phys. 2006, 8, 1724

2. Königsmann, M.; Donati, N.; Stein, D.; Schönberg, H.; Harmer, J.; Sreekanth, A.; Grützmacher, H., Angew. Chem. Int. Ed. 2007, 46, 3567.

3. Bonitatibus, P. J.; Rainka, M. P.; Peters, A. J.; Simone, D. L.; Doherty, M. D., Chem. Communs 2013, 49, 10581.
Porphyrin-Based Supramolecular Alternating Block Copolymer
Authors: Haino Takeharu
Published: February 2020

S-shaped tetrakisporphyrin 1 forms supramolecular polymeric assemblies via a complementary affinity1,2 of its bisporphyrin units in solution.3 The self-association constant determined by applying the isodesmic model is more than 106 L mol–1, which suggests that a sizable polymer forms at millimolar concentrations at room temperature. Trinitrofluorenone (TNF) binds within the molecular clefts provided by the bisporphyrin units via a charge transfer interaction. Thus, bisTNF guest can connect the tetrakisporphyrin via host-guest interaction to form an alternating block copolymer. In this presentation, we will discuss the structure transition from the tetrakisporphyrin-based supramolecular homopolymer to an alternating AB type block copolymer through competitive ditopic guest complexation.

1) Haino, T. et al., Y. Tetrahedron Lett.
2005, 46, 257.

2) Haino, T. et al., Y. J. Org. Chem.
2006, 71, 2572.

3) Haino, T. et al., U. Proc. Natl. Acad. Sci. USA
2009, 106, 10477.
Processing Challenges of CMOS Integration of Finfets with All-Last Gate Stacks
Authors: Zhao Chao , Ye Tianchun , Zhu Huilong , Yin Huaxiang , Luo Jun , Yang Hong , Li Chunlong , Yang Tao , Cui Hushan , Gao Jianfeng , Wang Guilei , Xu Qiang , Xiang Jinjuan , Zhang Yongkui , Zhao Zhiguo , Liu Jinbiao , Hong Peizhen , Meng Lingkuan , Li Tingting , Li Junjie , He Xiaobin , Xiong Wenjuan , Wang Dahai , Lu Yihong , Li Junfeng , Zhong Huicai , Yin Haizhou , Yan Jiang , Wang Wenwu
Published: February 2020

FinFETs with 20nm BEOL with one generation improvement in performance and power efficiency has announced for mass production by leading IC companies. The processing details, however, have never been reported. In this talk, processing challenges of CMOS integration of FinFETs with all-last gate stacks is presented based on our recent results. Special processing issues in Fin and the replacement gate (RMG) formation, RMG filling with high-k/metal gate and self-aligned contact (SAC) module will be discussed. It is found that the etching of dummy gate of FinFETs behaves differently from that in planar MOSFETs. Thick enough dummy SiO2 is needed for protecting the Fin from plasma damage during dummy gate etch. Wet removal of dummy SiO2 in gate area faces also the risk of Fin damage, due to galvanic corrosion, and thus prefers to a thin SiO2 for control of the wet processing window. It is shown that TaN coverage of the channel area is important in single dielectric dual metal gate stack, where a p-FET stack is first deposited in both n- and p-area, and then the top work function metals in n-area will be removed before n-FET metal deposition. ALD TaN is studied systematically for the the etch stopper application. It is found that the largest issue in the CMOS integration of the FinFETS is n-work function metal deposition. Poor TiAl coverage induces large Vt variation. ALD TiAl could be a good solution for n-work function metal deposition. Filling of the RMG, which has extremely large AR in FinFETs, and SAC is a big challenge. A systematic study of ALD W shows that its advantage in properties such as adhesion, conformality and good constraint by TiN barrier enables good fill of the gaps. Electrical characterizations of the FinFETs are presented in order to show the impact of the above issues to device behavior variation.
Flexible Nanocomposite Polymer Based Sensors for Breast Cancer Diagnostics
Authors: Khosla Ajit
Published: February 2020

According to the data published by WHO, it is estimated that 226,870 women in United States will be diagnosed with breast cancer and 39,510 women will die of breast cancer in 2012. On average, 110 american women will die of breast cancer every day. Mammography, the current standard in screening breast cancer, is uncomfortable, requires specialized facilities and exposes the breast to a small but significant amount of radiation. It is known that exposing the breast to mammography radiation can lead to breast cancer later in life, and is not recommended for women below the age of 39. Over last decade, with hightened awareness, survival rate for women with breast cancer is increased dramatically when diagnosed at an early stage and has resulted an increase in survival rates.

In order to slove the isssues with mamography, we are developing an Electrical Impedance Tomography (EIT) system. We have developed a high density flexible sensor array on a silicone polymer sheets, to deliver small electrical impulses to the breast and measure the resistance of the underlying tissue. These measurements allow us to generate a 3-D map of the breast, with abnormalities indicated as areas of higher resistance/impedance. This radiation-less technique, termed Electrical Impedance Tomography (EIT), aims to solve the problems associated with mammography while enhancing early detection capabilities.
(Invited) Reference Materials 8096 and 8097 - The Microelectromechanical Systems 5-in-1 Reference Materials: Homogeneous and Stable
Authors: Cassard Janet , Geist Jon , Kramar John
Published: February 2020

The NIST Microelectromechanical Systems (MEMS) 5-in-1 Reference Materials (RMs) were developed to assist users in validating their use of five documentary standard test methods. A Reference Material can be defined as a material whose property values are sufficiently homogeneous, stable, and well established such that the values can be used in the assessment of a measurement method. This paper presents the data that are used to characterize the RMs as homogeneous and stable.
Impact of Thermal History on Grain Size and Grain Size Distribution of Thermally Cycled Cu-Tsvs
Authors: Marro James Brandon , Okoro Chukwudi A , Obeng Yaw S. , Richardson Kathleen A
Published: February 2020

Through silicon vias (TSV) are copper (Cu) interconnects used in three dimensional integrated circuits (3D-IC) and other packaging to allow inter-chip communication. Since Cu is anisotropic, understanding the evolution of microstructure in TSVs is of major importance as it can influence the Cu’s electrical properties, such as resistance and electro-migration resistance, as well as mechanical properties. These properties can affect the materials response to thermo-mechanical stresses undergone by Cu-TSVs. Microstructural studies have focused on isothermal holding temperatures and times to imitate fabrication conditions [1-3], however, in-use conditions, which are typically of lower temperatures and higher frequencies to replicate thermal cycling over a chip’s lifetime, have not been greatly explored. This study correlates simulated in-use cycling parameters, such as cycling temperature and number of cycles, to microstructural changes, specifically grain size, observed in the Cu of TSVs. Silicon (Si) chips containing blind Cu-TSVs underwent 2000 thermal cycles from room temperature to maximum temperatures of 100 °C, 150 °C, or 200 °C. Grinding, polishing, and focus ion beam (FIB) milling were used to cross-section the TSVs and provide sufficient surface quality for electron backscattering diffraction (EBSD) to evaluate microstructural changes from thermal cycling. The average grain size remained around 3 μm and no significant differences were documented for average grain sizes along the length of TSVs before and after cycling. Furthermore grain size distribution also, showed little change with peaks around 1 μm for samples containing minimal voiding and approximately 2.5 μm for samples with significant pre-existing voids. While the low cycling temperatures used in this study are indicative of the conditions used in a majority of applications, they are too low to activate grain boundary migration and cause much microstructural changes in the Cu-TSVs.

References:

1. C. Okoro, R. Labie, K. Vanstreels, A. Franquet, M. Gonzalez, B. Vandevelde, E. Beyne, D. Vandepitte and B. Verlinden, Journal of Materials Science, 46 [11] 3868-3882 (2011).

2. A. Heryanto, W. N. Putra, A. Trigg, S. Gao, W. S. Kwon, F. X. Che, X. F. Ang, J. Wei, R. I Made, C. L. Gan and K. L. Pey, Journal of Electronic Materials, 41 [9] 2533-2542 (2012).

3. H. Shin, B. Kim, J. Kim, S. Hwang, A. Budiman, H. Son, K. Byun, N. Tamura, M. Kunz, D. Kim and Y. Joo, Journal of Electronic Materials, 41 [4] 712-719 (2012).
Development of 3-D Chemical Mechanical Polishing Process for Nanostructuring of Bioimplant Surfaces
Authors: Ozdemir Zeynep , Orhan Orcun , Bebek Ozkan , Basim G. Bahar
Published: February 2020

This study focuses on the development of a three dimensional chemical mechanical polishing (CMP) process to induce smoothness or controlled nano-structures on the bio-implant material surfaces, particularly for an application on the dental implants. CMP helps produce implant surfaces that are cleaned from potentially contaminated surface layers by removing a nano-scale top layer during the process. Simultaneously, it creates a protective oxide film on the surface to limit any further contamination to minimize risk of infection [1]. Furthermore, the process can induce controlled surface topography. Therefore, we propose CMP as a synergistic method for nano-structuring of implant surfaces. In our earlier work, we have demonstrated that the CMP induced controlled surface roughness on the titanium based bio-materials helped control the infection resistance through formation of a self-protective titanium oxide film on the implant surfaces [2]. Yet, it is critical to be able to extent these findings to a 3-D platform to make the dental implants processed by CMP application.

The 3-D CMP process is established through use of robotics and control systems by integrating a robotic arm to the sample to be polished through a force-torque sensor. This technique, once programmed, can induce the same force on the various regions of the bio-implant sample and effectively smoothen or nano-structure the alternative surfaces on the implant. Considering the wide applications [3] of the implants as dental implants, orthopedic devices, cardiac pacemakers and catheters, this new application of CMP is believed to help create a new market for the process.

References:

Basim, G.B., Karagoz, A., Ozdemir, Z., “Characterization of Chemically Modified Thin Films for Optimization of Metal CMP Applications”. MRS Online Proceedings, 1560 (2013) DOI: 10.1557/opl.2013.876.

Basim, G.B., Ozdemir Z., Mutlu, Özal “Biomedical Applications of Chemical Mechanical Polishing" Proceedings of the International Conference on Planarization/CMP Technology, pp. 385, October 2012

Shirkhanzadeh, M., Azadegan, M., Liu, G. Q., Mater. Lett., 24 (1995) 7-12.
Effect of La Doping of Ceria Abrasives on STI CMP Selectivity
Authors: Bulusu Venkata Sesha Praveen , Park Jin-Goo , Ramanathan S
Published: February 2020

Shallow trench isolation (STI) is used to isolate the transistors in an integrated chip and chemical mechanical planarization (CMP) is a key step in the STI integration scheme [1]. Ideally a high silicon dioxide removal rate and a low silicon nitride removal rate (i.e. high selectivity) is needed. High selectivity can be achieved when amino acids such as L-proline are used as additives along with ceria abrasives [2-3] but they do not work well with other abrasives [4]. Even when ceria is used as abrasive high selectivity is not observed in some cases [5].

In the present study, ceria is synthesized using sol gel and liquid phase synthesis (LPS). Polishing experiments are done on different ceria abrasives with same additives. To study the effect of impurity on polishing, lanthanum is added to ceria during the synthesis stage. The polishing results show that ceria without any impurity give high selectivity with L-proline while ceria with lanthanum as impurity does not give high selectivity.

To compare the results of polishing, commercial ceria with high and low purity obtained from sigma aldrich (ceria-SA) are considered for polishing experiments. Polishing with commercial ceria show similar results obtained with synthesized ceria. The ceria particles both commercial and synthesized were characterized by x-ray diffraction, energy dispersive spectra and scanning electron microscopy techniques. Polishing experiments were also conducted with milling the commercial ceria to evaluate if the size of ceria abrasive plays a role in modifying the selectivity.

References:

[1] J.M. Steigerwald, S.P. Murarka, R.J. Gutmann, Chemical Mechanical Planarization of Microelectronic Materials, John Wiley & Sons, New York, 1997.

[2] W.G. America, S.V. Babu, Electrochem. Solid-State Lett. 7 (2004) G327 – G330.

[3] R. Srinivasan, S.V. Babu, W.G. America, Y.-S. Her, US Patent 6,468,910 B1 (2002).

[4] R. Manivannan, S. Ramanathan, Microelectron. Eng. 85 (2008) 1748 - 1753.

[5] P.W. Carter, T.P. Johns, Electrochem. Solid-State Lett. 8 (2005) G218 – G221.
(Invited) Spatial ALD, Deposition of Al2O3 Films at Throughputs Exceeding 3000 Wafers per Hour
Authors: Granneman Ernst H.A. , Kuznetsov Vladimir I. , Vermont P.
Published: February 2020

During the last few years various types of ALD films have successfully been introduced in high-volume manufacturing in a number of industries. Particularly in the semiconductor industry the implementation is wide spread (high-k gate stacks, capacitor dielectrics, diffusion barriers, etc.).

More recently a specific type of ALD film, Al2O3, was widely researched as a potential surface passivation layer for solar cell surfaces in the PV industry. Thin (< 10nm) Al2O3 films passivate p-type surfaces very effectively. On the one hand intrinsic negative charges in the dielectric film repel charge carriers, while on the other hand hydrogen that is present in the ALD films passivates dangling bonds at the Si/SiO2/ Al2O3 interface. The combination of both effects reduces the charge recombination losses considerably. The overall result is an increase in cell efficiency of 0.5-1% (absolute). Based on extensive testing of these films, it is to be expected that Implementation in PV manufacturing will take place in the near future.

There is a large difference in film and process requirements of ALD films applied in the semiconductor and PV industries. Whereas uniformity and defects (particles) are very important in the IC industry this is much less so in PV. Much more important in the PV industry are cost and throughput. Typical numbers for both industries are a Cost of Ownership of 2-10 vs. 0.02-0.05$/wafer, respectively, and 10-50 vs 1500-2500 wfrs/hr..

As ALD processes are notoriously slow, ways must be found to increase the throughputs considerably. This is done by either using batch furnaces loaded with 500-1000 wafers per batch, or in-line systems in which wafers are loaded, processed and unloaded in a continuous flow of 0.5-0.8 wafers/s.

The latter type of system is based on the so-called spatial ALD process. An example is shown in the figure. In this system (Levitrack) wafers are loaded in a track in which zones with precursors TMA and H2O are spatially separated by zones of inert gas. While floating on a gas cushion, the wafers pass ALD ‘cells’ with fixed sequences of TMA and water, adding a thin layer of Al2O3 with each passage through a cell. The advantages of this approach are several: high throughput, atmospheric processing, no deposition on the inside walls of the track, no moving parts such as valves, pumps, etc.

Typical results obtained with this system are: film uniformity 3-4%, life time of solar cell charge carriers > 3ms, efficiency enhancement 0.4-0.8%, CoO ~ 0.04$/wfr.

In the paper more details will be provided on the economy of this type of system, as well as on film characteristics and efficiency enhancements realized in a variety of solar cell structures.
Optochemical Self-Organisation of Functional Microstructures
Authors: Saravanamuttu Kalaichelvi , Hosein Ian Dean , Lin Hao , Ponte Matthew R , Basker Dinesh Kumar
Published: February 2020

Our group previously reported an optochemical organization route to 3-D optical and microstructural lattices that combines the spontaneity of self-organisation to the precision and directionality of lithography. This method exploits the inherent instability of a broad, uniform beam of white light propagating in a photopolymer and its consequent division into identical filaments of light. By imposing spatially controlled noise on the light beam, the self-organizing filaments can be coaxed into 2-D and 3-D lattices. Unlike any other known self-organised or lithographically constructed structure, these lattices comprise functional, multimode and multi-wavelength cylindrical waveguides.

The objective of the work presented here is to apply multidirectional waveguide lattices (MWGLs) as wide-angled, light-capturing coatings that increase the intensity of light that is incident on optical devices including photovoltaic (PV) cells. Our approach is strongly motivated by the fact that even small increments of energy conversion efficiency (<1%) of PV modules are critical in the field. Furthermore, wide-angled, light-capture could eliminate (expensive) mechanised rotation of solar panels to track the Sun’s diurnal trajectory. We employ optochemical organization to prepare elastomer films comprising up to 5 intersecting arrays of waveguide lattices, which are oriented over a large range of angles with respect to the surface normal. When integrated into solar cell devices for example, the MWGLs could capture light seamlessly over a large range of angles and deliver intensity to the photovoltaic module and in this way, could increase conversion efficiencies.
Label-Free and Real-Time Photonic Sensors As Analytical Platforms for Environmental Monitoring of Pollutants and Medical Diagnosis
Authors: Marsal Lluis F. , Alba Maria , Macias Gerard , Formentin Pilar , Ferre-Borrull Josep , Pallares Josep , Santos Abel
Published: February 2020

Nowadays, most diagnostic techniques employ labelled samples with fluorescent markers, making analyses time-consuming and expensive. Recently, the development of highly sensitive and label-free nanoporous-based sensors has shown promising results for applications in areas such as environmental science, biomedical research and medical diagnostics [1-2]. Among the variety of possible materials, nanoporous anodic alumina (NAA) and nanoporous silicon (NPSi) have demonstrated to be excellent sensing platforms by their outstanding set of properties and cost-effective fabrication processes [3-4]. Optical and photonic properties as reflectance, transmittance, absorbance and photoluminescence can be structurally engineered by modifying the effective medium of these nanoporous materials [5-6]. Furthermore, further chemical functionalization endows these nanoporous platforms with chemical selectivity for detection of specific analytes.

In this scenario, herein, we present some strategies for the production of label-free optical sensors based on NAA and NPSi. These strategies are based on the design and fabrication of specific nanoporous structures with enhanced optical response (e.g. microcavities, Fabry-Pérot structures, filters, etc.) and additional chemical functionalization of the inner surface to make these nanostructures sensitive to specific analytes. Figure 1 shows some scanning electron microscopy (SEM) images of NPSi and NAA structures. Furthermore, we analyze and discuss different detection techniques such as reflectometric interference spectroscopy, photoluminescent spectroscopy and test their performance in the detection of proteins and heavy metal ions. Finally, we discuss about the future and potential applications of these sensing platforms in areas such as environmental monitoring, biotechnology, medical diagnostics, drug screening, food safety and security.

References

[1]Amarie, D., Glazier, J.A., Sensors, 2012, 12, 17262.

[2] Rapp, B.E., Gruhl, F.J., Länge, K., Analytical and Bioanalytical Chemistry, 2010, 398, 2403.

[3] Sailor, M.J., Wu, E.C., Advanced Functional Materials, 2009, 19, 3195.

[4] Md Jani, A.M., Losic, D., Voelcker, N.H., Progress in Materials Science, 2013, 58, 636.

[5] Santos, A., Macias, G., Ferré-Borrull, J., Pallarés, J., Marsal, L.F., ACS Applied Materials & Interfaces, 2012, 4, 3584.

[6] Kumeria, T., Santos, A., Losic, D., ACS Applied Materials & Interfaces, DOI: 10.1021/am403465x.

Acknowledgements

This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) under grant No. TEC2012-34397 and AGAUR 2009 SGR 549.
Design of Extremely Proximity Gettering Using Hydrogen Ion Implantation for Si CMOS Image-Sensor
Authors: Kim Il-Hwan , Park Jun-Seong , Song Seung-Hyun , Park Joo-Hyeong , Park Jea-Gun
Published: February 2020

As the pixel size in CMOS image-sensor has scaled down less than 1 μm, photo sensitivity which is a ratio of photo and dark current has been important. To improve photo sensitivity in CMOS image-sensor, the achievement of lower dark current is essential. Leakage current is influenced by crystallographic, trapped charge at the SiO2/Si interface, structural defects, and especially metallic contaminant impurities. Also, these contaminant impurities degrade the minority-carrier recombination lifetime.

Thus, we investigated the dependency of the properties of CMOS image-sensor on metallic contamination. Standard aqueous solutions of metallic ion were dropped on the surface of silicon wafers and the wafers were spin dry. They were heated to drive the metallic ion contaminants into the silicon bulk. After that, we fabricated 4-Tr CMOS image-sensor cells. In silicon bulk wafer, the minority-carrier recombination lifetime decreased with increasing a metallic contaminant concentration. These contaminations result in degradation of dark current, sensitivity of photodiode and sensing margin of CMOS image-sensor. These results indicate that metallic contaminants are critical for increasing dark current because metallic contaminants remain inside the photo-diode region, ~3 μm.

In our study, we applied a proximity relaxation-type gettering method. We formed the nano-cavities close to the depletion region using hydrogen ion implantation, as shown in Fig 1. These cavities getter metallic impurities on the cavities wall. Sensing margin of CMOS image-sensor implanted by hydrogen ion was dramatically improved, as shown in Fig 2. In addition, although metallic contaminant concentration increased, the device performances of CMOS image-sensor were constant compare with that of bulk wafer which were not implanted (Fig. 3). These results indicates that proximity gettering by using hydrogen ion implantation was effective in metal gettering for image-sensor. We investigated the correlation of metallic contaminant and sensing margin of CMOS image-sensor. Finally, we will suggest an extremely proximity gettering method for removing metallic contaminants of CMOS image-sensor.

* This work was financially supported by the Brain Korea 21 Plus Program in 2013 and SiWEDS (Silicon Wafer Engineering and Defect Science).
(Invited) High Brightness, Large Scale GaN Based Light-Emitting Diode Grown on 8-Inch Si Substrate
Authors: Lee Seung-Jae , Park Hyung-Jo , Park Jun-Beom , Jeon Dae-Woo , Baek Jong Hyeob , Li Hongwei , Krishnan Balakrishnan , Su Jie , Paranjpe Ajit , Lee Dong S.
Published: February 2020

GaN based light-emitting diodes(LEDs) grown on a Si substrate is one of promising future technologies in LED industry due to its scalability and costeffectiveness compare to the conventional sapphire based LEDs.One of major technical issues in GaN/Si LED is the severemismatch oflattice and thermal expansion coefficientsbetween GaNand Si, which induces significant tensile strain in the GaNepilayer that often leads to wafer cracking. Optical loss by the absorbing Si substrate is another barrier to overcome for realizing high-brightness LEDs competitive to those on sapphire or SiC substrates.

In this study, we demonstrated blue LEDs grown on 8-inch diameter Si substrate and fabricated high brightness devicesutilizing vertical chip process Thecrack-free InGaN/GaN LED waferswith strain-engineered buffer structure were grown on 8-inch diameter Si(111) substrates by metalorganic chemical vapor deposition (MOCVD) system (Veeco TurboDisk k465i).The optimized growth conditions of AlN buffer layer improved the crystalline quality of GaNepilayers. The FWHM of (002) and (102) ω-scan is 280 and 420 arcsec, respectively. These values are comparable to the best reported so far for GaN on silicon. The surface morphology of GaN layer investigated using atomic force microscopy (AFM) exhibits very smooth surface and clear atomic step flow patterns. The root-mean-square (RMS) roughness is 0.15 nm in a 5x5 μm2 scan area.For LED on 8-inch Si, MQW PL wavelength uniformity of ~0.5% (2.4 nm) has been achieved using the proper strain/curvature engineering with optimized wafer carrier designs. These are among the lowest values reported to date.

After the epitaxial growth with silicon substrate, a 1mm × 1mm sized vertical type LED(VLED) was fabricated using both wafer bonding process and Si removing process. While the GaN on sapphire employs a laser lift-off technique to remove the substrate, we developed the wet etching process in order to remove the silicon substrate without any damageon the surface of LED structure. The electro-optical characteristics of the fabricated VLED in this work shows good efficiency(almost 1W light power at 1A inject current) with operating voltage of 4.0V.