bluuebunny/crossref_metadata_2025 huggingface dataset:
DFT Study of Oxygen Reduction Reaction on Pt-Zr Catalysts
Authors: Merinov Boris V , Tsai Ho-Cheng , Yu Ted H , Goddard William A
Published: February 2020

The sluggish oxygen reduction reaction (ORR) kinetics at cathode and expensive Pt electrocatalysts are two main issues that retard fuel cell technology commercialization.1-3 To overcome these problems, alloying Pt with transition metals, core-shell structures, and non-Pt catalysts are applied to improve the catalytic activity and reduce the catalyst cost.4-8 It was found that Pt3Ni, Pt3Co, and Pt3Fe have better activity than pure Pt.9-11 However, stability of these alloys needs to be improved. Pt3Zr, Pt3Y, Pt3Sc show greater stability and high catalytic activity,9,10,12but these materials need further experimental and theoretical investigations.

We used DFT calculations to study the origins of the better ORR performance and greater stability of Pt-Zr catalysts. To accurately evaluate the activity of Pt-Zr catalysts, we examined binding energies of ORR intermediates and reaction energy barriers for ORR steps both in gas phase and solution. Based on the results obtained, ORR mechanisms on Pt-Zr catalysts will be considered and compared to pure Pt and Pt alloys. Some related experimental results will be discussed as well.

Acknowledgement. This work is financially supported by the National Science Foundation (grant CBET-1067848).

References

1. K. Kordesch and G. Simader, Fuel Cell and Their Applications, VCH: New York (1996).

2. R. P. O'Hayre, S. W. Cha, W. Colella and F. B. Prinz, Fuel Cell Fundamentals, John Wiley and Sons: New York (2006).

3. A. J. Appleby and F. R. Foulkes, Fuel Cell Handbook, Van Nostrand Reinhold: New York (1989).

4. R. Bashyam and P. Zelenay, Nature, 443, 63 (2006).

5. M. K. Debe, Nature, 486, 43 (2012).

6. R. Othman, A. L. Dicks and Z. Zhu, Int. J. Hydrogen Energy, 37, 357 (2012).

7. H. Yang, Angew. Chem. Int. Ed., 50, 2674 (2011).

8. B. Wang, J. Power Sources, 152, 1 (2005).

9. J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff and J. K. Norskov, Nat Chem, 1, 552 (2009).

10. V. Stamenkovic, B. S. Mun, K. J. J. Mayrhofer, P. N. Ross, N. M. Markovic, J. Rossmeisl, J. Greeley and J. K. Nørskov, Angew. Chem., 118, 2963 (2006).

11. V. R. Stamenkovic, B. S. Mun, M. Arenz, K. J. Mayrhofer, C. A. Lucas, G. Wang, P. N. Ross and N. M. Markovic, Nature materials, 6, 241 (2007).

12. S. J. Hwang, S. K. Kim, J. G. Lee, S. C. Lee, J. H. Jang, P. Kim, T. H. Lim, Y. E. Sung and S. J. Yoo, J. Am. Chem. Soc., 134, 19508 (2012).
New Spectroscopic Methods for Characterizing Single-Walled Carbon Nanotubes
Authors: Weisman R. Bruce , Streit Jason K. , Bachilo Sergei M. , Ghosh Saunab
Published: February 2020

Many important photophysical properties of SWCNTs remain inadequately determined, including (n,m)-specific absorption cross sections, emissive quantum yields, and fluorescence action cross sections. A major challenge has been quantifying structure-specific SWCNT concentrations in dispersed mixed samples. We have used short-wave IR fluorescence microscopy to image and count individual nanotubes within known volumes of structurally sorted samples, thereby directly finding (n,m)-specific particle concentrations. Separate measurements of the length distribution and bulk absorbance then give absolute absorption cross sections per SWCNT carbon atom. We find cross sections that are inversely related to nanotube diameter. E11 cross sections are larger for mod 1 species than for mod 2, whereas the opposite pattern is found for E22 transitions.

We also describe a new experimental method, Spectral Analysis of Fluorescence Fluctuations (SAFF). Here, long sequences of millisecond-scale emission spectra are captured from dispersed SWCNT samples that are dilute and thin enough to show clear intensity variations reflecting statistical variations in the numbers of nanotubes inside the small probed volume. Unlike normal fluorescence correlation spectroscopy, the SAFF method is spectrally resolved. The set of sequentially measured spectra is analyzed to reveal relative abundances of (n,m) species, isolate emission spectra of single species from complex mixtures, and sensitively monitor the presence of small SWCNT aggregates through spectral cross-correlations.

Reference

J. K. Streit, et al., Nano Letters 14
, 1530 (2014).
Invited: Atmospheric-Pressure Plasmas Processes for Third Generation Photovoltaics
Authors: Mariotti Davide , Askari Sadegh , Mitra Somak , Svrcek Vladimir , Belmonte Thierry , Maguire Paul
Published: February 2020

Non-thermal atmospheric pressure plasmas (APPs) have attracted great interest due the potential cost reductions in manufacturing and processing of materials for a wide range of applications [1]. Although APPs present several challenges, considerable progress has been achieved in recent years with an increasing number of industrial and commercial applications utilizing different forms of APPs. One of the most attractive application of APPs is for the synthesis and processing of nanomaterials with specific focus on materials for energy applications.

In this contribution we will present recent advances in both the synthesis and surface engineering of quantum confined silicon-based nanoparticles [2-5]. In particular we will discuss a range of synthesis methods that rely on atmospheric pressure plasmas for producing crystalline silicon nanoparticles as well as alloyed silicon-tin nanoparticles; these will include laser-produced plasmas, rf-APPs and plasmas in liquids. The analysis will include, in some of the cases, theoeretical models that highlight key mechanisms of nanoparticle heating [6].

We will then discuss the integration of silicon-based nanoparticles in photovoltaic devices, demonstrating their contribution as down-converters and/or as part of the active layer. In this context we will show how APP-based surface engineering can offer great opportunities for tailoring surface properties of the nanoparticles. Device parameters will be presented and analysed for different device architectures.

Finally, tha applicability of APPs in different aspect of photovoltaic device fabrication will be discussed presenting opportunities and challenges for large scale nanomanufacturing.

Acknowledgement

This work was partially supported by a NEDO project, the Royal Society International Exchange Scheme (IE120884), the Leverhulme International Network (IN-2012-136) and EPSRC (EP/K022237/1). DM also acknowledges the support of the JSPS Bridge Fellowship. SM and SA thank the financial support of the University of Ulster Vice-Chancellor Studentship.

References

[1] Mariotti D et al. J. Phys. D Appl. Phys. 43 (2010) 323001

[2] Mariotti D et al. Adv. Funct. Mater. 22 (2012) 954

[3] Švrček V et al. Appl. Phys. Lett. 97 (2010) 161502

[4] Švrček V et al. Chem. Phys. Lett. 478 (2009) 224

[5] Levchenko I et al. Carbon 47 (2009) 2379

[6] Askari S et al. Appl. Phys. Lett. submitted
Invited: Nanopartilce Composite Plasma CVD Films and Some Applications
Authors: Shiratani Masaharu , Koga Kazunori
Published: February 2020

Nanoparticle composite films contains nanoparticles to tune optical, electrical, and mechanical properties of the films. Contribution of nanoparticles nucleated homogenously in reactive plasmas to formation of film structure is commonly discarded, because flux of nanoparticles to film surface is low and heterogeneous reactions on film surfaces are believed to determine predominantly the film structure. Here we overview nanoparticle formation in reactive plasmas [1] and then we show three examples in which nanoparticle flux can modify significantly film structure and hence film properties. The first example is a-Si:H. A-Si:H p-i-n solar cells show a performance degradation under prolonged light illumination. It is widely accepted that this effect is related to the creation of metastable defects. We have succeeded in depositing highly stable a-Si:H films using a multi-hollow discharge plasma CVD method by which the volume fraction of amorphous Si nanoparticles in films deposited in the upstream region is significantly reduced by driving clusters towards the downstream region [2, 3]. Conventional a-Si:H films contain a few % of amorphous Si nanoparticles in their volume, whereas our stable a-Si:H films contain less than 0.01%. The second example is Ge nanoparticle films. We report electrical power generation of Ge quantum-dot (QD) sensitized solar cells with rectification in a TiO2/Ge/polysulfide electrolyte system. We analyzes the effect of adding Sn in Ge films on device performance, where a band-gap Eg value of Ge1-xSnx alloys is tunable from 0.34 < Eg < 0.61 eV for Sn composition ratio x = 0.06 to 0.15[4,5]. The third example is porous low-k film. We have succeeded in depositing porous films with relatively high young modulus by depositing “isolated nanoparticles” [6]. Nanoparticles can be employed as another tuning knob of film structure control.

Work supported by MEXT, JSPS, JST, NEDO, and PVTEC.

[1] M. Shiratani, et al., J. Phys. D: Appl. Phys., 44, 174038 (2011).

[2] M. Shiratani, et al., MRS Proc. 1426 (2012) DOI:http://dx.doi.org/10.1557/opl.2012.1245.

[3] Y. Kim, et al., Thin Solid Films 523, 29 (2012).

[4] G. Uchida, et al., Jpn. J. Appl. Phys. 51, 01AD01 (2011).

[5] H. Seo, et al., Electrochim. Atca 87, 213 (2013).

[6] S. Nunomura, et al., Jpn. J. Appl. Phys., 44, L1509 (2005).
Application of Anodizing Method Templates for Electrochemical Capacitors
Authors: Park Soo-gil , Choi Jin-Kwon , Yi Hyeon-Seok , Kim Hongil , Kim Han-Joo
Published: February 2020

Introduction

Lithium ion batteries (LIBs) and electro double layer capacitors (EDLCs) are regarded as electrical energy storage systems (ESS). LIBs are high energy density, but EDLCs have low energy density general information. The lithium ion capacitor (LIC) has advantages of LIBs and EDLCs. LIC has high energy density, high power density and high safety than LIBs. LIC comprises of a cathode electrode; active carbon, anode; graphitized carbon. It is similar to LIB and EDLC.

Porous anodic oxide films of aluminum (anodic porous alumina) have been widely investigated as nano templates and resist-films with good insulating properties for various micro and nano technology applications, such as magnetic recording media, electronic devices, biosensors, photonic crystals, micro lens arrays, plasmonic devices, three-dimensional microstructures and other basic nano-devices. When aluminum is anodized in appropriate acidic electrolytes, porous alumina develops, which exhibits a uniform array of hexagonal cells, each containing a uniform cylindrical nano-pore at the center.

In this study, we prepared carbon nano fibers (CNFs) by anodizing method on anodized alumina oxide (AAO) templates that were anodized in oxalic acid at 40V or phosphoric acid at 195V. These two types anodizing conditions determine the pore size of AAO and diameter of CNF. Mixture of anodic porous templates and PAA was carbonized in nitrogen at 600°C. The CNFs were heated up to 1400°C to increase the crystalline.

Experimental

We have discussed the effect of diameter change of CNFs on the electrochemical properties as an anode material in LICs. CNFs were prepared by carbonization using precursors with the polymer. Surface morphology of AAO templates and prepared CNFs were investigated by scanning electron microscopy (SEM) and Transmission electron microscopy (TEM). The physical properties were performed by X-ray diffraction (XRD) and nitrogen gas adsorption measurements.

The electrode was prepared by slurry type. Electrochemical properties were evaluated that cyclic voltammetry (CV), electrochemical impedance spectroscope (EIS) and charge-discharge test.

Result & Discussion

Figure 1 shows the SEM images of Anodized Alumina Templates, (a) anodized at phosphoric acid, (b) anodized at oxalic acid

Figure shows SEM images of the AAO templates after pore-expansion treatment with 2nd anodized AAO templates at different electrolyte. The results of the electrolyte change bring result that change of pore size of AAO templates can be seen clearly. and we can prepared that the CNFs by AAO template shows a well-ordered diameter. The CNFs were heated up to 600, 1000, and 1400°C to increase the crystallite degree. As results, we confirmed that CNF has become platelet structure.
Examining the Charge Storage Mechanisms of Materials Used in Electrochemical Capacitors Using Electrochemical Impedance Spectroscopy
Authors: Donne Scott W , Dupont Madeleine F
Published: February 2020

Electrochemical capacitors are a type of energy storage device which are characterised by their high specific energy, fast discharge rates and high cyclability. Electrochemical capacitors store energy in the electrical double layer which is formed at an electrode-electrolyte interface under an applied potential. These electrodes do not undergo any faradaic reactions and as a result, can charge and discharge very quickly and do not degrade significantly during cycling.

Pseudo-capacitors are a type of electrochemical capacitor in which the electrodes exhibit fast, highly reversible redox reactions in addition to double layer charging. This pseudo-capacitance increases the charge storage capabilities of these devices.

Electrodes used for electrochemical capacitors rely on high surface area materials to provide high capacitance, such as activated carbon. Whereas pseudo-capacitors utilise materials which can undergo fast redox reactions without causing any compositional or phase changes in the electrode, such as ruthenium dioxide and manganese dioxide.

Typically, electrochemical performance analysis of electrodes is conducted using potential sweep (cyclic voltammetry) or constant current charge discharge methods. These techniques provide a total capacitance for the electrode but do not allow for extensive analysis of the charge storage mechanisms. This is evident in the similar cycling behaviour of activated carbon, ruthenium dioxide and manganese dioxide, despite these materials having significantly different charge storage mechanisms.

In this work, these methods are used in conjunction with electrochemical impedance spectroscopy (EIS) to separate the capacitance arising from double layer charge storage compared to that stored through pseudo-capacitance. Three commonly used electrode materials were examined, each known to have different capacitance and charge storage mechanisms: (1) activated carbon, which has purely double layer capacitance in the order of ~150 F/g [1], (2) ruthenium dioxide, which exhibits pseudo-capacitance at the surface (due to its high conductivity) resulting in capacitance of ~900 F/g [2] and (3) manganese dioxide, which is reduced and oxidized throughout the bulk of the material leading to extremely high capacitance of 2000 F/g [3] (for electrodeposited thin films) and 260 F/g [4](for powdered electrodes).

1. Beguin, F. and E. Frackowiak, eds. Supercapacitors Materials, Systems, and Applications. ed. M. Lu2013, Wiley-VCH: Weinheim.

2. Long, J.W., et al., Langmuir, 15 (1999) 780-784.

3. Cross, A., et al., Journal of Power Sources, 196 (2011) 7847-7853.

4. Yang, X.-h., et al., Electrochimica Acta, 53 (2007) 752-757.
Formation of Aligned Nanoporous/Nanotubular Layers of Vanadium Oxy-Nitrides
Authors: Kirchgeorg Robin , Yang Yang , Hahn Robert , Schmuki P.
Published: February 2020

This talk will present self-organized vanadium oxy-fluoride nanotubular layers grown by electrochemical anodization of vanadium in a [BF4]- electrolyte. In a thermal conversion of this amorphous VOxFy precursor structure in ammonia gas, aligned vanadium oxy-nitride (VOxNy) nanoporous/nanotubular layers could be formed. We established conditions to reach conversion of precursor structures to a well crystallized VOxNy nanotube structure, without the formation of any secondary phases or the collapse of the ordered morphology. The formed VON structures were investigated by SEM, EDX, XRD, XPS and electrochemical measurements for capacitor applications. The overall capacitance of the vanadium oxy-nitride structures showed a value of 250 F/g.

Reference:

Y. Yang, R. Kirchgeorg, R. Hahn, P. Schmuki Electrochemistry Communications, accepted
Electrochemical Characteristics of Cyclic Structure Additives in EDLCs
Authors: Park Soo-gil , Yi Hyeon-Seok , Choi Jin-Kwon , Yuk Young-Jae , Kim Han-Joo
Published: February 2020

Introduction

Electrochemical double-layer capacitor (EDLC) is on a rise as a kind of Energy storage system (ESS), nowadays.[1] EDLCs work by physical charge and discharge electrons at double-layer (also known as Helmholtz layer). Therefore, EDLCs have high power density and long cycle life, but energy density is very low.[2] The internal structure of EDLCs are consist of cathodic/anodic electrode, electrolyte and separator for prevention of short. Among of them, electrolyte is influence at internal resistance of EDLCs. Because of electrolytes were composed solvent and electrolytic salts.[3] So, we need to consider characteristics of solvent and salts. Characteristics of electrolyte are those; electrical stability, ion conductivity, viscosity, high temperature work, cell application.[4] Before papers are almost suggest cyclic structure carbonate as additives in PC, EC or AN-based electrolyte like DEC, DMC, etc. But GBL and PC addition can affirmative affects ion conductivity and potential stability.

In this study, we experiment additives for electrolyte in EDLCs. Especially, we focused on the cyclic structure solvents addition. The additive was used Tetrahydrofuran(THF), γ-butyrolactone (GBL) and Propylene Carbonate(PC). Furthermore, we applied electrolyte samples to EDLC cell.

Experiment

First of all, 1M TEABF4 in PC as reference, THF and GBL is added at propylene carbonate 0 to 30% by volume. In this process, whole salt concentration kept as 1M. Each concentration of sample was 5% interval.

Next, we approach PC addition to 1M SBPBF4 in AN. PC addition experiment goes same condition with upper experiment(0~30%, 5% interval).

As Electrochemical properties, Ion Conductivity and LSV were accepted. Ion conductivity determines almost specification of electrolyte. LSV shows electrical stability. Apply to EDLC unit cell, those examine was measured; CV, impedance, charge/dis-charge

Result& Discussion

THF and GBL addition shows low viscosity than pristine PC. By using THF and GBL, PC-based electrolyte can decrease viscosity. But THF has not enough electrical stability. In LSV results, yield point was decreased by THF addition. Theoretically, boiling point of GBL is 206°C and flash point is over 80°C. So, GBL addition is enlarge non-flammable properties.

Ion conductivity was observed by impedance. To suggest colligate property, the temperature range set 20°C to 80°C, and the interval is 10°C. By measuring LSV, current plateau area was detected that the area is stable potential range. GBL and PC addition gives electrical stability to Cell application shows overall effects at the electrolyte in EDLCs.

References

[1] R. Ko¨tz a, M. Carlen, Electrochimica Acta 45 (2000) 2483–2498

[2] P. Sharma, T.S. Bhatti, Energy Conversion and Management 51 (2010) 2901–2912

[3] S. Takeuchi, K. Miyazaki, F. Sagane, T. Fukutsuka, S.K. Jeong, T. Abe, Electrochimica Acta 56 (2011) 10450– 10453

[4] A. Laheaar, H. Kurig, A. Janes, E. Lust , Electrochimica Acta 54 (2009) 4587–4594
In-Situ Atomic Force Microscopy Studies of Ti3C2: A Promising New Material for Electrochemical Capacitors
Authors: Black Jennifer , Beidaghi Majid , Kalinin Sergei V. , Gogotsi Yury , Balke Nina
Published: February 2020

MXenes are a newly discovered class of two-dimensional materials prepared through extraction of metals such as Al from MAX phases, whose general formula is Mn+1AXn, where M is an early transition metal, A an A-group element, and X is carbon and/or nitrogen.[1-3] Ti3C2 is one member of this MXene family which is capable of capacitances of up to 350 F cm-3, making this an attractive material for electrochemical capacitors.[4] The high storage capacity of this material is attributed to rapid intercalation of electrolyte ions within the layered structure [Figure 1a]. In this work we use in-situ atomic force microscopy (AFM) to probe the macroscopic expansion of Ti3C2 during electrochemical cycling. The in-situ electrochemical AFM cell used for this study as well as the relative height change of a Ti3C2 electrode in 1 M KOH electrolyte are shown in Figures 1b and c. During negative polarization of the material K+ ions are incorporated into the Ti3C2 structure associated with a macroscopic expansion of the electrode. Studies are performed on various Ti3C2 electrodes in several electrolytes to determine the effect of different ions and electrode structure on the electrochemical behavior and observed strain response.

References:

Naguib, M.;Come, J.;Dyatkin, B.;Presser, V.;Taberna, P.-L.;Simon, P.;Barsoum, M. W.; Gogotsi, Y. MXene: a promising transition metal carbide anode for lithium-ion batteries. Electrochemistry Communications 2012, 16, 61-64.

Naguib, M.;Kurtoglu, M.;Presser, V.;Lu, J.;Niu, J.;Heon, M.;Hultman, L.;Gogotsi, Y.; Barsoum, M. W. Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Advanced Materials 2011, 23, 4248-4253.

Naguib, M.;Mashtalir, O.;Carle, J.;Presser, V.;Lu, J.;Hultman, L.;Gogotsi, Y.; Barsoum, M. W. Two-Dimensional Transition Metal Carbides. ACS Nano 2012, 6, 1322-1331.

Lukatskaya, M. R.;Mashtalir, O.;Ren, C. E.;Dall’Agnese, Y.;Rozier, P.;Taberna, P. L.;Naguib, M.;Simon, P.;Barsoum, M. W.; Gogotsi, Y. Cation Intercalation and High Volumetric Capacitance of Two-Dimensional Titanium Carbide. Science 2013, 341, 1502-1505.

Figure 1: a) SEM image of Ti3C2 working electrode. b) Photograph of in-situ electrochemical AFM cell. c) Cyclic voltammogram of Ti3C2 working electrode in 1 M KOH electrolyte and corresponding relative height change measured using in-situ AFM.
High Voltage AC/AC Capacitors Using the Carbon/Iodine Interface in Ionic Liquid Electrolyte
Authors: Frackowiak Elzbieta , Béguin François , Skowron Piotr
Published: February 2020

Lately we have demonstrated that huge pseudo-capacitive contributions can be originated from the electrolyte when using high surface area activated carbon electrodes, for example by using iodide based solutions in water [1]. Although the use of such concept allows very high capacitance values to be reached, the energy of the AC/AC capacitors based on these electrolytes is limited by the relatively low value of voltage inherent to use of water. Therefore, in this work, we have investigated the performance of the carbon/iodine interface in ionic liquid electrolytes, both protic (PIL) and aprotic (AIL).

The PILs selected were triethylammonium bis(tetrafluoromethylsulfonyl)imide [Et3NH]-[TFSI] and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide [Emim]-[FSI]. Organic iodides - triethylammonium iodide [Et3NH]-[I] and tetraethylammonium iodide [Et4N]-[I] at a concentration of 0.25 mol·L-1 and inorganic iodides (LiI and KI) at a concentration of 0.2 mol·L-1 were introduced in the ionic liquid. The electrochemical experiments as cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy were conducted using a two-electrode cell construction. In some experiments, a silver wire was added as pseudo-reference to monitor the potential of individual electrodes. Activated carbon (AC) activated by KOH (4:1) with high microporosity ( SBET = 2180 m2·g-1, Vmicro = 0.96 cm3·g-1, L0 = 1.55 nm) was used as working and counter electrode. Glass microfiber paper (Whatman) was utilized as separator.

Galvanostatic (0.2 A·g-1) cycling up to 1.8 V in two-electrode cell with reference electrode (Figure 1B) demonstrates a remarkable increase of capacitance when KI is added to [Et3NH]-[TFSI], from 122 to 184 F·g-1. The voltammograms of figure 1A show clearly that the increase of capacitance is caused by the positive electrode where faradaic processes occur. The capacitance values of the positive electrode for 0.25 mol·L-1 [Et3NH]-[I] and 0.2 mol·L-1 LiI dissolved in [Et3NH]-[TFSI] reached 199 and 238 F·g-1
, respectively; for the negative electrode the capacitance reached 163 and 121 F·g-1
, respectively. The addition of 0.2 mol·L-1 inorganic iodide to aprotic IL also enhanced the capacitance from 116 F·g-1 for the pure AIL to 129 and 153 F·g-1for the KI and LiI solutions, respectively. Regardless of the different type of iodide derivatives dissolved in IL medium, faradaic processes occur at the positive electrode greatly increasing the capacitance of the whole capacitor system. However, iodide solutions in PILs seem to be more effective than the AILs ones.

Acknowledgements:The Foundation for Polish Science is acknowledged for supporting the ECOLCAP Project realized within the WELCOME Program, co-financed from European Union Regional Development Fund.

References

[1] G. Lota, E. Frackowiak, Electrochem. Comm. 11 (2009) 87-90
Plasma Enhanced Atomic Layer Deposition on Powders
Authors: Rampelberg Geert , Longrie Delphine , Deduytsche Davy , Detavernier C.
Published: February 2020

Surface engineering of micro- and nanoparticles is of great importance in fields such as catalysis, energy and sensing. For many of these applications particles are required with different bulk and surface properties. A popular technique to achieve this is to coat the particle surface with a nanometer thick layer. Only a few techniques have been explored for depositing such thin conformal coatings. Chemical vapor deposition (CVD) has been used extensively for this purpose, but suffers from a lot of disadvantages, such as imperfect control over layer thickness and uniformity of the coating over all individual particles, particle agglomeration and formation of additional undesired particles due to gas phase reactions between the CVD reactants. In contrast, atomic layer deposition (ALD) is known as a reliable technique for covering complex 3D objects with ultrathin conformal coatings. However, to perform ALD on large quantities of powders, the individual particles need to be fluidized or agitated. Fluidized bed reactors are most often used for ALD on particles, but this reactor concept does not seem to be compatible with plasma enhanced ALD, which is advantages for e.g. coating on temperature sensitive polymer particles or deposition of metals and metal nitrides.

In this work, a rotary reactor was used to agitate particles, enabling the deposition of conformal coatings by thermal and plasma-enhanced ALD. Particles ranging from nanometer size to millimeter size were successfully coated with layers of Al2O3, TiO2, AlN and TiN.[1]In-situ mass spectroscopy confirmed that ALD was performed by detecting the expected reaction products. By monitoring the formation of these reaction products over time, it was possible to optimize precursor and reactant usage, which is linearly dependent on the effective surface area of the particles. In the case of plasma enhanced ALD, in-situ optical emission spectroscopy confirmed the mass spectroscopy data. X-ray fluorescence revealed the expected linear relationship between the amount of ALD cycles and the deposited amount of material, while X-ray photo-electron spectroscopy was used to confirm the composition and purity of the coatings. Transmission electron spectroscopy finally showed that the individual particles were coated uniformly and conformally. Our results prove that the proposed rotary reactor enables conformal deposition on nano- and micropowders by thermal and plasma enhanced ALD. In this way, surface engineering of such particles can be achieved.

[1] D. Longrie et al., Surface & Coating Technology 213 (2013) 183-191
Molecular Layer Deposition of Nanoscale Organic Films for Nanoelectronics Applications
Authors: Bergsman David , Zhou Han , Bent Stacey F.
Published: February 2020

The trend toward nanoelectronics motivates the development of new materials and processes. Novel organic materials are of interest for various applications, and this talk will focus on the development of nanoscale organic films for lithography and patterning. Current photoresist materials are facing many challenges introduced by advanced lithography, particularly the need for excellent compositional homogeneity and ultrathin film thickness. Traditional spin-on polymeric resists have inherent limitations in achieving a high level of control over the chemical composition, leading to interest in alternative methods for making photoresists. In this work, we demonstrate that molecular layer deposition (MLD) is a promising method for synthesizing photoresists because it allows for precise control over organic film thickness and composition. As an analogue to atomic layer deposition (ALD), MLD utilizes sequential, self-limiting reactions of organic precursors to build a thin film directly on a substrate surface. An advantage of MLD is that it grows organic films by depositing only one molecular layer at each precursor dose, which in turn allows for fine tuning of the position and concentration of various functionalities in the deposited film. In our study, we use bifunctional precursors, diamine and diisocyanate, to build polyurea resist films via urea coupling reaction. Acid-labile groups are embedded in the backbone of the diamine precursor and incorporated into the resist film with a highly uniform distribution. Two methods of incorporating photo acid generator (PAG) are employed. The first method is to soak a PAG into the resist film after deposition and the second approach is to form in-situ polymer-bound PAG. By this novel synthetic approach, both aromatic and aliphatic polyurea films were successfully deposited by MLD and characterized for both materials properties and resist response. Electron-beam lithographic tests are carried on the MLD photoresists. Among the various MLD films studied, the aliphatic film performed best as a photoresist material, with a good sensitivity of 30 µC/cm2 with 100kV e-beam exposure, and a patterned line resolution of sub-100 nm. Other uses of MLD for advanced patterning methods, as well as fundamental studies into the mechanism of MLD, will also be described.
Growth of Al Doped ZnO Thin Films by Atomic Layer Deposition Process
Authors: Zhang Kai , Chen Xin , Lin Pengtao , Obulreddy Santosh Kumar Reddy , Baumgart Helmut
Published: February 2020

ZnO is a transparent semiconductor with a wide and direct band gape of 3.37 eV, large excitonic binding energy of ~60 meV, high mechanical and thermal stabilities, and good electrical conductivity. Therefore, ZnO based materials are extensively investigated in spintronics, gas and biological sensors, solar cells, catalysts, electronics, piezoelectric devices and high-efficiency short-wavelength optoelectronic nanodevices. In solar cell application, especially Al doped ZnO (AZO) thin films have been extensively developed and investigated due to their low cost, high thermal stability, high optical transparency and high conductivity [1, 2 , 3].

Several methods have been applied to deposit ZnO thin films in the past, such as sol gel spin coating, magnetron sputtering, pulsed laser deposition (PLD), chemical vapor deposition (CVD), and atomic layer deposition (ALD). Among these, ALD is considered as a novel technique to deposit ZnO thin films, because it possesses self-limiting surface reactions in each ALD cycle, which consequently control the layer thickness with unprecedented atomic level precision, stoichiometry, composition, uniformity of large area and maintain excellent conformity of complex nanostructures. In addition, ALD process is able to introduce separately each precursor to react on the surface of the structure. The concentration of dopant in the ZnO films can be precisely controlled by the number of ALD cycles, so that the physical properties of AZO films, such as carrier density and conductivity, can be adjusted to meet the requirements of different applications.

In this study, Al doped ZnO thin films were deposited by the ALD technique with trimethylaluminium (TMA), diethylzinc (DEZ) and water vapor as aluminium, zinc and oxygen precursors, respectively. The films were grown in Savannah 100 cross-flow thermal ALD reactor. The growth temperature was maintained at 250 oC during the reaction. N2 was used as a carrier gas with a flow rate of 20 sccm. The ALD AZO films with various Al doping level were prepared by introducing TMA cycles once in every 30 pulses of DEZ and H2O injection.

The structural, optical and electrical properties of the AZO films prepared by using ALD processes were investigated. The crystal structure of ZnO was analyzed by X-ray diffraction (XRD). The AZO film surface morphology was inspected using a field emission scanning electron microscopy (FE-SEM). The surface roughness was analyzed by atomic force microscopy (AFM). The sheet resistivity of AZO films was determined by using four-point probe measurements. The optical reflection was carried out by UV-VIS-NIR spectrometer.

References:

P. Genevée, F. Donsanti, G. Renou, D. Lincot, Applied Surface Science 264, 464 (2013)

G. Luka, T. A. Krajewski, B. S. Witkowski, G. Wisz, I. S. Virt, E. Guziewicz, M. Godlewski, J. Mater. Sci: Mater. Electron 22, 1810 (2011)

J. W. Elam, D. Routkevitch, S. M. George, Journal of The Electrochemical Society, 150 (6) G339 (2003).
Design, Synthesis and ALD Assessment of Organometallic Precursors for Semiconductor Applications
Authors: Dussarrat Christian
Published: February 2020

While transistors continue scaling in both density and performance and as technological improvements allows dramatic cost reduction, the utilization of most performing transistors also requires most effective interconnects. The delays in interconnects are increasingly contributing to the overall circuit delays in a severe manner as dimensions shrink. New challenges are thus arising in processes for scaling and integration needed to obtain the required performances, including the usage of novel architectures at a change of semiconductor nodes. For example, one announced the implementation of FinFET structures, with the usage of vertical transistors, at 22nm, and several other players will follow ; ST Microelectronics and associated partners were successful in the implementation of FDSOI technology.

The new associated manufacturing challenges, especially the needs to deposit more conformal metallic thin films, can be translated as new opportunities to introduce the usage of organometallic materials in electronic industry. In order to perform that transition effectively for all the stakeholders involved, synergetic interactions need to occur between the chemical solution supplier that provides a new organometallic molecule and the corresponding screening test results, the equipment manufacturers that adapt and fine tune the process to the specification to its reactor and the chip manufacturers that validate the process and work on integration aspects.
The Effect of SPA-SiO2 Tunnel Oxide Thickness for Metal-Insulator-Silicon Photoelectrochemical Cells
Authors: Scheuermann Andrew G. , Lu David Q. , Ito Toru , Chidsey Christopher E.D. , McIntyre Paul C.
Published: February 2020

Photoelectrochemical cells are becoming increasingly attractive for the on-site production of clean chemicals and fuels, both as end-use products and as an integrated energy storage solution for mitigating the intermittency of solar radiation. One persistent challenge in this field is the difficulty of simultaneously achieving high photovoltaic efficiency and chemical stability of semiconductor photoelectrodes during water oxidation under wide-ranging pH conditions. Wide band gap semiconducting metal oxides are frequently stable under water oxidation conditions but have inherent photocurrent limitations. We have recently demonstrated that atomic layer deposition (ALD) of a thin and chemically-protective TiO2 layer can avoid oxidation of the surface of a silicon photoanode during long-duration oxygen evolution. Our initial work showed that it was possible to decouple efficient light absorption by the silicon anode from the oxygen evolution reaction (OER) occurring on the surface of a water oxidation catalyst layer by the presence of an interposed ALD-TiO2 layer. This conformal and pinhole-free oxide layer was found to be dense enough to block the solution from oxidizing the underlying semiconductor (greatly increasing its stability), but still thin enough to allow efficient hole transport between an n-type silicon substrate and the iridium OER catalyst [1]. In more recent work, we have showed that ALD-TiO2 could be used with a variety of other catalysts to produce efficient devices with more than 600mV of open circuit voltage, high saturation currents, and similar stability. In addition, by studying thicker ALD-TiO2 films, we found that protection could be increased with a minor increase in anode resistance. The additional resistance is associated with bulk conduction of electronic carriers through states in the TiO2 band-gap between the catalyst and anode [2]. Together, these findings indicate that atomic layer deposited coatings in metal-insulator-semiconductor (MIS) photoanodes serve as a general protection method for a variety of semiconductor-catalyst systems. In addition to summarizing prior reports and the most recent results on such MIS photoelectrodes, this presentation will touch on future directions for efficient artificial photosynthesis using ALD surface protection layers.

[1] YW Chen, J.D. Prange, et al. Nat. Mater. 2011, 10, 539-44.

[2] A.G. Scheuermann, et al. Energy Environ. Sci. 2013, 6, 2487 – 96.
Morphology of Oxygen Precipitates in RTA Pre-Treated Czochralski Silicon Wafers Investigated by FTIR Spectroscopy and STEM
Authors: Kot Dawid , Kissinger Gudrun , Schubert Markus Andreas , Sattler Andreas
Published: February 2020

Rapid thermal annealing (RTA) is a commonly used technique to control precipitation of oxygen in Czochralski silicon wafers (1,2). RTA pre-treatment leads to the formation of intrinsic point defects, mainly vacancies, which are responsible for the enhanced precipitation of oxygen. Oxygen precipitates are widely known as getter sites for metal impurities in the silicon microelectronic technology (3). The getter efficiency of oxygen precipitates depends on their density and morphology (4,5). The density of the precipitates can be controlled by the temperature of RTA and it can be easily determined by preferential etching. The morphology of oxygen precipitates depends on the type and the concentration of dopants, the thermal history, and the annealing temperature and time (6-8). Recently, it was shown that the supersaturation of vacancies impacts the morphology of oxygen precipitates (9). Since RTA pre-treatments introduce vacancy supersaturation in silicon wafers its usage before nucleation annealing could modify the morphology of precipitates compared to wafers without RTA. The morphology of oxygen precipitates can be determined by transmission electron microscopy, however the preparation of samples is demanding. An alternative is the Fourier transform infrared (FTIR) spectroscopy at liquid helium temperature, which also allows distinguishing different types of oxygen precipitates. The oxygen precipitates give rise to absorption bands in the range between 1000 and 1300 cm-1. There are two characteristic broad bands at 1095 cm-1 and at 1225 cm-1 which belong to spherical and plate-like precipitates, respectively (10-12). The sharp bands (1136 cm-1 and satellites and 1205 cm-1) are attributed to interstitial oxygen.

In this work, we investigate the morphology of oxygen precipitates by FTIR spectroscopy at liquid helium temperature and by scanning transmission electron microscopy (STEM) in silicon samples pre-treated by RTA at 1250°C for 30s in O2 containing Ar atmosphere subsequently annealed in the temperature range between 800°C and 1000°C in N2. The results show that the morphology of the oxygen precipitates in RTA pre-treated samples depends on the nucleation temperature. Fig. 1 presents absorption spectra of silicon samples pre-treated by RTA at 1250°C and annealed at 800°C (a), 900°C (b) and 1000°C (c) for 64h. As can be seen from the deconvolution of the spectra, the number and position of the bands is different for each annealing temperature. Based on the effective medium theory (EMT) (13) and STEM investigations the absorption bands can be matched to relevant morphologies.
Plasma Etch in the Era of Atomic Scale Fidelity
Authors: Lill Thorsten , Singh Harmeet , Kamarthy Gowri , Kanarik Keren J. , Cohen Andy , Eppler Aaron , Holland John , Fischer Andreas , Shen Meihua , Marks Jeff , Gottscho Richard A. , Vahedi Vahid
Published: February 2020

In IC manufacturing, the ultimate goal is to produce the structures that are conceived and modeled by design engineers in the real world with high fidelity. The term “fidelity”is chosen deliberately to express that what is needed in the end is the highest possible degree to which a material structure matches the design intent. It includes but is not limited to statistical criteria such as accuracy and precision.

Plasma etch plays a key role in obtaining structural fidelityin all three dimensions. Accuracy is obtained by control of proximity and 3D effects such as critical dimension (CD) loading, profile loading, aspect ratio dependent etching (ARDE), and selectivity. Precision, on the other hand, is obtained by means of wafer-to-wafer, chamber-to-chamber, and tool-to-tool matching.

Atomic scale fidelity is required as we approach devices with a half pitch of 10 nm and below because the device dimensions and their allowed tolerances are of the same order of magnitude as the inter-atomic distances in the crystal lattice. This type of performance can be obtained when the material is removed layer by layer. Each step in the etch process uses the simplest possible chemistry to surgically target specific reactions at the wafer surface such as activation, removal, and passivation. We call this layer-by-layer etch with atomic fidelity atomic layer etch /1/.

We will introduce the framework of high productivity, production-worthy atomic layer etch and discuss the implications for hardware and process development.

References:

Kanarik, et al., Solid State Technology, 56 (2013) 14-17.
Etch Challenges for 3D NAND Flash Technology
Authors: Khan Anisul Haque , Srinivasan Sunil , Choi Jinhan , Athayde Amulya , Achutharaman Raman
Published: February 2020

Current 2D NAND scaling is approaching technology limitation in both lithography and device performance arena. To address the lithography challenges at the 1x nodes and the well-known scaling issues associated with planar NAND, 3D flash technology is being developed and is expected to greatly reduce the lithography burden albeit shifting it to deposition and etch. The emerging 3D flash architecture requires depositing alternating layer stacks and then etching those stacked layers with extreme precision. Staircase etch for contact landing, hard mask etch, gate trench etch, channel hole etch and staircase contact etch are the main critical etches required to manufacture 3D flash device (Figure 1).

Plasma etching processes involved in the fabrication of 3D flash devices are becoming increasingly challenging. The staircase etch, which requires lateral resist mask etch followed by vertical stacked layer etch, repeated in multiple the lateral/vertical etch cycles, to form staircase shaped contact landing pads, offers unique challenges in lateral to vertical etch rate control of resist mask, resist mask shape control, selectivity control of the stacked layer etch, staircase step width control and step width uniformity control. Hardmask open, gate trench etch, channel hole etch, and staircase contact etch create significant challenges for etching, especially of high aspect ratio (HAR) features ranging in aspect ratio from 30:1 to >80:1. Furthermore, etching through the HAR alternating layer stacks intensifies the demands on the etch process, which must be capable of etching distortion free, vertical profiles free of bending, faceting and feature clogging. Additionally, smooth sidewall transitions in the alternating stack, and very high selectivity to the tiny pad are required, especially for the staircase contact etch application, which combines extreme simultaneous multi-level etch at aspect ratios ranging from 30:1 to >80:1 along with extremely high selectivity for negligible loss of the underlying contacted material.

In this paper we will present etch hardware and process development solutions provided to overcome these difficult etch challenges for staircase etch, hard mask open, gate trench etch, channel hole etch, and staircase contact etch applications to enable 3D NAND flash technology.
SiC Power Devices in a Soft Switching Converter, Including Aspects on Packaging
Authors: Ranstad Per , Bakowski Mietek , Tolstoy Georg , Lim Jang-Kwon , Giezendanner Florian , Ranstad Anton
Published: February 2020

In many applications of power electronic converters efficiency and size are important figures of merit. Low losses in the power semiconductors and high frequency operation are important factors. The converters considered in this paper are off-line powered and in the power range of 50 – 150 kW with a high-voltage dc-output. The switching frequency is 20-40 kHz. With modern IGBTs an efficient operation (n> 95%) can be obtained when using soft-switching topologies. Fig 1(a) shows the schematic diagram of an SLR, series loaded resonant converter [1]. In Fig 1(b) typical waveforms of transformer current and voltage are depicted.

In a recent paper, [2], frequency dependent IGBT losses are evaluated. Fig 2 shows the on-state voltage of an IGBT when conducting a sinusoidal current at different frequencies. At the higher frequency (30 kHz, Tr4) the increase of conduction losses is evident.

Power switches made from SIC show excellent properties enabling; low conduction losses, high frequency operation and an ability to operate at high die temperatures [3]. Fig 3 (a) shows the on-state voltage of an unipolar SIC switch while Fig 3(b) shows the on-state voltage of a bipolar switch. Measurements have been performed up to 200 kHz without showing any high-frequency effects.

High voltage SiC PiN diodes can replace several series connected Si diodes due to the higher critical field strength in SiC. This enables substantially reduced conduction losses in the output rectifier. In Fig 4 on-state voltages of 10 kV SiC and Si-diodes are shown, indicating a 50% reduction of losses.

References

[1] V. Vlatkovic, M. J. Schutten, and R. L. Steigerwald, “Auxiliary Series Resonant Converter: a New Converter for High-Voltage, High-Power Applications,” in Proc. of PESC -96, 1996.

[2] P. Ranstad, and H-P. Nee, “On dynamic effects influencing IGBT losses in soft switching converters,” IEEE Transactions on Power Electronics, vol. 26, No. 6, December 2010.

[3] P. Ranstad, H-P. Nee, J. Linner, and D. Peftitsis “An experimental evaluation of SiC switches in soft-switching converter,” IEEE Transactions on Power Electronics, 2014