bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation Mechanism of Alumina Nanotubes By Anodization of Aluminum Alloy
Authors: Ono Sachiko , Hashimoto Hideki , Asoh Hidetaka
Published: February 2020

Anodic porous alumina film, a typical self-ordered nanohole material formed by anodizing aluminum in an appropriate acidic solution, is used as a starting material of nanofabrication of functional devices besides a corrosion resistant surface oxide. In contrast to anodic titania nanotubes, anodic porous alumina is generally compact without spacing between the cell boundary. The tubular shape of anodic titania is resulted in enrichment of fluoride between cells which is originated form electrolyte and more soluble than anodic titania. In the case of aluminum, it is reported that enrichment of only sulfate or ethylene glycol originated form electrolytes produces alumina nanotubes by anodization. In the present paper, the formation mechanism of anodic alumina nanotubes will be discussed.

STEM image of vertical cross section prepared by ion-milling of the anodic film, which was formed on 99.99 % pure aluminum in oxalic acid at 160V, indicated close-packed hexagonal cell arrays with small voids of 15-20 nm at the triple cell points. Dark field STEM image clearly revealed a bright particle in the each void suggesting the presence of a heavy metal because of Z-contrast. By EDX point analysis, Cu enriched particles were found in the voids at the triple points. Nevertheless, in the case of anodic film formed at the similar condition on AC8A cast alloy including 0.97 % of Cu, tubular cells with the space of approximately 50 nm between cell boundary were formed unlike the case of pure aluminum including 60 ppm of Cu. Numerous branching of pores were also observed. EDX mapping revealed that Si was enriched in the outer layer of the cells and Cu was enriched at the area near cell boundaries. Therefore, it is deduced that enrichment of Cu at the cell boundaries produces the tubular cells by accelerating oxide dissolution similar to the cases of enrichment of sulfate and ethylene glycol.
Effect of Adsorbed Organic Thin Films on Electrochemical Interaction Mechanisms of Metal Reducing Bacteria with Steel Surfaces
Authors: Wurzler Nina , Ozcan Ozlem
Published: February 2020

The interface of a metal substrate and a biofilm can differ significantly from the surrounding environment. Metal reducing bacteria (MRB), for instance, are capable of utilizing various metallic compounds as electron acceptors. Besides chromium, uranium and manganese as well as many organic compounds, Fe(III) is converted to the soluble form Fe(II) during the bacterial metabolism. This could lead to a weakening of the protective passivation layer on stainless steel and thereby facilitate microbiologically influenced corrosion (MIC). Even tough the processes of electron transfer are not yet entirely explained, the contribution of flavins and other humic substances as electron shuttles is widely discussed in the literature. Moreover, the adsorption of organic thin films on steel surfaces can lead to surface preconditioning and thus to changes in adhesion behavior of bacteria.

The aim of this work is to understand the chemical and electrochemical interaction mechanisms of MRB with steel surfaces by combining electrochemistry and surface-analytical techniques. The investigations primarily focus on the effect of pre-adsorbed thin organic films and self-assembled monolayers (SAMs) on the electron transfer processes between bacteria and steel surfaces. Electrochemical Quartz Crystal Microbalance (eQCM) studies have been performed to investigate the adsorption/desorption kinetics of organic films as well as the formation of biofilms on FeCr electrodes. Furthermore, the evolution of the biofilms on steel surfaces has been analyzed by means of electrochemical impedance spectroscopy (EIS) to support the QCM studies with information on structural changes during different stages of biofilm growth. Electron transfer and corrosion processes have been analyzed by means of square wave voltammetry (SWV) and linear sweep voltammetry (LSV), respectively. The results of electrochemical studies are complemented with microscopic and spectroscopic characterisation of organic adsorbates and analysis of changes in the passive film chemistry and surface morphology.

This presentation will summarize our results on the chemical and electrochemical interaction mechanisms of MRB on steel surfaces leading to passive film degradation. The role of flavins in accelerating corrosion processes will be elucidated in detail to provide useful insights from a fundamental aspect for the understanding of the initial stages of microbiologically influenced corrosion in the presence of MRB.
Inhibition of Filiform Corrosion on Organic-Coated Magnesium-Containing Galvanized Steel By Smart-Release Ion Exchange Pigments
Authors: Michailidou Emmanouela , McMurray Hamilton Neil , Williams Geraint
Published: February 2020

Zinc-(1-2 w%) Magnesium-(1-2 w%) Aluminium coated galvanized steel presents a superior corrosion resistance over conventional galvanized steel as a result of the Al and Mg additions to the bulk composition of the coating. It has been previously demonstrated that cathodic delamination does not occur on organically-coated ZMA galvanized steel due to the unfavourable potential gradient formed between the intact interface and the defect. Contrary, the potential at the intact interface is more negative than the potential at the defect thus triggering anodic undermining in the form of filiform corrosion. Smart-release exchange pigments have been proven to be a promising approach towards the suppression of undermining corrosion. In the current research, the ability of hydrotalcite (HT) based pigments on the inhibition of induced filiform corrosion on organic coated ZMA galvanized steel has been investigated.

This paper describes a systematic kinetic study on the inhibitory effect of anion exchange HT-based pigments on filiform corroding hot dipped Zn-(1-2 w%)Mg-(1-2 w%)Al galvanized steel. The samples were alkaline degreased in 1M KOH and 1M NaOH at 70oC and 3 min immersion time and were coated with a model organic coating of 15.5% PVB containing the exchange pigments via bar casting. Filiform corrosion was then initiated via scribing the samples and introducing a corrosive electrolyte in the defect. The kinetics of filiform corrosion were followed by optical recording over a period of six weeks.

It is positively demonstrated that the addition of smart-release pigments in the organic coating greatly suppresses the rate of filiform corrosion. The inhibitory effect of the pigments has been further investigated by systematically varying the volume fraction of the pigment on the organic coating presenting the reduction of filiform corrosion rate with respect to the concentration of the pigment in the organic coating. The effect of anion exchange HT-based pigments on filiform kinetics is analysed and described in terms of an inhibition mechanism.
Investigation of the “Protection Zone” Phenomenon Established By Conducting Polymers in Coatings for Corrosion Protection
Authors: Merz Anna , Rohwerder Michael
Published: February 2020

Conducting polymers (CPs), such as polypyrrole (PPy), polyaniline (PANi) or poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT: PSS), can be employed for the corrosion protection of metals when certain design rules are followed [1, 2].

Based on the capability of a conducting polymer to work as a strong oxidant to the metallic substrate, which induces the potential to shift to a noble direction, several possible protection mechanisms based on different electrochemical effects have already been reported. However, these mechanisms often seem to work only under certain special conditions. For instance, a CP containing coating might be very effective in preventing corrosion in pin holes by passivating the metal exposed therein to the corrosive environment, while it fails disastrously in the presence of larger defects [2]. So this work focuses on the investigation of an innovative protection system which provides a long term coating stability. It was found that separated particles of conductive polymer when distributed on a zinc or iron matrix establish a “protection zone” around their boundary. The above proposed effect hinders the oxygen reduction rate at the very delamination front, establishing a region where no or only very slow delamination occurs, i.e. a degradation free zone is created. This phenomenon was investigated for the following CPs: polyaniline, polypyrrole as well as PEDOT.

Homogeneous and strongly adherent conducting polymer deposits (dots of conducting polymer) have been prepared with different thickness. Evaluation of the anticorrosion performance of the deposits covered by an organic coating was investigated with Scanning Kelvin Probe (SKP) and the role of the conducting polymer thickness and kind of metal on the corrosion performance was also examined. The experiments carried out revealed that the investigated deposit configurations are highly efficient, in fact provide a real break-through for the design of corrosion protection coatings based on conducting polymers.

Keywords: Corrosion protection; Conducting polymer; Protection zone; Scanning Kelvin Probe.

[1] Rohwerder, M.; Duc, L.; Michalik, A.: In situ investigation of corrosion localised at the buried interface between metal and conducting polymer based composite coatings. Electrochimica Acta 54 (25), pp. 6075-6081 (2009)

[2] Rohwerder, M. (2009). Conducting polymers for corrosion protection: A review. International Journal of Materials Research, 100(10), 1331-1342. doi:10.3139/146.110205.
(Invited) Anticorrosive Polymer Nanocomposites Coating
Authors: Wei Huige , Guo Jiang , Du Huayun , Shao Qian
Published: February 2020

In the present study, conductive polyurethane (PU) nanocomposite coatings filled with multiwalled carbon nanotube (MWNTs) prepared via an in situ surface-initiated-polymerization method were evaluated for anticorrosion purpose. Scanning electron microscopy (SEM) reveals a uniformly dispersed MWNTs nanoparticles in the PU matrix. Thermogravimetric analysis (TGA) shows an enhanced thermal stability of the composite as compared to pure PU. The nanocomposite exhibits a good response of electrical conductivity change to the varying strain during the cyclic strain test. The anticorrosion tests in 3.0 wt% NaCl aqueous solution suggest that the composite coatings possess a good chemical stability over long immersion time in the corrosive environment. A significantly positive shift of nearly 1.0 V in the open current potential (E
ocp) was observed from the E -time curve of MWNTs/PU composite-coated stainless steel electrode. Extrapolation of Tafel plots gave a much more positive corrosion potential (E
corr) and much lower corrosion current (I
corr). A protection efficiency as high as 97.70% was obtained. Electrochemical impedance spectroscopy (EIS) was conducted as well to investigate and obtain the anticorrosion mechanism of the composite coating. An equivalent circuit of the coating was proposed to fit the EIS data, confirming an effective corrosion protection for the stainless steel. The results indicate that the polyurethane matrix combined with the well dispersed MWNTs reinforcements provides an effective physical barrier against the attack of corrosive ions in the solution for the stainless steel. In this talk, new anticoating polymer was also synthesized and presented.
Anodizing with Simultaneous Silanization for Hidrophobicity Enhancement and Corrosion Protection of Aluminum Alloys
Authors: Atz Dick Pedro , Rátiva Melo Yesenia , Vignoli Machado Thiago , Cipolatto da Rosa Micheli , Dick Luís Frederico Pinheiro
Published: February 2020

In refrigeration systems, aluminum sheets are continually submitted to condensation of water, which provides a corrosive environment and eventually results in the formation of ice and impairment of heat exchange. Therefore, hydrophobic surfaces are highly desirable, in order to extend life and improve performance of refrigeration systems. In this work, we propose a novel anodizing method combining porous anodic oxidation with simultaneous incorporation of hydrophobic organosilanes. Commercially pure aluminum (AA1100) was used as substrate and anodizing baths consisted of different portions of sulfuric acid, water, ethanol and hexadecyl-trimethoxysilane (HDTMS). In some cases, HDTMS hydrolysis was started in controlled environment before anodizing. Anodizing was performed galvanostatically, starting at different temperatures with a current density of 15 mA/cm2, for 25 minutes. The anodic layers obtained were characterized by scanning electron microscopy, Raman spectroscopy and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR). Contact angles were measured by the sessile drop technique. The anodic layers obtained are circa 10 µm thick with incorporation of silanes inside pores and on the surface, partially blocking the pores. Hydrophobicity was significantly enhanced by adding organosilanes, achieving contact angles greater than 130°. The effects of ethanol concentration, HDTMS concentration and curing process on contact angles and potential transients during anodizing were studied. Corrosion resistance of anodic layers was evaluated using potentiostatic methods and standard salt spray exposure and compared to other traditional anodizing methods. Corrosion resistance was greatly increased by the developed process.
Effect of Passive Film on Corrosion Behavior of Passivated Electroless Ni-P Coating
Authors: Sun Chong , Leitch Michael , Zeng Hongbo , Luo Jing-Li
Published: February 2020

In heavy oil wells, carbon steel casing and tubing often suffers from severe corrosion due to the presence of corrosive gases, chlorine compounds and solid particles in the corrosive medium. An electroless Ni-P coating (EN coating) has been applied to the carbon steel surface, which presents better corrosion resistance than the substrate. However, defects such as microscopic pores, as the corrosion paths, will be inevitably present in EN coating, which can cause the corrosion of carbon steel substrate despite the coating. To solve this problem, passivation treatment can be used to create a passive film on EN coating surface and improve the corrosion resistance of the coating. However, erosion-corrosion also occurs when solid particles are suspended in the corrosive medium, and the erosion-corrosion mechanism of the passivated Ni-P coating is not known.

In this work, a passive film was formed on the EN coating in the K2Cr2O7-containing bath with and without an applied passivation potential. The corrosion properties of passive films were evaluated by means of electrochemical measurements and compared to the non-passivated EN coating. SEM, XPS, and EDS were employed to analyze the chemical composition and surface morphology of the films. The results showed an obvious passive region of passive film on EN coating in the potential range of -0.1 – 0.45 V (vs. SCE). The corrosion current of the passivated EN coating through chemical passivation treatment (CPT) was reduced by 61 % than that of non-passivated EN coating film, while it was reduced by 79 % through a combination of CPT and electrochemical passivation treatment (EPT) with an applied passivation potential of 0.2V (vs. SCE). These results demonstrate how EPT can significantly improve the corrosion resistance of the passive film.

Erosion-corrosion of passivated EN coatings through CPT and EPT was studied under an applied passivation potential by means of a single particle impingement technique. The transient current response to disruption of the passive film was obtained at different impact angles and velocities, which was the result of different damaged surface area produced by solid particle impingement. Correspondingly, the hydrodynamic effects on erosion-corrosion of passivated EN coating were predictable with a theoretical model based on kinetic analysis.
Malic-Sulfuric Acid Anodizing of AA 2024 Compared to Other Dicarboxilic-Sulfuric Acid Anodizing Processes
Authors: Dick Luís Frederico Pinheiro , Knörnschild Gerhard , Atz Dick Pedro , Vignoli Machado Thiago
Published: February 2020

Aiming to develop hexavalent chromium (CrVI)-free anodizing baths for Al-alloys, the porous anodizing of AA2024 was studied in different mixtures of sulphuric acid-organic acid formulations with similar concentrations. Mixtures of sulphuric with dicarboxylic acids as malic, malonic, oxalic and tartaric and with the tricarboxylic citric acid were tested. The corrosion behavior of the unsealed anodized layers exposed to 0.1M NaCl were compared by voltammetry and chronoamperometry at polarizations slightly above the pitting potential of blank AA2024 with the behaviour of standard chromic acid anodizing. The obtained oxide layers were characterized by SEM, FTIR and micro-Raman spectroscopy, which confirmed the incorporation of organic acids in relative different amounts. Best corrosion resistances expressed in terms of pitting nucleation time were observed for malic-sulphuric, followed by tartaric-sulphuric anodizing. However, none of the formulations achieved the resistance conferred by the chromic acid anodizing. A direct correlation between mesoporosity of the anodizing layer and corrosion resistance was verified.
3D Impedance Mapping of Internal Concrete Block By Using Multichannel Wire Grid
Authors: Azumi Kazuhisa , Saito Shu
Published: February 2020

Monitoring of corrosion environment for reinforced steel inside the concrete structure was investigated using 3D impedance mapping method. In this method many iron wires in grid alignment were embedded in a test cement block and impedance between two iron wires sequentially chosen from the grid was measured to obtain the resistance map inside the cement block. From the resultant 3D impedance map, corrosion environment for steel inside the concrete such as penetration of water or salt can be speculated.

In the experiment, test cement block of 200 mm x 200 mm x 60 mm in size was made in which iron wires of 99.5% impurity and 0.2mmφ in diameter were embedded in a grid alignment of 8 line with 20 mm spacing in lateral direction and 4 layer with 10 mm spacing in depth, a total number of iron wires was 8 x 4 = 32. Top face of cement block was open to air and the other faces were covered with PVC plates as a casting mold. Impedance was measured for a combination of crossing two wires in two neighbor layers, and a number of combination was 8 x 8 x 3 = 192. To choose the appropriate two wires from 32 embedded wires to connect impedance analyzer, computer controlled analog multiplexer array was used. Impedance analyzer was built in laboratory using one-chip impedance converter (Analog Devices, model AD5933) which integrates components necessary for impedance analysis as direct digital synthesizer (DDS) as AC source, digital signal processor (DSP) engine for FFT (DFT, discrete fourier transformation), operational amplifier as AC output driver and input current / voltage converter, and 12bit analog digital converter. In this study, impedance was measured at a fixed frequency of 270Hz with modulation voltage of 20mV. About 1400 s was required to complete a single impedance mapping.

Example of impedance map inside the test cement block is shown in Fig.1. The value of resistance was in the range from ca. 3kΩ at the central area of deep (30-40 mm) cement block to a several 100kΩ close to the surface (10-20 mm). Relatively low resistance deep inside the cement block indicates that the inside of the cement block was not dried out. On the other hand, not only the surface but also the side faces of cement block were dried because a gap was formed between the PVC mold and side faces of the cement block due to volume shrinking when a cement block had set. Transition of impedance map during drying and penetration of water from the top face were also investigated.

Figure 1
(Invited) Amorphous Zr-Doped HfO2 high-K Dielectric Thin Film for Electronic and Optoelectronic Applications
Authors: Kuo Yue
Published: February 2020

Metal oxides have been used as the high-k dielectric materials in ICs and TFTs for several decades. Recently, they are used as the gate dielectric in the nano-sized MOSFET to take the advantage of the low leakage current and other device properties.

HfO2 is the most popular high-k gate dielectric for sub 1 nm EOT transistors and circuits. One of its main drawbacks is the low crystallization temperature, i.e., < 700°C, which can be a serious reliability problem. We have solved this problem by adding Zr into HfO2 to form the Zr-doped HfO2 (ZrHfO) film. This kind of high-k film can remain amorphous after been heated to above 900ºC. The material and electrical properties can be optimized by controlling the concentration of Zr in the film and the post deposition annealing (PDA) condition. In this talk, the author reviews his works in dielectric and non-dielectric applications of the amorphous ZrHfO thin film. They are highly dependent on the structure of the film.

The amorphous ZrHfO high-k thin film can be transformed into heterogeneous structures for non-dielectric applications. For example, one or more of the nanocrystalline materials have been embedded into the ZrHfO thin film to serve as charge trapping media. Electrons and holes can be stored in this kind of film separately with the selection of the proper nanocrystal materials and the gate bias condition. This kind of nonvolatile memory device has a lifetime more than 10 years

The amorphous ZrHfO high-k thin film can be prepared into another type of heterogeneous structure. After the hard breakdown process, many nano-resistors can be permanently and uniformly formed in the high-k thin film. Light can be emitted from nano-resistors upon the application of a voltage. This is a solid state incandescent light emitting device (SSI-LED) became the principle of light emission is the black body emission. The emitted light has the broad-band spectrum covering the whole visible and part of the near-IR wavelength range. Applications of SSI-LEDs include lighting, on-chip optical interconnect, and others. The nano-resistor structure can also be used as one-time-programmed memory devices, i.e., antifuses, because the leakage current ratio after and before the breakdown process can be larger than 105. Separately, the nano-resistor structure has the current rectification function, which makes it a diode device. However, different from the on-off function of the conventional p-n junction diode, which has a drastic change of the current upon a small increase of the driving voltage, the nano-resistor based diode has the gray-scale capability because of the gradual change of the current vs. voltage curve.

There are many other possible applications of the amorphous ZrHfO high-k thin film beyond the conventional electronics and optoelectronics, which will also be discussed.

This talk is dedicated to the memory of Prof. Samares Kar for his seminal contribution to this important ECS symposium series.
(Invited) The Dynamics of Nickelidation for Self-Aligned Contacts to InGaAs Channels
Authors: Chen Renjie , Dai Xing , Jungjohann Katherine L , Mook William Moyer , Nogan John , Soci Cesare , Dayeh Shadi
Published: February 2020

Alloyed and compound contacts, formed by thermal annealing of metal-semiconductor nanowires (NWs), are prescribed for lithography-free self-aligned gate designs. Prior work revealed astounding differences at nanoscale in the formation of such alloys and compounds evoking reevaluation of the thermodynamics, kinetics, and resultant phases during their formation. Some of these studies were carried out by in-situ heating and imaging inside a transmission electron microscopy (TEM) and investigated phase transformations in real-time and at atomic resolutions in elemental semiconductors, i.e. Si and Ge NWs but not in III-V NW channels. Here, we carried out in-situ heating TEM experiments to study the contact metallization process in between Ni contact and In0.53Ga0.47As NW channels fabricated by top-down method, and observed at atomic resolution the detailed ledge formation and movement behaviors in both the NW cross-section and along the NW channel. At typical temperatures at which crystalline Ni2In0.53Ga0.47As phase grow on planar In0.53Ga0.47As surfaces, the NW cross-section experienced a solid-state amorphization step and formed NixIn0.53Ga0.47As (x<2). During this amorphization process, nickelide reacted in a layer-by-layer manner with ledge moving on {111} facets and along <112> directions. The interfacial property between Ni and InGaAs NW was found to significantly influence the reaction kinetics and was captured by a model that was specifically developed for the cross-sectional geometry of NW channels. Finally, the amorphous NixIn0.53Ga0.47As (x<2) phase regrow into a single crystalline Ni2In0.53Ga0.47As phase at temperatures above 375 °C by additional incorporation of Ni adatoms from the contact reservoir. Along the NW channel direction, we found that the reacted interface followed the In0.53Ga0.47As (111) || Ni2In0.53Ga0.47As (0001) atomic plane, and that the ledges nucleated as a train of strained single-bilayers. Once the strain energy in single bilayer ledges was relieved in part by forming misfit dislocations, their velocity decreased permitting the formation of associated single-bilayer ledges, the double-bilayer ledges. Consequently, these nickelide ledges moved with a double-bilayer height that became the unit height of ledges in this phase transformation. Our in-situ studies demonstrated the applicability of interfacial disconnection theory in contact metallization for compound semiconductor nanoscale channels in the ternary to quaternary compound phase transformation, and may guide for the phase selection of crystalline self-aligned contacts in nanoscale channel cross-sections.
Breakdown Characteristics of TiN/HfxZr1-xO2/Al2O3/Ge Gate Stacks
Authors: Shao Pai , Bhuyian Md Nasir Uddin , Ding Yiming , Misra Durgamadhab
Published: February 2020

Ge has been considered as an alternative channel material in place of Si because of its higher electron and hole mobility. Since direct deposition of high-k material on Ge leads to degradation of interface quality ultrathin Al2O3 is used as a passivation layer prior to high-k layer deposition. In addition, ZrO2/Al2O3 bilayer as gate dielectric on Ge is becoming popular since ZrO2 showed lower leakage current than HfO2 (1, 2). To further scale the effective oxide thickness (EOT) on Ge higher-k dielectric materials like Hf1-xZrxO2, with different Hf to Zr compositions has been explored. Furthermore, the recent introduction of post-deposition slot plane antenna plasma oxidation (SPAO) of the dielectric seems to enhance the interface as well as gate stack quality (3).

In this work, we investigate the Time Dependent Dielectric Breakdown (TDDB) characteristics of the impact of TiN/HfxZr1-xO2/Al2O3/Ge gate stacks by changing the Zr content. Slot-plane antenna plasma oxidation (SPAO) was performed on these devices after the ALD deposition of the high-k layers. It was observed that the equivalent oxide thickness (EOT) decreases with Zr addition in HfO2 with up to 75% of Zr incorporation. With 100% Zr incorporation EOT increased significantly. This is possibly due to the formation of low-k interfacial GeO2 at the interface for 100% Zr whereas for other samples have comparatively thinner GeOx interfacial layers (3). Weibull plots shows that charge to breakdown (Q
BD) increased with increase the Zr percentage. However, the breakdown acceleration factor decreased with Zr percentage up to 75% and increased rapidly for 100% Zr content. It is reported earlier (3) that GeO2 has the worst resistance to stress in terms of device stability compared to GeOx. Therefore, formation of thick GeO2 degrades the device with 100% Zr rapidly as compared to lower percentage of Zr.

The authors would like to acknowledge K. Tapily, R. D. Clark, S. Consiglio, C. S. Wajda, and G. J. Leusink of TEL Technology Center, Albany, NY for their help in device preparation.

References:

X.-F. Li et al, ECS Solid State Letters 1 (2), N10-N12 (2012).

M. N Bhuyian et al, ECS Journal of Solid State Science and Technology 3 (5), N83-N88 (2014).

Y. Ming et al, IEEE Transactions on Device and Materials Reliability, DOI: 10.1109/TDMR.2017.2681428
(Invited) Modifying Silicon/Dielectric & Silicon/Metal Interfaces Using Sub-2 Nm Pt Nanoparticles
Authors: Gangopadhyay Shubhra , Mukherjee Somik , Zheng Haisheng , Gangopadhyay Keshab
Published: February 2020

Understanding the nature/density/energy levels of interface traps at Si/dielectric and Si/metal interfaces is essential towards producing reliable functioning devices. Typically high temperature post processing H2 anneals are utilized in industry to reduce these interface traps, but stability of these H passivated traps is questionable, especially if the device undergoes other high temperature processes downstream. Our studies show that by utilizing sub-nm Pt nanoparticles at Si/dielectric and Si/metal interfaces the degree of fermi-level pinning can be modulated. These sub-nm Pt nanoparticles can be used to modify metal/Si contact barrier in combination with either a 0.98 nm Atomic Layer Deposited Al2O3 or a 1.6 nm chemically grown SiO2 dielectric layer, or both. We have studied the role of these Pt NP’s size dependent properties, i.e., the Pt NP-metal surface dipole, the Coulomb blockade and quantum confinement effect in determining the degree of Fermi level depinning observed at the studied metal/p-Si interfaces. By varying only the embedded Pt NP size and its areal density, the nature of the contact can also be modulated to be either Schottky or Ohmic upon utilizing the same gate metal. 0.74 nm Pt NPs with an areal density of 1.1 × 1013 cm−2 show ~382 times higher current densities compared to the control sample embedded with similarly sized Pt NPs with ~1.6 X reduction in areal densities. We further demonstrate that both Schottky (Ti/p-Si) and poor Ohmic (Au/p-Si) contact can be modulated into a good Ohmic contact with current density of 18.7 ± 0.6 A/cm2 and 10.4 ± 0.4 A/cm2, respectively, showing ~18 and ~30 times improvement. A perfect forward/reverse current ratio of 1.041 is achieved for these low doped p-Si samples. In addition, we have also explored the influence of Pt NP-induced border traps within dielectrics near Si surface and the surface coverage dependent pinning of embedded Pt NP work function. The pinning of these nanocrystal work-function was found to be induced by a high density of dangling bonds near the Pt NP/Al2O3 interface which skews the expected charging/discharging characteristics with electron programming favored over holes. The degree of this pinning was probed utilizing C–V measurements and seems to be dependent on the density of Al2O3 dangling bonds near Pt NP surface. This density of dangling bonds acting as border traps has been observed as an increasing function of the Pt NP surface percent coverage. Gaining adequate understanding the location, energy, and positioning of the energy levels of these defects at the metal/high-k interface relative to Si band gap can help overcome poor retention and leakage issues that typically compromise the performance of new generation memory devices.
A Rational Co-Design Approach for Next Generation Dielectric Materials with the Transition Metal Containing Coordination Polymers
Authors: Nasreen Shamima , Treich Gregory Martin , Baczkowski Matthew Lucas , Mannodi-Kanakkithodi Arun K. , Cao Yang , Ramprasad Ramamurthy , Sotzing Gregory Allen
Published: February 2020

A rational co-design process involves a synergistic approach towards the synthesis and development of new dielectric materials with high throughput screening and testing. This approach is gradually replacing the traditional Edisonian approach of using trial and error to a more sophisticated, data driven, approach for designing next generation dielectric materials. Recently, advancements in dielectric materials are achieved by the incorporation of group 14 metal in the main chain of polymer as an organometallic systems. Here in, we introduce transition metal based metal-organic framework (MOF) polymers as a dielectric materials. Transition metals zinc and cadmium are incorporated in the main chain of polymer through metal-oxygen bonds with varying number of methylene spacers in the repeat units. High molecular weight coordination complex polyesters are obtained, which exhibit high band gaps and low loss compared to their oxide counterparts while maintaining high dielectric constants. The rational co-design of these materials are motivated by DFT computations of the electronic, ionic and total dielectric constant contributions, band gap energies, along with their structural predictions of the local environments. Polymers are characterized with Nuclear Magnetic Resonance Spectroscopy (1H-NMR), Fourier Transform Infrared Spectroscopy (FTIR) and with X-Ray Diffraction (XRD) for their structural properties and features which shows strong correlation to the experimental findings. Thermal behaviors are observed with Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). Dielectric Spectroscopy and Optical Band Gap are measured and found strong correlation with the Density Functional Theory (DFT) predictions. These initial studies give insight into the potential advantages an expansion of chemical space for energy storage applications through a rational co-design approach. This work provides valuable validation and feedback to computational predictions to fulfill the goals of this approach.
Manipulation on Crystallization of Perovskite Thin-films during Blade Coating Fabrication in Air
Authors: Li Jing , Lin Yichuan , Yin Jun , Zheng Nanfeng
Published: February 2020

Organometal trihalide perovskite solar cells (PSCs) have drawn more and attention in the past few years due to the merits of low-cost preparation processes and rapidly improved power conversion efficiency (PCE) with latest certified efficiency of 22.1%.1-4 Commonly, solution processes, including one- or two-step spin-coating methods, are often employed to produce perovskite films.5, 6 Recently, the blade coating technique, with the advantages of large scale fabrication and mass production besides the well-accepted low-cost manner, has also attracted researchers’ interest for the rapid growth of perovskite films.7-8 However, nucleation and crystal growth during the film’s crystallization by blade coating are still lack of controlling, generally resulting in relatively poorer crystal quality and film uniformity. So, further strategies are required to improve the crystallization of perovskite films and ultimate device efficiencies.

In this work, different strategies were introduced during the blade-coating process to control and manipulate the crystallization of perovskite films. In depth understanding in the nucleation mechanisms and growth dynamics of films were well accomplished. As a result, the rapid growth of perovskite films with high quality and good optical performances were successfully produced. Correspondingly, efficient PSCs were correspondingly fabricated.

References

1. A. Kojima, K. Teshima, Y. Shirai and T. Miyasaka, J. Am. Chem. Soc., 2009, 131, 6050-6051.

2. M. D. McGehee, Nature Mater., 2014, 13, 845-846.

3. J. Seo, J. H. Noh and S. I. Seok, Accounts of chemical research, 2016, 49, 562-572.

4. http://www.nrel.gov/ncpv/images/efficiency_chart.jpg

5. H. S. Jung and N. G. Park, Small, 2015, 11, 10-25.

6. J.-H. Im, H.-S. Kim and N.-G. Park, APL Materials, 2014, 2, 081510.

7. J. H. Kim, S. T. Williams, N. Cho, C.-C. Chueh and A. K. Y. Jen, Adv. Energy Mater., 2015, 5, 1401229.

8. Y. Deng, E. Peng, Y. Shao, Z. Xiao, Q. Dong and J. Huang, Energy Environ. Sci., 2015, 8,1544-1550.
Intense Pulsed Light Processing of Perovskite Thin Films
Authors: Druffel Thad
Published: February 2020

The manufacturing of solar photovoltaic panels has seen dramatic reductions in costs primarily through business innovations to the extent that the industry is quite large. The industry is dominated by a single technology, crystalline solar cells. The implementation of newer technologies that could further reduce costs are very attractive, especially technologies that can be adapted to continuous printing particularly involving polymer film substrate. The perovskite solar cells offers this; however, most of the processing techniques rely on extended thermal process or very exact solvent control. The Intense Pulsed Light (IPL) technology has been shown to rapidly process perovskite thin films and our recent work explores how the technology can open up the processing window.

The Intense Pulsed Light technology is well suited to continuous manufacturing platforms such as roll-to-roll due to its very large processing area and rapid processing time scales. The IPL technique delivers high energy pulses of broad spectrum light (UV-Vis-NIR) in a very short duration (ms) over a large processing area (100 cm2). In the past few years, the method has found a number of applications within the flexible electronics industry as printed structures for wire traces, transparent conductors and RFID and is now gaining traction with more complex materials. The most promising opportunity for the IPL within photovoltaics is the application towards the flexible large area roll-to-roll production offered by the solution phase processed perovskites.

In this paper we will discuss our work with the IPL and the extremely rapid processing of perovskite thin films using a number of precursor materials. We have shown the process for both the two-step and the single step deposition producing devices that perform as well as the traditional thermal processing at significantly faster speeds. This paper will also discuss the morphological changes that occur during the IPL with an intent to develop a robust process. Data from X-ray diffraction and scanning electron microscopy is used to describe the changes to the films, and current-voltage and electrochemical impedance spectroscopy is used to probe the devices.
Application of Electrodeposition for the Preparation of TiO2 Compact Layer in Perovskite Solar Cells
Authors: Su Tzu-Sen , Wei Tzu Chien
Published: February 2020

Compact layer (CL) with pinhole-free and excellent electron conductivity is critical in high-efficient scaffold-type perovskite solar cells. In this study, we thoroughly investigated electrodeposited TiOX (ED-TiOX) on FTO glass from aqueous TiCl3 solution including the kinetics of the electrodeposition, film morphology, optical and electronic properties. Furthermore, by controlling the total charge amount, the thickness of ED-TiOX films as well as device performance are tunable. When applying this method to fabricate the CL for scaffold-type perovskite solar cells, we compared the hole blocking effectiveness, charge extraction capability and photovoltaic performance of TiO2 CLs made by electrodeposition and other common methods such as dip coating (DC), spin coating (SC) and spray pyrolysis (SP). Current results reveal ED-TiOX CL performs best for its full coverage, thinnest thickness and mossy surface, rendering high shunt resistance and low ohmic resistance. In addition, our results also confirm in scaffold-type perovskite solar cell configuration, CL still provides charge extraction function in addition to the mesoporous scaffold. The device using ED-TiOX CL currently shows highest power conversion efficiency (PCE) up to 15.48%.

Figure 1
Efficient Two-Dimensional Layered Perovskite Solar Cells with Technologically Relevant Reliability
Authors: Gupta Gautam , Mohite Aditya
Published: February 2020

Three-dimensional organic-inorganic perovskites have emerged as one of the most promising thin-film solar cell materials due to their remarkable photophysical properties that have led to power conversion efficiencies exceeding 22%, with the prospect of further improvements towards Shockley-Queisser limit for a single‐junction solar cell (~33.5%). Alongside efficiency, a critical factor for photovoltaics and other optoelectronic applications is environmental and photostability under operating conditions. In contrast to their 3D counterparts, Ruddlesden-Popper phases, layered two-dimensional (2D) perovskite films, have shown promising stability, but poor efficiency at only 4.73%. This is attributed to the inhibition of out-of-plane charge transport by organic cations, which act like insulating spacing layers between the conducting inorganic components. Here we overcome this fundamental issue in layered perovskites by producing near single-crystalline quality thin-films with a strongly preferential out-of-plane alignment of the inorganic perovskite component to facilitate efficient charge transport. We report a photovoltaic efficiency of 12.5 % with no hysteresis, and devices that exhibit greatly improved stability in comparison to their 3D counterparts when subjected to aggressive stress tests of light, humidity and heat. Unencapsulated 2D perovskite devices retain over 70% of their efficiency for over 2000 hours under constant 1 Sun illumination, and exhibit greater tolerance to 65% relative humidity than 3D equivalents. When the devices are encapsulated, the layered devices do not show any degradation under constant 1 Sun illumination or humidity.
In-Situ Structural Characterization of CH3NH3PbI3 Nano-Crystal Using Advance Synchrotron-Radiation Techniques
Authors: Hwang Bing Joe , Su Wei-Nien , Berhe Taame Abraha
Published: February 2020

Although CH3NH3PbI3 is a promising light harvesting material1, 2, its structural fluctuations and instability impede our understanding and its technological applications. It is now demonstrated for the first time that advanced synchrotron techniques: in-situ extended X-ray absorption fine structure, X-ray absorption near edge structure and temporally coherent X-ray diffraction and coherent X-ray scattering were used to study in-situ microstructure and structural evolution of CH3NH3PbI3 nano-crystals during thermal heating. The measurements were performed from room temperature up to 100 0C. Microstructure evolution, oxidation state, coordination number, structural distortion and phase heterogeneity changes were examined. Except the microstructure, there was no change in oxidation state and coordination number with increase in temperature.
Enhancing the Photovoltaic Performance of Dye-Sensitized Solar Cells with Rare-Earth Metal Oxide Nanoparticles
Authors: Zamborini Franscis P. , Alphenaar Bruce W. , Kharel Pom L.
Published: February 2020

Dye-sensitized solar cells consist of a photoanode of a mesoporous film of titania sensitized with dye sandwiched with a counter electrode, which is usually a platinum-coated transparent conducting oxide, and a redox couple injected between the photoanode and counter electrode. Doping titania with rare-earth metals has been an interesting approach to improve the conversion efficiency of dye sensitized solar cells. Rare-earth metals have been doped into titania paste to show an improvement in the photovoltaic performance of dye-sensitized solar cells, however, most of the reported cells are not efficient enough to conclude whether the enhancement is due to doping or it is because of the cell quality. We incorporated nanoparticles (<100 nm) of oxides of rare-earth metal (neodymium and erbium) in titania paste and built dye-sensitized solar cells using amphiphilic C101 dye and nitrile based iodide/triiodide redox couple, Z960 electrolyte. The doping level for optimized cells was 2.0 % for neodymium oxide and 1.0 % for erbium oxide. Our cells exhibit efficiencies more than 10 % and the best erbium oxide doped cell displayed an efficiency above 11 %. We measured the photocurrent, impedance, IPCE, dye loading, and film conductivity to investigate the enhancement of the photovoltaic performace by rare-earth metal oxides. Electrochemical impedance spectroscopy (EIS) measurements showed that doping with rare-earth metals decreased the total impedance of the cell and IPCE measurements revealed enhanced photon absorption by the dye in rare-earth metal doped cells. In the same fashion, the rare-earth metal -doped anodes showed larger dye loading compared to undoped anodes, which was maximum for 1.0 % doping of erbium oxide and 2.0 % doping of neodymium oxide. Rare earth metal oxides not only enhance dye adsorption but also facilitate electron tranport through the mesoporous layer, thereby increasing the collection efficiency of the photoexcited electrons.
(Invited) 2D-Functionality in Full 3D: A New Paradigm of Graphene-Metal Epitaxial Systems
Authors: Alamgir Faisal M
Published: February 2020

An unprecedented dual role for graphene in electrochemical systems will be shown in this presentation. First, graphene (GR) plays the role of an enabler, allowing a large-area, fully-wetted, growth of two-dimensional Pt films that are one to several monolayers thick. Next, it also serves the role of a ‘chemically transparent’ barrier that allows catalytic chemistry to take place above it, while protecting the catalyst below it from cyclical loss. In the latter case, we will specifically show that graphene does not restrict access of the reactants for the canonical oxygen reduction reaction (ORR) but does block Pt from dissolution or agglomeration. Using these architectures, we show that it is possible to simultaneously achieve enhanced catalytic activity and unprecedented stability,e.g. retaining full activity for ORR beyond 1000 cycles . Using x-ray photoemission/absorption spectroscopy (XPS/XAS), high resolution TEM, AFM, Raman, and electrochemical methods, we show that, due to intimate graphene-Pt epitaxial contact, Pt/GR hybrid architectures are able to induce a compressive strain on the supported Pt adlayer and increase catalytic activity for ORR. We further investigate graphene as a sandwiched layer between metal films as a membrane that limits interfussion and, therefore, helps retain the integrity of core-shell architectures. We find that at operating temperatures above 100 °C (not uncommon in low-temperature fuel cells), there is appreciable interdiffusion between the primary and support metals of the catalyst system, which can diminish the catalyst activity. A single-layer of graphene acts as a barrier that prevents unwanted surface alloying between layered metals, while allowing interlayer charge transfer. Our demonstration of a the room-temperature, wetted synthesis approach, should allow for efficient transfer of charge, strain, and phonons and photons, impacting not just catalysts, but also electronic, thermoelectric and optical materials.
Metal Underpotential Deposition to Quantify Defects in 2D Materials
Authors: Dorner Iris , Müllner Matthias , Mertens Stijn F. L.
Published: February 2020

We demonstrate how metal UPD may find use as a general tool to determine the collective defect area in hybrids between 2D materials (graphene, hexagonal boron nitride, etc.) and various substrate metals. By investigating copper UPD on a monolayer of hexagonal boron nitride (h-BN) on Rh(111), we explore how this process can be used to quantify the defects in the h-BN monolayer which form during its chemical vapor deposition. In addition, the UPD signature allows assessing the potential window of the h-BN/metal hybrid, which is important to explore its functionality under ambient and electrochemical conditions. Importantly, UPD itself does not alter the defect area on repeated cycling. Overpotential deposition, on the other hand, is shown to have significant consequences on the defect area. We show that this non-innocent Cu electrodeposition involves intercalation originating at initial defects, causing irreversible delamination of the h-BN layer; this effect therefore may be used for 2D material nanoengineering.