Properties Of Stacks Research Articles

Preload dependent material properties of lamination stacks for electric machines

AbstractThe design of electric machines is motivated by electromagnetic and mechanical requirements. The magnetic flux is confined and guided by ferrite cores which consist of coated electrical sheets with a thickness of only a few tenths of a millimeter in order to minimize the eddy current losses. This heterogeneous structure causes preload dependent transversal isotropic material properties which affect the fatigue behavior and structural dynamic behavior of the machine. The material constitutive equations are defined by five parameters which must be derived from experimental investigations with respect to compression in the stacking direction. In this paper, a test procedure is introduced to determine the elastic and torsional stiffness as well as the lateral elongation of the stack depending on its preload.

Stacking as a Key Property for Creating Nanoparticles with Tunable Shape: The Case of Squalenoyl-Doxorubicin.

The development of elongated nanoparticles for drug delivery is of growing interest in recent years, due to longer blood circulation and improved efficacy compared to spherical counterparts. Squalenoyl-doxorubicin (SQ-Dox) conjugate was previously shown to form elongated nanoparticles with improved therapeutic efficacy and decreased toxicity compared to free doxorubicin. By using experimental and computational techniques, we demonstrate here that the specific physical properties of SQ-Dox, which include stacking and electrostatic interactions of doxorubicin as well as hydrophobic interactions of squalene, are involved in the formation of nanoassemblies with diverse elongated structures. We show that SQ-Dox bioconjugate concentration, ionic strength, and anion nature can be used to modulate the shape and stiffness of SQ-Dox nanoparticles. As those parameters are involved in nanoparticle behavior in biological media, these findings could bring interesting opportunities for drug delivery and serve as an example for the design of original nanodrugs with stacking properties tuned for particular clinical purposes.

Sensitivity of resonance properties of all-dielectric multilayers driven by statistical fluctuations.

In photonics and emerging fields of quantum and topological materials, increasing demands are placed upon the state and control of electromagnetic fields. Dielectric multilayer materials may be designed and optimized to possess extremely sharp spectral and angular photonic resonances allowing for the creation of fields orders of magnitude larger than the exciting field. With enhancements of 104 and higher, the extreme nature of these resonances places high constraints on the statistical properties of the physical and optical characteristics of the materials. To what extent the spectral and angular shifts occur as a result of fluctuations in the refractive indices and morphologies of the involved low-loss subdomains have not been considered previously. Here, we present how parameter variations such as those caused by fluctuations in deposition rate, yielding bias, random and compensated errors, may affect the resonance properties of low-loss all-dielectric stacks.

Gate Insulator Engineering in Top-Gated Indium-Tin-Oxide-Stabilized ZnO Thin-Film Transistors

This letter proposes a high-quality plasma-enhanced chemical vapor deposition (PECVD) SiO2 stack for thin-film transistors (TFTs), which contains a layer of SiH4-sourced PECVD SiO2 (SiH4-SiO2) with a layer of tetraethyl-orthosilicate (TEOS)-sourced PECVD SiO2 (TEOS-SiO2) underneath. The issues of high hydrogen content in the SiH4-SiO2 and rich hydroxyl groups in the TEOS-SiO2 were found to be well addressed by capping the TEOS-SiO2 with SiH4-SiO2. Moreover, the electrical properties of the SiO2 stacks were shown to be strengthened in comparison with their single-layer counterparts. This is owing to the mutual interactions between hydrogen groups in the SiH4-SiO2 and hydroxyl groups in the TEOS-SiO2. Top-gated indium–tin-oxide-stabilized ZnO TFTs with stacked gate insulators (GIs) were demonstrated after the optimizations of the GI layer thickness and deposition order and were shown to be free of hysteresis with a high ON–OFF ratio of over 1010 and a sharp subthreshold swing of 96.9 mV/decade. The combination of TEOS-SiO2 and SiH4-SiO2 initiates an economical strategy to achieve reliable GIs for high-performance top-gated metal-oxide TFTs.

Cover Feature: Small Structural Changes in the Alkyl Substituents of Macrocyclic π‐Extended Thiophene Oligomers Causes a Key Effect on Their Stacking and Functional Properties (ChemPlusChem 6/2019)

Cover Feature: Small Structural Changes in the Alkyl Substituents of Macrocyclic π‐Extended Thiophene Oligomers Causes a Key Effect on Their Stacking and Functional Properties (ChemPlusChem 6/2019)

Small Structural Changes in the Alkyl Substituents of Macrocyclic π-Extended Thiophene Oligomers Causes a Key Effect on Their Stacking and Functional Properties.

Three new macrocyclic π-extended thiophene hexamers composed of four thienylene-ethynylene and two thienylene-vinylene units with or without four alkyl substituents have been synthesized. Despite similar shape-persistent structures in solution, the alkyl substituents control the solid-state structures and morphologies. The unsubstituted hexamer exhibited a planar conformation with a theoretically predicted structure in the solid state; however, the planar hexamer with four ethyl substituents formed a closely stacked columnar crystal structure to exhibit π-π interactions. Interestingly, the hexamer with four butyl substituents adopted both planar and twisted conformations in the solid state, exhibiting polymorphism based on induced-fit stacking of molecules. Thus, the butyl-substituted hexamer produces a mixture of yellow, orange, and red single crystals from toluene/acetone, and X-ray analysis revealed six different conformations. Consequently, the small structural difference in the macrocycles causes a key effect on their functional properties in the solid state, and their morphology governs electrical conductivity and organic field-effect-transistor activity. The polymorphism of the hexamers was applied to the switching of film morphology.

Self-assembled two-dimensional layered oxide supercells with modulated layer stacking and tunable physical properties

Layered materials, represented by graphene and transition metal dichalcogenides, have aroused significant research interest with the intriguing physical phenomena behind and enormous nanoscale device applications. Here, we report two types of novel modulated Bi-based layered supercell (LSC) structures via combined experimental and first-principles investigation. These two types of oxide-based LSC structures are prepared through self-assembly fabrication from both BiMnO3 and Bi2NiMnO6 by pulsed lased deposition under well-controlled growth conditions. Both LSC structures are composed of alternative layer stacking of two sublattices along the film growth direction, i.e. sublattice 1 of Mn–O or Ni–Mn–O octahedral slab and sublattice 2 of Bi2O2 or Bi3O3 slab, respectively. Moreover, these two LSC structures can be tuned by changing the compositions of Bi–O sublattice from Bi2O2 to Bi3O3 for the same material system by precise control of growth conditions. The experimental characterizations reveal that these new LSCs with modulated layer stacking sequence results in tunable physical properties including robust room-temperature ferromagnetism and unique optical properties, which is well consistent with our first-principles electronic structure calculations. This work demonstrates the possibility of tuning layered oxide stacking by self-assembly thin film growth for designed material functionalities. The Bi-based LSC can be epitaxially grown on flexible mica substrate which is of great significance toward future flexible layered oxide–based electronic applications such as magnetic data storage.

Comparative Evaluation of Corrosion Effects between Nanocrystalline Silver Alloy and Tradition Gold Stacks Using Spring Probe Contacts

Although silver is evaluated as an alternative of gold, it is more prone to tarnishing, oxidization and corrosion. Recent advancements in nano materials research resulted in a nanocrystalline silver alloy which has several advantages like high hardness, thermal stability, non-coarsen with age, hence a viable solution for connector applications. In this work, the performance of nanocrystalline silver alloy against corrosion was studied. Two different set of spring probes were electroplated on inner and outer regions and tested using force deflection resistance (FDR), life cycle test (LCT), SEM, EDS and X-Ray CT scan. First set of spring probes were electroplated with nanocrystalline silver alloy, nanocrystalline Ni-W, Ni sulfamate and Ni strike with thicknesses of 2.4 µm, 1.8 µm, 2.0 µm and 0.5 µm respectively. Second set of spring probes were electroplated with Gold, Ni sulfamate and Ni strike with thicknesses of 0.9 µm 1.9 µm and 0.5 µm respectively. The body of spring probes was made up of copper alloy. This work reports the changes in electrical, mechanical and material properties of nanocrystalline silver alloy and gold stacks after reliability operations like humidity test for 24 hours and 96 hours, porosity test for 60 mins and salt-fog test for 24 hours. Although hard gold is preferred as a final finish for contacts, the demand of finding its alternative has increased because of increase in market price. Further, practices to reduce gold thickness increase the porosity of gold layer which inversely effects the performance of connectors. Nanocrystalline silver alloy is a potential candidate as an alternative of gold in high speed applications [1]. It behaves differently than pure silver because its thermally stable nanostructure improves hardness and eliminates surface sulfidation [2]. All tests in this work were performed on spring probes which is one of the products of Smiths Interconnect used for contacts and connector applications [3]. In FDR, the spring compressed from normal position to 0.14 inch and extended back to normal position. By this way, it completes a hysteresis and measures coefficient of friction between barrel and plunger of spring probes. After reliability operations, the highest compression force in the case of gold was reached up to 12 oz and in the case of nanocrystalline silver alloy, it reached up to 9.5 oz. The difference in the magnitude of compression and extension force at 0.14 inch measures friction. Higher difference between these two forces measures lower Q values which result in higher coefficient of friction. After reliability operations, the range of this difference was from 6 oz to 7 oz in the case of gold but in the case of nanocrystalline silver alloy this range was from 3.5 oz to 4 oz. Moreover the difference in resistance during compression and extension was 2 mΩ in the case of gold and 1 mΩ in the case of nanocrystalline silver alloy. Meaning the alloy of nanocrystalline silver did not allow silver sulfidation. In life cycle test (LCT), 32 spring probes were installed into receptacles that have been press fitted into a matrix of holes drilled into fiber block and the resistance was measured in 10,000 life cycles. The maximum resistance was reached up to 11 mΩ in the case of gold stack but in the case of nanocrystalline silver alloy it was reached up to 8 mΩ only. In the reliability tests, many probes failed to measure contact resistance in the case of gold stack, but in the case of nanocrystalline silver stack it maintained below 6 mΩ. This means that the failure of probes was limited by the wear performance of the gold in the mating pair between barrel and plunger. The failed probes in reliability operations were tested using front and cross section SEM and the elemental composition was observed using point and line scan of EDS. The mechanical marks, which is a function of wear rate, were observed in SEM on the inner regions of the probes at the mating of barrels and plungers. The failure of the probes was further tested from X-Ray CT scanning. In the final version of the manuscript additional results and discussions will be presented.

Surface Self-Assembly, Film Morphology, and Charge Transport Properties of Semiconducting Triazoloarenes.

Surface-assisted molecular self-assembly is a powerful strategy for forming molecular-scale architectures on surfaces. These molecular self-assemblies have potential applications in organic electronics, catalysis, photovoltaics, and many other technologies. Understanding the intermolecular interactions on a surface can help predict packing, stacking, and charge transport properties of films and allow for new molecular designs to be tailored for a required function. We have previously studied a molecular platform, tris( N-phenyltriazole) (TPT), that exhibits planar stacking through >20 molecular layers through donor-acceptor-type intermolecular π-π contacts between the electron-deficient tris(triazole) core and electron-rich peripheral phenyl units. Here, we investigate an expanded family of TPT-based molecules with variations made on the peripheral aryl groups to modulate the molecular electron distribution and examine the impact on molecular packing and charge transport properties. Molecular-resolution scanning tunneling microscopy was used to compare the molecular packing in the monolayer and to investigate the effects that the structural and electronic modifications have on the stacking in subsequent layers. Conductivity measurements were made using the four-point probe van der Pauw technique to demonstrate charge transport properties comparable to pentacene. Although molecular packing is clearly impacted by the chemical structure, we find that the charge transport efficiency is quite tolerant to small structural variations.

Tuning the optical bandgap in layered hybrid perovskites through variation of alkyl chain length

Recently, layered hybrid perovskites have been attracting huge interest due to a wide range of possible chemical compositions and the resulting tunability of the materials’ properties. In this study, we investigate the effect of the chain length of the organic ligands on the optical properties of stacks of two-dimensional perovskite layers consisting of alkylammonium lead iodide (CnH2n+1NH3)2PbI4 with n = 4, …, 18. Photoluminescence and absorption spectroscopy reveal a blueshift with increasing chain length n including a jump of 110 meV between the n = 10 and n = 12 ligands due to a change in octahedral tilting. Using X-ray diffraction, we determine the crystal structure and find the octahedral tilting to be the main cause of this blueshift. However, for very short chain lengths, additional effects further reduce the transition energy. Results of effective mass approximation model calculations show good agreement between the expected reduction of transition energy and measured photoluminescence emission wavelength for these samples. This highlights how octahedral tilting plays a major role in determining the optical bandgap and suggests that miniband formation plays only a minor role in this material.

Low-Energy-Loss Polymer Solar Cells with 14.52% Efficiency Enabled by Wide-Band-Gap Copolymers

SummaryTwo wide band-gap copolymers poly[4,8-bis(5-(2-butylhexylthio)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-TZNT] (PBDTS-TZNT) and poly[4,8-bis(4-fluoro-5-(2-butylhexylthio)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-TZNT] (PBDTSF-TZNT) based on naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole) (TZNT) and benzo[1,2-b:4,5-b']dithiophene (BDT) with different conjugated side chains have been developed for efficient nonfullerene polymer solar cells (NF-PSCs). The rigid planar backbone of BDT and TZNT units imparted high crystallinity and good molecular stacking property to these copolymers. Using 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]-dithiophene (ITIC) as the acceptor, PBDTSF-TZNT devices showed a high Voc of 0.98 V with an Eloss of 0.61 eV. On selecting 3,9-bis(2-methylene-(5,6-difluoro-(3-(1,1-dicyanomethylene)-indanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b’]-dithiophene (IT-4F) instead of ITIC, the devices maintained the high Voc of 0.93 V with an even lower Eloss of 0.59 eV. The combination of the above-mentioned low Eloss, broadened absorption, better matched energy level, improved crystallinity, and fine-tuned morphology promoted the power conversion efficiency (PCE) of PBDTSF-TZNT:IT-4F devices from 12.16% to 13.25%. Homo-tandem devices based on PBDTSF-TZNT:IT-4F subcells further enhanced the light-harvesting ability and boosted the PCE of 14.52%, which is the best value for homo-tandem NF-PSCs at present.

High throughput scanning of dimer interactions to facilitate confirmation of the molecular stacking mode: a case of 1,3,5-trinitrobenzene and its amino-derivatives.

Exactly predicting the packing structures of a given molecule is a crucial topic in crystal engineering, while it remains still challenging, as it requires huge calculations, largely above common computation cost and time limitations. However, current progress in high throughput calculations makes the fast screening of structures and properties feasible. In the present work, we exemplify this by considering a special case of ascertainment of the molecular stacking mode and shear properties of energetic materials. Four energetic π-bonded molecules, 1,3,5-trinitrobenzene, 2,4,6-trinitroaniline, 1,3-diamino-2,4,6-trinitrobenzene and 2,4,6-triamino-1,3,5-trinitrobenzene, with a different number of H atoms replaced by amino groups, are adopted as samples to scan the potential energy surfaces (PESs) of dimers through high throughput calculations. It is found that the parallel stacking mode is the most energetically favored, followed by the T-shaped, coplanar and crossing ones. Such an energetically favored stacking mode is observed in all related π-stacked crystal structures at ambient conditions or low temperatures. It shows that the stacking mode can be ascertained through the PES scanning of dimers, and thereby, the stacking structures and properties related to the stacking mode, like mechanical anisotropism, can be quickly screened by means of high throughput calculations.

Characterizing Skeleton Structure and Stacking Properties of Continuous and Gap Graded Aggregate Mixtures

In order to optimize the skeletal properties of granular pavement materials, a numerical discrete element model for continuous and gap graded aggregate mixtures was developed using a step‐by‐step filling method. The penetration tests were conducted, and indexes such as penetrating resistance, average coordination number, California bearing ratio, and void ratio of coarse aggregates obtained from the tests were used to evaluate the skeleton structure and the stacking properties of aggregate mixtures. The results show that the skeleton structure of aggregate mixtures is closely related to the combination of particle size. Smaller difference in particle size leads to stronger interference effect. The parameters of stacking properties of continuous and gap graded aggregate mixtures are not significantly different in the natural stacking condition. However, gap graded aggregate mixtures are affected by external loads significantly due to structural reconstruction.

Design, experiment and verification of a refined resonance method for property measurement of piezoelectric stack

A refined resonance method, which is based on the theoretical model of a piezoelectric stack under constraint boundary condition is developed and proposed to measure the properties of piezoelectric stack which are relevant to the prestress. The method can transcend the limitation of the conventional resonance method in which the piezoelectric stack under measurement must be free to vibrate. An experimental setup has been designed and built according to the theoretical model, and the properties of a piezoelectric stack are characterized for a wide range of prestress to demonstrate the validity of this method. The experimental results show that properties including relative dielectric constant, piezoelectric constant, electromechanical coupling coefficient and elastic compliance exhibit strong pressure dependence. Among them, the piezoelectric constant measured by this method is compared with measurement by traditional static method, and the deviation between the refined and conventional method is less than 3.25% for a pressure range from 0 to 6 MPa, which indicates that the experimental results of the two test methods are consistent and the presented theoretical model for piezoelectric stack under preload manifests accuracy by means of the correctness and feasibility verification of the proposed method though cross validation and relevant discussions. Consequently, the refined resonance method could be extended to analyze the variation of piezoelectric stack properties that occurs under operational conditions with varied pressure.

Influence of Bridging Groups on the Photovoltaic Properties of Wide-Bandgap Poly(BDTT- alt-BDD)s.

To further advance polymer solar cells requires the fast evolution of π-conjugated materials as well as a better understanding of their structure-property relationships. Herein, we present three copolymers (PT1, PT2, PT3) made through tuning π-bridges (without any group, thiophene, and 3-hexylthieno[3,2- b]thiophene) between electron-rich (D: BDTT) and -deficient (A: BDD) units. The comparative studies reveal the unique correlation that the tune of π-bridge on the polymeric backbone governs the solid stacking and photovoltaic properties of resultant poly(BDTT- alt-BDD)s, which provide an effective way to deliver new and efficient polymer with feasible processability. That is, polymers with either twist zigzag backbone (PT1) or with linear coplanar backbone (PT2) result in inferior photovoltaic performance upon simple solution casting. Among them, PT3 with extended zigzag backbone and planar segments exhibits suitable processability and retains good efficiency in nonfullerene solar cells through a single-solvent cast without involving tedious treatments. This work illustrates that the tuning of the D-π-A polymer backbone facilitates efficient materials with feasible processability, promising for scale-up fabrication.

A-D1-A-D2-type regioregular and random terpolymers based on oligothiophene and dialkyloxy- benzothiadiazole units for polymer solar cells

Through different routes, A-D1-A-D2-type regioregular polymer P1 (via two steps method) and random polymer PR1 (via one step of Stille polymerization) with the similar polymer backbone, incorporating one acceptor unit (dialkyloxy-benzothiadiazole (ROBT)) and two different donor units (thieno[3,2-b]thiophene (TT) and terthiophene (3 T)) in the polymers, have been synthesized. Both TT and 3 T units could cause extended π-orbital conjugation and induce strong π–π stacking properties. Besides, the noncovalent S⋯O coulombic interactions between ROBT and oligothiophenes (TT and 3 T) intrachain ensured good planarity. Compared with the regioregular polymer P1, the random polymer PR1 showed higher power conversion efficiency of 3.40% because of its higher hole mobility and improved short-circuit current. Our results suggest that the random polymer is benefited to improving the photovoltaic performances, and it is significant to further understand the design conjugated polymers backbone of PSCs.

Tuning the Electron Affinity and Stacking Properties of Corannulene by Introduction of Fluorinated Thioethers.

Trifluoromethylthio-substituted corannulene can be easily synthesized in good yield by the reaction of iodocorannulene with CuSCF3 . Oxidation with meta-chloroperbenzoic acid (mCPBA) yields the corresponding sulfonyl compound which exhibits the largest anodic shift of the redox potential caused by a single substituent. Similarly, four SCF3 , SC6 F5 and SeC6 F5 substituents are introduced in the 1,2,5,6-positions of corannulene starting with 1,2,5,6-tetraiodo- or 1,2,5,6-tetrabromocorannulene, respectively. The reactions are performed in polar aprotic solvents and are believed to follow SN Ar-type substitution mechanisms. Crystal and molecular structures of selected compounds were elucidated by X-ray crystallography. Trifluoromethanesulfonyl corannulene and the fourfold-substituted trifluoromethylthioether exhibit a perfect columnar stacking of the bowls. The substituted corannulenes were investigated electrochemically by cyclic voltammetry giving raise to large anodic shifts owing to substitution with electron-withdrawing groups.

Trefoil-Shaped Porous Nanographenes Bearing a Tribenzotriquinacene Core by Three-fold Scholl Macrocyclization.

Porous curved polycyclic aromatic compounds 6 and 14 bearing a tribenzotriquinacene (TBTQ) core encircled by an m,p,p,m,m,p,p,m,m,p,p,m-cyclododecaphenylene belt were synthesized and characterized by NMR spectroscopy and mass spectrometry. These trefoil hydrocarbon macrocycles were constructed in high yield using an intramolecular three-fold Scholl macrocyclization. X-ray crystal analysis of 14 demonstrated a large wizard-hat-shaped structure with three pores (radii 2.9-3.0 Å). The π-stacking aggregation of the hexa-n-dodecyloxy derivative 6 a and the chloride anion binding properties of 14 were studied by NMR spectroscopy. Such stacking and anion binding properties were much weaker in the singly 11 and doubly macrocyclized products 12.

Trefoil‐Shaped Porous Nanographenes Bearing a Tribenzotriquinacene Core by Three‐fold Scholl Macrocyclization

AbstractPorous curved polycyclic aromatic compounds 6 and 14 bearing a tribenzotriquinacene (TBTQ) core encircled by an m,p,p,m,m,p,p,m,m,p,p,m‐cyclododecaphenylene belt were synthesized and characterized by NMR spectroscopy and mass spectrometry. These trefoil hydrocarbon macrocycles were constructed in high yield using an intramolecular three‐fold Scholl macrocyclization. X‐ray crystal analysis of 14 demonstrated a large wizard‐hat‐shaped structure with three pores (radii 2.9–3.0 Å). The π‐stacking aggregation of the hexa‐n‐dodecyloxy derivative 6 a and the chloride anion binding properties of 14 were studied by NMR spectroscopy. Such stacking and anion binding properties were much weaker in the singly 11 and doubly macrocyclized products 12.

Crystal stacking: A route to control photoelectrochemical behavior of BiOBr films

Two types of BiOBr thin films with substantially different crystal stacking and photoelectrochemical (PEC) properties were grown on conducting ITO substrates. In the first case, electrophoretically deposited closely-packed layers with parallel arrangement of (001) faceted plate crystallites (BiOBr||) exhibit p-type PEC behavior in Br2/Br− aqueous solution generating cathodic photocurrent under electrochemical polarization. In the second case, BiOBr electrodes composed of plates with predominant perpendicular orientation to the ITO surface (BiOBr⊥) demonstrate opposite PEC behavior and generate anodic photocurrent. This fundamental difference in PEC properties of BiOBr⊥ and BiOBr|| photoelectrodes, which have close values of BET specific surface area (25 and 18 m2/g), plate thickness (15 and 16 nm) and comparable non-equilibrium charge carrier lifetime (in a sub-ns range), is explained by different stacking of plate crystals in them. Since BiOBr has better electronic conductivity within the (001) plane compared to that along the [001] direction, BiOBr⊥ crystallites have better electrical contact with ITO and are subjected to electrochemical polarization, while BiOBr|| crystallites are predominantly in an open circuit condition and their properties are influenced by the boundaries between plate crystals.