Specific Crystal Orientation Research Articles

Electrochemical grafting of diazonium salts on silica-terminated versus H-terminated silicon

Diazonium salts are one of the most widely used molecules for functionalising electrode surfaces, due to their high reactivity toward a range of different electrodes but have mostly been studied on carbon and gold. Recent work has demonstrated that diazonium salts can be reduced on silica-terminated silicon (Si/SiOx) despite silica (SiOx) being an electrically insulating material, but this interesting phenomenon was only demonstrated on one specific crystal orientation, Si(111) using specific diazonium salts molecules – a more complete understanding of the electrochemical properties of these silica-terminated silicon electrodes remains unclear. In this work, we develop a thorough understanding of the reduction of diazonium compounds on silica-terminated silicon using silicon with different crystal orientation and using nano-structured silicon surfaces that are chemically etched to simultaneously expose different crystal orientations. A comparison between the reduction process on oxide free silicon (Si–H) and silica-terminated Si is then made to reveal the effect of the crystal orientation (amorphous vs crystalline) and the insulating nature of the distal surface (Si‒H vs SiOx) on the reduction process. Results show that diazonium salts form, well-packed thin films on silica-terminated silicon regardless of the crystal orientation of the silicon. The rate of diazonium reduction was found to be sensitive to the crystal orientation of Si only when the diazonium salts are in direct contact with the crystal plane (i.e. in contact with Si–H) as opposed to when there is a thin layer of native amorphous oxide material in between. The reduction rate is sufficiently slow on silica-terminated silicon that at slow scan rates, the system reaches a steady state current and become diffusion controlled. This is not observed on oxide-free silicon electrodes which are observed to be governed by a kinetically driven mechanism. These findings deepen our understanding of the electrochemical activity of silica-terminated silicon surfaces which are widely used in solar cells, electronics, chemical and biosensors.

Transient Phase-Mediated Li+ Transportation in the Lithium Lanthanum Titanate Solid-State Electrolyte.

The lithium lanthanum titanium oxide (LLTO) perovskite is one type of superior lithium (Li)-ion conductor that is of great interest as a solid-state electrolyte for all-solid-state lithium batteries. Structural defects and impurity phases formed during the synthesis of LLTO largely affect its Li-ion conductivity, yet the underlying Li+ diffusion mechanism at the atomic scale is still under scrutiny. Herein, we use aberration-corrected transmission electron microscopy to perform a thorough structural characterization of the LLTO ceramic pellet. We reveal a prevalent transient phase transition of (La, Ti)2O3 existing at the antiphase boundaries between single-crystalline LLTO domains. This transient phase exhibits a specific crystal orientation with the LLTO phase and shows a gradual structural transition to a tetragonal LLTO structure, which enables detailed crystallographic analysis to correlate their formation to the sintering process of LLTO powders into ceramic pellets. We also find that Li diffusion is retarded by this phase and correlated with the excess amount of La, which is corroborated by the theoretical evaluation of the atomistic mechanisms of Li diffusion across this phase.

Preferred crystal surface exposure and near-crystal surface desolvation construct efficient Zn plating/stripping reversibility

The Zn/electrolyte interface stability is related to HER, passivation, dendrites, corrosion and Zn2+ deposition orientation. Reducing the occupation of H2O dipoles in the inner layer of electrical double layer (EDL) is conducive to the inhibition of interfacial side reactions and directing the deposition of Zn2+ along the (002) crystalline surface, which are beneficial to the reduction of dendrites and the improvement of plating/stripping reversibility. A mechanism is elucidated by which Acetyl-L-carnitine Hydrochloride (A-L-CN) reconfigures the EDL structure and guides the selective deposition of Zn2+ in this paper. Theoretical calculations show that A-L-CN can cover the high-energy active sites on the Zn (101) crystal plane and control the specific crystal orientation of the deposits along the (002) crystal plane to produce faceted epitaxial growth. The electrochemical test results show that the Zn anode has excellent plating/stripping reversibility as well as good cumulative capacity (10 mA cm−2, 1 mA h cm−2, ACE of 99.80 %, CPC of 7,753 mA h cm−2). The assembled Zn2+ hybrid supercapacitor (ZHS) and Zn//PANI full cell show excellent performance (ZHS up to 60,000 cycles; the capacity retention ratio of Zn//PANI full cell is 76.7 % after 1,000 cycles). The work offers the possibility of achieving stabilized Zn/electrolyte interface performance.

Plasmon‐Enhanced Circular Polarization High‐Harmonic Generation from Silicon

AbstractHigh harmonics of circular polarization can be directly generated by monochromatic circularly polarized incident light owing to the high density and stable structure of crystal media. If the arrangement of multiple coplanar atoms in the unit structure of the crystal exhibits rotational symmetry, the polarization state of the high harmonics generated from the crystal follows specific selection rules that have been observed in the 2D crystal medium. In addition, the geometric symmetry of the coplanar atom distribution is related to the orientation of cubic crystals. This implies that only the polarization along a specific crystal orientation can achieve a selection of high‐harmonic polarization states. However, this is a very weak process in cubic crystals owing to the attenuation of crystal anisotropy to circularly polarized light and the dependence of the electron transition rate on the crystal orientation. In this study, plasmonic nanoantennas are designed on silicon crystal films to enhance this process. The harmonic emission is more than ten times brighter than that without nanoantennas and conformed to the selection rules for high harmonics. The research results offer a new approach for deep­ultraviolet space filtering, carrier control, and the development of compact extreme­ultraviolet light sources.

Nonequilibrium Lattice Dynamics of Individual and Attached PbSe Quantum Dots under Photoexcitation.

Quantum dot (QD) solids are emerging materials for many optoelectronic applications. To enhance interdot coupling and charge transport, surface ligands can be removed, allowing individual QDs to be attached along specific crystal orientations (termed "oriented attachment"). Optimizing the electronic and optical properties of QD solids demands a comprehensive understanding of the nanoscale energy flow in individual and attached QDs under photoexcitation. In this work, we employed ultrafast electron diffraction to directly measure how oriented attachment along ⟨100⟩ directions affects the nonequilibrium lattice dynamics of lead selenide QDs. The oriented attachment anisotropically alters the ultrafast energy relaxation along specific crystal axes. Along the ⟨100⟩ directions, both the lattice deformation and atomistic random motions are suppressed in comparison with those of individual QDs. Conversely, the effects are enhanced along the unattached ⟨111⟩ directions due to ligand removal. The oriented attachment switches the major lattice thermalization pathways from ⟨100⟩ to ⟨111⟩ directions.

Facet-engineered ruthenium oxide on titanium oxide oxygen evolution electrocatalysts for proton-exchange membrane water electrolysis

Ruthenium oxide-based catalysts exhibit an active oxygen evolution reaction (OER) in acidic media but suffer from low stability, limiting their practical application in proton-exchange membrane water electrolyzers (PEMWEs). Herein, we present an effective acidic OER catalyst comprising RuO2 nanolayers on an isostructural rutile TiO2 support (NL-RuO2-250) that maximizes exposure to specific crystal orientations. RuO2 morphology and growth mechanism on the TiO2 surface were affected by the interfacial charge states during hydrothermal process, with the crystal structure similarity between the RuO2 catalyst and TiO2 support advantageous for maximizing compatibility at the interface. Density functional theory combined with experimental analyses revealed that NL-RuO2-250 is an optimized form for improving OER performance. As-prepared NL-RuO2-250 required a low overpotential (230 mV at 10 mA cm−2) and a PEMWE single cell assembled with NL-RuO2-250 exhibited an insignificant voltage drop for 24 h under 0.2 A cm−2, demonstrating a practical design strategy for acidic OER catalysts.

Vacancy modulation dramatically enhances the thermoelectric performance of InTe single crystal

InTe single crystals have demonstrated great promise in the field of thermoelectric materials, particularly when oriented along the [110] direction. This specific crystal orientation exhibits higher electronic conductivity and lower thermal conductivity compared to other orientations of InTe. Through first-principles calculations, we identified the anisotropic valence band and phonon dispersion as the underlying factors. Moreover, reducing the density of In+ vacancies in InTe was found to lower the band effective mass and modulate carrier scattering, enhancing the material quality factor (B). To explore these findings, we systematically grew InTe single crystals, achieving exceptional thermoelectric performance. A record-breaking power factor of 12.0 μW·cm−1·K−2 and a dimensionless figure of merit (zT) of 0.5 at room temperature were obtained. Notably, InTe crystals oriented along [110] with low In+ vacancy density exhibited the highest average zT of 0.63 among InTe-based thermoelectric materials within the 300–473 K temperature range. Furthermore, we introduced an effective method of reducing In+ vacancies through Indium vapor annealing, resulting in the highest reported carrier mobility of 182 cm2·V−1·s−1 for InTe. Our study highlights the potential for improving InTe's thermoelectric performance near room temperature through vacancy modulation and crystal orientation.

Novel Ti3SiC2-(Ti, Zr)B2 toughened (Ti, Zr)C-based composites with enhanced mechanical properties fabricated by dual in situ reactions hot-pressing at low temperature

The fully dense Ti3SiC2-(Ti, Zr)B2 toughened (Ti, Zr)C-based composites were fabricated at 1400–1600 °C for the first time by dual in situ reactions hot-pressing with TiC, ZrB2, and Si as the initial powders. The influence of ZrB2, Si content and sintering temperature on the microstructure and mechanical properties of the composite was reported. When 10 mol% ZrB2 was added, Si combined with residual TiC to form Ti3SiC2 and SiC. However, with the addition of ZrB2 increase to 20 mol% and 30 mol%, Si participated in the formation of ZrSi and was not enough to react with TiC to form Ti3SiC2. The low-temperature in situ reactions, multiphase coupling effects, and the pinning effect of nano-SiC refine the microstructure of the composites. There are specific crystal orientation relationships between (Zr, Ti)C and (Ti, Zr)B2, as well as between (Ti, Zr)C and SiC. The layered Ti3SiC2 and plate-like (Ti, Zr)B2 by dual in situ reactions effectively improve the fracture toughness of the composites. The 10 ZB-15 possesses a highest fracture toughness of 6.1 MPa⋅m1/2. The 30 ZB-16 has the good comprehensive mechanical properties. The fracture toughness, flexural strength, and hardness of 30 ZB-16 is 5.6 MPa⋅m1/2, 679 MPa, and 26.4 GPa, respectively. The Ti3SiC2 and TiB2 formed during dual in situ reactions enables the composite to exhibit excellent oxidation resistance and wear resistance.

Vapor-transport-deposited Sb2S3 thin-film solar cells: Tailoring photovoltaic properties through deposition temperature

Crystal orientation plays a crucial role in the performance of Sb2S3 thin-film solar cells (TFSCs). Among various deposition techniques, vapor transport deposition (VTD) stands out as a viable technique for producing scalable and uniformly deposited thin films, particularly in the solar industry. This study explores temperature-modulated VTD-Sb2S3 deposition to enable efficient carrier transport in photovoltaic cells. In the VTD process, the deposition temperature is altered between 480 °C and 540 °C. XRD, SEM, EDS, and AFM techniques are employed to obtain the characteristics of the Sb2S3 thin films at varying temperatures and evaluate critical features like crystal structure and orientation, surface morphology, composition, and roughness. The prominent crystal orientation changes from the (hk0) to the (hk1) plane after increasing the deposition temperature from 500 to 520 °C. The (211)- and (221)-planes become more prominent when the deposition temperature exceeds 520 °C. The device with the architecture SLG/Mo/Sb2S3/CdS/i-ZnO/AZO/Al, a substrate-configured TFSC, yields a maximum power conversion efficiency of 0.22% when the VTD-Sb2S3 absorber film is deposited at 520 °C. This study presents a promising approach to producing thin films with a preference for specific crystal orientations. The primary aim is to enhance the efficiency of solar cells that utilize VTD-Sb2S3 absorbers.

Building Near‐Unity Stacked (002) Texture for High‐Stable Zinc Anode

AbstractDendrite‐free Zn anode is the key to avoiding battery failure, which is largely determined by the crystal growth during the electrodeposition process. Therefore, controlling the specific crystal orientation growth of Zn is imperative for high‐performing aqueous zinc ion batteries. Herein, an electrocrystallization orientation regulation strategy is proposed to achieve near‐unity stacked Zn (002) texture growth. Featuring the zincophilic nature and high electronegative carboxylate radical, disodium maleate molecules tend to selectively adsorb on the Zn (002) crystal plane, forming a dynamic protection layer. This adsorption layer regulates Zn2+ diffusion along [100] and [101] orientations with the lowest deposition rate on the (002) plane, homogenizes Zn2+ flux, and keeps away water from Zn surface, constructing the flattened and horizontally arranged Zn deposition layer with dominantly Zn (002) texture and inhibited side‐reaction. Consequently, the Zn anode with near‐unity stacked (002) texture exhibits a 40‐fold enhancement in running lifetime beyond 3200 h and improved coulombic efficiency of 99.81% over 3000 cycles than that with bare ZnSO4 electrolyte. Even at harsh plating/stripping conditions of 30 and 30 mAh cm−2, the Zn anode still sustains state‐of‐the‐art stability over 120 h, enabling a substantial advance in the long‐term stability of the battery.

Perspective on the Preparation Methods of Single Crystalline High Nickel Oxide Cathode Materials

AbstractLi(NixCoyMnz)O2 (x + y + z = 1, NCM), as one of the most dominant cathode materials in electric vehicle (EV) batteries, faces the challenges of poor cycling stability and safety concerns with the increase of Ni content and charge/discharge capacity. Single crystalline NCM (SC‐NCM) materials have been developed to mitigate these challenges, owing to their lower surface areas, fewer grain boundaries, and better morphological stability. Here, the preparation strategies of SC‐NCM are summarized, including continuous high‐temperature sintering (CHTS), molten salt method, pulse high‐temperature sintering (PHTS), and controllable growth with special orientations or sizes. CHTS produces irregular SC‐NCM particles, but is accompanied by Li‐volatilization and agglomeration during long‐term sintering. The molten salt helps to lower calcination temperature and generate well‐defined crystalline material, but generally causes large capacity loss due to the Li/H exchange in the following water rinsing procedure. To address the above challenges, the PHTS strategy has recently been recently proposed, which mitigates Li‐loss through shortened high‐temperature stage and avoids further water rinsing steps. For improving the C‐rate performance, controllable crystal growth with specific sizes and crystal orientations is highly desired, which calls for further investigation and upgrading of current large‐scale preparation technology.

Nonlinear and Anisotropic Ion Transport in Black Phosphorus Nanochannels.

Two-dimensional material nanochannels with molecular-scale confinement can be constructed by Van der Waals assembly and show unexpected fluid transport phenomena. The crystal structure of the channel surface plays a key role in controlling fluid transportation, and many strange properties are explored in these confined channels. Here, we use black phosphorus as the channel surface to enable ion transport along a specific crystal orientation. We observed a significant nonlinear and anisotropic ion transport phenomenon in the black phosphorus nanochannels. Theoretical results revealed an anisotropy of ion transport energy barrier on the black phosphorus surface, with the minimum energy barrier along the armchair direction approximately ten times larger than that along the zigzag direction. This difference in energy barrier affects the electrophoretic and electroosmotic transport of ions in the channel. This anisotropic transport, which depends on the orientation of the crystal, may provide new approaches to controlling the transport of fluids.

Improvement of Magnetic Properties of Zn-bonded Sm-Fe-N Magnets and Investigation of Microstructural Changes at Sm<sub>2</sub>Fe<sub>17</sub>–Zn Interface

This paper reviewed development of Zn-bonded Sm-Fe-N magnets in our group, and reported interfacial diffusion and phase changes at the Sm2Fe17–Zn interface during annealing. For increasing magnetic properties of Zn-bonded Sm-Fe-N magnets, decreasing oxygen content, improving dispersibility of Zn, and increasing relative density are necessary, therefore we prepared low oxygen content Sm-Fe-N and fine Zn powders. The powders were sintered by spark plasma sintering process for increasing density under low oxygen atmosphere resulting in obtaining high (BH)max of 200 kJm-3 with relatively high coercivity of 1.28 MAm-1 and β(HcJ) of –0.34%C-1. In order to further improve the (BH)max, it is necessary to control interfacial diffusion and reaction between Sm2Fe17N3 and Zn phases. Thus, as a first step, microstructural changes and interdiffusion coefficient at the Sm2Fe17–Zn interface were investigated using Sm2Fe17–Zn diffusion couples, in this study. It was clear that interdiffusion of Zn, Fe and Sm occurred during annealing below melting temperature of Zn, and the diffusion rate of Zn was faster than those of Fe and Sm. Furthermore, with Zn diffusing into Sm2Fe17 phase, the Sm2Fe17 decompose to ThMn12-Sm(Zn,Fe)12 and α-FeZn phases with specific crystal orientation relationship.

Indentation cracking in mono and polycrystalline cubic zirconia: Methodology of an apparent fracture toughness evaluation

Indentation-induced cracking with sharp tips is studied on mono- and polycrystalline cubic zirconia. Tests at different applied loads are carried out, ranging below and above a threshold load above which visible surface cracking is noted after testing. This threshold load does not appear to be correlated to any discontinuity in the evolution of either the hardness or the irreversible energy ratio with applied load. The crystal orientation and the presence of grain boundaries clearly affects the shape of the cracks generated around the residual imprint. Polycrystalline samples show significantly shorter indentation induced cracks and therefore a higher apparent toughness than single crystals for the same load. In addition, for single crystals, cracks are deflected towards {110} type planes, appearing to be the most susceptible to cracking, and thus logically presenting the lowest apparent toughness. Tests with a Berkovich tip leads to an average of different crystal orientations, while tests with a Vickers tip can be used to test a specific crystal orientation in the case of a cubic crystal such as zirconia.

Generating polycrystalline microstructures with prescribed tensorial texture coefficients

This work is concerned with synthetic microstructure models of polycrystalline materials. Once a representation of the microstructure is generated, the individual grains need to be furnished with suitable crystal orientations, matching a specific crystal orientation distribution. We introduce a novel method for this task, which permits to prescribe the orientations based on tensorial Fourier coefficients. This compact representation gives rise to the texture coefficient optimization for prescribing orientations method, enabling the determination of representative orientations for digital polycrystalline microstructures. We compare the proposed method to established and dedicated algorithms in terms of the linear elastic as well as the non-linear plastic behavior of a polycrystalline material.

Surface alteration and chemical durability of hollandite (Cr, Al and Ti) consolidated by spark plasma sintering in acid solution

For the development of pyrochemical reprocessing of spent fuels in which a substantial amount of Cs-containing waste is confronted, appropriate management of the long-lived radioactive Cs is required. In the present study, solid state reaction and Spark plasma sintering (SPS) were applied to prepare three types of dense hollandite samples as advanced waste form matrix including Ba1.23Al2.46Ti5.54O16, Ba1.15Cr2.3Ti5.7O16 and Ba1.15Ti2.3Ti5.7O16 with a relative density higher than 95%. The thermogravimetric analysis (TGA) results show that the three hollandite dense pellets prepared by SPS have good thermal stability and high temperature oxidation resistance, which can be used as potential waste forms for 135Cs. Ba1.15Cr2.3Ti5.7O16 demonstrates the best Ba immobilization among three pellets due to its best chemical durability based on a 240-h leaching test, with a cumulative release amount of 0.62 mmol/m2 for Ba at semi-dynamic leaching (pH = 2). The leaching rates of elements decrease continuously with time, and finally reach a dynamic equilibrium as the long-term leaching rates tend to be constant. It is because the dominant leaching mechanism switches from initial rapid dissolution and surface effects to the long-term diffusion. The Ba1.15Cr2.3Ti5.7O16 sample surface was corroded after 14 days of static leaching in HCl solution with pH = 2, with corrosion pits found on the grain surface of specific crystal orientations, which demonstrates that different crystal orientations have different corrosion resistance. Ba1.15Cr2.3Ti5.7O16 displays good thermal stability and high corrosion resistance, and thus could be used as a potential nuclear waste form for the immobilization of the long-lived and highly mobile Cs.

An epitaxial coating with preferred orientation stabilizing High-Energy Ni-Rich NCA cathodes

Surficial activity and stability of layered Ni-Rich cathodes are important and interactive electrochemical characteristics of lithium-ion batteries (LIBs), especially under aggressive working conditions (e.g., high cutoff voltages, or high charging/discharging rates, or a moist storage/assembling environment). Here, we construct metal–organic framework (MOF)-derived α-LiAlO2 epitaxial coatings (5 ∼ 10 nm) on LiNi0.80Co0.15Al0.05O2 (NCA) surface, in which α-LiAlO2 are realized by the controlled-pyrolysis of MOF and in-situ lithiation with surficial lithium impurities on NCA particles. The α-LiAlO2 epitaxial coatings share the same crystal structure and orientation with the NCA substrate, which enable the surface-engineered NCA cathodes to achieve enhanced chemical stability and Li+-migration kinetics (including the interface between NCA substrates and α-LiAlO2 layers). In detail, the epitaxial α-LiAlO2-coated NCA displays a high capacity of 178.3 mA h g−1 at 5C, a capacity retention of 70.1% after 200 cycles (vs. 42.2% of the pristine NCA, 3.0–4.5 V), and a much-improved chemical/electro- stabilities in the air-exposure testing. DFT calculation shows that the induced Fermi-level in spin-up channel supports the increased electrical conductivity of the α-LiAlO2 coated NCA materials. This work demonstrates a new idea for design of specific crystal orientations, which would be applied to fulfill efficient production, machining, and applications of functional electrode materials.

Large anisotropic Dzyaloshinskii–Moriya interaction in CoFeB(211)/Pt(110) films

We investigated the crystalline direction dependent Dzyaloshinskii–Moriya interaction (DMI) in single crystal CoFeB(211)/Pt(110) films utilizing the Brillouin light scattering technique. The in-plane magnetic anisotropy and the DMI coefficient show a clear 1/tCFB relation. The quantified DMI strength is −2.5 pJ/m along Pt [001] and −1.2 pJ/m along Pt [11¯0] with a large anisotropy ratio of 2.1. Such a strong anisotropy of DMI is attributed to the C2v crystal symmetry at the CoFeB/Pt(110) interface. Our results provide a route toward designing topological magnetic textures by tailoring the DMI strength along the specific crystal orientation in ferromagnet/Pt(110) systems.

Robust Polarization Stability in a Self‐Assembled Ultrathin Organic Ferroelectric Nano Lamellae

AbstractSpontaneous polarization is a characteristic feature of a ferroelectric material that can be switched by the application of an external electric field. However, in a practical scenario, the switched polarization should be stable for the realization of functional devices. In this study, an ultrathin (≈40 nm) poly(vinylidene fluoride‐trifluoroethylene (PVDF‐TrFE) film self‐assembled on a monolayer (≈1 nm) graphene oxide (GO) film is exploited. Oxygen‐functional groups and defective structure of GO can act as domain pinning sites to provide strong ferroelectric domain stability along with a specific crystal orientation to PVDF‐TrFE through hydrogen bonds and columbic interactions. Scanning probe microscopy based switching experiments reveal excellent piezoelectric response (d33 = −145 pm V−1) along with high polarization retention (over 1500 h with no volatilization) in these ultrathin films, paving new pathways toward high performance miniaturized organic ferroelectric devices.

Understanding the Anomalous Discontinuous Precipitation in Cu-Ni-X (X = Co,Fe) Alloys Based on CALPHAD Method and Phase-Field Simulation

The anomalous discontinuous precipitation which is called “Cellular Decomposition (CD)” has been observed in Cu-Ni-X (X = Co,Fe) ternary systems, i.e., the precipitate morphology in cell region is a nanoscale fine fiber, the direction of the fibers does not take specific crystal orientation, and the morphology is wavy. In this study, we elucidated the reason why such an unusual cellular decomposition occurs by means of the Calphad method and phase-field simulations. In particular, we focused on the spinodal decomposition inside the grain before CD. The results showed that the Ni component preferentially segregates at the interface region between precipitate and matrix phase in the two-phase microstructure by spinodal decomposition, and the Ostwald ripening is suppressed due to the low solute solubility of the matrix phase in the Cu-Ni-X (X = Co,Fe) system. Hence, the spinodal microstructure formed inside the grain before CD is trapped into high-energy level, which induces the discontinuous precipitation with high speed grain boundary migration, that provides “Cellular Decomposition”.