Gold Crystals Research Articles

Autonomous Thermal Modulator Based on Gold Film‐Coated Liquid Crystal Elastsomer

AbstractRadiative cooling has been recently intensively explored for thermal management and enhancing energy efficiency. Yet, traditional materials with singular emissivity fall short in dynamic thermal management, highlighting the need for materials that can adjust their thermal radiation in real time. Active modulation methods, requiring external stimuli such as mechanical stretch, electric potential, or humidity change, offer adaptability but can increase energy use and complexity. Passive approaches, using materials' inherent thermal‐responsive properties, face manufacturing and scalability challenges. Here, a scalable yet effective passive approach is introduced for adaptive thermal modulation based on gold (Au) and liquid crystal elastomer (LCE) with a reversible response to environmental temperature changes. This modulator enables a “low thermal resistance” state through actuation‐induced microcracks that expose a high‐emissivity polymer substrate, and a “high thermal resistance” state by closing these microcracks and forming a high thermal resistance air gap between the modulator and the target object. The flexible design and fixed external dimensions of the Au‐LCE thermal modulator make it adaptable to various surface geometries. Furthermore, by adjusting the LCE's chemical composition, the modulator's transition temperature can be tailored, broadening its applications from enhancing building energy efficiency to improving clothing thermal comfort.

Computation of differential and integral operators using [formula omitted]-polynomials of gold crystal

Gold is generally considered a noble metal since it is inherently inert in its bulk state. However, gold demonstrates reactivity when it is in its ionic state. The inherent inertness of bulk gold has resulted in its widespread recognition as a vital raw material in various biomedical processes. The applications of these technologies include drug delivery microchips, dental prostheses, reconstructive surgery, culinary additives, and cardiovascular stents. Gold can also exist in molecules or ions, particularly gold ions, which facilitates the production of gold nanomaterials. In this paper, we have computed differential and integral operators by using the M-Polynomial of gold crystals and by utilizing this polynomial, we have also computed eleven topological indices like 1st Zagreb, 2nd Zagreb, Hyper, Sigma, Second Modified, General Randic, General Reciprocal Randic, 3rd Redefined Zagreb, Symmetric Division Degree, Harmonic, Inverse Sum indices for the structure of Gold crystal.

Investigation of reduced reverse degree based polynomials & indices of gold crystals

Gold is widely recognized as a noble metal due to its inherent inertness in its bulk form. Nevertheless, gold exhibits reactivity in its ionic form. The inert qualities of bulk gold have led to its extensive recognition as a fundamental raw ingredient in several biomedical processes. These applications encompass drug delivery microchips, dental prostheses, reconstructive surgery, food additives, and endovascular stents. Gold in large amounts can be thought of as safe. Gold can also exist as molecules or ions, specifically gold ions, making it easier to make gold nanomaterials. The distinctive characteristics of gold set it apart from its molecular or bulk states, making its execution a very efficient instrument in the field of nanomedicine. Some of these traits are ease of synthesis, a higher ratio of surface area to volume, more reactive particles, the ability to withstand changes to the surface, and strong optical properties. The reduced reverse degree-based polynomials and topological descriptors of the molecular structure of the gold crystal are investigated in this manuscript. The numerical and graphical analysis of outcomes this study are also described.

Single Crystal and Pentatwinned Gold Nanorods Result in Chiral Nanocrystals with Reverse Handedness.

Handedness is an essential attribute of chiral nanocrystals, having a major influence on their properties. During chemical growth, the handedness of nanocrystals is usually tuned by selecting the corresponding enantiomer of chiral molecules involved in asymmetric growth, often known as chiral inducers. We report that, even using the same chiral inducer enantiomer, the handedness of chiral gold nanocrystals can be reversed by using Au nanorod seeds with either single crystalline or pentatwinned structure. This effect holds for chiral growth induced both by amino acids and by chiral micelles. Although it was challenging to discern the morphological handedness for L-cystine-directed particles, even using electron tomography, both cases showed circular dichroism bands of opposite sign, with nearly mirrored chiroptical signatures for chiral micelle-directed growth, along with quasi-helical wrinkles of inverted handedness. These results expand the chiral growth toolbox with an effect that might be exploited to yield a host of interesting morphologies with tunable optical properties.

Single Crystal and Pentatwinned Gold Nanorods Result in Chiral Nanocrystals with Reverse Handedness

AbstractHandedness is an essential attribute of chiral nanocrystals, having a major influence on their properties. During chemical growth, the handedness of nanocrystals is usually tuned by selecting the corresponding enantiomer of chiral molecules involved in asymmetric growth, often known as chiral inducers. We report that, even using the same chiral inducer enantiomer, the handedness of chiral gold nanocrystals can be reversed by using Au nanorod seeds with either single crystalline or pentatwinned structure. This effect holds for chiral growth induced both by amino acids and by chiral micelles. Although it was challenging to discern the morphological handedness for L‐cystine‐directed particles, even using electron tomography, both cases showed circular dichroism bands of opposite sign, with nearly mirrored chiroptical signatures for chiral micelle‐directed growth, along with quasi‐helical wrinkles of inverted handedness. These results expand the chiral growth toolbox with an effect that might be exploited to yield a host of interesting morphologies with tunable optical properties.

Green synthesis and characterization of gold nanoparticles from discarded computer PCBs on reduction of environmental pollution

The economic value of gold content in electronic waste, particularly waste printed circuit boards (PCBs), has generated interest in recovering gold from this material. Unfortunately, due to the severe environmental hazards associated with such waste, there is a pressing need for efficient and selective methods of gold nanoparticle recovery. A novel technique has been developed to synthesize gold nanoparticles that employ chlorate leaching and Punica granatum extract to minimize the environmental impact of electronic waste. Multiple analytical methods, including UV-Vis, XRD, EDS, SEM, and TEM analysis, were utilized to identify and characterize the extracted gold nanoparticles. The UV-Vis spectrum showed GNP-absorption peaks at a narrow range of wavelengths, primarily at 520 nm, confirming the formation of gold nanoparticles from the e-waste. The XRD analysis identified the material as metallic gold with characteristic peaks of gold crystals (111), (200), (220), and (311), corresponding to the FCC crystal structure. The SEM and TEM analysis revealed that most of the Au nanoparticles were less than 40 nm in size, with some larger particles resulting from the agglomeration of smaller ones. The EDS spectrum analysis indicated that the gold atoms emitted strong signals. At the same time, other elements such as carbon, oxygen, and metals such as Sn, Zn, Pd, Cu, and Cd showed weaker signals. The recovered gold nanoparticles were found to have a bandgap of 2.2 eV, indicating that they are a direct bandgap semiconductor suitable for use in optoelectronic applications. The environmental impact of the PCBs and the chemicals used in the process were also analyzed to address the necessity of using discarded electronic waste to reduce environmental pollution. The proposed method showed high efficiency for extracting gold nanoparticles from e-waste, with simple process steps, low chemical usage, and low cost, as demonstrated by the results.

Large area single crystal gold of single nanometer thickness for nanophotonics

Two-dimensional single crystal metals, in which the behavior of highly confined optical modes is intertwined with quantum phenomena, are highly sought after for next-generation technologies. Here, we report large area (>104 μm2), single crystal two-dimensional gold flakes (2DGFs) with thicknesses down to a single nanometer level, employing an atomic-level precision chemical etching approach. The decrease of the thickness down to such scales leads to the quantization of the electronic states, endowing 2DGFs with quantum-confinement-augmented optical nonlinearity, particularly leading to more than two orders of magnitude enhancement in harmonic generation compared with their thick polycrystalline counterparts. The nanometer-scale thickness and single crystal quality makes 2DGFs a promising platform for realizing plasmonic nanostructures with nanoscale optical confinement. This is demonstrated by patterning 2DGFs into nanoribbon arrays, exhibiting strongly confined near infrared plasmonic resonances with high quality factors. The developed 2DGFs provide an emerging platform for nanophotonic research and open up opportunities for applications in ultrathin plasmonic, optoelectronic and quantum devices.

Local Heating Induced Single-Crystalline Phase Control in Electrochemical Synthesis of Nanomaterials.

Development of synthetic strategies selectively yielding single crystals is desired owing to the facet-dependent chemical reactivities. Recent advances in electrochemical materials synthesis yielded nanomaterials that are surfactant-free, however, typically in polycrystalline forms. In this work, an electrochemical synthetic strategy selectively yielding single-crystalline nanoparticles by implementation of surface-selective heating of the working electrode is developed. Single crystals of copper, silver, gold, and platinum are afforded, and the crystallinity verified by electron diffraction and chemical reactivity studies. Notably, Cu (100) surface prepared by electrochemical synthesis yielded high single product selectivity when applied to electrochemical CO2 reduction catalysis.

Deformation twin traces on gold surfaces: A pathway to tailored epitaxial growth of 1D semiconductors.

The field of one-dimensional semiconducting materials holds a wide variety of captivating applications, such as photovoltaic cells, electronic devices, catalysis cells, lasers, and more. The tunability of electrical, mechanical, or optical attributes of a semiconductor crystal relies on the ability to control and pattern the crystal's growth direction, orientation, and dimensions. In this study, we harvest the unique properties of crystallographic defects in Au substrates, specifically twin boundaries, to fabricate selective epitaxial growth of semiconducting nanocrystals. Different crystallographic defects were previously shown to enhance materials properties, such as, screw dislocations providing spiral crystal growth, dislocation outcrops, and vacancies increasing their catalytic activity, dislocation strengthening, and atomic doping changing the crystal's electrical properties. Here, we present a unique phenomenon of directed growth of semiconductor crystals of gold(I)-cyanide (AuCN) on the surface of thin Au layers, using traces of deformation twins on the surface. We show that emergence of deformation twins to the {111} Au surface leads to the formation of ledges, exposing new {001} and {111} facets on the surface. We propose that this phenomenon leads to epitaxial growth of AuCN on the freshly exposed {111} facets of the twin boundary trace ledges. Specific orientations of the twin boundaries with respect to the Au surface allow for patterned growth of AuCN in the <110> orientations. Nano-scale patterning of AuCN semiconductors may provide an avenue for property tuning, particularly the band gap acquired.

Detrital gold morphology and recycling around the early Miocene St Bathans paleovalley, Central Otago, New Zealand

ABSTRACT The St Bathans paleovalley developed as a major southwest-draining fluvial system during early Miocene rejuvenation of the Central Otago landscape. Rounded quartz pebbles and detrital gold were recycled from Eocene quartz pebble conglomerates into the headwaters of this Miocene paleodrainage system on the northern margin of the Otago Schist belt. Gold particle morphology is mostly irregular and rough, locally with relict gold crystal shapes, plus a minor component of well-defined flakes. Incremental rounding and surface deformation at the 10 µm scale has occurred through several recycling events in Central Otago, hindering linkage of Miocene and younger placer gold to ultimate basement sources. More intense deformation of the gold, forming thin flakes, occurred in the lower reaches of the Miocene paleodrainage system as gold was transported >100 km to eastern Southland. Hence, the St Bathans paleovalley has been an important source of gold for historic mining in Central Otago and Southland.

Tailoring hierarchical nanostructures of tannin acid/alginate beads for straightforward selective recovery of high-purity Au(0) from aqueous solution

The utilization of biomass materials with functional properties and rational porous structures holds significant potential for the recovery of precious metals from secondary resources, while facing challenges in achieving rapid reduction and high recovery rates of metallic Au(0). Herein, a novel concept of achieving high-purity Au(0) efficiently by tailoring tannin acid (TA) architecture and porous structure of TA-functionalized alginate beads (P-TOSA). Optimized by structural engineering, the hierarchically nanostructured P-TOSA beads demonstrate exceptional selectivity and recovery capacity (756.1 ± 2.7 mg/g at pH 5), while maintaining a recovery efficiency of over 99 % across a broad range of pH values (1.0–8.0) through the synergistic combination of chelation-based chemisorption and phenolic groups-based redox reaction. Notably, the TA-based nanostructure-boosted reduced Au(0) served as nucleation sites, facilitating elongation and migration of gold crystals across the vein network, thus forming a shell composed with 90.4 ± 0.4 % of element gold. UV radiation exposure could further generate a dynamic redox system and expedite Au (III) reduction to ultra-high purity Au(0) (93.3 ± 1.1 %) via abnormal grain growth mode. Therefore, this study presents a practical and straightforward approach utilizing biomass microbeads for recycling precious metals in metallic form without the use of toxic eluents or additional reductants.

Mineralogical and technological features of gold from placers of the southern slope of Belaya Gora (Khabarovsk Krai) and stages of its formation

The gold-placer deposit of Pokrovsky-Verny streams is formed on the southern slope of Belaya Gora (Khabarovsk Krai), where streams drain gold formations of the same-name deposit. The gold content in the waste dumps of past years often reaches commercial concentrations, which allows to be re-processed them and some of the gold goes back into the dumps. The field formed by ore and alluvial formations is a complex volcanic structure with a concentric-zone structure underlined by faults. At the initial stage of research, the goal was to determine the content of the precious metal in gravity concentrate samples from the placers, the study of the mineralogical and technological characteristics of gold going into dumps. 135 gold grains ranging in size from 10–15 µm to 3 mm were studied using an electron scanning microscope. Six main species were distinguished by composition and morphology: high-grade in the form of isometric crystals; aggregates of gold crystals with 0–29% silver admixture; dendrites with up to 41% silver admixture; grayish gold and silver amalgams; loose weishanite (Au,Ag)3Hg2 formations of gray color; aggregates of ore-bearing and nonmetalliferous minerals with gold, in which the precious metal is less than half the grain. All gold grains have a flattened shape, variably contain inclusions of clay minerals, quartz, hematite, ilmenite, magnetite, limonite. Grains of native metals and intermetallic compounds are isolated in mineral association with gold. The revealed features of gold show that the formation of the precious metal is associated with hypogenic and epithermal processes, as well as with fluid emanations coming through late deep faults. Effective gold recovery requires several stages mineral processing.

Double pseudo-polymeric complexes of [Au(S2CNR2)2][TlCl4], R2 = (CH2)5, (CH2)6: preparation, structural organization, and thermal behavior (low-temperature reduction and crystallization of gold)

The capability of thallium(I) alkylenedithiocarbamates to bind gold(III) from solutions in 2 M HCl was studied. Double complexes of [Au{S2CN(CH2)5}2][TlCl4] and [Au{S2CN(CH2)6}2][TlCl4] were preparatively isolated as individual forms of gold(III) binding into the solid phase. In the crystalline state, the ionic structural units of the complexes are combined together due to the secondary Au···S, Tl···S and S···Cl bonds that results in complicated supramolecular architectures. Thermal behavior of compounds was studied using the simultaneous thermal analysis technique; both reduced elemental gold and thallium(I) chloride were identified as the final thermolysis products.

Double Pseudo-Polymeric Complexes of [Au(S2CNR2)2][TlCl4], R2 = (CH2)5, (CH2)6: Preparation, Structural Organization, and Thermal Behavior (Low-Temperature Reduction and Crystallization of Gold)

Double Pseudo-Polymeric Complexes of [Au(S2CNR2)2][TlCl4], R2 = (CH2)5, (CH2)6: Preparation, Structural Organization, and Thermal Behavior (Low-Temperature Reduction and Crystallization of Gold)

Morphological Study of a Self-Organized Corrole Film on a Gold Crystal, both in Solution and after Solvent Evaporation

Morphological Study of a Self-Organized Corrole Film on a Gold Crystal, both in Solution and after Solvent Evaporation

Parallel SPR and QCM-D Quantitative Analysis of CD9, CD63, and CD81 Tetraspanins: A Simple and Sensitive Way to Determine the Concentration of Extracellular Vesicles Isolated from Human Lung Cancer Cells.

Tetraspanins, including CD9, CD63, and CD81, are transmembrane biomarkers that play a crucial role in regulating cancer cell proliferation, invasion, and metastasis, as well as plasma membrane dynamics and protein trafficking. In this study, we developed simple, fast, and sensitive immunosensors to determine the concentration of extracellular vesicles (EVs) isolated from human lung cancer cells using tetraspanins as biomarkers. We employed surface plasmon resonance (SPR) and quartz crystal microbalance with dissipation (QCM-D) as detectors. The monoclonal antibodies targeting CD9, CD63, and CD81 were oriented vertically in the receptor layer using either a protein A sensor chip (SPR) or a cysteamine layer that modified the gold crystal (QCM-D) without the use of amplifiers. The SPR studies demonstrated that the interaction of EVs with antibodies could be described by the two-state reaction model. Furthermore, the EVs' affinity to monoclonal antibodies against tetraspanins decreased in the following order: CD9, CD63, and CD81, as confirmed by the QCM-D studies. The results indicated that the developed immunosensors were characterized by high stability, a wide analytical range from 6.1 × 104 particles·mL-1 to 6.1 × 107 particles·mL-1, and a low detection limit (0.6-1.8) × 104 particles·mL-1. A very good agreement between the results obtained using the SPR and QCM-D detectors and nanoparticle tracking analysis demonstrated that the developed immunosensors could be successfully applied to clinical samples.

FRET Imaging of Nonuniformly Distributed DNA SAMs on Gold Reveals the Role Played by the Donor/Acceptor Ratio and the Local Environment in Measuring the Rate of Hybridization.

Mixed DNA SAMs labeled with a fluorophore (either AlexaFluor488 or AlexaFluor647) were prepared on a single crystal gold bead electrode using potential-assisted thiol exchange and studied using Förster resonance energy transfer (FRET). A measure of the local environment of the DNA SAM (e.g., crowding) was possible using FRET imaging on these surfaces since electrodes prepared this way have a range of surface densities (ΓDNA). The FRET signal was strongly dependent on ΓDNA and on the ratio of AlexaFluor488 to AlexaFluor647 used to make the DNA SAM, which were consistent with a model of FRET in 2D systems. FRET was shown to provide a direct measure of the local DNA SAM arrangement on each crystallographic region of interest providing a direct assessment of the probe environment and its influence on the rate of hybridization. The kinetics of duplex formation for these DNA SAMs was also studied using FRET imaging over a range of coverages and DNA SAM compositions. Hybridization of the surface-bound DNA increased the average distance between the fluorophore label and the gold electrode surface and decreased the distance between the donor (D) and acceptor (A), both of which result in an increase in FRET intensity. This increase in FRET was modeled using a second order Langmuir adsorption rate equation, reflecting the fact that both D and A labeled DNA are required to become hybridized to observe a FRET signal. The self-consistent analysis of the hybridization rates on low and high coverage regions on the same electrode showed that the low coverage regions achieved full hybridization 5× faster than the higher coverage regions, approaching rates typically found in solution. The relative increase in FRET intensity from each region of interest was controlled by manipulating the donor to acceptor composition of the DNA SAM without changing the rate of hybridization. The FRET response can be optimized by controlling the coverage and the composition of the DNA SAM sensor surface and could be further improved with the use of a FRET pair with a larger (e.g., > 5 nm) Förster radius.

Near-white light emission from single crystals of cationic dinuclear gold(I) complexes with bridged diphosphine ligands.

Three cationic dinuclear Au(I) complexes containing acetonitrile (AN) as an ancillary ligand were synthesized: [μ-LMe(AuAN)2]·2BF4 (1), [μ-LEt(AuAN)2]·2BF4 (2), and [μ-LiPr(AuAN)2]·2BF4 (3) (LMe = {1,2-bis[bis(2-methylphenyl)phosphino]benzene}, LEt = {1,2-bis[bis(2-ethylphenyl)phosphino]benzene}, and LiPr = {1,2-bis[bis(2-isopropylphenyl)phosphino]benzene}). The unique structures of complexes 1-3 with two P-Au(I)-AN rods bridged by rigid diphosphine ligands were determined through X-ray analysis. The Au(I)-Au(I) distances observed for complexes 1-3 were as short as 2.9804-3.0457 Å, indicating an aurophilic interaction between two Au(I) atoms. Unlike complexes 2 and 3, complex 1 incorporated CH2Cl2 into the crystals as crystalline solvent molecules. Luminescence studies in the crystalline state revealed that complexes 1 and 2 mainly exhibited bluish-purple phosphorescence (PH) at 293 K: the former had a PH peak wavelength at 415 nm with the photoluminescence quantum yield ΦPL = 0.12, and the latter at 430 nm with ΦPL = 0.13. Meanwhile, complex 3 displayed near-white PH, that is dual PH with two PH bands centered at 425 and 580 nm with ΦPL = 0.44. The PH spectra and lifetimes of complexes 2 and 3 were measured in the temperature range of 77-293 K. The two PH bands observed for complex 3 were suggested to originate from the two emissive excited triplet states, which were in thermal equilibrium. From theoretical calculations, the dual PH observed for complex 3 is explained to occur from the two excited triplet states, T1H and T1L: the former exhibits a high-energy PH band (bluish-purple) and the latter exhibits a low-energy PH band (orange). The T1H state is considered 3ILCT with a structure similar to that of the S0-optimized structure. Conversely, the T1L state is assumed to be a 3MLCT with a T1-optimized structure, which has a short Au(I)-Au(I) bond and two bent rods (Au-AN). The thermal equilibrium between the two excited states is discussed based on computational calculations and photophysical data in the temperature range of 77-293 K. With regard to the crystal of complex 1, we were unable to precisely measure the temperature-dependent emission spectra and lifetimes, particularly at low temperatures, because the cooled crystals became irreversibly turbid over time.

Quasi-van der Waals Epitaxial Recrystallization of a Gold Thin Film into Crystallographically Aligned Single Crystals.

Heterointerfaces between two-dimensional (2D) materials and bulk metals determine the electrical and optical properties of their heterostructures. Although deposition of various metals on 2D materials has been studied, there is still a lack of studies on the interaction at the van der Waals (vdW) heterointerface between 2D materials and metals. Here, we report quasi-van der Waals (qvdW) epitaxial recrystallization of a gold thin film into crystallographically aligned single crystals by encapsulation annealing of a gold thin film with hexagonal boron nitride (hBN). When a polycrystalline gold thin film passivated with hBN was annealed, it was recrystallized into single gold crystals with a planar shape and crystallographic alignment with hBN due to a strong interaction between the gold film and hBN at the heterointerface. This reflects that a weak vdW force at the heterointerface is sufficiently strong to induce epitaxial recrystallization. Using this method, we fabricated a gold nanocrystal array with the same crystalline orientation and smooth top surface. Our work demonstrates a new method for epitaxial recrystallization of bulk crystals and provides a deep understanding of the interaction at the vdW heterointerface of 2D materials and metals.

Synthesis of Self-Assembled Single Atomic Layer Gold Crystals-Goldene.

We report, for the first time, a technique to synthesize free-standing, one-atom thick 2D gold crystals (namely, goldene) and self-assembled 2D periodic arrays of goldene. High-resolution transmission electron microscopy (HRTEM) imaging of goldene revealed herringbone and honeycomb lattices, which are primarily gold surface features due to its reconstruction. Imaging of these surface-only features by a nonsurface characterization technique such as HRTEM is an unequivocal proof of the absence of three-dimensionality in goldene. Atomic force microscopy confirmed 1-2 Å thickness of goldene. High-resolution X-ray photoelectron spectroscopy (HR-XPS), selective area electron diffraction, and energy-dispersive X-ray spectroscopy confirmed the chemical identity of goldene. We discovered the phenomenon of electric field-induced self-assembly of goldene supracrystals with a herringbone structure and developed an electric field printing (e-print) technique for goldene arrays. Goldene showed a semiconductor response with a knee voltage of ∼3.2 V, and I/V spectroscopy revealed periodic room temperature Coulomb blockade oscillations. These observations are consistent with the theoretical calculations reported in the literature predicting enhanced Coulombic interactions between gold valence electrons and the nucleus in stable 2D gold. Goldene exhibited multiple, intense, and well-resolved optical absorption peaks and several fine bands across the UV-vis region, and we calculated its optical band gap to be 3.59 eV. Magnetic force microscopy measurements of goldene periodic arrays showed a ∼5 mV peak amplitude confirming its ferromagnetism. Optical and magnetic properties of goldene are consistent with those reported in the literature for 2D planar gold clusters with less than 12 atoms.