Semiconductor Clusters Research Articles

Ion exchange in semiconductor magic-size clusters.

As a crucial post-synthesis method, ion exchange allows for precise control over the composition, interface, and morphology of nanocrystals at the atomic scale, achieving material properties that are difficult to obtain with traditional synthesis techniques. In nanomaterial science, semiconductor magic-size clusters (MSCs), with their atomic-level precision and unique quantum confinement effects, serve as a bridge between molecules and nanocrystals. Despite this, research on ion exchange in MSCs is still in its infancy. This review introduces the principles of ion exchange and reactions in colloidal nanocrystals and MSCs, analyzing the importance and challenges of ion exchange in studying MSCs. This paper begins with a focus on the current research progress of cation and anion exchange in II-VI and III-V semiconductor MSCs. Then, the common methods for characterizing MSCs during the ion exchange process are discussed. Finally, the article envisions future research directions based on MSCs' ion exchange. Research on MSCs' ion exchange not only aids in designing MSCs with complex functionalities, but also plays an essential role in elucidating the ion exchange mechanisms in nanocrystals, providing new insights for the innovative design and synthesis of nanomaterials.

Atomically precise semiconductor clusters of rare-earth tellurides

Atomically precise semiconductor clusters of rare-earth tellurides

Analysis of Competitiveness in the Domestic Semiconductor Cluster Using Entropy Technique: Based on the GEM-ESG Model

Purpose - The study aims to conduct an empirical analysis of semiconductor cluster integrated competitiveness with a focus on the GEM-ESG model. Specifically, the study seeks to compare and analyze the development factors of semiconductor clusters in different regions. The results of the empirical study will reveal a clear concentration phenomenon in the semiconductor industry clusters of some regions.
 Design/Methodology/Approach - Previous research has established the factors influencing the competitive advantage of industrial clusters. The study collected competitive indicators from major South Korean cities and regions, incorporating these into the GEM model, and exploring ESG indicators relevant to the semiconductor industry. The study utilized Entropy Technique analysis to empirically assess the competitiveness of the South Korean semiconductor cluster and conduct comparative testing of the research findings.
 Findings - The results revealed a concentration phenomenon in the semiconductor industry clusters of Yongin and Chungbuk Province. Additionally, the study highlighted the importance of factors such as “groundings (G)”, “enterprise management (E)”, “market conditions (M)”, and ESG practices in determining competitiveness.
 Research Implications - Through empirical analyses, the study emphasizes the significance of GEM and ESG factors in the analysis of industrial clusters, particularly in contributing to long-term sustainability and competitive advantage focusing on the collaboration and alignment of ESG values.

Formation and Transformation of CdS Clusters during the Prenucleation Stage and in a Dilute Dispersion at Room Temperature.

The formation and transformation of colloidal semiconductor clusters remain poorly understood. With CdS as a model system, we show that, in the reaction of cadmium myristate (Cd(MA)2) and S powder in 1-octadecene (ODE), clusters form in the prenucleation stage of quantum dots (QDs). Called precursor compounds (PCs), the clusters can transform to magic-size clusters (MSCs) in reaction at a relatively high temperature (MSC-322 displaying optical absorption peaking at 322 nm) or in a dispersion at room temperature (MSC-360). When the reaction temperature is increased, PC-360 forms at 140 °C, while PC-322 and MSC-322 form at 180 °C. In a dispersion of cyclohexane and octylamine, MSC-322 transforms to MSC-360 via MSC-345. The MSC-345 to MSC-360 transformation displays continuous and discontinuous shifts in the optical absorption. The PCs and MSCs are a group of isomers. The present findings bring insight into the cluster formation and isomerization in the prenucleation stage of QDs and in a dispersion.

Exploring the stability and aromaticity of rare earth doped tin cluster MSn16- (M = Sc, Y, La).

Rare earth elements have high chemical reactivity, and doping them into semiconductor clusters can induce novel physicochemical properties. The study of the physicochemical mechanisms of interactions between rare earth and tin atoms will enhance our understanding of rare earth functional materials from a microscopic perspective. Hence, the structure, electronic characteristics, stability, and aromaticity of endohedral cages MSn16- (M = Sc, Y, La) have been investigated using a combination of the hybrid PBE0 functional, stochastic kicking, and artificial bee colony global search technology. By comparing the simulated results with experimental photoelectron spectra, it is determined that the most stable structure of these clusters is the Frank-Kasper polyhedron. The doping of atoms has a minimal influence on density of states of the pure tin system, except for causing a widening of the energy gap. Various methods such as ab initio molecular dynamics simulations, the spherical jellium model, adaptive natural density partitioning, localized orbital locator, and electron density difference are employed to analyze the stability of these clusters. The aromaticity of the clusters is examined using iso-chemical shielding surfaces and the gauge-including magnetically induced currents. This study demonstrates that the stability and aromaticity of a tin cage can be systematically adjusted through doping.

Discovery of a series of silicon-based ferrimagnets in CrMnSin (n = 4-20) clusters.

Herein, the structural evolution, electronic and magnetic properties of silicon clusters with two different dopants, CrMnSin (n = 4-20) clusters were investigated at density functional theory (DFT) level. Small-sized CrMnSin (n = 4-9) clusters tend to adopt bipyramid-based geometries, while clusters with sizes n = 10 and 11 prefer to opening cage-like structures. For sizes n = 12 to 14, the half-encapsulated structures gradually transform into closed-cage Cr@Sin structures, with the Mn atom exposed outside. Starting from size 15, both the Cr and Mn atoms are completely encapsulated by silicon atoms. Meanwhile, the Cr and Mn atoms in smaller-sized CrMnSin (n = 4-7) clusters tend to be separated, while they prefer to stay together for larger sizes. Cr atom always acts as electron donor, but not for Mn atom. From the average binding energies, one can conclude that it is easier to form larger size clusters. Smaller and larger sized CrMnSin (n = 4-9 and 19-20) clusters prefer to exhibit ferromagnetic Cr-Mn coupling, while sizes n = 10-18 always exhibit ferrimagnetic state. To our knowledge, the CrMnSin clusters is the first kind of neutral transition-metal doped semiconductor clusters that show ferrimagnetic state within a wide size range.

Precursor Compound-Assisted Formation of CdS Magic-Size Clusters in Aqueous Solutions.

Investigations of the formation pathway of semiconductor magic-size clusters (MSCs) in aqueous solutions are quite limited. Here, we present our understanding about a precursor compound (PC)-assisted formation pathway of aqueous-phase CdS MSCs exhibiting a characteristic absorption peak at about 360 nm (MSC-360). The reaction uses CdCl2 as the Cd source and thioglycolic acid (TGA) as both the S source and ligand in alkaline aqueous solutions. The mixture remains absorption featureless upon incubation at room temperature but with MSC-360 absorption observed upon adding butylamine. The longer the incubation period of the aqueous solution, the more MSC-360 forms after adding butylamine. We propose that Cd-TGA complexes form first, in which the TGA moieties then decompose partially to form PC of MSC-360 (PC-360) that cannot be observed in the optical absorption spectrum. The resulting PC-360 transforms to MSC-360 via quasi-isomerization in the presence of butylamine. The present study provides an in-depth understanding about the formation of aqueous-phase MSCs.

Nanoclusters for photoelectrochemical water splitting: Bridging the photosensitizer and carrier transporter

AbstractIncreasing global environmental deterioration is becoming a serious concern, leading to an exponential increase in scientific interest in renewable energy as an alternative to replace fossil fuels. Photoelectrochemical (PEC) water splitting, which directly converts sunlight into hydrogen fuel, offers a promising renewable energy technology. Semiconductors, used as photoelectrodes, provide the most feasible method for converting solar energy into electrical energy and chemical fuels. Unfortunately, most of the common semiconductors used in PEC water splitting have wide bandgaps, which greatly restrict the utilization efficiency of sunlight. To promote the solar‐to‐hydrogen (STH) efficiency of PEC water splitting, atomically precise clusters with regular crystal structures have been introduced in the PEC systems. In this review, the recent advances in nanoclusters for PEC water splitting, including metal clusters, polyoxometalates, semiconductor clusters, and carbon clusters, are summarized. At last, major challenges and outlook for the development of clusters for PEC water splitting are provided.

Ligand and solvent effects on the absorption spectra of CdS magic-sized clusters.

The absorption spectra of congenetic wurtzite (WZ) and zincblende (ZB) CdS magic-sized clusters are investigated. We demonstrate that the exciton peak positions can be tuned by up to 500meV by varying the strong coupling between X-type ligands and the semiconductor cores, while the addition of L-type ligands primarily affects cluster midgap states. When Z-type ligands are displaced by L-type ligands, red shifts in the absorption spectra are observed, despite the fact there is a small decrease in cluster size. Density functional theory calculations are used to explain these findings and they reveal the importance of Cd and S dangling bonds on the midgap states during the Z- to L-type ligand exchange process. Overall, ZB CdS clusters show higher chemical stability than WZ clusters but their optical properties exhibit greater sensitivity to the solvent. Conversely, WZ CdS clusters are not stable in a Lewis base-rich environment, resulting in various changes in their spectra. Our findings enable researchers to select capping ligands that modulate the optical properties of semiconductor clusters while maintaining precise control over their solvent interactions.

Unraveling the Transformation Pathways in Semiconductor Clusters by Studying the Formation of Spectroscopically Pure (CdS)13 Magic-Size Clusters

Unraveling the Transformation Pathways in Semiconductor Clusters by Studying the Formation of Spectroscopically Pure (CdS)₁₃ Magic-Size Clusters

Structural evolution and electronic properties of neutral and anionic TiASil (A = Sc, Ti; l ≤ 12): relatively stable TiASi4 as a structural unit.

Simulated photoelectron spectroscopy was conducted to investigate the structural evolution and electronic properties of TiASil (A = Sc, Ti; l ≤ 12) clusters and their anions via the Perdew-Burke-Enzerhof scheme and extensive cluster search using the ABCluster software. The results revealed that the ground-state structures of the TiASil (A = Sc, Ti) clusters generally exhibited similar configurations except for the Ti2Si3, ScTiSi3, and TiScSi10 clusters. Furthermore, the TiASil clusters exhibited an adsorptive evolution pattern, and the TiASi4 unit was considered the basic constituent framework of the structure, excluding several distortions and minor changes. With the increase in the cluster size, the lowest-energy structures varied from the exohedral to the cage structures of the single-metal atom at the center. Regarding the second energy difference data, the neutral TiASi4 clusters exhibited better stability among the neutral and anionic TiASil (A = Sc, Ti; l ≤ 12) clusters. Furthermore, the chemical bonding in the TiASi4 clusters was analyzed by molecular orbitals (MOs), highest occupied MO-lowest unoccupied MO gaps, and adaptive natural density partitioning analyses for the best Ti2Si4 cluster especially, and the results were combined with the natural population analysis data. The hybridization of the spd orbital of the metal atoms, eight localized bonds, and four delocalized bonds may primarily account for the relative stabilities of the neutral, square bipyramidal structure of Ti2Si4. Thus, the TiASi4 clusters may be assembled as the basic units of silicon-based semiconductor clusters of large-size neutral and anionic TiASil.

Semiconductor clusters: Synthetic precursors for colloidal quantum dots

Semiconductor clusters have been implicated as reaction intermediates between molecular precursors and colloidal quantum dots (CQDs). The success of isolation of semiconductor clusters have enabled detailed investigation of the atomic information of semiconductor clusters. The identification of atomic information has emerged as an important topic because knowledge of the structure-function relationship of intermediate clusters has been helpful to reveal the synthetic mechanism of CQDs. Recently, they have been utilized as the synthetic precursors for CQDs, which was not readily achieved using conventional molecular precursors. This mini review briefly introduces the current understanding of their atomic information such as the composition, structure, and surface. We then discuss advantages, limitations, and the perspective of semiconductor clusters as a precursor for synthesis of CQDs.

Structure of a subnanometer-sized semiconductor Cd14Se13 cluster

Structure of a subnanometer-sized semiconductor Cd14Se13 cluster

Magic-Size Semiconductor Nanostructures: Where Does the Magic Come from?

The quest for atomically precise synthesis of colloidal semiconductor nanostructures has attracted increasing attention in recent years and remains a formidable challenge. Nevertheless, atomically precise clusters of semiconductors, known as magic-size clusters (MSCs), are readily accessible. Ultrathin one-dimensional nanowires and two-dimensional nanoplatelets and nanosheets can also be categorized as magic-size nanocrystals (MSNCs). Further, the magic-size growth regime has been recently extended into the size range of colloidal QDs (up to 3.5 nm). Nevertheless, the underlying reasons for the enhanced stability of magic-size nanostructures and their formation mechanisms remain obscure. In this Perspective, we address these intriguing questions by critically analyzing the currently available knowledge on the formation and stability of both MSCs and MSNCs (0D, 1D, and 2D). We conclude that research on magic-size colloidal nanostructures is still in its infancy, and many fundamental questions remain unanswered. Nonetheless, we identify several correlations between the formation of MSCs and 0D, 1D and 2D MSNSs. From our analysis, it appears that the “magic” originates from the complexity of a dynamic and multivariate system running under reaction control. Under conditions that impose a prohibitively high energy barrier for classical nucleation and growth, the reaction proceeds through a complex and dynamic potential landscape, searching for the pathway with the lowest energy barrier, thereby sequentially forming metastable products as it jumps from one local minimum to the next until it eventually becomes trapped into a minimum that is too deep with respect to the available thermal energy. The intricacies of this complex interplay between several synergistic and antagonistic processes are, however, not yet understood and should be further investigated by carefully designed experiments combining multiple complementary in situ characterization techniques.

Theoretical studies on the two-photon absorption of II\u2013VI semiconductor nano clusters

Semiconductor clusters, ZnnOn, ZnnSn, and CdnSn (n = 2–8), were optimized and the corresponding stable structures were acquired. The symmetry, bond length, bond angle, and energy gap between HOMO and LUMO were analyzed. According to reasonable calculation and comparative analysis for small clusters Zn2O2, Zn2S2, and Cd2S2, an effective method based on density function theory (DFT) and basis set which lay the foundation for the calculation of the large clusters have been obtained. The two-photon absorption (TPA) results show that for the nano clusters with planar configuration, sizes play important role on the TPA cross section, while symmetries determine the TPA cross section under circumstance of 3D stable structures. All our conclusions provide theoretical support for the development of related experiments.

Nonlocal and nonadiabatic Pauli potential for time-dependent orbital-free density functional theory

Time-dependent orbital-free density functional theory (TD-OFDFT) is an efficient ab-initio method for calculating the electronic dynamics of large systems. In comparison to standard TD-DFT, it computes only a single electronic state regardless of system size, but it requires an additional time-dependent Pauli potential term. We propose a nonadiabatic and nonlocal Pauli potential whose main ingredients are the time-dependent particle and current densities. Our calculations of the optical spectra of metallic and semiconductor clusters indicate that nonlocal and nonadiabatic TD-OFDFT performs accurately for metallic systems and semiquantitatively for semiconductors. This work opens the door to wide applicability of TD-OFDFT for nonequilibrium electron and electron-nuclear dynamics of materials.

The Effect of ­High-Tech Clusters on the Productivity of Top Inventors

The high-tech sector is concentrated in a small number of cities. The ten largest clusters in computer science, semiconductors, and biology account for 69 percent, 77 percent, and 59 percent of all US inventors, respectively. Using longitudinal data on 109,846 inventors, I find that geographical agglomeration results in significant productivity gains. When an inventor moves to a city with a large cluster of inventors in the same field, she experiences a sizable increase in the number and quality of patents produced. The presence of significant productivity externalities implies that the agglomeration of inventors generates large gains in the aggregate amount of innovation produced in the United States. (JEL D62, J24, L60, O31, 034, R32)

Ultrafast intraband Auger process in self-doped colloidal quantum dots

Summary Investigating the separate dynamics of electrons and holes has been challenging, although it is critical for the fundamental understanding of semiconducting nanomaterials. n-Type self-doped colloidal quantum dots (CQDs) with excess electrons occupying the low-lying state in the conduction band (CB) have attracted a great deal of attention because of not only their potential applications to infrared optoelectronics but also their intrinsic system that offers a platform for investigating electron dynamics without elusive contributions from holes in the valence band. Here, we show an unprecedented ultrafast intraband Auger process, electron relaxation between spin-orbit coupling states, and exciton-to-ligand vibrational energy transfer process that all occur exclusively in the CB of the self-doped β-HgS CQDs. The electron dynamics obtained by femtosecond mid-infrared spectroscopy will pave the way for further understanding of the blinking phenomenon, disproportionate charging in light-emitting diodes, and hot electron dynamics in higher quantum states coupled to surface states of CQDs.

Niobium pentoxide ultra-thin nanosheets: A photocatalytic degradation and recyclable surface-enhanced Raman scattering substrate

Although the traditional SERS metal substrates have high sensitivity, their unrepeatable and ecological environment unfriendly performance greatly limits their applications. Therefore, it is necessary to explore multi-functional SERS substrates with recyclability, photocatalytic degradation, and ultra-sensitive detection ability. Herein, the Nb2O5 ultra-thin nanosheets were successfully synthesized by a simple hydrothermal method. Based on the coupled resonance effect, the SERS sensitivity of Nb2O5 substrates was optimized by the Mo doping process. The SERS enhanced factor EF of Mo-Nb2O5-MV at 1617 cm−1 with the irradiation laser of 532 nm is determined to 2.09 × 107 and the corresponding substrate possesses a low detection limit of 10−8 M, which can parallel the noble metal SERS substrates without “hot spots”. The enhanced Raman signals of MV on Mo-Nb2O5 substrates are mainly originated from photo-induced charge transfer resonance between molecules and semiconductor clusters. It is noticeable that Mo-Nb2O5 ultra-thin nanosheets substrates not only exhibit excellent SERS sensitivity and uniformity but also have recyclability, stability and rapidly photocatalytic degradation ability of dye molecules in visible-light, which expend the application of semiconductor SERS substrates in the detection and treatment of pollutants.

Direct observation of charge transfer between molecular heterojunctions based on inorganic semiconductor clusters.

A deep understanding of the dynamics of photogenerated charge carriers is extremely important for promoting their germination in semiconductors to enhance the efficiency of solar energy conversion. In contrast to that of organic molecular heterojunctions (which are widely employed in organic solar cells), the charge transfer dynamics of purely inorganic molecular heterojunctions remains unexplored. Herein, we reveal the dynamics of charge transfer between inorganic semiconductor molecular heteroclusters by selecting a group of open-framework metal chalcogenides as unique structure models constructed from supertetrahedral T3-InS ([In10S20]) and T4-MInS ([M4In16S35], M = Mn or Fe) clusters. The staggered band gap alignment in T3-T4-MInS molecular heterojunctions enables the photogenerated charge carriers to be directionally transferred from T3-InS clusters to adjacent T4-MInS clusters upon irradiation or application of an external electric field. The simultaneous independence of and interactions between such two heteroclusters are investigated by theoretical calculations, steady- and transient-state absorption/photoluminescence spectroscopy, and surface photovoltage analysis. Moreover, the dynamics of cluster-to-cluster-to-dopant photogenerated charge transfer is deliberately elucidated. Thus, this work demonstrates the direct observation of charge transfer between molecular heterojunctions based on purely inorganic semiconductor clusters and is expected to promote the development of cluster-based semiconductors for solar cells.