Silicon Clusters Research Articles

INVESTIGATION OF VARIOUS MECHANISMS OF RADIATIVE RECOMBINATION OF SILICON NITRIDE AS AN EFFECTIVE WAY TO BROADENING THE PHOTOLUMINESCENCE SPECTRUM

The development of devices combining optical and electrical functions based on silicon-containing materials is one of the challenges in microelectronics. By plasma enhanced chemical vapor deposition synthesis and subsequent annealing, silicon nitride samples with both excess silicon and excess nitrogen were formed. The high concentration of Si-H and N-H bonds was determined by Raman spectroscopy in samples before annealing. By the transmission electron microscopy, it was determined that in addition to silicon nitride, silicon clusters were formed in the sample’s matrix. The photoluminescence spectra changed significantly for both types of samples during annealing in different gas atmospheres. Heat treatment of samples at 1100 °C after synthesis led to the disappearance of the PL spectrum, and after annealing at 800 °C, photoluminescence increases. It is noted that the highest intensity of photoluminescence was detected after annealing in the air atmosphere and the lowest in the nitrogen. The participation of N centers in recombination processes was confirmed by the method of electron paramagnetic resonance. The different mechanisms of particle interaction leading to photoluminescence and charge storage are considered. Thus, the conditions for the synthesis and annealing of silicon nitride layers are selected to obtain controlled luminescent properties in various spectral ranges.

Theoretical exploration of the effects of alkali metal atoms on the structures and electronic properties of silicon clusters

The effects of alkali metals (Li, Na, K, Rb) on the geometric configurations and electronic properties of silicon clusters Sin− (n = 3 − 16) were studied through a genetic algorithm code coupled with density functional theory (DFT) calculations. Almost all of these AMSin− clusters share the same configurations and adopt the ground-state Sin− clusters as the structural motifs with the AM atoms adsorbed on the surface without severely distorting their structures. All Li, Na, K and Rb atoms act as electron donors in all these clusters as that of Cs atoms in CsSin− clusters. These AMSin− clusters possess similar electronic properties from the results of the on-site charges, vertical detachment energies (VDEs), HOMO-LUMO gaps, average binding energies, and secondary energy differences, especially for AM=K, Rb and Cs with closed values. Sizes n = 5, 10 and 13 for all these AMSin− and pure Sin− clusters are magic numbers.

Structural evolution, electronic and optical properties of praseodymium doped silicon cluster PrSin0/- (n = 10–20): A theoretical investigation

The rare earth dope d nano-cluster can be a building block for the next-generation photo-electrical industry, so the imminent discovery of novel, suitable nano-functional material is urgent. Praseodymium element as a wonderful dopant, bestow a novel photoelectrochemical properties for nanomaterials especially for semiconductor, derived from its unfulfilled 4f electrons configuration and active electronic transitions between 4f to 4f and 4f to 5d. In view of this, the neutral and anionic clusters of PrSin0/- with a medium size of n = 10–20 are comprehensively investigated by the quantum chemistry method of mPW2PLYP associated with the global searching potential energy surface techniques. The geometry evolution in medium size for PrSin can be attributed to three stages of replaced (n = 10–12), linked (n = 13–19), and cage (n = 20) structure. For PrSin-, two evolution phases are obviously observed by linked (n = 10–19) and cage (n = 20) structure. The PES spectra of the anionic most stable cluster and several degeneracy structures are simulated to identify the ground state structure. Each cluster of AEA, charge transfer, and VDE values are all calculated. Combined with binding energy, HOMO-LUMO gap, molecular orbital analysis, and a series of optical properties estimated, including simulated UV–vis, IR, and Raman spectra, excitation behavior shows PrSi20- has not only prominent stability but also has a proper range of lighting absorption, higher electron-hole recombination, possible as a functional material for optoelectronic devices.

From structure to surface tension of small silicon clusters by Quantum Monte Carlo simulations

We investigate the structural, surface and electronic properties of small silicon clusters Sin (for n=2 to 15) using HF, DFT and FN-DMC calculations. We analyze the atomic configurations, surface properties and electronic structures and show that the radius and average surface area of the clusters can be modeled by a Jellium-type model. We found that the surface tension σ of the clusters decreases with increasing cluster size in the range of the clusters under investigation. An estimate of the surface tension for bulk silicon yields σbulk=0.88(3) J/m2 in agreement with recent experiments. The average bond length of the clusters shows a non-monotonic behavior. Smaller clusters exhibit a high spin state influenced by electron correlation, especially during the 2D to 3D structural transition, which occurs at n=4 to n=5. We also find that the Si4, Si10 and Si12 clusters exhibit enhanced stability due to electron correlation. Our results are consistent with the experiments on bond length, binding energy and dissociation energy.

Comparative studies of GaN, n-GaN and n+-GaN contact layers on GaN/c-Al2O3 virtual substrates synthesized by PA MBE

An approach to create ohmic contacts to GaN layers without using the high-temperature annealing procedure is described in the paper. The results of comparative studies of structural, morphological, optical, and electrical properties of undoped GaN and silicon-doped n-GaN and n+-GaN doped contact layers are presented.The contact layer technology can be successfully realized using a plasma-assisted molecular beam epitaxy (PA MBE) setup of industrial type, where due to characteristic design features, the growth of nitride AIIIN compounds occurs using small streams of activated nitrogen, which significantly limits the possibility of varying the technological parameters.For the first time it is demonstrated that using the proposed technology for the creation of post-grown GaN, n-GaN and n+-GaN contact layers to GaN/c-Al2O3 virtual substrates in Ga-enriched conditions of epitaxial PA MBE growth at relatively low temperatures Ts = 700oC an effective filtration of dislocations threading from the buffer GaN layer of the virtual substrate formed by MOCVD can be realized.Calculations of in-plane εxx and out-of-plane εzz deformations, as well as residual biaxial stresses based on X-ray diffraction and Raman microspectroscopy data indicate at high structural quality of the formed contact layer regardless of the silicon doping level. At the same time PA MBE contact layers GaN, n-GaN and n+-GaN demonstrate close optical properties (refractive index and photoluminescence) in a wide range (400–850 nm), as well as minimal influence of defects associated with the formation of silicon clusters at high doping levels.The contact resistance reduced to the pad width determined using the transmission line method for the structure with n+-GaN contact layer was of ∼0.11 Ohm*mm and ∼0.5 Ohm*mm for n-GaN. Note that electrophysical characteristics of n-GaN and n+-GaN contact layers do not degrade under high-dose exposure of high-energy X-ray irradiation.The technique developed in our work to create ohmic contacts to GaN layers, as well as the obtained experimental results, have important implications for understanding the physics of AIIIN nanoheterostructures and will contribute to their potential applications in their fabrication.

Element partitioning and stabilization for impurities removal between liquid silicon and silicate melts: Ab initio insights into electronic structure

The partitioning and stabilization of common impurity elements challenge the impurity removal process during slag refining for developing high-purity metals. The role of electronic properties remains indistinct in the stability of non-metallic, alkaline earth metal, and transition metal impurity clusters in silicon and silicate melts, impeding the advancement of separation medium and purification process. Herein, local structures of impurity atoms are explored through ab initio molecular dynamics, and notable configurations are [PSi4], [TiSi10], [MgSi12] in silicon melts and [PO4], [TiO5], [MgO5] in silicate melts. A novel partition model based on impurity coordination predicted the impurity atoms’ distribution behavior consistent with industrial experiments. Furthermore, this model proposes a critical parameter k that evaluates impurity oxidation levels in coexisting systems and establishes a quantitative link between melt structures and distribution ratio, enabling precise predictions from two-phase ab initio calculations. Innovatively, the electronic structure analysis assessed element partitioning through bonding characteristics and interactions within impurity clusters via parameters: electron density distribution, partial density of states, electron localization function, and Mayer bond order. This yields a distinctive mapping relationship between impurity distribution ratio and stability, evidenced by quantitative associations with 12 key ab initio-derived descriptors through Pearson correlation analysis. This work unveils the electronic properties governing partitioning and endows modeling approach for distribution, driven by cluster structure analysis and ab initio calculations.

Unveiling the structural and bonding properties of AuSi2- and AuSi3- clusters: A comprehensive analysis of anion photoelectron spectroscopy and abinitio calculations.

Silicon clusters infused with transition metals, notably gold, exhibit distinct characteristics crucial for advancing microelectronics, catalysts, and energy storage technologies. This investigation delves into the structural and bonding attributes of gold-infused silicon clusters, specifically AuSi2- and AuSi3-. Utilizing anion photoelectron spectroscopy and abinitio computations, we explored the most stable isomers of these clusters. The analysis incorporated Natural Population Analysis, electron localization function, molecular orbital diagrams, adaptive natural density partitioning, and Wiberg bond index for a comprehensive bond assessment. Our discoveries reveal that cyclic configurations with the Au atom atop the Si-Si linkage within the fundamental Si2 and Si3 clusters offer the most energetically favorable structures for AuSi2- and AuSi3- anions, alongside their neutral counterparts. These anions exhibit notable highest occupied molecular orbital-lowest unoccupied molecular orbital gaps and significant σ and π bonding patterns, contributing to their chemical stability. Furthermore, AuSi2- demonstrates π aromaticity, while AuSi3- showcases a distinctive blend of σ antiaromaticity and π aromaticity, crucial for their structural robustness. These revelations expand our comprehension of gold-infused silicon clusters, laying a theoretical groundwork for their potential applications in high-performance solar cells and advanced functional materials.

Dielectric Behavior and Prolate Growth Patterns of Silicon Clusters SiN with N = 12-30 by Cryogenic Electric Beam Deflection.

We present a comprehensive investigation of the dielectric behavior and geometric structures of cold neutral SiN clusters of intermediate size with N = 12-30 atoms. For this, cryogenic electric beam deflection experiments were carried out for the first time for Si clusters at nozzle temperatures below 30 K. In combination with quantum chemical calculations based on density functional theory and classical trajectory simulations of the rotational dynamics in the electric field, the geometric structures of the clusters are discriminated. Clusters with N < 15 favor a single-capped square antiprism as a nucleus for cluster growth, forming compact geometries in the molecular beam. Starting with 15 atoms, a prolate-like growth is observed. The prolate structures are based on stable building blocks which reappear for numerous sizes throughout the cluster growth. Finally, the transition from prolate to quasi-spherical shapes is shown to take place around Si29/Si30 as predicted theoretically by the literature. The influence of the exchange-correlation functional on the predicted structure and dielectric properties is discussed in detail for some clusters. Relaxation of the electric-dipole moment and therefore quenching of the observed electric response due to vibrational excitation and collisions with the background gas are also considered, which explains deviations between experiment and theory.

Carrier-induced formation of electrically active boron-interstitial clusters in irradiated boron-doped silicon

Excess minority carriers create boron-related recombination centers that degrade the efficiency of the non-particle-irradiated silicon solar cells. However, the carrier-induced reactions among the radiation-induced defects are poorly understood for devices exposed to particle radiation. This study investigates the structure, electronic properties, formation and annihilation mechanisms, and diffusion dynamics of the carrier-induced defects in particle-irradiated boron-doped silicon using density-functional modeling and junction spectroscopy. By revisiting the ground-state structures of the boron-di-interstitial clusters (BI2), we find that the calculated acceptor and donor levels of such defects agree well quantitatively with the carrier-induced deep-level transient spectroscopy (DLTS) hole emission signatures at 0.43 and 0.53 eV above the valence band edge (Ev), respectively. We also find that the formation of BI2 is thermally activated by an energy of 0.50 eV, which we explain theoretically by the reduction of the migration barrier of mono-interstitials to 0.53 eV in the presence of excess minority carriers. Moreover, we discover that the BI2 are potentially mobile with a migration barrier of 1.18 eV, contrary to the present understanding.

Determination of Ground State Structures of Snx - (x=21-35) Clusters.

In this work, an unbiased global search with a homemade genetic algorithm was performed to investigate the structural evolution and electronic properties of Snx - (x=21-35) clusters with density functional theory (DFT) calculations. All the ground-state structures for all these Snx - (x=21-35) clusters have been confirmed by the comparison of the experimental and simulated photoelectron spectra (PESs). It has been revealed that all Snx - (x=21-35) clusters are tricapped trigonal prism (TTP)-based structures consisting of two (for sizes x=21-28) or three (for x=29-35) TTP units, with the remaining atoms adsorbed on the surface or inserted between TTP units. The gradually decreasing HOMO-LUMO gaps indicate that these clusters are undergoing semiconductor-to-metal transformation. The average binding energies show that the structural stabilities of Snx - clusters are not as good as that of silicon and germanium clusters. It found that sizes x=23, 25, 29, 33 show high relative stability.

The Mechanism Behind the Annealing‐Induced Reduction of Infrared Absorption in Zinc‐Hyperdoped Silicon

Pulsed laser hyperdoping is widely investigated as an effective method for expanding the infrared absorption of silicon. Prior to further device fabrication, thermal treatment is commonly applied to hyperdoped silicon to repair lattice defects and activate dopants. However, it is observed that thermal treatment adversely affects the infrared absorption of hyperdoped silicon, and the underlying mechanisms remain incompletely understood. Herein, zinc‐hyperdoped silicon (Si:Zn) is prepared using vacuum magnetron sputtering combined with femtosecond laser pulses, and the mechanisms of the reduction in infrared absorption during conventional annealing of Si:Zn samples are investigated. The diffusion of zinc and its precipitation as zinc clusters in silicon are observed during the annealing process, leading to a decrease in the concentration of zinc dopants within the silicon lattice and consequent attenuation of infrared absorption. Building upon this understanding, the approach of short timescale annealing subjected to infrared rapid thermal annealing furnace is proposed to be employed as a method to mitigate the adverse effects of zinc transitional precipitation, resulting in enhancement of the performance of Si:Zn optoelectronic devices.

Size-dependent linear and nonlinear optical responses of silicon clusters.

Owing to strong quantum confinement effects and no periodic constraints, the geometric and electronic structures of silicon clusters differ from those of crystalline silicon. Although previous studies have elucidated the optical properties of silicon clusters, some issues remain unresolved. To address these, this study examined the size-dependent linear and nonlinear optical responses of silicon clusters through first-principles calculations. Silicon clusters exhibited lone-pair-electron-dominated optical response behaviors. With the investigated size range, the orientationally average polarizability (αave) and second-order hyperpolarizability (γave) increased with cluster size. However, αave and γave per atom exhibited no evident size-dependent trends owing to co-modulation of the lone-pair-number-to-atomic-number ratio and geometry. αave and γave were notably sensitive to the nuclear binding strength of lone-pair electrons. Thus, the nonlinear optical effects of silicon clusters are superior to those of phosphorus and sulfur clusters. This investigation offers valuable insights into the optical responses of atomic-precision clusters.

A Computational Exploration of Exohedrally Transition Metal Doped Si94- Superatom Based Magnetic MSi9M' Clusters (M, M' = Sc(II) to Cu(II)).

Nanosized clusters are drawing immense attention of the scientific community due to their size and composition dependent tunability of physical and chemical properties. Silicon nanoclusters are especially important because of their abundance and ample utility in the domains of electronics and semiconductor industry. Zintl phases of Si offer an excellent opportunity in the domain of nanocluster research owing to their superior stability and multifarious possibilities of tunability of electronic properties through doping with other elements. Doping silicon clusters with transition elements is a prevalent strategy to induce magnetic properties in such clusters. Although doping silicon clusters with single transition metal atoms can induce significant magnetism in nanoclusters, the dominant covalent interaction between silicon and the transition metal causes the magnetic moment to quench. The rational strategy of inducing a sustainable magnetic moment can be to introduce ferromagnetic interaction between two sites carrying nonvanishing magnetic moments. In the present work, such a possibility is explored in terms of the stability of the clusters and corresponding magnetic exchange coupling in them. The Si94-superatomic cluster is doped with two transition metal atoms exohedrally and the neutral clusters designed thereby are investigated computationally if they reduce or reinforce the high stability of the superatom and substantiate the possibility of obtaining nanosized magnetic units as building blocks of tunable materials for various applications.

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.

Ultra-high NA optical image differentiator based on dielectric metasurfaces

Metasurface-based optical differentiators have recently attracted attention for their potential advantages in real-time and high-throughput image processing technology. However, the existing differentiators suffer from limitations in numerical aperture (NA). Here, we propose a differential metasurface based on silicon clusters covered with polydimethylsiloxane, achieving a remarkable NA of 0.7. We numerically demonstrate the proposed differentiator can perform second-order differentiation on a 1D spatial function and high NA can accurately compute smaller-scale variations. We further demonstrate its ability to achieve edge detection on 2D images. Our results advance the development of ultra-high numerical aperture optical differentiator and provide new opportunities for image processing.

Accelerating GW calculations through machine-learned dielectric matrices

The GW approach produces highly accurate quasiparticle energies, but its application to large systems is computationally challenging due to the difficulty in computing the inverse dielectric matrix. To address this challenge, we develop a machine learning approach to efficiently predict density–density response functions (DDRF) in materials. An atomic decomposition of the DDRF is introduced, as well as the neighborhood density–matrix descriptor, both of which transform in the same way under rotations. The resulting DDRFs are then used to evaluate quasiparticle energies via the GW approach. To assess the accuracy of this method, we apply it to hydrogenated silicon clusters and find that it reliably reproduces HOMO–LUMO gaps and quasiparticle energy levels. The accuracy of the predictions deteriorates when the approach is applied to larger clusters than those in the training set. These advances pave the way for GW calculations of complex systems, such as disordered materials, liquids, interfaces, and nanoparticles.

Structural Evolution and Electronic Properties of V2Sin-/0 (n = 7-14) Clusters: Anion Photoelectron Spectroscopy and Theoretical Calculations.

A systematic study of the structures and electronic properties of V2-doped silicon clusters, V2Sin-/0 (n = 7-14), was carried out by anion photoelectron spectroscopic experiments combined with theoretical calculations. According to the experimental spectra of V2Sin- (n = 7-14) clusters, the V2Si12- cluster has the highest vertical detachment energy (VDE) of 3.66 eV, while V2Si7- and V2Si14- clusters have lower VDEs of 2.81 and 2.84 eV, respectively. The most stable structure searches find that two V atoms in the V2Sin- clusters with size n = 7 and 8 are located at the surface, while V2Sin- clusters with n ≥ 9 prefer cage-like structures. Based on the analysis of the structural evolution of V2Sin- (n = 9-14) clusters, it can be clearly seen how the antihexagonal prism with one V encapsulated in the cage is gradually built from n = 9 to 12 and further developed from n = 12 to 14 with the extra silicon atoms located at the surface of the Si12 cage. The molecular orbital and the atoms in molecule analysis of the V2Sin- (n = 7-14) anions demonstrate that the strong V-V bond and the delocalized interaction between the V2 moiety and the Sin ligand play a significant role in stabilizing the cluster structures. A strong linear correlation has been found between the Wiberg bond order of the V-V bond and the electron density at the V-V bond critical points.

Effects of ErF3 Particles on the Structure and Physicomechanical Properties of A359 Alloy

In this work, the impact of ErF3 submicroparticles on the microstructure and mechanical properties of the A359 alloy was studied. ErF3 particles provided a homogeneous structure in castings produced via the casting method. The modifying effect of ErF3 particles on the structure of Al–Si alloys is realized through the mechanism of restraining the crystallization front and is achieved through the reduction in the formation of clusters of iron phases and eutectic lamellar silicon. It was found that the addition of 1 wt% ErF3 to the A359 alloy leads to a decrease in the average grain size by 21% and an increase in the yield strength by 14%, in tensile strength by 16%, in the microhardness of Al15(FeMn)3Si2 phase by 34% and in the Al15(FeMnCr)3Si2 phase by 7%. The heat treatment of the A359 alloy with ErF3 particles increased the yield strength by 36% and the tensile strength by 34%. The absence of an effect of ErF3 particles on the hardness values of the A359 alloy, as well as on the fracture process of the A359 alloy, was observed. The negative influence of ErF3 particle agglomerates and clusters on the strength characteristics of the investigated alloys was observed. Approaches for further exploring the potential of ErF3 particles as a strengthening phase in cast aluminum alloys of the Al–Si system were proposed.

Electric Field-Induced Nano-Assembly Formation: First Evidence of Silicon Superclusters with a Giant Permanent Dipole Moment.

The outstanding properties of silicon nanoparticles have been extensively investigated during the last few decades. Experimental evidence and applications of their theoretically predicted permanent electric dipole moment, however, have only been reported for silicon nanoclusters (SiNCs) for a size of about one to two nanometers. Here, we have explored the question of whether suitable plasma conditions could lead to much larger silicon clusters with significantly stronger permanent electric dipole moments. A pulsed plasma approach was used for SiNC production and surface deposition. The absorption spectra of the deposited SiNCs were recorded using enhanced darkfield hyperspectral microscopy and compared to time-dependent DFT calculations. Atomic force microscopy and transmission electron microscopy observations completed our study, showing that one-to-two-nanometer SiNCs can, indeed, be used to assemble much larger "superclusters" with a size of tens of nanometers. These superclusters possess extremely high permanent electric dipole moments that can be exploited to orient and guide these clusters with external electric fields, opening the path to the controlled architecture of silicon nanostructures.

3D CNN and grad-CAM based visualization for predicting generation of dislocation clusters in multicrystalline silicon

We propose a machine learning-based technique to address the crystallographic characteristics responsible for the generation of crystal defects. A convolutional neural network was trained with pairs of optical images that display the characteristics of the crystal and photoluminescence images that show the distributions of crystal defects. The model was trained to predict the existence of crystal defects at the center pixel of the given image from its optical features. Prediction accuracy and separability were enhanced by feeding three-dimensional data and data augmentation. The prediction was successful with a high area under the curve of over 0.9 in a receiver operating characteristic curve. Likelihood maps showing the distributions of the predicted defects are in good resemblance with the correct distributions. Using the trained model, we visualized the most important regions to the predicted class by gradient-based class activation mapping. The extracted regions were found to contain mostly particular grains where the grain boundaries changed greatly due to crystal growth and clusters of small grains. This technique is beneficial in providing a rapid and statistical analysis of various crystal characteristics because the features of optical images are often complex and difficult to interpret. The interpretations can help us understand the physics of crystal growth and the effects of crystallographic characteristics on the generation of detrimental defects. We believe that this technique will contribute to the development of a better fabrication process for high-performance multicrystalline materials.