Introduction Of Lattice Defects Research Articles

Behavior of Microstrain in Nd3+-Sensitized Near-Infrared Upconverting Core-Shell Nanocrystals for Defect-Induced Tailoring of Luminescence Intensity.

In an attempt to optimize the upconversion luminescence (UCL) output of a Nd3+-sensitized near-infrared (808 nm) upconverting core-shell (CS) nanocrystal through deliberate incorporation of lattice defects, a comprehensive analysis of microstrain both at the CS interface and within the core layer was performed using integral breadth calculation of high-energy synchrotron X-ray (λ = 0.568551 Å) diffraction. An atomic level interpretation of such microstrain was performed using pair distribution function analysis of the high-energy total scattering. The core NC developed compressive microstrain, which gradually transformed into tensile microstrain with the growth of the epitaxial shell. Such a reversal was rationalized in terms of a consistent negative lattice mismatch. Upon introduction of lattice defects into the CS systems upon incorporation of Li+, the corresponding UCL intensity was maximized at some specific Li+ incorporation, where the tensile microstrain of CS, compressive microstrain of the core, and atomic level disorders exhibited their respective extreme values irrespective of the activator ions.

The multifield regulation on resistance of PbPd0.9Co0.1O2/PMN-PT(001) laminate film

Spin gapless semiconductor (SGS) presents abundant electric and magnetic properties and is highly sensitive to external factors, such as current, electric field, magnetic field, and stress. This paper reports on a PbPd0.9Co0.1O2/PMNPT(001) laminate thin film with the “SGS/ferroelectrics” structure, which exhibits significant current-induced resistance (I-ER) effect. More importantly, the colossal static electric-field-induced resistance (E-ER) effect in such a laminate film was observed for the first time. The introduction of lattice defects (Pb vacancies) induces a local electric field, electron spin ordering state, and ferroelectric polarization field effect to explain the excellent physical properties. The reported laminate thin film composite exhibits promising application potential in spintronic devices, composite sensor units, storage systems, and other low-energy semiconductor electronic device fields. This work proposes an alternative way to investigate the novel properties for spin gapless semiconductors and expand the research fields of multi-field modulation effect in magnetoelectric composites.

In Situ Construction of Black Titanium Oxide with a Multilevel Structure on a Titanium Alloy for Photothermal Antibacterial Therapy.

Postsurgical infection of orthopedic fixation materials is considered to be the main cause of fixation failure. To address the problem, clinical treatment often relies on long-term antibiotics, secondary surgery, and so forth, which cause pain and suffering to patients. Constructing a light-responsive surface structure on the implant has attracted widespread attention for the management of postsurgical infections because of its noninvasiveness and controllability. Nevertheless, the application of light-responsive structures on implants is still limited by their unsafety and instability. In this work, a black titanium oxide layer with a multilevel structure and lattice defects was in situ constructed on a titanium alloy through pulsed laser ablation treatment. Under the synergistic effect of the multilevel structure and crystal defects, the surface of the titanium alloy exhibited good near-infrared light-responsive photothermal ability. The black titanium oxide multilevel structure reached high antibacterial efficiencies of about 99.37 and 99.29% against Staphylococcus aureus and Escherichia coli under 10 min near-infrared light irradiation. Furthermore, the black titanium oxide layer possessed similar biocompatibility compared with the titanium alloy. This near-infrared light-responsive photothermal therapy based on the construction of a multilevel structure and introduction of lattice defects provides an effective strategy for clinical postsurgical infections of orthopedic fixation.

Microstructural evolution and phase transformation in proton-irradiated NiTi films

In the present work, the microstructural characteristics, martensitic transformation behavior, and mechanical performance of NiTi thin films irradiated with different proton fluences were investigated. Multiple-layer structures formed in the NiTi thin films owing to proton irradiation. As the proton fluences were 1.0 × 1015 p/cm2 and 5.0 × 1015 p/cm2, a two-layer structure containing a B2 phase and a B19’ martensite phase was introduced. In addition, thickness of B2 phase layer becomes larger and larger for irradiated NiTi thin films at room temperature, as the proton irradiation fluence increases. With further increasing proton irradiation fluence to 2.0 × 1016 p/cm2, an amorphous layer forms at the outmost layer of NiTi thin film. Moreover, an R phase and GP zones were detected in the interior of the B2 layer. The twin type of B19’ martensite also changed to release the stored elastic energy induced by proton irradiation. The martensite variant related (111‾) type I twins and the substructure of the <011> type II twins gradually evolved into (111) type I twins and (001) compound twins, respectively, with increasing proton irradiation fluence. The formation of a multiple-layer structure resulted in the presence of two endothermic and exothermic peaks corresponding to the B19’ ⇌ B2 martensitic transformation. The introduction of lattice defects was responsible for the reduction in the martensitic transformation temperature. The strength of the irradiated NiTi films was enhanced as a result of dislocation strengthening. However, the introduction of higher density of defects also leads to the deterioration of ductility.

Structural damage response of lanthanum and yttrium aluminate crystals to nuclear collisions and electronic excitation: Threshold assessment of irradiation damage

A comparative analysis is performed on the structural damage response and associated mechanisms in lanthanum aluminate and yttrium aluminate crystals under various irradiation conditions by a combination of experimental and theoretical approaches. Under low-energy Au+ irradiation, the damage accumulation curve shows a higher damage rate for LaAlO3 crystals than YAlO3 crystals. The relatively low irradiation tolerance of LaAlO3 to the action of nuclear collisions is ascribed to the large amorphization cross-section and effective cross-section for defect-stimulated amorphization. Under swift Ar12+, Ni19+ and Kr17+ irradiation with different ion energies and velocities, the formed highly-disordered/amorphous latent tracks with different morphologies in pristine and predamaged crystals are discussed, and the corresponding electronic energy loss and lattice temperature thresholds are quantitatively determined. Compared to YAlO3, LaAlO3 exhibits lower sensitivity and higher damage tolerance to the electronic energy loss process, attributing to its relatively high recrystallization efficiency during the rapid quenching process. Furthermore, the introduction of lattice defects into LaAlO3 and YAlO3 crystals considerably enhances the sensitivity and intensity of thermal spike response to the electronic energy loss, and the induced effective modification of track morphologies demonstrates the synergistic effect between the electronic energy loss and pre-existing defects created by nuclear collisions. In this case, even under the action of electronic energy loss below the threshold, the lattice temperature in the nuclear-collision damaged crystalline system could still meet the criterion for track production. The irradiation energy deposited to atoms and induced lattice temperature evolution discussed in this work provide a deeper insight into the complex processes involved in irradiation-induced latent track behaviors.

Alkalized SnS Nanoflakes with Enhanced Sensing Properties towards Methanol Vapor

Two-dimensional (2D) group-Ⅳ monochalcogenides MX (M = Ge, Sn; X = S, Se) are isoelectronic and isostructural analogues to phosphorene. Due to superior oxidation resistance relative to black phosphorus, MX are recently explored to be potentialsubstitute of phosphorene for highly sensitive gas sensor applications. In this work, nanoflakes of tin monosulfide (SnS) was synthesized by a one-step solvothermal method and then employed for methanol-sensing at room temperature. The as-synthesized SnS shows nanoflower-like hierarchical architecture assembled by 2D nanoflakes. To achieve satisfactory gas response magnitude, a KOH alkalization process for post-treatment of the synthesized SnS was developed further. It is proved that appropriate alkalization could induce the ultrathin nanoflakes and introduce additional –O function terminals on the surface, which are favorable for methanol adsorption and response. The resultant alkalized SnS sensor displays a ∼3.2-fold enhancement in gas response to 5 ppm methanol. And it is capable of sensing rarefied methanol vapor as low as 100 ppb. The response enhancement could attribute to the alkalization-induced ultrathin geometry of SnS nanoflakes, introduction of lattice defects and –O functional terminals available for active adsorption of gas molecules. Further first-principles calculations clarify the crucial contribution and underlying mechanism of attached –O terminal on methanol adsorption and reaction clearly.

Synthesis of Defect and Valence State Tuned Metal Oxide Nanoparticles with Colloid Chemical Solution Process: Control of Optical and Electrical Characteristics

Abstract Dialysis and peptization, which are colloid chemical solution processes, are simple and effective techniques for controlling hydrolysis of hydrated metal cations. These synthetic processes preparation of stable sol with dispersion of doped oxide nanoparticles with wide molar fraction range from metal chloride aqueous and glycol solutions. Furthermore, control and introduction of lattice defects can be possible due to low temperature synthesis below 373 K. Design of optical and electrical characteristics of oxide nanoparticles by the solutions processes can be realized by controlling the situation of doping and lattice defects.

In-situ formation and evolution of atomic defects in monolayer WSe2 under electron irradiation

Transition metal dichalcogenide (TMD) monolayers such as MoS2, MoSe2, MoTe2, WS2 and WSe2 have attracted significant interest due to their remarkable electronic and optical properties, exhibiting a direct band gap, enabling usability in electronics and optics. Their properties can be altered further by the introduction of lattice defects. In this work, the dynamics of the formation of electron-beam-induced lattice defects in monolayer WSe2 are investigated by in-situ spherical and chromatic aberration-corrected low-voltage transmission electron microscopy. We show and analyze the electron-dose-limited life of a monolayer WSe2 from the formation of isolated Se vacancies over extended defects such as vacancy lines, mirror twin boundaries (MTBs) and inversion domains towards the loss of W atoms leading to the formation of holes and finally the destruction of the monolayer. We identify, moreover, a new type of MTB. Our study extends the basic understanding of defect dynamics in monolayer WSe2, sheds further light on the electron radiation response and suggests new ways for engineering the in-plane architecture of TMDs.

Resonant phonon modes in fullerene functionalized graphene lead to large tunability of thermal conductivity without impacting the mechanical properties

We investigate the effects of fullerene functionalization on the thermal transport properties of graphene monolayers via atomistic simulations. Our systematic molecular dynamics simulations reveal that the thermal conductivity of pristine graphene can be lowered by more than an order of magnitude at room temperature (and as much as by ∼93% as compared to the thermal conductivity of pristine graphene) via the introduction of covalently bonded fullerenes on the surface of the graphene sheets. We demonstrate large tunability in the thermal conductivity by the inclusion of covalently bonded fullerene molecules at different periodic inclusions, and we attribute the large reduction in thermal conductivities to a combination of resonant phonon localization effects, leading to band anticrossings and vibrational scattering at the sp3 bonded carbon atoms. The torsional force exerted by the fullerene molecules on the graphene sheets and the number of covalent bonds formed between the two carbon allotropes is shown to significantly affect the heat flow across the hybrid structures, while the size of the fullerene molecules is shown to have a negligible effect on their thermal properties. Moreover, we show that even for a large surface coverage, the mechanical properties of these novel materials are uncompromised. Taken together, our work reveals a unique way to manipulate vibrational thermal transport without the introduction of lattice defects, which could potentially lead to high thermoelectric efficiencies in these materials.

(Invited) The Effects of Laser Ablation Texturing and Nanoparticles on Anodic Nanotube and Porous Film Formation

Pits and pores in oxidized metals and silicon can be produce by a variety of self-limiting and, in some cases, self-organizing electrochemical processes. Here we discuss both high voltage anodization – which is well known for making oxidized metal nanostructures – and stain etching to produce porous silicon. High-voltage anodization – denoted Matsuda-Schmuki chemistry with reference to the work, e.g., of Masuda et al. for Al1-4 and Schmuki et al. for Ti or other metals,5,6 – involves an intricate balance between oxide growth and dissolution in which pore initiation and propagation is convoluted with the need for strain relief because of the expansion inherent to oxide formation. We use laser ablation with a nanosecond pulsed Nd:YAG laser operating at 532 nm to introduce texture (pillars, pits and nanoparticles) prior to anodization.7 Texturing of the substrate prior to anodization introduces features that can modify either the initiation of pores or strain relief during oxidation. Thereby it can affect the development of the resulting structures. Texturization also increases reaction rates by the introduction of lattice defects as well as increased surface area. Results for a number of metals including Al, Ti and Zn will be discussed. The SEM image shown in Figure (a) is of a porous F-doped ZnO layer grown on a laser ablated Zn substrate when anodized in an NH4F/ethylene glycol solution at 60 V. As shown in Fig. (b), TiO2 nanotube formation by anodization of pillar and nanoparticle Ti substrates is extremely facile. Stain etching of Si powders can produce high surface area and highly photoluminescent porous powders. PL bands from blue to red have been observed, as shown in Figure (c). PL in the red to near IR is extremely long lived, exhibiting multi-exponential decay with lifetime components in excess of 100 µs. Biological tissue autofluorescence exhibits lifetimes in the nanosecond range. Thus, the long-lived PL from Si nanoparticles is promising for bioimaging applications in which image acquisition is delayed after the initial photoexcitation.8 Furthermore, porous powders are readily terminated and chemically passivated with alkyl groups by hydrosilylation with, e.g., 1-alkenes. These alkyl-terminated powders not only retain their photoluminescence, they also retain long-lived PL. The characteristics of the porous powder respond to changes in the starting material (wafer reclaim chunks, reactor powder, metallurgical grade powder), etching conditions and chemical passivation of the powder after etching. We will discuss factors that influence the specific surface area, PL and structure of the porous particles. 1 H. Masuda, H. Yamada, M. Satoh, H. Asoh, M. Nakao, and T. Tamamura, Appl. Phys. Lett. 71, 2770 (1997). 2 H. Masuda, F. Hasegwa, and S. Ono, J. Electrochem. Soc. 144, L127 (1997). 3 H. Masuda and M. Satoh, Jpn. J. Appl. Phys. 35, L126 (1996). 4 H. Masuda and K. Fukuda, Science 268, 1466 (1995). 5 K. Lee, A. Mazare, and P. Schmuki, Chem. Rev. 114, 9385 (2014). 6 J. M. Macak, H. Tsuchiya, A. Ghicov, K. Yasuda, R. Hahn, S. Bauer, and P. Schmuki, Curr. Opin. Solid State Mater. Sci. 11, 3 (2007). 7 A. S. Ganas, D. A. Znamensky, N. M. Alba, J. L. Hernández-Pozos, and Kurt W. Kolasinski, ECS Trans. 69, 155 (2015). 8 L. Gu, D. J. Hall, Z. T. Qin, E. Anglin, J. Joo, D. J. Mooney, S. B. Howell, and M. J. Sailor, Nature Communications 4, 2326 (2013). Figure 1

Determining factor of median diameter in intermetallic compound nanoparticles prepared by pulsed wire discharge

The preparation of NiAl intermetallic compound nanoparticles was carried out by pulsed wire discharge (PWD) using twisted pure Ni and Al wires in N2 ambient gas with varying number of turns of the wire (Nt), energy ratio (K), and ambient gas pressure (P). From the voltage and current waveforms during the wire heating, the energy deposition ratio up to the voltage peak (Kp) was calculated. It increased with an increase in Nt to 0.4 turns/mm and with increases in K and P. Under all the conditions, with an increase in Kp, the Ni composition ratio of the prepared particles (CNi) became closer to that of the wire (= 51.2 mol %). Furthermore, the collection rate (Rc) increased and the median particle diameter (d50) decreased. In particular, the change in d50 due to the change in Nt was not predicted by the relationship of d50 and Dth in our previous report. Single-phase NiAl intermetallic compound nanoparticles were successfully prepared under the condition in which Nt is 0.4 turns/mm, K is 3.4, and P is 100 kPa, where relatively high value of Kp was obtained. From these results, Kp was determined to be an important factor that determines the composition, collection rate, and median diameter of intermetallic compound nanoparticles synthesized by PWD using different kinds of twisted wires under various experimental conditions. This may be because of the selective wire heating in high-resistance parts that are associated with the introduction of lattice defects and/or necks by overwinding.

Deformation behavior of perfect and imperfect nanomaterials made of intermetallic compounds with bcc lattice

The paper reviews the literature devoted to the stress-strain behavior of nanomaterials made of NiAl and FeAl intermetallics having B2 superstructure with body-centered cubic (bcc) lattice. Such nanomaterials demonstrate elastic deformation up to the point of their failure. In a concave region of a strain dependence of the potential energies P(e), the materials demonstrate thermodynamic instability and the non-homogeneous elastic deformation which is accompanied by the appearance of domains of two strain levels. Stretching behavior of NiAl and FeAl nanomaterials depends on lattice defects and sample geometry. An introduction of lattice defects which result in an appearance of residual stresses in structures can lead to the nanomaterial strengthening.

Electron-irradiation-induced solid-state amorphization in supersaturated Ni–Zr solid solutions

Electron-irradiation-induced solid-state amorphization (SSA) in supersaturated Ni–Zr solid solution models was investigated by molecular dynamics (MD) simulations, focusing on the threshold composition for the occurrence of SSA. The threshold composition for the MeV electron irradiation-induced SSA can be estimated to be around Ni 82Zr 18. A Ni 82Zr 18 solid solution shows SSA, while a Ni 83Zr 17 solid solution can maintain its original crystalline structure against irradiation. Thermal recovery of the lattice defects introduced during electron irradiation can be seen in both Ni 83Zr 17 and Ni 82Zr 18 solid solutions. There is a significant difference between Ni 83Zr 17 and Ni 82Zr 18 in terms of changes in the number of 12-faced volonoi polyhedrons, namely, the number of constituent atoms whose coordination number is 12. A change in the combination of various volonoi polyhedrons (a change in coordination number of constituent atoms) during the introduction of lattice defects and thermal recovery precedes SSA in the Ni–Zr solid solution model.

The influence of diffusion-induced dislocations on high efficiency silicon solar cells

Heavy boron and phosphorus diffusions are used in many high efficiency, monocrystalline silicon solar cell designs to form localized contact diffusions and back surface fields. It is important to cell performance that these diffusion processes do not increase bulk recombination by the introduction of lattice defects. This paper investigates the effect of boron and phosphorus misfit dislocation networks on the bulk recombination parameters, and performance of high efficiency silicon solar cells. It demonstrates that the formation of either a boron or phosphorus misfit dislocation network generates bulk asymmetric Shockley-Read-Hall recombination centers, and that these adversely affect the current-voltage curve, local ideality factor, and ultimately the performance of p-type silicon solar cells.

Confocal fluorescence spectrometry for observation of crystal dissolution kinetics

We have developed a confocal fluorescence microscope for observation of the dissolution kinetics at various crystal faces under varying conditions. Natural calcite (CaCO 3) was chosen for the experimental samples and the dissolution kinetics was estimated from the increase in the pH value of the solution using a fluorescent pH indicator, seminaphthorhodafluors-1. Using this instrument, we investigated not only the difference in dissolution rate among various crystal faces but also the effects of the surface roughness, subsurface structure (such as lattice defects) and inhibitor on the dissolution rate. Among the (1 0 1 ̄ 4) , (1 0 1 ̄ 0) and (2 1 3 ̄ 4) faces of calcite samples, the (1 0 1 ̄ 4) face dissolved most slowly and the (1 0 1 ̄ 0) face fastest. Increasing the surface area of (1 0 1 ̄ 4) face in contact with water by scratching increased the dissolution rate. Introduction of lattice defects on the (1 0 1 ̄ 4) face by He + irradiation significantly increased the dissolution rate. Inhibition of the calcite dissolution by La 3+ occurred in the order of (1 0 1 ̄ 4) > (1 0 1 ̄ 0) > (2 1 3 ̄ 4) .

MA-SHS of ZrC and ZrB&lt;sub&gt;2&lt;/sub&gt; in Air from the Zr/B/C Powder Mixtures

MA-SHS of ZrC and ZrB&lt;sub&gt;2&lt;/sub&gt; in Air from the Zr/B/C Powder Mixtures

Radiation damage of Si photodiodes by high-temperature irradiation

Results are presented of a detailed study of the effects of high-temperature 4-MeV neutron irradiation on the performance degradation of Si pin photodiodes. The macroscopic device performance is correlated with the radiation-induced defects observed by DLTS. It was found that the dark current increases after irradiation, while the photocurrent decreases. After irradiation, two majority electron capture levels (Ec 0.40 eV) were induced in the n-Si substrate. Additionally, degradation of device performance and the rate of introduction of lattice defects decrease with increasing irradiation temperature. For 250 °C irradiation, the reduction of the photocurrent is only 10% of the starting value. This result suggests that the creation and recovery of radiation damage proceed simultaneously at high temperatures.

Effect of radiation induced deep level traps on Si detector performance

The main factor, which leads to semiconductor detector degradation in high-energy physics experiments, is the introduction of lattice defects in the detector material produced by radiation. Based on the spectrum of radiation induced defects in the silicon bulk, the overview of effects and mechanisms responsible for the changes in the main detector parameters such as effective concentration of the space charge in the depleted region, space charge sign inversion, charge collection efficiency, and detector breakdown voltage are considered. Special attention is paid to the electric field distortion related with high concentration of radiation induced deep traps, which is the key question for the design of detectors operating at cryogenic temperature. In particular, the charge collection recovery at low temperature, often refereed as the Lazarus effect, and the limitation for the detection rate related to the polarization effect are considered.

Tuning the electronic structure of solids by means of nanometer-sized microstructures

Most materials studied and/or used technologically today are electrically neutral, i.e the positive and negative electric charges are balanced. The properties of these materials are varied prodominantly by modifying the atomic structure (e.g. by alloying, introduction of lattice defects, etc.) Limited attention has been paid so far to the option of influencing the properties of materials by deviating from charge neutrality. In fact, solids with nanometer-sized microstructures may open the way to generate materials with an excess of a deficit of electrons or holes of up to 0.3 electrons/holes per atom. Such deviations from charge neutrality may be achieved either by means of an extremely applied voltage or by space charges at interfaces between materials with different chemical compositions (or combinations of both). As many properties of solid materials depend on their electronic structure, significant deviations from charge neutrality result in materials with new, yet mostly unexplored properties such as modified electric, ferromagnetic, optical etc. properties. In fact, two types of property variations may be distinguished: Variations that last as long as the external voltage is applied and subsequently vanish reversibly once the external voltage is removed. These properties may be tuned by tuning the applied voltage. The second type of property changes are the persistent ones. They remain even if the material returns to the electrically neutral state. New types of alloys or materials with new types of atomic structures seem to be examples of persistent variations. Existing and conceivable new technological applications of solids deviation from charge neutrality are discussed.

Influence of germanium content on the degradation of strained Si1−xGex epitaxial diodes by electron irradiation

The degradation of strained n+-Si/p+-Si1−xGex epitaxial diodes, which are irradiated at room temperature with 1 MeV electrons in a high-voltage transmission electron microscope, is investigated. Special attention is given to the influence of the germanium content on the degradation of electrical characteristics and on the introduction of lattice defects into the epitaxial layer. The diode degradation and the deep level density for the x = 0.12 diodes are larger than for the x = 0.16 diodes. This can be explained by the fact that germanium atoms act as recombination centres for vacancies and interstitials thus decreasing the generation rate of stable radiation defects and by the fact that the energy absorbed in the epitaxial layer during irradiation decreases with increasing germanium content due to the smaller stopping power of germanium atoms.