Inert Gas Condensation Method Research Articles

Characterization on microstructure evolution of a bulk nanograined TiZrHfNb refractory high-entropy alloy

A bulk TiZrHfNb nanograined refractory high-entropy alloy (NG-RHEA) with an average grain size of 31.6 nm was prepared by inert gas condensation (IGC) method. In the initial as-IGC sample, it is composed of a body-centered cubic structure and an amorphous phase accounting for about 25%. Then the microstructure was regulated by annealing at 200 °C, 400 °C and 600 °C for 0.5 h. The results show that a dual-phase structure composed of body-centered cubic phase nanograins and amorphous phase was maintained below 400 °C. Significant grain growth was observed when annealed at 600 °C, with obvious phase decomposition detected. The hardness of as-IGC TiZrHfNb NG-RHEA increases from 348 HV to 432 HV after annealed at 400 °C. The relationship between microstructure and hardness was discussed. This work provides insights into the preparation and structure modulation of bulk NG-RHEAs.

Synthesis of Free-Standing Pd-Ni-P Metallic Glass Nanoparticles with Durable Medium-Range Ordered Structure for Enhanced Electrocatalytic Properties.

Topologically disordered metallic glass nanoparticles (MGNPs) with highly active and tailorable surface chemistries have immense potential for functional uses. The synthesis of free-standing MGNPs is crucial and intensively pursued because their activity strongly depends on their exposed surfaces. Herein, a novel laser-evaporated inert-gas condensation method is designed and successfully developed for synthesizing free-standing MGNPs without substrates or capping agents, which is implemented via pulse laser-induced atomic vapor deposition under an inert helium atmosphere. In this way, the metallic atoms vaporized from the targets collide with helium atoms and then condense into short-range-order (SRO) clusters, which mutually assemble to form the MGNPs. Using this method, free-standing Pd40 Ni40 P20 MGNPs with a spherical morphology are synthesized, which demonstrates satisfactory electrocatalytic activity and durability in oxygen reduction reactions. Moreover, local structure investigations using synchrotron pair distribution function techniques reveal the transformation of SRO cluster connection motifs of the MGNPs from face-sharing to edge-sharing modes during cyclic voltammetry cycles, which enhances the electrochemical stability by blocking crystallization. This approach provides a general strategy for preparing free-standing MGNPs with high surface activities, which may have widespread functional applications.

Pd–Ni–P metallic glass nanoparticles for nonenzymatic glucose sensing

Metallic glass nanoparticles hold great promise as nonenzymatic glucose sensors due to their rich low-coordinated active sites and high biocompatibility. However, their non-periodic atomic structure and unclear structure-property relationship pose significant challenges for realizing and optimizing their sensing performance. In this work, Pd–Ni–P metallic glass nanoparticles with variable compositions were successfully prepared as nonenzymatic glucose sensors via a laser-evaporated inert-gas condensation method. The electrochemical tests show that the sensor based on Pd41·25Ni41·25P17.5 nanoparticles shows a wide linear detection range (0.003–1.31 ​mM), high sensitivity (516 ​μA ​mM−1 ​cm−2), and high stability (∼97.8% current retention after 1000 cycles). Local structural investigations using synchrotron pair distribution function and high-resolution microscopic techniques reveal a strong structural correlation within short-to medium-range orders in the Pd41·25Ni41·25P17.5 nanoparticles, which can be well retained after electrochemical cycling. These atomic-scale structural characteristics might be responsible for the high sensing performance. This study demonstrates the high applicability of Pd–Ni–P metallic glass nanoparticles as sensitive and stable non-enzymatic glucose sensors.

Structure, composition and enhanced magnetic properties of novel ternary multicore-shell Ni–Co–Cr nanoclusters prepared by one-step inert gas condensation method

We have synthesized ternary Ni–Co–Cr nanoclusters using one step method by simultaneous sputtering of metallic targets through inert gas condensation (IGC) deposition process. The difference in surface energy between the component atoms creates a preferential surface phase leading to the formation of multi core/shell structures. Surface structure and composition analysis reveal metallic and oxide phases characterized by extraordinary 1.43 μm periodicity strong magnetic stripe domains with weak magnetic force microscopy signal attenuation up to a lift height value of 2.5 μm. In addition, the ternary nanoclusters exhibit strong ferromagnetic behavior below the blocking temperature of 139 K with coercivity of 700 Oe at 4 K. The enhanced magnetic properties are attributed to Volmer-Weber growth mechanism and pave a facile way for preparing ternary core/shell magnetic structures needed for applications which require strong magnetic anisotropy along their growth direction.

CO2 Hydrogenation over Unsupported Fe-Co Nanoalloy Catalysts.

The thermo-catalytic synthesis of hydrocarbons from CO2 and H2 is of great interest for the conversion of CO2 into valuable chemicals and fuels. In this work, we aim to contribute to the fundamental understanding of the effect of alloying on the reaction yield and selectivity to a specific product. For this purpose, Fe-Co alloy nanoparticles (nanoalloys) with 30, 50 and 76 wt% Co content are synthesized via the Inert Gas Condensation method. The nanoalloys show a uniform composition and a size distribution between 10 and 25 nm, determined by means of X-ray diffraction and electron microscopy. The catalytic activity for CO2 hydrogenation is investigated in a plug flow reactor coupled with a mass spectrometer, carrying out the reaction as a function of temperature (393–823 K) at ambient pressure. The Fe-Co nanoalloys prove to be more active and more selective to CO than elemental Fe and Co nanoparticles prepared by the same method. Furthermore, the Fe-Co nanoalloys catalyze the formation of C2-C5 hydrocarbon products, while Co and Fe nanoparticles yield only CH4 and CO, respectively. We explain this synergistic effect by the simultaneous variation in CO2 binding energy and decomposition barrier as the Fe/Co ratio in the nanoalloy changes. With increasing Fe content, increased activation temperatures for the formation of CH4 (from 440 K to 560 K) and C2-C5 hydrocarbons (from 460 K to 560 K) are observed.

Designing sandwich-type single-layer graphene decorated by copper nanoparticles for enhanced sensing properties

It has already been theoretically shown that sandwich-type structures prepared by stacking metal nanoparticles in two graphene layers would have exceptional optical and electrical properties for practical applications. These sandwich structures designed by band gap engineering could lead to materials capable of being developed to meet industrial demands. In order to confirm this theoretical approach, copper nanoparticle (CuNP) islands decorated in sandwich-type single-layer graphene (SLG) have been designed and used as a non-enzymatic sensor platform for the first time. Firstly, SLG has been synthesized on copper foil using a chemical vapor deposition technique and transferred onto a fluorine-doped tin oxide surface. Next, CuNPs on this SLG have been prepared using an inert-gas condensation method based on DC magnetron sputtering. A sensor platform based on the sandwich-type hetero-structure (SLG/CuNP/SLG) has been constructed by transferring another single layer of graphene onto the prepared CuNP-decorated graphene layer. In this way, a unique sandwich structure has been obtained for further applications by stacking nanoparticles with high stability, controlled size and regular particle distribution between impurity-free, large-area single layers of graphene. The sensor properties of this sandwich structure to the saccharides have been compared with those of the single-layer sensor platform (CuNP/SLG). In accordance with the theoretical studies in the literature, it has been found that the sandwich structure greatly improves sensor properties such as limit of detection, stability and response time. More importantly, it was determined that the sandwich structure acts as a shielding layer, protecting nanoparticles from electrochemical/optical and other environmental conditions.

Deformation-induced atomic rearrangements and crystallization in the shear bands of a Tb75Fe25 nanoglass

Tb75Fe25 nanoglass samples were prepared by cold pressing amorphous nanoparticles (produced by the inert gas condensation method). One of the bulk nanoglass samples was severely plastically deformed using high-pressure torsion. The structure of the deformed and non-deformed nanoglass samples was examined by X-ray diffraction. Differential scanning calorimetry of the samples showed a higher thermal stability of the non-deformed sample when compared to the severely plastically deformed sample. The results suggest a more relaxed structure being present in the non-deformed sample as compared to that of the deformed sample. Transmission electron microscopy performed on the deformed sample revealed the presence of shear band-like features with indications of crystalline terbium precipitates. Atom probe tomography was used to identify compositional changes in both the non-deformed and the deformed samples. The non-deformed structure showed a homogeneous distribution of both Tb and Fe, whereas a terbium enhancement (up to 90%) was observed within the shear bands of the deformed sample. The Tb segregation and crystallization within the shear bands observed both by electron microscopy and atom probe tomography are clear indications of the structural changes occurring in the shear band regions during the deformation. It is concluded that the diffusion is enhanced leading to the compositional variation within the shear bands.

Atom Probe Tomography of Au–Cu Bimetallic Nanoparticles Synthesized by Inert Gas Condensation

The inert gas condensation method (IGC) produces multimetallic nanoparticles in a metastable state that may exhibit heterogeneities of size, structure, and composition. The deposition of IGC-fabricated nanoparticles on substrates allows for a detailed characterization by combination of aberration-corrected scanning transmission electron microscopy (TEM) and atom probe tomography (APT). Multiple particle monitoring and high-resolution scanning TEM give access to the size distribution of Au–Cu nanoparticles ( 7 nm), while Cu is more randomly distributed in smaller particles.

Forming pressure effect on microstructure and mechanical properties of nanocrystalline aluminum synthesized by inert gas condensation

The preparation of nanocrystalline aluminum (NC Al) was conducted in two steps. After the NC Al powder was synthesized by an Inert gas condensation (IGC) method in a helium atmosphere of 500 Pa, the NC Al powder was in-situ compacted into a pellet with a 10 mm diameter and 250 μm-300 μm thickness in a high vacuum (10-6Pa-10-7Pa) at room temperature. The NC Al samples were not exposed to air during the entire process. After the pressure reached 6 GPa, the relative density could reach 99.83%. The results showed that the grain size decreased with the increased of in-situ forming pressure. The NC Al samples present obvious ductile fracture, and the tensile properties were greatly changed with the increase of forming pressure.

Facile Green Synthesis of LaCe Co-Doped ZnO Nanoparticles and Their Structural, Optical and Antibacterial Properties

This present work describes the synthesis of LaCe co-doped zinc oxide (ZnO) nanoparticles (NPs) prepared by green method using Gymnema sylvestre (G. sylvestre) leaves as reducing as well as capping agent. Green synthesis method avoids inert gases, high pressure, laser radiation, high temperature, toxic chemicals etc. as compared to conventional method like sol-gel technique method, laser ablation method, solvothermal method, inert gas condensation method and chemical reduction method. The synthesized LaCe co-doped ZnO NPs was characterized by X-Ray diffraction (XRD), field emission scanning electron microscopy (FESEM), elemental analysis (EADX), Fourier transform infrared spectroscopy (FTIR), UV-vis spectroscopy and photoluminescence (PL). The LaCe co-doped ZnO NPs was tested against clinical pathogens such as gram positive G+ (Staphylococcus aureus and Streptococcus pneumoniae) and gram negative G- (Klebsiella pneumoniae, Shigella sydenteriae, Escherichia coli, Pseudomonas aeruginosa and Protus vulgaris) bacterial strains using agar well diffusion method.

Hydrogen Sorption of Porous Tungsten Oxide Nanomaterial and Effect of a Pd Coating on its Storage Capacity Under Hydrogenation Cycles

The H2 uptake performance at room temperature of porous tungsten oxide nanomaterials with and without a catalytic Pd coating was studied by the quartz crystal microbalance technique. Tungsten oxide composed mainly of WO3 was synthesized by inert gas condensation method using He. The samples consisted of semi-amorphous nanomaterials of low crystallinity and high porosity, as revealed by SAED, TEM, XRD, Raman spectroscopy and N2 adsorption–desorption isotherms. The H2 uptake capacity of the porous oxide was studied under increasing H2 exposure pressures (1000–7000[Formula: see text]Pa), with and without Pd coating. After reaching a maximum value of 1.2 H2[Formula: see text]wt.%, at 1160[Formula: see text]Pa, the H2 uptake capacity of the Pd-coated oxide consistently decreased. Successive hydrogenation cycles were carried out on the Pd-coated oxide at 3300 Pa and 6000 Pa to evaluate the H2 uptake performance of the sample under this H2 loading and unloading process. It was found that the H2 uptake capacity decreased from around 1 to values below 0.53[Formula: see text]H2[Formula: see text]wt.%, which is the reference H2 storage capacity achieved by a 15[Formula: see text]nm-thick Pd film. We argued that water molecule formation in the Pd/oxide interface and sublayers negatively affects the H2 uptake capacity of the oxide under successive hydrogenation cycles at room temperature.

An effective non-enzymatic biosensor platform based on copper nanoparticles decorated by sputtering on CVD graphene

It has become inevitable to design non-enzymatic biosensors to eliminate the drawbacks of enzymatic biosensors prepared using enzymes which are expensive and without long-term stability. For this purpose, a single layer graphene film was prepared by chemical vapor deposition method on Cu foil and transferred to the FTO glass slide. After that copper nanoparticles (CuNP) were decorated by the inert-gas condensation method based on DC magnetron sputtering on it. The prepared CuNP decorated graphene film was characterized and used as a non-enzymatic sensor platform for the detection of glucose. The sensor platform exhibited a fast response time of less than 4 s and the sensitivity of 430.52 μA mM−1 cm-2 with linear concentration range (0.01–1.0 mM) having detection limit 7.2 μM. Electrochemical investigations indicate that the sensor platform which is decorated CuNP graphene film possess an excellent performance toward glucose.Prepared biosensors platform could be used and applied in the field of new drug discovery, biomedical, clinical diagnosis and forensic science to miniaturize of detection instrument and reduce detection sample and period.

A thermodynamics model for morphology prediction of aluminum nano crystals fabricated by the inert gas condensation method

The purpose of this study is to provide scientific guidance for the morphological control of nanoparticle synthesis using the gas phase method. A universal thermodynamics model is developed to predict the morphology of nanoparticles fabricated using the inert gas condensation method. By using this model, the morphologies of aluminum nanocrystals are predicted under various preparation conditions. There are two types of energy that jointly determine the formation of nanoparticle morphology—Gibbs free energy for nanoparticles and energy variation during the process. The results show that energy variation dominates morphology formation when the cooling rate is less than 2 × 1011 K s−1 in the aluminum nanocrystal production process. At the beginning of the nanoparticle growth, the most stable morphology is predicted to be spherical, but the energetically preferred morphology becomes cubic as the particle grows. The turning point in the particle size at which spherical morphology is no longer the most stable morphology is exhibited as a function of pressure in a condensation chamber for different cooling rates. In this paper, we focus on the need for morphology prediction based on preparation conditions. It is concluded that nanoparticles with various morphologies could be obtained by adjusting the cooling rate and pressure in the condensation chamber.

Particle size prediction of magnesium nanoparticle produced by inert gas condensation method

Properties of nanoparticles are normally depending on particle size; therefore, developing a model to predict particle size is of vital importance. This paper established an energy analysis model to predict average particle size of magnesium nanoparticles fabricated by inert gas condensation method. Predictions of average particle size ranging from 20 to 50 nm by energy analysis model have relative errors of less than 10% compared with experimental research. Further, the model is applied to investigate operation conditions to decrease the average particle size of magnesium nanoparticles. It is found that decreasing the absolute pressure in the condensation room and increasing the temperature rise of the inert gas can both produce nanoparticles with smaller average particle sizes. Temperature rise of the inert gas plays a more important role in effect on average nanoparticle size than the absolute pressure in the condensation room. Energy transformed by collision bonding and dissipated by convection are the dominant processes for particle growth when number of atoms in one particle is greater than 2000 atoms.

Thermally and optical induced effects on the structural and electrical parameters of nc-CdS thin films

Nanocrystalline cadmium sulfide (nc-CdS) thin films have been prepared on well-cleaned glass substrates at room temperature (300 K) by thermal evaporation technique using inert gas condensation method. The effect of light soaking and annealing on the structural and optoelectrical properties of CdS thin films have been studied in this paper. SEM analysis reveals that the grains are irregular in shape and are uniformly distributed over the glass substrate. XRD study indicates an increase in the crystallite size after thermal annealing and a decrease in the crystallite size after light soaking treatment. The current transport mechanisms have been studied as a function of temperature over the temperature range 125–370 K. Above 330 K, thermionic emission contributes to the conduction mechanism. Both thermally assisted tunneling of carriers through and thermionic emission over the grain boundary potential have contributions to the conduction in the temperature range 170–330 K. Below 170 K, Mott’s hopping process appears to be the predominant conduction mechanism. The photosensitivity increases after annealing and decreases after light soaking. Transient photoconductivity measurements indicate that the decay of photoconductivity is slow and non-exponential indicating the presence of continuous distribution of defect states in the energy gap.

Investigations of the drift mobility of carriers and density of states in nanocrystalline CdS thin films

Nanocrystalline Cadmium Sulfide (nc-CdS) thin films have been prepared on well-cleaned glass substrate at room temperature (300K) by thermal evaporation technique using inert gas condensation (IGC) method. X-ray diffraction (XRD) analysis reveals that the films crystallize in hexagonal structure with preferred orientation along [002] direction. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) studies reveal that grains are spherical in shape and uniformly distributed over the glass substrates. The optical band gap of the film is estimated from the transmittance spectra. Electrical parameters such as Hall coefficient, carrier type, carrier concentration, resistivity and mobility are determined using Hall measurements at 300K. Transit time and mobility are estimated from Time of Flight (TOF) transient photocurrent technique in gap cell configuration. The measured values of electron drift mobility from TOF and Hall measurements are of the same order. Constant Photocurrent Method in ac-mode (ac-CPM) is used to measure the absorption spectra in low absorption region. By applying derivative method, we have converted the measured absorption data into a density of states (DOS) distribution in the lower part of the energy gap. The value of Urbach energy, steepness parameter and density of defect states have been calculated from the absorption and DOS spectra.

Influence of thermal process on particle size distribution of ultrafine magnesium powder prepared by inert gas condensation method

Ultrafine magnesium powder has become a research hotspot for the last few years because of its high-activity and low-density. Inert gas condensation method is a better method compared to mechanical pulverization method to produce magnesium ultrafine powder with high-purity, narrow particle size distribution and short production cycle. As particle size distribution is a vital factor when it comes to determine the application area, it is necessary to investigate particle size distribution of ultrafine magnesium powder prepared by inert gas condensation method. The purpose of this research is to determine particle size distribution of ultrafine powder produced by inert gas condensation method under different thermal conditions, then to provide a reliable method for optimum thermal parameter selection. Thermal mechanisms of ultrafine magnesium powder preparation using inert gas condensation method are proposed. Dynamic equations for the nucleation, evaporation/condensation, coagulation and deposition processes are established. This paper develops a convenient way for the prediction of the particle size distribution by deriving a modified Monte Carlo method, which is able to calculate the particle size distribution giving only a relative error less than 3%, compared with the experiments. An attempt to discover the relation between particle size and absolute pressure is conducted in the discussion part. The particle size increases exponentially with the condensation pressure increases. The method derived here may offer a mathematical method to predict particle size distribution of other ultrafine metal powder prepared by inert gas condensation method, then to choose appropriate thermal conditions for different applications.

Thermally and Optical-Induced Effect on Optical and Electrical Parameters of Ag-Doped CdSe Thin Films

Thin films of Ag-doped CdSe are deposited on the glass substrates by thermal evaporation technique using inert gas condensation method. The elemental composition of the prepared thin film is confirmed by EDX spectra. SEM analysis reveals the uniform distribution of the grains over the substrate. TEM analysis reveals the spherical nature of nanoparticles having size in the range of 25–30 nm. X-ray diffraction study indicates an increase in the grain size after thermal annealing and the decrease in the grain size after light soaking treatment. Transmittance spectra are found to decrease with corresponding red shift after annealing and light soaking of as-deposited thin films. The value of the band gap is found to decreases and refractive index increases, after annealing and light soaking treatment. The dispersion of refractive index is described using the Wemple–DiDomenico single oscillator model and the effects of the annealing and the light soaking on the dispersion parameters are studied. The dark conductivity is found to change from 2.24 × 10−8 to 1.54 × 10−7 and 1.45 × 10−9 Ω−1 cm−1 after annealing and light soaking of thin films, respectively. Hall effect measurement reveals n-type behavior of as-deposited, annealed and light-soaked thin films.

Pb dopant induced changes in structural, optical and electrical properties of CdSe thin films

Thin films of Pb doped CdSe at 1% and 5% dopant concentrations have been prepared by thermal evaporation technique using inert gas condensation method on glass substrates. The effect of Pb doping on structural, optical and electrical properties of CdSe thin films has been studied. Elemental composition of the thin films has been analyzed using Energy Dispersive X-ray analysis (EDX) spectra. Transmission electron microscope (TEM) images show the spherical nature of the nanoparticles. X-ray diffraction spectra indicate the presence of hexagonal phase of CdSe in undoped and Pb doped CdSe thin films, and formation of cubic phase of PbSe with the increase in amount of Pb dopant. A decrease in the band gap with increase in Pb doping in CdSe lattice has been observed due to the formation of band tails in the band gap and increase in crystallite size after doping. The photoluminescence (PL) spectra of thin films have been studied and enhancement in the PL intensity is observed after Pb doping. The dark conductivity of the prepared thin films has also been studied and two types of conduction mechanisms have been observed. Hall measurements indicate change in conduction mechanism from n-type to p-type after Pb doping in CdSe.

Characterization of Pb24Te76 quantum dot thin film synthesized by inert gas condensation

Air-stable and thermal-stable lead telluride quantum dot was successfully prepared on glass substrate by inert gas condensation (IGC) method. Argon (Ar) is the inert gas used during deposition process with a constant flow rate of 3×10−3Torr. The effect of heat-treatment process at different times was studies for structure, optical and electrical properties for nanocrystalline thin films. The structures of the as deposited and heat-treated films were investigated using grazing incident in-plane X-ray diffraction (GIIXD). The GIIXD pattern showed nanostructure face centered cubic structure of PbTe thin films. The energy dispersive X-ray analysis (EDX) of as deposited PbTe thin film was carried out and showed that the atomic ratio of Pb/Te was 24/76. The particle size of the as deposited PbTe film and after stored it in an unhumid atmosphere are 6.8±0.3nm and 7.2±0.3nm respectively as estimated form TEM image (i.e. in the same level of particle size). However, the particle size was changed to be 11.8±0.3nm after heat-treated for 5h at 473K. These particle size values of PbTe thin film are smaller than its Bohr radius. The estimated value of optical band gap Eg decreased from 1.71eV for the as deposited film to 1.62eV for film heat-treated (5h at 473K). The dc electrical conductivity is increased with raising temperature in the range (303–473K) for all thin films under investigation. The deduced activation energy decreased from 0.222eV for as deposited sample to 0.125eV after heat-treated at 473K for 5h.