High Vacuum Annealing Research Articles

Contraction, cation oxidation state and size effects in cerium oxide nanoparticles

An accurate description of the structural and chemical modifications of cerium oxide nanoparticles (NPs) is mandatory for understanding their functionality in applications. In this work we investigate the relation between local atomic structure, oxidation state, defectivity and size in cerium oxide NPs with variable diameter below 10 nm, using x-ray absorption fine structure analysis in the near and extended energy range. The NPs are prepared by physical methods under controlled conditions and analyzed in morphology and crystalline quality by high resolution transmission electron microscopy. We resolve here an important question on the local structure of cerium oxide NPs: we demonstrate a progressive contraction in the Ce–O interatomic distance with decreasing NP diameter and we relate the observed effect to the reduced dimensionality. The contraction is not significantly modified by inducing a 4%–6% higher Ce3+ concentration through thermal annealing in high vacuum. The consequences of the observed average cation–anion distance contraction on the properties of the NPs are discussed.

Oxygen Passivation Mediated Tunability of Trion and Excitons in MoS_{2}.

Using wide spectral range insitu spectroscopic ellipsometry with systematic ultrahigh vacuum annealing and insitu exposure to oxygen, we report the complex dielectric function of MoS_{2} isolating the environmental effects and revealing the crucial role of unpassivated and passivated sulphur vacancies. The spectral weights of the A (1.92eV) and B (2.02eV) exciton peaks in the dielectric function reduce significantly upon annealing, accompanied by spectral weight transfer in a broad energy range. Interestingly, the original spectral weights are recovered upon controlled oxygen exposure. This tunability of the excitonic effects is likely due to passivation and reemergence of the gap states in the band structure during oxygen adsorption and desorption, respectively, as indicated by abinitio density functional theory calculation results. This Letter unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS_{2}.

Fast detection of water nanopockets underneath wet-transferred graphene

We report an investigation of the graphene/substrate interface morphology in large-area polycrystalline graphene grown by chemical-vapour deposition and wet-transferred onto Si wafers. We combined spectroscopic ellipsometry, X-ray photoelectron spectroscopy and atomic-force microscopy in order to yield morphological and chemical information about the system. The data showed that wet-transferred samples may randomly exhibit nanosized relief patterns indicative of small water nanopockets trapped between graphene and the underlying substrate. These pockets affect the adhesion of graphene to the substrate, but can be efficiently removed upon a mild annealing in high vacuum. We show that ellipsometry is capable of successfully and reliably detecting, via multilayer dielectric modelling, both the presence of such a spurious intercalation layer and its removal. The fast, broadly applicable and non-invasive character of this technique can therefore promote its application for quickly and reliably assessing the degree of adhesion of graphene transferred onto target substrates, either for ex-post evaluation or in-line process monitoring.

Influence of defects on electrical properties of electrodeposited co-doped ZnO nanocoatings

We present a systematic investigation of the electrical properties of undoped and Co-doped ZnO nanostructures at room temperature as an extensive study of the role of defects in ZnO. The ZnO nanostructures were fabricated by the electrodeposition method at low bath temperature (80 °C) and the Co concentration was varied from 0.01 to 0.2 mM. Electrical properties of the undoped and Co-doped ZnO nanostructures were studied in detail. The carrier concentration increases while the mobility reduces with increase in Co-concentration. The resistivity increases with an increase in Co-concentration and the reason is correlated with the defects in ZnO. In order to understand more details of the role of defects in the present I–V characteristic behavior of the Co-doped ZnO, high temperature vacuum annealing of ZnO sample was carried out. Electrical, optical and magnetic properties of the high temperature vacuum annealed ZnO were studied in detail. Photoluminescence spectroscopy (PL) results revealed more information of the defect levels which act as scattering centers for the carriers. Co-doping as well as annealing at high temperature in vacuum environment tunes the defects in ZnO and which influence the optical, magnetic and electrical behavior of the ZnO nanostructures.

Light-emitting structures based on colloidal quantum dots of cadmium sulphide having a high color rendering index

Quantum dots created by colloidal synthesis (CQDs) were investigated. The paper shows how by changing the size and concentration of CQDs the emission spectrum of the structure with a color rendering index greater than 90 was achieved. Creation of the light- emitting structures involved spin-coating of CdS CQDs onto the glass substrate and consequent high-vacuum annealing. Methods allowing the increase of the emission intensity to achieve better approximation of the radiation spectra shape of white LEDs’ spectra.

Investigation of the Differential Capacitance of Highly Ordered Pyrolytic Graphite as a Model Material of Graphene.

A study of the differences among the capacitances of freshly exfoliated highly ordered pyrolytic graphite (HOPG, sample denoted FEG), HOPG aged in air (denoted AAG), and HOPG aged in an inert atmosphere (hereafter IAG) is presented in this work. The FEG is found to be more hydrophilic than AAG and IAG because the aqueous electrolyte contact angle (CA) increases from 61.7° to 72.5° and 81.8° after aging in Ar and air, respectively. Electrochemical impedance spectroscopy shows the FEG has an intrinsic capacitance (6.0 μF cm-2 at the potential of minimum capacitance) higher than those of AAG (4.3 μF cm-2) and IAG (4.7 μF cm-2). The observed changes in the electrochemical response are correlated with spectroscopic characterization (Raman spectroscopy and X-ray photoelectron spectroscopy), which show that the surface of HOPG was doped or contaminated after exposure to air. Taken together, these changes upon atmospheric exposure are attributed to oxygen molecule, moisture, and airborne organic contaminations: high-vacuum annealing was applied for the removal of the adsorbed contaminants. It was found that annealing the aged sample at 500 °C leads to partial removal of the contaminants, as gauged by the recovery of the measured capacitance. To the best of our knowledge, this is first study of the effect of the airborne contaminants on the capacitance of carbon-based materials.

Наукоемкая технология уменьшения водородного изнашивания рабочих поверхностей трения

This paper reports the problems considered regarding the hydrogen wear decrease in steel parts operating in hydrogen medium and, in particular, in hydrocarbon liquids. The comparative researches are carried out with samples after thermal treatment, high-vacuum annealing and ionic implantation and also after a combination of these methods. The structure of samples surface layer is investigated after a combined working and the values of micro-hardness of layers formed are given. The investigation of surface quality changes is carried out. The results of comparative abrasion tests of samples are presented. It is defined that after a combined working samples wear decreased. There are shown data on the hydrogen concentration in a surface layer of samples and the analysis of surface properties for hydrogen concentration and hydrogen wear intensity is carried out.

Формирование структуры в поверхностном слое деталей машин методами высоковакуумного отжига и ионной имплантации

This paper reports the problems of hydrogen wear decrease in steel parts operating in hydrogen medium. The friction couples of particular machine parts subjected to hydrogen wear are shown. Steel grades of the samples analyzed and their hardness are pointed out. The technologies of high- vacuum annealing and ion implantation used in investigations are de-scribed. The modes for the carrying out of high-vacuum annealing and ion implantation of silicon into a surface of the samples investigated are presented. It is determined that in a surface layer after the carrying out of high-vacuum annealing and ion implantation appear new structures with their form similar to roundish spots. The dimensions of spots and their distribution according to depth are defined. The sample breaking tests are carried out. It is established that technological operations carried out affect only the surface layers of samples. The investigation results can be used at the analysis of methods for hydrogen wear decrease of parts operating in hydrogen medium.

Low-temperature growth of layered molybdenum disulphide with controlled clusters.

Layered molybdenum disulphide was grown at a low-temperature of 350 °C using chemical vapour deposition by elaborately controlling the cluster size. The molybdenum disulphide grown under various sulphur-reaction-gas to molybdenum-precursor partial-pressure ratios were examined. Using spectroscopy and microscopy, the effect of the cluster size on the layered growth was investigated in terms of the morphology, grain size, and impurity incorporation. Triangular single-crystal domains were grown at an optimized sulphur-reaction-gas to molybdenum-precursor partial-pressure ratio. Furthermore, it is proved that the nucleation sites on the silicon-dioxide substrate were related with the grain size. A polycrystalline monolayer with the 100-nm grain size was grown on a nucleation site confined substrate by high-vacuum annealing. In addition, a field-effect transistor was fabricated with a MoS2 monolayer and exhibited a mobility and on/off ratio of 0.15 cm2 V−1 s−1 and 105, respectively.

Characterization of magnetic Ni clusters on graphene scaffold after high vacuum annealing

Magnetic Ni nanoclusters were synthesized by electron beam deposition utilizing CVD graphene as a scaffold. The subsequent clusters were subjected to high vacuum (5−8 x10−7 torr) annealing between 300 and 600 °C. The chemical stability, optical and morphological changes were characterized by X-ray photoemission microscopy, Raman spectroscopy, atomic force microscopy and magnetic measurement. Under ambient exposure, nickel nanoparticles were observed to be oxidized quickly, forming antiferromagnetic nickel oxide. Here, we report that the majority of the oxidized nickel is in non-stoichiometric form and can be reduced under high vacuum at temperature as low as 300 °C. Importantly, the resulting annealed clusters were relatively stable and no further oxidation was detectable after three weeks of air exposure at room temperature.

Titanium oxide films with vacuum thermal treatment for enhanced hemocompatibility

Blood compatibility is a key property of biomaterials contacting blood. Titanium oxide film has been deposited on Si wafers (110) by unbalanced reactive magnetron sputtering and successive vacuum annealing. The structure, chemical composition, hydrophilicity and surface energy of the films have been investigated by X-ray diffraction, X-ray photoelectron spectroscopy and contact angle measurement respectively. The results revealed that high vacuum annealing increased the surface energy, hydrophilicity and the rate of of Lewis base in the film. In vitro evaluation of hemocompatibility, including platelet adhesion, fibrinogen denaturation, activated partial thromboplastin time and thrombin time test, proved that the hydrophilic titanium oxide films have excellent blood compatibility.

Self-assembly of Ge quantum dots on periodically corrugated Si surfaces

The fabrication of regularly ordered Ge quantum dot arrays on Si surfaces usually requires extensive preparation processing, ensuring clean and atomically ordered substrates, while the ordering parameters are quite limited by the surface properties of the substrate. Here, we demonstrate a simple method for fabrication of ordered Ge quantum dots with highly tunable ordering parameters on rippled Si surfaces. The ordering is achieved by magnetron sputter deposition, followed by an annealing in high vacuum. We show that the type of ordering and lattice vector parameters of the formed Ge quantum dot lattice are determined by the crystallographic properties of the ripples, i.e., by their shape and orientation. Moreover, the ordering is achieved regardless the initial amorphisation of the ripples surface and the presence of a thin oxide layer.

FIB 加工Si ナノワイヤの機械信頼性に及ぼす高真空アニール効果

FIB 加工Si ナノワイヤの機械信頼性に及ぼす高真空アニール効果

N‐V‐related fluorescence of the monoenergetic high‐energy electron‐irradiated diamond nanoparticles

Fluorescent diamond nanoparticles (FND) have recently been introduced as promising luminescent probes for bioimaging to compete with more commonly used fluorophores and quantum dots. In this work, we investigate the formation of NV color centers in diamond nanocrystallites using monoenergetic electrons. A large quantity (1.4 g) of FNDs has been irradiated in the cyclic relativistic electron accelerator (Microtron) with the surface charge up to 3C/cm2 using collimated accelerated electrons extracted with monochromatic energies 6−25 MeV. The nitrogen‐vacancy (NV) color centers have been activated by the high temperature vacuum annealing followed by the oxidation and sonification to remove sp2 carbon from the surface and to form stable colloid solutions with the concentration 1 mg/ml and the electro‐kinetic (zeta) potential about −35 mV. The steady state fluorescence spectra show that the fluorescence yield increases linearly with the surface charge irradiation.

Vacuum or flowing argon: What is the best synthesis atmosphere for nanodiamond-derived carbon onions for supercapacitor electrodes?

We present a comprehensive study on the influence of the synthesis atmosphere on the structure and properties of nanodiamond-derived carbon onions. Carbon onions were synthesized at 1300 and 1700°C in high vacuum or argon flow, using rapid dynamic heating and cooling. High vacuum annealing yielded carbon onions with nearly perfect spherical shape. An increase in surface area was caused by a decrease in particle density when transitioning from sp3 to sp2 hybridization and negligible amounts of disordered carbon were produced. In contrast, carbon onions from annealing nanodiamonds in flowing argon are highly interconnected by few-layer graphene nanoribbons. The presence of the latter improves the electrical conductivity, which is reflected by an enhanced power handling ability of supercapacitor electrodes operated in an organic electrolyte (1M tetraethylammonium tetrafluoroborate in acetonitrile). Carbon onions synthesized in argon flow at 1700°C show a specific capacitance of 20F/g at 20A/g current density and 2.7V cell voltage which is an improvement of more than 40% compared to vacuum annealing. The same effect was measured for a synthesis temperature of 1300°C, with a 140% higher capacitance at 20A/g for argon flow compared to vacuum annealing.

Investigation of thermal stability and reliability of HfO2 based resistive random access memory devices with cross-bar structure

The effect of the annealing treatment of a HfO2 resistive switching layer and the memory performance of a HfO2-based resistive random access memory (cross-bar structure) device were investigated. Oxygen is released from HfO2 resistive switching layers during vacuum annealing, leading to unstable resistive switching properties. This oxygen release problem can be suppressed by inserting an Al2O3 thin film, which has a lower Gibbs free energy, between the HfO2 layer and top electrode to form a Ti/Al2O3/HfO2/TiN structure. This device structure exhibited good reliability after high temperature vacuum annealing and post metal annealing (PMA) treatments. Moreover, the endurance and retention properties of the device were also improved after the PMA treatment.

The role of operations after the deposition on the performance of SiOx films in optoelectronics devices

In this study, we have investigated phase separation, silicon Nano crystal (Si-NC) formation and optoelectronics properties of Si oxide (SiOx, 0.7<x<1.3) films in high-vacuum annealing and ion bombardment conditions. The SiOx films were deposited by physical vapor deposition (PVD). The internal structure properties of these films were the main factor in applications of optoelectronic. Possible changes in the structure, composition and electro physical properties were investigated by FTIR and TEM spectroscopy. The measurements show that SiOx film is the dominant phase in the ultra-thin layer. Also, high-temperature annealing ion bombardment results in further increase of the phase separation of the whole layer.

Transformation of the electronic structure of the SnO2 − x /MWCNT nanocomposite under high-vacuum annealing conditions

The transformation of the structural phase state and the electronic structure of the SnO2 − x/MWCNT composite has been studied using X-ray spectroscopy and high-resolution transmission electron microscopy. It has been shown that the character of the interaction of the metal-oxide component of the composite with the array of carbon nanotubes depends on the structural state of tin oxide in globules of the metal-oxide component. In the initial composite with a large content of amorphous tin oxide, covalent functionalization of the MWCNT surface occurs. High-vacuum annealing results in the formation of a nanocrystalline structure in globules of the metal-oxide component and is accompanied by changes in the character of its interaction with carbon tubes.

Ultra-smooth and lattice relaxed ZnO thin films

The crystal structure and quality of ZnO thin films were enhanced by high temperature vacuum annealing. High quality ZnO thin films have been grown on a-plane sapphire substrate by radio frequency (rf) magnetron sputtering method at a substrate temperature of 600°C. A remarkable improvement in the epilayer quality were established by in situ high temperature annealing. The film quality, smoothness, the in plane stress, and the degree of epitaxy of the films have been evaluated. The crystalline quality was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and Raman spectroscopy analyses. An extremely smooth ZnO films were achieved at higher annealing temperatures with root mean square roughness of 0.3nm. The transverse optical mode A1(TO) observed in all the samples and the longitudinal optical mode A1(LO) appeared only at higher annealing temperatures over 800°C in the micro-Raman scattering measurements. The strain of c-axis were relaxed and the lattice parameter was comparable to that of bulk ZnO at high annealing temperature of 900°C.

Study of depth profile of hydrogen in hydrogenated diamond like carbon thin film using ion beam analysis techniques

The Hydrogenated Diamond Like Carbon (HDLC) thin films are deposited on Silicon substrate at room temperature using asymmetric capacitively coupled RF plasma with varying flow rates of methane. These films are undergone annealing at high vacuum (∼10−7torr) and high temperature (750 and 1050°C) furnace. The as-prepared and annealed HDLC films have been depth profiled for hydrogen using the resonance at 6.44MeV in 1H(19F,αγ)16O nuclear reaction. The as prepared films exhibit non-uniform depth distribution of hydrogen: it decreases with depth. Annealing in vacuum brings about is a significant desorption of hydrogen from the films. Loss of hydrogen, albeit in much lower proportions, is also induced by the bombarding beam. The films also experience a mild loss of carbon, as shown by proton backscattering spectrometry, during high vacuum annealing. The depth profiles of hydrogen in the annealed films are indicative of the prevalence of graphitic carbon near film–substrate interface.