Changes In Surface Energy Research Articles

(Invited) Controlling Nano-Scale Chemically Modified Thin Films for Chemical Mechanical Planarization

This is a review paper on the effect of chemicals modified thin films on CMP process development. As the microelectronics manufacturing faces the challenges related to the Beyond Moore’s Scale adaptation, Chemical Mechanical Planarization (CMP) process control becomes much more critical yet difficult simultaneously. The need for planarizing larger scale wafers at an atomic scale precision with superior removal rate selectivity and zero defect focus demands a nano-scale control on the process performance. This study reviews the atomic scale chemical and mechanical interactions on CMP as it applies to traditional as well as the next generation materials in microelectronics manufacturing. Once the behavior of the wafer surface is understood at an atomic level, the process control metrics can be tuned accordingly.In an attempt to come up with the design criteria for the slurry chemistry, chemically modified layer formation is evaluated on conducting, semiconducting and insulating materials as a function of evaluating the nano-scale surface topography and change in surface energy. Metallic films are studied in terms of their corrosion and passivation behavior through macro-scale electrochemical evaluations as well as the surface sensitive characterization techniques such as XRR, XRD and FTIR [1, 2]. In addition, a modeling approach is introduced through Cahn Hilliard Equation (CHE) approximation to the surface energy minimization on the metal-oxide formation by nucleation [3]. Furthermore, removal rate selectivity properties of the semiconductor materials are discussed on conventional and III-V semiconductors and insulators as a function of chemically modified film alteration [4-5]. Some high-end applications such as (i) tungsten T-gate transistors, (ii) new liner/barrier materials [6], (iii) germanium based high-speed, shallow trench isolation transistors and (iv) high-power transistors and LED applications where III/V semiconductors are deliberated. As a new challenge, 3-D implementations of the CMP process, where the chemically modified nano-films impact the materials performance are also introduced. Ozdemir, Basim, G.B. "Effect of Chemical Mechanical Polishing on Surface Nature of Titanium Implants FT-IR and Wettability Data of Titanium Implants Surface After Chemical Mechanical Polishing Implementation," Data, in Brief, 10, P 20-25, 2017. Karagoz, A., and Basim, G.B. “Controlling Germanium CMP Selectivity through Slurry Mediation by Surface Active Agents," ECS Journal of Solid State Science and Technology, CMP Special Issue, 4 (11) P5097-P5104, 2015. Karagoz, A., Sengul, , Basim, G.B., “A Cahn Hilliard Modeling of Metal Oxide Thin Films for Advanced CMP Applications," 225th ECS Meeting – Orlando, Florida, USA, May 11-15, 2014, ECS Transactions, 61 (17) 15-20 (2014). Karagoz, A., Craciun, V., Basim, G.B., “Characterization of Nano-Scale Protective Oxide Films_ Application on Metal Chemical Mechanical Planarization”. ECS Journal of Solid State Science and Technology, 4 (2) P1-P8, 2015. Ozbek, S., Akbar, W., Basim, G.B. “ Optimized Process Design for GaN Chemical Mechanical Planarization” ECS Journal of Solid State Science and Technology, Special Issue on GaN-Based Electronics for Power, RF, and Rad-Hard Applications , 6-11, P S3084-S3092, 2017. Yagan, R., Basim, G.B., “A Fundamental Approach to Electrochemical Analyses on Chemically Modified Thin Films for Barrier CMP Optimization," ECS J. Solid State Sci. Technol. 8-5, P3118-P3127, 2019.

Changes in Surface Free Energy and Surface Conductivity of Carbon Nanotube/Polyimide Nanocomposite Films Induced by UV Irradiation.

Changes in surface energy and electrical conductivity of polyimide (PI)-based nanocomposite films filled with carbon nanotubes (CNTs) induced by UV exposure are gaining considerable interest in microelectronic, aeronautical, and aerospace applications. However, the underlying mechanism of PI photochemistry and oxidation reactions induced by UV irradiation upon the surface in the presence of CNTs is still not clear. Here, we probed the interplay between CNTs and PIs under UV exposure in the surface properties of CNT/PI nanocomposite films. Changes in contact angles and surface electrical conductivity at the surface of CNT/PI nanocomposite films after UV exposure were measured. The unpaired electron intensity of free radicals generated by UV exposure was monitored by electron paramagnetic resonance. Our study indicates that the covalent interactions between CNTs and radicals generated by UV irradiation on the PI surfaces tailor the surface energy and surface conductivity through anchoring radicals on CNTs. Surprisingly, adding CNTs into PI films exposed to UV leads to antagonistic contributions of dispersion and polar components to the surface energy. The surface electrical conductivity of the CNT/PI nanocomposite films has been improved due to an enhanced hopping behavior with dense π-conjugated CNT sites. To explain the observed changes in surface energy and surface conductivity of CNT/PI nanocomposite films induced by UV exposure, a qualitative model was put forward describing the covalent interactions between UV-induced PI free radicals and CNTs, which govern the chemical nature of surface components. This study is helpful for characterizing and optimizing nanocomposite surface properties by tuning the covalent interactions between components at the nanoscale.

Insight into the effect of He atmospheric pressure plasma jets on low-density polyethylene surfaces by fixed-point treatment

In order to further investigate the modification effect of atmospheric pressure plasma jets (APPJ) on the surface of low-density polyethylene (LDPE) film and related mechanisms, a series of experiments and simulations were carried out in this paper. A laminar helium flow with a flow rate of 6.0 standard liters per minute was used as a working gas and a homogeneous glow-like He APPJ was generated by an AC voltage with a peak-to-peak voltage of 10.1 kV and a frequency of 20 kHz. After 15 min He APPJ treatment at a fixed point on the film, the surface properties at different radial positions from this point were analyzed. This study was performed using water contact angle (WCA) measurement, x-ray photoelectron spectroscopy and atomic force microscopy. The results of WCA and surface free energy (SFE) indicate that the modification effect range is larger than APPJ’s spread range on the surface. Along the radial direction, the surface properties did not change monotonously but had extreme points: the change of the surface morphology was first etching and then deposition; APPJ incorporated oxygen containing functional groups including C–O, C=O/O–C–O and O–C=O into the LDPE surface, and their distributions on the surface were different. To explore what caused the difference, quantum chemical simulation analysis by ORCA software was used to explain the relationship between the change of surface energy and oxygen-containing functional groups. The simulation showed that C–O has more influence on the SFE of the LDPE surface.

Engineering electrode/electrolyte interfacial properties of nanotube arrays for high-capacitance supercapacitors

In this study, the effect of imbibition-induced electrolyte wettability over charge carrier density and hence the increase in electric double layer is investigated for morphology-controlled TiO2 nanotube arrays. The nanotube morphology brings in good control over change in surface energy that induces electrolyte wettability. Electrolytes of HCl, KCl, and NaCl were utilized to determine surface energy, surface wettability, and electrochemical studies. The percentage of electrolyte imbibition inside nanopores varies in the order of HCl > KCl > NaCl. The double-layer formation is higher for highly wettable surfaces and is dependent on the percentage of electrolyte imbibition inside nanotube pores. From the observations, it is deduced that the storage performance of nanotube electrodes can be markedly increased by enhancing the molar conductivity and ionic mobility of electrolyte. An areal capacitance of 14.9 mF/cm2 is observed for HCl electrolyte-based supercapacitor. In addition, the cationic radius of electrolyte influences the stability of electrode with a capacitance retention of 87%.

Interfacial Structure Change and Selective Dissolution of Columbite–(Fe) Mineral during HF Acid Leaching

The goal of the paper is to study the charge transfer and reactions at the columbite-(Fe) (FeNb2O6) mineral surface during the HF leaching process. In this paper, X-ray photoelectron spectroscopy (XPS), leaching experiments, and density functional theory (DFT) calculations were used to study the surface element adsorption, charge distribution, chemical state, and energy changes of the mineral surface during the process of leaching columbite–(Fe) with different concentrations of hydrofluoric acid. The results showed that as the concentration of F atoms was increased during the acid leaching process, the Nb–O bond was more likely to be broken than the Fe–O bond; the amount of charge transferred from Nb atom to F atom (0.78 e–0.94 e/atom) was greater than that from Fe atom to the F atom (0.25 e–0.28 e/atom), so it was determined that compared to Fe atoms, it was easier for the Nb atoms to bind to F. The results of XPS analysis showed that the electron binding energies of Nb5+–O, Fe3+–O, and Fe2+–O bonds on the mineral surface increased sequentially, and the M–O bond broke during the acid leaching process, forming more stable M–F bonds. Therefore, the Nb5+–F bonds were easier to form a stable structure. Combined with the ICP results, it was found that in the filtrate after 5M HF and 10M HF acid leaching minerals, c(Nb)/c(Fe) were 2.69 and 2.95, respectively, and the concentration ratio of Nb to Fe element in the mineral was 2 which was lower than 2.69 and 2.95, confirming the result of DFT calculation and illustrating that Nb atoms in columbite-(Fe) mineral were more soluble than Fe atoms.

Transparent Light‐Driven Hydrogel Actuator Based on Photothermal Marangoni Effect and Buoyancy Flow for Three‐Dimensional Motion

AbstractMarangoni‐effect‐driven actuators (MDAs) have the advantages of direct light‐to‐work conversion and convenient operation, which makes it widely researched in the cutting‐edge fields including robots, micromachines, and intelligent systems. However, the MDA relies on the surface tension difference and it only works on the 2D liquid–air interface. Besides, the MDAs are normally pure black due to the light‐absorption material limitation. Herein, a transparent light‐driven 3D movable actuator (LTMA) and a 3D manipulation strategy are proposed. The LTMA is composed of photothermal nanoparticles‐doped temperature‐responsive hydrogel, whose surface energy changes as the nanoparticles absorb light energy. The 3D manipulation strategy combines Marangoni effect with photothermal buoyancy flow for realizing complex self‐propellant and floating/sinking motions. The LTMA can perform more advanced tasks such as 3D obstacle avoidance and 3D sampling. Benefiting from the porous structure of hydrogel, LTMA can naturally absorb the chemical molecules for remote sampling and automated drug delivery. The light‐driven, transparent, three‐dimensionally movable, and programmable actuator has promising prospects in the field of micromachines and intelligent systems.

Graphene Coating as an Effective Barrier to Prevent Bacteria-Mediated Dissolution of Gold

The interaction of biofilms with metallic surfaces produces two biologically induced degradation processes of materials: microbial induced corrosion and bioleaching. Both phenomena affect most metallic materials, but in the case of noble metals such as gold, which is inert to corrosion, metallophilic bacteria can cause its direct or in direct dissolution. When this process is controlled, it can be used for hydrometallurgical applications, such as the recovery of precious metals from electronic waste. However, the presence of unwanted bioleaching-producing bacteria can be detrimental to metallic materials in specific environments. In this work, we propose the use of single-layer graphene as a protective coating to reduce Au bioleaching by Cupriavidus metallidurans, a strain adapted to metal contaminated environments and capable of dissolving Au. By means of Scanning Tunneling Microscopy, we demonstrate that graphene coatings are an effective barrier to prevent the complex interactions responsible for Au dissolution. This behavior can be understood in terms of graphene pore size, which creates an impermeable barrier that prevents the pass of Au-complexing ligands produced by C.metallidurans through graphene coating. In addition, changes in surface energy and electrostatic interaction are presumably reducing bacterial adhesion to graphene-coated Au surfaces. Our findings provide a novel approach to reduce the deterioration of metallic materials in devices in environments where biofilms have been found to cause unwanted bioleaching.

Long-Term Variability of Relationships between Potential Large-Scale Drivers and Summer Precipitation in North China in the CERA-20C Reanalysis

Although much progress has been made in identifying the large-scale drivers of recent summer precipitation variability in North China, the evolution of these drivers over longer time scales remains unclear. We investigate multidecadal and interannual variability in North China summer precipitation in the 110-year Coupled ECMWF Reanalysis of the Twentieth Century (CERA-20C), considering changes in regional moisture and surface energy budgets along with nine circulation indices linked to anomalous precipitation in this region. The CERA-20C record is separated into three distinct periods according to the running climatology of summer precipitation: 1901–1944 (neutral), 1945–1979 (wet), and 1980–2010 (dry). CERA-20C reproduces expected relationships between large-scale drivers and regional summer precipitation anomalies well during 1980–2010, but these relationships generally do not extend to earlier periods. For example, a strong relationship with the Eurasian teleconnection pattern only emerges in the late 1970s, while correlations with the El Niño-Southern Oscillation and the Pacific–Japan pattern change sign in the mid-twentieth century. We evaluate two possible reasons for this nonstationarity: (1) the underlying atmospheric model may require strong data assimilation constraints to capture large-scale circulation influences on North China, or (2) large-scale drivers inferred from recent records may be less general than expected. Our analysis indicates that both factors contribute to the identified nonstationarity in CERA-20C, with implications for the reliability of seasonal forecasts and climate projections based on current models.

INFLUENCE OF THE COPPER AND STEEL SURFACES’ ROUGHNESS ON SURFACE ENERGY AND WETTABILITY

This article aims at solving the fundamental problem of thermal physics. This problem includes controlling small volumes of liquids on the heat exchange surfaces of special devices (for example, thermosyphons and heat pipes) working in a closed evaporative-condensation cycle. The authors analyze the effect of roughness on surface energy and wettability of different textures on typical heat exchange surfaces made of copper and steel prepared for operation by mechanical (abrasive) processing. Six textures were created on the copper and steel surfaces using a grinding and polishing machine. The roughness of the textures was evaluated based on the analysis of three-dimensional roughness characteristics (amplitude and hybrid). The surface wettability was studied on the experimental setup with the shadow method. The surface free energy of abrasively processed surfaces was determined by the Owens—Wendt—Rabel—Kaelble method. The results show the necessity of using at least one three-dimensional amplitude and hybrid characteristics to evaluate the textures. The authors have determined the conditions for the formation of Gaussian and sinusoidal textures. A significant increase in surface area is achieved when copper and steel are processed with the abrasive discs with an average grit size of up to 100 μm. This increase is up to 7% for copper and up to 2.7%. After abrasive processing of copper and steel surfaces, the proportion of the polar component in their total surface energy changes. This is a consequence of changes in dipole interactions and hydrogen bonds between atoms.

Analysis of Land Surface Energy Changes at Zhufeng Station in Qinghai Tibet Plateau in 2008

The surface radiation balance and partial meteorological elements in the Qomolangma region were analyzed by using the flux observation data of Qomolangma stations in 2008 in the High-Resolution Integrated Observation Dataset of Earth-Atmosphere Interaction Process of the National Tibetan Plateau Scientific Data Center. The main conclusions are as follows: 1) The influence of weather conditions on the total solar radiation is more significant at high altitudes. For 2008, radiation on average each component change after comparative analysis, not only from atmospheric radiation, upward curve comparison verified the surface temperature in the plateau area affected by the solar total radiation that largest at the same time from the curve of the downward shortwave radiation found in contrast, although the Everest region influenced by latitude and longitude and altitude. However, the maximum value of short- wave downward solar radiation at noon appears in spring and April, and the maximum value of summer radiation at noon is even lower than that in autumn. 2) In the analysis of the typical weather conditions of continuous sunny days and continuous rainstorm, it is found that the net radiation and the Upward short-wave radiation are affected by the underlying surface change, and the amplitude of the net radiation and Upward short-wave radiation are close to the original atmosphere because the atmospheric environment in the Qomolangma region is close to the original atmosphere, so the net radiation and Upward short-wave radiation are affected by the underlying surface change under any weather conditions. 3) Surface water content has obvious influence on radiation and reflectivity by changing the properties of underlying surface, and the response energy changes the fastest when the upward shortwave radiation has higher humidity.

Surface modification of polyamide by 50 Hz dielectric barrier discharge (DBD) produced in air at atmospheric pressure

Industrial applications of the dielectric barrier discharge (DBD) have a long tradition. However, lack of understanding in some of its fundamental issues, such as the stochastic behaviors, is still a challenge for DBD researchers. The work was carried out at line frequency, 15 kV and at atmospheric pressure. This work focuses on the study of the electrical and optical characteristics of DBD at atmospheric pressure to determine a suitable condition for utilization of the device for surface modification of polyamides (PA) (Nylon 6/6). In this work, films were treated by dielectric barrier discharge and the effects on the morphology and chemistry of the material was studied. Surface characteristics were examined via contact angle measurements and SEM. The wettability tests revealed the improvement of the hydrophilic character of the surface of polyamide films as the water contact angle measured after the plasma treatments significantly decreased. The corresponding changes of the total surface energy revealed a significant increase in its polar component. The improvement of the wettability of PA strongly depends on the treatment time. The outcomes of the experiments proved that the modification of surface properties via plasma treatment reach to its saturation point after certain treatment time thus reducing the necessity of further treatment.
 BIBECHANA 18 (2021) 19-25

Analysis of Land Surface Energy and Water Cycle Changes in Naqu Region of Qinghai-Tibet Plateau during 2005-2016

In order to improve the integrity of the research on the thermal conditions of the Qinghai-Tibet Plateau and the plateau energy cycle, and strengthen the understanding of the climate change and water cycle in the Nagqu area, this article uses the 2005—provided by the Naqu Alpine Climate and Environmental Observation and Research Station of the Northwest Institute of Eco- Environmental Resources, Chinese Academy of Sciences. In 2016, the hour by hour high-resolution data set of atmospheric, soil and eddy observations analyzed the surface radiation budget, energy conversion, energy balance, and energy closure in the Naqu region of the Qinghai-Tibet Plateau. The following conclusions are obtained: compared with sunny days, the diurnal variation of the various components of surface energy in Nagqu in cloudy weather is very irregular, and the reflectivity of cloudy weather becomes larger. In cloudy weather, the thermal process between the surface and the atmosphere and deep soil is more violent than short-wave radiation. The albedo at each moment of the day in winter is greater than that in summer because of the unique surface characteristics of the plateau. Both summer and winter sensible heat flux and latent heat flux have the same diurnal variation trend as net radiation. The sensible heat flux and latent heat flux in summer are significantly higher than those in winter, but the latent heat flux changes more significantly with the seasons. When considering the soil heat storage term, the energy closure degree in summer is 0.301 and that in winter is 0.701. The energy closure degree in winter is significantly higher than that in summer.

Topochemical Engineering of Cellulose-Carboxymethyl Cellulose Beads: A Low-Field NMR Relaxometry Study.

The demand for more ecological, highly engineered hydrogel beads is driven by a multitude of applications such as enzyme immobilization, tissue engineering and superabsorbent materials. Despite great interest in hydrogel fabrication and utilization, the interaction of hydrogels with water is not fully understood. In this work, NMR relaxometry experiments were performed to study bead–water interactions, by probing the changes in bead morphology and surface energy resulting from the incorporation of carboxymethyl cellulose (CMC) into a cellulose matrix. The results show that CMC improves the swelling capacity of the beads, from 1.99 to 17.49, for pure cellulose beads and beads prepared with 30% CMC, respectively. Changes in water mobility and interaction energy were evaluated by NMR relaxometry. Our findings indicate a 2-fold effect arising from the CMC incorporation: bead/water interactions were enhanced by the addition of CMC, with minor additions having a greater effect on the surface energy parameter. At the same time, bead swelling was recorded, leading to a reduction in surface-bound water, enhancing water mobility inside the hydrogels. These findings suggest that topochemical engineering by adjusting the carboxymethyl cellulose content allows the tuning of water mobility and porosity in hybrid beads and potentially opens up new areas of application for this biomaterial.

Micromechanism Study of Strengthening Effect of Copper on Gold Thiosulfate Leaching

To study the effect of copper on gold thiosulfate leaching, the gold dissolution of three different sample powders (gold, gold/copper, and gold/copper oxide) in a solution of 5 mM Cu2+, 0.4 M ammonia, and 0.1 M thiosulfate was studied. Scanning electron microscopy analysis showed no sulfur passivation on the gold surface, and there were more prominent corrosion pits on the gold surfaces of samples that were ground with copper or copper oxide. The Evans diagrams showed that copper and copper oxide can promote both the anode and cathode processes of gold dissolution. Based on first principle simulations, copper and copper oxide exhibited the ability to disrupt the stability of gold surface atoms and cause different degrees of relaxation. Both copper and copper oxide reduce the d-band center of the gold surface atoms and the adsorption between gold and thiosulfate. In addition, the bond length of the S–S bond of thiosulfate adsorbed onto the gold surface was longer when copper or copper oxide were not present. According to the change in the potential surface energy, the energy barriers for gold atom dissolution from gold, gold/copper, and gold/copper oxide surfaces were 1.79, 0.72, and 1.01 eV, respectively.

Experimental study on the surface and interface phenomenon changes by means of contact angle measurement on slot milled nimonic 263 alloy

The primary aim of this work is to analyze the interaction behavior between the machining process and surfaces and interface phenomenon of slot milled nimonic 263 alloy. In this investigation, the quantitative contribution of the cutter nomenclature such as cutter with variations in Radial Rake Angle (RRA) and the machining parameters on the surface energy and the wettability of the machined samples are examined through surface roughness and contact angle measurement over the slot milled surface. From the above experimentation, it is stated that the cutter with the Negative RRA machined sample has shown better and significant changes in surface energy which leads to increase the surface wettability related to the nascent nimonic sample. In addition to the above, the surface morphology variations are examined using scanning electron microscope to investigate the impact of slot milling process over the surface topography of the machined samples.

Investigation on Phase-Induced Surface Energy Change of HfO2 Thin Films Prepared By Plasma Enhanced Atomic Layer Deposition

Wettability of nanomaterials has been researched for the scientific physics based on solid/liquid interfaces. In particular, wettability of ceramic materials which is directly relevant to the surface free energy has been researched for its nature continuously in terms of thin film coatings.1 The development of such materials with finely tunable surface free energy and adequate stability under harsh conditions has been attracted enormous interests involving various applications.2,3 Among them, Hafnium oxide (HfO2), one of the representative transition metal oxides, has been recently studied for robust coating materials with investigation of its surface free energy. However, due to the complexity derived from environmental factors in a stack and differences between variety of deposition parameters, the surface free energy of HfO2 films has not been fully understood. Apart from the fact that the previously reported water contact angle (WCA) of HfO2 thin or bulk films highly vary between literatures, the interpretation of surface free energy of HfO2 and its intrinsic wettability still lacks of systematic approaches. In this study, we comprehensively investigated the surface free energy variation in HfO2 films prepared by plasma enhanced atomic layer deposition (PE-ALD). Upon precise control of film thickness with the aid of PE-ALD technique, we analyzed the surface free energy changes depending on the various properties of HfO2 films including film thickness, chemical composition, surface roughness, film crystallinity. We focused on a dependency of surface free energy of HfO2 films on film crystallinity as a determining factor for wettability changes. For in-depth studies, we performed thermal annealing treatment on PE-ALD HfO2 films and observed apparent correlation between wettability and film crystallinity. Based on the control of film crystallinity, PE-ALD HfO2 thin films show versatile wetting behaviors as to exposure of liquids with different surface energies. The experimental results from our work will contribute to the fundamental understanding of surface free energy of thin film HfO2 and its scientific backgrounds, and can also lead to feasible applications including liquid separation and purifications using HfO2 as robust coating film.

Impacts of Greenland Block Location on Clouds and Surface Energy Fluxes Over the Greenland Ice Sheet

AbstractClouds and blocking activity have been implicated as causes of increased Greenland Ice Sheet (GrIS) melt in the 21st century. Although Greenland blocks (i.e., long‐lasting, mostly stationary anticyclones) generally reduce cloud cover and move warm air over Greenland, the elevated GrIS perturbs air and moisture transport in complex ways, implying a need to better understand how blocks affect cloud and surface energy flux anomaly patterns. In this study, we use a combination of daily MODIS cloud data and meteorological and energy flux data from MERRA‐2 reanalysis to better understand how Greenland block location, separated into four equal‐area quadrants, affects regional cloud and surface energy flux spatial patterns in the summer months of 2002–2018. Overall, cloud fraction and cloud water path reductions are approximately four times greater during northern block days than southern block days. Net cloud radiative forcing anomalies are negative for all Greenland block locations because negative longwave cloud radiative forcing anomalies exceed positive shortwave cloud radiative forcing changes. However, greater cloud cover reductions during northern block days produce more negative net cloud radiative forcing anomalies than southern block days. Greenland‐average (i.e., latitude‐weighted average of all GrIS grids) net surface energy flux anomalies range from +7 to +12W/m2 for all block quadrants. While net shortwave energy anomalies dominate the total surface energy response during western Greenland block days, sensible heating is responsible for approximately half of positive total surface energy change during eastern Greenland block days.

Dynamics of freezing/thawing indices and frozen ground from 1900 to 2017 in the upper Brahmaputra River Basin, Tibetan Plateau

Dynamics of the frozen ground are key to understand the changes of eco-environment in cold regions, especially for areas with limited field observations. In this study, we analyzed the spatial and temporal variations of the ground surface freezing and thawing indices from 1900 to 2017 for the upper Brahmaputra River (also called the Yarlung Zangbo River in China) Basin (UBRB), southwestern Tibetan Plateau, with the air freezing and thawing indices using the University of Delaware (UDEL) monthly gridded air temperature dataset. The abrupt change years for air freezing index (AFI) and ground surface freezing index (GFI) were detected in 1999 and 2002, respectively, and for both air thawing index (ATI) and ground surface thawing index (GTI) were 2009. With the air temperature rising at a rate of 0.006 °C per year over 1900–2017, the AFI and GFI decreased at a rate of −0.1 °C d per year, while the ATI and GTI increased at rates of 0.3 and 0.5 °C d per year before the abrupt change year, respectively; all changing trends of freezing/thawing indices increased after the abrupt year, which was −2.9, −0.8, 7.3, and 21.7 °C d per year for the AFI, GFI, ATI, and GTI, respectively. We utilized the surface frost number model to obtain the dynamics of the frozen ground over the UBRB. When the empirical coefficient of E was assigned to 1.2, the simulated frozen ground occupied about 53.2% of the whole UBRB in the 1990s, which agreed well with the existing permafrost map published in 1996. The area of frozen ground accounts for 51.5%–54.5% of the UBRB during 1900–2017. This result may facilitate further studies of the multi-interactions among the frozen ground and relevant eco-environment, such as the air-ground surface energy exchange, hydrological cycles, and changes of the active layer thickness over the UBRB.

Изменение свойств железа при ОЦК-ГЦК-фазовом переходе

Using the previously developed method for calculating crystal properties based on the Mie–Lennard-Jones pair potential, the thermodynamic properties of the BCC and FCC phases of iron at the temperature of the polymorphic BCC-FCC phase transition are calculated. 23 properties of iron and their changes during the BCC-FCC transition are calculated. Calculations have shown that properties such as the Gruneisen parameter, the coefficient of thermal expansion, and the heat capacity practically do not change during the BCC-FCC transition. The elastic modulus, specific entropy, Poisson's ratio, and specific surface energy change in the same way as the molar volume, i.e. within 1%. The Debye temperature and its pressure derivative decrease at the BCC-FCC transition in the same way as the distance between the centers of the nearest atoms increases, i.e. within 2-3%. Based on the analysis of experimental data known from the literature, it is shown that even relatively accurately measured parameters such as the coefficient of thermal expansion and elastic modulus are measured with an error exceeding the values of jumps in these parameters at the BCC-FCC transition. It is indicated that amorphization or nanostructuring of a certain portion of iron during the BCC-FCC transition can contribute to changes in the properties of iron during this phase transition.

C4F8 plasma treatment for the modification of the focal length of liquid-based plano-convex lenses on different substrates

In this contribution, we present a plasma-based approach for modifying the focal length of plano-convex lenses realised by the deposition of droplets made of optical cement. For this purpose, PMMA and soda-lime glass substrates were treated with a direct dielectric barrier discharge plasma at low pressure. To obtain plasma-induced changes in surface energy of the substrates by the formation of functional groups, octafluorocyclobutane (C4F8) was used as process gas. Such treatment lead to a notable decrease in surface energy and especially its polar fraction, which is attributed to the generation of fluorocarbon compounds such as polytetrafluoroethylene (PTFE) as also confirmed by FTIR spectroscopic measurements. It is shown that this effect has a considerable impact on the contact angle and radius of curvature, respectively, of the deposited cement droplets where differences by a factor of about two were obtained. After curing of the cement, front focal lengths in the range from approx. 5 to 13 mm were realised depending on the duration of the plasma pre-treatment. The cement lenses finally feature dimensions in the range of some millimetres.