The influence of the substrate temperature on the preparation of DNA films for studies under vacuum conditions

Experiments were carried out to determine the dependence of the physical form of supercoiled DNA films on the initial temperature of the substrate. Such films are often used in irradiation experiments involving low energy particles, like electrons or photons. In order to obtain absolute values for cross sections for such experiments, the spatial distribution of the sample in the film has to be well estimated. These investigations aim to correlate the size and form of a DNA film with the initial temperature of the substrate, on which the liquid sample is deposited prior to evacuation. From our previous studies we concluded that the presence of agents preventing DNA structural water evaporation is required in order to preserve the supercoiled plasmid DNA form under vacuum conditions. Therefore, we examined the temperature dependence on films prepared from plasmid suspended in solutions containing magnesium hydroxide, Tris-Cl buffer and various concentrations of sodium hydroxide. To visualise the films we used a conventional light microscope with a CCD camera and a scanning electron microscope. The results revealed a significant influence of the temperature of the substrate on both the area of the substrate covered by the film as well as on the spatial distribution of DNA molecules. An increase in the amount of sodium hydroxide that stabilises supercoiled DNA under vacuum increases DNA aggregation. After these investigations we conclude that the best temperature of the substrate to produce uniform and thin films should be between –5 °C and -10 °C for substrates which are not atomically flat and above 0 °C for atomically flat substrates.     

真空条件下介质窗表面微波击穿实验

介绍了介质表面真空微波击穿研究实验装置的设计以及介质表面刻凹槽实验。微波源为S波段速调管,中心频率2.86 GHz,脉宽1μs。为确保击穿发生在后端介质样品处,而前端用于和速调管源隔离的陶瓷微波窗不击穿,实验装置采用先分后合的方法,利用两个陶瓷窗,每个陶瓷窗传输总功率的一半。为了抑制三相点带来的效应,采用凹形的圆柱介质,三相点处于电场强度弱的位置,有效消除了三相点的影响。在此实验装置上做了表面刻凹槽实验,初步实验结果表明,与光滑表面击穿阈值相比较,刻凹槽可使功率容量提高2倍以上。     

Laser induced incandescence under high vacuum conditions

This paper reports on a study of laser-induced incandescence of carbon particles in free space within a high vacuum (<10^-3 mbar) excited by an Nd:YAG laser pulse. We have conducted an experimental study using samples of carbon black placed within an evacuated, sealed glass vessel which is slowly tumbled to cause a cascade of carbon black particles in free space. Our experiments show that under a high vacuum two important phenomena are observed. Due to the absence of gaseous conduction, in comparison to particles in ambient air, incandescence lifetime in a vacuum is dramatically extended to more than 50 μs with a corresponding increase of a factor of over 10⁴ in the integrated or total number of photons emitted by each soot primary particle. For large aggregates and/or agglomerates in a vacuum after a delay of the order of 2 to 10 μs, the large particles fragment into smaller entities. We have also modelled the incandescence behaviour using well established methods. PACS 42.79.-e; 44.05.+e; 61.46.Bc     

Surface potentials of few-layer graphene films in high vacuum and ambient conditions

The surface potentials of few-layer graphene (FLG) films in high vacuum and ambient conditions have been investigated by employing electrostatic force microscopy. It is found that the surface potential of FLG films in ambient air has a constant large depression compared to that measured in a high vacuum. Our experimental results indicate that the shift is most likely caused by the presence of ambient adsorbates on the outmost graphene surfaces. The surface potentials increase with the number of graphene layers and approach the bulk value for five or more graphene layers in high vacuum as well as in ambient air. Since the contribution of the surface adsorbates is a constant value, we further show that the thickness dependence of the surface potential can be sufficiently explained by the nonlinear Thomas-Fermi Theory in both conditions.     

Damage investigations of AR coating under atmospheric and vacuum conditions

The damage characteristics of anti-reflection films exposed to 1064 nm nanosecond laser pulses in vacuum and air were investigated. The laser-induced damage thresholds (LIDT) in vacuum and air environments were compared. The damage morphologies were locally analyzed using optical microscopy and scanning electron microscopy (SEM). The depth of the damage sites in the two environments was analyzed by Alpha2Step 500 m. The differences between the damage observed in the two environments were discussed based on the temperature distribution, absorption and vacuum gaseous composition measurements and gas pressure influence analysis. Increased coupling of the plasma shock wave and adsorbing water in the coating layer may be considered as the primary cause of the low LIDT observed in vacuum.     

Nanocrystalline cobalt films prepared under ultrafast condensation conditions

The magnetic and electrical properties and the temperature dependence of these properties of cobalt films prepared at high condensation rates (10⁵–10⁶ Å/s) are investigated. Incremented annealing reveals several nonequilibrium states of cobalt in transition from the asprepared metastable structure to the ordinary hcp structure. The anomalies of the properties are analyzed from the standpoint of the nanocrystalline state of the samples. Model concepts of microcluster formations in the investigated films are also discussed.     

Fundamental processes of aluminium corrosion studied under ultra high vacuum conditions

Surface sensitive electron spectroscopy was applied to study the fundamental processes of aluminium corrosion. We used metastable induced electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS) for the investigation of the densities of states of surface and bulk, respectively. Furthermore we applied X-ray photoelectron spectroscopy (XPS) to investigate the chemical composition of the top surface layers. All measurements were performed under ultra high vacuum conditions.Al films with thicknesses of 7 nm were investigated. Both the interaction of oxygen and water with these films leads to the formation of an aluminium-oxygen layer, which is partly composed of stoichiometric Al₂O₃. Weak heat treatment at 770 K transforms the surface layer into Al₂O₃ with a thickness of about 2 nm. Further gas offer does not lead to an increase of this thickness, neither for oxygen nor for water. Additional to the oxygen offer, water exposure leads to the formation of OH species in the top aluminium-oxygen layer to a small amount. Weak heat treatment to 770 K removes this species completely. Water exposure leads to a much faster oxide formation than oxygen exposure. We try to give a model for the fundamental corrosion processes on a molecular scale.     

Preparation of monodisperse magnetite nanoparticles under mild conditions

In this paper, we reported a method to prepare monodisperse magnetite nanoparticles at mild temperature using cheap and non-toxic precursors. It overcomes the shortages of chemical co-precipitation method and thermal decomposition method and combines the advantages of facile, cheap, large-scale, monodisperse, nanosize, and low synthesis temperature and low toxic. In this method, FeCl₃ · 6H₂O, FeCl₂ · 4H₂O and sodium oleate were mixed in toluene/ethanol/water mixture solvent and refluxed at 74 °C to prepare magnetite nanoparticles directly. The nanoparticles were characterized by transmission electron microscopy, dynamic light scattering, X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectrometer and thermogravimetric analysis. The magnetic properties of nanoparticles were measured by superconducting quantum interference device. The results showed that the nanoparticles are well-monodisperse with about 4–5 nm of average diameter. The nanoparticles were proved to be superparamagnetic with saturated magnetization 23.6 emu/g and blocking temperature 24.4 K. A possible formation mechanism of monodisperse magnetite nanoparticles was presented at the same time.     

Deposition of C60 polymer films under various plasma conditions

We studied the deposition of C₆₀ polymer films under different Ar plasma conditions. The films were deposited at a pressure range between 1.3 and 40 Pa, and the input power was varied from 10 to 70 W. The films were investigated by Raman spectroscopy to confirm the C-C valence states of the polymeric phases. C₆₀ polymers were formed under various experimental conditions. However, the depositions resulted in non-uniform films consisting of unpolymerized C₆₀, dimers, linear chains and polymeric planes. Amorphous carbon was found in the films deposited at 13 and 20 Pa (50 W input power) and 13 Pa (70 W).     

Ignition of hydrocarbon films under the conditions of surface microwave discharge

In the present work, rapid plasma-stimulated ignition of liquid hydrocarbons was carried out in still air under conditions of surface microwave discharge. It was shown that, depending on the microwave input power, the breakdown time changed in a range from 5 to 30μs, ignition occurred on an antenna in the area of the surface microwave discharge at a temperature not exceeding 1000 K, and the speed of the front boundary propagation of the intense ignition region near the antenna was 300 m s^?1.     

Optimization of the conditions for vacuum thermal deposition of bismuth films with control of their imperfection by atomic force microscopy

The structure and defects of bismuth films prepared through vacuum thermal deposition on mica substrates under different conditions (deposition rates, substrate temperatures, temperatures and times of annealing) have been investigated using atomic force microscopy. The conditions are determined under which recrystallization occurs with increasing crystallite size during annealing, which provides a decrease in the degree of imperfection of the films and an increase in the mobility of charge carriers.     

Preparation of p-type CdS thin films and in situ dark conductivity in vacuum deposited CdS:Cu films

CdS:Cu thin films were prepared using a vacuum co-evaporation technique. The Hall measurements indicate that the conductivity characteristic of CdS thin films transformed from highly compensated in as-grown or weakly annealed materials to p-type conductive in strongly annealed materials. X-ray diffraction spectra show that as-deposited thin films were the hexagonal phase of CdS except the presence of copper for high Cu doping and the diffraction peaks of Cu disappeared after annealing. From the X-ray photoelectron spectroscopy we found the ionization of Cu atoms and the formation of an acceptor level. In situ dark conductivity in vacuum as-deposited CdS:Cu was performed in the temperature range between 27 and 250 °C. An abnormal temperature dependence of conductivity was observed in medium and heavily Cu-doped films. The formation of a p-type material at a certain temperature was also studied by the hot probe measurements, which indicates a complex compensation process in the Cu-doped CdS films.     

Spin-wave resonance in magnetic films under conditions of the skin effect

The spin-wave resonance spectrum of a ferromagnetic film magnetized normally to its surface is investigated as a function of the finite depth of penetration of the high-frequency field into the film with due regard for damping in the spin system and different types of surface-spin pinning. The exact numerical solution of the equation of motion for magnetization is obtained by considering the finite thickness of the skin layer. For a substantially inhomogeneous distribution of the high-frequency field over the layer thickness, the change in the resonance shape at frequencies close to the ferromagnetic resonance frequency is observed in addition to the broadening of all the resonance peaks and the decrease in their amplitudes.     

真空条件下LiCl溶液蒸发量随浓度变化规律研究

除湿溶液再生是除湿空调系统的核心过程,为了提高除湿溶液再生效率,以蒸发量作为评价标准,在不同的真空度下对不同浓度LiCl溶液进行再生。对不同再生条件下,溶液的再生情况进行数学模拟及实验研究,并将模拟结果与实验结果进行对比分析,结果表明,实验结果同模拟结果具有相同的变化趋势。在6 kPa和8 kPa的压强下,LiCl溶液的蒸发量随浓度的增大先上升后下降,而在1 kPa的压强下,LiCl溶液的蒸发量随浓度的增大呈现出先下降再升高接着又下降的趋势。     

Understanding the friction behavior of sulfur-terminated diamond-like carbon films under high vacuum by first-principles calculations

Generally, the repulsive force was a key factor account for superlow friction of H or F doped diamond-like carbon (DLC) films under high vacuum. As we known, H or F doped DLC usually exhibited superlow friction under high vacuum. However, the superlow friction of S doped DLC under high vacuum was not found so far. This phenomenon was desirable to be well investigated. In this work, S-terminated diamond interfaces also exhibited strong repulsive force, however, the estimated friction coefficient was variable for S-terminated diamond interfaces. The lowest and largest friction coefficient was about 0.003 and 0.4 respectively, which indicated that the superlow friction of S doped DLC could achieve in theory. In order to well probe the unusual friction behavior of S doped DLC under high vacuum, using first-principles method, the repulsive interaction between sliding surfaces was well investigated in order to understand the unusual friction behavior of S doped DLC films.     

Thermoelectric power of vacuum evaporated PbTe films

Variation of thermoelectric power with thickness of the vacuum evaporated PbTe films has been investigated. The films were deposited on mica, glass, quartz and LiF substrates, under identical conditions. Attempts have been made to derive a relation which represents the variation of thermoelectric power with thickness of the film. The temperature variation of thermoelectric power has also bsen studied.     

Effect of vacuum conditions on breakdown voltage between electrodes in vacuum

The electrical breakdown in vacuum was studied in the configuration: wire —plane. Measurements were performed in two different experimental systems: with technical vacuum and with the clean one. It was found that the value of breakdown voltage decreases with increasing vacuum and that at the same pressure the insulating properties of electrodes are better in the technical vacuum than in the oilless one.     

An ultrahigh vacuum electron spectrometer for surface studies

A high-resolution electron spectrometer has been constructed for the study of clean metal surfaces and their interactions with gases. In its present form it is most suitable for the study of evaporated films but may also be used for ribbons, single crystals, or powders. Electron spectra induced by three sources, X-ray, vacuum ultraviolet, or electron impact, may be recorded sequentially. Electron energy analysis is normally performed by settin the analyzer (10 cm radius, hemispherical) to pass electrons of a fixed energy and applying a scanning retarding potential to the sample. The limiting instrument absolute resolution is about 25 meV FWHM at 5 eV analyzing energy, as judged by an He I gaseous argon spectrum. Resolution can be traded for sensitivity by analyzing at higher electron energies (up to 100 eV), or by means of an external slit-width adjustment mechanism. The spectrometer carri a preparation chamber which has a variety of demountable sample preparation, cleaning, and reaction monitoring devices. Spectra from gold, silver, and     

Preparation and surface modification of silicon nanowires under normal conditions

Preparation and surface modification of silicon nanowires (SiNWs) grown by the metal catalyzed solution method under normal conditions (room temperature, 1 atm) had been studied in this paper. Firstly, SiNWs using a simple solution method via electroless metal deposition (EMD) of silver under room temperature, standard pressure had been prepared. The influence of the growth parameters such as solution concentration, etching time on the SiNWs formation had been studied. Secondly, the surface modification of SiNWs with platinum and copper had been investigated. The results indicated that the SiNWs modified with Pt and Cu showed different surface morphologies. Pt modification on SiNWs presented in the form of nanoparticles, whereas Cu modification in the form of membrane. Therefore, the Pt modified SiNWs have more vast surface-to-bulk ratio than the unmodified ones, and SiNWs modified with copper nanoparticles will lead to the smaller surface-to-bulk ratio. So the platinum-modified SiNWs have a promising application in sensors’ field.