Medium Vacuum Conditions Research Articles

Characterization of Sucrose Thin Films for Biomedical Applications

Sucrose is a natural osmolyte accumulated in the cells of organisms as they adapt to environmental stress. In vitro sucrose increases protein stability and forces partially unfolded structures to refold. Thin films of sucrose (C12H22O11) were deposited on thin cut glass substrates by the thermal evaporation technique (P∼10−5torr). Characteristics of thin films were put into evidence by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Photoelectron Spectroscopy (XPS), scanning electron microscopy (SEM), and differential thermal analysis and thermal gravimetric analysis (TG/DTA). The experimental results confirm a uniform deposition of an adherent layer. In this paper we present a part of the characteristics of sucrose thin films deposited on glass in medium vacuum conditions, as a part of a culture medium for osteoblast cells. Osteoblast cells were used to determine proliferation, viability, and cytotoxicity interactions with sucrose powder and sucrose thin films. The osteoblast cells have been provided from the American Type Culture Collection (ATCC) Centre. The outcome of this study demonstrated the effectiveness of sucrose thin films as a possible nontoxic agent for biomedical applications.

Vacuum Variable Medium Temperature Blackbody

This article describes the vacuum variable medium-temperature blackbody (VMTBB) constructed to serve as a highly stable reference source with an aperture diameter of 20 mm in the temperature range from 150 °C to 430 °C under medium-vacuum conditions (10−3 Pa) and in a reduced background environment (liquid-nitrogen-cooled shroud). The VMTBB was realized for the calibration facility at the PTB in the field of reduced background radiation thermometry under vacuum. This facility is intended for performing radiometric and radiation thermometric measurements under vacuum conditions in the temperature range from −173 °C to 430 °C and spectral emissivity measurements in the temperature range from 0 °C to 600 °C without atmospheric interferences. It is difficult to realize a precision blackbody with high emissivity for temperatures above 400 °C. Cavities of such blackbodies are normally made of copper and coated by a paint with high emissivity. But any paint put on copper does not survive several cycles of heating to temperatures up to 450 °C. As a result of investigations at PTB, a special procedure of coating the surface of the cavity by paint with high emissivity has been developed. The cavity surface is coated by chemical nickel plating before covering it by a paint with high emissivity. The general concept and the design of the VMTBB are given. For realization of good temperature uniformity along the complete radiating cavity, a three module design is used consisting of a heat exchanger and two stages of temperature control of the cavity, based on two precision PID controllers. The temperature of the cavity is determined by 15 precision Pt resistance thermometers. Six of them are used for the VMTBB cavity and heat exchanger temperature control, and the others are used for the cavity temperature measurement and correction. A description of the temperature control and measurement system of the VMTBB is presented. Optical ray tracing with a Monte Carlo method (STEEP 3) indicated that the effective emissivity of this blackbody cavity is not worse than 0.9994. Tests of the VMTBB were carried out at the PTB facility, and the radiation of the VMTBB was measured in comparison to the vacuum variable low-temperature blackbody (VLTBB) in the temperature range from 150 °C to 170 °C with the vacuum infrared standard radiation thermometer (VIRST). The temperature uniformity of the blackbody from the bottom to the front of the cavity is better than ±100 mK in the whole temperature range. The stability of the temperature of the blackbody is within 50 mK in the whole temperature range.

Temporal evolution of the laser-induced plasma generated by IR CO2 pulsed laser on carbon targets

Time-resolved optical emission analysis was carried out for the plasma plume, produced by high-power tunable IR CO2 pulsed laser ablation of graphite, at λ=10.591 μm and in a regime of relatively high laser fluences (123–402 J/cm2). Wavelength-dispersed spectra of the plasma plume, at medium-vacuum conditions (4 Pa) and at 9.0 mm from the target, show ionized species (C+, C2+, C3+, C4+, N2+ , N+, and O+), neutral atoms (C, H, N, and O), and neutral diatomic molecules (C2, CN, OH, CH, and N2). In this work, we focus our attention on the temporal evolution of different atomic/ionic and molecular species over a broad spectral range from 190 to 1000 nm. The results show a faster decay for ionic fragments than for neutral atomic and molecular species. The velocity and kinetic energy distributions for different species were obtained from time-of-flight measurements using time-resolved optical emission spectroscopy. Possible mechanisms for the production of these distributions are discussed. Excitation temperature, electron density, and vibrational temperature in the laser-induced plasma were estimated from the analysis of spectral data at various times from the laser pulse incidence.

Spatial characterization of the laser-induced plasma plumes generated by IR CO2 pulsed laser on carbon targets

Spatially resolved optical emission analysis was carried out for the plasma plume, produced by high-power tunable IR CO2 pulsed laser ablation of graphite, at λ=9.621 μm and with laser fluence of 342 J cm−2. Wavelength-dispersed spectra of the plume, at medium vacuum conditions (Pair=4 Pa) and concentrated close to the target, reveal C, C+, C2+, C3+, C4+, N, H, O, and molecular emissions between different electronic states of C2, CN, OH, CH, and NH. The characteristics of the spectral emission intensities from different species have been investigated as functions of the distance (up to 20 cm) from the sample surface. Vibrational temperatures in the laser-induced plasma have been estimated at various distances from the target surface.

Vacuum Variable-Temperature Blackbody VTBB100

The present state-of-the-art of precision radiometry based on the vacuum variable-low-temperature blackbody source VTBB100 developed for the low-background calibration facility at PTB is analyzed. This article describes the vacuum variable-low-temperature blackbody (VTBB) constructed to serve as a highly stable reference source for the calibration of blackbody sources in the temperature range from 100 K to 450 K under medium-vacuum conditions (10−3 Pa) in a medium-background environment (liquid-nitrogen-cooled shroud). The general concept and the design of the VTBB100 are given. The numerical investigation of the effective emissivity of the VTBB100 is performed. A description of the temperature control and measurement system of the VTBB100 is presented. Cooling of the VTBB100 is by liquid nitrogen. Heating of the VTBB100 is by a two-stage temperature control scheme. A thermal model of the radiator was developed. As a result of the analysis, it was shown that the system achieves an instability of the blackbody temperature of less than 20 mK. The characteristics of the blackbody operation—now at PTB—are described.

Study on Ergun Equation at Vacuum Pressures for Sodium Fluoride Adsorbents

The most important parameters in adsorption column design are pressure drop, adsorbent capacity, reaction kinetics and adsorbent regeneration. However for those applications where flow losses have to be minimized, the pressure drop is the most important parameter. The Ergun equation is used for pressure drop calculations. For atmospheric operations, it does have good results, but it is inconsequential for sub atmospheric conditions and should be revised. The empirical data deviation from Ergun equation results for sodium fluoride adsorbents and medium vacuum conditions is studied in this paper. It shows that, the deviation risies up with vacuum increasing. As a result, using the Ergun equation in sub atmospheric conditions has too much error and causes useless adsorption column design.

Difficulties with Ti-Ni Powder Metallurgy Process and Multi-Stage Sintering Technique for TiNi SMA

A study of the exothermic behavior of reactions that occur within Ni and Ti elemental powder mixtures during heating in medium vacuum (4 x 10 -3 Pa) has been conducted. In comparison with several other ordered intermetallic compound mixes, a much more violently released exothermic heat was observed in the Ti-50Ni mixture. It indicates that the difficulties associated with a common powder metallurgy process for TiNi shape memory alloy (SMA) include the possible oxygen interaction in a low vacuum condition and the large and rapidly generated exothermic heat in a medium or high vacuum condition. Therefore, a multi-stage sintering process is proposed to fabricate the TiNi SMA powder metallurgy (P/M) specimens and their composites. In order to prevent the violently released exothermic heat, the sintering process was divided into several repeated cycles with intermediate cold deformation, and a relatively low sintering temperature, 1030°C (or 1080°C), was employed. Further study of the SMA composites, Ti 50 Ni 50 + 5vol%TiC and Ti 50 Ni 50 + 10vol%TiC, with this technique was presented in this article. The obtained sintering density is above 85%. In the meantime, 94.5% (50%) recovery of Ti 50 Ni 50 + 5vol%TiC (Ti 50 Ni 50 + 10vol%TiC) after 1.0% tensile strain then heated to 80°C were observed. The results of phase transformation and microstructure examination will also be discussed.

Effect of medium vacuum on low temperature wafer bonding

Direct wafer bonding was performed under medium vacuum conditions. The effects of the sequence of wafer contact and vacuum application, annealing temperature, and annealing time on the bonding quality and bonding speed were investigated. From the comparison of the bonding efficiency, contacting two wafers in air rather than in vacuum produces much less bubbles. For vacuum bonding, good bonding, such as high bonding strength and high bonding efficiency, can be achieved at temperatures as low as 300 °C. From the comparison between air wafer bonding and medium vacuum wafer bonding, it is obvious that medium vacuum annealing can improve the bonding strength and accelerate the bonding process. Based on the results observed, a qualitative mechanism of medium vacuum wafer bonding at low temperatures was proposed.

Making Wafer Bonding Viable for Mass Production

AbstractDirect wafer bonding was performed under medium vacuum condition. High bonding strength (larger than 20 MPa) is achieved at the bonding temperature of only 400°C, and the annealing time for complete bonding is less than 5 hours. The bonding efficiency (percentage of the bonded area over entire wafer area) of the medium vacuum wafer bonding (MVWB) is also found to be better than the traditional wafer bonding.Qualitative description of the mechanism of MVWB is proposed in present work. It is believed that the medium vacuum can enhance the out-diffusion of the water molecules and other trapped impurities through the bonding interface which is porous initially. This enhanced diffusion speeds up the chemical reaction for the formation of Si-O-Si, and thus more bonding sites are available before the interface close-up. As a result, we observe an increase in bonding strength, bonding efficiency and the bonding speed.

High speed lithium flow experiments for IFMIF target

Lithium flow was tested in a free surface test channel under pressurized or evacuated condition for the IFMIF target. The test channel, with a two-staged contraction nozzle designed after water test, was newly added to the Li loop facility in Osaka. Stable flow was obtained at the velocity of up to 13.8 m/s in 0.15 MPa, and up to 8.5 m/s at medium vacuum condition. In the course of circulation, wakes on free surface were begun to be observed due to small adhesives on the channel wall. These from the nozzle edge are considered to be prevented by keeping the edge clean. Those from the corners of the nozzle and sidewall were also observed. The shape was found to agree well with the theoretical prediction, Wake shape was estimated for IFMIF geometry, and it was indicated that the wakes emerge from the corners will not disturb the presently designed beam region.

The Brookhaven muon (g−2) storage ring high voltage quadrupoles

The design, construction, and operation of the electrostatic quadrupoles used in the muon ( g −2) experiment E821 of BNL are described in detail. A new lead design allowed the construction of a very reliable system which could operate for hundreds of thousands pulses with no sparking. The new design also made possible the elimination of systematic errors associated with the E , B fields generated by the low energy trapped electrons present in Penning traps under medium vacuum conditions.

Nickel-enhanced low-temperature epitaxial growth of silicon

Evaporated Si grew epitaxially on Si(1 0 0) at approximately 500 °C when very thin Ni layers were deposited on the substrate even under a medium vacuum condition of 10 −7 torr. Cross-sectional TEM and electron diffraction showed the formation of a thin and uniform epitaxial NiSi 2 layer on the Si substrate. Thus the Ni enhanced low-temperature Si epitaxial growth can be explained by a Si/NiSi 2/Si hetero-epitaxial model. Agglomerated NiSi 2 particles were also observed in the NiSi 2 layer, and the density increased with increasing deposited Ni layer thickness. Lattice defects were generated in the Si epitaxial layer from the agglomerated NiSi 2. Thus, the thinner the Ni deposited layer, the better the crystallinity of the Si epiaxial layer obtained.

Imaging of the boron doping in silicon using low energy SEM

Scanning electron imaging of plan views of boron-doped patterns in silicon is examined, together with the mechanism of formation of the electronic contrast in this kind of structures. Main to-date published results are critically reviewed and new data are presented concerning the secondary, backscattered and total-emission electron contrasts, including their qualitative and quantitative behaviour, particularly in the low energy range achieved with the help of the cathode lens (the scanning low energy electron microscopy mode, SLEEM). Surface analysis of the structure by means of Auger electron spectrometer has been performed, too, both before and after ion beam bombardment. The scanning electron microscope micrographs, acquired after the oxide mask removal in HF, are examined in a variety of detection modes, aiming at identification of the signal component primarily bearing the contrast. The energy dependence of the contrasts is presented as well as its change owing to alteration in the vacuum conditions. The most important findings include an extremely high contrast obtained in the SLEEM mode and even more enhanced under medium vacuum conditions at which the carbonaceous layer of surface contamination plays its role. The observed phenomena are partly explained in the frame of the “flat band” model of a passivated surface. The increased contrast in the SLEEM mode is understood as connected with the above-surface electric field of the cathode lens, generating space charge layers inside the semiconductor. In addition, charge carriers, injected via the primary electron beam, are considered as influencing the contrast vs. energy dependence.

Novel method for chemical vapor deposition and atomic layer epitaxy using radical chemistry

A novel method for chemical vapor deposition and atomic layer epitaxy using radical precursors under medium vacuum conditions is being developed. Fluorine atoms are generated by thermal dissociation in a hot tube and abstract hydrogen atoms from precursor molecules injected immediately downstream of the source, generating radicals with complete chemical specificity. The radical precursors are then transported to the growing substrate surface under nearly collision-free conditions. To date we have grown diamond films from CCl 3 radicals together with atomic hydrogen, generated by injecting CHCl 3 and H 2 into the fluorine atom stream at reactor pressures between 10 −3 and 10 −2 Torr. This approach should be ideal for low-temperature growth and atomic layer epitaxy: growth rates remain relatively high because activation energies for radical reactions are typically small and because the cycle times for atomic layer epitaxy can be reduced to the millisecond range by fast gas-stream switching, and contamination and segregation are minimized by keeping the surface “capped” by chemisorbed intermediates and working under ultraclean conditions.

Low Pressure Diamond Growth Using a Secondary Radical Source

ABSTRACTA novel method for chemical vapor deposition and atomic layer epitaxyusing radical precursors under medium vacuum conditions is being developed. Fluorine atoms are generated by thermal dissociation in a hot tube and abstract hydrogen atoms from precursor molecules injected immediately downstream of the source, generating radicals with completechemical specificity. The radical precursors are then transported to the growing substrate surface under nearly collision-free conditions. To date we have grown diamond films from CCl3 or CH3 radicals together with atomic hydrogen, generated by injecting CHCI3 or CH4 and H2 into the F atom stream at reactor pressures between 10−4 and 10−2 Torn This approach should be ideal for low-temperature growth and atomic layer epitaxy: growth rates remain relatively high because activation energies for radical reactions are typically small and because the cycle times for atomic layer epitaxy can be reduced to die msec range by fast gas-stream switching, and contamination and segregation are minimized by keeping the surface “capped” by chemisorbed intermediates.