Surface Science at the Solid Liquid Interface

DTIC Science & Technology

1993-10-06

prominent experimental avenue, developed originally by Hubbard et al,_ involves emersing monocrystalline elec- As for metal surfaces in ultrahigh vacuum...reliable means of both preparing and dosateizn ordered monocrystalline metal surfaces in UHV has led to ing appropriate molecular components of...surface atoms in place of bottom panel of Fig. 2, equal intensity contours are shown 23 underlying surface atoms, the compression is 24/23 - I in the

Conservative and dissipative force imaging of switchable rotaxanes with frequency-modulation atomic force microscopy

NASA Astrophysics Data System (ADS)

Farrell, Alan A.; Fukuma, Takeshi; Uchihashi, Takayuki; Kay, Euan R.; Bottari, Giovanni; Leigh, David A.; Yamada, Hirofumi; Jarvis, Suzanne P.

2005-09-01

We compare constant amplitude frequency modulation atomic force microscopy (FM-AFM) in ambient conditions to ultrahigh vacuum (UHV) experiments by analysis of thin films of rotaxane molecules. Working in ambient conditions is important for the development of real-world molecular devices. We show that the FM-AFM technique allows quantitative measurement of conservative and dissipative forces without instabilities caused by any native water layer. Molecular resolution is achieved despite the low Q-factor in the air. Furthermore, contrast in the energy dissipation is observed even at the molecular level. This should allow investigations into stimuli-induced sub-molecular motion of organic films.

Ultra-high speed vacuum pump system with first stage turbofan and second stage turbomolecular pump

DOEpatents

Jostlein, Hans

2006-04-04

An ultra-high speed vacuum pump evacuation system includes a first stage ultra-high speed turbofan and a second stage conventional turbomolecular pump. The turbofan is either connected in series to a chamber to be evacuated, or is optionally disposed entirely within the chamber. The turbofan employs large diameter rotor blades operating at high linear blade velocity to impart an ultra-high pumping speed to a fluid. The second stage turbomolecular pump is fluidly connected downstream from the first stage turbofan. In operation, the first stage turbofan operates in a pre-existing vacuum, with the fluid asserting only small axial forces upon the rotor blades. The turbofan imparts a velocity to fluid particles towards an outlet at a high volume rate, but moderate compression ratio. The second stage conventional turbomolecular pump then compresses the fluid to pressures for evacuation by a roughing pump.

Baking enables McLeod gauge to measure in ultrahigh vacuum range

NASA Technical Reports Server (NTRS)

Kreisman, W. S.

1965-01-01

Accurate measurements in the ultrahigh vacuum range by a conventional McLeod gage requires degassing of the gage's glass walls. A closed system, in which mercury is forced into the gage by gravity alone, and in which the gage components are baked out for long periods, is used to achieve this degassing.

Experimental system for drilling simulated lunar rock in ultrahigh vacuum

NASA Technical Reports Server (NTRS)

Roepke, W. W.

1975-01-01

An experimental apparatus designed for studying drillability of hard volcanic rock in a simulated lunar vacuum of 5 x 10 to the minus 10th power torr is described. The engineering techniques used to provide suitable drilling torque inside the ultrahigh vacuum chamber while excluding all hydrocarbon are detailed. Totally unlubricated bearings and gears were used to better approximate the true lunar surface conditions within the ultrahigh vacuum system. The drilling system has a starting torque of 30 in-lb with an unloaded running torque of 4 in-lb. Nominal torque increase during drilling is 4.5 in-lb or a total drilling torque of 8.5 in-lb with a 100-lb load on the drill bit at 210 rpm. The research shows conclusively that it is possible to design operational equipment for moderate loads operating under UHV conditions without the use of sealed bearings or any need of lubricants whatsoever.

Single molecular orientation switching of an endohedral metallofullerene.

PubMed

Yasutake, Yuhsuke; Shi, Zujin; Okazaki, Toshiya; Shinohara, Hisanori; Majima, Yutaka

2005-06-01

The single molecular orientation switching of the Tb@C82 endohedral metallofullerene has been studied by using low-temperature ultrahigh vacuum (UHV) scanning tunneling microscopy (STM). An octanethiol self-assembled monolayer (SAM) was introduced between Tb@C82 and the Au111 substrate to control the thermal rotational states of Tb@C82. Scanning tunneling spectroscopy (STS) of Tb@C82 on an octanethiol SAM at 13 K demonstrated hysteresis including negative differential conductance (NDC). This observed hysteresis and NDC is interpreted in terms of a switching of the Tb@C82 molecular orientation caused by the interaction between its electric dipole moment and an external electric field.

Commissioning of the vacuum system of the KATRIN Main Spectrometer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arenz, M.; Babutzka, M.; Bahr, M.

The KATRIN experiment will probe the neutrino mass by measuring the β-electron energy spectrum near the endpoint of tritium β-decay. We performed an integral energy analysis by an electro-static spectrometer (``Main Spectrometer''), an ultra-high vacuum vessel with a length of 23.2 m, a volume of 1240 m 3, and a complex inner electrode system with about 120 000 individual parts. The strong magnetic field that guides the β-electrons is provided by super-conducting solenoids at both ends of the spectrometer. Its influence on turbo-molecular pumps and vacuum gauges had to be considered. Furthermore, a system consisting of 6 turbo-molecular pumps andmore » 3 km of non-evaporable getter strips has been deployed and was tested during the commissioning of the spectrometer. In this paper the configuration, the commissioning with bake-out at 300 °C, and the performance of this system are presented in detail. The vacuum system has to maintain a pressure in the 10 -11 mbar range. We demonstrated that the performance of the system is already close to these stringent functional requirements for the KATRIN experiment, which will start at the end of 2016.« less

Commissioning of the vacuum system of the KATRIN Main Spectrometer

DOE PAGES

Arenz, M.; Babutzka, M.; Bahr, M.; ...

2016-04-07

The KATRIN experiment will probe the neutrino mass by measuring the β-electron energy spectrum near the endpoint of tritium β-decay. We performed an integral energy analysis by an electro-static spectrometer (``Main Spectrometer''), an ultra-high vacuum vessel with a length of 23.2 m, a volume of 1240 m 3, and a complex inner electrode system with about 120 000 individual parts. The strong magnetic field that guides the β-electrons is provided by super-conducting solenoids at both ends of the spectrometer. Its influence on turbo-molecular pumps and vacuum gauges had to be considered. Furthermore, a system consisting of 6 turbo-molecular pumps andmore » 3 km of non-evaporable getter strips has been deployed and was tested during the commissioning of the spectrometer. In this paper the configuration, the commissioning with bake-out at 300 °C, and the performance of this system are presented in detail. The vacuum system has to maintain a pressure in the 10 -11 mbar range. We demonstrated that the performance of the system is already close to these stringent functional requirements for the KATRIN experiment, which will start at the end of 2016.« less

Ultrahigh vacuum/high pressure chamber for surface x-ray diffraction experiments

NASA Astrophysics Data System (ADS)

Bernard, P.; Peters, K.; Alvarez, J.; Ferrer, S.

1999-02-01

We describe an ultrahigh vacuum chamber that can be internally pressurized to several bars and that is designed to perform surface x-ray diffraction experiments on solid-gas interfaces. The chamber has a cylindrical beryllium window that serves as the entrance and exit for the x rays. The sample surface can be ion bombarded with an ancillary ion gun and annealed to 1200 K.

Adsorption behavior of Zn porphyrins on a (1 0 1) face of anatase TiO2

NASA Astrophysics Data System (ADS)

Zajac, Lukasz; Bodek, Lukasz; Such, Bartosz

2018-06-01

The adsorption behavior of porphyrin molecules on anatase TiO2(1 0 1) has been investigated with scanning tunneling microscopy (STM) in ultra-high vacuum (UHV) at room temperature. At low coverage, the ZnTPP molecules have a tendency to adsorb on the one type of step edges forming molecular chains. Due to relatively high mobility of molecules stable assemblies appear only close to a monolayer coverage. Zn porphyrins in self-assembled molecular domains form a commensurate structure. In-plane rotation of the molecules leads to formation of two domains of different chirality.

Adsorption of alcohols on a two-dimensional SiO2 single crystal - Alcohol adsorption on silicatene

NASA Astrophysics Data System (ADS)

Nayakasinghe, M. T.; Sivapragasam, N.; Burghaus, U.

2017-12-01

The adsorption kinetics of alcohols (methanol, ethanol, 1-propanol, 1-butanol, 1-pentanol) was studied on monoatomic, two-dimensional SiO2 single crystals (silicatene) using thermal desorption spectroscopy (TDS). Silicatene was grown on Mo(1 1 2) at ultra-high vacuum. In contrast to Mo, the alcohols physisorb molecularly on the hydrophobic SiO2/Mo surface. Zero coverage binding energies vary from 46.5 to 65.5 kJ/mol and increase with molecular size. Silicatene was characterized by Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and water TDS.

Ge quantum dot arrays grown by ultrahigh vacuum molecular-beam epitaxy on the Si(001) surface: nucleation, morphology, and CMOS compatibility.

PubMed

Yuryev, Vladimir A; Arapkina, Larisa V

2011-09-05

Issues of morphology, nucleation, and growth of Ge cluster arrays deposited by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface are considered. Difference in nucleation of quantum dots during Ge deposition at low (≲600°C) and high (≳600°C) temperatures is studied by high resolution scanning tunneling microscopy. The atomic models of growth of both species of Ge huts--pyramids and wedges-- are proposed. The growth cycle of Ge QD arrays at low temperatures is explored. A problem of lowering of the array formation temperature is discussed with the focus on CMOS compatibility of the entire process; a special attention is paid upon approaches to reduction of treatment temperature during the Si(001) surface pre-growth cleaning, which is at once a key and the highest-temperature phase of the Ge/Si(001) quantum dot dense array formation process. The temperature of the Si clean surface preparation, the final high-temperature step of which is, as a rule, carried out directly in the MBE chamber just before the structure deposition, determines the compatibility of formation process of Ge-QD-array based devices with the CMOS manufacturing cycle. Silicon surface hydrogenation at the final stage of its wet chemical etching during the preliminary cleaning is proposed as a possible way of efficient reduction of the Si wafer pre-growth annealing temperature.

Advanced Photonic Sensors Enabled by Semiconductor Bonding

DTIC Science & Technology

2010-05-31

a dry scroll backing pump to maintain the high differential pressure between the UV gun and the sample/analysis chamber. We also replaced the...semiconductor materials in an ultra-high vacuum (UHV) environment where the properties of the interface can be controlled with atomic-level precision. Such...year research program, we designed and constructed a unique system capable of fusion bonding two wafers in an ultra-high vacuum environment. This system

Tools to Study Interfaces for Superconducting, Thermoelectric, and Magnetic Materials at the University of Houston

DTIC Science & Technology

2016-09-01

The MBE system, which grows crystalline thin films in ultrahigh vacuum (UHV) with precise control of thickness, composition, and morphology, will...used on our sputtering system to fabricate thin films with interfaces. - The electronic structures of these materials will be investigated using the...magnetization/transport measurements. The MBE system, which grows crystalline thin films in ultrahigh vacuum (UHV) with precise control of thickness, composition

Portable ultrahigh-vacuum sample storage system for polarization-dependent total-reflection fluorescence x-ray absorption fine structure spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Watanabe, Yoshihide, E-mail: e0827@mosk.tytlabs.co.jp; Nishimura, Yusaku F.; Suzuki, Ryo

A portable ultrahigh-vacuum sample storage system was designed and built to investigate the detailed geometric structures of mass-selected metal clusters on oxide substrates by polarization-dependent total-reflection fluorescence x-ray absorption fine structure spectroscopy (PTRF-XAFS). This ultrahigh-vacuum (UHV) sample storage system provides the handover of samples between two different sample manipulating systems. The sample storage system is adaptable for public transportation, facilitating experiments using air-sensitive samples in synchrotron radiation or other quantum beam facilities. The samples were transferred by the developed portable UHV transfer system via a public transportation at a distance over 400 km. The performance of the transfer system was demonstratedmore » by a successful PTRF-XAFS study of Pt{sub 4} clusters deposited on a TiO{sub 2}(110) surface.« less

Exploratory Thermal-mechanical Fatigue Results for Rene' 80 in Ultrahigh Vacuum

NASA Technical Reports Server (NTRS)

Sheinker, A. A.

1978-01-01

A limited study was conducted of the use of strainage partitioning for predicting the thermalmechanical fatigue life of cast nickel-base superalloy Rene' 80. The fatigue lives obtained by combined inphase thermal and mechanical strain cycling between 400 C (752 F) and 1000 C (1802 F) in an ultrahigh vacuum were considerably shorter than those represented by the four basic partitioned inelastic strainrange fatigue life relationships established previously for this alloy at 871 C (1600 F) and 1000 C (1832 F) in an ultrahigh vacuum. This behavior was attributed to the drastic decrease in ductility with decreasing temperature for this alloy. These results indicated that the prediction of the thermal-mechanical fatigue life of Rene' 80 by the method of strainrange partioning may be improved if based on the four basic fatigue life relationships determined at a lower temperature in the thermal-mechanical strain cycle.

Ultra-high vacuum compatible induction-heated rod casting furnace

NASA Astrophysics Data System (ADS)

Bauer, A.; Neubauer, A.; Münzer, W.; Regnat, A.; Benka, G.; Meven, M.; Pedersen, B.; Pfleiderer, C.

2016-06-01

We report the design of a radio-frequency induction-heated rod casting furnace that permits the preparation of polycrystalline ingots of intermetallic compounds under ultra-high vacuum compatible conditions. The central part of the system is a bespoke water-cooled Hukin crucible supporting a casting mold. Depending on the choice of the mold, typical rods have a diameter between 6 mm and 10 mm and a length up to 90 mm, suitable for single-crystal growth by means of float-zoning. The setup is all-metal sealed and may be baked out. We find that the resulting ultra-high vacuum represents an important precondition for processing compounds with high vapor pressures under a high-purity argon atmosphere up to 3 bars. Using the rod casting furnace, we succeeded to prepare large high-quality single crystals of two half-Heusler compounds, namely, the itinerant antiferromagnet CuMnSb and the half-metallic ferromagnet NiMnSb.

Ultra-high vacuum compatible induction-heated rod casting furnace.

PubMed

Bauer, A; Neubauer, A; Münzer, W; Regnat, A; Benka, G; Meven, M; Pedersen, B; Pfleiderer, C

2016-06-01

We report the design of a radio-frequency induction-heated rod casting furnace that permits the preparation of polycrystalline ingots of intermetallic compounds under ultra-high vacuum compatible conditions. The central part of the system is a bespoke water-cooled Hukin crucible supporting a casting mold. Depending on the choice of the mold, typical rods have a diameter between 6 mm and 10 mm and a length up to 90 mm, suitable for single-crystal growth by means of float-zoning. The setup is all-metal sealed and may be baked out. We find that the resulting ultra-high vacuum represents an important precondition for processing compounds with high vapor pressures under a high-purity argon atmosphere up to 3 bars. Using the rod casting furnace, we succeeded to prepare large high-quality single crystals of two half-Heusler compounds, namely, the itinerant antiferromagnet CuMnSb and the half-metallic ferromagnet NiMnSb.

Surface Design and Engineering Toward Wear-Resistant, Self-Lubricating Diamond Films and Coatings

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1999-01-01

The tribological properties of chemical-vapor-deposited (CVD) diamond films vary with the environment, possessing a Jekyll-and-Hyde character. CVD diamond has low coefficient of friction and high wear resistance in air but high coefficient of friction and low wear resistance in vacuum. Improving the tribological functionality of materials (such as achieving low friction and good wear resistance) was an aim of this investigation. Three studies on the surface design, surface engineering, and tribology of CVD diamond have shown that its friction and wear are significantly reduced in ultrahigh vacuum. The main criteria for judging whether diamond films are an effective wear-resistant, self-lubricating material were coefficient of friction and wear rate, which must be less than 0.1 and on the order of 10(exp 6) cu mm/N(dot)m, respectively. In the first study the presence of a thin film (less than 1 micron thick) of amorphous, nondiamond carbon (hydrogenated carbon, also called diamondlike carbon or DLC) on CVD diamond greatly decreased the coefficient of friction and the wear rate. Therefore, a thin DLC film on CVD diamond can be an effective wear-resistant, lubricating coating in ultrahigh vacuum. In the second study the presence of an amorphous, nondiamond carbon surface layer formed on CVD diamond by ion implantation significantly reduced the coefficient of friction and the wear rate in ultrahigh vacuum. Therefore, such surface layers are acceptable for effective self-lubricating, wear-resistant applications of CVD diamond. In the third study CVD diamond in contact with cubic boron nitride exhibited low coefficient of friction in ultra high vacuum. Therefore, this materials combination can provide an effective self-lubricating, wear-resistant couple in ultrahigh vacuum.

The development of a portable ultrahigh vacuum chamber via silicon block.

PubMed

Chuang, Ho-Chiao; Huang, Chia-Shiuan

2014-05-01

This paper describes a nonmetallic, light weight portable chamber for ultra-high vacuum (UHV) applications. The chamber consists of a processed silicon block anodically bonding five polished Pyrex glass windows and a Pyrex glass adapter, without using any screws, bolts or vacuum adhesives. The design features provide an alternative chamber for UHV applications which require nonmetallic components. We have cyclically baked the chamber up to 180 °C for 160 h and have achieved an ultimate pressure of 1.4 × 10(-9) Torr (limited by our pumping station), with no leak detected. Both Pyrex glass windows and Pyrex glass adapter have been used successfully.

Cold-welding test environment

NASA Technical Reports Server (NTRS)

Wang, J. T.

1972-01-01

A flight test was conducted and compared with ground test data. Sixteen typical spacecraft material couples were mounted on an experimental research satellite in which a motor intermittently drove the spherical moving specimens across the faces of the fixed flat specimens in an oscillating motion. Friction coefficients were measured over a period of 14-month orbital time. Surface-to-surface sliding was found to be the controlling factor of generating friction in a vacuum environment. Friction appears to be independent of passive vacuum exposure time. Prelaunch and postlaunch tests identical to the flight test were performed in an oil-diffusion-pumped ultrahigh vacuum chamber. Only 50% of the resultant data agreed with the flight data owing to pump oil contamination. Identical ground tests were run in an ultrahigh vacuum facility and a ion-pumped vacuum chamber. The agreement (90%) between data from these tests and flight data established the adequacy of these test environments and facilities.

Ge quantum dot arrays grown by ultrahigh vacuum molecular-beam epitaxy on the Si(001) surface: nucleation, morphology, and CMOS compatibility

PubMed Central

2011-01-01

Issues of morphology, nucleation, and growth of Ge cluster arrays deposited by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface are considered. Difference in nucleation of quantum dots during Ge deposition at low (≲600°C) and high (≳600°C) temperatures is studied by high resolution scanning tunneling microscopy. The atomic models of growth of both species of Ge huts--pyramids and wedges-- are proposed. The growth cycle of Ge QD arrays at low temperatures is explored. A problem of lowering of the array formation temperature is discussed with the focus on CMOS compatibility of the entire process; a special attention is paid upon approaches to reduction of treatment temperature during the Si(001) surface pre-growth cleaning, which is at once a key and the highest-temperature phase of the Ge/Si(001) quantum dot dense array formation process. The temperature of the Si clean surface preparation, the final high-temperature step of which is, as a rule, carried out directly in the MBE chamber just before the structure deposition, determines the compatibility of formation process of Ge-QD-array based devices with the CMOS manufacturing cycle. Silicon surface hydrogenation at the final stage of its wet chemical etching during the preliminary cleaning is proposed as a possible way of efficient reduction of the Si wafer pre-growth annealing temperature. PMID:21892938

BAKABLE ULTRA-HIGH VACUUM VALVE

DOEpatents

Mark, J.T.; Gantz, I.H.

1962-07-10

S>This patent relates to a valve useful in applications involving successively closing and opening a communication between a chamber evacuated to an ultra-high vacuum condition of the order of 10/sup -10/ millimeters of mercury and another chamber or the ambient. The valve is capable of withstanding extended baking at 450 deg C and repeated opening and closing without repiacement of the valve seat (approximately 200 cycle limit). The seal is formed by mutual interdiffusion weld, coerced by a pneumatic actuator. (AEC)

Tribological reactions of perfluoroalkyl polyether oils with stainless steel under ultrahigh vacuum conditions at room temperature

NASA Technical Reports Server (NTRS)

Mori, Shigeyuki; Morales, Wilfredo

1989-01-01

The reaction between three types of commercial perfluoroalkyl polyether (PFPE) oils and stainless steel 440C was investigated experimentally during sliding under ultrahigh vacuum conditions at room temperature. It is found that the tribological reaction of PFPE is mainly affected by the activity of the mechanically formed fresh surfaces of metals rather than the heat generated at the sliding contacts. The fluorides formed on the wear track act as a boundary layer, reducing the friction coefficient.

Sidewall GaAs tunnel junctions fabricated using molecular layer epitaxy

PubMed Central

Ohno, Takeo; Oyama, Yutaka

2012-01-01

In this article we review the fundamental properties and applications of sidewall GaAs tunnel junctions. Heavily impurity-doped GaAs epitaxial layers were prepared using molecular layer epitaxy (MLE), in which intermittent injections of precursors in ultrahigh vacuum were applied, and sidewall tunnel junctions were fabricated using a combination of device mesa wet etching of the GaAs MLE layer and low-temperature area-selective regrowth. The fabricated tunnel junctions on the GaAs sidewall with normal mesa orientation showed a record peak current density of 35 000 A cm-2. They can potentially be used as terahertz devices such as a tunnel injection transit time effect diode or an ideal static induction transistor. PMID:27877466

Method for producing an atomic oxygen beam

NASA Technical Reports Server (NTRS)

Outlaw, Ronald A. (Inventor)

1989-01-01

A method for producing an atomic oxygen beam is provided by the present invention. First, a material 10' is provided which dissociates molecular oxygen and dissolves atomic oxygen into its bulk. Next, molecular oxygen is exposed to entrance surface 11' of material 10'. Next, material 10' is heated by heater 17' to facilitate the permeation of atomic oxygen through material 10' to the UHV side 12'. UHV side 12' is interfaced with an ultra-high vacuum (UHV) environment provided by UHV pump 15'. The atomic oxygen on the UHV side 12' is excited to a non-binding state by exciter 14' thus producing the release of atomic oxygen to form an atomic oxygen beam 35'.

Three-configurational surface magneto-optical Kerr effect measurement system for an ultrahigh vacuum in situ study of ultrathin magnetic films

NASA Astrophysics Data System (ADS)

Lee, J.-W.; Jeong, J.-R.; Kim, D.-H.; Ahn, J. S.; Kim, J.; Shin, S.-C.

2000-10-01

We have constructed a three-configurational surface magneto-optical Kerr effect system, which provides the simultaneous measurements of the "polar," "longitudinal," and "transverse" Kerr hysteresis loops at the position where deposition is carried out in an ultrahigh vacuum growth chamber. The present system enables in situ three-dimensional vectorial studies of ultrathin film magnetism with a submonolayer sensitivity. We present three-configurational hysteresis loops measured during the growth of Co films on Pd(111), glass, and Pd/glass substrates.

Ultrahigh vacuum, high temperature, low cycle fatigue of coated and uncoated Rene 80

NASA Technical Reports Server (NTRS)

Kortovich, C. S.

1976-01-01

A study was conducted on the ultrahigh vacuum strain controlled by low cycle fatigue behavior of uncoated and CODEP B-1 aluminide coated Rene' 80 nickel-base superalloy at 1000 C (1832 F) and 871 C (1600 F). The results indicated little effect of coating or temperature on the fatigue properties. There was, however, a significant effect on fatigue life when creep was introduced into the strain cycles. The effect of this creep component was analyzed in terms of the method of strainrange partitioning.

Achieving ultrahigh vacuum in an unbaked chamber with glow discharge conditioning

NASA Astrophysics Data System (ADS)

Khan, Ziauddin; Semwal, Pratibha; Dhanani, Kalpesh R.; Raval, Dilip C.; Pradhan, Subrata

2017-01-01

Glow discharge conditioning (GDC) has long been accepted as one of the basic wall conditioning techniques for achieving ultrahigh vacuum in an unbaked chamber. As a part of this fundamental experimental study, a test chamber has been fabricated from stainless steel 304 L with its inner surface electropolished on which a detailed investigation has been carried out. Both helium and hydrogen gases have been employed as discharge cleaning medium. The discharge cleaning was carried out at 0.1 A / m 2 current density with working pressure maintained at 1.0 × 10 -2 mbar. It was experimentally observed that the pump-down time to attain the base pressure 10 -8 mbar was reduced by 62% compared to the unbaked chamber being pumped to this ultimate vacuum. The results were similar irrespective of whether the discharge cleaning medium is either hydrogen or helium. It was also experimentally established that a better ultimate vacuum could be achieved as compared to theoretically calculated ultimate vacuum with the help of discharge cleaning.

Ferroelectric triggering of carbon monoxide adsorption on lead zirco-titanate (001) surfaces

PubMed Central

Tănase, Liviu Cristian; Apostol, Nicoleta Georgiana; Abramiuc, Laura Elena; Tache, Cristian Alexandru; Hrib, Luminița; Trupină, Lucian; Pintilie, Lucian; Teodorescu, Cristian Mihail

2016-01-01

Atomically clean lead zirco-titanate PbZr0.2Ti0.8O3 (001) layers exhibit a polarization oriented inwards P(−), visible by a band bending of all core levels towards lower binding energies, whereas as introduced layers exhibit P(+) polarization under air or in ultrahigh vacuum. The magnitude of the inwards polarization decreases when the temperature is increased at 700 K. CO adsorption on P(−) polarized surfaces saturates at about one quarter of a monolayer of carbon, and occurs in both molecular (oxidized) and dissociated (reduced) states of carbon, with a large majority of reduced state. The sticking of CO on the surface in ultrahigh vacuum is found to be directly related to the P(−) polarization state of the surface. A simple electrostatic mechanism is proposed to explain these dissociation processes and the sticking of carbon on P(−) polarized areas. Carbon desorbs also when the surface is irradiated with soft X-rays. Carbon desorption when the polarization is lost proceeds most probably in form of CO2. Upon carbon desorption cycles, the ferroelectric surface is depleted in oxygen and at some point reverses its polarization, owing to electrons provided by oxygen vacancies which are able to screen the depolarization field produced by positive fixed charges at the surface. PMID:27739461

Scanning Probe Microscopy | Materials Science | NREL

Science.gov Websites

. Capability of use with ultra-high vacuum makes NREL Scanning Probe Microscopy particularly valuable for vacuum, as appropriate Field of view from atoms up to about 100 µm (vertical limit of about 7 µm

Tunneling electron induced molecular electroluminescence from individual porphyrin J-aggregates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meng, Qiushi; Zhang, Chao; Zhang, Yang, E-mail: zhyangnano@ustc.edu.cn, E-mail: zcdong@ustc.edu.cn

2015-07-27

We investigate molecular electroluminescence from individual tubular porphyrin J-aggregates on Au(111) by tunneling electron excitations in an ultrahigh-vacuum scanning tunneling microscope (STM). High-resolution STM images suggest a spiral tubular structure for the porphyrin J-aggregate with highly ordered “brickwork”-like arrangements. Such aggregated nanotube is found to behave like a self-decoupled molecular architecture and shows red-shifted electroluminescence characteristics of J-aggregates originated from the delocalized excitons. The positions of the emission peaks are found to shift slightly depending on the excitation sites, which, together with the changes in the observed spectral profiles with vibronic progressions, suggest a limited exciton coherence number within severalmore » molecules. The J-aggregate electroluminescence is also found unipolar, occurring only at negative sample voltages, which is presumably related to the junction asymmetry in the context of molecular excitations via the carrier injection mechanism.« less

Distillation Kinetics of Solid Mixtures of Hydrogen Peroxide and Water and the Isolation of Pure Hydrogen Peroxide in Ultrahigh Vacuum

NASA Technical Reports Server (NTRS)

Teolis, B. D.; Baragiola, R. A.

2006-01-01

We present results of the growth of thin films of crystalline H2O2 and H2O2.2H2O (dihydrate) in ultrahigh vacuum by distilling an aqueous solution of hydrogen peroxide. We traced the process using infrared reflectance spectroscopy, mass loss on a quartz crystal microbalance, and in a few cases ultraviolet-visible reflectance. We find that the different crystalline phases-water, dihydrate, and hydrogen peroxide-have very different sublimation rates, making distillation efficient to isolate the less volatile component, crystalline H2O2.

Wide band cryogenic ultra-high vacuum microwave absorber

DOEpatents

Campisi, I.E.

1992-05-12

An absorber waveguide assembly for absorbing higher order modes of microwave energy under cryogenic ultra-high vacuum conditions, that absorbs wide-band multi-mode energy. The absorber is of a special triangular shape, made from flat tiles of silicon carbide and aluminum nitride. The leading sharp end of the absorber is located in a corner of the waveguide and tapers to a larger cross-sectional area whose center is located approximately in the center of the wave guide. The absorber is relatively short, being of less height than the maximum width of the waveguide. 11 figs.

Wide band cryogenic ultra-high vacuum microwave absorber

DOEpatents

Campisi, Isidoro E.

1992-01-01

An absorber wave guide assembly for absorbing higher order modes of microwave energy under cryogenic ultra-high vacuum conditions, that absorbs wide-band multi-mode energy. The absorber is of a special triangular shape, made from flat tiles of silicon carbide and aluminum nitride. The leading sharp end of the absorber is located in a corner of the wave guide and tapers to a larger cross-sectional area whose center is located approximately in the center of the wave guide. The absorber is relatively short, being of less height than the maximum width of the wave guide.

O-Ring sealing arrangements for ultra-high vacuum systems

DOEpatents

Kim, Chang-Kyo; Flaherty, Robert

1981-01-01

An all metal reusable O-ring sealing arrangement for sealing two concentric tubes in an ultra-high vacuum system. An O-ring of a heat recoverable alloy such as Nitinol is concentrically positioned between protruding sealing rings of the concentric tubes. The O-ring is installed between the tubes while in a stressed martensitic state and is made to undergo a thermally induced transformation to an austenitic state. During the transformation the O-ring expands outwardly and contracts inwardly toward a previously sized austenitic configuration, thereby sealing against the protruding sealing rings of the concentric tubes.

Refined tip preparation by electrochemical etching and ultrahigh vacuum treatment to obtain atomically sharp tips for scanning tunneling microscope and atomic force microscope.

PubMed

Hagedorn, Till; El Ouali, Mehdi; Paul, William; Oliver, David; Miyahara, Yoichi; Grütter, Peter

2011-11-01

A modification of the common electrochemical etching setup is presented. The described method reproducibly yields sharp tungsten tips for usage in the scanning tunneling microscope and tuning fork atomic force microscope. In situ treatment under ultrahigh vacuum (p ≤10(-10) mbar) conditions for cleaning and fine sharpening with minimal blunting is described. The structure of the microscopic apex of these tips is atomically resolved with field ion microscopy and cross checked with field emission. © 2011 American Institute of Physics

Transferring pharmaceuticals into the gas phase

NASA Astrophysics Data System (ADS)

Christen, Wolfgang; Krause, Tim; Rademann, Klaus

2008-11-01

The dissolution of molecules of biological interest in supercritical carbon dioxide is investigated using pulsed molecular beam mass spectrometry. Due to the mild processing temperatures of most supercritical fluids, their adiabatic expansion into vacuum permits to transfer even thermally very sensitive substances into the gas phase, which is particularly attractive for pharmaceutical and biomedical applications. In addition, supercritical CO2constitutes a chemically inert solvent that is compatible with hydrocarbon-free ultrahigh vacuum conditions. Here, we report on the dissolution and pulsed supersonic jet expansion of caffeine (C8H10N4O2), the provitamin menadione (C11H8O2), and the amino acid derivative l-phenylalanine tert-butyl ester hydrochloride (C6H5CH2CH(NH2)COOC(CH3)3[dot operator]HCl), into vacuum. An on-axis residual gas analyzer is used to monitor the relative amounts of solute and solvent in the molecular beam as a function of solvent densityE The excellent selectivity and sensitivity provided by mass spectrometry permits to probe even trace amounts of solutes. The strong density variation of CO2 close to the critical point results in a pronounced pressure dependence of the relative ion currents of solute and solvent molecules, reflecting a substantial change in solubility.

Scanning tunneling microscopy studies of pulse deposition of dinuclear organometallic molecules on Au(111)

NASA Astrophysics Data System (ADS)

Guo, Song; Alex Kandel, S.

2008-01-01

Ultrahigh-vacuum scanning tunneling microscopy (STM) was used to study trans-[Cl(dppe)2Ru(CC)6Ru(dppe)2Cl] [abbreviated as Ru2, diphenylphosphinoethane (dppe)] on Au(111). This large organometallic molecule was pulse deposited onto the Au(111) surface under ultrahigh-vacuum (UHV) conditions. UHV STM studies on the prepared sample were carried out at room temperature and 77K in order to probe molecular adsorption and to characterize the surface produced by the pulse deposition process. Isolated Ru2 molecules were successfully imaged by STM at room temperature; however, STM images were degraded by mobile toluene solvent molecules that remain on the surface after the deposition. Cooling the sample to 77K allows the solvent molecules to be observed directly using STM, and under these conditions, toluene forms organized striped domains with regular domain boundaries and a lattice characterized by 5.3 and 2.7Å intermolecular distances. When methylene chloride is used as the solvent, it forms analogous domains on the surface at 77K. Mild annealing under vacuum causes most toluene molecules to desorb from the surface; however, this annealing process may lead to thermal degradation of Ru2 molecules. Although pulse deposition is an effective way to deposit molecules on surfaces, the presence of solvent on the surface after pulse deposition is unavoidable without thermal annealing, and this annealing may cause undesired chemical changes in the adsorbates under study. Preparation of samples using pulse deposition must take into account the characteristics of sample molecules, solvent, and surfaces.

Note: Work function change measurement via improved Anderson method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabik, A., E-mail: sabik@ifd.uni.wroc.pl; Gołek, F.; Antczak, G.

We propose the modification to the Anderson method of work function change (Δϕ) measurements. In this technique, the kinetic energy of the probing electrons is already low enough for non-destructive investigation of delicate molecular systems. However, in our implementation, all electrodes including filament of the electron gun are polarized positively. As a consequence, electron bombardment of any elements of experimental system is eliminated. Our modification improves cleanliness of the ultra-high vacuum system. As an illustration of the solution capabilities, we present Δϕ of the Ag(100) surface induced by cobalt phthalocyanine layers.

Electrospray deposition of organic molecules on bulk insulator surfaces.

PubMed

Hinaut, Antoine; Pawlak, Rémy; Meyer, Ernst; Glatzel, Thilo

2015-01-01

Large organic molecules are of important interest for organic-based devices such as hybrid photovoltaics or molecular electronics. Knowing their adsorption geometries and electronic structures allows to design and predict macroscopic device properties. Fundamental investigations in ultra-high vacuum (UHV) are thus mandatory to analyze and engineer processes in this prospects. With increasing size, complexity or chemical reactivity, depositing molecules by thermal evaporation becomes challenging. A recent way to deposit molecules in clean conditions is Electrospray Ionization (ESI). ESI keeps the possibility to work with large molecules, to introduce them in vacuum, and to deposit them on a large variety of surfaces. Here, ESI has been successfully applied to deposit triply fused porphyrin molecules on an insulating KBr(001) surface in UHV environment. Different deposition coverages have been obtained and characterization of the surface by in-situ atomic force microscopy working in the non-contact mode shows details of the molecular structures adsorbed on the surface. We show that UHV-ESI, can be performed on insulating surfaces in the sub-monolayer regime and to single molecules which opens the possibility to study a variety of complex molecules.

Degassing procedure for ultrahigh vacuum

NASA Technical Reports Server (NTRS)

Moore, B. C.

1979-01-01

Calculations based on diffusion coefficients and degassing rates for stainless-steel vacuum chambers indicate that baking at lower temperatures for longer periods give lower ultimate pressures than rapid baking at high temperatures. Process could reduce pressures in chambers for particle accelerators, fusion reactors, material research, and other applications.

Surface oxidation of GaN(0001): Nitrogen plasma-assisted cleaning for ultrahigh vacuum applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gangopadhyay, Subhashis; Schmidt, Thomas, E-mail: tschmidt@ifp.uni-bremen.de; Kruse, Carsten

The cleaning of metal-organic vapor-phase epitaxial GaN(0001) template layers grown on sapphire has been investigated. Different procedures, performed under ultrahigh vacuum conditions, including degassing and exposure to active nitrogen from a radio frequency nitrogen plasma source have been compared. For this purpose, x-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and scanning tunneling microscopy have been employed in order to assess chemical as well as structural and morphological surface properties. Initial degassing at 600 °C under ultrahigh vacuum conditions only partially eliminates the surface contaminants. In contrast to plasma assisted nitrogen cleaning at temperatures as low as 300 °C, active-nitrogen exposure at temperaturesmore » as high as 700 °C removes the majority of oxide species from the surface. However, extended high-temperature active-nitrogen cleaning leads to severe surface roughening. Optimum results regarding both the removal of surface oxides as well as the surface structural and morphological quality have been achieved for a combination of initial low-temperature plasma-assisted cleaning, followed by a rapid nitrogen plasma-assisted cleaning at high temperature.« less

Molecular electronics--resonant transport through single molecules.

PubMed

Lörtscher, Emanuel; Riel, Heike

2010-01-01

The mechanically controllable break-junction technique (MCBJ) enables us to investigate charge transport through an individually contacted and addressed molecule in ultra-high vacuum (UHV) environment at variable temperature ranging from room temperature down to 4 K. Using a statistical measurement and analysis approach, we acquire current-voltage (I-V) characteristics during the repeated formation, manipulation, and breaking of a molecular junction. At low temperatures, voltages accessing the first molecular orbitals in resonance can be applied, providing spectroscopic information about the junction's energy landscape, in particular about the molecular level alignment in respect to the Fermi energy of the electrodes. Thereby, we can investigate the non-linear transport properties of various types of functional molecules and explore their potential use as functional building blocks for future nano-electronics. An example will be given by the reversible and controllable switching between two distinct conductive states of a single molecule. As a proof-of-principle for functional molecular devices, a single-molecule memory element will be demonstrated.

X-Ray Photoelectron Spectroscopy and Ultrahigh Vacuum Contactless Capacitance-Voltage Characterization of Novel Oxide-Free InP Passivation Process Using a Silicon Surface Quantum Well

NASA Astrophysics Data System (ADS)

Takahashi, Hiroshi; Hashizume, Tamotsu; Hasegawa, Hideki

1999-02-01

In order to understand and optimize a novel oxide-free InP passivation process using a silicon surface quantum well, a detailed in situ X-ray photoelectron spectroscopy (XPS) and ultrahigh vacuum (UHV) contactless capacitance-voltage (C-V) study of the interface was carried out. Calculation of quantum levels in the silicon quantum well was performed on the basis of the band lineup of the strained Si3N4/Si/InP interface and the result indicated that the interface should become free of gap states when the silicon layer thickness is below 5 Å. Experimentally, such a delicate Si3N4/Si/InP structure was realized by partial nitridation of a molecular beam epitaxially (MBE) grown pseudomorphic silicon layer using an electron cyclotron resonance (ECR) N2 plasma. The progress of nitridation was investigated in detail by angle-resolved XPS. A newly developed UHV contactless C-V method realized in situ characterization of surface electronic properties of InP at each processing step for passivation. It was found that the interface state density decreased substantially into the 1010 cm-2 eV-1 range by optimizing the nitridation process of the silicon layer. It was concluded that both the surface bond termination and state removal by quantum confinement are responsible for the NSS reduction.

An ultra-high vacuum chamber for scattering experiments featuring in-vacuum continuous in-plane variation of the angle between entrance and exit vacuum ports

DOE Office of Scientific and Technical Information (OSTI.GOV)

Englund, Carl-Johan; Agåker, Marcus, E-mail: marcus.agaker@physics.uu.se; Fredriksson, Pierre

2015-09-15

A concept that enables in-vacuum continuous variation of the angle between two ports in one plane has been developed and implemented. The vacuum chamber allows for measuring scattering cross sections as a function of scattering angle and is intended for resonant inelastic X-ray scattering experiments. The angle between the ports can be varied in the range of 30°-150°, while the pressure change is less than 2 × 10{sup −10} mbars.

An advanced molecule-surface scattering instrument for study of vibrational energy transfer in gas-solid collisions.

PubMed

Ran, Qin; Matsiev, Daniel; Wodtke, Alec M; Auerbach, Daniel J

2007-10-01

We describe an advanced and highly sensitive instrument for quantum state-resolved molecule-surface energy transfer studies under ultrahigh vacuum (UHV) conditions. The apparatus includes a beam source chamber, two differential pumping chambers, and a UHV chamber for surface preparation, surface characterization, and molecular beam scattering. Pulsed and collimated supersonic molecular beams are generated by expanding target molecule mixtures through a home-built pulsed nozzle, and excited quantum state-selected molecules were prepared via tunable, narrow-band laser overtone pumping. Detection systems have been designed to measure specific vibrational-rotational state, time-of-flight, angular and velocity distributions of molecular beams coming to and scattered off the surface. Facilities are provided to clean and characterize the surface under UHV conditions. Initial experiments on the scattering of HCl(v = 0) from Au(111) show many advantages of this new instrument for fundamental studies of the energy transfer at the gas-surface interface.

Electron-stimulated reactions in nanoscale water films adsorbed on (alpha)-Al2O3(0001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrik, Nikolay G.; Kimmel, Gregory A.

2018-05-11

The radiation-induced decomposition and desorption of nanoscale amorphous solid water (D2O) films adsorbed on -Al2O3(0001) surface was studied at low temperature in ultrahigh vacuum using temperature programmed desorption (TPD) and electron stimulated desorption (ESD) with a mono-energetic, low energy electron source. ESD yields of molecular products ( D2, O2 and D¬2O) and the total sputtering yield increased with increasing D2O coverage up to ~15 water monolayers (i.e. ~15 1015 cm-2) to a coverage-independent level for thicker water films. Experiments with isotopically-layered water films (D2O and H2O) demonstrated that the highest water decomposition yields occurred at the interfaces of the nanoscalemore » water films with the alumina substrate and vacuum. However, the increased reactivity of the water/alumina interface is relatively small compared to the enhancements in the non-thermal reactions previously observed at the water/Pt(111) and water/TiO2(110) interfaces. We propose that the relatively low activity of Al2O3(0001) for the radiation-induced production of molecular hydrogen is associated with lower reactivity of this surface with hydrogen atoms, which are likely precursors for the molecular hydrogen.« less

Electron-stimulated reactions in nanoscale water films adsorbed on α-Al 2 O 3 (0001)

DOE PAGES

Petrik, Nikolay G.; Kimmel, Greg A.

2018-04-11

The radiation-induced decomposition and desorption of nanoscale amorphous solid water (D 2O) films adsorbed on an α-Al 2O 3(0001) surface was studied at low temperature in ultrahigh vacuum using temperature programmed desorption (TPD) and electron stimulated desorption (ESD) with a mono-energetic, low energy electron source. ESD yields of molecular products (D 2, O 2 and D 2O) and the total sputtering yield increased with increasing D 2O coverage up to ~15 water monolayers (i.e. ~15 x 10 15 cm -2) to a coverage-independent level for thicker water films. Experiments with isotopically-layered water films (D 2O and H 2O) demonstrated thatmore » the highest water decomposition yields occurred at the interfaces of the nanoscale water films with the alumina substrate and vacuum. However, the increased reactivity of the water/alumina interface is relatively small compared to the enhancements in the non-thermal reactions previously observed at the water/Pt(111) and water/TiO 2(110) interfaces. Here, we propose that the relatively low activity of Al 2O 3(0001) for the radiation-induced production of molecular hydrogen is associated with lower reactivity of this surface with hydrogen atoms, which are likely precursors for the formation of molecular hydrogen.« less

Electron-stimulated reactions in nanoscale water films adsorbed on α-Al 2 O 3 (0001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrik, Nikolay G.; Kimmel, Greg A.

The radiation-induced decomposition and desorption of nanoscale amorphous solid water (D 2O) films adsorbed on an α-Al 2O 3(0001) surface was studied at low temperature in ultrahigh vacuum using temperature programmed desorption (TPD) and electron stimulated desorption (ESD) with a mono-energetic, low energy electron source. ESD yields of molecular products (D 2, O 2 and D 2O) and the total sputtering yield increased with increasing D 2O coverage up to ~15 water monolayers (i.e. ~15 x 10 15 cm -2) to a coverage-independent level for thicker water films. Experiments with isotopically-layered water films (D 2O and H 2O) demonstrated thatmore » the highest water decomposition yields occurred at the interfaces of the nanoscale water films with the alumina substrate and vacuum. However, the increased reactivity of the water/alumina interface is relatively small compared to the enhancements in the non-thermal reactions previously observed at the water/Pt(111) and water/TiO 2(110) interfaces. Here, we propose that the relatively low activity of Al 2O 3(0001) for the radiation-induced production of molecular hydrogen is associated with lower reactivity of this surface with hydrogen atoms, which are likely precursors for the formation of molecular hydrogen.« less

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Epitaxial Growth of Graphene on 6H-SiC (0001) by Thermal Annealing

NASA Astrophysics Data System (ADS)

Tang, Jun; Liu, Zhong-Liang; Kang, Chao-Yang; Pan, Hai-Bin; Wei, Shi-Qiang; Xu, Peng-Shou; Gao, Yu-Qiang; Xu, Xian-Gang

2009-08-01

An epitaxial graphene (EG) layer is successfully grown on a Si-terminated 6H-SiC (0001) substrate by the method of thermal annealing in an ultrahigh vacuum molecular beam epitaxy chamber. The structure and morphology of the EG sample are characterized by reflection high energy diffraction (RHEED), Raman spectroscopy and atomic force microscopy (AFM). Graphene diffraction streaks can be seen in RHEED. The G and 2D peaks of graphene are clearly observed in the Raman spectrum. The AFM results show that the graphene nominal thickness is about 4-10 layers.

Construction of vacuum system for Tristan accumulation ring

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ishimaru, H.; Horikoshi, G.; Kobayashi, M.

1983-08-01

An all aluminum-alloy vacuum system for the TRISTAN accumulation ring is now under construction. Aluminum and aluminum alloys are preferred materials for ultrahigh vacuum systems of large electron storage rings because of their good thermal conductivity, extremely low outgassing rate, and low residual radioactivity. Vacuum beam chambers for the dipole and quadrupole magnets are extruded using porthole dies. The aluminum alloy 6063-T6 provides superior performance in extrusion. For ultrahigh vacuum performance, a special extrusion technique is applied which, along with the outgassing procedure used, is described in detail. Aluminum alloy 3004 seamless elliptical bellows are inserted between the dipole andmore » quadrupole magnet chambers. These bellows are produced by the hydraulic forming of a seamless tube. The seamless bellows and the beam chambers are joined by fully automatic welding. The ceramic chambers for the kicker magnets, the fast bump magnets, and the slow beam intensity monitor are inserted in the aluminum alloy beam chambers. The ceramic chamber (98% alumina) and elliptical bellows are brazed with brazing sheets (4003-3003-4003) in a vacuum furnace. The brazing technique is described. The inner surface of the ceramic chamber is coated with a TiMo alloy by vacuum evaporation to permit a smooth flow of the RF wall current. Other suitable aluminum alloy components, including fittings, feedthroughs, gauges, optical windows, sputter ion pumps, turbomolecular pumps, and valves have been developed; their fabrication is described.« less

The surface variation of Ti-14Al-21Nb as a function of temperature under ultrahigh vacuum conditions

NASA Technical Reports Server (NTRS)

Lee, W. S.; Sankaran, S. N.; Outlaw, R. A.; Clark, R. K.

1990-01-01

The effect of temperature, at conditions of ultrahigh vacuum, on the surface composition of the Ti-14Al-21Nb (in wt pct) alloy was investigated in samples heated to 1000 C in 100 C increments. Results of AES spectroscopy revealed that the Ti-14Al-21Nb alloy surface is extremely sensitive to temperature. At 300 C, the carbon and oxygen began to rapidly dissolve into the alloy, and at 600 C, bulk S segregated to the surface. The variation in the surface composition was extensive and different over the temperature range studied, indicating that there may be substantial changes in the hydrogen transport.

Fullerene-derivative PC61BM forms three types of phase-pure monolayer on the surface of Au(111)

NASA Astrophysics Data System (ADS)

Li, Wen-Jie; Du, Ying-Ying; Zhang, Han-Jie; Chen, Guang-Hua; Sheng, Chun-Qi; Wu, Rui; Wang, Jia-Ou; Qian, Hai-Jie; Ibrahim, Kurash; He, Pi-Mo; Li, Hong-Nian

2016-12-01

We have studied the packing structures of C60-derivative PC61BM on the surface of Au(111) in ultrahigh vacuum using scanning tunneling microscopy. The Au(111) has a triangle-like reconstructed surface, which results in some packing structures different from those reported for low coverages. PC61BM can form three types of phase-pure monolayer, namely, the compact straight molecular double-row monolayer, the hexagonal-packing monolayer and the glassy monolayer. The different types of monolayer form for different molecular densities and different annealing temperatures. In addition to the already known inter-molecular interactions (Van de Waals interaction and hydrogen bond), the steric effect of the phenyl-butyric-acid-methyl-ester side tail plays conspicuous role in the molecular self-assembly at high coverages. The steric effect makes it difficult to prepare a hexagonal-packing monolayer at room temperature and decides the instability of the hexagonal-packing monolayer prepared by thermal annealing.

Ultra-high speed visualization of the flashing instability under vacuum conditions

NASA Astrophysics Data System (ADS)

Hernández Sánchez, Jose Federico; Al-Ghamdi, Tariq; Thoroddsen, Sigurdur T.

2017-11-01

We investigated experimentally the flashing instability of a jet of perfluoro-n-hexane (PFnH) released into a low-pressure environment. Using a ultra-high speed camera we observed the jet fragmentation occurring close to the nozzle. Using a fixed total driving pressure, we decreased systematically the vacuum pressure, investigating the transition from a laminar jet to a fully flashing jet. Our high temporal resolution allowed to visualize the detailed dynamics of external flash-boiling for the first time. We identified different mechanisms of jet break-up. At chamber pressures lower than the vapor pressure the laminar jet evolves to a meandering stream. In this stage, bubbles start to nucleate and violently expand upstream the nozzle. At lower vacuum pressures the initially cylindrical jet elongates, forming a liquid sheet that breaks in branches and later in drops. At very low pressures both mechanisms are responsible for the jet breaking. We calculated the size distribution of the ejected droplets, their individual trajectories, velocities as well as the spray angle as a function of the dimensionless vacuum pressure.

High-resolution microscope for tip-enhanced optical processes in ultrahigh vacuum

NASA Astrophysics Data System (ADS)

Steidtner, Jens; Pettinger, Bruno

2007-10-01

An optical microscope based on tip-enhanced optical processes that can be used for studies on adsorbates as well as thin layers and nanostructures is presented. The microscope provides chemical and topographic informations with a resolution of a few nanometers and can be employed in ultrahigh vacuum as well as gas phase. The construction involves a number of improvements compared to conventional instruments. The central idea is to mount, within an UHV system, an optical platform with all necessary optical elements to a rigid frame that also carries the scanning tunneling microscope unit and to integrate a high numerical aperture parabolic mirror between the scanning probe microscope head and the sample. The parabolic mirror serves to focus the incident light and to collect a large fraction of the scattered light. The first experimental results of Raman measurements on silicon samples as well as brilliant cresyl blue layers on single crystalline gold and platinum surfaces in ultrahigh vacuum are presented. For dye adsorbates a Raman enhancement of ˜106 and a net signal gain of up to 4000 was observed. The focus diameter (˜λ/2) was measured by Raman imaging the focal region on a Si surface. The requirements of the parabolic mirror in terms of alignment accuracy were experimentally determined as well.

Photocatalysis and the origin of life: synthesis of nucleoside bases from formamide on TiO2(001) single surfaces.

PubMed

Senanayake, S D; Idriss, H

2006-01-31

We report the conversion of a large fraction of formamide (NH(2)CHO) to high-molecular-weight compounds attributed to nucleoside bases on the surface of a TiO(2) (001) single crystal in ultra-high vacuum conditions. If true, we present previously unreported evidence for making biologically relevant molecules from a C1 compound on any single crystal surface in high vacuum and in dry conditions. An UV light of 3.2 eV was necessary to make the reaction. This UV light excites the semiconductor surface but not directly the adsorbed formamide molecules or the reaction products. There thus is no need to use high energy in the form of photons or electrical discharge to make the carbon-carbon and carbon-nitrogen bonds necessary for life. Consequently, the reaction products may accumulate with time and may not be subject to decomposition by the excitation source. The formation of these molecules, by surface reaction of formamide, is proof that some minerals in the form of oxide semiconductors are active materials for making high-molecular-weight organic molecules that may have acted as precursors for biological compounds required for life in the universe.

MoS2-Filled PEEK Composite as a Self-Lubricating Material for Aerospace Applications

NASA Technical Reports Server (NTRS)

Theiler, Geraldine; Gradt, Thomas

2010-01-01

At BAM, several projects were conducted in the past years dealing with the tribological properties of friction couples at cryogenic temperature and in vacuum environment. Promising candidates for vacuum application are MoS2-filled PEEK/PTFE composites, which showed a friction coefficient as low as 0.03 in high vacuum. To complete the tribological profile of these composites, further tests were performed in ultra-high vacuum (UHV) at room temperature. In this paper, friction and stick slip behavior, as well as outgassing characteristics during the test are presented.

Materials processing in space, 1980 science planning document. [crystal growth, containerless processing, solidification, bioprocessing, and ultrahigh vacuum processes

NASA Technical Reports Server (NTRS)

Naumann, R. J.

1980-01-01

The scientific aspects of the Materials Processing in Space program are described with emphasis on the major categories of interest: (1) crystal growth; (2) solidification of metals, alloys, and composites; (3) fluids and chemical processes; (4) containerless processing, glasses, and refractories; (5) ultrahigh vacuum processes; and (6) bioprocessing. An index is provided for each of these areas. The possible contributions that materials science experiments in space can make to the various disciplines are summarized, and the necessity for performing experiments in space is justified. What has been learned from previous experiments relating to space processing, current investigations, and remaining issues that require resolution are discussed. Recommendations for the future direction of the program are included.

An efficient, movable single-particle detector for use in cryogenic ultra-high vacuum environments.

PubMed

Spruck, Kaija; Becker, Arno; Fellenberger, Florian; Grieser, Manfred; von Hahn, Robert; Klinkhamer, Vincent; Novotný, Oldřich; Schippers, Stefan; Vogel, Stephen; Wolf, Andreas; Krantz, Claude

2015-02-01

A compact, highly efficient single-particle counting detector for ions of keV/u kinetic energy, movable by a long-stroke mechanical translation stage, has been developed at the Max-Planck-Institut für Kernphysik (Max Planck Institute for Nuclear Physics, MPIK). Both, detector and translation mechanics, can operate at ambient temperatures down to ∼10 K and consist fully of ultra-high vacuum compatible, high-temperature bakeable, and non-magnetic materials. The set-up is designed to meet the technical demands of MPIK's Cryogenic Storage Ring. We present a series of functional tests that demonstrate full suitability for this application and characterise the set-up with regard to its particle detection efficiency.

In situ scanning tunneling microscope tip treatment device for spin polarization imaging

DOEpatents

Li, An-Ping [Oak Ridge, TN; Jianxing, Ma [Oak Ridge, TN; Shen, Jian [Knoxville, TN

2008-04-22

A tip treatment device for use in an ultrahigh vacuum in situ scanning tunneling microscope (STM). The device provides spin polarization functionality to new or existing variable temperature STM systems. The tip treatment device readily converts a conventional STM to a spin-polarized tip, and thereby converts a standard STM system into a spin-polarized STM system. The tip treatment device also has functions of tip cleaning and tip flashing a STM tip to high temperature (>2000.degree. C.) in an extremely localized fashion. Tip coating functions can also be carried out, providing the tip sharp end with monolayers of coating materials including magnetic films. The device is also fully compatible with ultrahigh vacuum sample transfer setups.

Surface Chemistry, Friction, and Wear Properties of Untreated and Laser-Annealed Surfaces of Pulsed-Laser-Deposited WS(sub 2) Coatings

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Wheeler, Donald R.; Zabinski, Jeffrey S.

1996-01-01

An investigation was conducted to examine the surface chemistry, friction, and wear behavior of untreated and annealed tungsten disulfide (WS2) coatings in sliding contact with a 6-mm-diameter 440C stainless-steel ball. The WS2 coatings and annealing were performed using the pulsed-laser-deposition technique. All sliding friction experiments were conducted with a load of 0.98 N (100 g), an average Hertzian contact pressure of 0.44 GPa, and a constant rotating speed of 120 rpm. The sliding velocity ranged from 31 to 107 mm/s because of the range of wear track radii involved in the experiments. The experiment was performed at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7X(exp -10) Pa), dry nitrogen (relative humidity, less than 1 percent), and humid air (relative humidity, 15 to 40 percent). Analytical techniques, including scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDX), x-ray photo electron spectroscopy (XPS), surface profilometry, and Vickers hardness testing, were used to characterize the tribological surfaces of WS2 coatings. The results of the investigation indicate that the laser annealing decreased the wear of a WS2 coating in an ultrahigh vacuum. The wear rate was reduced by a factor of 30. Thus, the laser annealing increased the wear life and resistance of the WS2 coating. The annealed WS 2 coating had a low coefficient of friction (less than O.1) and a low wear rate ((10(exp -7) mm(exp 3)/N-m)) both of which are favorable in an ultrahigh vacuum.

Gas-liquid interface of room-temperature ionic liquids.

PubMed

Santos, Cherry S; Baldelli, Steven

2010-06-01

The organization of ions at the interface of ionic liquids and the vacuum is an ideal system to test new ideas and concepts on the interfacial chemistry of electrolyte systems in the limit of no solvent medium. Whilst electrolyte systems have numerous theoretical and experimental methods used to investigate their properties, the ionic liquids are relatively new and our understanding of the interfacial properties is just beginning to be explored. In this critical review, the gas-liquid interface is reviewed, as this interface does not depend on the preparation of another medium and thus produces a natural interface. The interface has been investigated by sum frequency generation vibrational spectroscopy and ultra-high vacuum techniques. The results provide a detailed molecular-level view of the surface composition and structure. These have been complemented by theoretical studies. The combinations of treatments on this interface are starting to provide a somewhat convergent description of how the ions are organized at this neat interface (108 references).

Note: reliable and reusable ultrahigh vacuum optical viewports.

PubMed

Arora, P; Sen Gupta, A

2012-04-01

We report a simple technique for the realization of ultrahigh vacuum optical viewports. The technique relies on using specially designed thin copper knife-edges and using a thin layer of Vacseal(®) on tip of the knife-edges between the optical flat and the ConFlat(®) (CF) flange. The design of the windows is such that it gives uniform pressure on the flat without breaking it. The assembled window is a complete unit, which can be mounted directly onto a CF flange of the vacuum chamber. It can be removed and reused without breaking the window seal. The design is reliable as more than a dozen such windows have survived several bake out and cooling cycles and have been leak tested up to 10(-11) Torr l/s level with a commercial Helium leak detector. The advantages of this technique are ease of assembly and leak proof sealing that survives multiple temperature cycling making the windows reliable and reusable. © 2012 American Institute of Physics

An ultrahigh vacuum fast-scanning and variable temperature scanning tunneling microscope for large scale imaging.

PubMed

Diaconescu, Bogdan; Nenchev, Georgi; de la Figuera, Juan; Pohl, Karsten

2007-10-01

We describe the design and performance of a fast-scanning, variable temperature scanning tunneling microscope (STM) operating from 80 to 700 K in ultrahigh vacuum (UHV), which routinely achieves large scale atomically resolved imaging of compact metallic surfaces. An efficient in-vacuum vibration isolation and cryogenic system allows for no external vibration isolation of the UHV chamber. The design of the sample holder and STM head permits imaging of the same nanometer-size area of the sample before and after sample preparation outside the STM base. Refractory metal samples are frequently annealed up to 2000 K and their cooldown time from room temperature to 80 K is 15 min. The vertical resolution of the instrument was found to be about 2 pm at room temperature. The coarse motor design allows both translation and rotation of the scanner tube. The total scanning area is about 8 x 8 microm(2). The sample temperature can be adjusted by a few tens of degrees while scanning over the same sample area.

Selenium capped monolayer NbSe 2 for two-dimensional superconductivity studies

DOE PAGES

Onishi, Seita; Ugeda, Miguel M.; Zhang, Yi; ...

2016-08-01

Superconductivity in monolayer niobium diselenide (NbSe 2) on bilayer graphene is studied by electrical transport. Monolayer NbSe 2 is grown on bilayer graphene by molecular beam epitaxy and capped with a selenium film to avoid degradation in air. The selenium capped samples have T C = 1.9 K. In situ measurements down to 4 K in ultrahigh vacuum show that the effect of the selenium layer on the transport is negligible. Lastly, the superconducting transition and upper critical fields in air exposed and selenium capped samples are compared. Schematic of monolayer NbSe 2/bilayer graphene with selenium capping layer and electricalmore » contacts.« less

Note: optical optimization for ultrasensitive photon mapping with submolecular resolution by scanning tunneling microscope induced luminescence.

PubMed

Chen, L G; Zhang, C; Zhang, R; Zhang, X L; Dong, Z C

2013-06-01

We report the development of a custom scanning tunneling microscope equipped with photon collection and detection systems. The optical optimization includes the comprehensive design of aspherical lens for light collimation and condensing, the sophisticated piezo stages for in situ lens adjustment inside ultrahigh vacuum, and the fiber-free coupling of collected photons directly onto the ultrasensitive single-photon detectors. We also demonstrate submolecular photon mapping for the molecular islands of porphyrin on Ag(111) under small tunneling currents down to 10 pA and short exposure time down to 1.2 ms/pixel. A high quantum efficiency up to 10(-2) was also observed.

Degradation and crosslinking of perfluoroalkyl polyethers under X-ray irradiation in ultrahigh vacuum

NASA Technical Reports Server (NTRS)

Mori, Shigeyuki; Morales, Wilfredo

1989-01-01

Degradation of three types of commercially available perfluoroalkyl polyethers (PFPE)-Demnum S200, Fomblin Z25, and Krytox 16256-by X-ray irradiation was studied by using X-ray photoemission spectroscopy (XPS) and a mass spectrometer under ultra-high-vacuum conditions. The carbons in the polymers were characterized by chemical shifts of Cls binding energies. Gaseous products containing COF2 and low-molecular-weight fluorocarbons were formed. From Fomblin Z25, which has acetal linkages (-OCF2O-), a large quantity of COF2 gas was evolved. Liquid products became tacky after a long irradiation time, and some did not dissolve in Freon. High-pressure liquid chromatography (HPLC) showed that molecular weight distribution became broader and that higher molecular weight polymers were formed from Demnum and Krytox. We concluded from these results that degradation and cross-linking took place simultaneously. Demnum crosslinked more easily than the other fluids. The time dependence of both XPS spectra of Cls and mass spectra showed that C-O-bonded carbons in PFPE'S were removed faster than other carbons. There was no substrate effect on the degradation reaction because the first-order rate constants calculated from the change of gaseous products were similar when stainless steel (440C) and gold-coated surfaces were used. Metal fluorides were formed on stainless steel during the reaction. A mechanism for the degradation of PFPE'S is discussed on the basis of their molecular structures.

Vacuum phonon tunneling.

PubMed

Altfeder, Igor; Voevodin, Andrey A; Roy, Ajit K

2010-10-15

Field-induced phonon tunneling, a previously unknown mechanism of interfacial thermal transport, has been revealed by ultrahigh vacuum inelastic scanning tunneling microscopy (STM). Using thermally broadened Fermi-Dirac distribution in the STM tip as in situ atomic-scale thermometer we found that thermal vibrations of the last tip atom are effectively transmitted to sample surface despite few angstroms wide vacuum gap. We show that phonon tunneling is driven by interfacial electric field and thermally vibrating image charges, and its rate is enhanced by surface electron-phonon interaction.

A robust molecular probe for Ångstrom-scale analytics in liquids

PubMed Central

Nirmalraj, Peter; Thompson, Damien; Dimitrakopoulos, Christos; Gotsmann, Bernd; Dumcenco, Dumitru; Kis, Andras; Riel, Heike

2016-01-01

Traditionally, nanomaterial profiling using a single-molecule-terminated scanning probe is performed at the vacuum–solid interface often at a few Kelvin, but is not a notion immediately associated with liquid–solid interface at room temperature. Here, using a scanning tunnelling probe functionalized with a single C60 molecule stabilized in a high-density liquid, we resolve low-dimensional surface defects, atomic interfaces and capture Ångstrom-level bond-length variations in single-layer graphene and MoS2. Atom-by-atom controllable imaging contrast is demonstrated at room temperature and the electronic structure of the C60–metal probe complex within the encompassing liquid molecules is clarified using density functional theory. Our findings demonstrates that operating a robust single-molecular probe is not restricted to ultra-high vacuum and cryogenic settings. Hence the scope of high-precision analytics can be extended towards resolving sub-molecular features of organic elements and gauging ambient compatibility of emerging layered materials with atomic-scale sensitivity under experimentally less stringent conditions. PMID:27516157

Self-assembly of dodecaphenyl POSS thin films

NASA Astrophysics Data System (ADS)

Handke, Bartosz; Klita, Łukasz; Niemiec, Wiktor

2017-12-01

The self-assembly abilities of Dodecaphenyl Polyhedral Oligomeric Silsesquioxane thin films on Si(1 0 0) surfaces were studied. Due to their thermal properties - relatively low sublimation temperature and preservation of molecular structure - cage type silsesquioxanes are ideal material for the preparation of a thin films by Physical Vapor Deposition. The Ultra-High Vacuum environment and the deposition precision of the PVD method enable the study of early stages of thin film growth and its molecular organization. X-ray Reflectivity and Atomic Force Microscopy measurements allow to pursuit size-effects in the structure of thin films with thickness ranges from less than a single molecular layer up to several tens of layers. Thermal treatment of the thin films triggered phase change: from a poorly ordered polycrystalline film into a well-ordered multilayer structure. Self-assembly of the layers is the effect of the π-stacking of phenyl rings, which force molecules to arrange in a superlattice, forming stacks of alternating organic-inorganic layers.

An ultrahigh vacuum multipurpose specimen chamber with sample introduction system for in situ transmission electron microscopy investigations

NASA Technical Reports Server (NTRS)

Heinemann, K.; Poppa, H.

1986-01-01

A commercial transmission electron microscope (TEM), with flat-plate upper pole piece configuration of the objective lens, and top-entry specimen introduction was modified by introducing an ultrahigh vacuum (UHV) specimen chamber for in situ TEM experimentation. The pumping and design principles and special features of this UHV chamber, which makes it possible to obtain 5 x 10 to the -10th mbar pressure at the site of the specimen, while maintaining the airlock system that allows operation in the 10 to the -10th mbar range within 15 min after specimen change, are described. Design operating pressures and image quality (resolution of metal particles smaller than 1 nm in size) were achieved. Schematic drawings and design dimensions are included.

Catalytic Chemistry of Hydrocarbon Conversion Reactions on Metallic Single Crystals

NASA Astrophysics Data System (ADS)

Tysoe, Wilfred T.

The ability to be able to follow the chemistry of adsorbates on model catalyst surfaces has, in principle, allowed us to peer inside the “black box” of a catalytic reaction and understand the pathway. Such a strategy is most simply implemented for well-ordered single crystal model catalysts for which the catalytic reaction proceeds in ultrahigh vacuum. Thus, in order to be a good model for the supported catalyst, the single crystal should catalyze the reactions with kinetics identical to those for the supported system. This chapter focuses on catalytic systems that fulfill these criteria, namely alkene and alkyne hydrogenation and acetylene cyclotrimerization on Pd(111). The surface chemistry and geometries of the reactants in ultrahigh vacuum are explored in detail allowing fundamental insights into the catalytic reaction pathways to be obtained.

In vivo oxidation in remelted highly cross-linked retrievals.

PubMed

Currier, B H; Van Citters, D W; Currier, J H; Collier, J P

2010-10-20

Elimination of free radicals to prevent oxidation has played a major role in the development and product differentiation of the latest generation of highly cross-linked ultra-high molecular weight polyethylene bearing materials. In the current study, we (1) examined oxidation in a series of retrieved remelted highly cross-linked ultra-high molecular weight polyethylene bearings from a number of device manufacturers and (2) compared the retrieval results with findings for shelf-stored control specimens. The hypothesis was that radiation-cross-linked remelted ultra-high molecular weight polyethylene would maintain oxidative stability in vivo comparable with the stability during shelf storage and in published laboratory aging tests. Fifty remelted highly cross-linked ultra-high molecular weight polyethylene acetabular liners and nineteen remelted highly cross-linked ultra-high molecular weight polyethylene tibial inserts were received after retrieval from twenty-one surgeons from across the U.S. Thirty-two of the retrievals had been in vivo for two years or more. Each was measured for oxidation with use of Fourier transform infrared spectroscopy. A control series of remelted highly cross-linked ultra-high molecular weight polyethylene acetabular liners from three manufacturers was analyzed with electron paramagnetic resonance spectroscopy to measure free radical content and with Fourier transform infrared spectroscopy to measure oxidation initially and after eight to nine years of shelf storage in air. The never-implanted, shelf-aged controls had no measurable free-radical content initially or after eight to nine years of shelf storage. The never-implanted controls showed no increase in oxidation during shelf storage. Oxidation measurements showed measurable oxidation in 22% of the retrieved remelted highly cross-linked liners and inserts after an average of two years in vivo. Because never-implanted remelted highly cross-linked ultra-high molecular weight polyethylene materials had no measurable free-radical concentration and no increase in oxidation during shelf storage, these materials were expected to be oxidation-resistant in vivo. However, some remelted highly cross-linked ultra-high molecular weight polyethylene retrievals showed measurable oxidation after an average of more than two years in vivo. This apparent departure from widely expected behavior requires continued study of the process of in vivo oxidation of ultra-high molecular weight polyethylene materials.

Note: Ultra-low birefringence dodecagonal vacuum glass cell.

PubMed

Brakhane, Stefan; Alt, Wolfgang; Meschede, Dieter; Robens, Carsten; Moon, Geol; Alberti, Andrea

2015-12-01

We report on an ultra-low birefringence dodecagonal glass cell for ultra-high vacuum applications. The epoxy-bonded trapezoidal windows of the cell are made of SF57 glass, which exhibits a very low stress-induced birefringence. We characterize the birefringence Δn of each window with the cell under vacuum conditions, obtaining values around 10(-8). After baking the cell at 150 °C, we reach a pressure below 10(-10) mbar. In addition, each window is antireflection coated on both sides, which is highly desirable for quantum optics experiments and precision measurements.

Note: Hollow cathode lamp with integral, high optical efficiency isolation valve: a modular vacuum ultraviolet source.

PubMed

Roberts, F Sloan; Anderson, Scott L

2013-12-01

The design and operating conditions of a hollow cathode discharge lamp for the generation of vacuum ultraviolet radiation, suitable for ultrahigh vacuum (UHV) application, are described in detail. The design is easily constructed, and modular, allowing it to be adapted to different experimental requirements. A thin isolation valve is built into one of the differential pumping stages, isolating the discharge section from the UHV section, both for vacuum safety and to allow lamp maintenance without venting the UHV chamber. The lamp has been used both for ultraviolet photoelectron spectroscopy of surfaces and as a "soft" photoionization source for gas-phase mass spectrometry.

A low-energy metal-ion source for primary ion deposition and accelerated ion doping during molecular-beam epitaxy

NASA Astrophysics Data System (ADS)

Hasan, M.-A.; Knall, J.; Barnett, S. A.; Rockett, A.; Sundgren, J.-E.

1987-10-01

A single-grid electron-impact ultrahigh vacuum (UHV) compatible low-energy ion gun capable of operating with a low vapor pressure solid source material such as In is presented. The gun consists of a single chamber which integrates the functions of an effusion cell, a vapor transport tube, and a glow discharge ionizer. The initial results of experiments designed to study the role of ion/surface interactions during nucleation and the early stages of crystal growth in UHV revealed that, for deposition on amorphous substrates, the use of a partially ionized In(+) beam resulted in a progressive shift towards larger island sizes, a decreased rate of secondary nucleation, and a more uniform island size distribution.

Electrons, Photons, and Force: Quantitative Single-Molecule Measurements from Physics to Biology

PubMed Central

2011-01-01

Single-molecule measurement techniques have illuminated unprecedented details of chemical behavior, including observations of the motion of a single molecule on a surface, and even the vibration of a single bond within a molecule. Such measurements are critical to our understanding of entities ranging from single atoms to the most complex protein assemblies. We provide an overview of the strikingly diverse classes of measurements that can be used to quantify single-molecule properties, including those of single macromolecules and single molecular assemblies, and discuss the quantitative insights they provide. Examples are drawn from across the single-molecule literature, ranging from ultrahigh vacuum scanning tunneling microscopy studies of adsorbate diffusion on surfaces to fluorescence studies of protein conformational changes in solution. PMID:21338175

Optical glow spectra arising from low-energy N2, N2(+) and electron bombardment of MgF2 surfaces

NASA Technical Reports Server (NTRS)

Qi, J.; Barnes, A. V.; Espy, S. L.; Riehl-Chudoba, M.; Sun, C.-N.; Albridge, R. G.; Tolk, N. H.

1991-01-01

Photon emission spectra resulting from the impact of N2, N2(+), and electron beams on magnesium fluoride in an ultrahigh vacuum environment were measured and compared for beam energies in the range 200-2000 eV. Unexpectedly, only the ion- and electron-induced spectra exhibited broad fluorescence. The observed data suggest that the broad fluorescence arising from low-energy ion bombardment is due primarily to the transfer of electronic energy to the surface by resonance or Auger neutralization. Since molecular nitrogen is a major constituent of the atmosphere at orbital altitudes, these measurements bear directly on radiation-induced glow and erosion processes on surfaces of spacecraft in low-earth orbit.

Multifunctional ultra-high vacuum apparatus for studies of the interactions of chemical warfare agents on complex surfaces

NASA Astrophysics Data System (ADS)

Wilmsmeyer, Amanda R.; Gordon, Wesley O.; Davis, Erin Durke; Mantooth, Brent A.; Lalain, Teri A.; Morris, John R.

2014-01-01

A fundamental understanding of the surface chemistry of chemical warfare agents is needed to fully predict the interaction of these toxic molecules with militarily relevant materials, catalysts, and environmental surfaces. For example, rules for predicting the surface chemistry of agents can be applied to the creation of next generation decontaminants, reactive coatings, and protective materials for the warfighter. Here, we describe a multifunctional ultra-high vacuum instrument for conducting comprehensive studies of the adsorption, desorption, and surface chemistry of chemical warfare agents on model and militarily relevant surfaces. The system applies reflection-absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and mass spectrometry to study adsorption and surface reactions of chemical warfare agents. Several novel components have been developed to address the unique safety and sample exposure challenges that accompany the research of these toxic, often very low vapor pressure, compounds. While results of vacuum-based surface science techniques may not necessarily translate directly to environmental processes, learning about the fundamental chemistry will begin to inform scientists about the critical aspects that impact real-world applications.

Multifunctional ultra-high vacuum apparatus for studies of the interactions of chemical warfare agents on complex surfaces.

PubMed

Wilmsmeyer, Amanda R; Gordon, Wesley O; Davis, Erin Durke; Mantooth, Brent A; Lalain, Teri A; Morris, John R

2014-01-01

A fundamental understanding of the surface chemistry of chemical warfare agents is needed to fully predict the interaction of these toxic molecules with militarily relevant materials, catalysts, and environmental surfaces. For example, rules for predicting the surface chemistry of agents can be applied to the creation of next generation decontaminants, reactive coatings, and protective materials for the warfighter. Here, we describe a multifunctional ultra-high vacuum instrument for conducting comprehensive studies of the adsorption, desorption, and surface chemistry of chemical warfare agents on model and militarily relevant surfaces. The system applies reflection-absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and mass spectrometry to study adsorption and surface reactions of chemical warfare agents. Several novel components have been developed to address the unique safety and sample exposure challenges that accompany the research of these toxic, often very low vapor pressure, compounds. While results of vacuum-based surface science techniques may not necessarily translate directly to environmental processes, learning about the fundamental chemistry will begin to inform scientists about the critical aspects that impact real-world applications.

Multifunctional ultra-high vacuum apparatus for studies of the interactions of chemical warfare agents on complex surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilmsmeyer, Amanda R.; Morris, John R.; Gordon, Wesley O.

2014-01-15

A fundamental understanding of the surface chemistry of chemical warfare agents is needed to fully predict the interaction of these toxic molecules with militarily relevant materials, catalysts, and environmental surfaces. For example, rules for predicting the surface chemistry of agents can be applied to the creation of next generation decontaminants, reactive coatings, and protective materials for the warfighter. Here, we describe a multifunctional ultra-high vacuum instrument for conducting comprehensive studies of the adsorption, desorption, and surface chemistry of chemical warfare agents on model and militarily relevant surfaces. The system applies reflection-absorption infrared spectroscopy, x-ray photoelectron spectroscopy, and mass spectrometry tomore » study adsorption and surface reactions of chemical warfare agents. Several novel components have been developed to address the unique safety and sample exposure challenges that accompany the research of these toxic, often very low vapor pressure, compounds. While results of vacuum-based surface science techniques may not necessarily translate directly to environmental processes, learning about the fundamental chemistry will begin to inform scientists about the critical aspects that impact real-world applications.« less

The influence of titanium adhesion layer oxygen stoichiometry on thermal boundary conductance at gold contacts

NASA Astrophysics Data System (ADS)

Olson, David H.; Freedy, Keren M.; McDonnell, Stephen J.; Hopkins, Patrick E.

2018-04-01

We experimentally demonstrate the role of oxygen stoichiometry on the thermal boundary conductance across Au/TiOx/substrate interfaces. By evaporating two different sets of Au/TiOx/substrate samples under both high vacuum and ultrahigh vacuum conditions, we vary the oxygen composition in the TiOx layer from 0 ≤ x ≤ 2.85. We measure the thermal boundary conductance across the Au/TiOx/substrate interfaces with time-domain thermoreflectance and characterize the interfacial chemistry with x-ray photoemission spectroscopy. Under high vacuum conditions, we speculate that the environment provides a sufficient flux of oxidizing species to the sample surface such that one essentially co-deposits Ti and these oxidizing species. We show that slower deposition rates correspond to a higher oxygen content in the TiOx layer, which results in a lower thermal boundary conductance across the Au/TiOx/substrate interfacial region. Under the ultrahigh vacuum evaporation conditions, pure metallic Ti is deposited on the substrate surface. In the case of quartz substrates, the metallic Ti reacts with the substrate and getters oxygen, leading to a TiOx layer. Our results suggest that Ti layers with relatively low oxygen compositions are best suited to maximize the thermal boundary conductance.

Features of Extrusion Processing of Ultrahigh Molecular Weight Polyethylene. Experiment and Theory

NASA Astrophysics Data System (ADS)

Skul‧skii, O. I.; Slavnov, E. V.

2018-05-01

Experimental studies have been made of the permissible regimes of processing ultrahigh molecular weight polyethylene GUR 2122 with molecular mass of 4.5 million g/moles in a laboratory extruder with an auger diameter 32 mm and a ratio L/D = 20 at temperatures of 155-165oC. On the basis of rotational viscometry, the rheological properties of the melt are described. A mathematical model and a numerical method for calculating the motion of ultrahigh molecular weight polyethylene melt in the auger and in the moulding rigging are proposed. The velocity and stress fields have been determined.

Water adsorption on a liquid surface.

PubMed

Lovelock, Kevin R J; Smith, Emily F; Deyko, Alexey; Villar-Garcia, Ignacio J; Licence, Peter; Jones, Robert G

2007-12-14

Monolayer adsorption of water onto an ionic liquid in ultra-high vacuum has been demonstrated, revealing a heat of adsorption which exceeds the heat of absorption into the bulk liquid by approximately 40 kJ mol(-1).

Industry-relevant magnetron sputtering and cathodic arc ultra-high vacuum deposition system for in situ x-ray diffraction studies of thin film growth using high energy synchrotron radiation.

PubMed

Schroeder, J L; Thomson, W; Howard, B; Schell, N; Näslund, L-Å; Rogström, L; Johansson-Jõesaar, M P; Ghafoor, N; Odén, M; Nothnagel, E; Shepard, A; Greer, J; Birch, J

2015-09-01

We present an industry-relevant, large-scale, ultra-high vacuum (UHV) magnetron sputtering and cathodic arc deposition system purposefully designed for time-resolved in situ thin film deposition/annealing studies using high-energy (>50 keV), high photon flux (>10(12) ph/s) synchrotron radiation. The high photon flux, combined with a fast-acquisition-time (<1 s) two-dimensional (2D) detector, permits time-resolved in situ structural analysis of thin film formation processes. The high-energy synchrotron-radiation based x-rays result in small scattering angles (<11°), allowing large areas of reciprocal space to be imaged with a 2D detector. The system has been designed for use on the 1-tonne, ultra-high load, high-resolution hexapod at the P07 High Energy Materials Science beamline at PETRA III at the Deutsches Elektronen-Synchrotron in Hamburg, Germany. The deposition system includes standard features of a typical UHV deposition system plus a range of special features suited for synchrotron radiation studies and industry-relevant processes. We openly encourage the materials research community to contact us for collaborative opportunities using this unique and versatile scientific instrument.

Tribological characteristics of a composite total-surface hip replacement

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.; Roberts, J. C.; Ling, F. F.

1982-01-01

Continuous fiber, woven E glass composite femoral shells having the same elastic properties as bone were fabricated. The shells were then encrusted with filled epoxy wear resistant coatings and run dry against ultrahigh molecular weight polyethylene acetabular cups in 42,000 and 250,000 cycle wear tests on a total hip simulator. The tribological characteristics of these continuous fiber particulate composite femoral shells articulating with ultrahigh molecular weight polyethylene acetabular cups were comparable to those of a vitallium ball articulating with an ultrahigh molecular weight polyethylene acetabular cup.

Note: Hollow cathode lamp with integral, high optical efficiency isolation valve: A modular vacuum ultraviolet source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sloan Roberts, F.; Anderson, Scott L.

2013-12-15

The design and operating conditions of a hollow cathode discharge lamp for the generation of vacuum ultraviolet radiation, suitable for ultrahigh vacuum (UHV) application, are described in detail. The design is easily constructed, and modular, allowing it to be adapted to different experimental requirements. A thin isolation valve is built into one of the differential pumping stages, isolating the discharge section from the UHV section, both for vacuum safety and to allow lamp maintenance without venting the UHV chamber. The lamp has been used both for ultraviolet photoelectron spectroscopy of surfaces and as a “soft” photoionization source for gas-phase massmore » spectrometry.« less

Multifunctional Ultra-high Vacuum Apparatus for Studies of the Interactions of Chemical Warfare Agents on Complex Surfaces

DTIC Science & Technology

2014-01-02

of the formation of a hydrogen-bonded hydroxyl. Characteristic modes of the sarin molecule itself are also ob- served. These experimental results show...chemical warfare agent, surface science, uptake, decontamination, filtration , UHV, XPS, FTIR, TPD REPORT DOCUMENTATION PAGE 11. SPONSOR/MONITOR’S...challenges that accompany the research of these toxic, often very low vapor pressure, compounds. While results of vacuum-based surface science

Etching of Cr tips for scanning tunneling microscopy of cleavable oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Huang, Dennis; Liu, Stephen; Zeljkovic, Ilija

Here, we report a detailed three-step roadmap for the fabrication and characterization of bulk Cr tips for spin-polarized scanning tunneling microscopy. Our strategy uniquely circumvents the need for ultra-high vacuum preparation of clean surfaces or films. First, we demonstrate the role of ex situ electrochemical etch parameters on Cr tip apex geometry, using scanning electron micrographs of over 70 etched tips. Second, we describe the suitability of the in situ cleaved surface of the layered antiferromagnet La 1.4Sr 1.6Mn 2O 7 to evaluate the spin characteristics of the Cr tip, replacing the ultra-high vacuum-prepared test samples that have been usedmore » in prior studies. Third, we outline a statistical algorithm that can effectively delineate closely spaced or irregular cleaved step edges, to maximize the accuracy of step height and spin-polarization measurements.« less

High pressure reaction cell and transfer mechanism for ultrahigh vacuum spectroscopic chambers

NASA Astrophysics Data System (ADS)

Nelson, A. E.; Schulz, K. H.

2000-06-01

A novel high pressure reaction cell and sample transfer mechanism for ultrahigh vacuum (UHV) spectroscopic chambers is described. The design employs a unique modification of a commercial load-lock transfer system to emulate a tractable microreactor. The reaction cell has an operating pressure range of <1×10-4 to 1000 Torr and can be evacuated to UHV conditions to enable sample transfer into the spectroscopic chamber. Additionally, a newly designed sample holder equipped with electrical and thermocouple contacts is described. The sample holder is capable of resistive specimen heating to 400 and 800 °C with current requirements of 14 A (2 V) and 25 A (3.5 V), respectively. The design enables thorough material science characterization of catalytic reactions and the surface chemistry of catalytic materials without exposing the specimen to atmospheric contaminants. The system is constructed primarily from readily available commercial equipment allowing its rapid implementation into existing laboratories.

Set-up of a high-resolution 300 mK atomic force microscope in an ultra-high vacuum compatible (3)He/10 T cryostat.

PubMed

von Allwörden, H; Ruschmeier, K; Köhler, A; Eelbo, T; Schwarz, A; Wiesendanger, R

2016-07-01

The design of an atomic force microscope with an all-fiber interferometric detection scheme capable of atomic resolution at about 500 mK is presented. The microscope body is connected to a small pumped (3)He reservoir with a base temperature of about 300 mK. The bakeable insert with the cooling stage can be moved from its measurement position inside the bore of a superconducting 10 T magnet into an ultra-high vacuum chamber, where the tip and sample can be exchanged in situ. Moreover, single atoms or molecules can be evaporated onto a cold substrate located inside the microscope. Two side chambers are equipped with standard surface preparation and surface analysis tools. The performance of the microscope at low temperatures is demonstrated by resolving single Co atoms on Mn/W(110) and by showing atomic resolution on NaCl(001).

Lubrication by Diamond and Diamondlike Carbon Coatings

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1997-01-01

Regardless of environment (ultrahigh vacuum, humid air, dry nitrogen, or water), ion-beam-deposited diamondlike carbon (DLC) and nitrogen-ion-implanted, chemical-vapor-deposited (CVD) diamond films had low steady-state coefficients of friction (less than 0.1) and low wear rates (less than or equal to 10(exp -6)cu mm/N(dot)m). These films can be used as effective wear-resistant, self-lubricating coatings regardless of environment. On the other hand, as-deposited, fine-grain CVD diamond films; polished, coarse-grain CVD diamond films; and polished and then fluorinated, coarse-grain CVD diamond films can be used as effective wear-resistant, self-lubricating coatings in humid air, in dry nitrogen, and in water, but they had a high coefficient of friction and a high wear rate in ultrahigh vacuum. The polished, coarse-grain CVD diamond film revealed an extremely low wear rate, far less than 10(exp 10) cu mm/N(dot)m, in water.

Etching of Cr tips for scanning tunneling microscopy of cleavable oxides

DOE PAGES

Huang, Dennis; Liu, Stephen; Zeljkovic, Ilija; ...

2017-02-21

Here, we report a detailed three-step roadmap for the fabrication and characterization of bulk Cr tips for spin-polarized scanning tunneling microscopy. Our strategy uniquely circumvents the need for ultra-high vacuum preparation of clean surfaces or films. First, we demonstrate the role of ex situ electrochemical etch parameters on Cr tip apex geometry, using scanning electron micrographs of over 70 etched tips. Second, we describe the suitability of the in situ cleaved surface of the layered antiferromagnet La 1.4Sr 1.6Mn 2O 7 to evaluate the spin characteristics of the Cr tip, replacing the ultra-high vacuum-prepared test samples that have been usedmore » in prior studies. Third, we outline a statistical algorithm that can effectively delineate closely spaced or irregular cleaved step edges, to maximize the accuracy of step height and spin-polarization measurements.« less

Note: Ultra-low birefringence dodecagonal vacuum glass cell

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brakhane, Stefan, E-mail: brakhane@iap.uni-bonn.de; Alt, Wolfgang; Meschede, Dieter

We report on an ultra-low birefringence dodecagonal glass cell for ultra-high vacuum applications. The epoxy-bonded trapezoidal windows of the cell are made of SF57 glass, which exhibits a very low stress-induced birefringence. We characterize the birefringence Δn of each window with the cell under vacuum conditions, obtaining values around 10{sup −8}. After baking the cell at 150 °C, we reach a pressure below 10{sup −10} mbar. In addition, each window is antireflection coated on both sides, which is highly desirable for quantum optics experiments and precision measurements.

Ultra high vacuum broad band high power microwave window

DOEpatents

Nguyen-Tuong, V.; Dylla, H.F. III

1997-11-04

An improved high vacuum microwave window has been developed that utilizes high density polyethylene coated on two sides with SiOx, SiNx, or a combination of the two. The resultant low dielectric and low loss tangent window creates a low outgassing, low permeation seal through which broad band, high power microwave energy may be passed. No matching device is necessary and the sealing technique is simple. The features of the window are broad band transmission, ultra-high vacuum compatibility with a simple sealing technique, low voltage standing wave ratio, high power transmission and low cost. 5 figs.

In-vacuum scattered light reduction with black cupric oxide surfaces for sensitive fluorescence detection.

PubMed

Norrgard, E B; Sitaraman, N; Barry, J F; McCarron, D J; Steinecker, M H; DeMille, D

2016-05-01

We demonstrate a simple and easy method for producing low-reflectivity surfaces that are ultra-high vacuum compatible, may be baked to high temperatures, and are easily applied even on complex surface geometries. Black cupric oxide (CuO) surfaces are chemically grown in minutes on any copper surface, allowing for low-cost, rapid prototyping, and production. The reflective properties are measured to be comparable to commercially available products for creating optically black surfaces. We describe a vacuum apparatus which uses multiple blackened copper surfaces for sensitive, low-background detection of molecules using laser-induced fluorescence.

Ultra high vacuum broad band high power microwave window

DOEpatents

Nguyen-Tuong, Viet; Dylla, III, Henry Frederick

1997-01-01

An improved high vacuum microwave window has been developed that utilizes high density polyethylene coated on two sides with SiOx, SiNx, or a combination of the two. The resultant low dielectric and low loss tangent window creates a low outgassing, low permeation seal through which broad band, high power microwave energy may be passed. No matching device is necessary and the sealing technique is simple. The features of the window are broad band transmission, ultra-high vacuum compatibility with a simple sealing technique, low voltage standing wave ratio, high power transmission and low cost.

Ethers on Si(001): A Prime Example for the Common Ground between Surface Science and Molecular Organic Chemistry.

PubMed

Pecher, Lisa; Laref, Slimane; Raupach, Marc; Tonner, Ralf

2017-11-20

By using computational chemistry it has been shown that the adsorption of ether molecules on Si(001) under ultrahigh vacuum conditions can be understood with classical concepts of organic chemistry. Detailed analysis of the two-step reaction mechanism-1) formation of a dative bond between the ether oxygen atom and a Lewis acidic surface atom and 2) nucleophilic attack of a nearby Lewis basic surface atom-shows that it mirrors acid-catalyzed ether cleavage in solution. The O-Si dative bond is the strongest of its kind, and the reactivity in step 2 defies the Bell-Evans-Polanyi principle. Electron rearrangement during C-O bond cleavage has been visualized with a newly developed method for analyzing bonding, which shows that the mechanism of nucleophilic substitutions on semiconductor surfaces is identical to molecular S N 2 reactions. Our findings illustrate how surface science and molecular chemistry can mutually benefit from each other and unexpected insight can be gained. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Friction and Wear Properties of As-Deposited and Carbon Ion-Implanted Diamond Films

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1996-01-01

Recent work on the friction and wear properties of as-deposited and carbon ion-implanted diamond films was reviewed. Diamond films were produced by the microwave plasma chemical vapor deposition (CVD) technique. Diamond films with various grain sizes and surface roughnesses were implanted with carbon ions at 60 keV ion energy, resulting in a dose of 1.2 x 10(exp 17) carbon ions per cm(exp 2). Various analytical techniques, including Raman spectroscopy, proton recoil analysis, Rutherford backscattering, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction, were utilized to characterize the diamond films. Sliding friction experiments were conducted with a polished natural diamond pin in contact with diamond films in the three environments: humid air (40% relative humidity), dry nitrogen (less than 1 percent relative humidity), and ultrahigh vacuum (10(exp -7) Pa). The CVD diamond films indeed have friction and wear properties similar to those of natural diamond in the three environments. The as-deposited, fine-grain diamond films can be effectively used as self-lubricating, wear-resistant coatings that have low coefficients of friction (0.02 to 0.04) and low wear rates (10(exp -7) to lO(exp -8) mm(exp 3) N(exp -1) m(exp -1)) in both humid air and dry nitrogen. However, they have high coefficients of friction (1.5 to 1.7) and a high wear rate (10(exp -4) mm(exp 7) N(exp -1) m(exp -1)) in ultrahigh vacuum. The carbon ion implantation produced a thin surficial layer (less than 0.1 micron thick) of amorphous, non-diamond carbon on the diamond films. In humid air and dry nitrogen, the ion-implanted, fine and coarse-grain diamond films have a low coefficient of friction (around 0.1) and a low wear rate (10(exp -7) mm(exp 3) N(exp -1) m(exp-1)). Even in ultrahigh vacuum, the presence of the non-diamond carbon layer reduced the coefficient of friction of fine-grain diamond films to 0.1 or lower and the wear rate to 10(exp -6) mm(exp 3) N(exp -1) m(exp -1). Thus, the carbon ion-implanted, fine-grain diamond films can be effectively used as wear-resistant, self-lubricating coatings not only in air and dry nitrogen, but also in ultrahigh vacuum.

Evaporation rate and vapor pressure of selected polymeric lubricating oils.

NASA Technical Reports Server (NTRS)

Gardos, M. N.

1973-01-01

A recently developed ultrahigh-vacuum quartz spring mass sorption microbalance has been utilized to measure the evaporation rates of several low-volatility polymeric lubricating oils at various temperatures. The evaporation rates are used to calculate the vapor pressures by the Langmuir equation. A method is presented to accurately estimate extended temperature range evaporation rate and vapor pressure data for polymeric oils, incorporating appropriate corrections for the increases in molecular weight and the change in volatility of the progressively evaporating polymer fractions. The logarithms of the calculated data appear to follow linear relationships within the test temperature ranges, when plotted versus 1000/T. These functions and the observed effusion characteristics of the fluids on progressive volatilization are useful in estimating evaporation rate and vapor pressure changes on evaporative depletion.

Fundamental insights into interfacial catalysis.

PubMed

Gong, Jinlong; Bao, Xinhe

2017-04-03

Surface and interfacial catalysis plays a vital role in chemical industries, electrochemistry and photochemical reactions. The challenges of modern chemistry are to optimize the chemical reaction processes and understand the detailed mechanism of chemical reactions. Since the early 1960s, the foundation of surface science systems has allowed the study of surface and interfacial phenomena on atomic/molecular level, and thus brought a number of significant developments to fundamental and technological processes, such as catalysis, material science and biochemistry, just to name a few. This themed issue describes the recent advances and developments in the fundamental understanding of surface and interfacial catalysis, encompassing areas of knowledge from metal to metal oxide, carbide, graphene, hexagonal boron nitride, and transition metal dichalcogenides under ultrahigh vacuum conditions, as well as under realistic reaction conditions.

Molecular beam epitaxy of quasi-freestanding transition metal disulphide monolayers on van der Waals substrates: a growth study

NASA Astrophysics Data System (ADS)

Hall, Joshua; Pielić, Borna; Murray, Clifford; Jolie, Wouter; Wekking, Tobias; Busse, Carsten; Kralj, Marko; Michely, Thomas

2018-04-01

Based on an ultra-high vacuum compatible two-step molecular beam epitaxy synthesis with elemental sulphur, we grow clean, well-oriented, and almost defect-free monolayer islands and layers of the transition metal disulphides MoS2, TaS2 and WS2. Using scanning tunneling microscopy and low energy electron diffraction we investigate systematically how to optimise the growth process, and provide insight into the growth and annealing mechanisms. A large band gap of 2.55 eV and the ability to move flakes with the scanning tunneling microscope tip both document the weak interaction of MoS2 with its substrate consisting of graphene grown on Ir(1 1 1). As the method works for the synthesis of a variety of transition metal disulphides on different substrates, we speculate that it could be of great use for providing hitherto unattainable high quality monolayers of transition metal disulphides for fundamental spectroscopic investigations.

Electronic structure of a laterally graded ZrO2-TiO2 film on Si(100) prepared by metal-organic chemical vapor deposition in ultrahigh vacuum

NASA Astrophysics Data System (ADS)

Richter, J. H.; Karlsson, P. G.; Sandell, A.

2008-05-01

A TiO2-ZrO2 film with laterally graded stoichiometry has been prepared by metal-organic chemical vapor deposition in ultrahigh vacuum. The film was characterized in situ using synchrotron radiation photoelectron spectroscopy (PES) and x-ray absorption spectroscopy. PES depth profiling clearly shows that Ti ions segregate toward the surface region when mixed with ZrO2. The binding energy of the ZrO2 electronic levels is constant with respect to the local vacuum level. The binding energy of the TiO2 electronic levels is aligned to the Fermi level down to a Ti /Zr ratio of about 0.5. At a Ti /Zr ratio between 0.1 and 0.5, the TiO2 related electronic levels become aligned to the local vacuum level. The addition of small amounts of TiO2 to ZrO2 results in a ZrO2 band alignment relative to the Fermi level that is less asymmetric than for pure ZrO2. The band edge positions shift by -0.6eV for a Ti /Zr ratio of 0.03. This is explained in terms of an increase in the work function when adding TiO2, an effect that becomes emphasized by Ti surface segregation.

Liquid gallium rotary electric contract

NASA Technical Reports Server (NTRS)

Przybyszewski, J. S.

1969-01-01

Due to its low vapor pressure, gallium, when substituted for mercury in a liquid slip ring system, transmits substantial amounts of electrical current to rotating components in an ultrahigh vacuum. It features low electrical loss, little or no wear, and long maintenance-free life.

Comprehensive investigation of HgCdTe metalorganic chemical vapor deposition

NASA Technical Reports Server (NTRS)

Raupp, Gregory B.

1993-01-01

The principal objective of this experimental and theoretical research program was to explore the possibility of depositing high quality epitaxial CdTe and HgCdTe at very low pressures through metalorganic chemical vapor deposition (MOCVD). We explored two important aspects of this potential process: (1) the interaction of molecular flow transport and deposition in an MOCVD reactor with a commercial configuration, and (2) the kinetics of metal alkyl source gas adsorption, decomposition and desorption from the growing film surface using ultra high vacuum surface science reaction techniques. To explore the transport-reaction issue, we have developed a reaction engineering analysis of a multiple wafer-in-tube ultrahigh vacuum chemical vapor deposition (UHV/CVD) reactor which allows an estimate of wafer or substrate throughput for a reactor of fixed geometry and a given deposition chemistry with specified film thickness uniformity constraints. The model employs a description of ballistic transport and reaction based on the pseudo-steady approximation to the Boltzmann equation in the limit of pure molecular flow. The model representation takes the form of an integral equation for the flux of each reactant or intermediate species to the wafer surfaces. Expressions for the reactive sticking coefficients (RSC) for each species must be incorporated in the term which represents reemission from a wafer surface. The interactions of MOCVD precursors with Si and CdTe were investigated using temperature programmed desorption (TPD) in ultra high vacuum combined with Auger electron spectroscopy (AES). These studies revealed that diethyltellurium (DETe) and dimethylcadmium (DMCd) adsorb weakly on clean Si(100) and desorb upon heating without decomposing. These precursors adsorb both weakly and strongly on CdTe(111)A, with DMCd exhibiting the stronger interaction with the surface than DETe.

A comparison of the wear of cross-linked polyethylene against itself with the wear of ultra-high molecular weight polyethylene against itself.

PubMed

Joyce, T J; Unsworth, A

1996-01-01

Wear tests were carried out on reciprocating pin-on-plate machines which had pins loaded at 10 N and 40 N. The materials tested were irradiated cross-linked polyethylene sliding against itself, irradiated ultra-high molecular weight polyethylene sliding against itself and non-irradiated ultra-high molecular weight polyethylene sliding against itself. After 153.5 km of sliding, the non-irradiated ultra-high molecular weight polyethylene plates and pins showed mean wear factors under 10 N loads, or a nominal contact stress of 0.51 MPa, of 84.0 x 10(-6) mm3/N m for the plates and 81.3 x 10(-6) mm3/N m for the pins. Under 40 N loads, or a nominal contact stress of 2.04 MPa, the non-irradiated ultra-high molecular weight polyethylene pins sheared at 22.3 km. At the last measurement point prior to this failure, 19.1 km, wear factors of 158 x 10(-6) mm3/N m for the plates and 85.0 x 10(-6) mm3/N m for the pins had been measured. After 152.8 km. the irradiated ultra-high molecular weight polyethylene plates and pins showed mean wear factors under 10 N loads of 59.8 x 10(-6) mm3/N m for the plates and 31.1 x 10(-6) mm3/N m for the pins. In contrast, after 150.2 km, a mean wear factor of 0.72 x 10(-6) mm3/N m was found for the irradiated cross-linked polyethylene plates compared with 0.053 x 10(-6) mm3/N m for the irradiated cross-linked polyethylene pins.

The Effect of O2, H2O, and N2 on the Fatigue Crack Growth Behavior of an Alpha + Beta Titanium Alloy at 24 C and 177 C

NASA Technical Reports Server (NTRS)

Smith, Stephen W.; Piascik, Robert S.

2001-01-01

To study the effects of atmospheric species on the fatigue crack growth behavior of an a+B titanium alloy (Ti 6-2-2-2-2) at room temperature and 177 C, fatigue tests were performed in laboratory air, ultrahigh vacuum, and high purity water vapor, oxygen, nitrogen and helium at various partial pressures. Accelerated fatigue crack growth rates in laboratory air compared to ultrahigh vacuum are linked to the damaging effects of both water vapor and oxygen. Observations of the fatigue crack growth behavior in ultrahigh purity environments, along with surface film analysis using X-ray photoelectron spectroscopy (XPS), suggest that multiple crack-tip processes govern the damaging effects of air. Three possible mechanisms are proposed: 1) at low pressure (less than 10(exp -1) Pa), accelerated da/dN is likely due to monolayer adsorption on crack-tip surfaces presumably resulting in decreased bond strengths at the fatigue crack tip, 2) for pressures greater than 10(exp -1) Pa, accelerated da/dN in oxygen may result from oxidation at the crack tip limiting reversible slip, and 3) in water vapor, absorption of atomic hydrogen at the reactive crack tip resulting in process zone embrittlement.

Electron-stimulated reactions in nanoscale water films adsorbed on α-Al 2O 3 (0001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Petrik, Nikolay G.; Kimmel, Gregory A.

The radiation-induced decomposition and desorption of nanoscale amorphous solid water (D2O) films adsorbed on -Al2O3(0001) surface was studied at low temperature in ultrahigh vacuum using temperature programmed desorption (TPD) and electron stimulated desorption (ESD) with a mono-energetic, low energy electron source. ESD yields of molecular products ( D2, O2 and D¬2O) and the total sputtering yield increased with increasing D2O coverage up to ~15 water monolayers (i.e. ~15 1015 cm-2) to a coverage-independent level for thicker water films. Experiments with isotopically-layered water films (D2O and H2O) demonstrated that the highest water decomposition yields occurred at the interfaces of the nanoscalemore » water films with the alumina substrate and vacuum. However, the increased reactivity of the water/alumina interface is relatively small compared to the enhancements in the non-thermal reactions previously observed at the water/Pt(111) and water/TiO2(110) interfaces. We propose that the relatively low activity of Al2O3(0001) for the radiation-induced production of molecular hydrogen is associated with lower reactivity of this surface with hydrogen atoms, which are likely precursors for the molecular hydrogen.100 eV electrons are stopped in the H 2O portion of the isotopically-layered nanoscale film on α-Al 2O 3(0001) but D 2is produced at the D 2O/alumina interface by mobile electronic excitations and/or hydronium ions.« less

Environmental Effects on Fatigue Crack Growth in High Performance Aluminum Alloys

DTIC Science & Technology

2009-03-13

tested for leaks to a rate of 2x 10൒ cm3/s with helium. All devices connected to the chamber, including pumps , gages and valves, are ultra-high- vacuum ...Pfeiffer TMU-262P), backed by a 5 L/s scroll pump (ULVAC DIS-250). This pump combination eliminates the possibility of contamination by pumping fluid used...both pumps are connected directly to the vacuum chamber to achieve optimum pump -down speeds. Pumping down the chamber is further facilitated by use of

Clean Room Facility

NASA Image and Video Library

2016-09-07

NASA Glenn technician Ariana Miller prepares an ultrahigh vacuum chamber used to test the materials used in silicon carbide based sensors and electronics that can operate at extremely high temperatures (500 degrees Celsius and higher) for applications such as sensor systems for aircraft engines and Venus exploration.

Precision requirements and innovative manufacturing for ultrahigh precision laser interferometry of gravitational-wave astronomy

NASA Astrophysics Data System (ADS)

Ni, Wei-Tou; Han, Sen; Jin, Tao

2016-11-01

With the LIGO announcement of the first direct detection of gravitational waves (GWs), the GW Astronomy was formally ushered into our age. After one-hundred years of theoretical investigation and fifty years of experimental endeavor, this is a historical landmark not just for physics and astronomy, but also for industry and manufacturing. The challenge and opportunity for industry is precision and innovative manufacturing in large size - production of large and homogeneous optical components, optical diagnosis of large components, high reflectance dielectric coating on large mirrors, manufacturing of components for ultrahigh vacuum of large volume, manufacturing of high attenuating vibration isolation system, production of high-power high-stability single-frequency lasers, production of high-resolution positioning systems etc. In this talk, we address the requirements and methods to satisfy these requirements. Optical diagnosis of large optical components requires large phase-shifting interferometer; the 1.06 μm Phase Shifting Interferometer for testing LIGO optics and the recently built 24" phase-shifting Interferometer in Chengdu, China are examples. High quality mirrors are crucial for laser interferometric GW detection, so as for ring laser gyroscope, high precision laser stabilization via optical cavities, quantum optomechanics, cavity quantum electrodynamics and vacuum birefringence measurement. There are stringent requirements on the substrate materials and coating methods. For cryogenic GW interferometer, appropriate coating on sapphire or silicon are required for good thermal and homogeneity properties. Large ultrahigh vacuum components and high attenuating vibration system together with an efficient metrology system are required and will be addressed. For space interferometry, drag-free technology and weak-light manipulation technology are must. Drag-free technology is well-developed. Weak-light phase locking is demonstrated in the laboratories while weak-light manipulation technology still needs developments.

Focused ion beam micromilling and articles therefrom

DOEpatents

Lamartine, Bruce C.; Stutz, Roger A.

1998-01-01

An ultrahigh vacuum focused ion beam micromilling apparatus and process are isclosed. Additionally, a durable data storage medium using the micromilling process is disclosed, the durable data storage medium capable of storing, e.g., digital or alphanumeric characters as well as graphical shapes or characters.

Solution-Synthesized Chevron Graphene Nanoribbons Exfoliated onto H:Si(100).

PubMed

Radocea, Adrian; Sun, Tao; Vo, Timothy H; Sinitskii, Alexander; Aluru, Narayana R; Lyding, Joseph W

2017-01-11

There has been tremendous progress in designing and synthesizing graphene nanoribbons (GNRs). The ability to control the width, edge structure, and dopant level with atomic precision has created a large class of accessible electronic landscapes for use in logic applications. One of the major limitations preventing the realization of GNR devices is the difficulty of transferring GNRs onto nonmetallic substrates. In this work, we developed a new approach for clean deposition of solution-synthesized atomically precise chevron GNRs onto H:Si(100) under ultrahigh vacuum. A clean transfer allowed ultrahigh-vacuum scanning tunneling microscopy (STM) to provide high-resolution imaging and spectroscopy and reveal details of the electronic structure of chevron nanoribbons that have not been previously reported. We also demonstrate STM nanomanipulation of GNRs, characterization of multilayer GNR cross-junctions, and STM nanolithography for local depassivation of H:Si(100), which allowed us to probe GNR-Si interactions and revealed a semiconducting-to-metallic transition. The results of STM measurements were shown to be in good agreement with first-principles computational modeling.

Cu(In,Ga)Se2 surface treatment with Na and NaF: A combined photoelectron spectroscopy and surface photovoltage study in ultra-high vacuum

NASA Astrophysics Data System (ADS)

Parvan, V.; Mizrak, A.; Majumdar, I.; Ümsür, B.; Calvet, W.; Greiner, D.; Kaufmann, C. A.; Dittrich, T.; Avancini, E.; Lauermann, I.

2018-06-01

Either metallic Na or NaF were deposited onto Cu(In,Ga)Se2 surfaces and studied by photoelectron spectroscopy and surface photovoltage spectroscopy without breaking the ultra-high vacuum. The deposition of elemental Na at room temperature led to the formation of an intermediate Cu and Ga rich layer at the CIGSe surface, whereas for NaF the composition of the CIGSe surface remained unchanged. A metal like surface induced by an inverted near surface region with a reduced number of defect states was formed after the deposition of Na. Under the chosen experimental conditions, the near surface layer was independent on the amount of Na and stable in time. In contrast, the usage of NaF weakened the inversion and led to an increased band bending compared to the untreated CIGSe sample. The SPV signals decreased with proceeding time after the deposition of NaF.

Set-up of a high-resolution 300 mK atomic force microscope in an ultra-high vacuum compatible {sup 3}He/10 T cryostat

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allwörden, H. von; Ruschmeier, K.; Köhler, A.

The design of an atomic force microscope with an all-fiber interferometric detection scheme capable of atomic resolution at about 500 mK is presented. The microscope body is connected to a small pumped {sup 3}He reservoir with a base temperature of about 300 mK. The bakeable insert with the cooling stage can be moved from its measurement position inside the bore of a superconducting 10 T magnet into an ultra-high vacuum chamber, where the tip and sample can be exchanged in situ. Moreover, single atoms or molecules can be evaporated onto a cold substrate located inside the microscope. Two side chambersmore » are equipped with standard surface preparation and surface analysis tools. The performance of the microscope at low temperatures is demonstrated by resolving single Co atoms on Mn/W(110) and by showing atomic resolution on NaCl(001).« less

Ultra-high vacuum compatible preparation chain for intermetallic compounds

NASA Astrophysics Data System (ADS)

Bauer, A.; Benka, G.; Regnat, A.; Franz, C.; Pfleiderer, C.

2016-11-01

We report the development of a versatile material preparation chain for intermetallic compounds, which focuses on the realization of a high-purity growth environment. The preparation chain comprises an argon glovebox, an inductively heated horizontal cold boat furnace, an arc melting furnace, an inductively heated rod casting furnace, an optically heated floating-zone furnace, a resistively heated annealing furnace, and an inductively heated annealing furnace. The cold boat furnace and the arc melting furnace may be loaded from the glovebox by means of a load-lock permitting to synthesize compounds starting with air-sensitive elements while handling the constituents exclusively in an inert gas atmosphere. All furnaces are all-metal sealed, bakeable, and may be pumped to ultra-high vacuum. We find that the latter represents an important prerequisite for handling compounds with high vapor pressure under high-purity argon atmosphere. We illustrate the operational aspects of the preparation chain in terms of the single-crystal growth of the heavy-fermion compound CeNi2Ge2.

Chirped pulse inverse free-electron laser vacuum accelerator

DOEpatents

Hartemann, Frederic V.; Baldis, Hector A.; Landahl, Eric C.

2002-01-01

A chirped pulse inverse free-electron laser (IFEL) vacuum accelerator for high gradient laser acceleration in vacuum. By the use of an ultrashort (femtosecond), ultrahigh intensity chirped laser pulse both the IFEL interaction bandwidth and accelerating gradient are increased, thus yielding large gains in a compact system. In addition, the IFEL resonance condition can be maintained throughout the interaction region by using a chirped drive laser wave. In addition, diffraction can be alleviated by taking advantage of the laser optical bandwidth with negative dispersion focusing optics to produce a chromatic line focus. The combination of these features results in a compact, efficient vacuum laser accelerator which finds many applications including high energy physics, compact table-top laser accelerator for medical imaging and therapy, material science, and basic physics.

Tribo-mechanical properties of thin boron coatings deposited on polished cobalt alloy surfaces for orthopedic applications

PubMed Central

Klepper, C. C.; Williams, J. M.; Truhan, J.J.; Qu, J.; Riester, L.; Hazelton, R. C.; Moschella, J.J.; Blau, P.J.; Anderson, J.P.; Popoola, O.O.; Keitz, M.D.

2008-01-01

This paper presents experimental evidence that thin (<∼200 nm) boron coatings, deposited with a (vacuum) cathodic arc technique on pre-polished Co-Cr-Mo surfaces, could potentially extend the life of metal-on-polymer orthopedic devices using cast Co-Cr-Mo alloy for the metal component. The primary tribological test used a linear, reciprocating pin-on-disc arrangement, with pins made of ultra-high molecular weight polyethylene. The disks were cast Co-Cr-Mo samples that were metallographically polished and then coated with boron at a substrate bias of 500 V and at about 100 °C. The wear tests were carried out in a saline solution to simulate the biological environment. The improvements were manifested by the absence of a detectable wear track scar on the coated metal component, while significant polymer transfer film was detected on the uncoated (control) samples tested under the same conditions. The polymer transfer track was characterized with both profilometry and Rutherford Backscattering Spectroscopy. Mechanical characterization of the thin films included nano-indentation, as well as additional pin-on-disk tests with a steel ball to demonstrate adhesion, using ultra-high frequency acoustic microscopy to probe for any void occurrence at the coating-substrate interface. PMID:19340285

Water Adsorption and Dissociation on Polycrystalline Copper Oxides: Effects of Environmental Contamination and Experimental Protocol

DOE PAGES

Trotochaud, Lena; Head, Ashley R.; Pletincx, Sven; ...

2017-11-02

We use ambient-pressure X-ray photoelectron spectroscopy (APXPS) to study chemical changes, including hydroxylation and water adsorption, at copper oxide surfaces from ultrahigh vacuum to ambient relative humidities of ~5%. Polycrystalline CuO and Cu 2O surfaces were prepared by selective oxidation of metallic copper foils. For both oxides, hydroxylation occurs readily, even at high-vacuum conditions. Hydroxylation on both oxides plateaus near ~0.01% relative humidity (RH) at a coverage of ~1 monolayer. In contrast to previous studies, neither oxide shows significant accumulation of molecular water; rather, both surfaces show a high affinity for adventitious carbon contaminants. Results of isobaric and isothermic experimentsmore » are compared, and the strengths and potential drawbacks of each method are discussed. We also provide critical evaluations of the effects of the hot filament of the ion pressure gauge on the reactivity of gas-phase species, the peak fitting procedure on the quantitative analysis of spectra, and rigorous accounting of carbon contamination on data analysis and interpretation. Lastly, this work underscores the importance of considering experimental design and data analysis protocols during APXPS experiments with water vapor in order to minimize misinterpretations arising from these factors.« less

Fabrication of high-quality single-crystal Cu thin films using radio-frequency sputtering.

PubMed

Lee, Seunghun; Kim, Ji Young; Lee, Tae-Woo; Kim, Won-Kyung; Kim, Bum-Su; Park, Ji Hun; Bae, Jong-Seong; Cho, Yong Chan; Kim, Jungdae; Oh, Min-Wook; Hwang, Cheol Seong; Jeong, Se-Young

2014-08-29

Copper (Cu) thin films have been widely used as electrodes and interconnection wires in integrated electronic circuits, and more recently as substrates for the synthesis of graphene. However, the ultra-high vacuum processes required for high-quality Cu film fabrication, such as molecular beam epitaxy (MBE), restricts mass production with low cost. In this work, we demonstrated high-quality Cu thin films using a single-crystal Cu target and radio-frequency (RF) sputtering technique; the resulting film quality was comparable to that produced using MBE, even under unfavorable conditions for pure Cu film growth. The Cu thin film was epitaxially grown on an Al2O3 (sapphire) (0001) substrate, and had high crystalline orientation along the (111) direction. Despite the 10(-3) Pa vacuum conditions, the resulting thin film was oxygen free due to the high chemical stability of the sputtered specimen from a single-crystal target; moreover, the deposited film had >5× higher adhesion force than that produced using a polycrystalline target. This fabrication method enabled Cu films to be obtained using a simple, manufacturing-friendly process on a large-area substrate, making our findings relevant for industrial applications.

Water Adsorption and Dissociation on Polycrystalline Copper Oxides: Effects of Environmental Contamination and Experimental Protocol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trotochaud, Lena; Head, Ashley R.; Pletincx, Sven

We use ambient-pressure X-ray photoelectron spectroscopy (APXPS) to study chemical changes, including hydroxylation and water adsorption, at copper oxide surfaces from ultrahigh vacuum to ambient relative humidities of ~5%. Polycrystalline CuO and Cu 2O surfaces were prepared by selective oxidation of metallic copper foils. For both oxides, hydroxylation occurs readily, even at high-vacuum conditions. Hydroxylation on both oxides plateaus near ~0.01% relative humidity (RH) at a coverage of ~1 monolayer. In contrast to previous studies, neither oxide shows significant accumulation of molecular water; rather, both surfaces show a high affinity for adventitious carbon contaminants. Results of isobaric and isothermic experimentsmore » are compared, and the strengths and potential drawbacks of each method are discussed. We also provide critical evaluations of the effects of the hot filament of the ion pressure gauge on the reactivity of gas-phase species, the peak fitting procedure on the quantitative analysis of spectra, and rigorous accounting of carbon contamination on data analysis and interpretation. Lastly, this work underscores the importance of considering experimental design and data analysis protocols during APXPS experiments with water vapor in order to minimize misinterpretations arising from these factors.« less

Hydrogen retention in lithium and lithium oxide films

NASA Astrophysics Data System (ADS)

Buzi, L.; Yang, Y.; Domínguez-Gutiérrez, F. J.; Nelson, A. O.; Hofman, M.; Krstić, P. S.; Kaita, R.; Koel, B. E.

2018-04-01

Pure lithium (Li) surfaces are difficult to maintain in fusion devices due to rapid oxide formation, therefore, parameterizing and understanding the mechanisms of hydrogen (H, D) retention in lithium oxide (Li2O) in addition to pure Li is crucial for Li plasma-facing material applications. To compare H retention in Li and Li2O films, measurements were made as a function of surface temperature (90-520 K) under ultrahigh vacuum (UHV) conditions using temperature programmed desorption (TPD). In both cases, the total retention dropped with surface temperature, from 95% at 90 K to 35% at 520 K Li2O films retained H in similar amounts as pure Li. Molecular Dynamics (MD) modeling was used to elucidate the mechanisms of H retention, and results were consistent with experiments in terms of both retention fraction and the drop of retention with temperature.

From tunneling to point contact: Correlation between forces and current

NASA Astrophysics Data System (ADS)

Sun, Yan; Mortensen, Henrik; Schär, Sacha; Lucier, Anne-Sophie; Miyahara, Yoichi; Grütter, Peter; Hofer, Werner

2005-05-01

We used a combined ultrahigh vacuum scanning tunneling and atomic force microscope (STM/AFM) to study W tip-Au(111) sample interactions in the regimes from weak coupling to strong interaction and simultaneously measure current changes from picoamperes to microamperes. Close correlation between conductance and interaction forces in a STM configuration was observed. In particular, the electrical and mechanical points of contact are determined based on the observed barrier collapse and adhesive bond formation, respectively. These points of contact, as defined by force and current measurements, coincide within measurement error. Ab initio calculations of the current as a function of distance in the tunneling regime is in quantitative agreement with experimental results. The obtained results are discussed in the context of dissipation in noncontact AFM as well as electrical contact formation in molecular electronics.

Final Technical Report for SISGR: Ultrafast Molecular Scale Chemical Imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hersam, Mark C.; Guest, Jeffrey R.; Guisinger, Nathan P.

2017-04-10

The Northwestern-Argonne SISGR program utilized newly developed instrumentation and techniques including integrated ultra-high vacuum tip-enhanced Raman spectroscopy/scanning tunneling microscopy (UHV-TERS/STM) and surface-enhanced femtosecond stimulated Raman scattering (SE-FSRS) to advance the spatial and temporal resolution of chemical imaging for the study of photoinduced dynamics of molecules on plasmonically active surfaces. An accompanying theory program addressed modeling of charge transfer processes using constrained density functional theory (DFT) in addition to modeling of SE-FSRS, thereby providing a detailed description of the excited state dynamics. This interdisciplinary and highly collaborative research resulted in 62 publications with ~ 48% of them being co-authored by multiplemore » SISGR team members. A summary of the scientific accomplishments from this SISGR program is provided in this final technical report.« less

Treatment of surfaces with low-energy electrons

NASA Astrophysics Data System (ADS)

Frank, L.; Mikmeková, E.; Lejeune, M.

2017-06-01

Electron-beam-induced deposition of various materials from suitable precursors has represented an established branch of nanotechnology for more than a decade. A specific alternative is carbon deposition on the basis of hydrocarbons as precursors that has been applied to grow various nanostructures including masks for subsequent technological steps. Our area of study was unintentional electron-beam-induced carbon deposition from spontaneously adsorbed hydrocarbon molecules. This process traditionally constitutes a challenge for scanning electron microscopy practice preventing one from performing any true surface studies outside an ultrahigh vacuum and without in-situ cleaning of samples, and also jeopardising other electron-optical devices such as electron beam lithographs. Here we show that when reducing the energy of irradiating electrons sufficiently, the e-beam-induced deposition can be converted to e-beam-induced release causing desorption of hydrocarbons and ultimate cleaning of surfaces in both an ultrahigh and a standard high vacuum. Using series of experiments with graphene samples, we demonstrate fundamental features of e-beam-induced desorption and present results of checks for possible radiation damage using Raman spectroscopy that led to optimisation of the electron energy for damage-free cleaning. The method of preventing carbon contamination described here paves the way for greatly enhanced surface sensitivity of imaging and substantially reduced demands on vacuum systems for nanotechnological applications.

Compact ultrahigh vacuum sample environments for x-ray nanobeam diffraction and imaging.

PubMed

Evans, P G; Chahine, G; Grifone, R; Jacques, V L R; Spalenka, J W; Schülli, T U

2013-11-01

X-ray nanobeams present the opportunity to obtain structural insight in materials with small volumes or nanoscale heterogeneity. The effective spatial resolution of the information derived from nanobeam techniques depends on the stability and precision with which the relative position of the x-ray optics and sample can be controlled. Nanobeam techniques include diffraction, imaging, and coherent scattering, with applications throughout materials science and condensed matter physics. Sample positioning is a significant mechanical challenge for x-ray instrumentation providing vacuum or controlled gas environments at elevated temperatures. Such environments often have masses that are too large for nanopositioners capable of the required positional accuracy of the order of a small fraction of the x-ray spot size. Similarly, the need to place x-ray optics as close as 1 cm to the sample places a constraint on the overall size of the sample environment. We illustrate a solution to the mechanical challenge in which compact ion-pumped ultrahigh vacuum chambers with masses of 1-2 kg are integrated with nanopositioners. The overall size of the environment is sufficiently small to allow their use with zone-plate focusing optics. We describe the design of sample environments for elevated-temperature nanobeam diffraction experiments demonstrate in situ diffraction, reflectivity, and scanning nanobeam imaging of the ripening of Au crystallites on Si substrates.

Compact ultrahigh vacuum sample environments for x-ray nanobeam diffraction and imaging

NASA Astrophysics Data System (ADS)

Evans, P. G.; Chahine, G.; Grifone, R.; Jacques, V. L. R.; Spalenka, J. W.; Schülli, T. U.

2013-11-01

X-ray nanobeams present the opportunity to obtain structural insight in materials with small volumes or nanoscale heterogeneity. The effective spatial resolution of the information derived from nanobeam techniques depends on the stability and precision with which the relative position of the x-ray optics and sample can be controlled. Nanobeam techniques include diffraction, imaging, and coherent scattering, with applications throughout materials science and condensed matter physics. Sample positioning is a significant mechanical challenge for x-ray instrumentation providing vacuum or controlled gas environments at elevated temperatures. Such environments often have masses that are too large for nanopositioners capable of the required positional accuracy of the order of a small fraction of the x-ray spot size. Similarly, the need to place x-ray optics as close as 1 cm to the sample places a constraint on the overall size of the sample environment. We illustrate a solution to the mechanical challenge in which compact ion-pumped ultrahigh vacuum chambers with masses of 1-2 kg are integrated with nanopositioners. The overall size of the environment is sufficiently small to allow their use with zone-plate focusing optics. We describe the design of sample environments for elevated-temperature nanobeam diffraction experiments demonstrate in situ diffraction, reflectivity, and scanning nanobeam imaging of the ripening of Au crystallites on Si substrates.

Focused ion beam micromilling and articles therefrom

DOEpatents

Lamartine, B.C.; Stutz, R.A.

1998-06-30

An ultrahigh vacuum focused ion beam micromilling apparatus and process are disclosed. Additionally, a durable data storage medium using the micromilling process is disclosed, the durable data storage medium capable of storing, e.g., digital or alphanumeric characters as well as graphical shapes or characters. 6 figs.

Radiation sterilization of medical devices. Effects of ionizing radiation on ultra-high molecular-weight polyethylene

NASA Astrophysics Data System (ADS)

Buchalla, R.; Schüttler, C.; Bögl, K. W.

1995-02-01

Sterilization by ionizing radiation has become, next to ethylene oxide treament, the most important "cold" sterilization process for medical devices made from plastics. The effects of ionizing radiation on the most important polymer for medical devices, ultra-high molecular-weight polyethylene, are briefly described in this review.

Friction and Wear Properties of As-deposited and Carbon Ion-implanted Diamond Films

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1994-01-01

Recent work on the friction and wear properties of as-deposited and carbon ion-implanted diamond films was reviewed. Diamond films were produced by the microwave plasma chemical vapor deposition (CVD) technique. Diamond films with various grain sizes and surface roughnesses were implanted with carbon ions at 60 ke V ion energy, resulting in a dose of 1.2310(exp 17) carbon ions/cm(exp 2). Various analytical techniques, including Raman spectroscopy, proton recoil analysis, Rutherford backscattering, transmission and scanning electron microscopy, x-ray photoelectron spectroscopy, and x-ray diffraction, were utilized to characterize the diamond films. Sliding friction experiments were conducted with a polished natural diamond pin in contact with diamond films in the three environments: humid air (40 percent relative humidity), dry nitrogen (less than 1 percent relative humidity), and ultrahigh vacuum (10(exp -7) Pa). The CVD diamond films indeed have friction and were properties similar to those of natural diamond in the three environments. The as-deposited, fine-grain diamond films can be effectively used as self-lubricating, wear-resistant coatings that have low coefficients of friction (0.02 to 0.04) and low wear rates (10(exp -7) to 10(exp -8)mm(exp 3)/N-m) in both humid air and dry nitrogen. However, they have high coefficients of friction (1.5 to 1.7) and a high wear rate (10(exp -4)mm(exp 3/N-m) in ultrahigh vacuum. The carbon ion implanation produced a thin surficial layer (less than 0.1 micron thick) of amorphous, nondiamond carbon on the diamond films. In humid air and dry nitrogen, the ion-implanted, fine- and coarse-grain diamond films have a low coefficient of friction (around 0.1) and a low wear rate (10(exp -7)mm(exp 3/N-m). Even in ultrahigh vacuum, the presence of the nondiamond carbon layer reduced the coefficient of friction of fine-grain diamond films to 0.1 or lower and the wear rate to 10(exp -6)mm(exp 3)/N-m. Thus, the carbon ion-implanted, fine-grain diamond films can be effectively used as wear-resistant, self-lubricating coatings not only in air and dry nitrogen, but also in ultrahigh vacuum. The wear mechanism of diamond films is that of small fragments chipping off the surface. The size of wear particles is related to the extent of wear rates.

High-temperature metal purification using a compact, portable rf heating and levitation system on the wake shield

NASA Technical Reports Server (NTRS)

Hahs, C. A.

1990-01-01

The potential use of a compact, battery-operated rf levitator and heating system to purify high-temperature melting materials in space is described. The wake shield now being fabricated for the Space Vacuum Epitaxy Center will provide an Ultra-high vacuum (10(exp -14) Torr hydrogen, 10(exp -14) Torr helium, 10(exp -30) Torr oxygen). The use of the wake shield to purify Nb, Ti, W, Ir, and other metals to a purity level not achievable on earth is described.

Compact scanning tunneling microscope for spin polarization measurements.

PubMed

Kim, Seong Heon; de Lozanne, Alex

2012-10-01

We present a design for a scanning tunneling microscope that operates in ultrahigh vacuum down to liquid helium temperatures in magnetic fields up to 8 T. The main design philosophy is to keep everything compact in order to minimize the consumption of cryogens for initial cool-down and for extended operation. In order to achieve this, new ideas were implemented in the design of the microscope body, dewars, vacuum chamber, manipulators, support frame, and vibration isolation. After a brief description of these designs, the results of initial tests are presented.

Ultra-high vacuum photoelectron linear accelerator

DOEpatents

Yu, David U.L.; Luo, Yan

2013-07-16

An rf linear accelerator for producing an electron beam. The outer wall of the rf cavity of said linear accelerator being perforated to allow gas inside said rf cavity to flow to a pressure chamber surrounding said rf cavity and having means of ultra high vacuum pumping of the cathode of said rf linear accelerator. Said rf linear accelerator is used to accelerate polarized or unpolarized electrons produced by a photocathode, or to accelerate thermally heated electrons produced by a thermionic cathode, or to accelerate rf heated field emission electrons produced by a field emission cathode.

Versatile, low-cost, computer-controlled, sample positioning system for vacuum applications

NASA Technical Reports Server (NTRS)

Vargas-Aburto, Carlos; Liff, Dale R.

1991-01-01

A versatile, low-cost, easy to implement, microprocessor-based motorized positioning system (MPS) suitable for accurate sample manipulation in a Second Ion Mass Spectrometry (SIMS) system, and for other ultra-high vacuum (UHV) applications was designed and built at NASA LeRC. The system can be operated manually or under computer control. In the latter case, local, as well as remote operation is possible via the IEEE-488 bus. The position of the sample can be controlled in three linear orthogonal and one angular coordinates.

Surface cleaning for negative electron affinity GaN photocathode

NASA Astrophysics Data System (ADS)

Qiao, Jianliang; Yin, Yingpeng; Gao, Youtang; Niu, Jun; Qian, Yunsheng; Chang, Benkang

2012-10-01

In the preparation process for negative electron affinity (NEA) GaN photocathode, the surface cleanness is very important to activation, it influences the sensitivity and stability of NEA GaN photocathode. The traditional corrosion methods based on oxidizing and dissolving can't remove oxygen (O) and carbon (C) on GaN surface effectively. How to get an ideal atom clean surface is still an important question at present. The cleaning techniques for GaN photocathode was studied by using NEA photocathode activation system and XPS surface analysis system. The experiment sample is p-type GaN doped with Mg, doped concentration is 1.37×1017 cm-3, the transfer rate is 3.08 cm2/V-S, and the thickness of activation layer is 0.51 μm, the substrate is 300 μm thick sapphire. The sample was dealed with chemical cleaning depuration at first. And to get the atom clean surface, the vacuum heat cleaning process was needed. The methods of chemical cleaning and the vacuum heating cleaning were given in detail. According to the X-ray photoelectron spectroscopy of GaN surface after chemical cleaning and the vacuum degree curve of the activation chamber during the heat cleaning, the cleaning effect and the cleaning mechanism were discussed. After the effective chemical cleaning and the heating of 700 Centigrade degree about 20 minutes in ultrahigh vacuum system, the oxides and carbon contaminants on cathode surface can be removed effectively, and the ideal atom clean surface can be obtained. The purpose of heating depuration process is that not only to get the atom clean GaN surface, but also to guarantee the contents of Ga, N on GaN surface stabilize and to keep the system ultra-high vacuum degree. Because of the volatilization of oxide and carbon impurity on the cathode surface, the vacuum degree curve drops with the rising of temperature on the whole.

Magnetron Sputtering System for Novel Intrinsically Switchable Thin Film Ferroelectric Resonators and Filters

DTIC Science & Technology

2012-08-03

the growth conditions and to improve film quality.    Mechanical  Scroll   Pump   The sputtering system requires a mechanical  scroll   pump  to bring the...load lock and main processing  chamber from atmospheric pressure to medium  vacuum . This particular type of  pump  does not expose  any part of the  vacuum ...additional  pump  to bring the main processing chamber from medium  vacuum  to ultrahigh  vacuum . Cryogenic  pumps  have no mechanical components and are

Characterization of the CEBAF 100 kV DC GaAs Photoelectron Gun Vacuum System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stutzman, M L; Adderley, P; Brittian, J

A vacuum system with pressure in the low ultra-high vacuum (UHV) range is essential for long photocathode lifetimes in DC high voltage GaAs photoguns. A discrepancy between predicted and measured base pressure in the CEBAF photoguns motivated this study of outgassing rates of three 304 stainless steel chambers with different pretreatments and pump speed measurements of non-evaporable getter (NEG) pumps. Outgassing rates were measured using two independent techniques. Lower outgassing rates were achieved by electropolishing and vacuum firing the chamber. The second part of the paper describes NEG pump speed measurements as a function of pressure through the lower partmore » of the UHV range. Measured NEG pump speed is high at pressures above 5×10 -11 Torr, but may decrease at lower pressures depending on the interpretation of the data. The final section investigates the pump speed of a locally produced NEG coating applied to the vacuum chamber walls. These studies represent the first detailed vacuum measurements of CEBAF photogun vacuum chambers.« less

Self-assembly of electronically abrupt borophene/organic lateral heterostructures

PubMed Central

Liu, Xiaolong; Wei, Zonghui; Balla, Itamar; Mannix, Andrew J.; Guisinger, Nathan P.; Luijten, Erik; Hersam, Mark C.

2017-01-01

Two-dimensional boron sheets (that is, borophene) have recently been realized experimentally and found to have promising electronic properties. Because electronic devices and systems require the integration of multiple materials with well-defined interfaces, it is of high interest to identify chemical methods for forming atomically abrupt heterostructures between borophene and electronically distinct materials. Toward this end, we demonstrate the self-assembly of lateral heterostructures between borophene and perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA). These lateral heterostructures spontaneously form upon deposition of PTCDA onto submonolayer borophene on Ag(111) substrates as a result of the higher adsorption enthalpy of PTCDA on Ag(111) and lateral hydrogen bonding among PTCDA molecules, as demonstrated by molecular dynamics simulations. In situ x-ray photoelectron spectroscopy confirms the weak chemical interaction between borophene and PTCDA, while molecular-resolution ultrahigh-vacuum scanning tunneling microscopy and spectroscopy reveal an electronically abrupt interface at the borophene/PTCDA lateral heterostructure interface. As the first demonstration of a borophene-based heterostructure, this work will inform emerging efforts to integrate borophene into nanoelectronic applications. PMID:28261662

Analysis of the performance of the space ultravacuum research facility in attached and free-flyer mode

NASA Technical Reports Server (NTRS)

Naumann, Robert J.

1988-01-01

The old concept of using the wake of a spacecraft to obtain an ultrahigh vacuum is revisited with a somewhat different emphasis. Since it is possible to configure a wake shield so that a surface of interest does not subtend any walls that could become contaminated, it appears that it should be possible to achieve a contamination-free, ultrahigh vacuum capability with infinite pumping speed even in the presence of high heat loads and moderate gas loads. With the new interest in developing thin films with precision controlled synthetic microstructures such as superlattices, mixed metal oxide high temperature superconductors, rare-earth magneto-optical devices, and nano-crystalline alloys, the ability to work with a variety of different materials without cross contamination should be of significance. This paper analyzes the performance of the conceptual design for a Space Ultravacuum Research Facility (SURF), both in a Shuttle-attached mode and as a free-flyer. It is shown that even in the Shuttle-attached mode, it should be possible to obtain vacuum levels equivalent to 10 to the -10 Torr with O and N2 as the primary constituents. This should be sufficient to demonstrate the feasibility of the concept, particularly the infinite pumping speed and virtual elimination of contamination aspects. As a free-flyer the SURF will be limited primarily by the gas load associated with the process being performed. For chemical beam epitaxy (CBE) it is shown that equivalent vacuum levels of 10 to the -14 Torr should be possible at 300 km.

Note: A simple sample transfer alignment for ultra-high vacuum systems.

PubMed

Tamtögl, A; Carter, E A; Ward, D J; Avidor, N; Kole, P R; Jardine, A P; Allison, W

2016-06-01

The alignment of ultra-high-vacuum sample transfer systems can be problematic when there is no direct line of sight to assist the user. We present the design of a simple and cheap system which greatly simplifies the alignment of sample transfer devices. Our method is based on the adaptation of a commercial digital camera which provides live views from within the vacuum chamber. The images of the camera are further processed using an image recognition and processing code which determines any misalignments and reports them to the user. Installation has proven to be extremely useful in order to align the sample with respect to the transfer mechanism. Furthermore, the alignment software can be easily adapted for other systems.

Molecular wake shield gas analyzer

NASA Technical Reports Server (NTRS)

Hoffman, J. H.

1980-01-01

Techniques for measuring and characterizing the ultrahigh vacuum in the wake of an orbiting spacecraft are studied. A high sensitivity mass spectrometer that contains a double mass analyzer consisting of an open source miniature magnetic sector field neutral gas analyzer and an identical ion analyzer is proposed. These are configured to detect and identify gas and ion species of hydrogen, helium, nitrogen, oxygen, nitric oxide, and carbon dioxide and any other gas or ion species in the 1 to 46 amu mass range. This range covers the normal atmospheric constituents. The sensitivity of the instrument is sufficient to measure ambient gases and ion with a particle density of the order of one per cc. A chemical pump, or getter, is mounted near the entrance aperture of the neutral gas analyzer which integrates the absorption of ambient gases for a selectable period of time for subsequent release and analysis. The sensitivity is realizable for all but rare gases using this technique.

Structural and electrical properties of single crystalline SrZrO 3 epitaxially grown on Ge (001)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lim, Z. H.; Ahmadi-Majlan, K.; Grimley, E. D.

We present structural and electrical characterization of SrZrO3 that has been epitaxially grown on Ge(001) by oxide molecular beam epitaxy. Single crystalline SrZrO3 can be nucleated on Ge via deposition at low temperatures followed by annealing at 550 ºC in ultra-high vacuum. Photoemission spectroscopy measurements reveal that SrZrO3 exhibits a type-I band arrangement with respect to Ge, with conduction and valence band offsets of 1.4 eV and 3.65 eV, respectively. As a standalone film, SrZrO3 exhibits several characteristics that are ideal for applications as a gate dielectric on Ge. We find that 4 nm thick films exhibit low leakage currentmore » densities, and a dielectric constant of κ ~ 25 that corresponds to an equivalent oxide thickness of 0.70 nm.« less

Hydrogen retention in lithium and lithium oxide films

DOE PAGES

Buzi, L.; Yang, Y.; Dominguez-Gutierrez, F. J.; ...

2018-02-09

Pure lithium (Li) surfaces are difficult to maintain in fusion devices due to rapid oxide formation, therefore, parameterizing and understanding the mechanisms of hydrogen (H, D) retention in lithium oxide (Li 2O) in addition to pure Li is crucial for Li plasma-facing material applications. To compare H retention in Li and Li 2O films, measurements were made as a function of surface temperature (90–520 K) under ultrahigh vacuum (UHV) conditions using temperature programmed desorption (TPD). In both cases, the total retention dropped with surface temperature, from 95% at 90 K to 35% at 520 K Li 2O films retained Hmore » in similar amounts as pure Li. Finally, Molecular Dynamics (MD) modeling was used to elucidate the mechanisms of H retention, and results were consistent with experiments in terms of both retention fraction and the drop of retention with temperature.« less

Hydrogen retention in lithium and lithium oxide films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Buzi, L.; Yang, Y.; Dominguez-Gutierrez, F. J.

Pure lithium (Li) surfaces are difficult to maintain in fusion devices due to rapid oxide formation, therefore, parameterizing and understanding the mechanisms of hydrogen (H, D) retention in lithium oxide (Li 2O) in addition to pure Li is crucial for Li plasma-facing material applications. To compare H retention in Li and Li 2O films, measurements were made as a function of surface temperature (90–520 K) under ultrahigh vacuum (UHV) conditions using temperature programmed desorption (TPD). In both cases, the total retention dropped with surface temperature, from 95% at 90 K to 35% at 520 K Li 2O films retained Hmore » in similar amounts as pure Li. Finally, Molecular Dynamics (MD) modeling was used to elucidate the mechanisms of H retention, and results were consistent with experiments in terms of both retention fraction and the drop of retention with temperature.« less

Structural and electrical properties of single crystalline SrZrO3 epitaxially grown on Ge (001)

NASA Astrophysics Data System (ADS)

Lim, Z. H.; Ahmadi-Majlan, K.; Grimley, E. D.; Du, Y.; Bowden, M.; Moghadam, R.; LeBeau, J. M.; Chambers, S. A.; Ngai, J. H.

2017-08-01

We present structural and electrical characterization of SrZrO3 that has been epitaxially grown on Ge(001) by oxide molecular beam epitaxy. Single crystalline SrZrO3 can be nucleated on Ge via deposition at low temperatures followed by annealing at 550 °C in ultra-high vacuum. Photoemission spectroscopy measurements reveal that SrZrO3 exhibits a type-I band arrangement with respect to Ge, with conduction and valence band offsets of 1.4 eV and 3.66 eV, respectively. Capacitance-voltage and current-voltage measurements on 4 nm thick films reveal low leakage current densities and an unpinned Fermi level at the interface that allows modulation of the surface potential of Ge. Ultra-thin films of epitaxial SrZrO3 can thus be explored as a potential gate dielectric for Ge.

Constitutional Dynamics of Metal-Organic Motifs on a Au(111) Surface.

PubMed

Kong, Huihui; Zhang, Chi; Xie, Lei; Wang, Likun; Xu, Wei

2016-06-13

Constitutional dynamic chemistry (CDC), including both dynamic covalent chemistry and dynamic noncovalent chemistry, relies on reversible formation and breakage of bonds to achieve continuous changes in constitution by reorganization of components. In this regard, CDC is considered to be an efficient and appealing strategy for selective fabrication of surface nanostructures by virtue of dynamic diversity. Although constitutional dynamics of monolayered structures has been recently demonstrated at liquid/solid interfaces, most of molecular reorganization/reaction processes were thought to be irreversible under ultrahigh vacuum (UHV) conditions where CDC is therefore a challenge to be achieved. Here, we have successfully constructed a system that presents constitutional dynamics on a solid surface based on dynamic coordination chemistry, in which selective formation of metal-organic motifs is achieved under UHV conditions. The key to making this reversible switching successful is the molecule-substrate interaction as revealed by DFT calculations. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nanowire growth kinetics in aberration corrected environmental transmission electron microscopy

DOE PAGES

Chou, Yi -Chia; Panciera, Federico; Reuter, Mark C.; ...

2016-03-15

Here, we visualize atomic level dynamics during Si nanowire growth using aberration corrected environmental transmission electron microscopy, and compare with lower pressure results from ultra-high vacuum microscopy. We discuss the importance of higher pressure observations for understanding growth mechanisms and describe protocols to minimize effects of the higher pressure background gas.

Photoelectron spectra of the decomposition of ethylene on /110/ tungsten

NASA Technical Reports Server (NTRS)

Plummer, E. W.; Waclawski, B. J.; Vorburger, T. V.

1974-01-01

The experimental apparatus used in the investigation consisted of an ultrahigh-vacuum chamber, a triple-grid, a microwave-excited resonance lamp, and an electron energy analyzer. The chemical nature of the chemisorbed species was studied, taking into account the energy distribution of photoemitted electrons, work function determinations, and low-energy electron diffraction patterns.

Ion-Implanted Diamond Films and Their Tribological Properties

NASA Technical Reports Server (NTRS)

Wu, Richard L. C.; Miyoshi, Kazuhisa; Korenyi-Both, Andras L.; Garscadden, Alan; Barnes, Paul N.

1993-01-01

This paper reports the physical characterization and tribological evaluation of ion-implanted diamond films. Diamond films were produced by microwave plasma, chemical vapor deposition technique. Diamond films with various grain sizes (0.3 and 3 microns) and roughness (9.1 and 92.1 nm r.m.s. respectively) were implanted with C(+) (m/e = 12) at an ion energy of 160 eV and a fluence of 6.72 x 10(exp 17) ions/sq cm. Unidirectional sliding friction experiments were conducted in ultrahigh vacuum (6.6 x 10(exp -7)Pa), dry nitrogen and humid air (40% RH) environments. The effects of C(+) ion bombardment on fine and coarse-grained diamond films are as follows: the surface morphology of the diamond films did not change; the surface roughness increased (16.3 and 135.3 nm r.m.s.); the diamond structures were damaged and formed a thin layer of amorphous non-diamond carbon; the friction coefficients dramatically decreased in the ultrahigh vacuum (0.1 and 0.4); the friction coefficients decreased slightly in the dry nitrogen and humid air environments.

Phosphorus doping of Si and Si1 - xGex grown by ultrahigh vacuum chemical vapor deposition using Si2H6 and GeH4

NASA Astrophysics Data System (ADS)

Chen, L. P.; Huang, G. W.; Chang, C. Y.

1996-03-01

100 ppm PH3 diluted in hydrogen is used as the n-type dopant gas in Si and Si1-xGex epilayers grown by ultrahigh vacuum chemical vapor deposition (UHVCVD) using Si2H6 and GeH4. The phosphorus concentration in Si increases linearly at a small PH3 flow rate and becomes nearly saturated at higher flow rates, while the phosphorus concentration in Si1-xGex only shows a nearly linear behavior with PH3 flow rate. The growth rates of Si and Si1-xGex epilayers decrease seriously (˜50%) and slightly (˜10%) with the increase of PH3 flow rate, respectively. These results can be explained by a model based on the enhancement of hydrogen desorption rate at smaller PH3 flow rates and different levels of the effects of phosphorus blocking of surface-activated sites between Si and Si1-xGex epilayers at higher PH3 flow rates.

Novel Ultrahigh Vacuum System for Chip-Scale Trapped Ion Quantum Computing

NASA Astrophysics Data System (ADS)

Chen, Shaw-Pin; Trapped Team

2011-05-01

This presentation reports the experimental results of an ultrahigh vacuum (UHV) system as a scheme to implement scalable trapped-ion quantum computers that use micro-fabricated ion traps as fundamental building blocks. The novelty of this system resides in our design, material selection, mechanical liability, low complexity of assembly, and reduced signal interference between DC and RF electrodes. Our system utilizes RF isolation and onsite-filtering topologies to attenuate AC signals generated from the resonator. We use a UHV compatible printed circuit board (PCB) material to perform DC routing, while the RF high and RF ground received separated routing via wire-wrapping. The standard PCB fabrication process enabled us to implement ceramic-based filter components adjacent to the chip trap. The DC electrodes are connected to air-side electrical feed through using four 25D adaptors made with polyether ether ketone (PEEK). The assembly process of this system is straight forward and in-chamber structure is self-supporting. We report on initial testing of this concept with a linear chip trap fabricated by the Sandia National Labs.

Highly precise and compact ultrahigh vacuum rotary feedthrough.

PubMed

Aiura, Y; Kitano, K

2012-03-01

The precision and rigidity of compact ultrahigh vacuum (UHV) rotary feedthroughs were substantially improved by preparing and installing an optimal crossed roller bearing with mounting holes. Since there are mounting holes on both the outer and inner races, the bearing can be mounted directly to rotary and stationary stages without any fixing plates and housing. As a result, it is possible to increase the thickness of the bearing or the size of the rolling elements in the bearing without increasing the distance between the rotating and fixing International Conflat flanges of the UHV rotary feedthrough. Larger rolling elements enhance the rigidity of the UHV rotary feedthrough. Moreover, owing to the structure having integrated inner and outer races and mounting holes, the performance is almost entirely unaffected by the installation of the bearing, allowing for a precise optical encoder to be installed in the compact UHV rotary feedthrough. Using position feedback via a worm gear system driven by a stepper motor and a precise rotary encoder, the actual angle of the compact UHV rotary feedthrough can be controlled with extremely high precision.

Highly precise and compact ultrahigh vacuum rotary feedthrough

NASA Astrophysics Data System (ADS)

Aiura, Y.; Kitano, K.

2012-03-01

The precision and rigidity of compact ultrahigh vacuum (UHV) rotary feedthroughs were substantially improved by preparing and installing an optimal crossed roller bearing with mounting holes. Since there are mounting holes on both the outer and inner races, the bearing can be mounted directly to rotary and stationary stages without any fixing plates and housing. As a result, it is possible to increase the thickness of the bearing or the size of the rolling elements in the bearing without increasing the distance between the rotating and fixing International Conflat flanges of the UHV rotary feedthrough. Larger rolling elements enhance the rigidity of the UHV rotary feedthrough. Moreover, owing to the structure having integrated inner and outer races and mounting holes, the performance is almost entirely unaffected by the installation of the bearing, allowing for a precise optical encoder to be installed in the compact UHV rotary feedthrough. Using position feedback via a worm gear system driven by a stepper motor and a precise rotary encoder, the actual angle of the compact UHV rotary feedthrough can be controlled with extremely high precision.

An ultrahigh-vacuum cryostat for simultaneous scanning tunneling microscopy and magneto-transport measurements down to 400 mK

NASA Astrophysics Data System (ADS)

Liebmann, Marcus; Bindel, Jan Raphael; Pezzotta, Mike; Becker, Stefan; Muckel, Florian; Johnsen, Tjorven; Saunus, Christian; Ast, Christian R.; Morgenstern, Markus

2017-12-01

We present the design and calibration measurements of a scanning tunneling microscope setup in a 3He ultrahigh-vacuum cryostat operating at 400 mK with a hold time of 10 days. With 2.70 m in height and 4.70 m free space needed for assembly, the cryostat fits in a one-story lab building. The microscope features optical access, an xy table, in situ tip and sample exchange, and enough contacts to facilitate atomic force microscopy in tuning fork operation and simultaneous magneto-transport measurements on the sample. Hence, it enables scanning tunneling spectroscopy on microstructured samples which are tuned into preselected transport regimes. A superconducting magnet provides a perpendicular field of up to 14 T. The vertical noise of the scanning tunneling microscope amounts to 1 pmrms within a 700 Hz bandwidth. Tunneling spectroscopy using one superconducting electrode revealed an energy resolution of 120 μeV. Data on tip-sample Josephson contacts yield an even smaller feature size of 60 μeV, implying that the system operates close to the physical noise limit.

An ultrahigh-vacuum cryostat for simultaneous scanning tunneling microscopy and magneto-transport measurements down to 400 mK.

PubMed

Liebmann, Marcus; Bindel, Jan Raphael; Pezzotta, Mike; Becker, Stefan; Muckel, Florian; Johnsen, Tjorven; Saunus, Christian; Ast, Christian R; Morgenstern, Markus

2017-12-01

We present the design and calibration measurements of a scanning tunneling microscope setup in a 3 He ultrahigh-vacuum cryostat operating at 400 mK with a hold time of 10 days. With 2.70 m in height and 4.70 m free space needed for assembly, the cryostat fits in a one-story lab building. The microscope features optical access, an xy table, in situ tip and sample exchange, and enough contacts to facilitate atomic force microscopy in tuning fork operation and simultaneous magneto-transport measurements on the sample. Hence, it enables scanning tunneling spectroscopy on microstructured samples which are tuned into preselected transport regimes. A superconducting magnet provides a perpendicular field of up to 14 T. The vertical noise of the scanning tunneling microscope amounts to 1 pm rms within a 700 Hz bandwidth. Tunneling spectroscopy using one superconducting electrode revealed an energy resolution of 120 μeV. Data on tip-sample Josephson contacts yield an even smaller feature size of 60 μeV, implying that the system operates close to the physical noise limit.

An ionization gauge for ultrahigh vacuum measurement based on a carbon nanotube cathode

NASA Astrophysics Data System (ADS)

Zhang, Huzhong; Cheng, Yongjun; Sun, Jian; Wang, Yongjun; Xi, Zhenhua; Dong, Meng; Li, Detian

2017-10-01

This work reports on the complete design and the properties of an ionization gauge based on a carbon nanotube cathode, which can measure ultrahigh vacuum without thermal effects. The gauge is composed of a pressure sensor and an electronic controller. This pressure sensor is constructed based on a hot-cathode ionization gauge, where the traditional hot filament is replaced by an electron source prepared with multi-wall nanotubes. Besides, an electronic controller was developed for bias voltage supply, low current detection, and pressure indication. The gauge was calibrated in the pressure range of 10-8 to 10-4 Pa in a XHV/UHV calibration apparatus. The gauge shows good linear characteristics in different gases. The calibrated sensitivity is 0.035 Pa-1 in N2, and the standard deviation of the sensitivity is about 1.1%. In addition, the stability of the sensitivity was learned in a long period. The standard deviation of the sensitivity factor "S" during one year is 2.0% for Ar and 1.6% for N2.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Clausing, R.E.

Equations based on kinetic theory relate the contamination of refractory metals in vacuum to the appropriate variables. Several examples are given for which the allowable system pressures are calculated. The examples illustrate the effect of varying several parameters. The importance of the sticking factor for active gases on hot refractory metals and its effect on the system design are discussed. The data for estimating the sticking factor for O/sub 2/ on Nb are given, along with some estimated values. Experimental data on the composition and rates of outgassing of ultrahigh-vacuum systems and their importance in system design are discussed. Severalmore » methods of reducing contamination rates and the relative ease and effectiveness of these methods are presented. It was concluded that tests of 1000 hr or longer will probably require system pressures of between 10/sup -9/ and 10/sup -6/ torr, the particular pressure depending upon the residual gas composition, test duration, allowable contamination level, and the other variables discussed. Since the most important source of contamination in a properly designed ultrahigh-vacuum system is the outgassing process, bakeable systems should be designed to operate with walls as cool as practical, and to have a minimum of surface area and outgassing materials inside. Considerable added protection may be obtained by incorporating sacrificial getter surfaces in the system, or, alternatively, higher pressures may be tolerated if proper getter design is used. (auth)« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gigax, Jonathan G.; Kim, Hyosim; Aydogan, Eda

Although accelerator-based ion irradiation has been widely accepted to simulate neutron damage, neutron-atypical features need to be carefully investigated. In this study, we have shown that Coulomb force drag by ion beams can introduce significant amounts of carbon, nitrogen, and oxygen into target materials even under ultra-high vacuum conditions. The resulting compositional and microstructural changes dramatically suppress void swelling. By applying a beam-filtering technique, introduction of vacuum contaminants is greatly minimized and the true swelling resistance of the alloys is revealed and matches neutron behavior closely. These findings are a significant step toward developing standardized procedures for emulating neutron damage.

VACUUM TRAP AND VALVE COMBINATION

DOEpatents

Milleron, N.; Levenson, L.

1963-02-19

This patent relates to a vacuum trap and valve combination suitable for use in large ultra-high vacuum systems. The vacuum trap is a chamber having an inlet and outlet opening which may be made to communicate with a chamber to be evacuated and a diffusion pump, respectively. A valve is designed to hermeticaliy seal with inlet opening and, when opened, block the line-of- sight'' between the inlet and outlet openings, while allowing a large flow path between the opened vaive and the side walls of the trap. The interior of the trap and the side of the valve facing the inlet opening are covered with an impurity absorbent, such as Zeolite or activated aluminum. Besides the advantage of combining two components of a vacuum system into one, the present invention removes the need for a baffle between the pump and the chamber to be evacuated. In one use of a specific embodiment of this invention, the transmission probability was 45 and the partial pressure of the pump fluid vapor in the vacuum chamber was at least 100 times lower than its vapor pressure. (AEC)

Ultrahigh vacuum and high-pressure coadsorption of CO and H2 on Pd(111): A combined SFG, TDS, and LEED study

NASA Astrophysics Data System (ADS)

Morkel, Matthias; Rupprechter, Günther; Freund, Hans-Joachim

2003-11-01

Sum frequency generation (SFG) vibrational spectroscopy was carried out in conjunction with thermal desorption spectroscopy, low-energy electron diffraction, and Auger electron spectroscopy to examine the coadsorption of CO and H2 on Pd(111). Sequential dosing as well as various CO/H2 mixtures was utilized to study intermolecular interactions between CO and H2. Preadsorbed CO effectively prevented the dissociative adsorption of hydrogen for CO coverages ⩾0.33 ML. While preadsorbed hydrogen was able to hinder CO adsorption at low temperature (100 K), hydrogen was replaced from the surface by CO at 150 K. When 1:1 mixtures of CO/H2 were used at 100 K, hydrogen selectively hindered CO adsorption on on-top sites, while above ˜125 K no blocking of CO adsorption was observed. The observations are explained in terms of mutual site blocking, of a CO-H phase separation, and of a CO-assisted hydrogen dissolution in the Pd bulk. The temperature-dependent site blocking effect of hydrogen is attributed to the ability (inability) of surface hydrogen to diffuse into the Pd bulk above (below) ˜125 K. Nonlinear optical SFG spectroscopy allowed us to study these effects not only in ultrahigh vacuum but also in a high-pressure environment. Using an SFG-compatible ultrahigh vacuum-high-pressure cell, spectra of 1:10 CO/H2 mixtures were acquired up to 55 mbar and 550 K, with simultaneous gas chromatographic and mass spectrometric gas phase analysis. Under reaction conditions, CO coverages ⩾0.5 ML were observed which strongly limit H2 adsorption and thus may be partly responsible for the low CO hydrogenation rate. The high-pressure and high-temperature SFG spectra also showed indications of a reversible surface roughening or a highly dynamic (not perfectly ordered) CO adsorbate phase. Implications of the observed adsorbate structures on catalytic CO hydrogenation on supported Pd nanoparticles are discussed.

Friction and Wear Properties of Selected Solid Lubricating Films

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Iwaki, Masanori; Gotoh, Kenichi; Obara, Shingo; Imagawa, Kichiro

1999-01-01

To evaluate commercially developed solid film lubricants for aerospace bearing applications, we investigated the friction and wear behavior of bonded molybdenum disulfide (MoS2), magnetron-sputtered MoS2 and ion-plated silver films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440 C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Herizian contact pressure of 0.79 GPa maximum 1.19 GPa), and a sliding velocity of 0.2 m/s at room temperature in three environments: ultrahigh vacuum (7x10 (exp -7Pa)), humid air (approx. 20 percent humidity), and dry nitrogen (less than 1 percent humidity). The resultant films were characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and surface profilometry. Marked differences in friction and wear resulted front the environmental conditions and the film materials. The main criteria for judging the performance were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 10 (exp -6mm exp 3/Nm or less), respectively. The bonded MoS2 and magnetron-sputtered MoS2 films met the criteria in all three environments. Also, the wear rates of the counterpart AISI 440 C stainless steel balls met that criterion in all three environments. The ion-plated silver films met the criteria only in ultrahigh vacuum. In ultrahigh vacuum the bonded MoS2 films were superior. In humid air the bonded MoS2 films had higher coefficient of friction and shorter wear life than did the magnetron-sputtered MoS2 films. The ion-plated silver films had a high coefficient of friction in humid air but relatively low coefficients of friction in the nonoxidative environments. Adhesion and plastic deformation played important roles in all three environments. All sliding involved adhesive transfer of materials.

From porphyrins to pyrphyrins: adsorption study and metalation of a molecular catalyst on Au(111)

NASA Astrophysics Data System (ADS)

Mette, Gerson; Sutter, Denys; Gurdal, Yeliz; Schnidrig, Stephan; Probst, Benjamin; Iannuzzi, Marcella; Hutter, Jürg; Alberto, Roger; Osterwalder, Jürg

2016-04-01

The molecular ligand pyrphyrin, a tetradentate bipyridine based macrocycle, represents an interesting but widely unexplored class of molecules. It resembles the well-known porphyrin, but consists of pyridyl subunits instead of pyrroles. Metal complexes based on pyrphyrin ligands have recently shown promise as water reduction catalysts in homogeneous photochemical water splitting reactions. In this study, the adsorption and metalation of pyrphyrin on a single crystalline Au(111) surface is investigated in an ultrahigh vacuum by means of scanning tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy and density functional theory. Pyrphyrin coverages of approximately one monolayer and less are obtained by sublimation of the molecules on the substrate kept at room temperature. The molecules self-assemble in two distinct phases of long-range molecular ordering depending on the surface coverage. The deposition of cobalt metal and subsequent annealing lead to the formation of Co-ligated pyrphyrin molecules accompanied by a pronounced change of the molecular self-assembly. Electronic structure calculations taking the herringbone reconstruction of Au(111) into account show that the molecules are physisorbed, but preferred adsorption sites are identified where Co and the N atoms of the two terminal cyano groups are optimally coordinated to the surface Au atoms. An intermediate state of the metalation reaction is observed and the reaction steps for the Co metalation of pyrphyrin molecules on Au(111) are established in a joint experimental and computational effort.The molecular ligand pyrphyrin, a tetradentate bipyridine based macrocycle, represents an interesting but widely unexplored class of molecules. It resembles the well-known porphyrin, but consists of pyridyl subunits instead of pyrroles. Metal complexes based on pyrphyrin ligands have recently shown promise as water reduction catalysts in homogeneous photochemical water splitting reactions. In this study, the adsorption and metalation of pyrphyrin on a single crystalline Au(111) surface is investigated in an ultrahigh vacuum by means of scanning tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy and density functional theory. Pyrphyrin coverages of approximately one monolayer and less are obtained by sublimation of the molecules on the substrate kept at room temperature. The molecules self-assemble in two distinct phases of long-range molecular ordering depending on the surface coverage. The deposition of cobalt metal and subsequent annealing lead to the formation of Co-ligated pyrphyrin molecules accompanied by a pronounced change of the molecular self-assembly. Electronic structure calculations taking the herringbone reconstruction of Au(111) into account show that the molecules are physisorbed, but preferred adsorption sites are identified where Co and the N atoms of the two terminal cyano groups are optimally coordinated to the surface Au atoms. An intermediate state of the metalation reaction is observed and the reaction steps for the Co metalation of pyrphyrin molecules on Au(111) are established in a joint experimental and computational effort. Electronic supplementary information (ESI) available: More details and results of the XPS experiments and the DFT calculation including also the coordinates of the calculated configurations. See DOI: 10.1039/C5NR08953K

Effect of sterilization irradiation on friction and wear of ultrahigh-molecular-weight polyethylene

NASA Technical Reports Server (NTRS)

Jones, W. R., Jr.; Hady, W. F.; Crugnola, A.

1979-01-01

The effect of sterilization gamma irradiation on the friction and wear properties of ultrahigh molecular weight polyethylene (UHMWPE) sliding against 316L stainless steel in dry air at 23 C was determined. A pin-on-disk apparatus was used. Experimental conditions included a 1-kilogram load, a 0.061- to 0.27-meter-per-second sliding velocity, and a 32000- to 578000-meter sliding distance. Although sterilization doses of 2.5 and 5.0 megarads greatly altered the average molecular weight and the molecular weight distribution, the friction and wear properties of the polymer were not significantly changed.

A vacuum (10 exp -9 torr) friction apparatus for determining friction and endurance life of MoS(x) films

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Honecy, Frank S.; Abel, Phillip B.; Pepper, Stephen V.; Spalvins, Talivaldis; Wheeler, Donald R.

1993-01-01

An ultrahigh-vacuum tribometer for use in a ball-on-disk configuration was specially designed for measuring the friction and endurance life of magnetron-sputtered solid lubricating MoS(x) films deposited on sputter-cleaned 400 C stainless-steel disks, when slid against a 6-mm-diameter 440 C stainless-steel ball. The results of tests showed that the tribometer performs satisfactorily in unidirectional rotation in vacuum at a pressure of 10 exp -7 Pa, 10 exp -9 torr. Similarities are observed in the life cycle friction behavior and the coefficient of friction as a function of the number of disk revolutions, for MoS(x) films at average Hertzian contact from 0.33 to 0.69 GPa.

Wear-resistant ball bearings for space applications. [coated with titanium carbide

NASA Technical Reports Server (NTRS)

Boving, H.; Hintermann, H. E.; Haenni, W.; Bondivenne, E.; Boeto, M.; Conde, M.

1977-01-01

Ball bearings for hostile environments were developed. They consist of normal ball bearing steel parts of which the rings are coated with hard, wear-resistant, chemical vapor deposited (C.V.D) TiC. Experiments in ultrahigh vacuum, using cages of various materials with self-lubricating properties, have shown that such bearings are suitable for space applications.

Mass Spectrometry as a Preparative Tool for the Surface Science of Large Molecules

NASA Astrophysics Data System (ADS)

Rauschenbach, Stephan; Ternes, Markus; Harnau, Ludger; Kern, Klaus

2016-06-01

Measuring and understanding the complexity that arises when nanostructures interact with their environment are one of the major current challenges of nanoscale science and technology. High-resolution microscopy methods such as scanning probe microscopy have the capacity to investigate nanoscale systems with ultimate precision, for which, however, atomic scale precise preparation methods of surface science are a necessity. Preparative mass spectrometry (pMS), defined as the controlled deposition of m/z filtered ion beams, with soft ionization sources links the world of large, biological molecules and surface science, enabling atomic scale chemical control of molecular deposition in ultrahigh vacuum (UHV). Here we explore the application of high-resolution scanning probe microscopy and spectroscopy to the characterization of structure and properties of large molecules. We introduce the fundamental principles of the combined experiments electrospray ion beam deposition and scanning tunneling microscopy. Examples for the deposition and investigation of single particles, for layer and film growth, and for the investigation of electronic properties of individual nonvolatile molecules show that state-of-the-art pMS technology provides a platform analog to thermal evaporation in conventional molecular beam epitaxy. Additionally, it offers additional, unique features due to the use of charged polyatomic particles. This new field is an enormous sandbox for novel molecular materials research and demands the development of advanced molecular ion beam technology.

3 MV hypervelocity dust accelerator at the Colorado Center for Lunar Dust and Atmospheric Studies.

PubMed

Shu, Anthony; Collette, Andrew; Drake, Keith; Grün, Eberhard; Horányi, Mihály; Kempf, Sascha; Mocker, Anna; Munsat, Tobin; Northway, Paige; Srama, Ralf; Sternovsky, Zoltán; Thomas, Evan

2012-07-01

A hypervelocity dust accelerator for studying micrometeorite impacts has been constructed at the Colorado Center for Lunar Dust and Atmospheric Studies (CCLDAS) at the University of Colorado. Based on the Max-Planck-Institüt für Kernphysik (MPI-K) accelerator, this accelerator is capable of emitting single particles of a specific mass and velocity selected by the user. The accelerator consists of a 3 MV Pelletron generator with a dust source, four image charge pickup detectors, and two interchangeable target chambers: a large high-vacuum test bed and an ultra-high vacuum impact study chamber. The large test bed is a 1.2 m diameter, 1.5 m long cylindrical vacuum chamber capable of pressures as low as 10(-7) torr while the ultra-high vacuum chamber is a 0.75 m diameter, 1.1 m long chamber capable of pressures as low as 10(-10) torr. Using iron dust of up to 2 microns in diameter, final velocities have been measured up to 52 km/s. The spread of the dust particles and the effect of electrostatic focusing have been measured using a long exposure CCD and a quartz target. Furthermore, a new technique of particle selection is being developed using real time digital filtering techniques. Signals are digitized and then cross-correlated with a shaped filter, resulting in a suppressed noise floor. Improvements over the MPI-K design, which include a higher operating voltage and digital filtering for detection, increase the available parameter space of dust emitted by the accelerator. The CCLDAS dust facility is a user facility open to the scientific community to assist with instrument calibrations and experiments.

Description of a dust particle detection system and measurements of particulate contamination from shock, gate valve, and ion pump under ultrahigh vacuum conditions

NASA Astrophysics Data System (ADS)

Dorier, J.-L.; Hilleret, N.

1998-11-01

Dust particle contamination is known to be responsible for reduced quality and yield in microelectronic processing. However it may also limit the operation of particle accelerators as a result of beam lifetime reduction or enhanced field emission in radio-frequency accelerating cavities. Intrinsic dust contamination from sources such as valves or ion pumps has not yet been studied due to the inability of commercial particle counters to be able to detect across large cross sections under ultrahigh vacuum (UHV) conditions. This motivated the development of the dust particle detector described here which is able to quantify, in situ, the level of contamination on a representative part of a vacuum vessel. This system operates under UHV conditions and measures flashes of scattered light from free falling dust particles as they cross a thin laser light sheet across a 100 mm diam vacuum vessel. A calibration using microspheres of known diameter has allowed estimation of the particle size from the scattered signal amplitude. Measurements of particulate contamination generated by shocks onto the vessel walls are presented and determination of the height of origin of dust particles from their transit time across the irradiation sheet is discussed. Measurements of dust particle release right to operation of an all-metal gate valve are also presented in the form of time resolved measurements of dust occurrence during the open/close cycles of the valve, as well as histograms of the particle size distribution. A partial self-cleaning effect is witnessed during the first 10 operation cycles following valve installation. The operation of an ion pump has also been investigated and revealed that, in our conditions, particles were released only at pump startup.

A review on nanomechanical resonators and their applications in sensors and molecular transportation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arash, Behrouz; Rabczuk, Timon, E-mail: timon.rabczuk@uni-weimar.de; Jiang, Jin-Wu

2015-06-15

Nanotechnology has opened a new area in science and engineering, leading to the development of novel nano-electromechanical systems such as nanoresonators with ultra-high resonant frequencies. The ultra-high-frequency resonators facilitate wide-ranging applications such as ultra-high sensitive sensing, molecular transportation, molecular separation, high-frequency signal processing, and biological imaging. This paper reviews recent studies on dynamic characteristics of nanoresonators. A variety of theoretical approaches, i.e., continuum modeling, molecular simulations, and multiscale methods, in modeling of nanoresonators are reviewed. The potential application of nanoresonators in design of sensor devices and molecular transportation systems is introduced. The essence of nanoresonator sensors for detection of atomsmore » and molecules with vibration and wave propagation analyses is outlined. The sensitivity of the resonator sensors and their feasibility in detecting different atoms and molecules are particularly discussed. Furthermore, the applicability of molecular transportation using the propagation of mechanical waves in nanoresonators is presented. An extended application of the transportation methods for building nanofiltering systems with ultra-high selectivity is surveyed. The article aims to provide an up-to-date review on the mechanical properties and applications of nanoresonators, and inspire additional potential of the resonators.« less

Development of a Robust Static Punch Experiment for Screening Unprocessed Ultra-High Molecular Weight Polyethylene (UHMWPE) Unidirectional Cross-Ply Material

DTIC Science & Technology

2014-09-01

Cross-Ply Material by David Gray, Robert Kaste , and Paul Moy ARL-TR-7090 September 2014...Screening Unprocessed Ultra-High Molecular Weight Polyethylene (UHMWPE) Unidirectional Cross-Ply Material David Gray, Robert Kaste , and Paul...ELEMENT NUMBER 6. AUTHOR(S) David Gray, Robert Kaste , and Paul Moy 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7

Voltage stress induced reversible diode behavior in pentacene thin films

NASA Astrophysics Data System (ADS)

Murdey, Richard; Sato, Naoki

2012-12-01

The current-voltage characteristics of a vacuum-deposited 100 nm pentacene thin film have been measured in situ under ultrahigh vacuum. Despite using bottom contact geometry with titanium for both electrodes, the I-V curves are asymmetric and the direction and degree of the diode-like behavior vary with sample and measurement history. After careful examination we have found that applying a high positive or negative bias voltage for about 24 h at elevated temperatures was sufficient to completely switch the diode forward direction. The switching action is fully reversible and the diode behavior, once switched, remains stable to repeated measurements at least over a period of several weeks.

NC-AFM observation of atomic scale structure of rutile-type TiO2(110) surface prepared by wet chemical process.

PubMed

Namai, Yoshimichi; Matsuoka, Osamu

2006-04-06

We succeeded in observing the atomic scale structure of a rutile-type TiO2(110) single-crystal surface prepared by the wet chemical method of chemical etching in an acid solution and surface annealing in air. Ultrahigh vacuum noncontact atomic force microscopy (UHV-NC-AFM) was used for observing the atomic scale structures of the surface. The UHV-NC-AFM measurements at 450 K, which is above a desorption temperature of molecularly adsorbed water on the TiO2(110) surface, enabled us to observe the atomic scale structure of the TiO2(110) surface prepared by the wet chemical method. In the UHV-NC-AFM measurements at room temperature (RT), however, the atomic scale structure of the TiO2(110) surface was not observed. The TiO2(110) surface may be covered with molecularly adsorbed water after the surface was prepared by the wet chemical method. The structure of the TiO2(110) surface that was prepared by the wet chemical method was consistent with the (1 x 1) bulk-terminated model of the TiO2(110) surface.

Design and performance of an ultra-high vacuum spin-polarized scanning tunneling microscope operating at 30 mK and in a vector magnetic field

NASA Astrophysics Data System (ADS)

von Allwörden, Henning; Eich, Andreas; Knol, Elze J.; Hermenau, Jan; Sonntag, Andreas; Gerritsen, Jan W.; Wegner, Daniel; Khajetoorians, Alexander A.

2018-03-01

We describe the design and performance of a scanning tunneling microscope (STM) that operates at a base temperature of 30 mK in a vector magnetic field. The cryogenics is based on an ultra-high vacuum (UHV) top-loading wet dilution refrigerator that contains a vector magnet allowing for fields up to 9 T perpendicular and 4 T parallel to the sample. The STM is placed in a multi-chamber UHV system, which allows in situ preparation and exchange of samples and tips. The entire system rests on a 150-ton concrete block suspended by pneumatic isolators, which is housed in an acoustically isolated and electromagnetically shielded laboratory optimized for extremely low noise scanning probe measurements. We demonstrate the overall performance by illustrating atomic resolution and quasiparticle interference imaging and detail the vibrational noise of both the laboratory and microscope. We also determine the electron temperature via measurement of the superconducting gap of Re(0001) and illustrate magnetic field-dependent measurements of the spin excitations of individual Fe atoms on Pt(111). Finally, we demonstrate spin resolution by imaging the magnetic structure of the Fe double layer on W(110).

Design and performance of an ultra-high vacuum spin-polarized scanning tunneling microscope operating at 30 mK and in a vector magnetic field.

PubMed

von Allwörden, Henning; Eich, Andreas; Knol, Elze J; Hermenau, Jan; Sonntag, Andreas; Gerritsen, Jan W; Wegner, Daniel; Khajetoorians, Alexander A

2018-03-01

We describe the design and performance of a scanning tunneling microscope (STM) that operates at a base temperature of 30 mK in a vector magnetic field. The cryogenics is based on an ultra-high vacuum (UHV) top-loading wet dilution refrigerator that contains a vector magnet allowing for fields up to 9 T perpendicular and 4 T parallel to the sample. The STM is placed in a multi-chamber UHV system, which allows in situ preparation and exchange of samples and tips. The entire system rests on a 150-ton concrete block suspended by pneumatic isolators, which is housed in an acoustically isolated and electromagnetically shielded laboratory optimized for extremely low noise scanning probe measurements. We demonstrate the overall performance by illustrating atomic resolution and quasiparticle interference imaging and detail the vibrational noise of both the laboratory and microscope. We also determine the electron temperature via measurement of the superconducting gap of Re(0001) and illustrate magnetic field-dependent measurements of the spin excitations of individual Fe atoms on Pt(111). Finally, we demonstrate spin resolution by imaging the magnetic structure of the Fe double layer on W(110).

Wear-Resistant, Self-Lubricating Surfaces of Diamond Coatings

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1995-01-01

In humid air and dry nitrogen, as-deposited, fine-grain diamond films and polished, coarse-grain diamond films have low steady-state coefficients of friction (less than 0.1) and low wear rates (less than or equal to 10(exp -6) mm(exp 3)/N-m). In an ultrahigh vacuum (10(exp -7) Pa), however, they have high steady-state coefficients of friction (greater than 0.6) and high wear rates (greater than or equal to 10(exp -4) mm(exp 3)/N-m). Therefore, the use of as-deposited, fine-grain and polished, coarse-grain diamond films as wear-resistant, self-lubricating coatings must be limited to normal air or gaseous environments such as dry nitrogen. On the other hand, carbon-ion-implanted, fine-grain diamond films and nitrogen-ion-implanted, coarse-grain diamond films have low steady-state coefficients of friction (less than 0.1) and low wear rates (less than or equal to 10(exp -6) mm(exp 3)/N-m) in all three environments. These films can be effectively used as wear-resistant, self-lubricating coatings in an ultrahigh vacuum as well as in normal air and dry nitrogen.

An ultra-high vacuum scanning tunneling microscope operating at sub-Kelvin temperatures and high magnetic fields for spin-resolved measurements

NASA Astrophysics Data System (ADS)

Salazar, C.; Baumann, D.; Hänke, T.; Scheffler, M.; Kühne, T.; Kaiser, M.; Voigtländer, R.; Lindackers, D.; Büchner, B.; Hess, C.

2018-06-01

We present the construction and performance of an ultra-low-temperature scanning tunneling microscope (STM), working in ultra-high vacuum (UHV) conditions and in high magnetic fields up to 9 T. The cryogenic environment of the STM is generated by a single-shot 3He magnet cryostat in combination with a 4He dewar system. At a base temperature (300 mK), the cryostat has an operation time of approximately 80 h. The special design of the microscope allows the transfer of the STM head from the cryostat to a UHV chamber system, where samples and STM tips can be easily exchanged. The UHV chambers are equipped with specific surface science treatment tools for the functionalization of samples and tips, including high-temperature treatments and thin film deposition. This, in particular, enables spin-resolved tunneling measurements. We present test measurements using well-known samples and tips based on superconductors and metallic materials such as LiFeAs, Nb, Fe, and W. The measurements demonstrate the outstanding performance of the STM with high spatial and energy resolution as well as the spin-resolved capability.

Design and performance of an ultra-high vacuum scanning tunneling microscope operating at dilution refrigerator temperatures and high magnetic fields.

PubMed

Misra, S; Zhou, B B; Drozdov, I K; Seo, J; Urban, L; Gyenis, A; Kingsley, S C J; Jones, H; Yazdani, A

2013-10-01

We describe the construction and performance of a scanning tunneling microscope capable of taking maps of the tunneling density of states with sub-atomic spatial resolution at dilution refrigerator temperatures and high (14 T) magnetic fields. The fully ultra-high vacuum system features visual access to a two-sample microscope stage at the end of a bottom-loading dilution refrigerator, which facilitates the transfer of in situ prepared tips and samples. The two-sample stage enables location of the best area of the sample under study and extends the experiment lifetime. The successful thermal anchoring of the microscope, described in detail, is confirmed through a base temperature reading of 20 mK, along with a measured electron temperature of 250 mK. Atomically resolved images, along with complementary vibration measurements, are presented to confirm the effectiveness of the vibration isolation scheme in this instrument. Finally, we demonstrate that the microscope is capable of the same level of performance as typical machines with more modest refrigeration by measuring spectroscopic maps at base temperature both at zero field and in an applied magnetic field.

Electrical and optical characteristics of n-Zno/p-GaN hetero-junction diode fabricated by ultra-high vacuum sputter.

PubMed

Cho, Seong Gook; Lee, Dong Uk; Kim, Eun Kyu

2013-09-01

We investigated the electrical and optical properties of n-ZnO/p-GaN hetero-junction diode fabricated by an ultra-high vacuum radio frequency magnetron sputter. A physical relationship between the rotation rate during deposition process and post annealing conditions after deposited ZnO layer on p-GaN layer was discussed. When the rotation rates during deposition process of n-ZnO layer were 5 rpm and 15 rpm, the full width at half maximum of photoluminescence spectra of ZnO layer on the p-GaN layer was about 106 and 133 meV, respectively. Also, the ratio of deep level emission to near band edge emission was dramatically increased as increasing the rotation rate from 5 to 15 rpm. The n-ZnO/p-GaN hetero-junction diode grown at 5 rpm has a higher ratio of forward to reverse currents than the diode grown at 15 rpm. Also, the 600 degrees C-annealed diodes with 5 rpm showed good rectifying behavior with the barrier height of 0.74 eV, the ideality factor of 12.2, and the forward to reverse current ratio of 614 at +/- 8 V.

Decomposition of L a2 -xS rxCu O4 into several L a2O3 phases at elevated temperatures in ultrahigh vacuum inside a transmission electron microscope

NASA Astrophysics Data System (ADS)

Jeong, Jong Seok; Wu, Wangzhou; Topsakal, Mehmet; Yu, Guichuan; Sasagawa, Takao; Greven, Martin; Mkhoyan, K. Andre

2018-05-01

We report the decomposition of L a2 -xS rxCu O4 into L a2O3 and Cu nanoparticles in ultrahigh vacuum, observed by in situ heating experiments in a transmission electron microscope. The analysis of electron diffraction data reveals that the phase decomposition process starts at about 150 °C and is considerably expedited in the temperature range of 350 °C-450 °C. Two major resultant solid phases are identified as metallic Cu and L a2O3 by electron diffraction, simulation, and electron energy-loss spectroscopy (EELS) analyses. With the aid of calculations, L a2O3 phases are further identified to be derivatives of a fluorite structure—fluorite, pyrochlore, and (distorted) bixbyite—characterized by different oxygen-vacancy order. Additionally, the bulk plasmon energy and the fine structures of the O K and La M4 ,5 EELS edges are reported for these structures, along with simulated O K x-ray absorption near-edge structure. The resultant Cu nanoparticles and L a2O3 phases remain unchanged after cooling to room temperature.

Vacuum Bloch-Siegert shift in Landau polaritons with ultra-high cooperativity

NASA Astrophysics Data System (ADS)

Li, Xinwei; Bamba, Motoaki; Zhang, Qi; Fallahi, Saeed; Gardner, Geoff C.; Gao, Weilu; Lou, Minhan; Yoshioka, Katsumasa; Manfra, Michael J.; Kono, Junichiro

2018-06-01

A two-level system resonantly interacting with an a.c. magnetic or electric field constitutes the physical basis of diverse phenomena and technologies. However, Schrödinger's equation for this seemingly simple system can be solved exactly only under the rotating-wave approximation, which neglects the counter-rotating field component. When the a.c. field is sufficiently strong, this approximation fails, leading to a resonance-frequency shift known as the Bloch-Siegert shift. Here, we report the vacuum Bloch-Siegert shift, which is induced by the ultra-strong coupling of matter with the counter-rotating component of the vacuum fluctuation field in a cavity. Specifically, an ultra-high-mobility two-dimensional electron gas inside a high-Q terahertz cavity in a quantizing magnetic field revealed ultra-narrow Landau polaritons, which exhibited a vacuum Bloch-Siegert shift up to 40 GHz. This shift, clearly distinguishable from the photon-field self-interaction effect, represents a unique manifestation of a strong-field phenomenon without a strong field.

Ultrahigh-resolution FT-ICR mass spectrometry characterization of a-pinene ozonolysis SOA

EPA Science Inventory

Secondary organic aerosol (SOA) of α-pinene ozonolysis with and without hydroxyl radical scavenging hexane was characterized by ultrahigh-resolution. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Molecular formulas for more than 900 negative ions were i...

Increasing the wear resistance of ultra-high molecular weight polyethylene by adding solid lubricating fillers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Panin, S. V., E-mail: svp@ispms.tsc.ru; Kornienko, L. A.; Poltaranin, M. A.

2014-11-14

In order to compare effectiveness of adding solid lubricating fillers for polymeric composites based on ultra-high molecular weight polyethylene (UHMWPE) with graphite, molybdenum disulfide and polytetrafluoroethylene, their tribotechnical characteristics under dry friction, boundary lubrication and abrasive wearing were investigated. The optimal weight fractions of fillers in terms of improving wear resistance have been determined. The supramolecular structure and topography of wear track surfaces of UHMWPE-based composites with different content of fillers have been studied.

Fabrication and wear test of a continuous fiber/particulate composite total surface hip replacement

NASA Technical Reports Server (NTRS)

Roberts, J. C.; Ling, F. F.; Jones, W. R., Jr.

1981-01-01

Continuous fiber woven E-glass composite femoral shells having the ame elastic properties as bone were fabricated. The shells were then encrusted with filled epoxy wear resistant coatings and run dry against ultrahigh molecular weight polyethylene acetabular cups in 42,000 and 250,000 cycle were tests on a total hip simulator. The tribological characteristics of these shells atriculating with the acetabular cups are comparable to a vitallium bal articulating with an ultrahigh molecular weight polyethylene cup.

Radiation cross-linking in ultra-high molecular weight polyethylene for orthopaedic applications

NASA Astrophysics Data System (ADS)

Oral, Ebru; Muratoglu, Orhun K.

2007-12-01

The motivation for radiation cross-linking of ultra-high molecular weight polyethylene (UHMWPE) is to increase its wear resistance to be used as bearing surfaces for total joint arthroplasty. However, radiation also leaves behind long-lived residual free radicals in this polymer, the reactions of which can detrimentally affect mechanical properties. In this review, we focus on the radiation cross-linking and oxidative stability of first and second generation highly cross-linked UHMWPEs developed in our laboratory.

Surface science and model catalysis with ionic liquid-modified materials.

PubMed

Steinrück, H-P; Libuda, J; Wasserscheid, P; Cremer, T; Kolbeck, C; Laurin, M; Maier, F; Sobota, M; Schulz, P S; Stark, M

2011-06-17

Materials making use of thin ionic liquid (IL) films as support-modifying functional layer open up a variety of new possibilities in heterogeneous catalysis, which range from the tailoring of gas-surface interactions to the immobilization of molecularly defined reactive sites. The present report reviews recent progress towards an understanding of "supported ionic liquid phase (SILP)" and "solid catalysts with ionic liquid layer (SCILL)" materials at the microscopic level, using a surface science and model catalysis type of approach. Thin film IL systems can be prepared not only ex-situ, but also in-situ under ultrahigh vacuum (UHV) conditions using atomically well-defined surfaces as substrates, for example by physical vapor deposition (PVD). Due to their low vapor pressure, these systems can be studied in UHV using the full spectrum of surface science techniques. We discuss general strategies and considerations of this approach and exemplify the information available from complementary methods, specifically photoelectron spectroscopy and surface vibrational spectroscopy. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Compression-Induced Conformation and Orientation Changes in an n-Alkane Monolayer on a Au(111) Surface.

PubMed

Endo, Osamu; Nakamura, Masashi; Amemiya, Kenta; Ozaki, Hiroyuki

2017-04-25

The influence of the preparation method and adsorbed amount of n-tetratetracontane (n-C 44 H 90 ) on its orientation in a monolayer on the Au(111) surface is studied by near carbon K-edge X-ray absorption fine structure spectroscopy (C K-NEXAFS), scanning tunneling microscopy (STM) under ultrahigh vacuum, and infrared reflection-absorption spectroscopy (IRAS) at the electrochemical interface in sulfuric acid solution. The n-C 44 H 90 molecules form self-assembled lamellar structures with the chain axis parallel to the surface, as observed by STM. For small amounts adsorbed, the carbon plane is parallel to the surface (flat-on orientation). An increase in the adsorbed amount by ∼10-20% induces compression of the lamellar structure either along the lamellar axis or alkyl chain axis. The compressed molecular arrangement is observed by STM, and induced conformation and orientation changes are confirmed by in situ IRAS and C K-NEXAFS.

Mn-doped Ge self-assembled quantum dots via dewetting of thin films

NASA Astrophysics Data System (ADS)

Aouassa, Mansour; Jadli, Imen; Bandyopadhyay, Anup; Kim, Sung Kyu; Karaman, Ibrahim; Lee, Jeong Yong

2017-03-01

In this study, we demonstrate an original elaboration route for producing a Mn-doped Ge self-assembled quantum dots on SiO2 thin layer for MOS structure. These magnetic quantum dots are elaborated using dewetting phenomenon at solid state by Ultra-High Vacuum (UHV) annealing at high temperature of an amorphous Ge:Mn (Mn: 40%) nanolayer deposed at very low temperature by high-precision Solid Source Molecular Beam Epitaxy on SiO2 thin film. The size of quantum dots is controlled with nanometer scale precision by varying the nominal thickness of amorphous film initially deposed. The magnetic properties of the quantum-dots layer have been investigated by superconducting quantum interference device (SQUID) magnetometry. Atomic force microscopy (AFM), x-ray energy dispersive spectroscopy (XEDS) and transmission electron microscopy (TEM) were used to examine the nanostructure of these materials. Obtained results indicate that GeMn QDs are crystalline, monodisperse and exhibit a ferromagnetic behavior with a Curie temperature (TC) above room temperature. They could be integrated into spintronic technology.

Induced Superconductivity and Engineered Josephson Tunneling Devices in Epitaxial (111)-Oriented Gold/Vanadium Heterostructures.

PubMed

Wei, Peng; Katmis, Ferhat; Chang, Cui-Zu; Moodera, Jagadeesh S

2016-04-13

We report a unique experimental approach to create topological superconductors by inducing superconductivity into epitaxial metallic thin film with strong spin-orbit coupling. Utilizing molecular beam epitaxy technique under ultrahigh vacuum conditions, we are able to achieve (111) oriented single phase of gold (Au) thin film grown on a well-oriented vanadium (V) s-wave superconductor film with clean interface. We obtained atomically smooth Au thin films with thicknesses even down to below a nanometer showing near-ideal surface quality. The as-grown V/Au bilayer heterostructure exhibits superconducting transition at around 3.9 K. Clear Josephson tunneling and Andreev reflection are observed in S-I-S tunnel junctions fabricated from the epitaxial bilayers. The barrier thickness dependent tunneling and the associated subharmonic gap structures (SGS) confirmed the induced superconductivity in Au (111), paving the way for engineering thin film heterostructures based on p-wave superconductivity and nano devices exploiting Majorana Fermions for quantum computing.

Process for depositing epitaxial alkaline earth oxide onto a substrate and structures prepared with the process

DOEpatents

McKee, Rodney A.; Walker, Frederick J.

1996-01-01

A process and structure involving a silicon substrate utilize molecular beam epitaxy (MBE) and/or electron beam evaporation methods and an ultra-high vacuum facility to grow a layup of epitaxial alkaline earth oxide films upon the substrate surface. By selecting metal constituents for the oxides and in the appropriate proportions so that the lattice parameter of each oxide grown closely approximates that of the substrate or base layer upon which oxide is grown, lattice strain at the film/film or film/substrate interface of adjacent films is appreciably reduced or relieved. Moreover, by selecting constituents for the oxides so that the lattice parameters of the materials of adjacent oxide films either increase or decrease in size from one parameter to another parameter, a graded layup of films can be grown (with reduced strain levels therebetween) so that the outer film has a lattice parameter which closely approximates that of, and thus accomodates the epitaxial growth of, a pervoskite chosen to be grown upon the outer film.

Postadsorption Work Function Tuning via Hydrogen Pressure Control

PubMed Central

2015-01-01

The work function of metal substrates can be easily tuned, for instance, by adsorbing layers of molecular electron donors and acceptors. In this work, we discuss the possibility of changing the donor/acceptor mixing ratio reversibly after adsorption by choosing a donor/acceptor pair that is coupled via a redox reaction and that is in equilibrium with a surrounding gas phase. We discuss such a situation for the example of tetrafluoro-1,4-benzenediol (TFBD)/tetrafluoro-1,4-benzoquinone (TFBQ), adsorbed on Cu(111) and Ag(111) surfaces. We use density functional theory and ab initio thermodynamics to show that arbitrary TFBD/TFBQ mixing ratios can be set using hydrogen pressures attainable in low to ultrahigh vacuum. Adjusting the mixing ratio allows modifying the work function over a range of about 1 eV. Finally, we contrast single-species submonolayers with mixed layers to discuss why the resulting inhomogeneities in the electrostatic energy above the surface have different impacts on the interfacial level alignment and the work function. PMID:26692915

Wear-resistant ball bearings for space applications

NASA Technical Reports Server (NTRS)

Boving, H.; Hintermann, H. E.; Hanni, W.; Bondivenne, E.; Boeto, M.; Conde, E.

1977-01-01

Ball bearings consisting of steel parts of which the rings are coated with hard, wear resistant, chemical vapor deposited TiC are described. Experiments conducted in ultrahigh vacuum, using cages of various materials with self-lubricating properties, show that such bearings are suitable for space applications. The results of laboratory tests on the ESA Meteosat Radiometer Focalizing mechanism, which contains six coated bearings, are summarized.

Magneto-ellipsometry as a powerful technique for investigating magneto-optical structures properties

NASA Astrophysics Data System (ADS)

Maximova, Olga; Kosyrev, Nikolay; Yakovlev, Ivan; Shevtsov, Dmitriy; Lyaschenko, Sergey; Varnakov, Sergey; Ovchinnikov, Sergey

2017-10-01

In this work we report on new magneto-ellipsometry set-up that allows to grow thin films and nanostructures by ultrahigh vacuum thermal evaporation as well as to conduct in situ measurements during the growth in order to analyze and control nanostructures properties. Ellipsometry and transverse magneto-optical Kerr effect measurements can be performed in situ inside this set-up. A uniform magnetic field of high intensity (more than 1 kOe) can be applied to samples inside the vacuum chamber. Also, we report on the developed method of data interpretation that is the base of the set-up software. Thus, we present a powerful tool for nanostructures synthesis and characterization.

Note: Sensitive fluorescence detection through minimizing the scattering light by anti-reflective nanostructured materials

NASA Astrophysics Data System (ADS)

Xu, Supeng; Yin, Yanning; Gu, Ruoxi; Xia, Meng; Xu, Liang; Chen, Li; Xia, Yong; Yin, Jianping

2018-04-01

We demonstrate a new approach with fabrication of anti-reflective coating to substantially reduce the scattering light in an ultra-high vacuum during laser induced fluorescence (LIF) detection. To do so, the surface of the vacuum chamber in the detection region was blackened and coated with the special solar heat absorbing nanomaterials. We demonstrate that more than 97.5% of the stray light in the chamber spanning from near infrared to ultraviolet can be absorbed which effectively improves the signal to noise (S/N) ratio. With this technique, the LIF signal from the cold magnesium monofluoride molecules has been observed with an S/N ratio of ˜4 times better than without that.

Surface temperature determination in surface analytic systems by infrared optical pyrometry

NASA Technical Reports Server (NTRS)

Wheeler, Donald R.; Jones, William R., Jr.; Pepper, Stephen V.

1988-01-01

An IR pyrometric technique for measuring the surface temperatures of metal specimens in an ultrahigh-vacuum analytic chamber is described and demonstrated. The experimental setup comprises a commercial IR microscope with a long-working-distance right-angle objective (focal spot diameter 1 mm at 53 cm), a metal-coated glass vacuum chamber with a Ta-mesh-covered quartz viewport, an Mo specimen stub with an internal heating element, and a Ta disk test specimen with a flat side coated with a high-emissivity graphite film. The results of an initial calibration test are presented graphically and briefly characterized. The measurement error at 450 C is found to be less than 10 C.

Effect of Test Environment on Lifetime of Two Vacuum Lubricants Determined by Spiral Orbit Tribometry

NASA Technical Reports Server (NTRS)

Pepper, Stephen V.

2011-01-01

The destruction rates of a perfluoropolyether (PFPE) lubricant, Krytox 143AC, subjected to rolling contact with 440C steel in a spiral orbit tribometer at room temperature have been evaluated as a function of test environment. The rates in ultrahigh vacuum, 0.213 kPa (1.6 torr) oxygen and one atmosphere of dry nitrogen were about the same. Water vapor in the test environment-a few ppm in one atmosphere of nitrogen-reduced the destruction rate by up to an order of magnitude. A similar effect of water vapor was found for the destruction rate of Pennzane 2001A, an unformulated multiply alkylated cyclopentane (MAC) hydrocarbon oil.

Beam-contamination-induced compositional alteration and its neutron-atypical consequences in ion simulation of neutron-induced void swelling

DOE PAGES

Gigax, Jonathan G.; Kim, Hyosim; Aydogan, Eda; ...

2017-05-16

Although accelerator-based ion irradiation has been widely accepted to simulate neutron damage, neutron-atypical features need to be carefully investigated. In this study, we have shown that Coulomb force drag by ion beams can introduce significant amounts of carbon, nitrogen, and oxygen into target materials even under ultra-high vacuum conditions. The resulting compositional and microstructural changes dramatically suppress void swelling. By applying a beam-filtering technique, introduction of vacuum contaminants is greatly minimized and the true swelling resistance of the alloys is revealed and matches neutron behavior closely. These findings are a significant step toward developing standardized procedures for emulating neutron damage.

Tribological Performance of Some Pennzane(Registered Trademark) Based Greases for Vacuum Applications

NASA Technical Reports Server (NTRS)

Marchetti, Mario; Jones, William R., Jr.; Street, Kenneth W.; Wheeler, Donald; Dixon, Duane; Jansen, Mark J.; Kimura, Hiroshi

2002-01-01

Commercial greases for space applications usually fulfill the requirements imposed by the severe conditions of use. The main requirement is their ability to create an EHL film, boundary film, or both under speed, load and temperature conditions that the mechanisms will operate. Three greases, all based on a multiply alkylated cyclopentane (Pennzan(R)) base oil, were studied. The thickeners were an n-octadecylterephthalamate soap, a lithium soap, and a urea derivative. A Four-Ball Tribometer and a Spiral Orbit Tribometer were employed to evaluate the greases under ultrahigh vacuum. Results indicated that all three greases yielded very low wear rates and extended lifetimes. In addition, routine physical property data is reported for each grease.

Ultra high vacuum heating and rotating specimen stage

DOEpatents

Coombs, III, Arthur W.

1995-01-01

A heating and rotating specimen stage provides for simultaneous specimen heating and rotating. The stage is ideally suited for operation in ultrahigh vacuum (1.times.10.sup.-9 torr or less), but is useful at atmosphere and in pressurized systems as well. A specimen is placed on a specimen holder that is attached to a heater that, in turn, is attached to a top housing. The top housing is rotated relative to a bottom housing and electrically connected thereto by electrically conductive brushes. This stage is made of materials that are compatible with UHV, able to withstand high temperatures, possess low outgassing rates, are gall and seize resistant, and are able to carry substantial electrical loading without overheating.

Ionization-Assisted Getter Pumping for Ultra-Stable Trapped Ion Frequency Standards

NASA Technical Reports Server (NTRS)

Tjoelker, Robert L.; Burt, Eric A.

2010-01-01

A method eliminates (or recovers from) residual methane buildup in getter-pumped atomic frequency standard systems by applying ionizing assistance. Ultra-high stability trapped ion frequency standards for applications requiring very high reliability, and/or low power and mass (both for ground-based and space-based platforms) benefit from using sealed vacuum systems. These systems require careful material selection and system processing (cleaning and high-temperature bake-out). Even under the most careful preparation, residual hydrogen outgassing from vacuum chamber walls typically limits the base pressure. Non-evaporable getter pumps (NEGs) provide a convenient pumping option for sealed systems because of low mass and volume, and no power once activated. An ion gauge in conjunction with a NEG can be used to provide a low mass, low-power method for avoiding the deleterious effects of methane buildup in high-performance frequency standard vacuum systems.

Interstellar and Planetary Analogs in the Laboratory

NASA Technical Reports Server (NTRS)

Salama, Farid

2013-01-01

We present and discuss the unique capabilities of the laboratory facility, COSmIC, that was developed at NASA Ames to investigate the interaction of ionizing radiation (UV, charged particles) with molecular species (neutral molecules, radicals and ions) and carbonaceous grains in the Solar System and in the Interstellar Medium (ISM). COSmIC stands for Cosmic Simulation Chamber, a laboratory chamber where interstellar and planetary analogs are generated, processed and analyzed. It is composed of a pulsed discharge nozzle (PDN) expansion that generates a free jet supersonic expansion in a plasma cavity coupled to two ultrahigh-sensitivity, complementary in situ diagnostics: a cavity ring down spectroscopy (CRDS) system for photonic detection and a Reflectron time-of-flight mass spectrometer (ReTOF-MS) for mass detection. This setup allows the study of molecules, ions and solids under the low temperature and high vacuum conditions that are required to simulate some interstellar, circumstellar and planetary physical environments providing new fundamental insights on the molecular level into the processes that are critical to the chemistry in the ISM, circumstellar and planet forming regions, and on icy objects in the Solar System. Recent laboratory results that were obtained using COSmIC will be discussed, in particular the progress that have been achieved in monitoring in the laboratory the formation of solid particles from their gas-phase molecular precursors in environments as varied as circumstellar outflow and planetary atmospheres.

Double-tilt in situ TEM holder with ultra-high stability.

PubMed

Xu, Mingjie; Dai, Sheng; Blum, Thomas; Li, Linze; Pan, Xiaoqing

2018-05-06

A double tilting holder with high stability is essential for acquiring atomic-scale information by transmission electron microscopy (TEM), but the availability of such holders for in situ TEM studies under various external stimuli is limited. Here, we report a unique design of seal-bearing components that provides ultra-high stability and multifunctionality (including double tilting) in an in situ TEM holder. The seal-bearing subsystem provides superior vibration damping and electrical insulation while maintaining excellent vacuum sealing and small form factor. A wide variety of in situ TEM applications including electrical measurement, STM mapping, photovoltaic studies, and CL spectroscopy can be performed on this platform with high spatial resolution imaging and electrical sensitivity at the pA scale. Copyright © 2018 Elsevier B.V. All rights reserved.

Large area scanning probe microscope in ultra-high vacuum demonstrated for electrostatic force measurements on high-voltage devices.

PubMed

Gysin, Urs; Glatzel, Thilo; Schmölzer, Thomas; Schöner, Adolf; Reshanov, Sergey; Bartolf, Holger; Meyer, Ernst

2015-01-01

The resolution in electrostatic force microscopy (EFM), a descendant of atomic force microscopy (AFM), has reached nanometre dimensions, necessary to investigate integrated circuits in modern electronic devices. However, the characterization of conducting or semiconducting power devices with EFM methods requires an accurate and reliable technique from the nanometre up to the micrometre scale. For high force sensitivity it is indispensable to operate the microscope under high to ultra-high vacuum (UHV) conditions to suppress viscous damping of the sensor. Furthermore, UHV environment allows for the analysis of clean surfaces under controlled environmental conditions. Because of these requirements we built a large area scanning probe microscope operating under UHV conditions at room temperature allowing to perform various electrical measurements, such as Kelvin probe force microscopy, scanning capacitance force microscopy, scanning spreading resistance microscopy, and also electrostatic force microscopy at higher harmonics. The instrument incorporates beside a standard beam deflection detection system a closed loop scanner with a scan range of 100 μm in lateral and 25 μm in vertical direction as well as an additional fibre optics. This enables the illumination of the tip-sample interface for optically excited measurements such as local surface photo voltage detection. We present Kelvin probe force microscopy (KPFM) measurements before and after sputtering of a copper alloy with chromium grains used as electrical contact surface in ultra-high power switches. In addition, we discuss KPFM measurements on cross sections of cleaved silicon carbide structures: a calibration layer sample and a power rectifier. To demonstrate the benefit of surface photo voltage measurements, we analysed the contact potential difference of a silicon carbide p/n-junction under illumination.

Tribochemical Competition within a MoS2/Ti Dry Lubricated Macroscale Contact in Ultrahigh Vacuum: A Time-of-Flight Secondary Ion Mass Spectrometry Investigation.

PubMed

Colas, Guillaume; Saulot, Aurélien; Philippon, David; Berthier, Yves; Léonard, Didier

2018-06-13

Controlling and predicting the tribological behavior of dry lubricants is a necessity to ensure low friction, long life, and low particle generation. Understanding the tribochemistry of the materials as a function of the environment is of primary interest as synergistic effects exist between the mechanics, the physicochemistry, and the thermodynamics within a contact. However, in most studies the role of the coating internal contaminants in the process is often discarded to the benefit of a more common approach in which the performances of the materials are compared as a function of different atmospheric pressure environments. The study focuses on the understanding of the tribochemical processes occurring between the materials and their internal contaminants inside an AISI440C contact lubricated by a MoS 2 /Ti coating. Time-of-flight secondary ion mass spectrometry is used to study at the molecular level, the material before and after friction. Friction tests with different durations are performed in ultrahigh vacuum at the macroscale to stay relevant to the real application (space). The adsorption/desorption of gaseous species during friction is monitored by mass spectrometry to ensure reliable study of the tribochemical processes inside the contact. The study shows that a competition exists between the Ti- and MoS 2 -based materials to create the appropriate lubricating materials via (i) recrystallization of MoS 2 materials with creation of a MoS x O y material via reactions with internal contaminants (presumably H 2 O), (ii) reaction of Ti-based materials with internal contaminants (mostly H 2 O and N 2 ). The biphasic material created is highly similar to the one created in both humid air and dry N 2 environments and providing low friction and low particle generation. However, the process is incomplete. The study thus brings insight into the possibility of controlling friction via a rational inclusion of reactants in a form of contaminants to control the tribochemical processes governing the low friction and long life.

Recent advances in vacuum sciences and applications

NASA Astrophysics Data System (ADS)

Mozetič, M.; Ostrikov, K.; Ruzic, D. N.; Curreli, D.; Cvelbar, U.; Vesel, A.; Primc, G.; Leisch, M.; Jousten, K.; Malyshev, O. B.; Hendricks, J. H.; Kövér, L.; Tagliaferro, A.; Conde, O.; Silvestre, A. J.; Giapintzakis, J.; Buljan, M.; Radić, N.; Dražić, G.; Bernstorff, S.; Biederman, H.; Kylián, O.; Hanuš, J.; Miloševič, S.; Galtayries, A.; Dietrich, P.; Unger, W.; Lehocky, M.; Sedlarik, V.; Stana-Kleinschek, K.; Drmota-Petrič, A.; Pireaux, J. J.; Rogers, J. W.; Anderle, M.

2014-04-01

Recent advances in vacuum sciences and applications are reviewed. Novel optical interferometer cavity devices enable pressure measurements with ppm accuracy. The innovative dynamic vacuum standard allows for pressure measurements with temporal resolution of 2 ms. Vacuum issues in the construction of huge ultra-high vacuum devices worldwide are reviewed. Recent advances in surface science and thin films include new phenomena observed in electron transport near solid surfaces as well as novel results on the properties of carbon nanomaterials. Precise techniques for surface and thin-film characterization have been applied in the conservation technology of cultural heritage objects and recent advances in the characterization of biointerfaces are presented. The combination of various vacuum and atmospheric-pressure techniques enables an insight into the complex phenomena of protein and other biomolecule conformations on solid surfaces. Studying these phenomena at solid-liquid interfaces is regarded as the main issue in the development of alternative techniques for drug delivery, tissue engineering and thus the development of innovative techniques for curing cancer and cardiovascular diseases. A review on recent advances in plasma medicine is presented as well as novel hypotheses on cell apoptosis upon treatment with gaseous plasma. Finally, recent advances in plasma nanoscience are illustrated with several examples and a roadmap for future activities is presented.

Measurement of Outgassing Rates of Steels.

PubMed

Park, Chongdo; Kim, Se-Hyun; Ki, Sanghoon; Ha, Taekyun; Cho, Boklae

2016-12-13

Steels are commonly used materials in the fabrication of vacuum systems because of their good mechanical, corrosion, and vacuum properties. A variety of steels meet the criterion of low outgassing required for high or ultrahigh vacuum applications. However, a given material can present different outgassing rates depending on its manufacturing process or the various pretreatment processes involved during the fabrication. Thus, the measurement of outgassing rates is highly desirable for a specific vacuum application. For this reason, the rate-of-pressure rise (RoR) method is often used to measure the outgassing of hydrogen after bakeout. In this article, a detailed description of the design and execution of the experimental protocol involved in the RoR method is provided. The RoR method uses a spinning rotor gauge to minimize errors that stem from outgassing or the pumping action of a vacuum gauge. The outgassing rates of two ordinary steels (stainless steel and mild steel) were measured. The measurements were made before and after the heat pretreatment of the steels. The heat pretreatment of steels was performed to reduce the outgassing. Extremely low rates of outgassing (on the order of 10 - 11 Pa m 3 sec - 1 m - 2 ) can be routinely measured using relatively small samples.

Construction of a Thermal Vacuum Chamber for Environment Test of Triple CubeSat Mission TRIO-CINEMA

NASA Astrophysics Data System (ADS)

Jeon, Jeheon; Lee, Seongwhan; Yoon, Seyoung; Seon, Jongho; Jin, Ho; Lee, Donghun; Lin, Robert P.

2013-12-01

TRiplet Ionospheric Observatory-CubeSat for Ion, Neutron, Electron & MAgnetic fields (TRIO-CINEMA) is a CubeSat with 3.14 kg in weight and 3-U (10 × 10 × 30 cm) in size, jointly developed by Kyung Hee University and UC Berkeley to measure magnetic fields of near Earth space and detect plasma particles. When a satellite is launched into orbit, it encounters ultrahigh vacuum and extreme temperature. To verify the operation and survivability of the satellite in such an extreme space environment, experimental tests are conducted on the ground using thermal vacuum chamber. This paper describes the temperature control device and monitoring system suitable for CubeSat test environment using the thermal vacuum chamber of the School of Space Research, Kyung Hee University. To build the chamber, we use a general purpose thermal analysis program and NX 6.0 TMG program. We carry out thermal vacuum tests on the two flight models developed by Kyung Hee University based on the thermal model of the TRIO-CINEMA satellite. It is expected from this experiment that proper operation of the satellite in the space environment will be achieved.

Adhesion in a Vacuum Environment and its Implications for Dust Mitigation Techniques on Airless Bodies

NASA Technical Reports Server (NTRS)

Berkebile, Stephen; Gaier, James R.

2012-01-01

During the Apollo missions, the adhesion of dust to critical spacecraft systems was a greater problem than anticipated and resulted in functional degradation of thermal control surfaces, spacesuit seals, and other spacecraft components. Notably, Earth-based simulation efforts did not predict the magnitude and effects of dust adhesion in the lunar environment. Forty years later, we understand that the ultrahigh vacuum (UHV) environment, coupled with micrometeorite impacts and constant ion and photon bombardment from the sun result in atomically clean and high surface energy dust particles and spacecraft surfaces. However, both the dominant mechanism of adhesion in airless environments and the conditions for high fidelity simulation tests have still to be determined. The experiments presented in here aim to aid in the development of dust mitigation techniques for airless bodies (e.g., lunar surface, asteroids, moons of outer planets). The approach taken consists of (a) quantifying the adhesion between common polymer and metallic spacecraft materials and a synthetic noritic volcanic glass, as a function of surface cleanliness and of triboelectric charge transfer in a UHV environment, and (b) determining parameters for high fidelity tests through investigation of adhesion dependence on vacuum environment and sample treatment. Adhesion force has been measured between pins of spacecraft materials and a plate of synthetic volcanic glass by determining the pull-off force with a torsion balance. Although no significant adhesion is generally observed directly as a result of high surface energies, the adhesion due to induced electrostatic charge is observed to increase with spacecraft material cleanliness, in some cases by over a factor of 10. Furthermore, electrostatically-induced adhesion is found to decrease rapidly above pressures of 10-6 torr. It is concluded that high-fidelity tests should be conducted in high to ultrahigh vacuum and include an ionized surface cleaning process.

A Systematic Cathode Study-Activation of a Thermionic Cathode, and Measuring Cesium Evaporation from a Dispenser Photocathode

DTIC Science & Technology

2010-06-01

QCM Quartz Crystal Deposition Monitor SEM Scanning Electron Microscope SRF Superconducting Radio Frequency T Torr Ti Titanium UHV Ultra...High Vacuum ( ᝺-7 Torr) UM University of Maryland QCM Quartz Crystal Deposition Monitor V Volt VAC Voltage-Alternating Current xvii...event. The two originally had problems with their tungsten filaments crystallizing and breaking. Being experimentalists, they added thorium in an

Frequency modulation detection atomic force microscopy in the liquid environment

NASA Astrophysics Data System (ADS)

Jarvis, S. P.; Ishida, T.; Uchihashi, T.; Nakayama, Y.; Tokumoto, H.

True atomic resolution imaging using frequency modulation detection is already well established in ultra-high vacuum. In this paper we demonstrate that it also has great potential in the liquid environment. Using a combination of magnetic activation and high-aspect-ratio carbon nanotube probes, we show that imaging can be readily combined with point spectroscopy, revealing both the tip-sample interaction and the structure of the intermediate liquid.

Tribological Characteristics and Applications of Superhard Coatings: CVD Diamond, DLC, and c-BN

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Murakawa, Masao; Watanabe, Shuichi; Takeuchi, Sadao; Wu, Richard L. C.

1999-01-01

Results of fundamental research on the tribological properties of chemical-vapor-deposited (CVD) diamond, diamondlike carbon, and cubic boron nitride films in sliding contact with CVD diamond in ultrahigh vacuum, dry nitrogen, humid air, and water are discussed. Furthermore, the actual and potential applications of the three different superhard coatings in the field of tribology technology, particularly for wear parts and tools, are reviewed.

JPRS Report, Science & Technology, China, High-Power Laser and Particle Beams

DTIC Science & Technology

1992-07-29

Thickness Nonuniformities on Polarization, Optical Image Properties of Laser, Beacon Light [Xiong Shengming, Zhang Yundong] 39 Effects of Phasing...superconducting cavity and an optical cathode high-intensity injector was presented with the objective of increasing the brightness of an FEL or...design was then revised and made simpler and more practical. The new design stresses safety and the ultrahigh-vacuum requirement associated with the Nb

Development of a torsion balance for adhesion measurements

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Maeda, Chikayoshi; Masuo, Ryuichi

1988-01-01

A new torsion balance for study of adhesion in ceramics is discussed. A torsion wire and a linear variable differential transformer are used to monitor load and to measure pull-off force (adhesion force). The investigation suggests that this torsion balance is valuable in studying the interfacial properties of ceramics in controlled environments such as in ultrahigh vacuum. The pull-off forces measured in dry, moist, and saturated nitrogen atmosphere demonstrate that the adhesion of silicon nitride contacts remains low at humidities below 80 percent but rises rapidly above that. The adhesion at saturation is 10 times or more greater than that below 80 percent relative humidity. The adhesion in a saturated atmosphere arises primarily from the surface tension effects of a thin film of water adsorbed on the surface. The surface tension of the water film was 58 x 10 to the minus 5 to 65 x 10 to the minus 5 power. The accepted value for water is 72.7 x 10 to the minus 5 power N/cm. Adhesion characteristics of silicon nitride in contact with metals, like the friction characteristics of silicon carbide to metal contacts, can be related to the relative chemical activity of metals in ultrahigh vacuum. The more active the metal, the higher the adhesion.

IN VITRO FLOW ANALYSIS OF NOVEL DOUBLE-CUTTING, OPEN-PORT, ULTRAHIGH-SPEED VITRECTOMY SYSTEMS.

PubMed

Zehetner, Claus; Moelgg, Marion; Bechrakis, Emmanouil; Linhart, Caroline; Bechrakis, Nikolaos E

2017-10-09

To analyze the performance and flow characteristics of novel double-cutting, open-port, 23-, 25-, and 27-gauge ultrahigh-speed vitrectomy systems. In vitro fluidic measurements were performed to assess the volumetric aspiration profiles of several vitrectomy systems in basic salt solution and egg white. Double-cutting open-port vitrectomy probes delivered stable aspiration flow rates that were less prone to flow variation affected by the cutting speed. Increase in cutting frequency to the maximum level resulted in flow reduction of less than 10% (0.0%-9.5%). Commercially available 23-, 25-, and 27-G double-cutting probes exhibited higher egg-white and basic salt solution flow rates at all evaluated cut rates, with aspirational efficiencies being 1.1 to 2.9 times the flow rates of standard single-blade vitrectomy probes of the same caliber at the maximum preset vacuum. The highest relative differences were observed at faster cut rates. The newly introduced double-cutting open-port vitrectomy probes delivered stable aspiration flow rates that were less prone to flow variation affected by the cutting speed. The fluidic principle of constant flow even at the highest cut rates and low vacuum levels might impact surgical strategies, especially when performing manipulations close to the retina.

Decomposition of L a 2 – x S r x Cu O 4 into several L a 2 O 3 phases at elevated temperatures in ultrahigh vacuum inside a transmission electron microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeong, Jong Seok; Wu, Wangzhou; Topsakal, Mehmet

Here, we report the decomposition of La 2–xSr xCuO 4 into La 2O 3 and Cu nanoparticles in ultrahigh vacuum, observed by in situ heating experiments in a transmission electron microscope. The analysis of electron diffraction data reveals that the phase decomposition process starts at about 150°C and is considerably expedited in the temperature range of 350°C–450°C. Two major resultant solid phases are identified as metallic Cu and La 2O 3 by electron diffraction, simulation, and electron energy-loss spectroscopy (EELS) analyses. With the aid of calculations, La 2O 3 phases are further identified to be derivatives of a fluorite structure—fluorite,more » pyrochlore, and (distorted) bixbyite—characterized by different oxygen-vacancy order. Additionally, the bulk plasmon energy and the fine structures of the O K and LaM 4,5 EELS edges are reported for these structures, along with simulated O K x-ray absorption near-edge structure. The resultant Cu nanoparticles and La 2O 3 phases remain unchanged after cooling to room temperature.« less

Sample mounting and transfer for coupling an ultrahigh vacuum variable temperature beetle scanning tunneling microscope with conventional surface probes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nafisi, Kourosh; Ranau, Werner; Hemminger, John C.

2001-01-01

We present a new ultrahigh vacuum (UHV) chamber for surface analysis and microscopy at controlled, variable temperatures. The new instrument allows surface analysis with Auger electron spectroscopy, low energy electron diffraction, quadrupole mass spectrometer, argon ion sputtering gun, and a variable temperature scanning tunneling microscope (VT-STM). In this system, we introduce a novel procedure for transferring a sample off a conventional UHV manipulator and onto a scanning tunneling microscope in the conventional ''beetle'' geometry, without disconnecting the heating or thermocouple wires. The microscope, a modified version of the Besocke beetle microscope, is mounted on a 2.75 in. outer diameter UHVmore » flange and is directly attached to the base of the chamber. The sample is attached to a tripod sample holder that is held by the main manipulator. Under UHV conditions the tripod sample holder can be removed from the main manipulator and placed onto the STM. The VT-STM has the capability of acquiring images between the temperature range of 180--500 K. The performance of the chamber is demonstrated here by producing an ordered array of island vacancy defects on a Pt(111) surface and obtaining STM images of these defects.« less

Construction and evaluation of an ultrahigh-vacuum-compatible sputter deposition source

NASA Astrophysics Data System (ADS)

Lackner, Peter; Choi, Joong Il Jake; Diebold, Ulrike; Schmid, Michael

2017-10-01

A sputter deposition source for the use in ultrahigh vacuum (UHV) is described, and some properties of the source are analyzed. The operating principle is based on the design developed by Mayr et al. [Rev. Sci. Instrum. 84, 094103 (2013)], where electrons emitted from a filament ionize argon gas and the Ar+ ions are accelerated to the target. In contrast to the original design, two grids are used to direct a large fraction of the Ar+ ions to the target, and the source has a housing cooled by liquid nitrogen to reduce contaminations. The source has been used for the deposition of zirconium, a material that is difficult to evaporate in standard UHV evaporators. At an Ar pressure of 9 ×1 0-6 mbar in the UHV chamber and moderate emission current, a highly reproducible deposition rate of ≈1 ML in 250 s was achieved at the substrate (at a distance of ≈50 mm from the target). Higher deposition rates are easily possible. X-ray photoelectron spectroscopy shows a high purity of the deposited films. Depending on the grid voltages, the substrate gets mildly sputtered by Ar+ ions; in addition, the substrate is also reached by electrons from the negatively biased sputter target.

Decomposition of L a 2 – x S r x Cu O 4 into several L a 2 O 3 phases at elevated temperatures in ultrahigh vacuum inside a transmission electron microscope

DOE PAGES

Jeong, Jong Seok; Wu, Wangzhou; Topsakal, Mehmet; ...

2018-05-15

Here, we report the decomposition of La 2–xSr xCuO 4 into La 2O 3 and Cu nanoparticles in ultrahigh vacuum, observed by in situ heating experiments in a transmission electron microscope. The analysis of electron diffraction data reveals that the phase decomposition process starts at about 150°C and is considerably expedited in the temperature range of 350°C–450°C. Two major resultant solid phases are identified as metallic Cu and La 2O 3 by electron diffraction, simulation, and electron energy-loss spectroscopy (EELS) analyses. With the aid of calculations, La 2O 3 phases are further identified to be derivatives of a fluorite structure—fluorite,more » pyrochlore, and (distorted) bixbyite—characterized by different oxygen-vacancy order. Additionally, the bulk plasmon energy and the fine structures of the O K and LaM 4,5 EELS edges are reported for these structures, along with simulated O K x-ray absorption near-edge structure. The resultant Cu nanoparticles and La 2O 3 phases remain unchanged after cooling to room temperature.« less

Effects of the local environment on CNT-based nanoelectronics: development of a microenvironment probe station.

PubMed

McClain, Devon; Thomas, Nicole; Nguyen, Tri; O'Brien, Kevin P; Jiao, Jun

2010-11-01

In this study, we report the development of a microenvironment probe station capable of detecting the effect of small changes to the local environment around a carbon nanotube conduction channel. The microenvironment probe station is highly versatile and is used to characterize alterations in carbon nanotube field effect transistor electrical behavior in response to changes in temperature, gas species, infrared and ultraviolet light. All devices were electrically characterized in atmospheric, ultrahigh vacuum and oxygen-rich environments. The results suggest that devices could be changed from n-type at 1 x 10(-8) torr through an intermediate ambipolar state at 1 x 10(-4) torr to p-type at atmosphere solely by increasing the oxygen concentration. The average resistance of these carbon nanotube field effect transistors after annealing was observed to decrease by approximately 54% from their initial value under ultrahigh vacuum to their final value in the presence of pure oxygen while corresponding threshold voltages shifts were also observed. Illumination with infrared light resulted in a approximately 10% increase in drain current with an estimated response time <1 fs due to photon-induced electron-hole pair generation. Illumination with ultraviolet light resulted in approximately 5-15% reduction in drain current due to photon-induced desorption of oxygen adsorbate.

Additive manufacturing of magnetic shielding and ultra-high vacuum flange for cold atom sensors.

PubMed

Vovrosh, Jamie; Voulazeris, Georgios; Petrov, Plamen G; Zou, Ji; Gaber, Youssef; Benn, Laura; Woolger, David; Attallah, Moataz M; Boyer, Vincent; Bongs, Kai; Holynski, Michael

2018-01-31

Recent advances in the understanding and control of quantum technologies, such as those based on cold atoms, have resulted in devices with extraordinary metrological performance. To realise this potential outside of a lab environment the size, weight and power consumption need to be reduced. Here we demonstrate the use of laser powder bed fusion, an additive manufacturing technique, as a production technique relevant to the manufacture of quantum sensors. As a demonstration we have constructed two key components using additive manufacturing, namely magnetic shielding and vacuum chambers. The initial prototypes for magnetic shields show shielding factors within a factor of 3 of conventional approaches. The vacuum demonstrator device shows that 3D-printed titanium structures are suitable for use as vacuum chambers, with the test system reaching base pressures of 5 ± 0.5 × 10 -10 mbar. These demonstrations show considerable promise for the use of additive manufacturing for cold atom based quantum technologies, in future enabling improved integrated structures, allowing for the reduction in size, weight and assembly complexity.

Ultrahigh mobility and efficient charge injection in monolayer organic thin-film transistors on boron nitride.

PubMed

He, Daowei; Qiao, Jingsi; Zhang, Linglong; Wang, Junya; Lan, Tu; Qian, Jun; Li, Yun; Shi, Yi; Chai, Yang; Lan, Wei; Ono, Luis K; Qi, Yabing; Xu, Jian-Bin; Ji, Wei; Wang, Xinran

2017-09-01

Organic thin-film transistors (OTFTs) with high mobility and low contact resistance have been actively pursued as building blocks for low-cost organic electronics. In conventional solution-processed or vacuum-deposited OTFTs, due to interfacial defects and traps, the organic film has to reach a certain thickness for efficient charge transport. Using an ultimate monolayer of 2,7-dioctyl[1]benzothieno[3,2- b ][1]benzothiophene (C 8 -BTBT) molecules as an OTFT channel, we demonstrate remarkable electrical characteristics, including intrinsic hole mobility over 30 cm 2 /Vs, Ohmic contact with 100 Ω · cm resistance, and band-like transport down to 150 K. Compared to conventional OTFTs, the main advantage of a monolayer channel is the direct, nondisruptive contact between the charge transport layer and metal leads, a feature that is vital for achieving low contact resistance and current saturation voltage. On the other hand, bilayer and thicker C 8 -BTBT OTFTs exhibit strong Schottky contact and much higher contact resistance but can be improved by inserting a doped graphene buffer layer. Our results suggest that highly crystalline molecular monolayers are promising form factors to build high-performance OTFTs and investigate device physics. They also allow us to precisely model how the molecular packing changes the transport and contact properties.

Ultrahigh mobility and efficient charge injection in monolayer organic thin-film transistors on boron nitride

PubMed Central

He, Daowei; Qiao, Jingsi; Zhang, Linglong; Wang, Junya; Lan, Tu; Qian, Jun; Li, Yun; Shi, Yi; Chai, Yang; Lan, Wei; Ono, Luis K.; Qi, Yabing; Xu, Jian-Bin; Ji, Wei; Wang, Xinran

2017-01-01

Organic thin-film transistors (OTFTs) with high mobility and low contact resistance have been actively pursued as building blocks for low-cost organic electronics. In conventional solution-processed or vacuum-deposited OTFTs, due to interfacial defects and traps, the organic film has to reach a certain thickness for efficient charge transport. Using an ultimate monolayer of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) molecules as an OTFT channel, we demonstrate remarkable electrical characteristics, including intrinsic hole mobility over 30 cm2/Vs, Ohmic contact with 100 Ω · cm resistance, and band-like transport down to 150 K. Compared to conventional OTFTs, the main advantage of a monolayer channel is the direct, nondisruptive contact between the charge transport layer and metal leads, a feature that is vital for achieving low contact resistance and current saturation voltage. On the other hand, bilayer and thicker C8-BTBT OTFTs exhibit strong Schottky contact and much higher contact resistance but can be improved by inserting a doped graphene buffer layer. Our results suggest that highly crystalline molecular monolayers are promising form factors to build high-performance OTFTs and investigate device physics. They also allow us to precisely model how the molecular packing changes the transport and contact properties. PMID:28913429

Ultra-high Temperature Emittance Measurements for Space and Missile Applications

NASA Technical Reports Server (NTRS)

Rogers, Jan; Crandall, David

2009-01-01

Advanced modeling and design efforts for many aerospace components require high temperature emittance data. Applications requiring emittance data include propulsion systems, radiators, aeroshells, heatshields/thermal protection systems, and leading edge surfaces. The objective of this work is to provide emittance data at ultra-high temperatures. MSFC has a new instrument for the measurement of emittance at ultra-high temperatures, the Ultra-High Temperature Emissometer System (Ultra-HITEMS). AZ Technology Inc. developed the instrument, designed to provide emittance measurements over the temperature range 700-3500K. The Ultra-HITEMS instrument measures the emittance of samples, heated by lasers, in vacuum, using a blackbody source and a Fourier Transform Spectrometer. Detectors in a Nicolet 6700 FT-IR spectrometer measure emittance over the spectral range of 0.4-25 microns. Emitted energy from the specimen and output from a Mikron M390S blackbody source at the same temperature with matched collection geometry are measured. Integrating emittance over the spectral range yields the total emittance. The ratio provides a direct measure of total hemispherical emittance. Samples are heated using lasers. Optical pyrometry provides temperature data. Optical filters prevent interference from the heating lasers. Data for Inconel 718 show excellent agreement with results from literature and ASTM 835. Measurements taken from levitated spherical specimens provide total hemispherical emittance data; measurements taken from flat specimens mounted in the chamber provide near-normal emittance data. Data from selected characterization studies will be presented. The Ultra-HITEMS technique could advance space and missile technologies by advancing the knowledge base and the technology readiness level for ultra-high temperature materials.

Quartz resonator processing system

DOEpatents

Peters, Roswell D. M.

1983-01-01

Disclosed is a single chamber ultra-high vacuum processing system for the oduction of hermetically sealed quartz resonators wherein electrode metallization and sealing are carried out along with cleaning and bake-out without any air exposure between the processing steps. The system includes a common vacuum chamber in which is located a rotatable wheel-like member which is adapted to move a plurality of individual component sets of a flat pack resonator unit past discretely located processing stations in said chamber whereupon electrode deposition takes place followed by the placement of ceramic covers over a frame containing a resonator element and then to a sealing stage where a pair of hydraulic rams including heating elements effect a metallized bonding of the covers to the frame.

Effect of Test Environment on Lifetime of Two Vacuum Lubricants Determined by Spiral Orbit Tribometry

NASA Technical Reports Server (NTRS)

Pepper, Stephen V.

2006-01-01

The destruction rates of a perfluoropolyether (PFPE) lubricant, Krytox 143AC(TradeMark), subjected to rolling contact with 440C steel in a spiral orbit tribometer at room temperature have been evaluated as a function of test environment. The rates in ultrahigh vacuum, 0.21 3 kPa (1.6 Torr) oxygen and one atmosphere of dry nitrogen were about the same. Water vapor in the test environment - a few ppm in one atmosphere of nitrogen - reduced the destruction rate by up to an order of magnitude. A similar effect of water vapor was found for the destruction rate of Pennzane(Registered TradeMark) 2001A , an unformulated multiply alkylated cyclopentane (MAC) hydrocarbon oil.

A UHV compatible source for a highly polarized thermal atomic beam of radioactive 8Li

NASA Astrophysics Data System (ADS)

Jänsch, H. J.; Kirchner, G.; Kühlert, O.; Lisowski, M.; Paggel, J. J.; Platzer, R.; Schillinger, R.; Tilsner, H.; Weindel, C.; Winnefeld, H.; Fick, D.

2000-12-01

A beam of the radioactive isotope 8Li is prepared at thermal velocities. The nuclei are highly spin polarized by transverse optical pumping of the thermal beam. The installation is ultra-high vacuum (UHV) compatible in a non-UHV accelerator environment. Since the atomic beam is used in a surface science experiment, where contamination must be avoided, special emphasis is given to the vacuum coupling of the accelerator/ 8Li production/surface experimental areas. The atomic beam is produced by stopping the nuclear reaction products and evaporating them again from high-temperature graphite. To enhance the atomic beam, a novel tubular thermalizer is applied. The thermal polarized atomic beam intensity is approximately 5×10 8 atoms/s sr.

Ultra high vacuum heating and rotating specimen stage

DOEpatents

Coombs, A.W. III

1995-05-02

A heating and rotating specimen stage provides for simultaneous specimen heating and rotating. The stage is ideally suited for operation in ultrahigh vacuum (1{times}10{sup {minus}9} torr or less), but is useful at atmosphere and in pressurized systems as well. A specimen is placed on a specimen holder that is attached to a heater that, in turn, is attached to a top housing. The top housing is rotated relative to a bottom housing and electrically connected thereto by electrically conductive brushes. This stage is made of materials that are compatible with UHV, able to withstand high temperatures, possess low outgassing rates, are gall and seize resistant, and are able to carry substantial electrical loading without overheating. 5 figs.

Interaction of sulfur dioxide and carbon dioxide with clean silver in ultrahigh vacuum.

NASA Technical Reports Server (NTRS)

Lassiter, W. S.

1972-01-01

It is shown that when a clean polycrystalline silver surface is subjected to sulfur dioxide at a pressure of 1 nanotorr, sulfur is chemisorbed to the silver. Heating the contaminated silver leads to an estimation of the minimum heat of desorption of 59 kcal/mol. Sulfur Auger peak height and relative function measurements of the surface during exposure show that adsorption occurs during 6 microtorr/sec exposure at 1 nanotorr.

Materials processing in space bibliography, 1983, revised

NASA Technical Reports Server (NTRS)

Pentecost, E. (Compiler)

1983-01-01

Flight experiments utilizing a low gravity environment to elucidate and control various processes, or ground based activities that provide supporting research are compiled. Six major categories: crystal growth; solidification of metals, alloys, and composites; fluids, transports, and chemical processes; glasses and ceramics; ultrahigh vacuum and containerless processing technologies; and combustion are included. A list of patents and appendices providing a compilation of anonymously authored collections and reports and a cross reference index are included.

Nanofabrication by advanced electron microscopy using intense and focused beam∗.

PubMed

Furuya, Kazuo

2008-01-01

The nanogrowth and nanofabrication of solid substances using an intense and focused electron beam are reviewed in terms of the application of scanning and transmission electron microscopy (SEM, TEM and STEM) to control the size, position and structure of nanomaterials. The first example discussed is the growth of freestanding nanotrees on insulator substrates by TEM. The growth process of the nanotrees was observed in situ and analyzed by high-resolution TEM (HRTEM) and was mainly controlled by the intensity of the electron beam. The second example is position- and size-controlled nanofabrication by STEM using a focused electron beam. The diameters of the nanostructures grown ranged from 4 to 20 nm depending on the size of the electron beam. Magnetic nanostructures were also obtained using an iron-containing precursor gas, Fe(CO) 5 . The freestanding iron nanoantennas were examined by electron holography. The magnetic field was observed to leak from the nanostructure body which appeared to act as a 'nanomagnet'. The third example described is the effect of a vacuum on the size and growth process of fabricated nanodots containing W in an ultrahigh-vacuum field-emission TEM (UHV-FE-TEM). The size of the dots can be controlled by changing the dose of electrons and the partial pressure of the precursor. The smallest particle size obtained was about 1.5 nm in diameter, which is the smallest size reported using this method. Finally, the importance of a smaller probe and a higher electron-beam current with atomic resolution is emphasized and an attempt to develop an ultrahigh-vacuum spherical aberration corrected STEM (Cs-corrected STEM) at NIMS is reported.

Nanofabrication by advanced electron microscopy using intense and focused beam∗

PubMed Central

Furuya, Kazuo

2008-01-01

The nanogrowth and nanofabrication of solid substances using an intense and focused electron beam are reviewed in terms of the application of scanning and transmission electron microscopy (SEM, TEM and STEM) to control the size, position and structure of nanomaterials. The first example discussed is the growth of freestanding nanotrees on insulator substrates by TEM. The growth process of the nanotrees was observed in situ and analyzed by high-resolution TEM (HRTEM) and was mainly controlled by the intensity of the electron beam. The second example is position- and size-controlled nanofabrication by STEM using a focused electron beam. The diameters of the nanostructures grown ranged from 4 to 20 nm depending on the size of the electron beam. Magnetic nanostructures were also obtained using an iron-containing precursor gas, Fe(CO)5. The freestanding iron nanoantennas were examined by electron holography. The magnetic field was observed to leak from the nanostructure body which appeared to act as a ‘nanomagnet’. The third example described is the effect of a vacuum on the size and growth process of fabricated nanodots containing W in an ultrahigh-vacuum field-emission TEM (UHV-FE-TEM). The size of the dots can be controlled by changing the dose of electrons and the partial pressure of the precursor. The smallest particle size obtained was about 1.5 nm in diameter, which is the smallest size reported using this method. Finally, the importance of a smaller probe and a higher electron-beam current with atomic resolution is emphasized and an attempt to develop an ultrahigh-vacuum spherical aberration corrected STEM (Cs-corrected STEM) at NIMS is reported. PMID:27877936

Dual analyzer system for surface analysis dedicated for angle-resolved photoelectron spectroscopy at liquid surfaces and interfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Niedermaier, Inga; Kolbeck, Claudia; Steinrück, Hans-Peter

The investigation of liquid surfaces and interfaces with the powerful toolbox of ultra-high vacuum (UHV)-based surface science techniques generally has to overcome the issue of liquid evaporation within the vacuum system. In the last decade, however, new classes of liquids with negligible vapor pressure at room temperature—in particular, ionic liquids (ILs)—have emerged for surface science studies. It has been demonstrated that particularly angle-resolved X-ray Photoelectron Spectroscopy (ARXPS) allows for investigating phenomena that occur at gas-liquid and liquid-solid interfaces on the molecular level. The results are not only relevant for IL systems but also for liquids in general. In all ofmore » these previous ARXPS studies, the sample holder had to be tilted in order to change the polar detection angle of emitted photoelectrons, which restricted the liquid systems to very thin viscous IL films coating a flat solid support. We now report on the concept and realization of a new and unique laboratory “Dual Analyzer System for Surface Analysis (DASSA)” which enables fast ARXPS, UV photoelectron spectroscopy, imaging XPS, and low-energy ion scattering at the horizontal surface plane of macroscopically thick non-volatile liquid samples. It comprises a UHV chamber equipped with two electron analyzers mounted for simultaneous measurements in 0° and 80° emission relative to the surface normal. The performance of DASSA on a first macroscopic liquid system will be demonstrated.« less

NOVEL CHAMBER DESIGN FOR AN IN-VACUUM CRYO-COOLED MINI-GAP UNDULATOR.

DOE Office of Scientific and Technical Information (OSTI.GOV)

HU, J.-P.; FOERSTER, C.L.; SKARITKA, J.R.

2006-05-24

A stainless steel, Ultra-High Vacuum (UHV) chamber, featuring a large vertical rectangular port (53''W by 16''H), has been fabricated to house the one-meter magnet assembly of a newly installed undulator insertion device for beamline X-25 at the National Synchrotron Light Source. To achieve UHV, the new chamber is equipped with a differential ion pump, NEG pump, nude ion gauge, residual gas analyzer, and an all metal roughing valve. Temperature of the magnet assembly is maintained below 90 C during vacuum bake. The large rectangular port cover is sealed to the main flange of the chamber using a one-piece flat aluminummore » gasket and special sealing surfaces developed exclusively by Nor-Cal Products, Inc. The large flange provides easy access to the gap of the installed magnet girders for in situ magnetic measurements and shimming. Special window ports were designed into the cover and chamber for manipulation of optical micrometers external to the chamber to provide precise measurements of the in-vacuum magnet gap. The vacuum chamber assembly features independently vacuum-isolated feedthroughs that can be used for either water-or-cryogenic refrigeration-cooling of the monolithic magnet girders. This would allow for cryogenic-cooled permanent magnet operation and has been successfully tested within temperature range of +100 C to -150 C. Details of the undulator assembly for beamline X-25 is described in the paper.« less

Manipulator having thermally conductive rotary joint for transferring heat from a test specimen

DOEpatents

Haney, Steven J.; Stulen, Richard H.; Toly, Norman F.

1985-01-01

A manipulator for rotatably moving a test specimen in an ultra-high vacuum chamber includes a translational unit movable in three mutually perpendicular directions. A manipulator frame is rigidly secured to the translational unit for rotatably supporting a rotary shaft. A first copper disc is rigidly secured to an end of the rotary shaft for rotary movement within the vacuum chamber. A second copper disc is supported upon the first disc. The second disc receives a cryogenic cold head and does not rotate with the first disc. A sapphire plate is interposed between the first and second discs to prevent galling of the copper material while maintaining high thermal conductivity between the first and second discs. A spring is disposed on the shaft to urge the second disc toward the first disc and compressingly engage the interposed sapphire plate. A specimen mount is secured to the first disc for rotation within the vacuum chamber. The specimen maintains high thermal conductivity with the second disc receiving the cryogenic transfer line.

Lubricated Bearing Lifetimes of a Multiply Alkylated Cyclopentane and a Linear Perfluoropolyether Fluid in Oscillatory Motion at Elevated Temperatures in Ultrahigh Vacuum

NASA Technical Reports Server (NTRS)

Braza, Joseph; Jansen, Mark J.; Jones, William R.

2009-01-01

Bearing life tests in vacuum with three space liquid lubricants, two multiply alkylated cyclopentanes (MACs) and a linear perfluoropolyether (PFPE) were performed. Test conditions included: an 89 N axial load (mean Hertzian stress 0.66 GPa), vacuum level below 7x10(exp -4) Pa, and a +/-30deg dither angle. Dither rate was 75 cycles per minute. Higher (110 to 122 C) and lower temperature tests (75 C) were performed. For the higher temperature tests, the PFPE, Fomblin (Ausimont SpA) Z25 outperformed Pennzane (Shell Global Solutions) X-2000 by more than an order of magnitude. Lubricant evaporation played a key role in these high temperature results. At 75 C, the order was reversed with both Pennzane X-1000 and X-2000 outperforming Fomblin Z25 by more than an order of magnitude. Most Pennzane tests were suspended without failure. The primary failure mechanism in these lower temperature tests was lubricant consumption in the tribocontacts.

High field electron paramagnetic resonance spectroscopy under ultrahigh vacuum conditions—A multipurpose machine to study paramagnetic species on well defined single crystal surfaces

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rocker, J.; Cornu, D.; Kieseritzky, E.

2014-08-01

A new ultrahigh vacuum (UHV) electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz to investigate paramagnetic centers on single crystal surfaces is described. It is particularly designed to study paramagnetic centers on well-defined model catalysts using epitaxial thin oxide films grown on metal single crystals. The EPR setup is based on a commercial Bruker E600 spectrometer, which is adapted to ultrahigh vacuum conditions using a home made Fabry Perot resonator. The key idea of the resonator is to use the planar metal single crystal required to grow the single crystalline oxide films as one of the mirrors of themore » resonator. EPR spectroscopy is solely sensitive to paramagnetic species, which are typically minority species in such a system. Hence, additional experimental characterization tools are required to allow for a comprehensive investigation of the surface. The apparatus includes a preparation chamber hosting equipment, which is required to prepare supported model catalysts. In addition, surface characterization tools such as low energy electron diffraction (LEED)/Auger spectroscopy, temperature programmed desorption (TPD), and infrared reflection absorption spectroscopy (IRAS) are available to characterize the surfaces. A second chamber used to perform EPR spectroscopy at 94 GHz has a room temperature scanning tunneling microscope attached to it, which allows for real space structural characterization. The heart of the UHV adaptation of the EPR experiment is the sealing of the Fabry-Perot resonator against atmosphere. To this end it is possible to use a thin sapphire window glued to the backside of the coupling orifice of the Fabry Perot resonator. With the help of a variety of stabilization measures reducing vibrations as well as thermal drift it is possible to accumulate data for a time span, which is for low temperature measurements only limited by the amount of liquid helium. Test measurements show that the system can detect paramagnetic species with a density of approximately 5 × 10{sup 11} spins/cm{sup 2}, which is comparable to the limit obtained for the presently available UHV-EPR spectrometer operating at 10 GHz (X-band). Investigation of electron trapped centers in MgO(001) films shows that the increased resolution offered by the experiments at W-band allows to identify new paramagnetic species, that cannot be differentiated with the currently available methodology.« less

Understanding the Reaction Chemistry of 2,2':5',2''-Terthiophene Films with Vapor-Deposited Ag, Al, and Ca

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sang, Lingzi; Matz, Dallas L.; Pemberton, Jeanne E.

The reaction chemistry of vapor-deposited 2,2':5',2''-terthiophene (α-3T) solid-state thin films with postdeposited Ag, Al, and Ca is investigated in ultrahigh vacuum using Raman spectroscopy. Vapor-deposited Ag forms nanoparticles on these films and induces considerable surface enhanced Raman scattering (SERS) along with a change in molecular symmetry of adjacent α-3T and formation of Ag–S bonds; no other reaction chemistry is observed. Vapor-deposited Al and Ca undergo chemical reaction with α-3T initiated by metal-to-α-3T electron transfer. For Al, the resulting product is predominantly amorphous carbon through initial radical formation and subsequent decomposition reactions. For Ca, the spectral evidence suggests two pathways: onemore » leading to α-3T polymerization and the other resulting in thiophene ring opening, both initiated by radical formation through Ca-to-α-3T electron transfer. These interfacial reactions reflect the complex chemistry that can occur between low work function metals and thiophene-based oligomers. This reactivity is strongly correlated with metal work function.« less

Understanding the Reaction Chemistry of 2,2':5',2"-Terthiophene Films with Vapor-Deposited Ag, Al, and Ca

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sang, Lingzi; Matz, Dallas L.; Pemberton, Jeanne E.

The reaction chemistry of vapor-deposited 2,2':5',2''-terthiophene (α-3T) solid-state thin films with postdeposited Ag, Al, and Ca is investigated in ultrahigh vacuum using Raman spectroscopy. Vapor-deposited Ag forms nanoparticles on these films and induces considerable surface enhanced Raman scattering (SERS) along with a change in molecular symmetry of adjacent α-3T and formation of Ag–S bonds; no other reaction chemistry is observed. Vapor-deposited Al and Ca undergo chemical reaction with α-3T initiated by metal-to-α-3T electron transfer. For Al, the resulting product is predominantly amorphous carbon through initial radical formation and subsequent decomposition reactions. For Ca, the spectral evidence suggests two pathways: onemore » leading to α-3T polymerization and the other resulting in thiophene ring opening, both initiated by radical formation through Ca-to-α-3T electron transfer. These interfacial reactions reflect the complex chemistry that can occur between low work function metals and thiophene-based oligomers. This reactivity is strongly correlated with metal work function.« less

In-situ ellipsometric studies of optical and surface properties of GaAs(100) at elevated temperatures

NASA Technical Reports Server (NTRS)

Yao, Huade; Snyder, Paul G.

1991-01-01

A rotating-polarizer ellipsometer was attached to an ultrahigh vacuum (UHV) chamber. A GaAs(100) sample was introduced into the UHV chamber and heated at anumber of fixed elevated temperatures, without arsenic overpressure. In-situ spectroscopic ellipsometric (SE) measurements were taken, through a pair of low-strain quartz windows, to monitor the surface changes and measure the pseudodielectric functions at elevated temperatures. Real-time data from GaAs surface covered with native oxide showed clearly the evolution of oxide desorption at approximately 580 C. In addition, surface degradation was found before and after the oxide desorption. An oxide free and smooth GaAs surface was obtained by depositing an arsenic protective coating onto a molecular beam epitaxy grown GaAs surface. The arsenic coating was evaporated immediately prior to SE measurements. A comparison showed that our room temperature data from this GaAs surface, measured in the UHV, are in good agreement with those in the literature obtained by wet-chemical etching. The surface also remained clean and smooth at higher temperatures, so that reliable temperature-dependent dielectric functions were obtained.

Scanning probe microscopy induced surface modifications of the topological insulator Bi2Te3 in different environments

NASA Astrophysics Data System (ADS)

Netsou, Asteriona-Maria; Thupakula, Umamahesh; Debehets, Jolien; Chen, Taishi; Hirsch, Brandon; Volodin, Alexander; Li, Zhe; Song, Fengqi; Seo, Jin Won; De Feyter, Steven; Schouteden, Koen; Van Haesendonck, Chris

2017-08-01

We investigated the topological insulator (TI) Bi2Te3 in four different environments (ambient, ultra-high vacuum (UHV), nitrogen gas and organic solvent environment) using scanning probe microscopy (SPM) techniques. Upon prolonged exposure to ambient conditions and organic solvent environments the cleaved surface of the pristine Bi2Te3 is observed to be strongly modified during SPM measurements, while imaging of freshly cleaved Bi2Te3 in UHV and nitrogen gas shows considerably less changes of the Bi2Te3 surface. We conclude that the reduced surface stability upon exposure to ambient conditions is triggered by adsorption of molecular species from ambient, including H2O, CO2, etc which is verified by Auger electron spectroscopy. Our findings of the drastic impact of exposure to ambient on the Bi2Te3 surface are crucial for further in-depth studies of the intrinsic properties of the TI Bi2Te3 and for potential applications that include room temperature TI based devices operated under ambient conditions.

Sulfur amino acids and alanine on pyrite (100) by X-ray photoemission spectroscopy: Surface or molecular role?

NASA Astrophysics Data System (ADS)

Sanchez-Arenillas, M.; Galvez-Martinez, S.; Mateo-Marti, E.

2017-08-01

This paper describes the first successful adsorption of the cysteine, cystine, methionine and alanine amino acids on the pyrite (100) surface under ultra-high vacuum conditions with crucial chemical adsorption parameters driving the process. We have demonstrated by X-ray photoemission spectroscopy (XPS) that the surface pretreatment annealing process on pyrite surfaces is a critical parameter driving surface reactivity. The presence of enriched monosulfide species on the pyrite (100) surface favours the amino acid NH2 chemical form, whereas a longer annealing surface pretreatment of over 3 h repairs the sulfur vacancies in the pyrite, enriching disulfide species on the pyrite surface, which promotes NH3+ adsorption due to the sulfur vacancies in the pyrite being replaced by sulfur atom dimers (S22-) on the surface. Furthermore, even if the surface chemistry (monosulfide or disulfide species enrichment) is the main factor promoting a partial conversion from NH2 to NH3+ species, the unique chemical structure of each amino acid provides a particular fingerprint in the process.

A versatile UHV transport and measurement chamber for neutron reflectometry under UHV conditions

NASA Astrophysics Data System (ADS)

Syed Mohd, A.; Pütter, S.; Mattauch, S.; Koutsioubas, A.; Schneider, H.; Weber, A.; Brückel, T.

2016-12-01

We report on a versatile mini ultra-high vacuum (UHV) chamber which is designed to be used on the MAgnetic Reflectometer with high Incident Angle of the Jülich Centre for Neutron Science at Heinz Maier-Leibnitz Zentrum in Garching, Germany. Samples are prepared in the adjacent thin film laboratory by molecular beam epitaxy and moved into the compact chamber for transfer without exposure to ambient air. The chamber is based on DN 40 CF flanges and equipped with sapphire view ports, a small getter pump, and a wobble stick, which serves also as sample holder. Here, we present polarized neutron reflectivity measurements which have been performed on Co thin films at room temperature in UHV and in ambient air in a magnetic field of 200 mT and in the Q-range of 0.18 Å-1. The results confirm that the Co film is not contaminated during the polarized neutron reflectivity measurement. Herewith it is demonstrated that the mini UHV transport chamber also works as a measurement chamber which opens new possibilities for polarized neutron measurements under UHV conditions.

Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Choudhary, B. S.; Rajasthan Technical University, Rawatbhata Road, Kota 324010; Singh, A.

We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surfacemore » with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.« less

A versatile UHV transport and measurement chamber for neutron reflectometry under UHV conditions.

PubMed

Syed Mohd, A; Pütter, S; Mattauch, S; Koutsioubas, A; Schneider, H; Weber, A; Brückel, T

2016-12-01

We report on a versatile mini ultra-high vacuum (UHV) chamber which is designed to be used on the MAgnetic Reflectometer with high Incident Angle of the Jülich Centre for Neutron Science at Heinz Maier-Leibnitz Zentrum in Garching, Germany. Samples are prepared in the adjacent thin film laboratory by molecular beam epitaxy and moved into the compact chamber for transfer without exposure to ambient air. The chamber is based on DN 40 CF flanges and equipped with sapphire view ports, a small getter pump, and a wobble stick, which serves also as sample holder. Here, we present polarized neutron reflectivity measurements which have been performed on Co thin films at room temperature in UHV and in ambient air in a magnetic field of 200 mT and in the Q-range of 0.18 Å -1 . The results confirm that the Co film is not contaminated during the polarized neutron reflectivity measurement. Herewith it is demonstrated that the mini UHV transport chamber also works as a measurement chamber which opens new possibilities for polarized neutron measurements under UHV conditions.

Untangling the Reaction Mechanisms Involved in the Explosive Decomposition of Model Compounds of Energetic Materials

DTIC Science & Technology

2014-06-11

typically of a few 10-11 torr using oil-free magnetically suspended turbomolecular pumps backed with dry scroll pumps . A cold finger assembled from...on line and in situ utilizing a Faraday cup mounted inside a differentially pumped chamber on an ultrahigh vacuum compatible translation state. The...down to a base pressure typically of a few 10-11 torr using oil-free magnetically suspended turbomolecular pumps backed with dry scroll pumps . A

A Low Temperature, Ultrahigh Vacuum, Microwave-Frequency-Compatible Scanning Tunneling Microscope

DTIC Science & Technology

1994-05-01

vibrationally decoupled from the chamber using a Subadmed oo -3.- 21 April 1994 Reviw of Sdent* k Immownu Low Topasom UHV ACS7M Stranick et al...molecules, two isolated clusters of benzene molecules on the upper terrace, and several vacancy defects in the Cu(111) surface on the lower terrace...fine and is easily removed and replaced. 11. National Electrostatics Corporation, Middleton, WI. 12. K . Besocke, Surf. Sci. 181, 145 (1987); J. Frohn, J

Strain of laser annealed silicon surfaces

NASA Astrophysics Data System (ADS)

Nemanich, R. J.; Haneman, D.

1982-05-01

High resolution Raman scattering measurements have been carried out on pulse and continuous-wave laser annealed silicon samples with various surface preparations. These included polished and ion-bombarded wafers, and saw-cut crystals. The pulse annealing treatments were carried out in ultrahigh vacuum and in air. The residual strain was inferred from the frequency shift of the first-order Raman active mode of Si, and was detectable in the range 10-2-10-3 in all except the polished samples.

Multifunctional Ultra-High Vacuum Apparatus for Studies of the Interactions of Chemical Warfare Agents on Complex Surfaces

DTIC Science & Technology

2014-01-02

colleagues employed solid state NMR to study the decomposition of CWAs on MgO,36 AgY and NaY zeolites ,37 CaO,38 and Al2O3.39 More recently, the...37G. W. Wagner and P. W. Bartram, “Reactions of VX, HD, and their simu- lants with NaY and AgY zeolites . Desulfurization of VX on AgY,” Lang- muir 15

Physical properties of nanometer graphene oxide films partially and fully reduced by annealing in ultra-high vacuum

NASA Astrophysics Data System (ADS)

Jernigan, Glenn G.; Nolde, Jill A.; Mahadik, Nadeem A.; Cleveland, Erin R.; Boercker, Janice E.; Katz, Michael B.; Robinson, Jeremy T.; Aifer, Edward H.

2017-08-01

The properties of reduced graphene oxide (GO) are reported from a non-chemical reduction method. Ultra-high vacuum annealing of GO films in the thickness of 1-80 nm was studied by XPS, AFM, UV-Vis-NIR, Raman, and TEM to observe the controlled removal of oxygen. We observed the loss of hydroxyl (C-OH) at low temperatures (<600 °C) followed by the complete loss of carbonyls (C = O) and epoxy (C-O-C) species by 1200 °C. As oxygen was removed, we observed a decrease in the layer spacing between the GO sheets and a concurrent decrease in the film resistance. While the Raman spectroscopy showed no change with reduction, indicating no change in the overall defect density or the general structure of the GO, the transmission spectra showed a shift in the transmission minimum from 245 nm to 260 nm, and a total decrease in transmission above 800 nm occurs as the films visibly darken. TEM indicated that there is turbostratic stacking of the graphene layers as the reduction occurs, leading us to conclude that at a certain threshold of reduction the film properties are similar to epitaxial graphene growth on the C-face of SiC, but that a reduction gone too far results in a layer spacing equivalent to graphite.

Heteroepitaxial Growth of Germanium-on-Silicon Using Ultrahigh-Vacuum Chemical Vapor Deposition with RF Plasma Enhancement

NASA Astrophysics Data System (ADS)

Alharthi, Bader; Grant, Joshua M.; Dou, Wei; Grant, Perry C.; Mosleh, Aboozar; Du, Wei; Mortazavi, Mansour; Li, Baohua; Naseem, Hameed; Yu, Shui-Qing

2018-05-01

Germanium (Ge) films have been grown on silicon (Si) substrate by ultrahigh-vacuum chemical vapor deposition with plasma enhancement (PE). Argon plasma was generated using high-power radiofrequency (50 W) to assist in germane decomposition at low temperature. The growth temperature was varied in the low range of 250°C to 450°C to make this growth process compatible with complementary metal-oxide-semiconductor technology. The material and optical properties of the grown Ge films were investigated. The material quality was determined by Raman and x-ray diffraction techniques, revealing growth of crystalline films in the temperature range of 350°C to 450°C. Photoluminescence spectra revealed improved optical quality at growth temperatures of 400°C and 450°C. Furthermore, material quality study using transmission electron microscopy revealed existence of defects in the Ge layer grown at 400°C. Based on the etch pit density, the average threading dislocation density in the Ge layer obtained at this growth temperature was measured to be 4.5 × 108 cm-2. This result was achieved without any material improvement steps such as use of graded buffer or thermal annealing. Comparison between PE and non-plasma-enhanced growth, in the same machine at otherwise the same growth conditions, indicated increased growth rate and improved material and optical qualities for PE growth.

Atomic-scale imaging of DNA using scanning tunnelling microscopy.

PubMed

Driscoll, R J; Youngquist, M G; Baldeschwieler, J D

1990-07-19

The scanning tunnelling microscope (STM) has been used to visualize DNA under water, under oil and in air. Images of single-stranded DNA have shown that submolecular resolution is possible. Here we describe atomic-resolution imaging of duplex DNA. Topographic STM images of uncoated duplex DNA on a graphite substrate obtained in ultra-high vacuum are presented that show double-helical structure, base pairs, and atomic-scale substructure. Experimental STM profiles show excellent correlation with atomic contours of the van der Waals surface of A-form DNA derived from X-ray crystallography. A comparison of variations in the barrier to quantum mechanical tunnelling (barrier-height) with atomic-scale topography shows correlation over the phosphate-sugar backbone but anticorrelation over the base pairs. This relationship may be due to the different chemical characteristics of parts of the molecule. Further investigation of this phenomenon should lead to a better understanding of the physics of imaging adsorbates with the STM and may prove useful in sequencing DNA. The improved resolution compared with previously published STM images of DNA may be attributable to ultra-high vacuum, high data-pixel density, slow scan rate, a fortuitously clean and sharp tip and/or a relatively dilute and extremely clean sample solution. This work demonstrates the potential of the STM for characterization of large biomolecular structures, but additional development will be required to make such high resolution imaging of DNA and other large molecules routine.

Study of Residual Gas Analyser (RGA) Response towards Known Leaks

NASA Astrophysics Data System (ADS)

Pathan, Firozkhan S.; Khan, Ziauddin; Semwal, Pratibha; George, Siju; Raval, Dilip C.; Thankey, Prashant L.; Manthena, Himabindu; Yuvakiran, Paravastu; Dhanani, Kalpesh R.

2012-11-01

Helium leak testing is the most versatile form of weld qualification test for any vacuum application. Almost every ultra-high vacuum (UHV) system utilizes this technique for insuring leak tightness for the weld joints as well as demountable joints. During UHV system under operational condition with many other integrated components, in-situ developed leaks identification becomes one of the prime aspect for maintaining the health of such system and for continuing the experiments onwards. Since online utilization of leak detector (LD) has many practical limitations, residual gas analyser (RGA) can be used as a potential instrument for online leak detection. For this purpose, a co-relation for a given leak rate between Leak Detector and RGA is experimentally established. This paper describes the experimental aspect and the relationship between leak detector and RGA.

Preparation of Y-Ba-Cu oxide superconductor thin films using pulsed laser evaporation from high T/sub c/ bulk material

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dijkkamp, D.; Venkatesan, T.; Wu, X.D.

We report the first successful preparation of thin films of Y-Ba-Cu-O superconductors using pulsed excimer laser evaporation of a single bulk material target in vacuum. Rutherford backscattering spectrometry showed the composition of these films to be close to that of the bulk material. Growth rates were typically 0.1 nm per laser shot. After an annealing treatment in oxygen the films exhibited superconductivity with an onset at 95 K and zero resistance at 85 and 75 K on SrTiO/sub 3/ and Al/sub 2/O/sub 3/ substrates, respectively. This new deposition method is relatively simple, very versatile, and does not require the usemore » of ultrahigh vacuum techniques.« less

Investigation of vacuum properties of CuCrZr alloy for high-heat-load absorber

NASA Astrophysics Data System (ADS)

Shueh, C.; Chan, C. K.; Chang, C. C.; Sheng, I. C.

2017-01-01

The Taiwan Photon Source (TPS) uses high-heat-load (HHL) absorbers to protect downstream ultrahigh-vacuum chambers from overheating. In this work, we propose to use the CuCrZr alloy (ASTM C18150) for the HHL absorber body and the ConFlat® flanges. We use the throughput method to measure the thermal outgassing rate and a helium leak detector to verify the vacuum seal between the CuCrZr alloy and stainless-steel flanges. The measured outgassing rate of the CuCrZr alloy was 5.8×10-10 Pa m/s after 72 h of pumping and decreased to 2.0 × 10-10 Pa m/s after 100 h of pumping. The leak rate through the vacuum seal between a CuCrZr flange and a stainless-steel flange was less than 1 × 10-10 Pa m3/s even after mounting and unmounting the flanges ten times and baking them at 250 °C. These results indicate that CuCrZr alloy is suitable for integrating HHL components with ConFlat® CuCrZr flanges for the absorption of the synchrotron radiation generated by the TPS.

Compact, compression-free, displaceable, and resealable vacuum feedthrough with built-in strain relief for sensitive components such as optical fibers.

PubMed

Buchholz, B; Ebert, V

2014-05-01

For the direct fiber coupling of small optical measurement cells, we developed a new compact vacuum feedthrough for glass fibers and other similarly shaped objects that are compact and that offer the possibility of adjusting the fiber in longitudinal and in circular direction. The feedthrough assembly avoids compression or torsion on the fiber and thus protects, e.g., highly frangible fiber materials. In the following, we will present a brief simulation of the tightness requirements for low-pressure and low-concentration water vapor measurements and we will explain an integrated concept for a displaceable and self-adjustable, compression-free, compact, ultra-high vacuum, resealable feedthrough with good strain relief. The feedthrough has been successfully tested in a laboratory test facility and in several extractive airborne tunable diode laser absorption spectroscopy hygrometers. The leakage rate of the feedthrough presented here was tested via a helium leak searcher and was quantified further in an 8-week vacuum measurement campaign. The leakage rate is determined to be 0.41 ± 0.04 × 10(-9) hPa l/s, which--to our knowledge--is the first time a leakage rate for such a feedthrough has been quantified.

Facility for low-temperature spin-polarized-scanning tunneling microscopy studies of magnetic/spintronic materials prepared in situ by nitride molecular beam epitaxy.

PubMed

Lin, Wenzhi; Foley, Andrew; Alam, Khan; Wang, Kangkang; Liu, Yinghao; Chen, Tianjiao; Pak, Jeongihm; Smith, Arthur R

2014-04-01

Based on the interest in, as well as exciting outlook for, nitride semiconductor based structures with regard to electronic, optoelectronic, and spintronic applications, it is compelling to investigate these systems using the powerful technique of spin-polarized scanning tunneling microscopy (STM), a technique capable of achieving magnetic resolution down to the atomic scale. However, the delicate surfaces of these materials are easily corrupted by in-air transfers, making it unfeasible to study them in stand-alone ultra-high vacuum STM facilities. Therefore, we have carried out the development of a hybrid system including a nitrogen plasma assisted molecular beam epitaxy/pulsed laser epitaxy facility for sample growth combined with a low-temperature, spin-polarized scanning tunneling microscope system. The custom-designed molecular beam epitaxy growth system supports up to eight sources, including up to seven effusion cells plus a radio frequency nitrogen plasma source, for epitaxially growing a variety of materials, such as nitride semiconductors, magnetic materials, and their hetero-structures, and also incorporating in situ reflection high energy electron diffraction. The growth system also enables integration of pulsed laser epitaxy. The STM unit has a modular design, consisting of an upper body and a lower body. The upper body contains the coarse approach mechanism and the scanner unit, while the lower body accepts molecular beam epitaxy grown samples using compression springs and sample skis. The design of the system employs two stages of vibration isolation as well as a layer of acoustic noise isolation in order to reduce noise during STM measurements. This isolation allows the system to effectively acquire STM data in a typical lab space, which during its construction had no special and highly costly elements included, (such as isolated slabs) which would lower the environmental noise. The design further enables tip exchange and tip coating without breaking vacuum, and convenient visual access to the sample and tip inside a superconducting magnet cryostat. A sample/tip handling system is optimized for both the molecular beam epitaxy growth system and the scanning tunneling microscope system. The sample/tip handing system enables in situ STM studies on epitaxially grown samples, and tip exchange in the superconducting magnet cryostat. The hybrid molecular beam epitaxy and low temperature scanning tunneling microscopy system is capable of growing semiconductor-based hetero-structures with controlled accuracy down to a single atomic-layer and imaging them down to atomic resolution.

New Effective Material Couple--Oxide Ceramic and Carbon Nanotube-- Developed for Aerospace Microsystem and Micromachine Technologies

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; VanderWal, Randall L.; Tomasek, Aaron J.; Sayir, Ali; Farmer, Serene C.

2004-01-01

The prime driving force for using microsystem and micromachine technologies in transport vehicles, such as spacecraft, aircraft, and automobiles, is to reduce the weight, power consumption, and volume of components and systems to lower costs and increase affordability and reliability. However, a number of specific issues need to be addressed with respect to using microsystems and micromachines in aerospace applications--such as the lack of understanding of material characteristics; methods for producing and testing the materials in small batches; the limited proven durability and lifetime of current microcomponents, packaging, and interconnections; a cultural change with respect to system designs; and the use of embedded software, which will require new product assurance guidelines. In regards to material characteristics, there are significant adhesion, friction, and wear issues in using microdevices. Because these issues are directly related to surface phenomena, they cannot be scaled down linearly and they become increasingly important as the devices become smaller. When microsystems have contacting surfaces in relative motion, the adhesion and friction affect performance, energy consumption, wear damage, maintenance, lifetime and catastrophic failure, and reliability. Ceramics, for the most part, do not have inherently good friction and wear properties. For example, coefficients of friction in excess of 0.7 have been reported for ceramics and ceramic composite materials. Under Alternate Fuels Foundation Technologies funding, two-phase oxide ceramics developed for superior high-temperature wear resistance in NASA's High Operating Temperature Propulsion Components (HOTPC) project and new two-layered carbon nanotube (CNT) coatings (CNT topcoat/iron bondcoat/quartz substrate) developed in NASA's Revolutionary Aeropropulsion Concepts (RAC) project have been chosen as a materials couple for aerospace applications, including micromachines, in the nanotechnology lubrication task because of their potential for superior friction and wearf properties in air and in an ultrahigh vacuum, spacelike environment. At the NASA Glenn Research Center, two-phase oxide ceramic eutectics, Al2O3/ZrO2(Y2O3), were directionally solidified using the laser-float-zone process, and carbon nanotubes were synthesized within a high-temperature tube furnace at 800 C. Physical vapor deposition was used to coat all quartz substrates with 5-nm-thick iron as catalyst and bondcoat, which formed iron islands resembling droplets and serving as catalyst particles on the quartz. A series of scanning electron micrographs showing multiwalled carbon nanotubes directionally grown as aligned "nanograss" on quartz is presented. Unidirectional sliding friction eperiments were conducted at Glenn with the two-layered CNT coatings in contact with the two-phase Al2O3/ZrO2(Y2O3) eutectics in air and in ultrachigh vacuum. The main criteria for judging the performance of the materials couple for solid lubrication and antistick applications in a space environment were the coefficient of friction and the wear resistance (reciprocal of wear rate), which had to be less than 0.2 and greater than 10(exp 5) N(raised dot)/cubic millimetes, respectively, in ultrahigh vacuum. In air, the coefficient of friction for the CNT coatings in contact with Al2O3/ZrO2 (Y2O3) eutectics was 0.04, one-fourth of that for quartz. In an ultrahigh vacuum, the coefficient of friction for CNT coatings in contact with Al2O3/ZrO2 (Y2O3) was one-third of that for quartz. The two-phase Al2O3/ZrO2 (Y2O3) eutectic coupled with the two-layered CNT coating met the coefficient of friction and wear resistance criteria both in air and in an ultrahigh vacuum, spacelike environment. This material's couple can dramatically improve the stiction (or adhesion), friction, and wear resistance of the contacting surfaces, which are major issues for microdevices and micromachines.

Ultrahigh-Density Nanowire Arrays Grown in Self-Assembled Diblock Copolymer Templates

NASA Astrophysics Data System (ADS)

Thurn-Albrecht, T.; Schotter, J.; Kästle, G. A.; Emley, N.; Shibauchi, T.; Krusin-Elbaum, L.; Guarini, K.; Black, C. T.; Tuominen, M. T.; Russell, T. P.

2000-12-01

We show a simple, robust, chemical route to the fabrication of ultrahigh-density arrays of nanopores with high aspect ratios using the equilibrium self-assembled morphology of asymmetric diblock copolymers. The dimensions and lateral density of the array are determined by segmental interactions and the copolymer molecular weight. Through direct current electrodeposition, we fabricated vertical arrays of nanowires with densities in excess of 1.9 × 1011 wires per square centimeter. We found markedly enhanced coercivities with ferromagnetic cobalt nanowires that point toward a route to ultrahigh-density storage media. The copolymer approach described is practical, parallel, compatible with current lithographic processes, and amenable to multilayered device fabrication.

Extremely low-outgassing material: 0.2% beryllium copper alloy

NASA Astrophysics Data System (ADS)

Watanabe, Fumio

2004-01-01

Exploration for low-outgassing materials for use in ultrahigh vacuum and extreme high-vacuum systems is one of the most important topics of a vacuum researcher. We have found that a copper alloy containing 0.2% beryllium (0.2% BeCu) can attain an extremely low hydrogen outgassing rate of 10-14 Pa (H2) m/s order. Almost the entire surface of 0.2% BeCu is dominated by a BeO layer, after a 400 °C×72 h prebakeout treatment in an ultrahigh vacuum. This layer functions as a barrier to the processes of oxidization and permeation of hydrogen. In addition, this layer resists carbon contamination. Temperature-programmed desorption spectra show only a single peak for water at 150 °C and small quantities of any other desorption gases. Therefore, an in situ bakeout process in which the temperature simply ramps up to 150 °C and immediately ramps back down is enough for degassing; it does not require an ordinary sustained-temperature bakeout. Using an outgassing sample consisting of 0.2% BeCu disks housed in a 0.2% BeCu nipple chamber, a lowest outgassing rate of the 5.6×10-14 Pa (H2) m/s was measured by the pressure-rise method after pump cutoff. The pressure-rise versus time curve was completely nonlinear. It rises over time to a constant slope of 1/2 in a log-log plot, due to hydrogen diffusion from the bulk, but this requires over a week at room temperature. The hydrogen outgassing from the 0.2% BeCu bulk is completely dominated by a diffusion-limited mechanism. This article will describe why we obtain such low-outgassing rates with 0.2% BeCu. It is based on the observed surface changes with prebakeout treatment seen by x-ray photoelectron spectroscopy, and the improvement of hydrogen outgassing measurements by the pressure-rise method. A comparison is made to ordinary stainless steel. In addition, the concept of an outgassing reduction method will be discussed from a review of the published ultralow-outgassing data and reduction methods. .

Influence of heteroatom pre-selection on the molecular formula assignment of soil organic matter components determined by ultrahigh resolution mass spectrometry.

PubMed

Ohno, Tsutomu; Ohno, Paul E

2013-04-01

Soil organic matter (SOM) is involved in many important ecosystem processes. Ultrahigh resolution mass spectrometry has become a powerful technique in the chemical characterization of SOM, allowing assignment of elemental formulae for thousands of peaks resolved in a typical mass spectrum. We investigated how the addition of N, S, and P heteroatoms in the formula calculation stage of the mass spectra processing workflow affected the formula assignments of mass spectra peaks. Dissolved organic matter extracted from plant biomass and soil as well as the soil humic acid fraction was studied. We show that the addition of S and P into the molecular formula calculation increased peak assignments on average by 17.3 % and 10.7 %, respectively, over the assignments based on the CHON elements frequently reported by SOM researchers using ultrahigh resolution mass spectrometry. The organic matter chemical characteristics as represented by van Krevelen diagrams were appreciably affected by differences in the heteroatom pre-selection for the three organic matter samples investigated, especially so for the wheat-derived dissolved organic matter. These results show that inclusion of both S and P heteroatoms into the formula calculation step, which is not routinely done, is important to obtain a more chemically complete interpretation of the ultrahigh resolution mass spectra of SOM.

The progeny of Skylab - The pioneering phase of our expansion into space

NASA Technical Reports Server (NTRS)

Schmitt, H. H.

1974-01-01

The opportunities provided by such near-earth space resources as the continuous view of the earth, sun, and stars, the presence of ultrahigh vacuum, and the absence of gravitational stress are briefly reviewed, along with the significance of manned observation and experimentation in near-earth space. The stimulation triggered in young minds by a week or summer in space, as the Apollo and Skylab experiences show, simply defies the imagination. The plea is made not to miss these opportunities.

International manned lunar base - Beginning the 21st century in space

NASA Astrophysics Data System (ADS)

Smith, Harlan J.; Gurshtejn, Aleksandr A.; Mendell, Wendell

An evaluation is made of requirements for, and advantages in, the creation of a manned lunar base whose functions emphasize astronomical investigations. These astronomical studies would be able to capitalize on the lunar environment's ultrahigh vacuum, highly stable surface, dark and cold sky, low-G, absence of wind, isolation from terrestrial 'noise', locally usable ceramic raw materials, and large radiotelescope dish-supporting hemispherical craters. Large telescope structures would be nearly free of the gravity and wind loads that complicate their design on earth.

Metallic transfer between metals in sliding contact examined by auger emission spectroscopy

NASA Technical Reports Server (NTRS)

Pepper, S. V.

1972-01-01

Metallic transfer between polycrystalline metals in sliding contact was examined. Hemispherical riders of iron, nickel, and cobalt were slid on tungsten, tantalum, niobium, and molybdenum disks in ultrahigh vacuum. Auger emission spectroscopy was used to monitor the elemental composition of the disk surfaces. Iron, nickel, and cobalt transferred to tungsten, whereas only cobalt transferred to tantalum, niobium, and molybdenum. The results of this investigation are discussed in terms of the cohesive energy and strain hardening characteristics of the specimen materials.

A time-of-flight system for the external target facility

NASA Astrophysics Data System (ADS)

Zhang, Xue-Heng; Yu, Yu-Hong; Sun, Zhi-Yu; Mao, Rui-Shi; Wang, Shi-Tao; Zhou, Yong; Yan, Duo; Liu, Long-Xiang

2013-05-01

A time-of-flight system with a plastic scintillator coupled to photomultipliers is developed for the external target facility (ETF). This system can satisfy the requirement of an ultrahigh vacuum (~10-9 mbar), a high counting rate (~106 particles per second) and a magnetic field environment. In the beam test experiment, a total time resolution of 580 ps FWHM was obtained for the whole system, and nuclei with a mass of up to 80 could be identified using this system.

Materials processing in space bibliography

NASA Technical Reports Server (NTRS)

Pentecost, E. (Compiler)

1982-01-01

Literature dealing with flight experiments utilizing a low gravity environment to elucidate and control various processes or with ground based activities that provide supporting research is listed. Included are Government reports, contractor reports, conference proceedings, and journal articles. Subdivisions of the bibliography include the five categories: crystal growth; metals, alloys, and composites, fluids and transport; glasses and ceramics; and Ultrahigh Vacuum and Containerless Processing Technologies, in addition to a list of patents and a compilation of anonymously authored collections and reports and a cross reference index.

Oxygen Interaction With Space-Power Materials

NASA Technical Reports Server (NTRS)

Eck, Thomas G.; Hoffman, Richard W.

1996-01-01

Four investigations were undertaken during the period of this grant: (1 ) oxidation of molybdenum and of niobium-1 % zirconium, (2) preparation of and examination of EOIM-3 samples, (3) sputtering of Teflon by oxygen ion bombardment,and (4) sputtering of Ions from copper and aluminum by oxygen and argon ion bombardment. Investigations (1), (3), and (4) used a low-energy Ion gun to bombard surfaces within an ultra-high vacuum system. Particles ejected from the surfaces were detected by a mass spectrometer.

Materials processing in space program tasks-supplement

NASA Technical Reports Server (NTRS)

Pentecost, E. (Compiler)

1983-01-01

An overview of the program scope for managers and scientists in industry, university, and government communities is provided. An introductory description of the program, its history, strategy, and overall goals; identification of the organizational structures and people involved; and a description of each research task, together with a list of recent publications are included. The tasks are grouped into six categories: crystal growth; solidification of metals, alloys, and composites; fluids, transports, and chemical processes; and ultrahigh vacuum and containerless processing technologies; combustion experiments; and experimental technology.

A Library of the Nanoscale Self-Assembly of Amino Acids on Metal Surfaces

NASA Astrophysics Data System (ADS)

Iski, Erin; Yitamben, Esmeralda; Guisinger, Nathan

2012-02-01

The investigation of the hierarchical self-assembly of amino acids on surfaces represents a unique test-bed for the origin of enantio-favoritism in biology and the transmission of chirality from single molecules to complete surface layers. These chiral systems, in particular the assembly of isoleucine and alanine on Cu(111), represent a direct link to the understanding of certain biological processes, specifically the preference for some amino acids to form alpha helices vs. beta-pleated sheets in the secondary structure of proteins. Low temperature, ultra-high vacuum, scanning tunneling microscopy (LT UHV-STM) is used to study the hierarchical self-assembly of different amino acids on a Cu(111) single crystal in an effort to build a library of their two-dimensional structure with molecular-scale resolution for enhanced protein and peptide studies. Both enantiopure and racemic structures are studied in order to elucidate how chirality can affect the self-assembly of the amino acids. In some cases, density functional theory (DFT) models can be used to confirm the experimental structure. The advent of such a library with fully resolved, two-dimensional structures at different molecular coverages would address some of the complex questions surrounding the preferential formation of alpha helices vs. beta-pleated sheets in proteins and lead to a better understanding of the key role played by these amino acids in protein sequencing.

Probing Nitrosyl Ligation of Surface-Confined Metalloporphyrins by Inelastic Electron Tunneling Spectroscopy

PubMed Central

2013-01-01

Complexes obtained by the ligation of nitric oxide (NO) to metalloporphyrins represent important model systems with biological relevance. Herein we report a molecular-level investigation of surface-confined cobalt tetraphenyl porphyrin (Co-TPP) species and their interaction with NO under ultrahigh vacuum conditions. It is demonstrated that individual NO adducts can be desorbed using the atomically sharp tip of a scanning tunneling microscope, whereby a writing process is implemented for fully saturated regular metalloporphyrin arrays. The low-energy vibrational characteristics of individual Co-TPP-nitrosyl complexes probed by inelastic electron tunneling spectroscopy (IETS) reveal a prominent signature at an energy of ≃31 meV. Using density functional theory-based IETS simulations—the first to be performed on such an extensive interfacial nanosystem—we succeed to reproduce the low-frequency spectrum for the NO-ligated complex and explain the absence of IETS activity for bare Co-TPP. Moreover, we can conclusively assign the IETS peak of NO-Co-TPP to a unique vibration mode involving the NO complexation site, namely, the in-plane Co–N–O rocking mode. In addition, we verify that the propensity rules previously designed on small aromatic systems and molecular fragments hold true for a metal–organic entity. This work notably permits one to envisage IETS spectroscopy as a sensitive tool to chemically characterize hybrid interfaces formed by complex metal–organic units and gaseous adducts. PMID:23718257

Wafer-level hermetic vacuum packaging by bonding with a copper-tin thin film sealing ring

NASA Astrophysics Data System (ADS)

Akashi, Teruhisa; Funabashi, Hirofumi; Takagi, Hideki; Omura, Yoshiteru; Hata, Yoshiyuki

2018-04-01

A wafer-level hermetic vacuum packaging technology intended for use with MEMS devices was developed based on a copper-tin (CuSn) thin film sealing ring. To allow hermetic packaging, the shear strength of the CuSn thin film bond was improved by optimizing the pretreatment conditions. As a result, an average shear strength of 72.3 MPa was obtained and a cavity that had been hermetically sealed using wafer-level packaging (WLP) maintained its vacuum for 1.84 years. The total pressures in the cavities and the partial pressures of residual gases were directly determined with an ultra-low outgassing residual gas analyzer (RGA) system. Hermeticity was evaluated based on helium leak rates, which were calculated from helium pressures determined with the RGA system. The resulting data showed that a vacuum cavity following 1.84 years storage had a total pressure of 83.1 Pa, contained argon as the main residual gas and exhibited a helium leak rate as low as 1.67  ×  10-17 Pa · m3 s-1, corresponding to an air leak rate of 6.19  ×  10-18 Pa · m3 s-1. The RGA data demonstrate that WLP using a CuSn thin film sealing ring permits ultra-high hermeticity in conjunction with long-term vacuum packaging that is applicable to MEMS devices.

Tungsten nanoparticles influence on radiation protection properties of polymers

NASA Astrophysics Data System (ADS)

Gavrish, V. M.; Baranov, G. A.; Chayka, T. V.; Derbasova, N. M.; Lvov, A. V.; Matsuk, Y. M.

2016-02-01

In the presented article the results of the study of metal-polymer composites based on the ultra-high molecular weight polyethylene GUR 4122 with the addition of superdispersed tungsten nanopowders with 5, 10, 20, 40, and 50 mass percent content levels are given, their thermophysical, radiation-shielding, and mechanical properties are shown, and the influence of content levels of tungsten superdispersed nanopowders on these properties is analyzed. The conducted studies have shown the increase in the listed properties depending on the content level of tungsten superdispersed and nanopowders in the ultra-high molecular weight polyethylene GUR 4122. Owing to their properties, the obtained materials may be used in various fields, such as aviation, space technologies, mechanical engineering, etc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Hao, E-mail: hc000211@ohio.edu; Nanoscale and Quantum Phenomena Institute, Physics & Astronomy Department, Ohio University, Athens, Ohio 45701; Cummings, Marvin

High-speed beam choppers are a crucial part of time-resolved x-ray studies as well as a necessary component to enable elemental contrast in synchrotron x-ray scanning tunneling microscopy (SX-STM). However, many chopper systems are not capable of operation in vacuum, which restricts their application to x-ray studies with high photon energies, where air absorption does not present a significant problem. To overcome this limitation, we present a fully ultra-high vacuum (UHV) compatible chopper system capable of operating at variable chopping frequencies up to 4 kHz. The lightweight aluminum chopper disk is coated with Ti and Au films to provide the required beammore » attenuation for soft and hard x-rays with photon energies up to about 12 keV. The chopper is used for lock-in detection of x-ray enhanced signals in SX-STM.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chang, Hao; Cummings, Marvin L.; Shirato, Nozomi

High-speed beam choppers are a crucial part of time-resolved x-ray studies as well as a necessary component to enable elemental contrast in synchrotron x-ray scanning tunneling microscopy (SX-STM). However, many chopper systems are not capable of operation in vacuum, which restricts their application to x-ray studies with high photon energies, where air absorption does not present a significant problem. To overcome this limitation, we present a fully ultra-high vacuum (UHV) compatible chopper system capable of operating at variable chopping frequencies up to 4 kHz. The lightweight aluminum chopper disk is coated with Ti and Au films to provide the requiredmore » beam attenuation for soft and hard x-rays with photon energies up to about 12 keV. The chopper is used for lock-in detection of x-ray enhanced signals in SX-STM.« less

Large-scale uniform bilayer graphene prepared by vacuum graphitization of 6H-SiC(0001) substrates

NASA Astrophysics Data System (ADS)

Wang, Qingyan; Zhang, Wenhao; Wang, Lili; He, Ke; Ma, Xucun; Xue, Qikun

2013-03-01

We report on the preparation of large-scale uniform bilayer graphenes on nominally flat Si-polar 6H-SiC(0001) substrates by flash annealing in ultrahigh vacuum. The resulting graphenes have a single thickness of one bilayer and consist of regular terraces separated by the triple SiC bilayer steps on the 6H-SiC(0001) substrates. In situ scanning tunneling microscopy reveals that suppression of pit formation on terraces and uniformity of SiC decomposition at step edges are the key factors to the uniform thickness. By studying the surface morphologies prepared under different annealing rates, it is found that the annealing rate is directly related to SiC decomposition, diffusion of the released Si/C atoms and strain relaxation, which together determine the final step structure and density of defects.

Large-scale uniform bilayer graphene prepared by vacuum graphitization of 6H-SiC(0001) substrates.

PubMed

Wang, Qingyan; Zhang, Wenhao; Wang, Lili; He, Ke; Ma, Xucun; Xue, Qikun

2013-03-06

We report on the preparation of large-scale uniform bilayer graphenes on nominally flat Si-polar 6H-SiC(0001) substrates by flash annealing in ultrahigh vacuum. The resulting graphenes have a single thickness of one bilayer and consist of regular terraces separated by the triple SiC bilayer steps on the 6H-SiC(0001) substrates. In situ scanning tunneling microscopy reveals that suppression of pit formation on terraces and uniformity of SiC decomposition at step edges are the key factors to the uniform thickness. By studying the surface morphologies prepared under different annealing rates, it is found that the annealing rate is directly related to SiC decomposition, diffusion of the released Si/C atoms and strain relaxation, which together determine the final step structure and density of defects.

Effects of the ultra-high pressure on structure and α-glucosidase inhibition of polysaccharide from Astragalus.

PubMed

Zhu, Zhen-Yuan; Luo, You; Dong, Guo-Ling; Ren, Yuan-Yuan; Chen, Li-Jing; Guo, Ming-Zhu; Wang, Xiao-Ting; Yang, Xue-Ying; Zhang, Yongmin

2016-06-01

A novel homogeneous polysaccharide fraction (APS) was extracted from Astragalus by hot water and purified by Sephadex G-100 and G-75 column. Its molecular weight was 693kDa. APS and APS with ultra-high pressure treatment exhibited significant inhibitory abilities on a-glucosidase, inhibition rate from high to low in order was 400MPa-APS, 300MPa-APS, 500MPa-APS and APS. The inhibition ​percentage of 400MPa-APS (1.5mg/mL) was 49% (max.). This suggested that the inhibitory activity of APS on a-glucosidase was improved by ultra-high pressure treatment. FT-IR, SEM, CD spectra, atomic force microscope and Congo red test analysis of APS and 400MPa-APS showed ultra-high pressure treatment didn't change the preliminary structure but had an effect on its advanced structure. Copyright © 2016 Elsevier B.V. All rights reserved.

Ultrahigh-density nanowire arrays grown in self-assembled diblock copolymer templates.

PubMed

Thurn-Albrecht, T; Schotter, J; Kästle, G A; Emley, N; Shibauchi, T; Krusin-Elbaum, L; Guarini, K; Black, C T; Tuominen, M T; Russell, T P

2000-12-15

We show a simple, robust, chemical route to the fabrication of ultrahigh-density arrays of nanopores with high aspect ratios using the equilibrium self-assembled morphology of asymmetric diblock copolymers. The dimensions and lateral density of the array are determined by segmental interactions and the copolymer molecular weight. Through direct current electrodeposition, we fabricated vertical arrays of nanowires with densities in excess of 1.9 x 10(11) wires per square centimeter. We found markedly enhanced coercivities with ferromagnetic cobalt nanowires that point toward a route to ultrahigh-density storage media. The copolymer approach described is practical, parallel, compatible with current lithographic processes, and amenable to multilayered device fabrication.

Manipulator having thermally conductive rotary joint for transferring heat from a test specimen

DOEpatents

Haney, S.J.; Stulen, R.H.; Toly, N.F.

1983-05-03

A manipulator for rotatably moving a test specimen in an ultra-high vacuum chamber includes a translational unit movable in three mutually perpendicular directions. A manipulator frame is rigidly secured to the translational unit for rotatably supporting a rotary shaft. A first copper disc is rigidly secured to an end of the rotary shaft for rotary movement within the vacuum chamber. A second copper disc is supported upon the first disc. The second disc receives a cryogenic cold head and does not rotate with the first disc. The second disc receives a cryogenic cold head and does not rotate with the first disc. A sapphire plate is interposed between the first and second discs to prevent galling of the copper material while maintaining high thermal conductivity between the first and second discs. A spring is disposed on the shaft to urge the second disc toward the first disc and compressingly engage the interposed sapphire plate. A specimen mount is secured to the first disc for rotation within the vacuum chamber. The specimen maintains high thermal conductivity with the second disc receiving the cryogenic transfer line.

A simple method for environmental cell depressurization for use with an electron microscope.

PubMed

Ogawa, Naoki; Mizokawa, Ryo; Saito, Minoru; Ishikawa, Akira

2017-12-01

With the aid of the environmental cell (EC) in electron microscopy, hydrated specimens have been observed at high resolutions that optical microscopy cannot attain. Due to the ultra-high vacuum conditions of the inner column of the electron microscope, the EC requires sealing films that are sufficiently thin to allow electron transmission and that are sufficiently tough to withstand the pressure difference between the inside and outside of the EC. However, most hydrated specimens can be observed at low vacuum because the saturated vapor pressure of water is known to be 0.02 atm at room temperature. These concepts have been used in the differential pumping system, but it is complicated and relatively expensive. In this work, we propose a simple method for depressurization of the EC using a 'balloon structure' and demonstrate the theoretical benefits and practical improvement for specimen observations in low-vacuum conditions. © The Author 2017. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schaefer, Michael, E-mail: mvschaefer@mail.usf.edu, E-mail: axk650@case.edu, E-mail: mohan@case.edu, E-mail: schlaf@mail.usf.edu; Kumar, Ajay, E-mail: mvschaefer@mail.usf.edu, E-mail: axk650@case.edu, E-mail: mohan@case.edu, E-mail: schlaf@mail.usf.edu; Mohan Sankaran, R., E-mail: mvschaefer@mail.usf.edu, E-mail: axk650@case.edu, E-mail: mohan@case.edu, E-mail: schlaf@mail.usf.edu

Microplasma-assisted gas-phase nucleation has emerged as an important new approach to produce high-purity, nanometer-sized, and narrowly dispersed particles. This study aims to integrate this technique with vacuum conditions to enable synthesis and deposition in an ultrahigh vacuum compatible environment. The ultimate goal is to combine nanoparticle synthesis with photoemission spectroscopy-based electronic structure analysis. Such measurements require in vacuo deposition to prevent surface contamination from sample transfer, which can be deleterious for nanoscale materials. A homebuilt microplasma reactor was integrated into an existing atomic layer deposition system attached to a surface science multi-chamber system equipped with photoemission spectroscopy. As proof-of-concept, wemore » studied the decomposition of ferrocene vapor in the microplasma to synthesize iron oxide nanoparticles. The injection parameters were optimized to achieve complete precursor decomposition under vacuum conditions, and nanoparticles were successfully deposited. The stoichiometry of the deposited samples was characterized in situ using X-ray photoelectron spectroscopy indicating that iron oxide was formed. Additional transmission electron spectroscopy characterization allowed the determination of the size, shape, and crystal lattice of the particles, confirming their structural properties.« less

Design of a diamond-crystal monochromator for the LCLS hard x-ray self-seeding project

NASA Astrophysics Data System (ADS)

Shu, D.; Shvyd'ko, Y.; Amann, J.; Emma, P.; Stoupin, S.; Quintana, J.

2013-03-01

As the result of collaborations between the Advanced Photon Source (APS), Argonne National Laboratory, and the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory, we have designed and constructed a diamond crystal monochromator for the LCLS hard x-ray self-seeding project. The novel monochromator is ultrahigh-vacuum compatible to meet the LCLS linear accelerator vacuum environmental requirement. A special graphite holder was designed for strain-free mount of the 110-μm thin synthetic diamond crystal plate provided by Technological Institute for Super-hard and Novel Carbon Materials of Russia (TISNCM). An in-vacuum multi-axis precision positioning mechanism is designed to manipulate the thin-film diamond holder with resolutions and stabilities required by the hard x-ray self-seeding physics. Optical encoders, limit switches, and hardware stops are established in the mechanism to ensure system reliability and to meet the accelerator personal and equipment safety interlock requirements. Molybdenum shields are installed in the monochromator to protect the encoders and associated electronics from radiation damage. Mechanical specifications, designs, and preliminary test results of the diamond monochromator are presented in this paper.

Direct formation of (CH sub 3 ) sub 2 HSiCl from silicon and CH sub 3 Cl

DOE Office of Scientific and Technical Information (OSTI.GOV)

Magrini, K.A.; Falconer, J.L.; Koel, B.E.

1989-07-13

A Cu-catalyzed reaction procedure was found for the selective formation of dimethylchlorosilane ((CH{sub 3}){sub 2}HSiCl) from the direct reaction of CH{sub 3}Cl with solid Si. The new procedure is a two-step process. A Cu/Si sample is prepared by evaporating Cu onto clean polycrystalline Si under ultrahigh vacuum, and the Cu/Si surface is first activated by exposure to 10% HSiCl{sub 3}/CH{sub 3}Cl at 598 K. After the HSiCl{sub 3}CH{sub 3}Cl mixture is evacuated from the reactor, the activated Cu/Si surface is reacted in fresh CH{sub 3}Cl. For low surface concentrations of Cu, the partially hydrogenated silane, (CH{sub 3}){sub 2}HSiCl, is selectivelymore » produced. Trichlorosilane was also found to activate polycrystalline Si (in the absence of Cu) for production of highly chlorinated methylchlorosilanes at a much higher rate than on the Cu/Si surface but with poor selectively to (CH{sub 3}){sub 2}HSiCl. All reactions are carried out at atmospheric pressure in a reactor that is attached to an ultrahigh-vacuum chamber. This allows surface analysis of Auger electron spectroscopy, which detected SiCl{sub x} on reacted surfaces. These SiCl{sub x} sites, which appear necessary for methylchlorosilane formation, are apparently formed during activation by HSiCl{sub 3}.« less

Friction and Wear of Ion-Beam-Deposited Diamondlike Carbon on Chemical-Vapor-Deposited, Fine-Grain Diamond

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Wu, Richard L. C.; Lanter, William C.

1996-01-01

Friction and wear behavior of ion-beam-deposited diamondlike carbon (DLC) films coated on chemical-vapor-deposited (CVD), fine-grain diamond coatings were examined in ultrahigh vacuum, dry nitrogen, and humid air environments. The DLC films were produced by the direct impact of an ion beam (composed of a 3:17 mixture of Ar and CH4) at ion energies of 1500 and 700 eV and an RF power of 99 W. Sliding friction experiments were conducted with hemispherical CVD diamond pins sliding on four different carbon-base coating systems: DLC films on CVD diamond; DLC films on silicon; as-deposited, fine-grain CVD diamond; and carbon-ion-implanted, fine-grain CVD diamond on silicon. Results indicate that in ultrahigh vacuum the ion-beam-deposited DLC films on fine-grain CVD diamond (similar to the ion-implanted CVD diamond) greatly decrease both the friction and wear of fine-grain CVD diamond films and provide solid lubrication. In dry nitrogen and in humid air, ion-beam-deposited DLC films on fine-grain CVD diamond films also had a low steady-state coefficient of friction and a low wear rate. These tribological performance benefits, coupled with a wider range of coating thicknesses, led to longer endurance life and improved wear resistance for the DLC deposited on fine-grain CVD diamond in comparison to the ion-implanted diamond films. Thus, DLC deposited on fine-grain CVD diamond films can be an effective wear-resistant, lubricating coating regardless of environment.

Thermal noise limit for ultra-high vacuum noncontact atomic force microscopy

PubMed Central

Lübbe, Jannis; Temmen, Matthias; Rode, Sebastian; Rahe, Philipp; Kühnle, Angelika

2013-01-01

Summary The noise of the frequency-shift signal Δf in noncontact atomic force microscopy (NC-AFM) consists of cantilever thermal noise, tip–surface-interaction noise and instrumental noise from the detection and signal processing systems. We investigate how the displacement-noise spectral density d z at the input of the frequency demodulator propagates to the frequency-shift-noise spectral density d Δ f at the demodulator output in dependence of cantilever properties and settings of the signal processing electronics in the limit of a negligible tip–surface interaction and a measurement under ultrahigh-vacuum conditions. For a quantification of the noise figures, we calibrate the cantilever displacement signal and determine the transfer function of the signal-processing electronics. From the transfer function and the measured d z, we predict d Δ f for specific filter settings, a given level of detection-system noise spectral density d z ds and the cantilever-thermal-noise spectral density d z th. We find an excellent agreement between the calculated and measured values for d Δ f. Furthermore, we demonstrate that thermal noise in d Δ f, defining the ultimate limit in NC-AFM signal detection, can be kept low by a proper choice of the cantilever whereby its Q-factor should be given most attention. A system with a low-noise signal detection and a suitable cantilever, operated with appropriate filter and feedback-loop settings allows room temperature NC-AFM measurements at a low thermal-noise limit with a significant bandwidth. PMID:23400758

System to measure accurate temperature dependence of electric conductivity down to 20 K in ultrahigh vacuum.

PubMed

Sakai, C; Takeda, S N; Daimon, H

2013-07-01

We have developed the new in situ electrical-conductivity measurement system which can be operated in ultrahigh vacuum (UHV) with accurate temperature measurement down to 20 K. This system is mainly composed of a new sample-holder fixing mechanism, a new movable conductivity-measurement mechanism, a cryostat, and two receptors for sample- and four-probe holders. Sample-holder is pushed strongly against the receptor, which is connected to a cryostat, by using this new sample-holder fixing mechanism to obtain high thermal conductivity. Test pieces on the sample-holders have been cooled down to about 20 K using this fixing mechanism, although they were cooled down to only about 60 K without this mechanism. Four probes are able to be touched to a sample surface using this new movable conductivity-measurement mechanism for measuring electrical conductivity after making film on substrates or obtaining clean surfaces by cleavage, flashing, and so on. Accurate temperature measurement is possible since the sample can be transferred with a thermocouple and∕or diode being attached directly to the sample. A single crystal of Bi-based copper oxide high-Tc superconductor (HTSC) was cleaved in UHV to obtain clean surface, and its superconducting critical temperature has been successfully measured in situ. The importance of in situ measurement of resistance in UHV was demonstrated for this HTSC before and after cesium (Cs) adsorption on its surface. The Tc onset increase and the Tc offset decrease by Cs adsorption were observed.

Small-volume, ultrahigh-vacuum-compatible high-pressure reaction cell for combined kinetic and in situ IR spectroscopic measurements on planar model catalysts

NASA Astrophysics Data System (ADS)

Zhao, Z.; Diemant, T.; Häring, T.; Rauscher, H.; Behm, R. J.

2005-12-01

We describe the design and performance of a high-pressure reaction cell for simultaneous kinetic and in situ infrared reflection (IR) spectroscopic measurements on model catalysts at elevated pressures, between 10-3 and 103mbars, which can be operated both as batch reactor and as flow reactor with defined gas flow. The cell is attached to an ultrahigh-vacuum (UHV) system, which is used for sample preparation and also contains facilities for sample characterization. Specific for this design is the combination of a small cell volume, which allows kinetic measurements with high sensitivity under batch or continuous flow conditions, the complete isolation of the cell from the UHV part during UHV measurements, continuous temperature control during both UHV and high-pressure operation, and rapid transfer between UHV and high-pressure stage. Gas dosing is performed by a designed gas-handling system, which allows operation as flow reactor with calibrated gas flows at adjustable pressures. To study the kinetics of reactions on the model catalysts, a quadrupole mass spectrometer is connected to the high-pressure cell. IR measurements are possible in situ by polarization-modulation infrared reflection-absorption spectroscopy, which also allows measurements at elevated pressures. The performance of the setup is demonstrated by test measurements on the kinetics for CO oxidation and the CO adsorption on a Au /TiO2/Ru(0001) model catalyst film at 1-50 mbar total pressure.

Thermal noise limit for ultra-high vacuum noncontact atomic force microscopy.

PubMed

Lübbe, Jannis; Temmen, Matthias; Rode, Sebastian; Rahe, Philipp; Kühnle, Angelika; Reichling, Michael

2013-01-01

The noise of the frequency-shift signal Δf in noncontact atomic force microscopy (NC-AFM) consists of cantilever thermal noise, tip-surface-interaction noise and instrumental noise from the detection and signal processing systems. We investigate how the displacement-noise spectral density d(z) at the input of the frequency demodulator propagates to the frequency-shift-noise spectral density d(Δ) (f) at the demodulator output in dependence of cantilever properties and settings of the signal processing electronics in the limit of a negligible tip-surface interaction and a measurement under ultrahigh-vacuum conditions. For a quantification of the noise figures, we calibrate the cantilever displacement signal and determine the transfer function of the signal-processing electronics. From the transfer function and the measured d(z), we predict d(Δ) (f) for specific filter settings, a given level of detection-system noise spectral density d(z) (ds) and the cantilever-thermal-noise spectral density d(z) (th). We find an excellent agreement between the calculated and measured values for d(Δ) (f). Furthermore, we demonstrate that thermal noise in d(Δ) (f), defining the ultimate limit in NC-AFM signal detection, can be kept low by a proper choice of the cantilever whereby its Q-factor should be given most attention. A system with a low-noise signal detection and a suitable cantilever, operated with appropriate filter and feedback-loop settings allows room temperature NC-AFM measurements at a low thermal-noise limit with a significant bandwidth.

Force microscopy experiments with ultrasensitive cantilevers.

PubMed

Rast, S; Gysin, U; Ruff, P; Gerber, Ch; Meyer, E; Lee, D W

2006-04-14

Force microscopy experiments with the pendulum geometry are performed with attonewton sensitivity (Rugar et al 2004 Nature 43 329). Single-crystalline cantilevers with sub-millinewton spring constants were annealed under ultrahigh-vacuum conditions. It is found that annealing with temperatures below 500 °C can improve the quality factor by an order of magnitude. The high force sensitivity of these ultrasoft cantilevers is used to characterize small magnetic and superconductive particles, which are mounted on the end of the cantilever. Their magnetic properties are analysed in magnetic fields as a function of temperature. The transition of a superconducting sample mounted on a cantilever is measured by the detection of frequency shifts. An increase of dissipation is observed below the critical temperature. The magnetic moment of ferromagnetic particles is determined by real time frequency detection with a phase-locked loop (PLL) as a function of the magnetic field. The dissipation between the probing tip and the sample is another important ingredient for ultrasensitive force measurements. It is found that dissipation increases at separations of 30 nm. The origins of this type of dissipation are poorly understood. However, it is predicted theoretically that adsorbates can increase this dissipation channel (Volokitin and Persson 2005 Phys. Rev. Lett. 94 086104). First experiments are performed under ultrahigh vacuum to investigate this type of dissipation. Long-range dissipation is closely related to long-range forces. The distance dependence of the contact potential is found to be an important aspect.

Influence of TiO2(110) surface roughness on growth and stability of thin organic films.

PubMed

Szajna, K; Kratzer, M; Wrana, D; Mennucci, C; Jany, B R; Buatier de Mongeot, F; Teichert, C; Krok, F

2016-10-14

We have investigated the growth and stability of molecular ultra-thin films, consisting of rod-like semiconducting para-hexaphenyl (6P) molecules vapor deposited on ion beam modified TiO 2 (110) surfaces. The ion bombarded TiO 2 (110) surfaces served as growth templates exhibiting nm-scale anisotropic ripple patterns with controllable parameters, like ripple depth and length. In turn, by varying the ripple depth one can tailor the average local slope angle and the local step density/terrace width of the stepped surface. Here, we distinguish three types of substrates: shallow, medium, and deep rippled surfaces. On these substrates, 6P sub-monolayer deposition was carried out in ultra-high vacuum by organic molecular beam evaporation (OMBE) at room temperature leading to the formation of islands consisting of upright standing 6P molecules, which could be imaged by scanning electron microscopy and atomic force microscopy (AFM). It has been found that the local slope and terrace width of the TiO 2 template strongly influences the stability of OMBE deposited 6P islands formed on the differently rippled substrates. This effect is demonstrated by means of tapping mode AFM, where an oscillating tip was used as a probe for testing the stability of the organic structures. We conclude that by increasing the local slope of the TiO 2 (110) surface the bonding strength between the nearest neighbor standing molecules is weakened due to the presence of vertical displacement in the molecular layer in correspondence to the TiO 2 atomic step height.

Products of Chemistry: Alkanes: Abundant, Pervasive, Important, and Essential.

ERIC Educational Resources Information Center

Seymour, Raymond B.

1989-01-01

Discusses the history and commercialization of alkanes. Examines the nomenclature and uses of alkanes. Studies polymerization and several types of polyethylenes: low-density, high-density, low-molecular-weight, cross-linked, linear low-density, and ultrahigh-molecular-weight. Includes a glossary of hydrocarbon terms. (MVL)

Friction and wear of plasma-deposited diamond films

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Wu, Richard L. C.; Garscadden, Alan; Barnes, Paul N.; Jackson, Howard E.

1993-01-01

Reciprocating sliding friction experiments in humid air and in dry nitrogen and unidirectional sliding friction experiments in ultrahigh vacuum were conducted with a natural diamond pin in contact with microwave-plasma-deposited diamond films. Diamond films with a surface roughness (R rms) ranging from 15 to 160 nm were produced by microwave-plasma-assisted chemical vapor deposition. In humid air and in dry nitrogen, abrasion occurred when the diamond pin made grooves in the surfaces of diamond films, and thus the initial coefficients of friction increased with increasing initial surface roughness. The equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. In vacuum the friction for diamond films contacting a diamond pin arose primarily from adhesion between the sliding surfaces. In these cases, the initial and equilibrium coefficients of friction were independent of the initial surface roughness of the diamond films. The equilibrium coefficients of friction were 0.02 to 0.04 in humid air and in dry nitrogen, but 1.5 to 1.8 in vacuum. The wear factor of the diamond films depended on the initial surface roughness, regardless of environment; it increased with increasing initial surface roughness. The wear factors were considerably higher in vacuum than in humid air and in dry nitrogen.

Design and qualification of an UHV system for operation on sounding rockets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Grosse, Jens, E-mail: jens.grosse@dlr.de; Braxmaier, Claus; Seidel, Stephan Tobias

The sounding rocket mission MAIUS-1 has the objective to create the first Bose–Einstein condensate in space; therefore, its scientific payload is a complete cold atom experiment built to be launched on a VSB-30 sounding rocket. An essential part of the setup is an ultrahigh vacuum system needed in order to sufficiently suppress interactions of the cooled atoms with the residual background gas. Contrary to vacuum systems on missions aboard satellites or the international space station, the required vacuum environment has to be reached within 47 s after motor burn-out. This paper contains a detailed description of the MAIUS-1 vacuum system, asmore » well as a description of its qualification process for the operation under vibrational loads of up to 8.1 g{sub RMS} (where RMS is root mean square). Even though a pressure rise dependent on the level of vibration was observed, the design presented herein is capable of regaining a pressure of below 5 × 10{sup −10} mbar in less than 40 s when tested at 5.4 g{sub RMS}. To the authors' best knowledge, it is the first UHV system qualified for operation on a sounding rocket.« less

Sliding Wear and Fretting Wear of DLC-Based, Functionally Graded Nanocomposite Coatings

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Pohlchuck, B.; Street, Kenneth W.; Zabinski, J. S.; Sanders, J. H.; Voevodin, A. a.; Wu, R. L. C.

1999-01-01

Improving the tribological functionality of diamondlike carbon (DLC) films--developing, good wear resistance, low friction, and high load-carrying capacity-was the aim of this investigation. Nanocomposite coatings consisting of an amorphous DLC (a-DLC) top layer and a functionally graded titanium-titanium carbon-diamondlike carbon (Ti-Ti(sub x) C(sub y)-DLC) underlayer were produced on AISI 440C stainless steel substrates by the hybrid technique of magnetron sputtering and pulsed-laser deposition. The resultant DLC films were characterized by Raman spectroscopy, scanning electron microscopy, and surface profilometry. Two types of wear experiment were conducted in this investioation: sliding friction experiments and fretting wear experiments. Unidirectional ball-on-disk sliding friction experiments were conducted to examine the wear behavior of an a-DLC/Ti-Ti(sub x) C(sub y)-DLC-coated AISI 440C stainless steel disk in sliding contact with a 6-mm-diameter AISI 440C stainless steel ball in ultrahigh vacuum, dry nitrogen, and humid air. Although the wear rates for both the coating and ball were low in all three environments, the humid air and dry nitrogen caused mild wear with burnishing, in the a-DLC top layer, and the ultrahigh vacuum caused relatively severe wear with brittle fracture in both the a-DLC top layer and the Ti-Ti(sub x) C(sub y)-DLC underlayer. For reference, amorphous hydrogenated carbon (H-DLC) films produced on a-DLC/Ti-Ti(sub x) C(sub y)-DLC nanocomposite coatings by using an ion beam were also examined in the same manner. The H-DLC films markedly reduced friction even in ultrahigh vacuum without sacrificing wear resistance. The H-DLC films behaved much like the a-DLC/Ti-Ti(sub x) C(sub y)-DLC nanocomposite coating in dry nitrogen and humid air, presenting low friction and low wear. Fretting wear experiments were conducted in humid air (approximately 50% relative humidity) at a frequency of 80 Hz and an amplitude of 75 micron on an a-DLC/Ti-Ti(sub x) C(sub y)-DLC-coated AISI 440C disk and on a titanium-6 wt % aluminum-4 wt% vanadium (Ti-6Al-4V) flat, both in contact with a 9.4-mm-diameter, hemispherical Ti-6Al-4V pin. The resistance to fretting wear and damage of the a-DLC/Ti-6Al-4V materials pair was superior to that of the Ti-6Al-4V/Ti-6AI-4V materials pair.

Friction and Wear Properties of Selected Solid Lubricating Films. Part 3; Magnetron-Sputtered and Plasma-Assisted, Chemical-Vapor-Deposited Diamondlike Carbon Films

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Iwaki, Masanori; Gotoh, Kenichi; Obara, Shingo; Imagawa, Kichiro

2000-01-01

To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of magnetron-sputtered diamondlike carbon (MS DLC) and plasma-assisted, chemical-vapor-deposited diamondlike carbon (PACVD DLC) films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of L-2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7x10(exp -7) Pa), humid air (relative humidity, approx.20 percent), and dry nitrogen (relative humidity, <1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and surface profilometry. Marked differences in the friction and wear of the DLC films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the DLC films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 10(exp -6) cu mm/N-m or less, respectively. MS DLC films and PACVD DLC films met the criteria in humid air and dry nitrogen but failed in ultrahigh vacuum, where the coefficients of friction were greater than the criterion, 0.3. In sliding contact with 440C stainless steel balls in all three environments the PACVD DLC films exhibited better tribological performance (i.e., lower friction and wear) than the MS DLC films. All sliding involved adhesive transfer of wear materials: transfer of DLC wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart DLC film.

Friction and Wear Properties of Selected Solid Lubricating Films. Part 2; Ion-Plated Lead Films

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa; Iwaki, Masanori; Gotoh, Kenichi; Obara, Shingo; Imagawa, Kichiro

2000-01-01

To evaluate commercially developed dry solid film lubricants for aerospace bearing applications, an investigation was conducted to examine the friction and wear behavior of ion-plated lead films in sliding contact with 6-mm-diameter American Iron and Steel Institute (AISI) 440C stainless steel balls. Unidirectional sliding friction experiments were conducted with a load of 5.9 N (600 g), a mean Hertzian contact pressure of 0.79 GPa (maximum Hertzian contact pressure of 1.2 GPa), and a sliding velocity of 0.2 m/s. The experiments were conducted at room temperature in three environments: ultrahigh vacuum (vacuum pressure, 7 x 10(exp -7 Pa), humid air (relative humidity, approx. 20 percent), and dry nitrogen (relative humidity, less then 1 percent). The resultant films were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and surface profilometry. Marked differences in the friction and wear of the ion-plated lead films investigated herein resulted from the environmental conditions. The main criteria for judging the performance of the ion-plated lead films were coefficient of friction and wear rate, which had to be less than 0.3 and on the order of 1(exp -6) cu mm/N.m or less, respectively. The ion-plated lead films met both criteria only in ultrahigh vacuum but failed in humid air and in dry nitrogen, where the coefficient of friction was higher than the criterion. Both the lead film wear rate and the ball wear rate met that criterion in all three environments. Adhesion and plastic deformation played important roles in the friction and wear of the ion-plated lead films in contact with 440C stainless steel balls in the three environments. All sliding involved adhesive transfer of materials: transfer of lead wear debris to the counterpart 440C stainless steel and transfer of 440C stainless steel wear debris to the counterpart lead.

RF cavity design and qualification for proton accelerator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Teotia, Vikas; Malhotra, Sanjay; Ukarde, Priti

Alvarez type Drift Tube Linac (DTL) is used for acceleration of proton beam in low energy section of beta ranging from 0.04 to 0.40. DTL is cylindrical RF cavity resonating in TM010 mode at 352.21 MHz frequency. It consists of array of drift tubes arranged ensuring that DTL centre and Drift Tube centre are concentric. The Drift Tubes also houses Permanent Magnet Quadrupole for transverse focusing of proton beam. A twelve cell prototype of DTL section is designed, developed and fabricated at Bhabha Atomic Research Centre, Trombay. Complete DTL accelerator consists of eight such DTL sections. High frequency microwave simulationsmore » are carried out in SOPRANO, vector fields and COMSOL simulation software. This prototype DTL is 1640.56 mm long cavity with 520 mm ID, 600 mm OD and consists of eleven Drift Tubes, two RF end flanges, three slug tuners, six post couplers, three RF field monitors, one RF waveguide coupler, two DN100 vacuum flanges and DTL tank platform with alignment features. Girder based Drift tube mounting arrangement utilizing uncompressing energy of disc springs for optimum combo RF-vacuum seal compression is worked out and implemented. This paper discusses design of this RF vacuum cavity operating at high accelerating field gradient in ultra-high vacuum. Detailed vacuum design and results of RF and vacuum qualifications are discussed. Results on mechanical accuracy achieved on scaled pre-prototype are also presented. Paper summarizes the engineering developments carried out for this RF cavity and brings out the future activities proposed in indigenous development of high gradient RF cavities for ion accelerators. (author)« less

Stoichiometric and Oxygen-Deficient VO2 as Versatile Hole Injection Electrode for Organic Semiconductors.

PubMed

Fu, Keke; Wang, Rongbin; Katase, Takayoshi; Ohta, Hiromichi; Koch, Norbert; Duhm, Steffen

2018-03-28

Using photoemission spectroscopy, we show that the surface electronic structure of VO 2 is determined by the temperature-dependent metal-insulator phase transition and the density of oxygen vacancies, which depends on the temperature and ultrahigh vacuum (UHV) conditions. The atomically clean and stoichiometric VO 2 surface is insulating at room temperature and features an ultrahigh work function of up to 6.7 eV. Heating in UHV just above the phase transition temperature induces the expected metallic phase, which goes in hand with the formation of oxygen defects (up to 6% in this study), but a high work function >6 eV is maintained. To demonstrate the suitability of VO 2 as hole injection contact for organic semiconductors, we investigated the energy-level alignment with the prototypical organic hole transport material N, N'-di(1-naphthyl)- N, N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPB). Evidence for strong Fermi-level pinning and the associated energy-level bending in NPB is found, rendering an Ohmic contact for holes.

FLUID PRESSURE AND CAM OPERATED VACUUM VALVE

DOEpatents

Batzer, T.H.

1963-11-26

An ultra-high vacuum valve that is bakable, reusable, and capable of being quickly opened and closed is described. A translationally movable valve gate having an annular ridge is adapted to contact an annular soft metal gasket disposed at the valve seat such that the soft metal gasket extends beyond the annular ridge on all sides. The valve gate is closed, by first laterally aligning the valve gate with the valve seat and then bringing the valve gate and valve seat into seating contact by the translational movement of a ramp-like wedging means that engages similar ramp-like stractures at the base of the valve gate to force the valve gate into essentially pressureless contact with the annular soft metal gasket. This gasket is then pressurized from beneath by a fluid thereby effecting a vacuura tight seal between the gasket and the ridge. (AEC)

Cavity Control and Cooling of Nanoparticles in High Vacuum

NASA Astrophysics Data System (ADS)

Millen, James

2016-05-01

Levitated systems are a fascinating addition to the world of optically-controlled mechanical resonators. It is predicted that nanoparticles can be cooled to their c.o.m. ground state via the interaction with an optical cavity. By freeing the oscillator from clamping forces dissipation and decoherence is greatly reduced, leading to the potential to produce long-lived, macroscopically spread, mechanical quantum states, allowing tests of collapse models and any mass limit of quantum physics. Reaching the low pressures required to cavity-cool to the ground state has proved challenging. Our approach is to cavity cool a beam of nanoparticles in high vacuum. We can cool the c.o.m. motion of nanospheres, and control the rotation of nanorods, with the potential to produce cold, aligned nanostructures. Looking forward, we will utilize novel microcavities to enhance optomechanical cooling, preparing particles in a coherent beam ideally suited to ultra-high mass interferometry at 107 a.m.u.

Space ultra-vacuum facility and method of operation

NASA Technical Reports Server (NTRS)

Naumann, Robert J. (Inventor)

1988-01-01

A wake shield space processing facility (10) for maintaining ultra-high levels of vacuum is described. The wake shield (12) is a truncated hemispherical section having a convex side (14) and a concave side (24). Material samples (68) to be processed are located on the convex side of the shield, which faces in the wake direction in operation in orbit. Necessary processing fixtures (20) and (22) are also located on the convex side. Support equipment including power supplies (40, 42), CMG package (46) and electronic control package (44) are located on the convex side (24) of the shield facing the ram direction. Prior to operation in orbit the wake shield is oriented in reverse with the convex side facing the ram direction to provide cleaning by exposure to ambient atomic oxygen. The shield is then baked-out by being pointed directed at the sun to obtain heating for a suitable period.

Efficient solar cells by space processing

NASA Technical Reports Server (NTRS)

Schmidt, F. A.; Campisi, G. J.; Bevolo, A.; Shanks, H. R.; Williams, D. E.

1979-01-01

Thin films of electron beam evaporated silicon were deposited on molybdenum, tantalum, tungsten and molybdenum disilicide under ultrahigh vacuum conditions. Mass spectra from a quadrapole residual gas analyzer were used to determine the partial pressure of 13 residual gases during each processing step. Surface contamination and interdiffusion were monitored by in situ Auger electron spectrometry. The presence of phosphorus in the silicon was responsible for attaining elevated temperatures with silicide formations. Heteroepitaxial silicon growth was sensitive to the presence of oxygen during deposition, the rate and length of deposition as well as the substrate orientation.

Shear strength of metal - SiO2 contacts

NASA Technical Reports Server (NTRS)

Pepper, S. V.

1978-01-01

The strength of the bond between metals and SiO2 is studied by measuring the static coefficient of friction of metals contacting alpha-quartz in ultrahigh vacuum. It was found that copper with either chemisorbed oxygen, nitrogen or sulphur exhibited higher contact strength on stoichiometric SiO2 than did clean copper. Since the surface density of states induced by these species on copper is similar, it appears that the strength of the interfacial bond can be related to the density of states on the metal surface.

Shear strength of metal - SiO2 contacts

NASA Technical Reports Server (NTRS)

Pepper, S. V.

1978-01-01

The strength of the bond between metals and SiO2 was studied by measuring the static coefficient of friction of metals contacting alpha-quartz in ultrahigh vacuum. It was found that copper with either chemisorbed oxygen, nitrogen, or sulphur exhibited higher contact strength on stoichiometric SiO2 than did clean copper. Since the surface density of states induced by these species on copper is similar, it appears that the strength of the interfacial bond can be related to the density of states on the metal surface.

Ultrahigh Vacuum Studies of the Fundamental Interactions of Chemical Warfare Agents and Their Simulants with Amorphous Silica

DTIC Science & Technology

2015-07-14

Aldao, C. M. Monte Carlo Study of Thermal Desorption Curves of Water from Zeolite Type A. Langmuir 1996, 12, 36-39. (83) Gorte, R. J. Design Parameters...and Diffusion-Limited TPD of Water from Zeolite Linde 4A. Thermochimica Acta 1998, 319, 177-184. (85) Palmero, A.; Loffler, D. G. Kinetics of Water...Desorption from Pelletized 4A and 5A Zeolites . Thermochimica Acta 1990, 159, 171-176. (86) Dean, J. A. Lange’s Handbook of Chemistry; Fifteenth

Investigation of local tunneling current noise spectra on the silicon crystal surfaces by means of STM/STS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mantsevich, V. N., E-mail: vmantsev@spmlab.phys.msu.su; Maslova, N. S.; Cao, G. Y.

We report on a careful analysis of the local tunneling conductivity by means of ultra-high vacuum scanning tunneling microscopy/spectroscopy (STM/STS) technique in the vicinity of low-dimensional structures on the Si(111)–(7 × 7) and Si(110)–(16 × 2) surfaces. The power-law exponent α of low-frequency tunneling current noise spectra is investigated for different values of the tunneling contact parameters: relaxation rates, the localized state coupling, and the tunneling barrier width and height.

Investigation of local tunneling current noise spectra on the silicon crystal surfaces by means of STM/STS

NASA Astrophysics Data System (ADS)

Mantsevich, V. N.; Maslova, N. S.; Cao, G. Y.

2015-08-01

We report on a careful analysis of the local tunneling conductivity by means of ultra-high vacuum scanning tunneling microscopy/spectroscopy (STM/STS) technique in the vicinity of low-dimensional structures on the Si(111)-(7 × 7) and Si(110)-(16 × 2) surfaces. The power-law exponent α of low-frequency tunneling current noise spectra is investigated for different values of the tunneling contact parameters: relaxation rates, the localized state coupling, and the tunneling barrier width and height.

Underpotential Deposition of Silver on Pt(111). Part 1. Concentration Dependence

DTIC Science & Technology

1990-01-01

acid (ULTREX, J.T. Baker) was used as the supporting electrolyte. Silver solutions of 1.00 mM, 0.10 mM, and 0.005 mM were prepared by dissolving Ag 2SO 4...were immersed in hot nitric acid for 10 minutes. For the ultra-high vacuum (UHV) experiments a thermocouple was also spot-welded to the edge of the...a Ford Foundation Post Doctoral Fellowship. HDA is a A.P. Sloan Foundation Fellow (1987-1991). 16 REFERENCES 1. G.W. Tindall and S. Bruckenstein

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, A. A.; Hesjedal, T.; Diamond Light Source, Didcot OX11 0DE

We present a miniaturized molecular beam epitaxy (miniMBE) system with an outer diameter of 206 mm, optimized for flexible and high-throughput operation. The three-chamber system, used here for oxide growth, consists of a sample loading chamber, a storage chamber, and a growth chamber. The growth chamber is equipped with eight identical effusion cell ports with linear shutters, one larger port for either a multi-pocket electron beam evaporator or an oxygen plasma source, an integrated cryoshroud, retractable beam-flux monitor or quartz-crystal microbalance, reflection high energy electron diffraction, substrate manipulator, main shutter, and quadrupole mass spectrometer. The system can be combined withmore » ultrahigh vacuum (UHV) end stations on synchrotron and neutron beamlines, or equivalently with other complex surface analysis systems, including low-temperature scanning probe microscopy systems. Substrate handling is compatible with most UHV surface characterization systems, as the miniMBE can accommodate standard surface science sample holders. We introduce the design of the system, and its specific capabilities and operational parameters, and we demonstrate the epitaxial thin film growth of magnetoelectric Cr{sub 2}O{sub 3} on c-plane sapphire and ferrimagnetic Fe{sub 3}O{sub 4} on MgO (001)« less

Low-Temperature Surface Preparation and Epitaxial Growth of ZnS and Cu 2ZnSnS 4 on ZnS(110) and GaP(100)

DOE PAGES

Harvey, Steven P; Wilson, Samual; Moutinho, Helio R; ...

2017-08-12

Here we give a summary of the low-temperature preparation methods of ZnS(110) and GaP(100) crystals for epitaxial growth of ZnS and Cu 2ZnSnS 4 (CZTS) via molecular beam epitaxy. Substrates were prepared for epitaxial growth by means of room-temperature aqueous surface treatments and subsequent ultra-high vacuum transfer to the deposition system. Epitaxial growth of ZnS was successful at 500 K on both ZnS(110) and GaP(100) as only single domains were observed with electron backscatter diffraction; furthermore, transmission electron microscopy measurements confirmed an epitaxial interface. Epitaxial growth of CZTS was successful on ZnS at 700 K. However, epitaxial growth was notmore » possible on GaP at 700 K due to Ga xS y formation, which significantly degraded the quality of the GaP crystal surface. Although CZTS was grown epitaxially on ZnS, growth of multiple crystallographic domains remains a problem that could inherently limit the viability of epitaxial CZTS for model system studies.« less

N ,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) on alkali halide (001) surfaces

NASA Astrophysics Data System (ADS)

Fendrich, Markus; Lange, Manfred; Weiss, Christian; Kunstmann, Tobias; Möller, Rolf

2009-05-01

The growth of N ,N'-dimethylperylene-3,4,9,10-bis(dicarboximide) (DiMe-PTCDI) on KBr(001) and NaCl(001) surfaces has been studied. Experimental results have been achieved using frequency modulation atomic force microscopy at room temperature under ultrahigh vacuum conditions. On both substrates, DiMe-PTCDI forms molecular wires with a width of 10nm, typically, and a length of up to 600nm at low coverages. All wires grow along either the [110] direction (or [11¯0] direction, respectively) of the alkali halide (001) substrates. There is no wetting layer of molecules: atomic resolution of the substrates can be achieved between the wires. The wires are mobile on KBr but substantially more stable on NaCl. A p(2×2) superstructure in a brickwall arrangement on the ionic crystal surfaces is proposed based on electrostatic considerations. Calculations and Monte Carlo simulations using empirical potentials reveal possible growth mechanisms for molecules within the first layer for both substrates, also showing a significantly higher binding energy for NaCl(001). For KBr, the p(2×2) superstructure is confirmed by the simulations; for NaCl, a less dense, incommensurate superstructure is predicted.

Use of radiation in biomaterials science

NASA Astrophysics Data System (ADS)

Benson, Roberto S.

2002-05-01

Radiation is widely used in the biomaterials science for surface modification, sterilization and to improve bulk properties. Radiation is also used to design of biochips, and in situ photopolymerizable of bioadhesives. The energy sources most commonly used in the irradiation of biomaterials are high-energy electrons, gamma radiation, ultraviolet (UV) and visible light. Surface modification involves placement of selective chemical moieties on the surface of a material by chemical reactions to improve biointeraction for cell adhesion and proliferation, hemocompatibility and water absorption. The exposure of a polymer to radiation, especially ionizing radiation, can lead to chain scission or crosslinking with changes in bulk and surface properties. Sterilization by irradiation is designed to inactivate most pathogens from the surface of biomedical devices. An overview of the use of gamma and UV radiation to improve surface tissue compatibility, bulk properties and surface properties for wear resistance, formation of hydrogels and curing dental sealants and bone adhesives is presented. Gamma and vacuum ultraviolet (VUV) irradiated ultrahigh molecular weight polyethylene (UHMWPE) exhibit improvement in surface modulus and hardness. The surface modulus and hardness of UHMWPE showed a dependence on type of radiation, dosage and processing. VUV surface modified e-PTFE vascular grafts exhibit increases in hydrophilicity and improvement towards adhesion of fibrin glue.

Self-organized nano-structuring of CoO islands on Fe(001)

NASA Astrophysics Data System (ADS)

Brambilla, A.; Picone, A.; Giannotti, D.; Riva, M.; Bussetti, G.; Berti, G.; Calloni, A.; Finazzi, M.; Ciccacci, F.; Duò, L.

2016-01-01

The realization of nanometer-scale structures through bottom-up strategies can be accomplished by exploiting a buried network of dislocations. We show that, by following appropriate growth steps in ultra-high vacuum molecular beam epitaxy, it is possible to grow nano-structured films of CoO coupled to Fe(001) substrates, with tunable sizes (both the lateral size and the maximum height scale linearly with coverage). The growth mode is discussed in terms of the evolution of surface morphology and chemical interactions as a function of the CoO thickness. Scanning tunneling microscopy measurements reveal that square mounds of CoO with lateral dimensions of less than 25 nm and heights below 10 atomic layers are obtained by growing few-nanometers-thick CoO films on a pre-oxidized Fe(001) surface covered by an ultra-thin Co buffer layer. In the early stages of growth, a network of misfit dislocations develops, which works as a template for the CoO nano-structuring. From a chemical point of view, at variance with typical CoO/Fe interfaces, neither Fe segregation at the surface nor Fe oxidation at the buried interface are observed, as seen by Auger electron spectroscopy and X-ray Photoemission Spectroscopy, respectively.

Low-Temperature Surface Preparation and Epitaxial Growth of ZnS and Cu 2ZnSnS 4 on ZnS(110) and GaP(100)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harvey, Steven P; Wilson, Samual; Moutinho, Helio R

Here we give a summary of the low-temperature preparation methods of ZnS(110) and GaP(100) crystals for epitaxial growth of ZnS and Cu 2ZnSnS 4 (CZTS) via molecular beam epitaxy. Substrates were prepared for epitaxial growth by means of room-temperature aqueous surface treatments and subsequent ultra-high vacuum transfer to the deposition system. Epitaxial growth of ZnS was successful at 500 K on both ZnS(110) and GaP(100) as only single domains were observed with electron backscatter diffraction; furthermore, transmission electron microscopy measurements confirmed an epitaxial interface. Epitaxial growth of CZTS was successful on ZnS at 700 K. However, epitaxial growth was notmore » possible on GaP at 700 K due to Ga xS y formation, which significantly degraded the quality of the GaP crystal surface. Although CZTS was grown epitaxially on ZnS, growth of multiple crystallographic domains remains a problem that could inherently limit the viability of epitaxial CZTS for model system studies.« less

Large-Area Atomic Layers of the Charge-Density-Wave Conductor TiSe2.

PubMed

Wang, Hong; Chen, Yu; Duchamp, Martial; Zeng, Qingsheng; Wang, Xuewen; Tsang, Siu Hon; Li, Hongling; Jing, Lin; Yu, Ting; Teo, Edwin Hang Tong; Liu, Zheng

2018-02-01

Layered transition metal (Ti, Ta, Nb, etc.) dichalcogenides are important prototypes for the study of the collective charge density wave (CDW). Reducing the system dimensionality is expected to lead to novel properties, as exemplified by the discovery of enhanced CDW order in ultrathin TiSe 2 . However, the syntheses of monolayer and large-area 2D CDW conductors can currently only be achieved by molecular beam epitaxy under ultrahigh vacuum. This study reports the growth of monolayer crystals and up to 5 × 10 5 µm 2 large films of the typical 2D CDW conductor-TiSe 2 -by ambient-pressure chemical vapor deposition. Atomic resolution scanning transmission electron microscopy indicates the as-grown samples are highly crystalline 1T-phase TiSe 2 . Variable-temperature Raman spectroscopy shows a CDW phase transition temperature of 212.5 K in few layer TiSe 2 , indicative of high crystal quality. This work not only allows the exploration of many-body state of TiSe 2 in 2D limit but also offers the possibility of utilizing large-area TiSe 2 in ultrathin electronic devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Perspective: Size selected clusters for catalysis and electrochemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Halder, Avik; Curtiss, Larry A.; Fortunelli, Alessandro

We report that size-selected clusters containing a handful of atoms may possess noble catalytic properties different from nano-sized or bulk catalysts. Size- and composition-selected clusters can also serve as models of the catalytic active site, where an addition or removal of a single atom can have a dramatic effect on their activity and selectivity. In this Perspective, we provide an overview of studies performed under both ultra-high vacuum and realistic reaction conditions aimed at the interrogation, characterization and understanding of the performance of supported size-selected clusters in heterogeneous and electrochemical reactions, which address the effects of cluster size, cluster composition,more » cluster-support interactions and reaction conditions, the key parameters for the understanding and control of catalyst functionality. Computational modelling based on density functional theory sampling of local minima and energy barriers or ab initio Molecular Dynamics simulations is an integral part of this research by providing fundamental understanding of the catalytic processes at the atomic level, as well as by predicting new materials compositions which can be validated in experiments. Lastly, we discuss approaches which aim at the scale up of the production of well-defined clusters for use in real world applications.« less

Perspective: Size selected clusters for catalysis and electrochemistry

DOE PAGES

Halder, Avik; Curtiss, Larry A.; Fortunelli, Alessandro; ...

2018-03-15

We report that size-selected clusters containing a handful of atoms may possess noble catalytic properties different from nano-sized or bulk catalysts. Size- and composition-selected clusters can also serve as models of the catalytic active site, where an addition or removal of a single atom can have a dramatic effect on their activity and selectivity. In this Perspective, we provide an overview of studies performed under both ultra-high vacuum and realistic reaction conditions aimed at the interrogation, characterization and understanding of the performance of supported size-selected clusters in heterogeneous and electrochemical reactions, which address the effects of cluster size, cluster composition,more » cluster-support interactions and reaction conditions, the key parameters for the understanding and control of catalyst functionality. Computational modelling based on density functional theory sampling of local minima and energy barriers or ab initio Molecular Dynamics simulations is an integral part of this research by providing fundamental understanding of the catalytic processes at the atomic level, as well as by predicting new materials compositions which can be validated in experiments. Lastly, we discuss approaches which aim at the scale up of the production of well-defined clusters for use in real world applications.« less

Elementary photocatalytic chemistry on TiO2 surfaces.

PubMed

Guo, Qing; Zhou, Chuanyao; Ma, Zhibo; Ren, Zefeng; Fan, Hongjun; Yang, Xueming

2016-07-07

Photocatalytic hydrogen production and pollutant degradation provided both great opportunities and challenges in the field of sustainable energy and environmental science. Over the past few decades, we have witnessed fast growing interest and efforts in developing new photocatalysts, improving catalytic efficiency and exploring the reaction mechanism at the atomic and molecular levels. Owing to its relatively high efficiency, nontoxicity, low cost and high stability, TiO2 becomes one of the most extensively investigated metal oxides in semiconductor photocatalysis. Fundamental studies on well characterized single crystals using ultrahigh vacuum based surface science techniques could provide key microscopic insight into the underlying mechanism of photocatalysis. In this review, we have summarized recent progress in the photocatalytic chemistry of hydrogen, water, oxygen, carbon monoxide, alcohols, aldehydes, ketones and carboxylic acids on TiO2 surfaces. We focused this review mainly on the rutile TiO2(110) surface, but some results on the rutile TiO2(011), anatase TiO2(101) and (001) surfaces are also discussed. These studies provided fundamental insights into surface photocatalysis as well as stimulated new investigations in this exciting field. At the end of this review, we have discussed how these studies can help us to develop new photocatalysis models.

Perspective: Size selected clusters for catalysis and electrochemistry

NASA Astrophysics Data System (ADS)

Halder, Avik; Curtiss, Larry A.; Fortunelli, Alessandro; Vajda, Stefan

2018-03-01

Size-selected clusters containing a handful of atoms may possess noble catalytic properties different from nano-sized or bulk catalysts. Size- and composition-selected clusters can also serve as models of the catalytic active site, where an addition or removal of a single atom can have a dramatic effect on their activity and selectivity. In this perspective, we provide an overview of studies performed under both ultra-high vacuum and realistic reaction conditions aimed at the interrogation, characterization, and understanding of the performance of supported size-selected clusters in heterogeneous and electrochemical reactions, which address the effects of cluster size, cluster composition, cluster-support interactions, and reaction conditions, the key parameters for the understanding and control of catalyst functionality. Computational modeling based on density functional theory sampling of local minima and energy barriers or ab initio molecular dynamics simulations is an integral part of this research by providing fundamental understanding of the catalytic processes at the atomic level, as well as by predicting new materials compositions which can be validated in experiments. Finally, we discuss approaches which aim at the scale up of the production of well-defined clusters for use in real world applications.

Investigation of Molecular Exchange Using DEXSY with Ultra-High Pulsed Field Gradients

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gratz, Marcel; Galvosas, Petrik

2008-12-05

Diffusion exchange spectroscopy has been employed for the investigation of water exchange between different regions of a cosmetic lotion as well as for the exchange of n-pentane between the inter- and intra-crystalline space in zeolite NaX. We successfully combined this two-dimensional (2D) NMR experiment with methods for the application of ultra-high pulsed field gradients of up to 35 T/m, resulting in observation times and mixing times as short as 2 ms and 2.8 ms, respectively.

The Formation of Solid Particles from their Gas-Phase Molecular Precursors in Cosmic Environments with NASA Ames' COSmIC Facility

NASA Technical Reports Server (NTRS)

Salama, Farid

2014-01-01

We present and discuss the unique characteristics and capabilities of the laboratory facility, COSmIC, that was developed at NASA Ames to generate, process and analyze interstellar, circumstellar and planetary analogs in the laboratory. COSmIC stands for Cosmic Simulation Chamber and is dedicated to the study of molecules and ions under the low temperature and high vacuum conditions that are required to simulate interstellar, circumstellar and planetary physical environments in space. COSmIC integrates a variety of state-of-the-art instruments that allow forming, processing and monitoring simulated space conditions for planetary, circumstellar and interstellar materials in the laboratory. COSmIC is composed of a Pulsed Discharge Nozzle (PDN) expansion that generates a free jet supersonic expansion coupled to two ultrahigh-sensitivity, complementary in situ diagnostics: a Cavity Ring Down Spectroscopy (CRDS) system for photonic detection and a Reflectron Time-Of-Flight Mass Spectrometer (ReTOF-MS) for mass detection. Recent, unique, laboratory astrophysics results that were obtained using the capabilities of COSmIC will be discussed, in particular the progress that have been achieved in monitoring in the laboratory the formation of solid gains from their gas-phase molecular precursors in environments as varied as stellar/circumstellar outflow and planetary atmospheres. Plans for future, next generation, laboratory experiments on cosmic molecules and grains in the growing field of laboratory astrophysics will also be addressed as well as the implications of these studies for current and upcoming space missions.

Chemical activation of molecules by metals: Experimental studies of electron distributions and bonding

NASA Astrophysics Data System (ADS)

Lichtenberg, Dennis L.

During this period some important breakthroughs were accomplished in understanding the relationships between molecular ionization energies and bond energies in transition metal complexes, in understanding the electronic factors of carbon-hydrogen bond activation by transition metals, in characterizing small molecule bonding interactions with transition metals, and in investigating intermolecular interactions in thin films of transition metal complexes. The formal relationship between measured molecular ionization energies and thermodynamic bond dissociation energies was developed into a single equation which unifies the treatment of covalent bonds, ionic bonds, and partially ionic bonds. The relationship was used to clarify the fundamental thermodynamic information relating to metal-hydrogen, metal-alkyl, and metal-metal bond energies. The ionization energies were also used to correlate the rates of carbonyl substitution reactions of (eta(sup 5)-C5H4X)Rh(CO)2 complexes, and to reveal the factors that control the stability of the transition state. The investigations of the fundamental interactions of C-H sigma and sigma* orbitals metals were continued with study of eta(sup 3)-1-methylallyl metal complexes. Direct observation and measurement of the stabilization energy provided by the agostic interaction of the C-H bond with the metal was obtained. The ability to observe the electronic effects of intermolecular interactions by comparing the ionizations of metal complexes in the gas phase with the ionizations of thin solid organometallic films prepared in ultra-high vacuum was established. Most significantly, the scanning tunneling microscope imaging of these thin films was accomplished.

From Supercomputer Modeling to Highest Mass Resolution in FT-ICR.

PubMed

N Nikolaev, Evgene; N Vladimirov, Gleb; Jertz, Roland; Baykut, Gökhan

2013-01-01

Understanding of behavior of ion ensembles inside FT-ICR cell based on the computer simulation of ion motion gives rise to the new ideas of cell designs. The recently introduced novel FT-ICR cell based on a Penning ion trap with specially shaped excitation and detection electrodes prevents distortion of ion cyclotron motion phases (normally caused by non-ideal electric trapping fields) by averaging the trapping DC electric field during the ion motion in the ICR cell. Detection times of 5 min resulting in resolving power close to 40,000,000 have been reached for reserpine at m/z 609 at a magnetic field of only 7 Tesla. Fine structures of resolved 13Cn isotopic cluster groups could be measured for molecular masses up to 5.7 kDa (insulin) with resolving power of 4,000,000 at 7 Tesla. Based on resolved fine structure patterns atomic compositions can be directly determined using a new developed algorithm for fine structure processing. Mass spectra of proteins and multimers of proteins reaching masses up to 186 kDa (enolase tetramer) could be measured with isotopic resolution. For instance, at 7 Tesla resolving power of 800,000 was achieved for enolase dimer (96 kDa) and 500,000 for molecular masses above 100 kDa. Experimental data indicate that there is practically no limit for the resolving power of this ICR cell except by collisional damping in the ultrahigh vacuum chamber.

Ultra-High Molecular Weight Polyethylene: Influence of the Chemical, Physical and Mechanical Properties on the Wear Behavior. A Review

PubMed Central

Bellare, Anuj; Bistolfi, Alessandro

2017-01-01

Ultra-high molecular weight polyethylene (UHMWPE) is the most common bearing material in total joint arthroplasty due to its unique combination of superior mechanical properties and wear resistance over other polymers. A great deal of research in recent decades has focused on further improving its performances, in order to provide durable implants in young and active patients. From “historical”, gamma-air sterilized polyethylenes, to the so-called first and second generation of highly crosslinked materials, a variety of different formulations have progressively appeared in the market. This paper reviews the structure–properties relationship of these materials, with a particular emphasis on the in vitro and in vivo wear performances, through an analysis of the existing literature. PMID:28773153

Mobile-bearing knee systems: ultra-high molecular weight polyethylene wear and design issues.

PubMed

Greenwald, A Seth; Heim, Christine S

2005-01-01

In June 2004, the U.S. Food and Drug Administration Orthopaedic Advisory Panel recommended the reclassification of mobile-bearing knee systems for general use. This reflects the increasing use of mobile-bearing knee systems internationally, which is currently limited in the United States by regulatory requirement. Mobile-bearing knee systems are distinguished from conventional, fixed-plateau systems in that they allow dual-surface articulation between an ultra-high molecular weight polyethylene insert and metallic femoral and tibial tray components. Their in vivo success is dependent on patient selection, design, and material choice, as well as surgical precision during implantation. Laboratory and clinical experience extending over 25 years with individual systems suggests that mobile-bearing knee systems represent a viable treatment option for patients with knee arthrosis.

Joint adsorption of light hydrogen by CuO and 5A molecular sieves

NASA Astrophysics Data System (ADS)

Wang, J.; Zhan, Y.; Wang, W.; Wang, R. S.

2018-03-01

H2 is the primary cause of the deteriorating vacuum degree of high-vacuum multilayer insulation tank (HVMLIT). At present, the precious metal PdO is used to adsorb H2 and maintain the high vacuum of HVMLIT. In this study, CA, a compound hydrogen adsorbent integrated with the cheap metal CuO and 5A molecular sieves, is adopted to jointly adsorb light hydrogen in HVMLIT. This work also investigates the adsorption characteristics and mechanisms of CA.

Optimization of the nanotwin-induced zigzag surface of copper by electromigration

NASA Astrophysics Data System (ADS)

Chen, Hsin-Ping; Huang, Chun-Wei; Wang, Chun-Wen; Wu, Wen-Wei; Liao, Chien-Neng; Chen, Lih-Juann; Tu, King-Ning

2016-01-01

By adding nanotwins to Cu, the surface electromigration (EM) slows down. The atomic mobility of the surface step-edges is retarded by the triple points where a twin meets a free surface to form a zigzag-type surface. We observed that EM can alter the zigzag surface structure to optimize the reduction of EM, according to Le Chatelier's principle. Statistically, the optimal alternation is to change an arbitrary (111)/(hkl) zigzag pair to a pair having a very low index (hkl) plane, especially the (200) plane. Using in situ ultrahigh vacuum and high-resolution transmission electron microscopy, we examined the effects of different zigzag surfaces on the rate of EM. The calculated rate of surface EM can be decreased by a factor of ten.By adding nanotwins to Cu, the surface electromigration (EM) slows down. The atomic mobility of the surface step-edges is retarded by the triple points where a twin meets a free surface to form a zigzag-type surface. We observed that EM can alter the zigzag surface structure to optimize the reduction of EM, according to Le Chatelier's principle. Statistically, the optimal alternation is to change an arbitrary (111)/(hkl) zigzag pair to a pair having a very low index (hkl) plane, especially the (200) plane. Using in situ ultrahigh vacuum and high-resolution transmission electron microscopy, we examined the effects of different zigzag surfaces on the rate of EM. The calculated rate of surface EM can be decreased by a factor of ten. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05418d

Atmospheric pressure reaction cell for operando sum frequency generation spectroscopy of ultrahigh vacuum grown model catalysts

NASA Astrophysics Data System (ADS)

Roiaz, Matteo; Pramhaas, Verena; Li, Xia; Rameshan, Christoph; Rupprechter, Günther

2018-04-01

A new custom-designed ultrahigh vacuum (UHV) chamber coupled to a UHV and atmospheric-pressure-compatible spectroscopic and catalytic reaction cell is described, which allows us to perform IR-vis sum frequency generation (SFG) vibrational spectroscopy during catalytic (kinetic) measurements. SFG spectroscopy is an exceptional tool to study vibrational properties of surface adsorbates under operando conditions, close to those of technical catalysis. This versatile setup allows performing surface science, SFG spectroscopy, catalysis, and electrochemical investigations on model systems, including single crystals, thin films, and deposited metal nanoparticles, under well-controlled conditions of gas composition, pressure, temperature, and potential. The UHV chamber enables us to prepare the model catalysts and to analyze their surface structure and composition by low energy electron diffraction and Auger electron spectroscopy, respectively. Thereafter, a sample transfer mechanism moves samples under UHV to the spectroscopic cell, avoiding air exposure. In the catalytic cell, SFG spectroscopy and catalytic tests (reactant/product analysis by mass spectrometry or gas chromatography) are performed simultaneously. A dedicated sample manipulation stage allows the model catalysts to be examined from LN2 temperature to 1273 K, with gaseous reactants in a pressure range from UHV to atmospheric. For post-reaction analysis, the SFG cell is rapidly evacuated and samples are transferred back to the UHV chamber. The capabilities of this new setup are demonstrated by benchmark results of CO adsorption on Pt and Pd(111) single crystal surfaces and of CO adsorption and oxidation on a ZrO2 supported Pt nanoparticle model catalyst grown by atomic layer deposition.

A nanosecond pulsed laser heating system for studying liquid and supercooled liquid films in ultrahigh vacuum

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Yuntao; Dibble, Collin J.; Petrik, Nikolay G.

2016-04-26

A pulsed laser heating system has been developed that enables investigations of the dynamics and kinetics of nanoscale liquid films and liquid/solid interfaces on the nanosecond timescale in ultrahigh vacuum (UHV). Details of the design, implementation and characterization of a nanosecond pulsed laser system for transiently heating nanoscale films are described. Nanosecond pulses from a Nd:YAG laser are used to rapidly heat thin films of adsorbed water or other volatile materials on a clean, well-characterized Pt(111) crystal in UHV. Heating rates of ~1010 K/s for temperature increases of ~100 – 200 K are obtained. Subsequent rapid cooling (~5 × 109more » K/s) quenches the film, permitting in-situ, post-mortem analysis using a variety of surface science techniques. Lateral variations in the laser pulse energy are ~ ± 3% leading to a temperature uncertainty of ~ ± 5 K for a temperature jump of 200 K. Initial experiments with the apparatus demonstrate that crystalline ice films initially held at 90 K can be rapidly transformed into liquid water films with T > 273 K. No discernable recrystallization occurs during the rapid cooling back to cryogenic temperatures. In contrast, amorphous solid water films heated below the melting point rapidly crystallize. The nanosecond pulsed laser heating system can prepare nanoscale liquid and supercooled liquid films that persist for nanoseconds per heat pulse in an UHV environment, enabling experimental studies of a wide range of phenomena in liquids and at liquid/solid interfaces.« less

Fatigue Crack Growth Characteristics of Thin Sheet Titanium Alloy Ti 6-2-2-2-2

NASA Technical Reports Server (NTRS)

Smith, Stephen W.; Piascik, Robert S.

2001-01-01

Fatigue crack growth rates of Ti 6-2-2-2-2 as a function of stress ratio, temperature (24 or 177 C), tensile orientation and environment (laboratory air or ultrahigh vacuum) are presented. Fatigue crack growth rates of Ti 6-2-2-2-2 are also compared with two more widely used titanium alloys (Timetal 21S and Ti 6Al-4V). The fatigue crack growth rate (da/dN) of Ti 6-2-2-2-2 in laboratory air is dependent upon stress ratio (R), particularly in the near-threshold and lower-Paris regimes. For low R (less than approximately 0.5), da/dN is influenced by crack closure behavior. At higher R (> 0.5), a maximum stress-intensity factor (K(sub max)) dependence is observed. Fatigue crack growth behavior is affected by test temperature between 24 and 177 C. For moderate to high applied cyclic-stress-intensity factors (delta-K), the slope of the log da/dN versus log delta-K curve is lower in 177 C laboratory air than 24 C laboratory air. The difference in slope results in lower values of da/dN for exposure to 177 C laboratory air compared to room temperature laboratory air. The onset of this temperature effect is dependent upon the applied R. This temperature effect has not been observed in ultrahigh vacuum. Specimen orientation has been shown to affect the slope of the log da/dN versus log delta-K curve in the Paris regime.

Large area and structured epitaxial graphene produced by confinement controlled sublimation of silicon carbide

PubMed Central

de Heer, Walt A.; Berger, Claire; Ruan, Ming; Sprinkle, Mike; Li, Xuebin; Hu, Yike; Zhang, Baiqian; Hankinson, John; Conrad, Edward

2011-01-01

After the pioneering investigations into graphene-based electronics at Georgia Tech, great strides have been made developing epitaxial graphene on silicon carbide (EG) as a new electronic material. EG has not only demonstrated its potential for large scale applications, it also has become an important material for fundamental two-dimensional electron gas physics. It was long known that graphene mono and multilayers grow on SiC crystals at high temperatures in ultrahigh vacuum. At these temperatures, silicon sublimes from the surface and the carbon rich surface layer transforms to graphene. However the quality of the graphene produced in ultrahigh vacuum is poor due to the high sublimation rates at relatively low temperatures. The Georgia Tech team developed growth methods involving encapsulating the SiC crystals in graphite enclosures, thereby sequestering the evaporated silicon and bringing growth process closer to equilibrium. In this confinement controlled sublimation (CCS) process, very high-quality graphene is grown on both polar faces of the SiC crystals. Since 2003, over 50 publications used CCS grown graphene, where it is known as the “furnace grown” graphene. Graphene multilayers grown on the carbon-terminated face of SiC, using the CCS method, were shown to consist of decoupled high mobility graphene layers. The CCS method is now applied on structured silicon carbide surfaces to produce high mobility nano-patterned graphene structures thereby demonstrating that EG is a viable contender for next-generation electronics. Here we present for the first time the CCS method that outperforms other epitaxial graphene production methods. PMID:21960446

A nanosecond pulsed laser heating system for studying liquid and supercooled liquid films in ultrahigh vacuum.

PubMed

Xu, Yuntao; Dibble, Collin J; Petrik, Nikolay G; Smith, R Scott; Joly, Alan G; Tonkyn, Russell G; Kay, Bruce D; Kimmel, Greg A

2016-04-28

A pulsed laser heating system has been developed that enables investigations of the dynamics and kinetics of nanoscale liquid films and liquid/solid interfaces on the nanosecond time scale in ultrahigh vacuum (UHV). Details of the design, implementation, and characterization of a nanosecond pulsed laser system for transiently heating nanoscale films are described. Nanosecond pulses from a Nd:YAG laser are used to rapidly heat thin films of adsorbed water or other volatile materials on a clean, well-characterized Pt(111) crystal in UHV. Heating rates of ∼10(10) K/s for temperature increases of ∼100-200 K are obtained. Subsequent rapid cooling (∼5 × 10(9) K/s) quenches the film, permitting in-situ, post-heating analysis using a variety of surface science techniques. Lateral variations in the laser pulse energy are ∼±2.7% leading to a temperature uncertainty of ∼±4.4 K for a temperature jump of 200 K. Initial experiments with the apparatus demonstrate that crystalline ice films initially held at 90 K can be rapidly transformed into liquid water films with T > 273 K. No discernable recrystallization occurs during the rapid cooling back to cryogenic temperatures. In contrast, amorphous solid water films heated below the melting point rapidly crystallize. The nanosecond pulsed laser heating system can prepare nanoscale liquid and supercooled liquid films that persist for nanoseconds per heat pulse in an UHV environment, enabling experimental studies of a wide range of phenomena in liquids and at liquid/solid interfaces.

Annealing-Induced Bi Bilayer on Bi2Te3 Investigated via Quasi-Particle-Interference Mapping.

PubMed

Schouteden, Koen; Govaerts, Kirsten; Debehets, Jolien; Thupakula, Umamahesh; Chen, Taishi; Li, Zhe; Netsou, Asteriona; Song, Fengqi; Lamoen, Dirk; Van Haesendonck, Chris; Partoens, Bart; Park, Kyungwha

2016-09-27

Topological insulators (TIs) are renowned for their exotic topological surface states (TSSs) that reside in the top atomic layers, and hence, detailed knowledge of the surface top atomic layers is of utmost importance. Here we present the remarkable morphology changes of Bi2Te3 surfaces, which have been freshly cleaved in air, upon subsequent systematic annealing in ultrahigh vacuum and the resulting effects on the local and area-averaging electronic properties of the surface states, which are investigated by combining scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS), and Auger electron spectroscopy (AES) experiments with density functional theory (DFT) calculations. Our findings demonstrate that the annealing induces the formation of a Bi bilayer atop the Bi2Te3 surface. The adlayer results in n-type doping, and the atomic defects act as scattering centers of the TSS electrons. We also investigated the annealing-induced Bi bilayer surface on Bi2Te3 via voltage-dependent quasi-particle-interference (QPI) mapping of the surface local density of states and via comparison with the calculated constant-energy contours and QPI patterns. We observed closed hexagonal patterns in the Fourier transform of real-space QPI maps with secondary outer spikes. DFT calculations attribute these complex QPI patterns to the appearance of a "second" cone due to the surface charge transfer between the Bi bilayer and the Bi2Te3. Annealing in ultrahigh vacuum offers a facile route for tuning of the topological properties and may yield similar results for other topological materials.

Product screening of fast reactions in IR-laser-heated liquid water filaments in a vacuum by mass spectrometry.

PubMed

Charvat, A; Stasicki, B; Abel, B

2006-03-09

In the present article a novel approach for rapid product screening of fast reactions in IR-laser-heated liquid microbeams in a vacuum is highlighted. From absorbed energies, a shock wave analysis, high-speed laser stroboscopy, and thermodynamic data of high-temperature water the enthalpy, temperature, density, pressure, and the reaction time window for the hot water filament could be characterized. The experimental conditions (30 kbar, 1750 K, density approximately 1 g/cm3) present during the lifetime of the filament (20-30 ns) were extreme and provided a unique environment for high-temperature water chemistry. For the probe of the reaction products liquid beam desorption mass spectrometry was employed. A decisive feature of the technique is that ionic species, as well as neutral products and intermediates may be detected (neutrals as protonated aggregates) via time-of-flight mass spectrometry without any additional ionization laser. After the explosive disintegration of the superheated beam, high-temperature water reactions are efficiently quenched via expansion and evaporative cooling. For first exploratory experiments for chemistry in ultrahigh-temperature, -pressure and -density water, we have chosen resorcinol as a benchmark system, simple enough and well studied in high-temperature water environments much below 1000 K. Contrary to oxidation reactions usually present under less extreme and dense supercritical conditions, we have observed hydration and little H-atom abstraction during the narrow time window of the experiment. Small amounts of radicals but no ionic intermediates other than simple proton adducts were detected. The experimental findings are discussed in terms of the energetic and dense environment and the small time window for reaction, and they provide firm evidence for additional thermal reaction channels in extreme molecular environments.

Effect of an Interfacial Layer on Electron Tunneling through Atomically Thin Al2O3 Tunnel Barriers.

PubMed

Wilt, Jamie; Sakidja, Ridwan; Goul, Ryan; Wu, Judy Z

2017-10-25

Electron tunneling through high-quality, atomically thin dielectric films can provide a critical enabling technology for future microelectronics, bringing enhanced quantum coherent transport, fast speed, small size, and high energy efficiency. A fundamental challenge is in controlling the interface between the dielectric and device electrodes. An interfacial layer (IL) will contain defects and introduce defects in the dielectric film grown atop, preventing electron tunneling through the formation of shorts. In this work, we present the first systematic investigation of the IL in Al 2 O 3 dielectric films of 1-6 Å's in thickness on an Al electrode. We integrated several advanced approaches: molecular dynamics to simulate IL formation, in situ high vacuum sputtering atomic layer deposition (ALD) to synthesize Al 2 O 3 on Al films, and in situ ultrahigh vacuum scanning tunneling spectroscopy to probe the electron tunneling through the Al 2 O 3 . The IL had a profound effect on electron tunneling. We observed a reduced tunnel barrier height and soft-type dielectric breakdown which indicate that defects are present in both the IL and in the Al 2 O 3 . The IL forms primarily due to exposure of the Al to trace O 2 and/or H 2 O during the pre-ALD heating step of fabrication. As the IL was systematically reduced, by controlling the pre-ALD sample heating, we observed an increase of the ALD Al 2 O 3 barrier height from 0.9 to 1.5 eV along with a transition from soft to hard dielectric breakdown. This work represents a key step toward the realization of high-quality, atomically thin dielectrics with electron tunneling for the next generation of microelectronics.

Characterization of oxygen and titanium diffusion at the anatase TiO2(001) surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herman, Gregory S.; Zehr, Robert T.; Henderson, Michael A.

2013-06-01

The diffusion of intrinsic defects in a single crystal anatase TiO2(001) film was explored by isotopic labeling and static secondary ion mass spectrometry. Using both 46Ti and 18O as isotopic labels, we show that the anatase surface responds to redox imbalances by diffusion of both Ti and O into the bulk under vacuum reduction and (at least) Ti from the bulk to the surface during oxidation. The diffusion of Ti between the bulk and surface in anatase TiO2(001) closely resembles what was observed in the literature for the rutile TiO2(110) surface, however the latter is not known to have oxygenmore » diffusion between the bulk and surface under typical ultrahigh vacuum conditions. We speculate that the open lattice of the anatase bulk structure may facilitate independent diffusion of both point defects (Ti interstitials and O vacancies) or concerted diffusion of "TiO" subunits. The authors gratefully acknowledge S.A. Chambers of Pacific Northwest National Laboratory (PNNL) for providing the anatase samples. This research was supported by the U.S. Department of Energy (DOE) Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, the Office of Naval Research Contract Number 200CAR262, and the Oregon Nanoscience and Microtechnologies Institute. PNNL is operated for the U.S. DOE by Battelle under Contract Number DE05-AC76RL0 1830. The research was performed in the William R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility funded by the U.S. DOE Office of Biological and Environmental Research.« less

Halogenated Organic Compounds Identified in Hydraulic Fracturing Wastewaters Using Ultrahigh Resolution Mass Spectrometry.

PubMed

Luek, Jenna L; Schmitt-Kopplin, Philippe; Mouser, Paula J; Petty, William Tyler; Richardson, Susan D; Gonsior, Michael

2017-05-16

Large volumes of water return to the surface following hydraulic fracturing of deep shale formations to retrieve oil and natural gas. Current understanding of the specific organic constituents in these hydraulic fracturing wastewaters is limited to hydrocarbons and a fraction of known chemical additives. In this study, we analyzed hydraulic fracturing wastewater samples using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) as a nontargeted technique to assign unambiguous molecular formulas to singly charged molecular ions. Halogenated molecular formulas were identified and confirmed using isotopic simulation and MS-MS fragmentation spectra. The abundance of halogenated organic compounds in flowback fluids rather than older wastewaters suggested that the observed molecular ions might have been related to hydraulic fracturing additives and related subsurface reactions, such as through the reaction of shale-extracted chloride, bromide, and iodide with strong oxidant additives (e.g., hypochlorite, persulfate, hydrogen peroxide) and subsequently with diverse dissolved organic matter. Some molecular ions matched the exact masses of known disinfection byproducts including diiodoacetic acid, dibromobenzoic acid, and diiodobenzoic acid. The identified halogenated organic compounds, particularly iodinated organic molecules, are absent from inland natural systems and these compounds could therefore play an important role as environmental tracers.

Ultrafast High Harmonic, Soft X-Ray Probing of Molecular Dynamics

DTIC Science & Technology

2013-04-30

590 L/s scroll pump and a titanium sublimation pump . A TOF-PES has been designed and constructed to analyze the energy of the photoelectrons...are studied using the quasi-continuous vacuum ultraviolet light of the Advanced Light Source at Lawrence Berkeley National Laboratory. The molecular...34), the method of high order harmonic generation of ultrashort vacuum ultraviolet pulses was used to investigate molecular photodissociation, ultrafast

Damage induced to DNA by low-energy (0-30 eV) electrons under vacuum and atmospheric conditions.

PubMed

Brun, Emilie; Cloutier, Pierre; Sicard-Roselli, Cécile; Fromm, Michel; Sanche, Léon

2009-07-23

In this study, we show that it is possible to obtain data on DNA damage induced by low-energy (0-30 eV) electrons under atmospheric conditions. Five monolayer films of plasmid DNA (3197 base pairs) deposited on glass and gold substrates are irradiated with 1.5 keV X-rays in ultrahigh vacuum and under atmospheric conditions. The total damage is analyzed by agarose gel electrophoresis. The damage produced on the glass substrate is attributed to energy absorption from X-rays, whereas that produced on the gold substrate arises from energy absorption from both the X-ray beam and secondary electrons emitted from the gold surface. By analysis of the energy of these secondary electrons, 96% are found to have energies below 30 eV with a distribution peaking at 1.4 eV. The differences in damage yields recorded with the gold and glass substrates is therefore essentially attributed to the interaction of low-energy electrons with DNA under vacuum and hydrated conditions. From these results, the G values for low-energy electrons are determined to be four and six strand breaks per 100 eV, respectively.

High Vacuum Creep Facility in the Materials Processing Laboratory

NASA Image and Video Library

1973-01-21

Technicians at work in the Materials Processing Laboratory’s Creep Facility at the National Aeronautics and Space Administration (NASA) Lewis Research Center. The technicians supported the engineers’ studies of refractory materials, metals, and advanced superalloys. The Materials Processing Laboratory contained laboratories and test areas equipped to prepare and develop these metals and materials. The ultra-high vacuum lab, seen in this photograph, contained creep and tensile test equipment. Creep testing is used to study a material’s ability to withstand long durations under constant pressure and temperatures. The equipment measured the strain over a long period of time. Tensile test equipment subjects the test material to strain until the material fails. The two tests were used to determine the strength and durability of different materials. The Materials Processing Laboratory also housed arc and electron beam melting furnaces, a hydraulic vertical extrusion press, compaction and forging equipment, and rolling mills and swagers. There were cryogenic and gas storage facilities and mechanical and oil diffusion vacuum pumps. The facility contained both instrumental and analytical chemistry laboratories for work on radioactive or toxic materials and the only shop to machine toxic materials in the Midwest.

A New Vacuum Brazing Route for Niobium-316L Stainless Steel Transition Joints for Superconducting RF Cavities

NASA Astrophysics Data System (ADS)

Kumar, Abhay; Ganesh, P.; Kaul, R.; Bhatnagar, V. K.; Yedle, K.; Ram Sankar, P.; Sindal, B. K.; Kumar, K. V. A. N. P. S.; Singh, M. K.; Rai, S. K.; Bose, A.; Veerbhadraiah, T.; Ramteke, S.; Sridhar, R.; Mundra, G.; Joshi, S. C.; Kukreja, L. M.

2015-02-01

The paper describes a new approach for vacuum brazing of niobium-316L stainless steel transition joints for application in superconducting radiofrequency cavities. The study exploited good wettability of titanium-activated silver-base brazing alloy (CuSil-ABA®), along with nickel as a diffusion barrier, to suppress brittle Fe-Nb intermetallic formation, which is well reported during the established vacuum brazing practice using pure copper filler. The brazed specimens displayed no brittle intermetallic layers on any of its interfaces, but instead carried well-distributed intermetallic particles in the ductile matrix. The transition joints displayed room temperature tensile and shear strengths of 122-143 MPa and 80-113 MPa, respectively. The joints not only exhibited required hermeticity (helium leak rate <1.1 × 10-10 mbar l/s) for service in ultra-high vacuum but also withstood twelve hour degassing heat treatment at 873 K (suppresses Q-disease in niobium cavities), without any noticeable degradation in the microstructure and the hermeticity. The joints retained their leak tightness even after undergoing ten thermal cycles between the room temperature and the liquid nitrogen temperature, thereby establishing their ability to withstand service-induced low cycle fatigue conditions. The study proposes a new lower temperature brazing route to form niobium-316L stainless steel transition joints, with improved microstructural characteristics and acceptable hermeticity and mechanical properties.

Photoelectron spectroscopic studies of ultra-thin CuPc layers on a Si(111)-(√3 × √3)R30°-B surface

NASA Astrophysics Data System (ADS)

Menzli, S.; Laribi, A.; Mrezguia, H.; Arbi, I.; Akremi, A.; Chefi, C.; Chérioux, F.; Palmino, F.

2016-12-01

The adsorption of copper phthalocyanine (CuPc) molecules on Si(111)-(√3 × √3)R30°-B surface is investigated at room temperature under ultra-high vacuum. Crystallographic, chemical and electronic properties of the interface are investigated by low energy electron diffraction (LEED), ultraviolet and X-ray photoemission spectroscopies (UPS, XPS) and X-ray photoemission diffraction (XPD). LEED and XPD results shed light on the growth mechanism of CuPc on this substrate. At one monolayer coverage the growth mode was characterized by the formation of crystalline 3D nanoislands. The molecular packing deduced from this study appears very close to the one of the bulk CuPc α phase. The 3D islands are formed by molecules aligned in a standing manner. XPS core level spectra of the substrate reveal that there is no discernible chemical interaction between molecules and substrate. However there is charge transfer from molecules to the substrate. During the growth, the work function (WF) was found to decrease from 4.50 eV for the clean substrate to 3.70 eV for the highest coverage (30 monolayers). Within a thickness of two monolayers deposition, an interface dipole of 0.50 eV was found. A substrate band bending of 0.25 eV was deduced over all the range of exposure. UPS spectra indicate the existence of a band bending of the highest occupied molecular orbital (HOMO) of 0.30 eV. The changes in the work function, in the Fermi level position and in the onset of the molecular HOMO state have been used to determine the energy level alignment at the interface.

Single-Molecule Interfacial Electron Transfer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ho, Wilson

Interfacial electron transfer (ET) plays an important role in many chemical and biological processes. Specifically, interfacial ET in TiO 2-based systems is important to solar energy technology, catalysis, and environmental remediation technology. However, the microscopic mechanism of interfacial ET is not well understood with regard to atomic surface structure, molecular structure, bonding, orientation, and motion. In this project, we used two complementary methodologies; single-molecule fluorescence spectroscopy, and scanning-tunneling microscopy and spectroscopy (STM and STS) to address this scientific need. The goal of this project was to integrate these techniques and measure the molecular dependence of ET between adsorbed molecules andmore » TiO 2 semiconductor surfaces and the ET induced reactions such as the splitting of water. The scanning probe techniques, STM and STS, are capable of providing the highest spatial resolution but not easily time-resolved data. Single-molecule fluorescence spectroscopy is capable of good time resolution but requires further development to match the spatial resolution of the STM. The integrated approach involving Peter Lu at Bowling Green State University (BGSU) and Wilson Ho at the University of California, Irvine (UC Irvine) produced methods for time and spatially resolved chemical imaging of interfacial electron transfer dynamics and photocatalytic reactions. An integral aspect of the joint research was a significant exchange of graduate students to work at the two institutions. This project bridged complementary approaches to investigate a set of common problems by working with the same molecules on a variety of solid surfaces, but using appropriate techniques to probe under ambient (BGSU) and ultrahigh vacuum (UCI) conditions. The molecular level understanding of the fundamental interfacial electron transfer processes obtained in this joint project will be important for developing efficient light harvesting, solar energy conversion, and broadly applicable to problems in interface chemistry and surface physics.« less

Control of the axial coordination of a surface-confined manganese (III) porphyrin complex.

PubMed

Beggan, J P; Krasnikov, S A; Sergeeva, N N; Senge, M O; Cafolla, A A

2012-06-15

The organization and thermal lability of chloro(5,10,15,20-tetraphenyl porphyrinato)manganese(III) (Cl-MnTPP) molecules on the Ag(111) surface have been investigated under ultra-high vacuum conditions, using scanning tunnelling microscopy, low energy electron diffraction and x-ray photoelectron spectroscopy. The findings reveal the epitaxial nature of the molecule-substrate interface, and moreover, offer a valuable insight into the latent coordination properties of surface-confined metalloporphyrins. The Cl-MnTPP molecules are found to self-assemble on the Ag(111) surface at room temperature, forming an ordered molecular overlayer described by a square unit cell. In accordance with the threefold symmetry of the Ag(111) surface, three rotationally equivalent domains of the molecular overlayer are observed. The primitive lattice vectors of the Cl-MnTPP overlayer show an azimuthal rotation of ±15° relative to those of the Ag(111) surface, while the principal molecular axes of the individual molecules are found to be aligned with the substrate (0(-)11) and ((-)211) crystallographic directions. The axial chloride (Cl) ligand is found to be orientated away from the Ag(111) surface, whereby the average plane of the porphyrin macrocycle lies parallel to that of the substrate. When adsorbed on the Ag(111) surface, the Cl-MnTPP molecules display a latent thermal lability resulting in the dissociation of the axial Cl ligand at ~423 K. The thermally induced dissociation of the Cl ligand leaves the porphyrin complex otherwise intact, giving rise to the coordinatively unsaturated Mn(III) derivative. Consistent with the surface conformation of the Cl-MnTPP precursor, the resulting (5,10,15,20-tetraphenyl porphyrinato)manganese(III) (MnTPP) molecules display the same lattice structure and registry with the Ag(111) surface.

On the origin of the electrostatic potential difference at a liquid-vacuum interface.

PubMed

Harder, Edward; Roux, Benoît

2008-12-21

The microscopic origin of the interface potential calculated from computer simulations is elucidated by considering a simple model of molecules near an interface. The model posits that molecules are isotropically oriented and their charge density is Gaussian distributed. Molecules that have a charge density that is more negative toward their interior tend to give rise to a negative interface potential relative to the gaseous phase, while charge densities more positive toward their interior give rise to a positive interface potential. The interface potential for the model is compared to the interface potential computed from molecular dynamics simulations of the nonpolar vacuum-methane system and the polar vacuum-water interface system. The computed vacuum-methane interface potential from a molecular dynamics simulation (-220 mV) is captured with quantitative precision by the model. For the vacuum-water interface system, the model predicts a potential of -400 mV compared to -510 mV, calculated from a molecular dynamics simulation. The physical implications of this isotropic contribution to the interface potential is examined using the example of ion solvation in liquid methane.

Bidirectional Reflectance Function Measurement of Molecular Contaminant Scattering in the Vacuum Ultraviolet

NASA Technical Reports Server (NTRS)

Herren, Kenneth A.; Gregory, Don A.

2006-01-01

Bi-directional reflectance distribution function (BRDF) measurements of optical surfaces both before and after molecular contamination were done using UV, VUV and visible light. Molecular contamination of optical surfaces from outgassed material has been shown in many cases to proceed from acclimation centers, and to produce many roughly hemispherical "islands" of contamination on the surface. Vacuum Ultraviolet (VW) wavelengths are used here to measure angularly scattered light from optical surfaces.

Spacecraft thermal energy accommodation from atomic recombination

NASA Technical Reports Server (NTRS)

Carleton, Karen L.; Marinelli, William J.

1991-01-01

Measurements of atomic recombination probabilities important in determining energy release to reusable spacecraft thermal protection surfaces during reentry are presented. An experimental apparatus constructed to examine recombination of atomic oxygen from thermal protection and reference materials at reentry temperatures is described. The materials are examined under ultrahigh vacuum conditions to develop and maintain well characterized surface conditions that are free of contamination. When compared with stagnation point heat transfer measurements performed in arc jet facilities, these measurements indicate that a significant fraction of the excess energy available from atom recombination is removed from the surface as metastable O2.

Evolution of magnetism of Cr nanoclusters on a Au(111) surface

NASA Astrophysics Data System (ADS)

Gotsis, Harry; Kioussis, Nicholas; Papaconstantopoulos, Dimitri

2004-03-01

Advances in low-temperature scanning tunneling microscopy under ultrahigh vacuum have provided new opportunities for investigating the magnetic structures of nanoclusters adsorbed on surfaces. Recent STM studies of Cr trimers on the Au(111) surface suggest a switching between two distinct electronic states. We have carried out ab initio electronic structure calculations to investigate the structural, electronic and magnetic properties of isolated Cr atoms, Cr dimers and trimers in different geometry. We will present results for the evolution of magnetic behavior including noncollinear magnetism and provide insight in the connection between magnetism and geometry.

Electron Beam-Induced Writing of Nanoscale Iron Wires on a Functional Metal Oxide

PubMed Central

2013-01-01

Electron beam-induced surface activation (EBISA) has been used to grow wires of iron on rutile TiO2(110)-(1 × 1) in ultrahigh vacuum. The wires have a width down to ∼20 nm and hence have potential utility as interconnects on this dielectric substrate. Wire formation was achieved using an electron beam from a scanning electron microscope to activate the surface, which was subsequently exposed to Fe(CO)5. On the basis of scanning tunneling microscopy and Auger electron spectroscopy measurements, the activation mechanism involves electron beam-induced surface reduction and restructuring. PMID:24159366

Experimental insight into the magnetic and electrical properties of amorphous Ge1-xMnx

NASA Astrophysics Data System (ADS)

Conta, Gianluca; Amato, Giampiero; Coïsson, Marco; Tiberto, Paola

2017-12-01

We present a study of the electrical and magnetic properties of the amorphous Ge1-xMnx.DMS, with 2% ≤ x ≤ 17%, by means of SQUID magnetometry and low temperature DC measurements. The thin films were grown by physical vapour deposition at 50°C in ultrahigh vacuum. The DC electrical characterizations show that variable range hopping is the main mechanism of charge transport below room temperature. Magnetic characterization reveals that a unique and smooth magnetic transition is present in our samples, which can be attributed to ferromagnetic percolation of bound magnetic polarons.

Alternative backing up pump for turbomolecular pumps

DOEpatents

Myneni, Ganapati Rao

2003-04-22

As an alternative to the use of a mechanical backing pump in the application of wide range turbomolecular pumps in ultra-high and extra high vacuum applications, palladium oxide is used to convert hydrogen present in the evacuation stream and related volumes to water with the water then being cryo-pumped to a low pressure of below about 1.e.sup.-3 Torr at 150.degree. K. Cryo-pumping is achieved using a low cost Kleemenco cycle cryocooler, a somewhat more expensive thermoelectric cooler, a Venturi cooler or a similar device to achieve the required minimization of hydrogen partial pressure.

Design and performance of a beetle-type double-tip scanning tunneling microscope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaschinsky, Philipp; Coenen, Peter; Pirug, Gerhard

2006-09-15

A combination of a double-tip scanning tunneling microscope with a scanning electron microscope in ultrahigh vacuum environment is presented. The compact beetle-type design made it possible to integrate two independently driven scanning tunneling microscopes in a small space. Moreover, an additional level for coarse movement allows the decoupling of the translation and approach of the tunneling tip. The position of the two tips can be controlled from the millimeter scale down to 50 nm with the help of an add-on electron microscope. The instrument is capable of atomic resolution imaging with each tip.

Microphysical, microchemical, and adhesive properties of lunar material. III - Gas interaction with lunar material.

NASA Technical Reports Server (NTRS)

Grossman, J. J.; Mukherjee, N. R.; Ryan, J. A.

1972-01-01

Gas adsorption measurements on an Apollo 12 ultrahigh vacuum-stored sample and Apollo 14 and 15 N2-stored samples, show that the cosmic ray track and solar wind damaged surface of lunar soil is very reactive. Room temperature monolayer adsorption of N2 by the Apollo 12 sample at 0.0001 atm was observed. Gas evolution of Apollo 14 lunar soil at liquid nitrogen temperature during adsorption/desorption cycling is probably due to cosmic ray track stored energy release accompanied by solar gas release from depths of 100-200 nm.

Development of first ever scanning probe microscopy capabilities for plutonium

NASA Astrophysics Data System (ADS)

Beaux, Miles F.; Cordoba, Miguel Santiago; Zocco, Adam T.; Vodnik, Douglas R.; Ramos, Michael; Richmond, Scott; Moore, David P.; Venhaus, Thomas J.; Joyce, Stephen A.; Usov, Igor O.

2017-04-01

Scanning probe microscopy capabilities have been developed for plutonium and its derivative compounds. Specifically, a scanning tunneling microscope and an atomic force microscope housed in an ultra-high vacuum system and an inert atmosphere glove box, respectively, were prepared for the introduction of small non-dispersible δ-Pu coupons. Experimental details, procedures, and preliminary imaging of δ-Pu coupons are presented to demonstrate the functionality of these new capabilities. These first of a kind capabilities for plutonium represent a significant step forward in the ability to characterize and understand plutonium surfaces with high spatial resolution.

Atomic force microscope studies of fullerene films - Highly stable C60 fcc (311) free surfaces

NASA Technical Reports Server (NTRS)

Snyder, Eric J.; Tong, William M.; Williams, R. S.; Anz, Samir J.; Anderson, Mark S.

1991-01-01

Atomic force microscopy and X-ray diffractometry were used to study 1500 A-thick films of pure C60 grown by sublimation in ultrahigh vacuum onto a CaF2 (111) substrte. Topographs of the films did not reveal the expected close-packed structures, but they showed instead large regions that correspond to a face-centered cubic (311) surface and distortions of this surface. The open (311) structure may have a relatively low free energy because the low packing density contributes to a high entropy of the exposed surface.

Development of first ever scanning probe microscopy capabilities for plutonium

DOE PAGES

Beaux, Miles F.; Cordoba, Miguel Santiago; Zocco, Adam T.; ...

2017-04-01

Scanning probe microscopy capabilities have been developed for plutonium and its derivative compounds. Specifically, a scanning tunneling microscope and an atomic force microscope housed in an ultra-high vacuum system and an inert atmosphere glove box, respectively, were prepared for the introduction of small non-dispersible δ-Pu coupons. Experimental details, procedures, and preliminary imaging of δ-Pu coupons are presented to demonstrate the functionality of these new capabilities. In conclusion, these first of a kind capabilities for plutonium represent a significant step forward in the ability to characterize and understand plutonium surfaces with high spatial resolution.

Hydrogen partitioning and transport in titanium aluminides

NASA Technical Reports Server (NTRS)

Han, Kwang S.; Lee, Weon S.

1993-01-01

This report gives the final summary of the research work perfomed from March 1, 1990 to August 28, 1993. Brief descriptions of the research findings are given on the surface variation of Ti-14Al-21Nb as a function of temperature under ultrahigh vacuum conditions; titanium aluminides: surface composition effects as a function of temperature; Auger electron intensity variation in oxygen-charged silver; and segregation of sulfur on a titanium surface studied by Auger electron spectroscopy. Each description details one or more of the attached corresponding figures. Published journal documents are provided as appendices to give further detail.

Surfactant Effects on Structure and Mechanical Properties of Ultrahigh-Molecular-Weight Polyethylene/Layered Silicate Composites.

PubMed

Nikiforov, Leonid A; Okhlopkova, Tatinana A; Kapitonova, Iullia V; Sleptsova, Sardana A; Okhlopkova, Aitalina A; Shim, Ee Le; Cho, Jin-Ho

2017-12-05

In this study, the reinforcement of ultrahigh-molecular-weight polyethylene (UHMWPE) with biotite was investigated. The biotite filler was mechanically activated with different dry surfactants to improve its compatibility with UHMWPE and decrease agglomeration among biotite particles. Alkyldimethylbenzylammonium chloride (ADBAC) and cetyltrimethylammonium bromide (CTAB) were selected as cationic surfactants. The tensile strength of composites containing 1 wt % of CTAB-treated biotite was increased by 30% relative to those with untreated biotite, but was unchanged with ADBAC treatment of the same biotite content. The stereochemistry of the surfactant may be critical to the composite structure and mechanical properties of the material. The stereochemistry of CTAB was preferable to that of ADBAC in enhancing mechanical properties because the stereochemistry of ADBAC impedes favorable interactions with the biotite surface during mechanical activation.

Investigation of tribological properties of graphene oxide reinforced ultrahigh molecular weight polyethylene under artificial seawater lubricating condition

NASA Astrophysics Data System (ADS)

Pang, Wenchao; Ni, Zifeng; Wu, JiaLiang; Zhao, Yongwu

2018-03-01

A range of ultrahigh molecular weight polyethylene (UHMWPE)/graphene oxide (GO) nanocomposites were fabricated using liquid-phase ultrasonication mixing followed by hot-pressing. The wettability, water absorption and corrosion resistance of composites were studied to prove the composites were suitable for application in liquid environment. The tribological properties of composites under dry, deionized water and seawater lubricating condition were investigated. The results showed that the incorporation of GO decreased the wear rate of UHMWPE under different lubricating conditions and with the increase of GO addition, the wear rate of UHMWPE/GO composites decreased. UHMWPE/GO composites exhibited better tribological behaviors under seawater lubricating condition than other conditions, because good corrosion resistance and excellent wear resistance of UHMWPE/GO composites, and the lubricating effect of seawater is also indispensable.

RAFT-Polymerization-Induced Self-Assembly and Reorganizations: Ultrahigh-Molecular-Weight Polymer and Morphology-Tunable Micro-/Nanoparticles in One Pot.

PubMed

Zhang, Xiao-Yun; Liu, Dong-Ming; Lv, Xin-Hu; Sun, Miao; Sun, Xiao-Li; Wan, Wen-Ming

2016-11-01

A one-pot method is introduced for the successful synthesis of narrow-distributed (Đ = 1.22) vinyl polymer with both ultrahigh molecular weight (UHMW) (M w = 1.31 × 10 6 g mol -1 ) and micro-/nanomorphology under mild conditions. The method involves the following four stages: homogeneous polymerization, polymerization-induced self-assembly (PISA), PISA and reorganization, and PISA and multiple reorganizations. The key points to the production of UHMW polystyrene are to minimize radical termination by segregating radicals in different nanoreactors and to ensure sufficient chain propagation by promoting further reorganizations of these reactors in situ. This method therefore endows polymeric materials with the outstanding properties of both UHMW and tunable micro-/nanoparticles under mild conditions in one pot. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

REQUIREMENTS AND GUIDELINES FOR NSLS EXPERIMENTAL BEAM LINE VACUUM SYSTEMS-REVISION B.

DOE Office of Scientific and Technical Information (OSTI.GOV)

FOERSTER,C.

Typical beam lines are comprised of an assembly of vacuum valves and shutters referred to as a ''front end'', optical elements to monochromatize, focus and split the photon beam, and an experimental area where a target sample is placed into the photon beam and data from the interaction is detected and recorded. Windows are used to separate sections of beam lines that are not compatible with storage ring ultra high vacuum. Some experimental beam lines share a common vacuum with storage rings. Sections of beam lines are only allowed to vent up to atmospheric pressure using pure nitrogen gas aftermore » a vacuum barrier is established to protect ring vacuum. The front end may only be bled up when there is no current in the machine. This is especially true on the VUV storage ring where for most experiments, windows are not used. For the shorter wavelength, more energetic photons of the x-ray ring, beryllium windows are used at various beam line locations so that the monochromator, mirror box or sample chamber may be used in a helium atmosphere or rough vacuum. The window separates ring vacuum from the environment of the downstream beam line components. The stored beam lifetime in the storage rings and the maintenance of desirable reflection properties of optical surfaces depend upon hydrocarbon-free, ultra-high vacuum systems. Storage ring vacuum systems will operate at pressures of {approximately} 1 x 10{sup {minus}10} Torr without beam and {approximately} 1 x 10{sup {minus}9} Torr with beam. Systems are free of hydrocarbons in the sense that no pumps, valves, etc. containing organics are used. Components are all-metal, chemically cleaned and bakeable. To the extent that beam lines share a common vacuum with the storage ring, the same criteria will hold for beam line components. The design philosophy for NSLS beam lines is to use all-metal, hydrocarbon-free front end components and recommend that experimenters use this approach for common vacuum hardware downstream of front ends. O-ring-sealed valves, if used, are not permitted upstream of the monochromator exit aperture. It will be the responsibility of users to demonstrate that their experiment will not degrade the pressure or quality of the storage ring vacuum. As a matter of operating policy, all beam lines will be monitored for prescribed pressure and the contribution of high mass gases to this pressure each time a beam line has been opened to ring vacuum.« less

Advanced performance of small diaphragm vacuum pumps through the use of mechatronics

NASA Astrophysics Data System (ADS)

Lachenmann, R.; Dirscherl, J.

Oil-free diaphragm vacuum pumps have proven to be the best way in vacuum generation for the chemical laboratory and they also find increasing use as backing pumps for modern wide-range turbo molecular pumps. The majority of vacuum pumps in practical use pump only a rather small percentage of their lifetime at full gas load. A pump backing a turbo molecular pump does not have to pump a significant gas load when the high-vacuum pump is running at ultimate vacuum pressure. Also, for a vacuum distillation the vacuum pump has to operate at full speed only at the beginning to lower the pressure inside the system to a vacuum level where evaporation starts. In a rather leak-tight system the distillation process continues by evaporating from the hot liquid and condensing at the cold condenser without the need of a mechanical vacuum pump. Rotational speed controlled diaphragm pumps are now available through progress in mechatronics and offer high pumping speed capability for fast pump-down cycles and precise pressure control for distillations. At low gas load the rotational speed can be reduced, improving maintenance intervals, power consumption, noise, vibration and - surprisingly - also ultimate pressure. The different behaviour in pumping speed and ultimate pressure of rotational speed controlled diaphragm pumps in comparison to constant-speed pumps is related to the mechanical properties of the valves and gas dynamics .

On The Detection Of Footprints From Strong Electron Acceleration In High-Intensity Laser Fields, Including The Unruh Effect

NASA Astrophysics Data System (ADS)

Thirolf, P. G.; Habs, D.; Homma, K.; Hörlein, R.; Karsch, S.; Krausz, F.; Maia, C.; Osterhoff, J.; Popp, A.; Schmid, K.; Schreiber, J.; Schützhold, R.; Tajima, T.; Veisz, L.; Wulz, J.; Yamazaki, T.

2010-04-01

The ultra-high fields of high-power short-pulse lasers are expected to contribute to understanding fundamental properties of the quantum vacuum and quantum theory in very strong fields. For example, the neutral QED vacuum breaks down at the Schwinger field strength of 1.3 1018V/m, where a virtual e+e- pair gains its rest mass energy over a Compton wavelength and materializes as a real pair. At such an ultra-high field strength, an electron experiences an acceleration of as = 2 1028 g and hence fundamental phenomena such as the long predicted Unruh effect start to play a role. The Unruh effect implies that the accelerated electron experiences the vacuum as a thermal bath with the Unruh temperature. In its accelerated frame the electron scatters photons off the thermal bath, corresponding to the emission of an entangled pair of photons in the laboratory frame. In upcoming experiments with intense accelerating fields, we will encounter a set of opportunities to experimentally study the radiation from electrons under extreme fields. Even before the Unruh radiation detection, we should run into the copious Larmor radiation. The detection of Larmor radiation and its characterization themselves have never been experimentally carried out to the best of our knowledge, and thus this amounts to a first serious study of physics at extreme acceleration. For example, we can study radiation damping effects like the Landau-Lifshitz radiation. Furthermore, the experiment should be able to confirm or disprove whether the Larmor and Landau-Lifshitz radiation components may be enhanced by a collective (N2) radiation, if a tightly clumped cluster of electrons is accelerated. The technique of laser driven dense electron sheet formation by irradiating a thin DLC foil target should provide such a coherent electron cluster with a very high density. If and when such mildly relativistic electron sheets are realized, a counterpropagating second laser can interact with them coherently. Under these conditions enhanced Larmor and Unruh radiation signals may be observed. Detection of the Unruh photons (together with its competing radiation components) is envisaged via Compton polarimetry in a novel highly granular 2D-segmented position-sensitive germanium detector.

Roles of vacuum tunnelling and contact mechanics in single-molecule thermopower

NASA Astrophysics Data System (ADS)

Tsutsui, Makusu; Yokota, Kazumichi; Morikawa, Takanori; Taniguchi, Masateru

2017-03-01

Molecular junction is a chemically-defined nanostructure whose discrete electronic states are expected to render enhanced thermoelectric figure of merit suitable for energy-harvesting applications. Here, we report on geometrical dependence of thermoelectricity in metal-molecule-metal structures. We performed simultaneous measurements of the electrical conductance and thermovoltage of aromatic molecules having different anchoring groups at room temperature in vacuum. We elucidated the mutual contributions of vacuum tunnelling on thermoelectricity in the short molecular bridges. We also found stretching-induced thermoelectric voltage enhancement in thiol-linked single-molecule bridges along with absence of the pulling effects in diamine counterparts, thereby suggested that the electromechanical effect would be a rather universal phenomenon in Au-S anchored molecular junctions that undergo substantial metal-molecule contact elongation upon stretching. The present results provide a novel concept for molecular design to achieve high thermopower with single-molecule junctions.

Electrical properties of lunar soil sample 15301,38

NASA Technical Reports Server (NTRS)

Olhoeft, G. R.; Frisillo, A. L.; Strangway, D. W.

1974-01-01

Electrical property measurements have been made on an Apollo 15 lunar soil sample in ultrahigh vacuum from room temperature to 827 C for the frequency spectrum from 100 Hz through 1 MHz. The dielectric constant, the total ac loss tangent, and the dc conductivity were measured. The dc conductivity showed no thermal hysteresis, but an irreversible (in vacuum) thermal effect was found in the dielectric loss tangent on heating above 700 C and during the subsequent cooling. This appears to be related to several effects associated with lunar glass above 700 C. The sample also showed characteristic low-frequency dispersion in the dielectric constant with increasing temperature, presumably due to Maxwell-Wagner intergranular effects. The dielectric properties may be fitted to a model involving a Cole-Cole frequency distribution that is relatively temperature-independent below 200 C and follows a Boltzmann temperature distribution with an activation energy of 2.5 eV above 200 C. The dc conductivity is fitted by an exponential temperature distribution and becomes the dominant loss above 700 C.

SnTe microcrystals: Surface cleaning of a topological crystalline insulator

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saghir, M., E-mail: M.Saghir@warwick.ac.uk, E-mail: G.Balakrishnan@warwick.ac.uk; Walker, M.; McConville, C. F.

Investigating nanometer and micron sized materials thought to exhibit topological surface properties that can present a challenge, as clean surfaces are a pre-requisite for band structure measurements when using nano-ARPES or laser-ARPES in ultra-high vacuum. This issue is exacerbated when dealing with nanometer or micron sized materials, which have been prepared ex-situ and so have been exposed to atmosphere. We present the findings of an XPS study where various cleaning methods have been employed to reduce the surface contamination and preserve the surface quality for surface sensitive measurements. Microcrystals of the topological crystalline insulator SnTe were grown ex-situ and transferredmore » into ultra high vacuum (UHV) before being treated with either atomic hydrogen, argon sputtering, annealing, or a combination of treatments. The samples were also characterised using the scanning electron microscopy, both before and after treatment. It was found that atomic hydrogen cleaning with an anneal cycle (200 °C) gave the best clean surface results.« less

Characterization and Evaluation of Ti-Zr-V Non-evaporable Getter Films Used in Vacuum Systems

NASA Astrophysics Data System (ADS)

Ferreira, M. J.; Seraphim, R. M.; Ramirez, A. J.; Tabacniks, M. H.; Nascente, P. A. P.

Among several methods used to obtain ultra-high vacuum (UHV) for particles accelerators chambers, it stands out the internal coating with metallic films capable of absorbing gases, called NEG (non-evaporable getter). Usually these materials are constituted by elements of great chemical reactivity and solubility (such as Ti, Zr, and V), at room temperature for oxygen and other gases typically found in UHV, such as H2, CO, and CO2. Gold and ternary Ti-Zr-V films were produced by magnetron sputtering, and their composition, structure, morphology, and aging characteristics were characterized by energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission gun sc anning electronmicroscopy (FEG-SEM), atomic force microscopy (AFM), high resolution transmission electron microscopy (HRTEM). The comparison between the produced films and commercial samples indicated that the desirable characteristics depend on the nanometric structure of the films and that this structure is sensitive to the heat treatments.

Effect of electronic structure of the diamond surface on the strength of the diamond-metal interface

NASA Technical Reports Server (NTRS)

Pepper, S. V.

1981-01-01

A diamond surface undergoes a transformation in its electronic structure by a vacuum anneal at approximately 900 C. The polished surface has no electronic states in the band gap, whereas the annealed surface has both occupied and unoccupied states in the and gap and exhibits some electrical conductivity. The effect of this transformation on the strength of the diamond metal interface was investigated by measuring the static friction force of an atomically clean meta sphere on a diamond flat in ultrahigh vacuum. It was found that low friction (weak bonding) is associated with the diamond surface devoid of gap states whereas high friction (strong bonding) is associated with the diamond surface with gap states. Exposure of the annealed surface to excited hydrogen also leads to weak bonding. The interfacial bond is discussed in terms of interaction of the metal conduction band electrons with the band gap states on the diamond surface. Effects of surface electrical conductivity on the interfacial bond are also be considered.

First direct visualization of spillover species emitted from pt nanoparticles.

PubMed

Takakusagi, Satoru; Fukui, Ken-ichi; Tero, Ryugo; Asakura, Kiyotaka; Iwasawa, Yasuhiro

2010-11-02

We studied the methanol adsorption behavior of Pt nanoparticles that were vacuum-deposited on a TiO(2)(110) surface at room temperature by using an ultrahigh vacuum (UHV) scanning tunneling microscope (STM). A large number of bright spots were observed on fivefold-coordinated Ti (Ti(5c)) rows of the TiO(2)(110) surface after exposure of the Pt/TiO(2)(110) to methanol vapor. We assigned the bright spots to methoxy species. These were mobile and were found to hop along the Ti(5c) rows. In situ time-resolved STM observations of the formation and migration of the bright spots on the Pt/TiO(2)(110) were carried out in the presence of methanol. The bright spots were produced at the periphery of the Pt nanoparticles and migrated to the substrate Ti(5c) rows. We discuss the spillover process and behavior of the methoxy species on the Pt/TiO(2)(110).

Bolt-on source of spin-polarized electrons for inverse photoemission

NASA Astrophysics Data System (ADS)

Schedin, Fredrik; Warburton, Ranald; Thornton, Geoff

1998-06-01

We have developed a portable spin-polarized electron gun which can be bolted on to an ultrahigh vacuum chamber. The gun has been successfully operated with an electron gun to target distance of about 150 mm. This allows accommodation of other surface science equipment in the same vacuum system. The spin-polarized electrons are obtained via photoemission from a negative electron affinity GaAs(001) surface with circularly polarized light. A transversely polarized beam is achieved with a 90° electrostatic deflector. A set of two three-element electrostatic tube lenses are employed to transport and to focus the electrons onto a target. The measured transmission through the electron optics is >70% for electron energies in the range 7-20 eV. This is achieved by using large diameter electron transport lenses. The energy resolution of the electron beam is measured to be better than 0.27 eV and the polarization is determined to be 25±5%.

Single and two-mode mechanical squeezing of an optically levitated nanodiamond via dressed-state coherence

NASA Astrophysics Data System (ADS)

Ge, Wenchao; Bhattacharya, M.

2016-10-01

Nonclassical states of macroscopic objects are promising for ultrasensitive metrology as well as testing quantum mechanics. In this work, we investigate dissipative mechanical quantum state engineering in an optically levitated nanodiamond. First, we study single-mode mechanical squeezed states by magnetically coupling the mechanical motion to a dressed three-level system provided by a nitrogen-vacancy center in the nanoparticle. Quantum coherence between the dressed levels is created via microwave fields to induce a two-phonon transition, which results in mechanical squeezing. Remarkably, we find that in ultrahigh vacuum quantum squeezing is achievable at room temperature with feedback cooling. For moderate vacuum, quantum squeezing is possible with cryogenic temperature. Second, we present a setup for two mechanical modes coupled to the dressed three levels, which results in two-mode squeezing analogous to the mechanism of the single-mode case. In contrast to previous works, our study provides a deterministic method for engineering macroscopic squeezed states without the requirement for a cavity.

Reaction of perfluoroalkylpolyethers (PFPE) with 440C steel in vacuum under sliding conditions at room temperature

NASA Technical Reports Server (NTRS)

Mori, Shigeyuki; Morales, Wilfredo

1989-01-01

Reactions of perfluoroalkylpolyethers (PFPE: Fomblin, Demnum and Krytox) were studied during the sliding contact of stainless steel specimens under ultrahigh vacuum conditions. All three fluids reacted with the steel specimens during sliding. Fomblin, which has acetal linkages, decomposed under the sliding conditions generating gaseous products, (COF2 and fluorinated carbons) which were detected by a quadrupole mass spectrometer. Gaseous products were not detected for the Demnum and Krytox fluids. The amount of gaseous products from Fomblin increased with increasing sliding speed. At the end of the sliding experiments, the wear scar and deposits on the specimens were examined by small spot size XPS. The oxide layer on the specimen surface was removed during sliding, and metal fluorides were formed on the worn surface. The surface of the wear scar and deposits were covered with adsorbed PFPE. Based on these results, it was concluded that the decomposition reaction on Fomblin was initiated by contacting the fluid with a fresh metal surface which was formed during sliding.

Spontaneous desorption and phase transitions of self-assembled alkanethiol and alicyclic thiol monolayers chemisorbed on Au(111) in ultrahigh vacuum at room temperature.

PubMed

Ito, Eisuke; Kang, Hungu; Lee, Dongjin; Park, Joon B; Hara, Masahiko; Noh, Jaegeun

2013-03-15

Scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) were used to examine the surface structure and adsorption conditions of hexanethiol (HT) and cyclohexanethiol (CHT) self-assembled monolayers (SAMs) on Au(111) as a function of storage period in ultrahigh vacuum (UHV) conditions of 3×10(-7) Pa at room temperature (RT). STM imaging revealed that after storage for 7 days, HT SAMs underwent phase transitions from c(4×2) phase to low coverage 4×√3 phase. This transition is due to a structural rearrangement of hexanethiolates that results from the spontaneous desorption of chemisorbed HT molecules on Au(111) surface. XPS measurements showed approximately 28% reduction in sulfur coverage, which indicates desorption of hexanethiolates from the surfaces. Contrary to HT SAMs, the structural order of CHT SAMs with (5×2√3)R35° phase completely disappeared after storage for 3 or 7 days. XPS results show desorption of more than 80% of the cyclohexanethiolates, even after storage for 3 days. We found that spontaneous desorption of CHT molecules on Au(111) in UHV at RT occurred quickly, whereas spontaneous desorption of HT molecules was much slower. Thermal desorption spectroscopy (TDS) results suggest CHT SAMs in UHV at RT can desorb more efficiently than HT SAMs due to formation of thiol desorption fragments that result from chemical reactions between surface hydrogen atoms and thiolates on Au(111) surfaces. This study clearly demonstrated that organic thiols chemisorbed on gold surfaces are desorbed spontaneously in UHV at RT and van der Waals interactions play an important role in determining the structural stability of thiolate SAMs in UHV. Copyright © 2012 Elsevier Inc. All rights reserved.

A compact sub-Kelvin ultrahigh vacuum scanning tunneling microscope with high energy resolution and high stability.

PubMed

Zhang, L; Miyamachi, T; Tomanić, T; Dehm, R; Wulfhekel, W

2011-10-01

We designed a scanning tunneling microscope working at sub-Kelvin temperatures in ultrahigh vacuum (UHV) in order to study the magnetic properties on the nanoscale. An entirely homebuilt three-stage cryostat is used to cool down the microscope head. The first stage is cooled with liquid nitrogen, the second stage with liquid (4)He. The third stage uses a closed-cycle Joule-Thomson refrigerator of a cooling power of 1 mW. A base temperature of 930 mK at the microscope head was achieved using expansion of (4)He, which can be reduced to ≈400 mK when using (3)He. The cryostat has a low liquid helium consumption of only 38 ml/h and standing times of up to 280 h. The fast cooling down of the samples (3 h) guarantees high sample throughput. Test experiments with a superconducting tip show a high energy resolution of 0.3 meV when performing scanning tunneling spectroscopy. The vertical stability of the tunnel junction is well below 1 pm (peak to peak) and the electric noise floor of tunneling current is about 6fA/√Hz. Atomic resolution with a tunneling current of 1 pA and 1 mV was achieved on Au(111). The lateral drift of the microscope at stable temperature is below 20 pm/h. A superconducting spilt-coil magnet allows to apply an out-of-plane magnetic field of up to 3 T at the sample surface. The flux vortices of a Nb(110) sample were clearly resolved in a map of differential conductance at 1.1 K and a magnetic field of 0.21 T. The setup is designed for in situ preparation of tip and samples under UHV condition.

Synergistic Effect of Molecular-Type Electrocatalysts with Ultrahigh Pore Volume Carbon Microspheres for Lithium-Sulfur Batteries.

PubMed

Lim, Won-Gwang; Mun, Yeongdong; Cho, Ara; Jo, Changshin; Lee, Seonggyu; Han, Jeong Woo; Lee, Jinwoo

2018-05-14

Lithium-sulfur (Li-S) batteries are regarded as potential high-energy storage devices due to their outstanding energy density. However, the low electrical conductivity of sulfur, dissolution of the active material, and sluggish reaction kinetics cause poor cycle stability and rate performance. A variety of approaches have been attempted to resolve the above issues and achieve enhanced electrochemical performance. However, inexpensive multifunctional host materials which can accommodate large quantities of sulfur and exhibit high electrode density are not widely available, which hinders the commercialization of Li-S batteries. Herein, mesoporous carbon microspheres with ultrahigh pore volume are synthesized, followed by the incorporation of Fe-N-C molecular catalysts into the mesopores, which can act as sulfur hosts. The ultrahigh pore volume of the prepared host material can accommodate up to ∼87 wt % sulfur, while the uniformly controlled spherical morphology and particle size of the carbon microspheres enable high areal/volumetric capacity with high electrode density. Furthermore, the uniform distribution of Fe-N-C (only 0.33 wt %) enhances the redox kinetics of the conversion reaction of sulfur and efficiently captures the soluble intermediates. The resulting electrode with 5.2 mg sulfur per cm 2 shows excellent cycle stability and 84% retention of the initial capacity even after 500 cycles at a 3 C rate.

Electronic and magnetic properties of Ni nanoparticles embedded in various organic semiconductor matrices.

PubMed

Bräuer, Björn; Vaynzof, Yana; Zhao, Wei; Kahn, Antoine; Li, Wen; Zahn, Dietrich R T; Fernández, César de Julián; Sangregorio, Claudio; Salvan, Georgeta

2009-04-09

Ni nanoparticles with a size distribution from 2 to 6 nm, embedded in various organic matrices, were fabricated in ultrahigh vacuum. For this purpose metal free and Ni phthalocyanine, fullerene C(60), and pentacene were coevaporated with Ni. When coevaporated, Ni and H(2)Pc react, leading to the formation of NiPc and Ni nanoparticles. The molecular structure of the matrix was found to have negligible effect on the size of the nanoparticles but to influence the magnetic anisotropy of the nanoparticles: Ni nanoparticles formed in the buckyball matrix have a cubic symmetry, while nanoparticles formed in matrices consisting of planar molecules exhibit a uniaxial symmetry. After exposure to atmosphere, photoelectron spectroscopy investigations demonstrate the presence of metallic Ni nanoparticles accompanied by Ni oxide and the existence of a charge transfer from the organic matrix to the particles in all investigated systems. The oxidized Ni nanoparticles exhibit a larger magnetic anisotropy compared to the freshly prepared particles which show superparamagnetic properties above 17 K. Moreover, photoelectron spectroscopy was used to probe the oxidation process of the Ni nanoparticles in different organic matrices. It could thus be shown that a matrix consisting of spherical molecules like C(60) prevent the particles much better from oxidation compared to matrices of flat molecules.

Optimization of exchange bias in Co/CoO magnetic nanocaps by tuning deposition parameters

NASA Astrophysics Data System (ADS)

Sharma, A.; Tripathi, J.; Ugochukwu, K. C.; Tripathi, S.

2017-03-01

In the present work, we report exchange bias tuning by varying thin film deposition parameters such as synthesis method and underlying layer patterning. The patterned substrates for this study were prepared by self-assembly of polystyrene (PS) latex spheres ( 530 nm) on Si (100) substrate. The desired magnetic nanocaps composed of CoO/Co bilayer film on these patterned substrates were prepared by molecular beam epitaxy technique under ultra-high vacuum conditions. For this, a Co layer of 10 nm thickness was deposited on the substrates and then oxidized in-situ to form CoO/Co/PS in-situ oxidized film or ex-situ in ambiance which also gives CoO/Co/PS naturally oxidized film. Simultaneously, reference thin films of Co ( 10 nm) were also prepared on plane Si substrate and similar oxidation treatments were performed on them respectively. The magnetic properties studied using SQUID technique revealed higher exchange bias ( 1736 Oe) in the in-situ oxidized Co/PS film as compared to that in naturally oxidized Co/PS film ( 1544 Oe) and also compared to the reference film. The observed variations in the magnetic properties are explained in terms of surface patterning induced structural changes of the deposited films and different oxidation methods.

Experimental bandstructure of the 5 d transition metal oxide IrO2

NASA Astrophysics Data System (ADS)

Kawasaki, Jason; Nie, Yuefeng; Uchida, Masaki; Schlom, Darrell; Shen, Kyle

2015-03-01

In the 5 d iridium oxides the close energy scales of spin-orbit coupling and electron-electron correlations lead to emergent quantum phenomena. Much research has focused on the ternary iridium oxides, e.g. the Ruddlesden-Poppers An + 1BnO3 n + 1 , which exhibit behavior from metal to antiferromagnetic insulator ground states, share common features with the cuprates, and may host a number of topological phases. The binary rutile IrO2 is another important 5 d oxide, which has technological importance for spintronics due to its large spin Hall effect and also applications in catalysis. IrO2 is expected to share similar physics as its perovskite-based cousins; however, due to bond-length distortions of the IrO6 octahedra in the rutile structure, the extent of similarities remains an open question. Here we use angle-resolved photoemission spectroscopy to perform momentum-resolved measurements of the electronic structure of IrO2 . IrO2 thin films were grown by molecular beam epitaxy on TiO2 (110) substrates using an Ir e-beam source and distilled ozone. Films were subsequently transferred through ultrahigh vacuum to a connected ARPES system. Combined with first-principles calculations we explore the interplay of spin-orbit coupling and correlations in IrO2 .

Atomic imaging of the irreversible sensing mechanism of NO2 adsorption on copper phthalocyanine.

PubMed

Park, Jun Hong; Royer, James E; Chagarov, Evgeniy; Kaufman-Osborn, Tobin; Edmonds, Mary; Kent, Tyler; Lee, Sangyeob; Trogler, William C; Kummel, Andrew C

2013-10-02

Ambient NO2 adsorption onto copper(II) phthalocyanine (CuPc) monolayers is observed using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) to elucidate the molecular sensing mechanism in CuPc chemical vapor sensors. For low doses (1 ppm for 5 min) of NO2 at ambient temperatures, isolated chemisorption sites on the CuPc metal centers are observed in STM images. These chemisorbates almost completely desorb from the CuPc monolayer after annealing at 100 °C for 30 min. Conversely, for high NO2 doses (10 ppm for 5 min), the NO2 induces a fracture of the CuPc domains. This domain fracture can only be reversed by annealing above 150 °C, which is consistent with dissociative chemisorption into NO and atomic O accompanied by surface restructuring. This high stability implies that the domain fracture results from tightly bound adsorbates, such as atomic O. Existence of atomic O on or under the CuPc layer, which results in domain fracture, is revealed by XPS analysis and ozone-dosing experiments. The observed CuPc domain fracturing is consistent with a mechanism for the dosimetric sensing of NO2 and other reactive gases by CuPc organic thin film transistors (OTFTs).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weiss, Paul

Spectroscopic imaging tools and methods, based on scanning tunneling microscopes (STMs), are being developed and applied to examine buried layers and interfaces with ultrahigh resolution. These new methods measure buried contacts, molecule-substrate bonds, buried dipoles in molecular layers, and key structural aspects of adsorbed molecules, such as tilt angles. We are developing the ability to locate lateral projections of molecular parts as a means of determining the structures of molecular layers. We are developing the ability to measure the orientation of buried functionality.

Ultra-High Aggregate Bandwidth Two-Dimensional Multiple-Wavelength Diode Laser Arrays

DTIC Science & Technology

1994-04-09

surface temperature across the wafer during the growth of the cavity spacer region using the fact that the molecular beam epitaxy (MBE) growth of GaAs...substrate surface temperature across the wafer during the growth of the cavity spacer region. Using the fact that, during an molecular beam epitaxy (MBE...K. Bacher and J.S. Harris, "Periodically Induced Mode Shift in Vertical Cavity Fabry Perot Etalons Grown by Molecular Beam Epitaxy ," to be presented

Piezo-Operated Shutter Mechanism Moves 1.5 cm

NASA Technical Reports Server (NTRS)

Glaser, Robert; Bamford, Robert

2005-01-01

The figure shows parts of a shutter mechanism designed to satisfy a number of requirements specific to its original intended application as a component of an atomic clock to be flown in outer space. The mechanism may also be suitable for use in laboratory and industrial vacuum systems on Earth for which there are similar requirements. The requirements include the following: a) To alternately close, then open, a 1.5-cm-diameter optical aperture twice per second, with a stroke time of no more than 15 ms, during a total operational lifetime of at least a year; b) To attenuate light by a factor of at least 1012 when in the closed position; c) To generate little or no magnetic field; d) To be capable of withstanding bakeout at a temperature of 200 C to minimize outgassing during subsequent operation in an ultrahigh vacuum; and e) To fit within a diameter of 12 in. (=305 mm) a size limit dictated by the size of an associated magnetic shield. The light-attenuation requirement is satisfied by use of overlapping shutter blades. The closure of the aperture involves, among other things, insertion of a single shutter blade between a pair of shutter blades. The requirement to minimize the magnetic field is satisfied by use of piezoelectric actuators. Because piezoelectric actuators cannot withstand bakeout, they must be mounted outside the vacuum chamber, and, hence, motion must be transmitted from the actuators to the shutter levers via a vacuum-chamber-wall diaphragm.

Mechanical properties of ultrahigh molecular weight PHEMA hydrogels synthesized using initiated chemical vapor deposition.

PubMed

Bose, Ranjita K; Lau, Kenneth K S

2010-08-09

In this work, poly(2-hydroxyethyl methacrylate) (PHEMA), a widely used hydrogel, is synthesized using initiated chemical vapor deposition (iCVD), a one-step surface polymerization that does not use any solvents. iCVD synthesis is capable of producing linear stoichiometric polymers that are free from entrained unreacted monomer or solvent and, thus, do not require additional purification steps. The resulting films, therefore, are found to be noncytotoxic and also have low nonspecific protein adsorption. The kinetics of iCVD polymerization are tuned so as to achieve rapid deposition rates ( approximately 1.5 microm/min), which in turn yield ultrahigh molecular weight polymer films that are mechanically robust with good water transport and swellability. The films have an extremely high degree of physical chain entanglement giving rise to high tensile modulus and storage modulus without the need for chemical cross-linking that compromises hydrophilicity.

In-Vacuum Dissociator for Atomic-Hydrogen Masers

NASA Technical Reports Server (NTRS)

Vessot, R. F.

1987-01-01

Thermal control and vacuum sealing achieved while contamination avoided. Simple, relatively inexpensive molecular-hydrogen dissociator for atomic-hydrogen masers used on Earth or in vacuum of space. No air cooling required, and absence of elastomeric O-ring seals prevents contamination. In-vacuum dissociator for atomic hydrogen masers, hydrogen gas in glass dissociator dissociated by radio-frequency signal transmitted from surrounding 3-turn coil. Heat in glass conducted away by contacting metal surfaces.

Vacuum system of the cyclotrons in VECC, Kolkata

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roy, Anindya; Bhole, R.B.; Akhtar, J.

2011-07-01

The vacuum system of the K=130 Room Temperature Cyclotron (RTC) (operational since 1978) has been recently modernized and the same of the K{sub bend}=520 Superconducting Cyclotron (SCC), currently under commissioning, is being deployed for remote monitoring and control. The vacuum system of RTC is designed to achieve and maintain vacuum level of 2 X 10{sup -6} mbar inside 23 m{sup 3} volume of Resonator tank and DEE tank. This has been upgraded by replacing several valves, Freon units, gauges and pumps. The relay based manual control system has been replaced by PLC based automated system. The SCC vacuum system alsomore » has an elaborate arrangement comprising of turbo molecular pumping modules with associated isolation valves and characteristic gauges. This paper describes essential elements, typically used to obtain high (1X10{sup -7} mbar) vacuum using rotary pumps, diffusion pumps and cold traps/turbo-molecular pumps and other system components such as valves, gauges and baffles. The supervisory control methodology/scheme of both the vacuum systems, developed in-house using EPICS (Experimental Physics and Industrial Control System), a standard open-source software tool for designing distributed control system, is also elaborated here. (author)« less

Application of Molecular Adsorber Coatings in Chamber A for the James Webb Space Telescope

NASA Technical Reports Server (NTRS)

Abraham, Nithin S.

2017-01-01

As a coating made of highly porous zeolite materials, the Molecular Adsorber Coating (MAC) was developed to capture outgassed molecular contaminants, such as hydrocarbons and silicones. For spaceflight applications, the adsorptive capabilities of the coating can alleviate on-orbit outgassing concerns on or near sensitive surfaces and instruments within the spacecraft. Similarly, this sprayable paint technology has proven to be significantly beneficial for ground-based space applications, in particular, for vacuum chamber environments. This presentation describes the application of the MAC technology for the James Webb Space Telescope (JWST) at NASA Johnson Space Center (JSC). The coating was used as a mitigation tool to entrap outgassed contaminants, specifically silicone-based diffusion pump oil, from within JSCs cryogenic optical vacuum chamber test facility called Chamber A. This presentation summarizes the background, fabrication, installation, chemical analysis test results, and future plans for the MAC technology, which was effectively used to protect the JWST test equipment from vacuum chamber contamination. As a coating made of highly porous zeolite materials, the Molecular Adsorber Coating (MAC) was developed to capture outgassed molecular contaminants, such as hydrocarbons and silicones. For spaceflight applications, the adsorptive capabilities of the coating can alleviate on-orbit outgassing concerns on or near sensitive surfaces and instruments within the spacecraft. Similarly, this sprayable paint technology has proven to be significantly beneficial for ground-based space applications, in particular, for vacuum chamber environments. This presentation describes the application of the MAC technology for the James Webb Space Telescope (JWST) at NASA Johnson Space Center (JSC). The coating was used as a mitigation tool to entrap outgassed contaminants, specifically silicone-based diffusion pump oil, from within JSCs cryogenic optical vacuum chamber test facility called Chamber A. This presentation summarizes the background, fabrication, installation, chemical analysis test results, and future plans for the MAC technology, which was effectively used to protect the JWST test equipment from vacuum chamber contamination.

Ultrahigh Molecular Weight Linear Block Copolymers: Rapid Access by Reversible-Deactivation Radical Polymerization and Self- Assembly into Large Domain Nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mapas, Jose Kenneth D.; Thomay, Tim; Cartwright, Alexander N.

2016-05-05

Block copolymer (BCP) derived periodic nanostructures with domain sizes larger than 150 nm present a versatile platform for the fabrication of photonic materials. So far, the access to such materials has been limited to highly synthetically involved protocols. Herein, we report a simple, “user-friendly” method for the preparation of ultrahigh molecular weight linear poly(solketal methacrylate-b-styrene) block copolymers by a combination of Cu-wire-mediated ATRP and RAFT polymerizations. The synthesized copolymers with molecular weights up to 1.6 million g/mol and moderate dispersities readily assemble into highly ordered cylindrical or lamella microstructures with domain sizes as large as 292 nm, as determined bymore » ultra-small-angle x-ray scattering and scanning electron microscopy analyses. Solvent cast films of the synthesized block copolymers exhibit stop bands in the visible spectrum correlated to their domain spacings. The described method opens new avenues for facilitated fabrication and the advancement of fundamental understanding of BCP-derived photonic nanomaterials for a variety of applications.« less

Multilayer Thin Film Polarizer Design for Far Ultraviolet using Induced Transmission and Absorption Technique

NASA Technical Reports Server (NTRS)

Kim, Jongmin; Zukic, Muamer; Wilson, Michele M.; Park, Jung Ho; Torr, Douglas G.

1994-01-01

Good theoretical designs of far ultraviolet polarizers have been reported using a MgF2/Al/MgF2 three layer structure on a thick Al layer as a substrate. The thicknesses were determined to induce transmission and absorption of p-polarized light. In these designs Al optical constants were used from films produced in ultrahigh vacuum (UHV: 10(exp -10) torr). Reflectance values for polarizers fabricated in a conventional high vacuum (p approx. 10(exp -6 torr)) using the UHV design parameters differed dramatically from the design predictions. Al is a highly reactive material and is oxidized even in a high vacuum chamber. In order to solve the problem other metals have been studied. It is found that a larger reflectance difference is closely related to higher amplitude and larger phase difference of Fresnel reflection coefficients between two polarizations at the boundary of MgF2/metal. It is also found that for one material a larger angle of incidence from the surface normal brings larger amplitude and phase difference. Be and Mo are found good materials to replace Al. Polarizers designed for 121.6 nm with Be at 60 deg and with Mo at 70 deg are shown as examples.

Enhancement of magnetocaloric effect in the Gd 2Al phase by Co alloying

DOE PAGES

Huang, Z. Y.; Fu, H.; Hadimani, R. L.; ...

2014-11-14

We observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and high level calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.

Synthesis, Properties, and Two-Dimensional Adsorption Characteristics of 5-Amino[6]hexahelicene.

PubMed

van der Meijden, Maarten W; Gelens, Edith; Quirós, Natalia Murillo; Fuhr, Javier D; Gayone, J Esteban; Ascolani, Hugo; Wurst, Klaus; Lingenfelder, Magalí; Kellogg, Richard M

2016-01-22

A convergent synthesis of racemic 5-amino[6]hexahelicene is described. Cross-coupling reactions are used to assemble a pentacyclic framework, and a metal-catalyzed ring-closure comprises the final step. The enantiomers were separated by means of chromatography and the absolute configurations were assigned by comparison of the CD spectra with hexahelicene. The t1/2  value for racemization at 210 °C was approximately 1 hour. Scanning tunneling microscopy (STM) measurements were carried out on enantiopure and racemic samples of aminohelicene on Au(111) under ultrahigh vacuum (UHV) conditions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electronic structure of the La 1 + xBa 2 - xCu 3O 7 + δ system studied by photoelectron spectroscopy

NASA Astrophysics Data System (ADS)

Lindberg, P. A. P.; Shen, Z.-X.; Hwang, J.; Shih, C. K.; Lindau, I.; Spicer, W. E.; Mitzi, D. B.; Kapitulnik, A.

1989-01-01

Photoemission experiments utilizing synchrotron radiation have been carried out on the high temperature superconductor La 1.075Ba 1.925Cu 3O 7.0. The valence band spectra show similar spectral features as those of YBa 2Cu 3O 6.9, even though large differences in relative peak intensities are observed. Oxygen-related states are identified by scanning the photon energy through the O2 s → O2 p absorption edge. The stability of the sample surface, and changes in the valence band spectra after annealing in ultrahigh vacuum are also briefly discussed.

Epi-cleaning of Ge/GeSn heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Di Gaspare, L.; Sabbagh, D.; De Seta, M.

2015-01-28

We demonstrate a very-low temperature cleaning technique based on atomic hydrogen irradiation for highly (1%) tensile strained Ge epilayers grown on metastable, partially strain relaxed GeSn buffer layers. Atomic hydrogen is obtained by catalytic cracking of hydrogen gas on a hot tungsten filament in an ultra-high vacuum chamber. X-ray photoemission spectroscopy, reflection high energy electron spectroscopy, atomic force microscopy, secondary ion mass spectroscopy, and micro-Raman showed that an O- and C-free Ge surface was achieved, while maintaining the same roughness and strain condition of the as-deposited sample and without any Sn segregation, at a process temperature in the 100–300 °C range.

Custom sample environments at the ALBA XPEEM.

PubMed

Foerster, Michael; Prat, Jordi; Massana, Valenti; Gonzalez, Nahikari; Fontsere, Abel; Molas, Bernat; Matilla, Oscar; Pellegrin, Eric; Aballe, Lucia

2016-12-01

A variety of custom-built sample holders offer users a wide range of non-standard measurements at the ALBA synchrotron PhotoEmission Electron Microscope (PEEM) experimental station. Some of the salient features are: an ultrahigh vacuum (UHV) suitcase compatible with many offline deposition and characterization systems, built-in electromagnets for uni- or biaxial in-plane (IP) and out-of-plane (OOP) fields, as well as the combination of magnetic fields with electric fields or current injection. Electronics providing a synchronized sinusoidal signal for sample excitation enable time-resolved measurements at the 500MHz storage ring RF frequency. Copyright © 2016 Elsevier B.V. All rights reserved.

The Ultrathin Limit and Dead-layer Effects in Local Polarization Switching of BiFeO3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maksymovych, Petro; Huijben, Mark; Pan, Minghu

Using piezoresponse force microscopy in ultra-high vacuum, polarization switching has been detected and quantified in epitaxial BiFeO3 films from 200 down to ~ 4 unit cells. Local remnant piezoresponse was used to infer the applied electric field inside the ferroelectric volume, and account for the elusive effect of dead-layers in ultrathin films. The dead-layer manifested itself in the slower than anticipated decrease of the switching bias with film thickness, yielding apparent Kay-Dunn scaling of the switching field, while the statistical analysis of hysteresis loops revealed lateral variation of the dead-layer with sub-10 nm resolution.

Epi-cleaning of Ge/GeSn heterostructures

NASA Astrophysics Data System (ADS)

Di Gaspare, L.; Sabbagh, D.; De Seta, M.; Sodo, A.; Wirths, S.; Buca, D.; Zaumseil, P.; Schroeder, T.; Capellini, G.

2015-01-01

We demonstrate a very-low temperature cleaning technique based on atomic hydrogen irradiation for highly (1%) tensile strained Ge epilayers grown on metastable, partially strain relaxed GeSn buffer layers. Atomic hydrogen is obtained by catalytic cracking of hydrogen gas on a hot tungsten filament in an ultra-high vacuum chamber. X-ray photoemission spectroscopy, reflection high energy electron spectroscopy, atomic force microscopy, secondary ion mass spectroscopy, and micro-Raman showed that an O- and C-free Ge surface was achieved, while maintaining the same roughness and strain condition of the as-deposited sample and without any Sn segregation, at a process temperature in the 100-300 °C range.

Determining whether metals nucleate homogeneously on graphite: A case study with copper

DOE PAGES

Appy, David; Lei, Huaping; Han, Yong; ...

2014-11-05

In this study, we observe that Cu clusters grow on surface terraces of graphite as a result of physical vapor deposition in ultrahigh vacuum. We show that the observation is incompatible with a variety of models incorporating homogeneous nucleation and calculations of atomic-scale energetics. An alternative explanation, ion-mediated heterogeneous nucleation, is proposed and validated, both with theory and experiment. This serves as a case study in identifying when and whether the simple, common observation of metal clusters on carbon-rich surfaces can be interpreted in terms of homogeneous nucleation. We describe a general approach for making system-specific and laboratory-specific predictions.

Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mannix, A. J.; Zhou, X. -F.; Kiraly, B.

At the atomic-cluster scale, pure boron is markedly similar to carbon, forming simple planar molecules and cage-like fullerenes. Theoretical studies predict that two-dimensional (2D) boron sheets will adopt an atomic configuration similar to that of boron atomic clusters. We synthesized atomically thin, crystalline 2D boron sheets (i.e., borophene) on silver surfaces under ultrahigh-vacuum conditions. Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters with multiple scales of anisotropic, out-of-plane buckling. Unlike bulk boron allotropes, borophene shows metallic characteristics that are consistent with predictions of a highly anisotropic, 2D metal.

Cherenkov-like emission of Z bosons

NASA Astrophysics Data System (ADS)

Colladay, D.; Noordmans, J. P.; Potting, R.

2017-07-01

We study CPT and Lorentz violation in the electroweak gauge sector of the Standard Model in the context of the Standard-Model Extension (SME). In particular, we show that any non-zero value of a certain relevant Lorentz violation parameter that is thus far unbounded by experiment would imply that for sufficiently large energies one of the helicity modes of the Z boson should propagate with spacelike four-momentum and become stable against decay in vacuum. In this scenario, Cherenkov-like radiation of Z bosons by ultra-high-energy cosmic-ray protons becomes possible. We deduce a bound on the Lorentz violation parameter from the observational data on ultra-high energy cosmic rays.

Probing the atomic structure of metallic nanoclusters with the tip of a scanning tunneling microscope.

PubMed

Schouteden, Koen; Lauwaet, Koen; Janssens, Ewald; Barcaro, Giovanni; Fortunelli, Alessandro; Van Haesendonck, Chris; Lievens, Peter

2014-02-21

Preformed Co clusters with an average diameter of 2.5 nm are produced in the gas phase and are deposited under controlled ultra-high vacuum conditions onto a thin insulating NaCl film on Au(111). Relying on a combined experimental and theoretical investigation, we demonstrate visualization of the three-dimensional atomic structure of the Co clusters by high-resolution scanning tunneling microscopy (STM) using a Cl functionalized STM tip that can be obtained on the NaCl surface. More generally, use of a functionalized STM tip may allow for systematic atomic structure determination with STM of nanoparticles that are deposited on metal surfaces.

Length-extension resonator as a force sensor for high-resolution frequency-modulation atomic force microscopy in air.

PubMed

Beyer, Hannes; Wagner, Tino; Stemmer, Andreas

2016-01-01

Frequency-modulation atomic force microscopy has turned into a well-established method to obtain atomic resolution on flat surfaces, but is often limited to ultra-high vacuum conditions and cryogenic temperatures. Measurements under ambient conditions are influenced by variations of the dew point and thin water layers present on practically every surface, complicating stable imaging with high resolution. We demonstrate high-resolution imaging in air using a length-extension resonator operating at small amplitudes. An additional slow feedback compensates for changes in the free resonance frequency, allowing stable imaging over a long period of time with changing environmental conditions.

Time Strengthening of Crystal Nanocontacts

NASA Astrophysics Data System (ADS)

Mazo, Juan J.; Dietzel, Dirk; Schirmeisen, Andre; Vilhena, J. G.; Gnecco, Enrico

2017-06-01

We demonstrate how an exponentially saturating increase of the contact area between a nanoasperity and a crystal surface, occurring on time scales governed by the Arrhenius equation, is consistent with measurements of the static friction and lateral contact stiffness on a model alkali-halide surface at different temperatures in ultrahigh vacuum. The "contact ageing" effect is attributed to atomic attrition and is eventually broken by thermally activated slip of the nanoasperity on the surface. The combination of the two effects also leads to regions of strengthening and weakening in the velocity dependence of the friction, which are well-reproduced by an extended version of the Prandtl-Tomlinson model.

Characterization of Cr/6H-SiC(0 0 0 1) nano-contacts by current-sensing AFM

NASA Astrophysics Data System (ADS)

Grodzicki, Miłosz; Smolarek, Szymon; Mazur, Piotr; Zuber, Stefan; Ciszewski, Antoni

2009-11-01

The electrical properties and interface chemistry of Cr/6H-SiC(0 0 0 1) contacts have been studied by current-sensing atomic force microscopy (CS-AFM) and X-ray photoelectron spectroscopy (XPS). Cr layers were vapor deposited under ultrahigh vacuum onto both ex situ etched in H 2 and in situ Ar + ion-bombarded samples. The Cr/SiC contacts are electrically non-uniform. Both the measured I- V characteristics and the modeling calculations enabled to estimate changes of the Schottky barrier height caused by Ar + bombardment. Formation of ohmic nano-contacts on Ar +-bombarded surfaces was observed.

One-step Ge/Si epitaxial growth.

PubMed

Wu, Hung-Chi; Lin, Bi-Hsuan; Chen, Huang-Chin; Chen, Po-Chin; Sheu, Hwo-Shuenn; Lin, I-Nan; Chiu, Hsin-Tien; Lee, Chi-Young

2011-07-01

Fabricating a low-cost virtual germanium (Ge) template by epitaxial growth of Ge films on silicon wafer with a Ge(x)Si(1-x) (0 < x < 1) graded buffer layer was demonstrated through a facile chemical vapor deposition method in one step by decomposing a hazardousless GeO(2) powder under hydrogen atmosphere without ultra-high vacuum condition and then depositing in a low-temperature region. X-ray diffraction analysis shows that the Ge film with an epitaxial relationship is along the in-plane direction of Si. The successful growth of epitaxial Ge films on Si substrate demonstrates the feasibility of integrating various functional devices on the Ge/Si substrates.

Adhesion and transfer of PTFE to metals studied by auger emission spectroscopy

NASA Technical Reports Server (NTRS)

Pepper, S. V.; Buckley, D. H.

1972-01-01

The adhesion and transfer of polytetrafluoroethylene (PTFE) to metals in ultrahigh vacuum has been studied using Auger emission spectroscopy. The transfer was effected both by compressive static contact and by sliding contact. The transfer observed after static contact was independent of the chemical constitution of the substrate. Electron induced desorption of the fluorine in the transferred PTFE showed that the fluorine had no chemical interaction with the metal substrate. The coefficient of friction on metals was independent of the chemical constitution of the substrate. However, sliding PTFE on soft metals such as aluminum, generated wear fragments that lodged in the PTFE and machined the substrate.

Adhesion and transfer of polytetrafluorethylene to metals studied by Auger emission spectroscopy

NASA Technical Reports Server (NTRS)

Pepper, S. V.; Buckley, D. H.

1972-01-01

The adhesion and transfer of polytetrafluoroethylene (PTFE) to metals in ultrahigh vacuum were studied. The transfer was effected both by compressive static contact and by sliding contact. The transfer observed after static contact was independent of the chemical constitution of the substrate. Electron-induced desorption of the fluorine in the transferred PTFE showed that the fluorine had no chemical interaction with the metal substrate. The coefficient of friction on metals was independent of the chemical constitution of the substrate. However, sliding PTFE on soft metals, such as aluminum, generated wear fragments that lodged in the PTFE and machined the substrate.

Cold atoms as a coolant for levitated optomechanical systems

NASA Astrophysics Data System (ADS)

Ranjit, Gambhir; Montoya, Cris; Geraci, Andrew A.

2015-01-01

Optically trapped dielectric objects are well suited for reaching the quantum regime of their center-of-mass motion in an ultrahigh-vacuum environment. We show that ground-state cooling of an optically trapped nanosphere is achievable when starting at room temperature, by sympathetic cooling of a cold-atomic gas optically coupled to the nanoparticle. Unlike cavity cooling in the resolved-sideband limit, this system requires only a modest cavity finesse and it allows the cooling to be turned off, permitting subsequent observation of strongly coupled dynamics between the atoms and sphere. Nanospheres cooled to their quantum ground state could have applications in quantum information science or in precision sensing.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wagner, Margareta; Lackner, Peter; Seiler, Steffen

Metal deposition on oxide surfaces usually results in adatoms, clusters, or islands of the deposited material, where defects in the surface often act as nucleation centers. An alternate configuration is reported. Afterwards the vapor deposition of Fe on the In 2O 3(111) surface at room temperature, ordered adatoms are observed with scanning tunneling microscopy (STM). These are identical to the In adatoms that form when the sample is reduced by heating in ultrahigh vacuum. Our density functional theory (DFT) calculations confirm that Fe interchanges with In in the topmost layer, pushing the excess In atoms to the surface where theymore » arrange as a well-ordered adatom array.« less

Columnar epitaxy of hexagonal and orthorhombic silicides on Si(111)

NASA Technical Reports Server (NTRS)

Fathauer, R. W.; Nieh, C. W.; Xiao, Q. F.; Hashimoto, Shin

1990-01-01

Columnar grains of PtSi and CrSi2 surrounded by high-quality epitaxial silicon are obtained by ultrahigh vacuum codeposition of Si and metal in an approximately 10:1 ratio on Si(111) substrates heated to 610-840 C. This result is similar to that found previously for CoSi2 (a nearly-lattice-matched cubic-fluorite crystal) on Si(111), in spite of the respective orthorhombic and hexagonal structures of PtSi and CrSi2. The PtSi grains are epitaxial and have one of three variants of the relation defined by PtSi(010)/Si(111), with PtSi 001 line/Si 110 line type.

Miniaturized transportable evaporator for molecule deposition inside cryogenic scanning probe microscopes.

PubMed

Lämmle, K; Schwarz, A; Wiesendanger, R

2010-05-01

Here, we present a very small evaporator unit suitable to deposit molecules onto a sample in a cryogenic environment. It can be transported in an ultrahigh vacuum system and loaded into Omicron-type cantilever stages. Thus, molecule deposition inside a low temperature force microscope is possible. The design features an insulating base plate with two embedded electrical contacts and a crucible with low power consumption, which is thermally well isolated from the surrounding. The current is supplied via a removable power clip. Details of the manufacturing process as well as the used material are described. Finally, the performance of the whole setup is demonstrated.

Chemistry and temperature-assisted dehydrogenation of C60H30 molecules on TiO2(110) surfaces

NASA Astrophysics Data System (ADS)

Sánchez-Sánchez, Carlos; Martínez, José Ignacio; Lanzilotto, Valeria; Biddau, Giulio; Gómez-Lor, Berta; Pérez, Rubén; Floreano, Luca; López, María Francisca; Martín-Gago, José Ángel

2013-10-01

The thermal induced on-surface chemistry of large polycyclic aromatic hydrocarbons (PAHs) deposited on dielectric substrates is very rich and complex. We evidence temperature-assisted (cyclo)dehydrogenation reactions for C60H30 molecules and the subsequent bottom-up formation of assembled nanostructures, such as nanodomes, on the TiO2(110) surface. To this aim we have deposited, under ultra-high vacuum, a submonolayer coverage of C60H30 and studied, by a combination of experimental techniques (STM, XPS and NEXAFS) and theoretical methods, the different chemical on-surface interaction stages induced by the increasing temperature. We show that room temperature adsorbed molecules exhibit a weak interaction and freely diffuse on the surface, as previously reported for other aromatics. Nevertheless, a slight annealing induces a transition from this (meta)stable configuration into chemisorbed molecules. This adsorbate-surface interaction deforms the C60H30 molecular structure and quenches surface diffusion. Higher annealing temperatures lead to partial dehydrogenation, in which the molecule loses some of the hydrogen atoms and LUMO levels spread in the gap inducing a net total energy gain. Further annealing, up to around 750 K, leads to complete dehydrogenation. At these temperatures the fully dehydrogenated molecules link between them in a bottom-up coupling, forming nanodomes or fullerene-like monodisperse species readily on the dielectric surface. This work opens the door to the use of on-surface chemistry to generate new bottom-up tailored structures directly on high-K dielectric surfaces.The thermal induced on-surface chemistry of large polycyclic aromatic hydrocarbons (PAHs) deposited on dielectric substrates is very rich and complex. We evidence temperature-assisted (cyclo)dehydrogenation reactions for C60H30 molecules and the subsequent bottom-up formation of assembled nanostructures, such as nanodomes, on the TiO2(110) surface. To this aim we have deposited, under ultra-high vacuum, a submonolayer coverage of C60H30 and studied, by a combination of experimental techniques (STM, XPS and NEXAFS) and theoretical methods, the different chemical on-surface interaction stages induced by the increasing temperature. We show that room temperature adsorbed molecules exhibit a weak interaction and freely diffuse on the surface, as previously reported for other aromatics. Nevertheless, a slight annealing induces a transition from this (meta)stable configuration into chemisorbed molecules. This adsorbate-surface interaction deforms the C60H30 molecular structure and quenches surface diffusion. Higher annealing temperatures lead to partial dehydrogenation, in which the molecule loses some of the hydrogen atoms and LUMO levels spread in the gap inducing a net total energy gain. Further annealing, up to around 750 K, leads to complete dehydrogenation. At these temperatures the fully dehydrogenated molecules link between them in a bottom-up coupling, forming nanodomes or fullerene-like monodisperse species readily on the dielectric surface. This work opens the door to the use of on-surface chemistry to generate new bottom-up tailored structures directly on high-K dielectric surfaces. Electronic supplementary information (ESI) available. See DOI: 10.1039/c3nr03706a

Optical spectroscopy of molecular positronium.

PubMed

Cassidy, D B; Hisakado, T H; Tom, H W K; Mills, A P

2012-03-30

We report optical spectroscopic measurements of molecular positronium (Ps(2)), performed via a previously unobserved L=1 excited state. Ps(2) molecules created in a porous silica film, and also in vacuum from an Al(111) crystal, were resonantly excited and then photoionized by pulsed lasers, providing conclusive evidence for the production of this molecular matter-antimatter system and its excited state. Future experiments making use of the photoionized vacuum L=1 Ps(2) could provide a source of Ps(+) ions, as well as other multipositronic systems, such as Ps(2)H(-) or Ps(2)O.

Space simulation ultimate pressure lowered two decades by removal of diffusion pump oil contaminants during operation

NASA Technical Reports Server (NTRS)

Buggele, A. E.

1973-01-01

The complex problem why large space simulation chambers do not realize the true ultimate vacuum was investigated. Some contaminating factors affecting diffusion pump performance have been identified and some advances in vacuum/distillation/fractionation technology have been achieved which resulted in a two decade or more lower ultimate pressure. Data are presented to show the overall or individual contaminating effect of commonly used phthalate ester plasticizers of 390 to 530 molecular weight on diffusion pump performance. Methods for removing contaminants from diffusion pump silicone oil during operation and reclaiming contaminated oil by high vacuum molecular distillation are described.

The Use of the Molecular Adsorber Coating Technology to Mitigate Vacuum Chamber Contamination During Pathfinder Testing for the James Webb Space Telescope

NASA Technical Reports Server (NTRS)

Abraham, Nithin S.; Hasegawa, Mark M.; Wooldridge, Eve M.; Henderson-Nelson, Kelly A.

2016-01-01

As a coating made of highly porous zeolite materials, the Molecular Adsorber Coating (MAC) was developed to capture outgassed molecular contaminants, such as hydrocarbons and silicones. For spaceflight applications, the adsorptive capabilities of the coating can alleviate on-orbit outgassing concerns on or near sensitive surfaces and instruments within the spacecraft. Similarly, this sprayable paint technology has proven to be significantly beneficial for ground based space applications, in particular, for vacuum chamber environments. This paper describes the recent use of the MAC technology during Pathfinder testing of the Optical Ground Support Equipment (OGSE) for the James Webb Space Telescope (JWST) at NASA Johnson Space Center (JSC). The coating was used as a mitigation tool to entrap persistent outgassed contaminants, specifically silicone based diffusion pump oil, from within JSC's cryogenic optical vacuum chamber test facility called Chamber A. This paper summarizes the sample fabrication, installation, laboratory testing, post-test chemical analysis results, and future plans for the MAC technology, which was effectively used to protect the JWST test equipment from vacuum chamber contamination.

The use of the Molecular Adsorber Coating technology to mitigate vacuum chamber contamination during Pathfinder testing for the James Webb Space Telescope

NASA Astrophysics Data System (ADS)

Abraham, Nithin S.; Hasegawa, Mark M.; Wooldridge, Eve M.; Henderson-Nelson, Kelly A.

2016-09-01

As a coating made of highly porous zeolite materials, the Molecular Adsorber Coating (MAC) was developed to capture outgassed molecular contaminants, such as hydrocarbons and silicones. For spaceflight applications, the adsorptive capabilities of the coating can alleviate on-orbit outgassing concerns on or near sensitive surfaces and instruments within the spacecraft. Similarly, this sprayable paint technology has proven to be significantly beneficial for ground based space applications, in particular, for vacuum chamber environments. This paper describes the recent use of the MAC technology during Pathfinder testing of the Optical Ground Support Equipment (OGSE) for the James Webb Space Telescope (JWST) at NASA Johnson Space Center (JSC). The coating was used as a mitigation tool to entrap persistent outgassed contaminants, specifically silicone based diffusion pump oil, from within JSC's cryogenic optical vacuum chamber test facility called Chamber A. This paper summarizes the sample fabrication, installation, laboratory testing, post-test chemical analysis results, and future plans for the MAC technology, which was effectively used to protect the JWST test equipment from vacuum chamber contamination.

Better vacuum by removal of diffusion-pump-oil contaminants

NASA Technical Reports Server (NTRS)

Buggele, A. E.

1975-01-01

The complex problem of why large space simulation chambers do not realize true ultimate vacuum was investigated. Some contaminating factors affecting diffusion pump performance were identified, and some advances in vacuum distillation-fractionation technology were achieved which resulted in a two-decade-or-more lower ultimate pressure. Data are presented to show the overall or individual contaminating effects of commonly used phthalate ester plasticizers of 390 to 530 molecular weight on diffusion pump performance. Methods for removing contaminants from diffusion pump silicone oil during operation and for reclaiming contaminated oil by high-vacuum molecular distillation are described. Conceptual self-cleansing designs and operating procedures are proposed for modifying large diffusion pumps into high-efficiency distillation devices. The potential exists for application of these technological advancements to other disciplines, such as medicine, biomedical materials, metallurgy, refining, and chemical (diffusion-enrichment) processing.

Variation of the Phytochemical Constituents and Antioxidant Activities of Zingiber officinale var. rubrum Theilade Associated with Different Drying Methods and Polyphenol Oxidase Activity.

PubMed

Ghasemzadeh, Ali; Jaafar, Hawa Z E; Rahmat, Asmah

2016-06-17

The effects of different drying methods (freeze drying, vacuum oven drying, and shade drying) on the phytochemical constituents associated with the antioxidant activities of Z. officinale var. rubrum Theilade were evaluated to determine the optimal drying process for these rhizomes. Total flavonoid content (TFC), total phenolic content (TPC), and polyphenol oxidase (PPO) activity were measured using the spectrophotometric method. Individual phenolic acids and flavonoids, 6- and 8-gingerol and shogaol were identified by ultra-high performance liquid chromatography method. Ferric reducing antioxidant potential (FRAP) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) assays were used for the evaluation of antioxidant activities. The highest reduction in moisture content was observed after freeze drying (82.97%), followed by vacuum oven drying (80.43%) and shade drying (72.65%). The highest TPC, TFC, and 6- and 8-shogaol contents were observed in samples dried by the vacuum oven drying method compared to other drying methods. The highest content of 6- and 8-gingerol was observed after freeze drying, followed by vacuum oven drying and shade drying methods. Fresh samples had the highest PPO activity and lowest content of flavonoid and phenolic acid compounds compared to dried samples. Rhizomes dried by the vacuum oven drying method represent the highest DPPH (52.9%) and FRAP activities (566.5 μM of Fe (II)/g DM), followed by freeze drying (48.3% and 527.1 μM of Fe (II)/g DM, respectively) and shade drying methods (37.64% and 471.8 μM of Fe (II)/g DM, respectively) with IC50 values of 27.2, 29.1, and 34.8 μg/mL, respectively. Negative and significant correlations were observed between PPO and antioxidant activity of rhizomes. Vacuum oven dried rhizomes can be utilized as an ingredient for the development of value-added food products as they contain high contents of phytochemicals with valuable antioxidant potential.

Solid oxygen revisited

NASA Astrophysics Data System (ADS)

Freiman, Yu. A.; Jodl, H. J.; Crespo, Yanier

2018-05-01

The paper provides an up-to-date review of the experimental and theoretical works on solid oxygen published over the past decade. The most important results presented in this review are the following: Detection of magnetic collapse in neutron studies under the delta-epsilon transition. Identification of the lattice structure of the ɛ phase. In this structure the O2 molecules retain their individuality, but there is an additional link leading to the formation of clusters of molecular quartets with the structural formula (O2)4. Discovery of the unique magnetic properties of the delta phase, which hosts three different magnetic structures in the domain of the same crystallographic structure. The extension of the phase diagram to the high-pressure high-temperature region which was previously beyond the reach for experiment; the molecular η and η‧ phases were found and their structures were identified. Behavior of the melting line up to 60 GPa (1750 K). Discovery of a new molecular θ phase in ultrahigh magnetic fields up to over 190 T and the construction of the thermodynamical magnetic-field-temperature H- T phase diagram on the base of the ultrahigh-field magnetization, optical magneto-transmission, and adiabatic magnetocaloric effect measurements. Prediction of the persistence of the molecular state of solid oxygen up to the pressure of 1.9 TPa which is significantly higher than the corresponding limits in solid hydrogen and nitrogen, other generic molecular solids.

High vacuum measurements and calibrations, molecular flow fluid transient effects

DOE PAGES

Leishear, Robert A.; Gavalas, Nickolas A.

2015-04-29

High vacuum pressure measurements and calibrations below 1 × 10 -8 Torr are problematic. Specifically, measurement accuracies change drastically for vacuum gauges when pressures are suddenly lowered in vacuum systems. How can gauges perform like this? A brief system description is first required to answer this question. Calibrations were performed using a vacuum calibration chamber with attached vacuum gauges. To control chamber pressures, vacuum pumps decreased the chamber pressure while nitrogen tanks increased the chamber pressure. By balancing these opposing pressures, equilibrium in the chamber was maintained at selected set point pressures to perform calibrations. When pressures were suddenly decreasedmore » during set point adjustments, a sudden rush of gas from the chamber also caused a surge of gas from the gauges to decrease the pressures in those gauges. Gauge pressures did not return to equilibrium as fast as chamber pressures due to the sparse distribution of gas molecules in the system. This disparity in the rate of pressure changes caused the pressures in different gauges to be different than expected. This discovery was experimentally proven to show that different gauge designs return to equilibrium at different rates, and that gauge accuracies vary for different gauge designs due to fluid transients in molecular flow.« less

Differential renal effects of candesartan at high and ultra-high doses in diabetic mice–potential role of the ACE2/AT2R/Mas axis

PubMed Central

Callera, Glaucia E.; Antunes, Tayze T.; Correa, Jose W.; Moorman, Danielle; Gutsol, Alexey; He, Ying; Cat, Aurelie Nguyen Dinh; Briones, Ana M.; Montezano, Augusto C.; Burns, Kevin D.; Touyz, Rhian M.

2016-01-01

High doses of Ang II receptor (AT1R) blockers (ARBs) are renoprotective in diabetes. Underlying mechanisms remain unclear. We evaluated whether high/ultra-high doses of candesartan (ARB) up-regulate angiotensin-converting enzyme 2 (ACE2)/Ang II type 2 receptor (AT2R)/Mas receptor [protective axis of the of the renin–angiotensin system (RAS)] in diabetic mice. Systolic blood pressure (SBP), albuminuria and expression/activity of RAS components were assessed in diabetic db/db and control db/+ mice treated with increasing candesartan doses (intermediate, 1 mg/kg/d; high, 5 mg/kg/d; ultra-high, 25 and 75 mg/kg/d; 4 weeks). Lower doses candesartan did not influence SBP, but ultra-high doses reduced SBP in both groups. Plasma glucose and albuminuria were increased in db/db compared with db/+ mice. In diabetic mice treated with intermediate dose candesartan, renal tubular damage and albuminuria were ameliorated and expression of ACE2, AT2R and Mas and activity of ACE2 were increased, effects associated with reduced ERK1/2 phosphorylation, decreased fibrosis and renal protection. Ultra-high doses did not influence the ACE2/AT2R/Mas axis and promoted renal injury with increased renal ERK1/2 activation and exaggerated fibronectin expression in db/db mice. Our study demonstrates dose-related effects of candesartan in diabetic nephropathy: intermediate–high dose candesartan is renoprotective, whereas ultra-high dose candesartan induces renal damage. Molecular processes associated with these effects involve differential modulation of the ACE2/AT2R/Mas axis: intermediate–high dose candesartan up-regulating RAS protective components and attenuating pro-fibrotic processes, and ultra-high doses having opposite effects. These findings suggest novel mechanisms through the protective RAS axis, whereby candesartan may ameliorate diabetic nephropathy. Our findings also highlight potential injurious renal effects of ultra-high dose candesartan in diabetes. PMID:27612496

Next-generation technologies for spatial proteomics: Integrating ultra-high speed MALDI-TOF and high mass resolution MALDI FTICR imaging mass spectrometry for protein analysis.

PubMed

Spraggins, Jeffrey M; Rizzo, David G; Moore, Jessica L; Noto, Michael J; Skaar, Eric P; Caprioli, Richard M

2016-06-01

MALDI imaging mass spectrometry is a powerful analytical tool enabling the visualization of biomolecules in tissue. However, there are unique challenges associated with protein imaging experiments including the need for higher spatial resolution capabilities, improved image acquisition rates, and better molecular specificity. Here we demonstrate the capabilities of ultra-high speed MALDI-TOF and high mass resolution MALDI FTICR IMS platforms as they relate to these challenges. High spatial resolution MALDI-TOF protein images of rat brain tissue and cystic fibrosis lung tissue were acquired at image acquisition rates >25 pixels/s. Structures as small as 50 μm were spatially resolved and proteins associated with host immune response were observed in cystic fibrosis lung tissue. Ultra-high speed MALDI-TOF enables unique applications including megapixel molecular imaging as demonstrated for lipid analysis of cystic fibrosis lung tissue. Additionally, imaging experiments using MALDI FTICR IMS were shown to produce data with high mass accuracy (<5 ppm) and resolving power (∼75 000 at m/z 5000) for proteins up to ∼20 kDa. Analysis of clear cell renal cell carcinoma using MALDI FTICR IMS identified specific proteins localized to healthy tissue regions, within the tumor, and also in areas of increased vascularization around the tumor. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ultra-high vacuum surface analysis study of rhodopsin incorporation into supported lipid bilayers.

PubMed

Michel, Roger; Subramaniam, Varuni; McArthur, Sally L; Bondurant, Bruce; D'Ambruoso, Gemma D; Hall, Henry K; Brown, Michael F; Ross, Eric E; Saavedra, S Scott; Castner, David G

2008-05-06

Planar supported lipid bilayers that are stable under ambient atmospheric and ultra-high-vacuum conditions were prepared by cross-linking polymerization of bis-sorbylphosphatidylcholine (bis-SorbPC). X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were employed to investigate bilayers that were cross-linked using either redox-initiated radical polymerization or ultraviolet photopolymerization. The redox method yields a more structurally intact bilayer; however, the UV method is more compatible with incorporation of transmembrane proteins. UV polymerization was therefore used to prepare cross-linked bilayers with incorporated bovine rhodopsin, a light-activated, G-protein-coupled receptor (GPCR). A previous study (Subramaniam, V.; Alves, I. D.; Salgado, G. F. J.; Lau, P. W.; Wysocki, R. J.; Salamon, Z.; Tollin, G.; Hruby, V. J.; Brown, M. F.; Saavedra, S. S. J. Am. Chem. Soc. 2005, 127, 5320-5321) showed that rhodopsin retains photoactivity after incorporation into UV-polymerized bis-SorbPC, but did not address how the protein is associated with the bilayer. In this study, we show that rhodopsin is retained in supported bilayers of poly(bis-SorbPC) under ultra-high-vacuum conditions, on the basis of the increase in the XPS nitrogen concentration and the presence of characteristic amino acid peaks in the ToF-SIMS data. Angle-resolved XPS data show that the protein is inserted into the bilayer, rather than adsorbed on the bilayer surface. This is the first study to demonstrate the use of ultra-high-vacuum techniques for structural studies of supported proteolipid bilayers.

Stepwise heating in Stille polycondensation toward no batch-to-batch variations in polymer solar cell performance.

PubMed

Lee, Sang Myeon; Park, Kwang Hyun; Jung, Seungon; Park, Hyesung; Yang, Changduk

2018-05-14

For a given π-conjugated polymer, the batch-to-batch variations in molecular weight (M w ) and polydispersity index (Ð) can lead to inconsistent process-dependent material properties and consequent performance variations in the device application. Using a stepwise-heating protocol in the Stille polycondensation in conjunction with optimized processing, we obtained an ultrahigh-quality PTB7 polymer having high M w and very narrow Ð. The resulting ultrahigh-quality polymer-based solar cells demonstrate up to 9.97% power conversion efficiencies (PCEs), which is over 24% enhancement from the control devices fabricated with commercially available PTB7. Moreover, we observe almost negligible batch-to-batch variations in the overall PCE values from ultrahigh-quality polymer-based devices. The proposed stepwise polymerization demonstrates a facile and effective strategy for synthesizing high-quality semiconducting polymers that can significantly improve device yield in polymer-based solar cells, an important factor for the commercialization of organic solar cells, by mitigating device-to-device variations.

Proteometabolomic response of Deinococcus radiodurans exposed to UVC and vacuum conditions: Initial studies prior to the Tanpopo space mission.

PubMed

Ott, Emanuel; Kawaguchi, Yuko; Kölbl, Denise; Chaturvedi, Palak; Nakagawa, Kazumichi; Yamagishi, Akihiko; Weckwerth, Wolfram; Milojevic, Tetyana

2017-01-01

The multiple extremes resistant bacterium Deinococcus radiodurans is able to withstand harsh conditions of simulated outer space environment. The Tanpopo orbital mission performs a long-term space exposure of D. radiodurans aiming to investigate the possibility of interplanetary transfer of life. The revealing of molecular machinery responsible for survivability of D. radiodurans in the outer space environment can improve our understanding of underlying stress response mechanisms. In this paper, we have evaluated the molecular response of D. radiodurans after the exposure to space-related conditions of UVC irradiation and vacuum. Notably, scanning electron microscopy investigations showed that neither morphology nor cellular integrity of irradiated cells was affected, while integrated proteomic and metabolomic analysis revealed numerous molecular alterations in metabolic and stress response pathways. Several molecular key mechanisms of D. radiodurans, including the tricarboxylic acid cycle, the DNA damage response systems, ROS scavenging systems and transcriptional regulators responded in order to cope with the stressful situation caused by UVC irradiation under vacuum conditions. These results reveal the effectiveness of the integrative proteometabolomic approach as a tool in molecular analysis of microbial stress response caused by space-related factors.

Improving the Molecular Ion Signal Intensity for In Situ Liquid SIMS Analysis.

PubMed

Zhou, Yufan; Yao, Juan; Ding, Yuanzhao; Yu, Jiachao; Hua, Xin; Evans, James E; Yu, Xiaofei; Lao, David B; Heldebrant, David J; Nune, Satish K; Cao, Bin; Bowden, Mark E; Yu, Xiao-Ying; Wang, Xue-Lin; Zhu, Zihua

2016-12-01

In situ liquid secondary ion mass spectrometry (SIMS) enabled by system for analysis at the liquid vacuum interface (SALVI) has proven to be a promising new tool to provide molecular information at solid-liquid and liquid-vacuum interfaces. However, the initial data showed that useful signals in positive ion spectra are too weak to be meaningful in most cases. In addition, it is difficult to obtain strong negative molecular ion signals when m/z>200. These two drawbacks have been the biggest obstacle towards practical use of this new analytical approach. In this study, we report that strong and reliable positive and negative molecular signals are achievable after optimizing the SIMS experimental conditions. Four model systems, including a 1,8-diazabicycloundec-7-ene (DBU)-base switchable ionic liquid, a live Shewanella oneidensis biofilm, a hydrated mammalian epithelia cell, and an electrolyte popularly used in Li ion batteries were studied. A signal enhancement of about two orders of magnitude was obtained in comparison with non-optimized conditions. Therefore, molecular ion signal intensity has become very acceptable for use of in situ liquid SIMS to study solid-liquid and liquid-vacuum interfaces. Graphical Abstract ᅟ.

Proteometabolomic response of Deinococcus radiodurans exposed to UVC and vacuum conditions: Initial studies prior to the Tanpopo space mission

PubMed Central

Ott, Emanuel; Kawaguchi, Yuko; Kölbl, Denise; Chaturvedi, Palak; Nakagawa, Kazumichi; Yamagishi, Akihiko; Weckwerth, Wolfram

2017-01-01

The multiple extremes resistant bacterium Deinococcus radiodurans is able to withstand harsh conditions of simulated outer space environment. The Tanpopo orbital mission performs a long-term space exposure of D. radiodurans aiming to investigate the possibility of interplanetary transfer of life. The revealing of molecular machinery responsible for survivability of D. radiodurans in the outer space environment can improve our understanding of underlying stress response mechanisms. In this paper, we have evaluated the molecular response of D. radiodurans after the exposure to space-related conditions of UVC irradiation and vacuum. Notably, scanning electron microscopy investigations showed that neither morphology nor cellular integrity of irradiated cells was affected, while integrated proteomic and metabolomic analysis revealed numerous molecular alterations in metabolic and stress response pathways. Several molecular key mechanisms of D. radiodurans, including the tricarboxylic acid cycle, the DNA damage response systems, ROS scavenging systems and transcriptional regulators responded in order to cope with the stressful situation caused by UVC irradiation under vacuum conditions. These results reveal the effectiveness of the integrative proteometabolomic approach as a tool in molecular analysis of microbial stress response caused by space-related factors. PMID:29244852

Perspective: Chemical reactions in ionic liquids monitored through the gas (vacuum)/liquid interface.

PubMed

Maier, F; Niedermaier, I; Steinrück, H-P

2017-05-07

This perspective analyzes the potential of X-ray photoelectron spectroscopy under ultrahigh vacuum (UHV) conditions to follow chemical reactions in ionic liquids in situ. Traditionally, only reactions occurring on solid surfaces were investigated by X-ray photoelectron spectroscopy (XPS) in situ. This was due to the high vapor pressures of common liquids or solvents, which are not compatible with the required UHV conditions. It was only recently realized that the situation is very different when studying reactions in Ionic Liquids (ILs), which have an inherently low vapor pressure, and first studies have been performed within the last years. Compared to classical spectroscopy techniques used to monitor chemical reactions, the advantage of XPS is that through the analysis of their core levels all relevant elements can be quantified and their chemical state can be analyzed under well-defined (ultraclean) conditions. In this perspective, we cover six very different reactions which occur in the IL, with the IL, or at an IL/support interface, demonstrating the outstanding potential of in situ XPS to gain insights into liquid phase reactions in the near-surface region.

Ultrahigh-throughput exfoliation of graphite into pristine 'single-layer' graphene using microwaves and molecularly engineered ionic liquids.

PubMed

Matsumoto, Michio; Saito, Yusuke; Park, Chiyoung; Fukushima, Takanori; Aida, Takuzo

2015-09-01

Graphene has shown much promise as an organic electronic material but, despite recent achievements in the production of few-layer graphene, the quantitative exfoliation of graphite into pristine single-layer graphene has remained one of the main challenges in developing practical devices. Recently, reduced graphene oxide has been recognized as a non-feasible alternative to graphene owing to variable defect types and levels, and attention is turning towards reliable methods for the high-throughput exfoliation of graphite. Here we report that microwave irradiation of graphite suspended in molecularly engineered oligomeric ionic liquids allows for ultrahigh-efficiency exfoliation (93% yield) with a high selectivity (95%) towards 'single-layer' graphene (that is, with thicknesses <1 nm) in a short processing time (30 minutes). The isolated graphene sheets show negligible structural deterioration. They are also readily redispersible in oligomeric ionic liquids up to ~100 mg ml(-1), and form physical gels in which an anisotropic orientation of graphene sheets, once induced by a magnetic field, is maintained.

Investigation of bio-oil produced by hydrothermal liquefaction of food waste using ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry.

PubMed

Kostyukevich, Yury; Vlaskin, Mikhail; Borisova, Ludmila; Zherebker, Alexander; Perminova, Irina; Kononikhin, Alexey; Popov, Igor; Nikolaev, Eugene

2018-02-01

Recent research has revealed that more than 1.3 billion tons of food is wasted globally every year. The disposal of such huge biomass has become a challenge. In the present paper, we report the production of the bio-oil by hydrothermal liquefaction of three classes of food waste: meat, cheese and fruits. The highest yield of the bio-oil was observed for meat (∼60%) and cheese (∼75%), while for fruits, it was considerably low (∼10%). The molecular composition of the obtained bio-oil was investigated using ultrahigh resolution Fourier Transform Ion Cyclotron Resonance mass spectrometry and was found to be similar to that obtained from algae. Several thousand heteroatom compounds (N, N 2 , ON 2 , etc. classes) were reliably identified from each sample. It was found that bio-oils produced from meat and cheese have many compounds (∼90%) with common molecular formulas, while bio-oil produced from fruits differs considerably (∼30% of compounds are unique).

Molecular signature of organic nitrogen in septic-impacted groundwater

USGS Publications Warehouse

Arnold, William A.; Longnecker, Krista; Kroeger, Kevin D.; Kujawinski, Elizabeth B.

2014-01-01

Dissolved inorganic and organic nitrogen levels are elevated in aquatic systems due to anthropogenic activities. Dissolved organic nitrogen (DON) arises from various sources, and its impact could be more clearly constrained if specific sources were identified and if the molecular-level composition of DON were better understood. In this work, the pharmaceutical carbamazepine was used to identify septic-impacted groundwater in a coastal watershed. Using ultrahigh resolution mass spectrometry data, the nitrogen-containing features of the dissolved organic matter in septic-impacted and non-impacted samples were compared. The septic-impacted groundwater samples have a larger abundance of nitrogen-containing formulas. Impacted samples have additional DON features in the regions ascribed as ‘protein-like’ and ‘lipid-like’ in van Krevelen space and have more intense nitrogen-containing features in a specific region of a carbon versus mass plot. These features are potential indicators of dissolved organic nitrogen arising from septic effluents, and this work suggests that ultrahigh resolution mass spectrometry is a valuable tool to identify and characterize sources of DON.

APPARATUS FOR VACUUM DEPOSITION OF METALS

DOEpatents

Milleron, N.

1962-03-13

An apparatus and a method are described for continuous vacuum deposition of metals for metallic coatings, for ultra-high vacuum work, for purification of metals, for maintaining high-density electron currents, and for other uses. The apparatus comprises an externally cooled feeder tube extending into a container and adapted to feed metal wire or strip so that it emerges in a generally vertical position therein. The tube also provides shielding from the heat produced by an electron beam therein focused to impinge from a vertical direction upon the tip of the emerging wire. By proper control of the wire feed, coolant feed, and electron beam intensity, a molten ball of metal forms upon the emerging tip and remains self-supported thereon by the interaction of various forces. The metal is vaporized and travels in a line of sight direction, while additional wire is fed from the tube, so that the size of the molten ball remains constant. In the preferred embodiments, the wire is selected from a number of gettering metals and is degassed by electrical resistance in an adjacent chamber which is also partially evacuated. The wire is then fed through the feed tube into the electron beam and vaporizes and adsorbs gases to provide pumping action while being continuously deposited upon surfaces within the chamber. Ion pump electrodes may also be provided within line of sight of the vaporizing metal source to enhance the pumping action. (AEC)

Mask aligner for ultrahigh vacuum with capacitive distance control

NASA Astrophysics Data System (ADS)

Bhaskar, Priyamvada; Mathioudakis, Simon; Olschewski, Tim; Muckel, Florian; Bindel, Jan Raphael; Pratzer, Marco; Liebmann, Marcus; Morgenstern, Markus

2018-04-01

We present a mask aligner driven by three piezomotors which guides and aligns a SiN shadow mask under capacitive control towards a sample surface. The three capacitors for read out are located at the backside of the thin mask such that the mask can be placed at a μm distance from the sample surface, while keeping it parallel to the surface, without touching the sample by the mask a priori. Samples and masks can be exchanged in-situ and the mask can additionally be displaced parallel to the surface. We demonstrate an edge sharpness of the deposited structures below 100 nm, which is likely limited by the diffusion of the deposited Au on Si(111).

Self-organization of gold nanoparticles on silanated surfaces.

PubMed

Kyaw, Htet H; Al-Harthi, Salim H; Sellai, Azzouz; Dutta, Joydeep

2015-01-01

The self-organization of monolayer gold nanoparticles (AuNPs) on 3-aminopropyltriethoxysilane (APTES)-functionalized glass substrate is reported. The orientation of APTES molecules on glass substrates plays an important role in the interaction between AuNPs and APTES molecules on the glass substrates. Different orientations of APTES affect the self-organization of AuNps on APTES-functionalized glass substrates. The as grown monolayers and films annealed in ultrahigh vacuum and air (600 °C) were studied by water contact angle measurements, atomic force microscopy, X-ray photoelectron spectroscopy, UV-visible spectroscopy and ultraviolet photoelectron spectroscopy. Results of this study are fundamentally important and also can be applied for designing and modelling of surface plasmon resonance based sensor applications.

From nucleation to coalescence of Cu2O islands during in situ oxidation of Cu(001)

NASA Astrophysics Data System (ADS)

Yang, J. C.; Evan, D.; Tropia, L.

2002-07-01

The nucleation, growth, and coalescence of Cu2O islands due to oxidation of Cu(001) films were visualized by in situ ultrahigh-vacuum transmission electron microscopy. We have previously demonstrated that the nucleation and initial growth of copper oxides is dominated by oxygen surface diffusion. These surface models have been extended to quantitatively represent the coalescence behavior of copper oxidation in the framework of the Johnson-Mehl-Avrami-Kolmogorov theory. An excellent agreement exists between the experimental data of nucleation to coalescence with the surface model. The implication could be an alternate paradigm for passivation and oxidation, since classic theories assume uniform film growth.

Materials processing in space program tasks

NASA Technical Reports Server (NTRS)

Pentecost, E. (Compiler)

1982-01-01

Active research areas as of the end of the fiscal year 1982 of the Materials Processing in Space Program, NASA-Office of Space and Terrestrial Applications, involving several NASA centers and other organizations are highlighted to provide an overview of the program scope for managers and scientists in industry, university, and government communities. The program is described as well as its history, strategy and overall goal; the organizational structures and people involved are identified and each research task is described together with a list of recent publications. The tasks are grouped into four categories: crystal growth; solidification of metals, alloys, and composites; fluids, transports, and chemical processes; and ultrahigh vacuum and containerless processing technologies.

Absolute vibrational excitation cross sections for 1-18 eV electron scattering from condensed dimethyl phosphate (DMP)

NASA Astrophysics Data System (ADS)

Lemelin, V.; Bass, A. D.; Wagner, J. R.; Sanche, L.

2017-12-01

Absolute cross sections (CSs) for vibrational excitation by 1-18 eV electrons incident on condensed dimethyl phosphate (DMP) were measured with a high-resolution electron energy loss (EEL) spectrometer. Absolute CSs were extracted from EEL spectra of DMP condensed on multilayer film of Ar held at about 20 K under ultra-high vacuum (˜1 × 10-11 Torr). Structures observed in the energy dependence of the CSs around 2, 4, 7, and 12 eV were compared with previous results of gas- and solid-phase experiments and with theoretical studies on dimethyl phosphate and related molecules. These structures were attributed to the formation of shape resonances.

Qualification Tests of Micro-camera Modules for Space Applications

NASA Astrophysics Data System (ADS)

Kimura, Shinichi; Miyasaka, Akira

Visual capability is very important for space-based activities, for which small, low-cost space cameras are desired. Although cameras for terrestrial applications are continually being improved, little progress has been made on cameras used in space, which must be extremely robust to withstand harsh environments. This study focuses on commercial off-the-shelf (COTS) CMOS digital cameras because they are very small and are based on an established mass-market technology. Radiation and ultrahigh-vacuum tests were conducted on a small COTS camera that weighs less than 100 mg (including optics). This paper presents the results of the qualification tests for COTS cameras and for a small, low-cost COTS-based space camera.

Synthesis of borophenes: Anisotropic, two-dimensional boron polymorphs.

PubMed

Mannix, Andrew J; Zhou, Xiang-Feng; Kiraly, Brian; Wood, Joshua D; Alducin, Diego; Myers, Benjamin D; Liu, Xiaolong; Fisher, Brandon L; Santiago, Ulises; Guest, Jeffrey R; Yacaman, Miguel Jose; Ponce, Arturo; Oganov, Artem R; Hersam, Mark C; Guisinger, Nathan P

2015-12-18

At the atomic-cluster scale, pure boron is markedly similar to carbon, forming simple planar molecules and cage-like fullerenes. Theoretical studies predict that two-dimensional (2D) boron sheets will adopt an atomic configuration similar to that of boron atomic clusters. We synthesized atomically thin, crystalline 2D boron sheets (i.e., borophene) on silver surfaces under ultrahigh-vacuum conditions. Atomic-scale characterization, supported by theoretical calculations, revealed structures reminiscent of fused boron clusters with multiple scales of anisotropic, out-of-plane buckling. Unlike bulk boron allotropes, borophene shows metallic characteristics that are consistent with predictions of a highly anisotropic, 2D metal. Copyright © 2015, American Association for the Advancement of Science.

Symposium on Space Industrialization, Huntsville, Ala., May 26, 27, 1976, Proceedings

NASA Technical Reports Server (NTRS)

1976-01-01

Space habitats are considered, with attention given the evolution of space station systems, space station habitability, space settlement planning methodology, and orbital assembly. Various aspects of the Space Transportation System are discussed, including Shuttle booster/propulsion growth concept, advanced earth orbital transportation systems technology, single-stage-to-orbit vehicles and aeromaneuvering orbit transfer vehicles. Materials processing in space is examined, with emphasis on biological materials, metallurgical materials, the uses of space ultrahigh vacuum, and extraterrestrial mining and industrial processing. Solar space power is investigated, with attention given the potential of satellite solar power stations, thermal engine power satellites and microwave power transmission to earth. Individual items are announced in this issue.

Fabrication of [001]-oriented tungsten tips for high resolution scanning tunneling microscopy

PubMed Central

Chaika, A. N.; Orlova, N. N.; Semenov, V. N.; Postnova, E. Yu.; Krasnikov, S. A.; Lazarev, M. G.; Chekmazov, S. V.; Aristov, V. Yu.; Glebovsky, V. G.; Bozhko, S. I.; Shvets, I. V.

2014-01-01

The structure of the [001]-oriented single crystalline tungsten probes sharpened in ultra-high vacuum using electron beam heating and ion sputtering has been studied using scanning and transmission electron microscopy. The electron microscopy data prove reproducible fabrication of the single-apex tips with nanoscale pyramids grained by the {011} planes at the apexes. These sharp, [001]-oriented tungsten tips have been successfully utilized in high resolution scanning tunneling microscopy imaging of HOPG(0001), SiC(001) and graphene/SiC(001) surfaces. The electron microscopy characterization performed before and after the high resolution STM experiments provides direct correlation between the tip structure and picoscale spatial resolution achieved in the experiments. PMID:24434734

Fabrication of silver tips for scanning tunneling microscope induced luminescence.

PubMed

Zhang, C; Gao, B; Chen, L G; Meng, Q S; Yang, H; Zhang, R; Tao, X; Gao, H Y; Liao, Y; Dong, Z C

2011-08-01

We describe a reliable fabrication procedure of silver tips for scanning tunneling microscope (STM) induced luminescence experiments. The tip was first etched electrochemically to yield a sharp cone shape using selected electrolyte solutions and then sputter cleaned in ultrahigh vacuum to remove surface oxidation. The tip status, in particular the tip induced plasmon mode and its emission intensity, can be further tuned through field emission and voltage pulse. The quality of silver tips thus fabricated not only offers atomically resolved STM imaging, but more importantly, also allows us to perform challenging "color" photon mapping with emission spectra taken at each pixel simultaneously during the STM scan under relatively small tunnel currents and relatively short exposure time.

Chemical surface modification of polycrystalline platinum thin-films to promote preferential chemisorption of n-hexane, piperidine, and cyclohexane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, V.; Schwank, J.; Gland, J.

In this study, hard/soft Lewis acid-base (HSAB) principles are used to modify a thin-polycrystalline platinum film to promote preferential chemisorption of molecules such as piperidine, n-hexane, and cyclohexane. Specifically, the particle size and electron density distribution of the platinum surface is modified using thermal treatment and co-adsorption of electro-positive and negative species. These studies are conducted in an ultra-high vacuum chamber. The platinum surface is characterized, before and after modification protocols, using a variety of in-situ and ex-situ techniques. These include temperature programmed desorption (TPD), both resistance change and work function measurements, and both X-ray photoelectron spectroscopy and diffraction.

Insulating Behavior in Graphene with Irradiation-induced Lattice Defects

NASA Astrophysics Data System (ADS)

Chen, Jian-Hao; Williams, Ellen; Fuhrer, Michael

2010-03-01

We irradiated cleaned graphene on silicon dioxide in ultra-high vacuum with low energy inert gas ions to produce lattice defects [1], and investigated in detail the transition from metallic to insulating temperature dependence of the conductivity as a function of defect density. We measured the low field magnetoresistance and temperature-dependent resistivity in situ and find that weak localization can only account for a small correction of the resistivity increase with decreasing temperature. We will discuss possible origins of the insulating temperature dependent resistivity in defected graphene in light of our recent experiments. [4pt] [1] Jian-Hao Chen, W. G. Cullen, C. Jang, M. S. Fuhrer, E. D. Williams, PRL 102, 236805 (2009)

UHV-TEM-REM Studies of Si(111) Surfaces

NASA Astrophysics Data System (ADS)

Yagi, K.; Yamanaka, A.; Sato, H.; Shima, M.; Ohse, H.; Ozawa, S.; Tanishiro, Y.

Recent progresses of ultra-high vacuum transmission and reflection electron microscope studies of clean Si(111) surfaces are described. Anisotropy of surface atomic steps such as step energy, bunching of steps, are studied. Out of phase boundaries are observed in transmission mode and its energy relative to the step energy is studied. The phase transition between the 1 × 1 and the 7 × 7 structures around 830°C, studied previously is re-examined under various conditions. Contraction strains of the 7 × 7 structure and adatom density on terraces play important role during the transition. Diffuse scattering observed by LEED and RHEED above the transition temperature is not observed in teh TED pattern from a thin film.

Low-energy electron point projection microscopy/diffraction study of suspended graphene

NASA Astrophysics Data System (ADS)

Hsu, Wei-Hao; Chang, Wei-Tse; Lin, Chun-Yueh; Chang, Mu-Tung; Hsieh, Chia-Tso; Wang, Chang-Ran; Lee, Wei-Li; Hwang, Ing-Shouh

2017-11-01

In this work, we present our study of suspended graphene with low-energy electrons based on a point projection microscopic/diffractive imaging technique. Both exfoliated and chemical vapor deposition (CVD) graphene samples were studied in an ultra-high vacuum chamber. This method allows imaging of individual adsorbates at the nanometer scale and characterizing graphene layers, graphene lattice orientations, ripples on graphene membranes, etc. We found that long-duration exposure to low-energy electron beams induced aggregation of adsorbates on graphene when the electron dose rate was above a certain level. We also discuss the potential of this technique to conduct coherent diffractive imaging for determining the atomic structures of biological molecules adsorbed on suspended graphene.

Amorphization reaction in thin films of elemental Cu and Y

NASA Astrophysics Data System (ADS)

Johnson, R. W.; Ahn, C. C.; Ratner, E. R.

1989-10-01

Compositionally modulated thin films of Cu and Y were prepared in an ultrahigh-vacuum dc ion-beam deposition chamber. The amorphization reaction was monitored by in situ x-ray-diffraction measurements. Growth of amorphous Cu1-xYx is observed at room temperature with the initial formation of a Cu-rich amorphous phase. Further annealing in the presence of unreacted Y leads to Y enrichment of the amorphous phase. Growth of crystalline CuY is observed for T=469 K. Transmission-electron-microscopy measurements provide real-space imaging of the amorphous interlayer and growth morphology. Models are developed, incorporating metastable interfacial and bulk free-energy diagrams, for the early stage of the amorphization reaction.

Dissociative Recombination of Molecular Ions for Astrochemistry

NASA Astrophysics Data System (ADS)

Novotny, Oldrich; Becker, A.; Buhr, H.; Fleischmann, Andreas; Gamer, Lisa; Geppert, W.; Krantz, C.; Kreckel, H.; Schwalm, D.; Spruck, K.; Wolf, A.; Savin, Daniel Wolf

2014-06-01

Dissociative recombination (DR) of molecular ions is a key chemical process in the cold interstellar medium (ISM). DR affects the composition, charge state, and energy balance of such environments. Astrochemical models of the ISM require reliable total DR cross sections as well as knowledge of the chemical composition of the neutral DR products. We have systematically measured DR for many astrophysically relevant molecular ions utilizing the TSR storage ring at the Max-Planck-Institute for Nuclear Physics (MPIK) in Heidelberg, Germany. We used the merged ion-electron beam technique combined with an energy- and position-sensitive imaging detector and are able to study DR down to plasma temperatures as low as 10 K. The DR count rate is used to obtain an absolute merged beams DR rate coefficient from which we can derive a thermal rate coefficient needed for plasma models. Additionally we determine the masses of the DR products by measuring their kinetic energy in the laboratory reference frame. This allows us to assign particular DR fragmentation channels and to obtain their branching ratios. All this information is particularly important for understanding DR of heteronuclear polyatomic ions. We will present DR results for several ions recently investigated at TSR. A new Cryogenic Storage Ring (CSR) is currently being commissioned at MPIK. With the chamber cooled down to ~10 K and a base pressure better than 10-13 mbar, this setup will allow internal cooling of the stored ions down to their rotational ground states, thus opening a new era in DR experiments. New technological challenges arise due to the ultracold, ultra-high vacuum environment of the CSR and thus the detection techniques used at TSR cannot be easily transferred to CSR. We will present new approaches for DR fragment detection in cryogenic environment. This work is supported in part by NASA and the NSF.

Low-energy electron-induced chemistry of condensed methanol: implications for the interstellar synthesis of prebiotic molecules.

PubMed

Boamah, Mavis D; Sullivan, Kristal K; Shulenberger, Katie E; Soe, ChanMyae M; Jacob, Lisa M; Yhee, Farrah C; Atkinson, Karen E; Boyer, Michael C; Haines, David R; Arumainayagam, Christopher R

2014-01-01

In the interstellar medium, UV photolysis of condensed methanol (CH3OH), contained in ice mantles surrounding dust grains, is thought to be the mechanism that drives the formation of "complex" molecules, such as methyl formate (HCOOCH3), dimethyl ether (CH3OCH3), acetic acid (CH3COOH), and glycolaldehyde (HOCH2CHO). The source of this reaction-initiating UV light is assumed to be local because externally sourced UV radiation cannot penetrate the ice-containing dark, dense molecular clouds. Specifically, exceedingly penetrative high-energy cosmic rays generate secondary electrons within the clouds through molecular ionizations. Hydrogen molecules, present within these dense molecular clouds, are excited in collisions with these secondary electrons. It is the UV light, emitted by these electronically excited hydrogen molecules, that is generally thought to photoprocess interstellar icy grain mantles to generate "complex" molecules. In addition to producing UV light, the large numbers of low-energy (< 20 eV) secondary electrons, produced by cosmic rays, can also directly initiate radiolysis reactions in the condensed phase. The goal of our studies is to understand the low-energy, electron-induced processes that occur when high-energy cosmic rays interact with interstellar ices, in which methanol, a precursor of several prebiotic species, is the most abundant organic species. Using post-irradiation temperature-programmed desorption, we have investigated the radiolysis initiated by low-energy (7 eV and 20 eV) electrons in condensed methanol at - 85 K under ultrahigh vacuum (5 x 10(-10) Torr) conditions. We have identified eleven electron-induced methanol radiolysis products, which include many that have been previously identified as being formed by methanol UV photolysis in the interstellar medium. These experimental results suggest that low-energy, electron-induced condensed phase reactions may contribute to the interstellar synthesis of "complex" molecules previously thought to form exclusively via UV photons.

Characterization of the liquid Li-solid Mo (1 1 0) interface from classical molecular dynamics for plasma-facing applications

DOE PAGES

Vella, Joseph R.; Chen, Mohan; Fürstenberg, Sven; ...

2017-08-11

An understanding of the wetting properties and a characterization of theinterface between liquid lithium (Li) and solid molybdenum (Mo) are relevant to assessing the efficacy of Li as a plasma-facing component in fusion reactors. Here, a new second-nearest neighbor modified embedded-atom method (2NN MEAM) force eld is parameterized to describe the interactions between Li and Mo. The new force eld reproduces several benchmark properties obtained from first-principles quantum mechanics simulations, including binding curves for Li at three different adsorption sites and the corresponding forces on Li atoms adsorbed on the Mo (110) surface. This force field is then used tomore » study the wetting of liquid Li on the (110) surface of Mo and to examine the Li-Mo interface using molecular dynamics simulations. From droplet simulations, we nd that liquid Li tends to completely wet the perfect Mo (110) surface, in contradiction with previous experimental measurements that found non-zero contact angles for liquid Li on a Mo substrate. However, these experiments were not carried out under ultra-high vacuum conditions or with a perfect (110) Mo surface, suggesting that the presence of impurities, such as oxygen, and surface structure play a crucial role in this wetting process. From thin- lm simulations, it is observed that the first layer of Li on the Mo (110) surface has many solid-like properties such as a low mobility and a larger degree of ordering when compared to layers further away from the surface, even at temperatures well above the bulk melting temperature of Li. Our findings are consistent with temperature-programmed desorption experiments.« less

Pathways to Oxygen-Bearing Molecules in the Interstellar Medium and in Planetary Atmospheres: Cyclopropenone (c-C3H2O) and Propynal (HCCCHO)

NASA Astrophysics Data System (ADS)

Zhou, Li; Kaiser, Ralf I.; Gao, Li Gyun; Chang, Agnes H. H.; Liang, Mao-Chang; Yung, Yuk L.

2008-10-01

We investigated the formation of two C3H2O isomers, i.e., cyclopropenone (c-C3H2O) and propynal (HCCCHO), in binary ice mixtures of carbon monoxide (CO) and acetylene (C2H2) at 10 K in an ultrahigh vacuum machine on high-energy electron irradiation. The chemical evolution of the ice samples was followed online and in situ via a Fourier transform infrared spectrometer and a quadrupole mass spectrometer. The temporal profiles of the cyclopropenone and propynal isomers suggest (pseudo-) first-order kinetics. The cyclic structure (c-C3H2O) is formed via an addition of triplet carbon monoxide to ground-state acetylene (or vice versa); propynal (HCCCHO) can be synthesized from a carbon monoxide-acetylene complex via a [HCO...CCH] radical pair inside the matrix cage. These laboratory studies showed for the first time that both C3H2O isomers can be formed in low-temperature ices via nonequilibrium chemistry initiated by energetic electrons as formed in the track of Galactic cosmic ray particles penetrating interstellar icy grains in cold molecular clouds. Our results can explain the hitherto unresolved gas phase abundances of cyclopropenone in star-forming regions via sublimation of c-C3H2O as formed on icy grains in the cold molecular cloud stage. Implications for the heterogeneous oxygen chemistry of Titan and icy terrestrial planets and satellites suggest that the production of oxygen-bearing molecules such as C3H2O may dominate on aerosol particles compared to pure gas phase chemistry.

Characterization of the liquid Li-solid Mo (1 1 0) interface from classical molecular dynamics for plasma-facing applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vella, Joseph R.; Chen, Mohan; Fürstenberg, Sven

An understanding of the wetting properties and a characterization of theinterface between liquid lithium (Li) and solid molybdenum (Mo) are relevant to assessing the efficacy of Li as a plasma-facing component in fusion reactors. Here, a new second-nearest neighbor modified embedded-atom method (2NN MEAM) force eld is parameterized to describe the interactions between Li and Mo. The new force eld reproduces several benchmark properties obtained from first-principles quantum mechanics simulations, including binding curves for Li at three different adsorption sites and the corresponding forces on Li atoms adsorbed on the Mo (110) surface. This force field is then used tomore » study the wetting of liquid Li on the (110) surface of Mo and to examine the Li-Mo interface using molecular dynamics simulations. From droplet simulations, we nd that liquid Li tends to completely wet the perfect Mo (110) surface, in contradiction with previous experimental measurements that found non-zero contact angles for liquid Li on a Mo substrate. However, these experiments were not carried out under ultra-high vacuum conditions or with a perfect (110) Mo surface, suggesting that the presence of impurities, such as oxygen, and surface structure play a crucial role in this wetting process. From thin- lm simulations, it is observed that the first layer of Li on the Mo (110) surface has many solid-like properties such as a low mobility and a larger degree of ordering when compared to layers further away from the surface, even at temperatures well above the bulk melting temperature of Li. Our findings are consistent with temperature-programmed desorption experiments.« less

Long-term stability of Cu surface nanotips

NASA Astrophysics Data System (ADS)

Jansson, V.; Baibuz, E.; Djurabekova, F.

2016-07-01

Sharp nanoscale tips on the metal surfaces of electrodes enhance locally applied electric fields. Strongly enhanced electric fields trigger electron field emission and atom evaporation from the apexes of nanotips. Together, these processes may explain electric discharges in the form of small local arcs observed near metal surfaces in the presence of electric fields, even in ultra-high vacuum conditions. In the present work, we investigate the stability of nanoscale tips by means of computer simulations of surface diffusion processes on copper, the main material used in high-voltage electronics. We study the stability and lifetime of thin copper (Cu) surface nanotips at different temperatures in terms of diffusion processes. For this purpose we have developed a surface kinetic Monte Carlo (KMC) model where the jump processes are described by tabulated precalculated energy barriers. We show that tall surface features with high aspect ratios can be fairly stable at room temperature. However, the stability was found to depend strongly on the temperature: 13 nm nanotips with the major axes in the < 110> crystallographic directions were found to flatten down to half of the original height in less than 100 ns at temperatures close to the melting point, whereas no significant change in the height of these nanotips was observed after 10 {{μ }}{{s}} at room temperature. Moreover, the nanotips built up along the < 110> crystallographic directions were found to be significantly more stable than those oriented in the < 100> or < 111> crystallographic directions. The proposed KMC model has been found to be well-suited for simulating atomic surface processes and was validated against molecular dynamics simulation results via the comparison of the flattening times obtained by both methods. We also note that the KMC simulations were two orders of magnitude computationally faster than the corresponding molecular dynamics calculations.

Characterization of the liquid Li-solid Mo (1 1 0) interface from classical molecular dynamics for plasma-facing applications

NASA Astrophysics Data System (ADS)

Vella, Joseph R.; Chen, Mohan; Fürstenberg, Sven; Stillinger, Frank H.; Carter, Emily A.; Debenedetti, Pablo G.; Panagiotopoulos, Athanassios Z.

2017-11-01

An understanding of the wetting properties and a characterization of the interface between liquid lithium (Li) and solid molybdenum (Mo) are relevant to assessing the efficacy of Li as a plasma-facing component in fusion reactors. In this work, a new second-nearest neighbor modified embedded-atom method (2NN MEAM) force field is parameterized to describe the interactions between Li and Mo. The new force field reproduces several benchmark properties obtained from first-principles quantum mechanics simulations, including binding curves for Li at three different adsorption sites and the corresponding forces on Li atoms adsorbed on the Mo (1 1 0) surface. This force field is then used to study the wetting of liquid Li on the (1 1 0) surface of Mo and to examine the Li-Mo interface using molecular dynamics simulations. From droplet simulations, we find that liquid Li tends to completely wet the perfect Mo (1 1 0) surface, in contradiction with previous experimental measurements that found non-zero contact angles for liquid Li on a Mo substrate. However, these experiments were not carried out under ultra-high vacuum conditions or with a perfect (1 1 0) Mo surface, suggesting that the presence of impurities, such as oxygen, and surface structure play a crucial role in this wetting process. From thin-film simulations, it is observed that the first layer of Li on the Mo (1 1 0) surface has many solid-like properties such as a low mobility and a larger degree of ordering when compared to layers further away from the surface, even at temperatures well above the bulk melting temperature of Li. These findings are consistent with temperature-programmed desorption experiments.

Comparing Ullmann Coupling on Noble Metal Surfaces: On-Surface Polymerization of 1,3,6,8-Tetrabromopyrene on Cu(111) and Au(111).

PubMed

Pham, Tuan Anh; Song, Fei; Nguyen, Manh-Thuong; Li, Zheshen; Studener, Florian; Stöhr, Meike

2016-04-18

The on-surface polymerization of 1,3,6,8-tetrabromopyrene (Br4 Py) on Cu(111) and Au(111) surfaces under ultrahigh vacuum conditions was investigated by a combination of scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Deposition of Br4 Py on Cu(111) held at 300 K resulted in a spontaneous debromination reaction, generating the formation of a branched coordination polymer network stabilized by C-Cu-C bonds. After annealing at 473 K, the C-Cu-C bonds were converted to covalent C-C bonds, leading to the formation of a covalently linked molecular network of short oligomers. In contrast, highly ordered self-assembled two-dimensional (2D) patterns stabilized by both Br-Br halogen and Br-H hydrogen bonds were observed upon deposition of Br4 Py on Au(111) held at 300 K. Subsequent annealing of the sample at 473 K led to a dissociation of the C-Br bonds and the formation of disordered metal-coordinated molecular networks. Further annealing at 573 K resulted in the formation of covalently linked disordered networks. Importantly, we found that the chosen substrate not only plays an important role as catalyst for the Ullmann reaction, but also influences the formation of different types of intermolecular bonds and thus, determines the final polymer network morphology. DFT calculations further support our experimental findings obtained by STM and XPS and add complementary information on the reaction pathway of Br4 Py on the different substrates. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Simultaneous measurement of friction and wear in hip simulators.

PubMed

Haider, Hani; Weisenburger, Joel N; Garvin, Kevin L

2016-05-01

We propose and have evaluated a method to measure hip friction during wear testing on a popular multi-station hip simulator. A 6-degree-of-freedom load cell underneath the specimen sensed forces and torques during implant wear testing of simulated walking. This included internal-external and adduction-abduction rotations which are often neglected during friction testing on pendulum-type machines. Robust mathematical analysis and data processing provided friction estimates in three simultaneous orthogonal rotations, over extended multi-million cycle wear tests. We tested various bearing couples including metal-on-plastic, ceramic-on-plastic, and metal-on-metal material couples. In one test series, new and intentionally scratched CoCrMo 40-mm-diameter femoral heads were tested against conventional ultrahigh-molecular-weight polyethylene, highly cross-linked, and highly cross-linked with vitamin E versions. The scratching significantly increased friction and doubled the wear of all groups. Before scratching, friction levels for the aforementioned plastic groups were 0.056 ± 0.0060, 0.062 ± 0.0080, and 0.070 ± 0.0045, respectively, but after scratching increased to 0.088 ± 0.018, 0.076 ± 0.0066, and 0.082 ± 0.0049, respectively, all statistically significant increases (p = 0.00059, 0.00005, 0.0115, respectively). In another test series of 44-mm femoral head diameter hips, metal-on-plastic hips with conventional ultrahigh-molecular-weight polyethylene showed the lowest friction at 0.045 ± 0.0085, followed by highly cross-linked with 0.046 ± 0.0035 (not significantly different). In a ceramic-on-plastic design with conventional ultrahigh-molecular-weight polyethylene, higher friction 0.079 ± 0.0070 was measured likely due to that ceramic surface being rougher than usual. Metal-on-metal hips were compared without and with a TiN coating, resulting in 0.049 ± 0.014 and 0.097 ± 0.020 friction factors, respectively (statistically significant, p < 0.001), and the coating wore away on all coated hips eventually. Higher friction mostly correlated with higher wear or damage to femoral heads or implant coatings, except for the highly cross-linked wear resistant ultrahigh-molecular-weight polyethylene which had slightly higher friction, confirming the same finding in other independent studies. This type of friction measurements can help screen for clamping and elevated wear of metal-on-metal and resurfacing total hip replacements, surgical malpositioning, and abraded and otherwise damaged surfaces. © IMechE 2016.

Surface science studies of ethene containing model interstellar ices

NASA Astrophysics Data System (ADS)

Puletti, F.; Whelan, M.; Brown, W. A.

2011-05-01

The formation of saturated hydrocarbons in the interstellar medium (ISM) is difficult to explain only by taking into account gas phase reactions. This is mostly due to the fact that carbonium ions only react with H_2 to make unsaturated hydrocarbons, and hence no viable route to saturated hydrocarbons has been postulated to date. It is therefore likely that saturation processes occur via surface reactions that take place on interstellar dust grains. One of the species of interest in this family of reactions is C_2H_4 (ethene) which is an intermediate in several molecular formation routes (e.g. C_2H_2 → C_2H_6). To help to understand some of the surface processes involving ethene, a study of ethene deposited on a dust grain analogue surface (highly oriented pyrolytic graphite) held under ultra-high vacuum at 20 K has been performed. The adsorption and desorption of ethene has been studied both in water-free and water-dominated model interstellar ices. A combination of temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS) have been used to identify the adsorbed and trapped species and to determine the kinetics of the desorption processes. In all cases, ethene is found to physisorb on the carbonaceous surface. As expected water has a very strong influence on the desorption of ethene, as previously observed for other model interstellar ice systems.

Ambient atomic resolution atomic force microscopy with qPlus sensors: Part 1.

PubMed

Wastl, Daniel S

2017-01-01

Atomic force microscopy (AFM) is an enormous tool to observe nature in highest resolution and understand fundamental processes like friction and tribology on the nanoscale. Atomic resolution in highest quality was possible only in well-controlled environments like ultrahigh vacuum (UHV) or controlled buffer environments (liquid conditions) and more specified for long-term high-resolution analysis at low temperatures (∼4 K) in UHV where drift is nearly completely absent. Atomic resolution in these environments is possible and is widely used. However, in uncontrolled environments like air, with all its pollutants and aerosols, unspecified thin liquid films as thin as a single molecular water-layer of 200 pm or thicker condensation films with thicknesses up to hundred nanometer, have been a problem for highest resolution since the invention of the AFM. The goal of true atomic resolution on hydrophilic as well as hydrophobic samples was reached recently. In this manuscript we want to review the concept of ambient AFM with atomic resolution. The reader will be introduced to the phenomenology in ambient conditions and the problems will be explained and analyzed while a method for scan parameter optimization will be explained. Recently developed concepts and techniques how to reach atomic resolution in air and ultra-thin liquid films will be shown and explained in detail, using several examples. Microsc. Res. Tech. 80:50-65, 2017. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Ultra-High Aggregate Bandwidth Two-Dimensional Multiple-Wavelength Diode Laser Arrays

DTIC Science & Technology

1993-12-09

during the growth of the cavity spacer region using the fact that the molecular beam epitaxy growth of GaAs is highly sensitive to the substrate... molecular beam epitaxy (MBE) crystal growth, the GaAs growth rate is highly sensitive to the substrate temperature above 650"C (2], a GaAs/AIGaAs... epitaxial growth technique to make reproducible and repeatable multi-wavelength VCSEL arrays. Our approach to fabricate the spatially graded layer

Tuning the superstructure of ultrahigh-molecular-weight polyethylene/low-molecular-weight polyethylene blend for artificial joint application.

PubMed

Xu, Ling; Chen, Chen; Zhong, Gan-Ji; Lei, Jun; Xu, Jia-Zhuang; Hsiao, Benjamin S; Li, Zhong-Ming

2012-03-01

An easy approach was reported to achieve high mechanical properties of ultrahigh-molecular-weight polyethylene (UHMWPE)-based polyethylene (PE) blend for artificial joint application without the sacrifice of the original excellent wear and fatigue behavior of UHMWPE. The PE blend with desirable fluidity was obtained by melt mixing UHMWPE and low molecular weight polyethylene (LMWPE), and then was processed by a modified injection molding technology-oscillatory shear injection molding (OSIM). Morphological observation of the OSIM PE blend showed LMWPE contained well-defined interlocking shish-kebab self-reinforced superstructure. Addition of a small amount of long chain polyethylene (2 wt %) to LMWPE greatly induced formation of rich shish-kebabs. The ultimate tensile strength considerably increased from 27.6 MPa for conventional compression molded UHMWPE up to 78.4 MPa for OSIM PE blend along the flow direction and up to 33.5 MPa in its transverse direction. The impact strength of OSIM PE blend was increased by 46% and 7% for OSIM PE blend in the direction parallel and vertical to the shear flow, respectively. Wear and fatigue resistance were comparable to conventional compression molded UHMWPE. The superb performance of the OSIM PE blend was originated from formation of rich interlocking shish-kebab superstructure while maintaining unique properties of UHMWPE. The present results suggested the OSIM PE blend has high potential for artificial joint application. © 2012 American Chemical Society

Final report on key comparison APMP.M.P-K3: Absolute pressure measurements in gas from 3 × 10-6 Pa to 9 × 10-4 Pa

NASA Astrophysics Data System (ADS)

Yoshida, H.; Arai, K.; Akimichi, H.; Hong, S. S.; Song, H. W.

2011-01-01

The results of a key comparison of ultra-high vacuum standards at two national metrology institutes (NMIJ/AIST and KRISS) are reported. This bilateral comparison was carried out from May 2010 to October 2010 within the framework of the Asia-Pacific Metrology Programme (APMP) to determine their degrees of equivalence at pressures in the range from 3 × 10-6 Pa to 9 × 10-4 Pa. The pilot institute was NMIJ/AIST. Two spinning rotor gauges and two hot cathode ionization gauges were used as the transfer standards. NMIJ/AIST used two calibration systems: the dynamic expansion system (NMIJ-DES) and two-stage flow-dividing system (NMIJ-TFS). KRISS used the dynamic expansion system. The transfer standards were sufficiently stable to meet the requirements of the comparison compared with those of previous international comparisons owing to some improvements of the protocol and the transfer standards. The ultra-high vacuum standards of NMIJ/AIST and KRISS were found to be equivalent within their claimed uncertainties in the range from 3 × 10-6 Pa to 9 × 10-5 Pa. The NMIJ-DES results, which have smaller uncertainty than NMIJ-TFS, were transferred to the corresponding CCM key comparison, CCM.P-K3, in the range from 3 × 10-6 Pa to 9 × 10-5 Pa and it is shown that the NMIJ values were equivalent to the CCM key comparison reference value within the claimed uncertainties. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Dynamic measurements of the spreading of liquid metals in controlled atmospheres with in situ surface preparation and analysis

NASA Astrophysics Data System (ADS)

Peebles, D. E.; Peebles, H. C.; Ohlhausen, J. A.; Hurst, M. J.

1996-02-01

A specially designed ultrahigh vacuum in situ surface analysis and wetting system has been constructed to study the spreading of liquid metal solders on carefully prepared and well-characterized solid substrates. The system consists of a standard ultrahigh vacuum surface analysis chamber linked to a reaction chamber for wetting or other experiments at pressures up to atmospheric. A sophisticated video system allows real-time monitoring of the spreading of the liquid metal through both side and top views. An infrared imaging system allows accurate remote temperature measurements. Sample surfaces are prepared and spreading experiments performed without intermediate exposure of the surfaces to the contaminating atmospheres. Solder spreading is performed under 50 Torr of highly purified helium gas to allow for adequate thermal coupling between the solder and the substrate. Initial studies have been completed for the spreading of pure tin solder on copper substrates in the absence of any fluxing agent. Three types of copper substrate surfaces were investigated in these experiments: the sputter-cleaned, air-exposed, and the as-received surface. Surface chemical analysis by x-ray photoelectron spectroscopy showed the air-exposed surface to consist of about 3 nm of Cu2O, while the as-received surface consisted of about 8 nm of Cu2O. The sputter-cleaned surface contained less than one monolayer (0.3 nm) of Cu2O. Spreading experiments utilizing a linear temperature ramp show that pure tin solder spreads readily on oxidized copper surfaces at elevated temperatures. The initiation temperature for rapid tin spreading on the as-received copper surface was 325 °C. Decreasing the thickness of the oxide on the surface lowered the observed temperature for the initiation of spreading and increased the rate of spreading. On the sputter-cleaned copper surface, rapid solder spreading was observed immediately upon melting of the solder.

Physical and Tribological Characteristics of Ion-Implanted Diamond Films

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Heidger, S.; Korenyi-Both, A. L.; Jayne, D. T.; Herrera-Fierro, P.; Shogrin, B.; Wilbur, P. J.; Wu, R. L. C.; Garscadden, A.; Barnes, P. N.

1994-01-01

Unidirectional sliding friction experiments were conducted with a natural, polished diamond pin in contact with both as-deposited and carbon-ion-implanted diamond films in ultrahigh vacuum. Diamond films were deposited on silicon, silicon carbide, and silicon nitride by microwave-plasma-assisted chemical vapor deposition. The as-deposited diamond films were impacted with carbon ions at an accelerating energy of 60 keV and a current density of 50 micron A/cm(exp 2) for approximately 6 min, resulting in a dose of 1.2 x 10(exp 17) carbon ions/cm(exp 2). The results indicate that the carbon ion implantation produced a thin surface layer of amorphous, nondiamond carbon. The nondiamond carbon greatly decreased both friction and wear of the diamond films. The coefficients of friction for the carbon-ion-implanted, fine-grain diamond films were less than 0.1, factors of 20 to 30 lower than those for the as-deposited, fine-grain diamond films. The coefficients of friction for the carbon-ion-implanted, coarse-grain diamond films were approximately 0.35, a factor of five lower than those for the as-deposited, coarse-grain diamond films. The wear rates for the carbon-ion-implanted, diamond films were on the order of 10(exp -6) mm(exp 3)/Nm, factors of 30 to 80 lower than that for the as-deposited diamond films, regardless of grain size. The friction of the carbon-ion-implanted diamond films was greatly reduced because the amorphous, nondiamond carbon, which had a low shear strength, was restricted to the surface layers (less than 0.1 micron thick) and because the underlying diamond materials retained their high hardness. In conclusion, the carbon-ion-implanted, fine-grain diamond films can be used effectively as wear resistant, self-lubricating coatings for ceramics, such as silicon nitride and silicon carbide, in ultrahigh vacuum.

New design for a time-of-flight mass spectrometer with a liquid beam laser desorption ion source for the analysis of biomolecules

NASA Astrophysics Data System (ADS)

Charvat, A.; Lugovoj, E.; Faubel, M.; Abel, B.

2004-05-01

We describe a novel liquid beam mass spectrometer, based on a recently discovered nanosecond laser desorption phenomenon, [W. Kleinekofort, J. Avdiev, and B. Brutschy, Int. J. Mass Ion. Processes 152, 135 (1996)] which allows the liquid-to-vacuum transfer, and subsequent mass analysis of pre-existing ions and ionic associates from liquid microjets of aqueous solutions. The goal of our novel technical approach is to establish a system with good mass resolution that implements improvements on critical components that make the system more reliable and easier to operate. For laser desorption pulsed dye-laser difference frequency mixing is used that provides tunable infrared light near the absorption maximum of liquid water around 3 μm. Different types of liquid beam glass nozzles (convergent capillary and aperture plate nozzles) are investigated and characterized. Starting from theoretical considerations of hydrodynamic drag forces on micrometer size droplets in supersonic rarefied gas flows we succeeded in capturing efficiently the liquid beam in a liquid beam recycling trap operating at the vapor pressure of liquid water. For improving the pollution resistance, the liquid jet high vacuum ion source region is spatially separated from the reflectron time-of-flight mass spectrometer (TOF-MS) working behind a gate valve in an ultrahigh vacuum environment. A simple (simulation optimized) ion optics is employed for the ion transfer from the source to the high vacuum region. This new feature is also mostly responsible for the improved mass resolution. With the present tandem-TOF-MS setup a resolution of m/Δm≈1800 for the low and m/Δm≈700 in the high mass region has been obtained for several biomolecules of different mass and complexity (amino acids, insulin, and cytochrome c).

Comparison of the adsorbed conformation of barley lipid transfer protein at the decane-water and vacuum-water interface: a molecular dynamics simulation.

PubMed

Euston, S R; Hughes, P; Naser, Md A; Westacott, R E

2008-05-01

Molecular dynamics simulation is used to model the adsorption of the barley lipid transfer protein (LTP) at the decane-water and vacuum-water interfaces. Adsorption at both surfaces is driven by displacement of water molecules from the interfacial region. LTP adsorbed at the decane surface exhibits significant changes in its tertiary structure, and penetrates a considerable distance into the decane phase. At the vacuum-water interface LTP shows small conformational changes away from its native structure and does not penetrate into the vacuum space. Modification of the conformational stability of LTP by reduction of its four disulphide bonds leads to an increase in conformational entropy of the molecules, which reduces the driving force for adsorption. Evidence for changes in the secondary structure are also observed for native LTP at the decane-water interface and reduced LTP at the vacuum-water interface. In particular, intermittent formation of short (six-residue) regions of beta-sheet is found in these two systems. Formation of interfacial beta-sheet in adsorbed proteins has been observed experimentally, notably in the globular milk protein beta-lactoglobulin and lysozyme.

Fluid Dynamics of Small, Rugged Vacuum Pumps of Viscous-Drag Type

NASA Technical Reports Server (NTRS)

Russell, John M.

2002-01-01

The need to identify spikes in the concentration of hazardous gases during countdowns to space shuttle launches has led Kennedy Space Center to acquire considerable expertise in the design, construction, and operation of special-purpose gas analyzers of mass-spectrometer type. If such devices could be miniaturized so as to fit in a small airborne package or backpack them their potential applications would include integrated vehicle health monitoring in later-generation space shuttles and in hazardous material detection in airports, to name two examples. The bulkiest components of such devices are vacuum pumps, particularly those that function in the low vacuum range. Now some pumps that operate in the high vacuum range (e.g. molecular-drag and turbomolecular pumps) are already small and rugged. The present work aims to determine whether, on physical grounds, one may or may not adopt the molecular-drag principle to the low-vacuum range (in which case viscous-drag principle is the appropriate term). The deliverable of the present effort is the derivation and justification of some key formulas and calculation methods for the preliminary design of a single-spool, spiral-channel viscous-drag pump.

Vacuum MOCVD fabrication of high efficience cells

NASA Technical Reports Server (NTRS)

Partain, L. D.; Fraas, L. M.; Mcleod, P. S.; Cape, J. A.

1985-01-01

Vacuum metal-organic-chemical-vapor-deposition (MOCVD) is a new fabrication process with improved safety and easier scalability due to its metal rather than glass construction and its uniform multiport gas injection system. It uses source materials more efficiently than other methods because the vacuum molecular flow conditions allow the high sticking coefficient reactants to reach the substrates as undeflected molecular beams and the hot chamber walls cause the low sticking coefficient reactants to bounce off the walls and interact with the substrates many times. This high source utilization reduces the materials costs power device and substantially decreases the amounts of toxic materials that must be handled as process effluents. The molecular beams allow precise growth control. With improved source purifications, vacuum MOCVD has provided p GaAs layers with 10-micron minority carrier diffusion lengths and GaAs and GaAsSb solar cells with 20% AMO efficiencies at 59X and 99X sunlight concentration ratios. Mechanical stacking has been identified as the quickest, most direct and logical path to stacked multiple-junction solar cells that perform better than the best single-junction devices. The mechanical stack is configured for immediate use in solar arrays and allows interconnections that improve the system end-of-life performance in space.

FOREWORD: The 4th CCM International Conference on Pressure Metrology from Ultra-High Vacuum to Very High Pressures (10-9 Pa to 109 Pa)

NASA Astrophysics Data System (ADS)

Legras, Jean-Claude; Jousten, Karl; Severn, Ian

2005-12-01

The fourth CCM (Consultative Committee for Mass and related quantities) International Conference on Pressure Metrology from Ultra-High Vacuum to Very High Pressures (10-9 Pa to 109 Pa) was held at the Institute of Physics in London from 19-21 April 2005. The event, which was organized by the Low, Medium and High Pressure working groups of the CCM, was attended by in excess of one hundred participants with representatives from five continents and every regional metrology organization. The purpose of this conference is to review all the work that is devoted to the highest quality of pressure measurement by primary standards as well as the dissemination of the pressure scale. A total of 52 papers were presented orally, and 26 as posters, in sessions that covered the following topics: Latest scientific advances in pressure and vacuum metrology Innovative transfer standards, advanced sensors and new instrument development Primary (top-level) measurement standards International and regional key comparisons New approaches to calibration It is interesting the note that since the third conference in 1999 the pressure range covered has increased by two orders of magnitude to 109 Pa, to take into account more exacting scientific and industrial demands for traceable vacuum measurement. A further feature of the conference was the increased range of instrumentation and techniques used in the realization and potential realization of pressure standards. Seton Bennett, Director of International Metrology at the National Physical Laboratory, opened the conference and Andrew Wallard, Director of the Bureau International des Poids et Mesures (BIPM), gave the keynote address which described the implementation of the mutual recognition arrangement and the resulting removal of metrological barriers to international trade. Many experts have contributed significant amounts of their time to organize the event and to review the submitted papers. Thanks are due to all of these people, particularly Gianfranco Molinar who offered much advice based on experience of organizing the previous conference. Special thanks must also be made to Mitsuru Tanaka, President of the CCM, and Andrew Wallard, Director of the BIPM, for their support of the event. The event was coordinated by Jasmina Bolfek-Radovani, of the Institute of Physics, without whose tireless efforts the event would not have been as successful. The production of this issue of Metrologia would not have been possible without the help and support of its editor, Jeffrey Williams. The National Measurement System Directorate of the Department of Trade and Industry supported the conference and it was sponsored by DH Instruments and BOC Edwards. Additional financial assistance was also received from Chell Instruments Ltd, DH-Budenberg, GE Infrastructure Sensing, Hi-Pro Pressure Products Ltd, Kurt J Lesker Company Ltd and Leybold Vacuum UK Ltd. Finally we would like to thank all of the conference participants who made the event both technically stimulating and enjoyable. By the time the next CCM Pressure conference is held in Berlin in 2011, pressure science and technology will undoubtedly have moved on still further and we may see the culmination of work to realize primary pressure standards by more fundamental methods.

Improving the Molecular Ion Signal Intensity for In Situ Liquid SIMS Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhou, Yufan; Yao, Juan; Ding, Yuanzhao

In situ liquid secondary ion mass spectrometry (SIMS) enabled by system for analysis at the liquid vacuum interface (SALVI) has proven to be a promising new tool to provide molecular information at solid–liquid and liquid–vacuum interfaces. However, the initial data showed that useful signals in positive ion spectra are too weak to be meaningful in most cases. In addition, it is difficult to obtain strong negative molecular ion signals when m/z>200. These two drawbacks have been the biggest obstacle towards practical use of this new analytical approach. In this study, we report that strong and reliable positive and negative molecularmore » signals are achievable after optimizing the SIMS experimental conditions. Four model systems, including a 1,8-diazabicycloundec-7-ene (DBU)-base switchable ionic liquid, a live Shewanella oneidensis biofilm, a hydrated mammalian epithelia cell, and an electrolyte popularly used in Li ion batteries were studied. A signal enhancement of about two orders of magnitude was obtained in comparison with non-optimized conditions. Therefore, molecular ion signal intensity has become very acceptable to use for in situ liquid SIMS to study solid–liquid and liquid–vacuum interfaces.« less

21 CFR 172.828 - Acetylated monoglycerides.

Code of Federal Regulations, 2014 CFR

2014-04-01

... or are authorized by regulation, followed by a molecular distillation or by steam stripping; or (2... molecular distillation, and with the removal by vacuum distillation, if necessary, of the acetic acid...

Argentation chromatography coupled to ultrahigh-resolution mass spectrometry for the separation of a heavy crude oil.

PubMed

Molnárné Guricza, Lilla; Schrader, Wolfgang

2017-02-10

Simplification of highly complex mixtures such as crude oil by using chromatographic methods makes it possible to get more detailed information about the composition of the analyte. Separation by argentation chromatography can be achieved based on the interaction of different strength between the silver ions (Ag + ) immobilized through a spacer on the silica gel surface and the π-bonds of the analytes. Heavy crude oils contain compounds with a high number of heteroatoms (N, O, S) and a high degree of unsaturation thus making them the perfect analyte for argentation chromatography. The direct coupling of argentation chromatography and ultrahigh-resolution mass spectrometry allows to continuously tracking the separation of the many different compounds by retention time and allows sensitive detection on a molecular level. Direct injection of a heavy crude oil into a ultrahigh-resolution mass spectrometer showed components with DBE of up to 25, whereas analytes with DBE of up to 35 could be detected only after separation with argentation chromatography. The reduced complexity achieved by the separation helps increasing the information depth. Copyright © 2016. Published by Elsevier B.V.

The integrity of welded interfaces in ultra-high molecular weight polyethylene: Part 2--interface toughness.

PubMed

Haughie, David W; Buckley, C Paul; Wu, Junjie

2006-07-01

In Part 2 of a study of welding of ultra-high molecular weight polyethylene (UHMWPE), experiments were conducted to measure the interfacial fracture energy of butt welds, for various welding times and temperatures above the melting point. Their toughness was investigated at 37 degrees C in terms of their fracture energy, obtained by adapting the essential work of fracture (EWF) method. However, a proportion of the welded samples (generally decreasing with increasing welding time or temperature) failed in dual ductile/brittle mode, hence invalidating the EWF test. Even those failing in purely ductile mode showed a measurable interface work of fracture only for the highest weld temperature and time: 188 degrees C and 90 min. Results from the model presented in Part 1 show that this corresponds to the maximum reptated molecular weight reaching close to the peak in the molar mass distribution. Hence this work provides the first experimental evidence that the slow rate of self-diffusion in UHMWPE leads to welded interfaces acting as low-toughness crack paths. Since such interfaces exist around every powder particle in processed UHMWPE this problem cannot be avoided, and it must be accommodated in design of hip and knee bearing surfaces made from this polymer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ohashi, Haruhiko, E-mail: hohashi@spring8.or.jp; Senba, Yasunori; Yumoto, Hirokatsu

We studied typical forms of contamination on X-ray mirrors that cause degradation of beam quality, investigated techniques to remove the contaminants, and propose methods to eliminate the sources of the contamination. The total amount of carbon-containing substances on various materials in the vicinity of a mirror was measured by thermal desorption-gas chromatography/mass spectrometry and thermal desorption spectroscopy. It was found that cleanliness and ultra-high vacuum techniques are required to produce the contamination-free surfaces that are essential for the propagation of high-quality X-ray beams. The reduction of carbonaceous residue adsorbed on the surfaces, and absorbed into the bulk, of the materialsmore » in the vicinity of the mirrors is a key step toward achieving contamination-free X-ray optics.« less

Revealing the 1 nm/s extensibility of nanoscale amorphous carbon in a scanning electron microscope.

PubMed

Zhang, Wei

2013-01-01

In an ultra-high vacuum scanning electron microscope, the edged branches of amorphous carbon film (∼10 nm thickness) can be continuously extended with an eye-identifying speed (on the order of ∼1 nm/s) under electron beam. Such unusual mobility of amorphous carbon may be associated with deformation promoted by the electric field, which resulted from an inner secondary electron potential difference from the main trunk of carbon film to the tip end of branches under electron beam. This result demonstrates importance of applying electrical effects to modify properties of carbon materials. It may have positive implications to explore some amorphous carbon as electron field emission device. © Wiley Periodicals, Inc.

A convenient method for large-scale STM mapping of freestanding atomically thin conductive membranes

NASA Astrophysics Data System (ADS)

Uder, B.; Hartmann, U.

2017-06-01

Two-dimensional atomically flat sheets with a high flexibility are very attractive as ultrathin membranes but are also inherently challenging for microscopic investigations. We report on a method using Scanning Tunneling Microscopy (STM) under ultra-high vacuum conditions for large-scale mapping of several-micrometer-sized freestanding single and multilayer graphene membranes. This is achieved by operating the STM at unusual parameters. We found that large-scale scanning on atomically thin membranes delivers valuable results using very high tip-scan speeds combined with high feedback-loop gain and low tunneling currents. The method ultimately relies on the particular behavior of the freestanding membrane in the STM which is much different from that of a solid substrate.

Surface electronic structure of SmB6(111)

NASA Astrophysics Data System (ADS)

Ohtsubo, Yoshiyuki; Hagiwara, Kenta; Wang, Chengwei; Yukawa, Ryu; Horiba, Koji; Kumigashira, Hiroshi; Hirano, Wataru; Iga, Fumitoshi; Kimura, Shin-ichi

2018-05-01

Samarium hexaboride (SmB6) is the most extensively studied candidate of topological Kondo insulators. To clarify the topological origin of metallic surface states observed on the SmB6(001) surfaces, we studied the surface electronic structure of SmB6 on the other surface orientation, SmB6(111). Although the SmB6(111) surface cannot be obtained by cleaving, we successfully obtained the well-defined clean surface by high-temperature annealing of the mechanically polished single crystal of SmB6(111) in an ultra-high vacuum. The valence band spectra obtained by photoelectron spectroscopy with the bulk and surface-sensitive incident photon energies imply that the surface is covered with B6 cluster without Sm atoms.

Deuterium microbomb rocket propulsion

NASA Astrophysics Data System (ADS)

Winterberg, F.

2010-01-01

Large scale manned space flight within the solar system is still confronted with the solution of two problems: (1) A propulsion system to transport large payloads with short transit times between different planetary orbits. (2) A cost effective lifting of large payloads into earth orbit. For the solution of the first problem a deuterium fusion bomb propulsion system is proposed where a thermonuclear detonation wave is ignited in a small cylindrical assembly of deuterium with a gigavolt-multimegaampere proton beam, drawn from the magnetically insulated spacecraft acting in the ultrahigh vacuum of space as a gigavolt capacitor. For the solution of the second problem, the ignition is done by argon ion lasers driven by high explosives, with the lasers destroyed in the fusion explosion and becoming part of the exhaust.

Surface Design and Engineering Toward Wear-Resistant, Self-Lubricant Diamond Films and Coatings. Chapter 10

NASA Technical Reports Server (NTRS)

Miyoshi, Kazuhisa

1999-01-01

This chapter describes three studies on the surface design, surface engineering, and tribology of chemical-vapor-deposited (CVD) diamond films and coatings toward wear-resistant, self-lubricating diamond films and coatings. Friction mechanisms and solid lubrication mechanisms of CVD diamond are stated. Effects of an amorphous hydrogenated carbon on CVD diamond, an amorphous, nondiamond carbon surface layer formed on CVD diamond by carbon and nitrogen ion implantation, and a materials combination of cubic boron nitride and CVD diamond on the adhesion, friction, and wear behaviors of CVD diamond in ultrahigh vacuum are described. How surface modification and the selected materials couple improved the tribological functionality of coatings, giving low coefficient of friction and good wear resistance, is explained.

Materials processing in space programs tasks. [NASA research tasks

NASA Technical Reports Server (NTRS)

Pentecost, E.

1981-01-01

Active research tasks as of the end of fiscal year 1981 of the materials processing in space program, NASA Office of Space and Terrestrial Applications are summarized to provide an overview of the program scope for managers and scientists in industry, university, and government communities. The program, its history, strategy, and overall goal are described the organizational structures and people involved are identified and a list of recent publications is given for each research task. Four categories: Crystal Growth; Solidification of Metals, Alloys, and Composites; Fluids, Transports, and Chemical Processes, and Ultrahigh Vacuum and Containerless Processing Technologies are used to group the tasks. Some tasks are placed in more than one category to insure complete coverage of each category.

In situ focus characterization by ablation technique to enable optics alignment at an XUV FEL source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gerasimova, N.; Dziarzhytski, S.; Weigelt, H.

2013-06-15

In situ focus characterization is demonstrated by working at an extreme ultraviolet (XUV) free-electron laser source using ablation technique. Design of the instrument reported here allows reaching a few micrometres resolution along with keeping the ultrahigh vacuum conditions and ensures high-contrast visibility of ablative imprints on optically transparent samples, e.g., PMMA. This enables on-line monitoring of the beam profile changes and thus makes possible in situ alignment of the XUV focusing optics. A good agreement between focal characterizations retrieved from in situ inspection of ablative imprints contours and from well-established accurate ex situ analysis with Nomarski microscope has been observedmore » for a typical micro-focus experiment.« less

Note: Mechanical in situ exfoliation of van der Waals materials

NASA Astrophysics Data System (ADS)

Pásztor, Á.; Scarfato, A.; Renner, Ch.

2017-07-01

Exfoliation, namely, the peeling of layered materials down to a single unit-cell thin foil, opens promising avenues to fabricate novel electronic materials. New properties and original functionalities emerge in the single and few layer configurations of a number of layered compounds, in particular in transition metal dichalcogenides. However, many of these thin exfoliated materials are very sensitive to ambient conditions impeding the exploration of this new and fascinating parameter space. Here we describe a method of mechanical exfoliation in ultra-high vacuum (UHV). This technique is easily adaptable to any UHV system and allows preparing and studying air sensitive nanoflakes in situ. We present the basic design and proof-of-concept scanning tunneling microscopy imaging of VSe2 nanoflakes.

Well-Ordered In Adatoms at the In 2 O 3 ( 111 ) Surface Created by Fe Deposition

DOE PAGES

Wagner, Margareta; Lackner, Peter; Seiler, Steffen; ...

2016-11-11

Metal deposition on oxide surfaces usually results in adatoms, clusters, or islands of the deposited material, where defects in the surface often act as nucleation centers. An alternate configuration is reported. Afterwards the vapor deposition of Fe on the In 2O 3(111) surface at room temperature, ordered adatoms are observed with scanning tunneling microscopy (STM). These are identical to the In adatoms that form when the sample is reduced by heating in ultrahigh vacuum. Our density functional theory (DFT) calculations confirm that Fe interchanges with In in the topmost layer, pushing the excess In atoms to the surface where theymore » arrange as a well-ordered adatom array.« less

Cooperative growth phenomena in silicon/germanium low-temperature epitaxy

NASA Astrophysics Data System (ADS)

Meyerson, Bernard S.; Uram, Kevin J.; LeGoues, Francoise K.

1988-12-01

A series of Si:Ge alloys and structures has been prepared by ultrahigh-vacuum chemical vapor deposition. Alloys of composition 0≤Ge/Si≤0.20 are readily deposited at T=550 °C. Commensurate, defect-free strained layers are deposited up to a critical thickness, whereupon the accumulated stress in the films is accommodated by the formation of dislocation networks in the substrate wafers. A cooperative growth phenomenon is observed where the addition of 10% germane to the gaseous deposition source accelerates silane's heterogeneous reaction rate by a factor of 25. A model is proposed where Ge acts as a desorption center for mobile hydrogen adatoms on the Si[100] surface, accelerating heterogeneous silane pyrolysis by the enhanced availability of chemisorption sites.