35 Matching Results

Search Results

Advanced search parameters have been applied.

Emission of secondary particles from metals and insulators at impact of slow highly charged ions

Description: Emission of secondary electrons and ions from clean Au, CxHy-Au, and SiO{sub 2} surfaces at impact of slow (v{approx}0.3 v{sub Bohr}) ions were measured as function of incident ion charge for 1+{le}q{le}75+. Electron yields from thermal SiO{sub 2} films (150 mm on Si) were found to be lower than those from the other two for q>3+. Yields of negative secondary ions from SiO{sub 2} and CxHy-Au were recorded in parallel with electron emission data and exhibit a q{sub 4} dependency on incident ion charge. Direct comparison of collisional and electronic contributions to secondary ion production from SiO{sub 2} films using a beam of charge state equilibrated Xe (at 2.75 keV/u) shows positive and negative secondary ion yield increases with incident ion charge of >400. Results are discussed in relation to key signatures of electronic sputtering by Coulomb explosions.
Date: October 31, 1996
Creator: Schenkel, T.
Partner: UNT Libraries Government Documents Department

Stark tuning of donor electron spins in silicon

Description: We report Stark shift measurements for 121Sb donor electronspins in silicon using pulsed electron spin resonance. Interdigitatedmetal gates on top of a Sb-implanted 28Si epi-layer are used to applyelectric fields. Two Stark effects are resolved: a decrease of thehyperfine coupling between electron and nuclear spins of the donor and adecrease in electron Zeeman g-factor. The hyperfine term prevails atX-band magnetic fields of 0.35T, while the g-factor term is expected todominate at higher magnetic fields. A significant linear Stark effect isalso resolved presumably arising from strain.
Date: March 12, 2006
Creator: Bradbury, F.R.; Tyryshkin, A.M.; Sabouret, G.; Bokor, J.; Schenkel, T. & Lyon, S.A.
Partner: UNT Libraries Government Documents Department

Electron emission and defect formation in the interaction of slow,highly charged ions with diamond surfaces

Description: We report on electron emission and defect formation in theinteraction between slow (v~;0.3 vBohr) highly charged ions (SHCI) withinsulating (type IIa) and semiconducting (type IIb) diamonds. Electronemission induced by 31Pq+ (q=5 to 13), and 136Xeq+ (q=34 to 44) withkinetic energies of 9 kVxq increase linearly with the ion charge states,reaching over 100 electrons per ion for high xenon charge states withoutsurface passivation of the diamond with hydrogen. Yields from bothdiamond types are up to a factor of two higher then from reference metalsurfaces. Crater like defects with diameters of 25 to 40 nm are formed bythe impact of single Xe44+ ions. High secondary electron yields andsingle ion induced defects enable the formation of single dopant arrayson diamond surfaces.
Date: May 31, 2006
Creator: Sideras-Haddad, E.; Shrivastava, S.; Rebuli, D.B.; Persaud, A.; Schneider, D.H. & Schenkel, T.
Partner: UNT Libraries Government Documents Department

Integration of Ion Implantation with Scanning ProbeAlignment

Description: We describe a scanning probe instrument which integrates ion beams with imaging and alignment functions of a piezo resistive scanning probe in high vacuum. Energetic ions (1 to a few hundred keV) are transported through holes in scanning probe tips [1]. Holes and imaging tips are formed by Focused Ion Beam (FIB) drilling and ion beam assisted thin film deposition. Transport of single ions can be monitored through detection of secondary electrons from highly charged dopant ions (e. g., Bi{sup 45+}) enabling single atom device formation. Fig. 1 shows SEM images of a scanning probe tip formed by ion beam assisted Pt deposition in a dual beam FIB. Ion beam collimating apertures are drilled through the silicon cantilever with a thickness of 5 {micro}m. Aspect ratio limitations preclude the direct drilling of holes with diameters well below 1 {micro}m, and smaller hole diameters are achieved through local thin film deposition [2]. The hole in Fig. 1 was reduced from 2 {micro}m to a residual opening of about 300 nm. Fig. 2 shows an in situ scanning probe image of an alignment dot pattern taken with the tip from Fig. 1. Transport of energetic ions through the aperture in the scanning probe tip allows formation of arbitrary implant patterns. In the example shown in Fig. 2 (right), a 30 nm thick PMMA resist layer on silicon was exposed to 7 keV Ar{sup 2+} ions with an equivalent dose of 10{sup 14} ions/cm{sup 2} to form the LBL logo. An exciting goal of this approach is the placement of single dopant ions into precise locations for integration of single atom devices, such as donor spin based quantum computers [3, 4]. In Fig. 3, we show a section of a micron size dot area exposed to a low dose (10{sup 11}/cm{sup 2}) of ...
Date: March 1, 2005
Creator: Persaud, A.; Rangelow, I.W. & Schenkel, T.
Partner: UNT Libraries Government Documents Department

Research and Development of H Ion Source and LEBT for a Kaon-neutrino Factory

Description: A baseline H{sup -} ion source and low energy beam transport system (LEBT) have been identified for Project X. The filament-discharge H{sup -} ion source has been fabricated by D-Pace, Inc. and is now in operation at LBNL. The source is capable of delivering over 10mA of H{sup -} beam in cw operation with normalized 4rms emittances less than 0.7 {pi} mm mrad. A two-solenoid magnetic lens LEBT system has been design. The design has been validated with simulations of beam transport for 5 mA 30 keV H- beams using various simulation codes.
Date: November 23, 2011
Creator: Ji, Q.; Staples, J.; Schenkel, T. & Li, D.
Partner: UNT Libraries Government Documents Department

Super TOF secondary ion mass spectroscopy using very highly charged primary ions up to Th{sup 70+}

Description: The LLNL Electron Beam Ion Trap (EBIT) has made low emittance beams of slow highly charged ions available for ion-solid interaction studies. Such interactions feature the dominance of electronic over collisional effects, and the shock waves generated by the ionized target atoms can desorb large numbers of large molecular species from the surface. This paper presents the first systematic study of the sputtering process due to the incidence of slow very highly charged ions; Th{sup 70+} ions are extracted from EBIT at 7 keV{sup *}q and directed onto thin SiO{sub 2} films on Si. Results suggest secondary ion yields of up to 25 per incident ion for Th{sup 70+} (secondary ion yield is increased over that for singly or moderately charged ions). Correlations of the negative, positive, and negative cluster ion yields show promise for application of highly charged ion induced sputtering for enhanced sensitivity and quantitative (absolute) SIMS analysis of deep submicron scale surface layers and polymeric and biomolecular material analysis.
Date: October 1, 1995
Creator: Briere, M.A.; Schenkel, T. & Schneider, D.
Partner: UNT Libraries Government Documents Department

Electronic sputtering and desorption effects in TOF-SIMS studies using slow highly charged ions like Au{sup 69+}

Description: Secondary ion yields from highly oriented pyrolytic graphite (HOPG) and SiO{sub 2} (native oxide on float zone silicon) targets at impact of slow (v {approx} 0.3 v{sub bohr}) highly charged ions have been measured by Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). A direct comparison of collisional and electronic effects in secondary ion production using a beam of charge state equilibrated 300 keV Xe{sup 1+} shows a secondary ion yield increase with incident ion charge of {>=}100.
Date: September 1, 1996
Creator: Schenkel, T.; Briere, M.A.; Schmidt-Boecking, H.; Bethge, K. & Schneider, D.
Partner: UNT Libraries Government Documents Department

Non-equilibrium energy loss for very highly charged ions in insulators

Description: The energy loss of 144 keV Ar{sup +16} ions on a bilayer structure of C-CaF{sub 2} has been measured. An asymmetry in the results is found depending on which layer is passed by the ion first: the energy loss is about four times larger when the CaF{sub 2} layer is traversed by the ion first. We interpret this as an indication of the existence of a nonequilibrium charge state of the Ar ions inside the solid in the case of the insulator.
Date: December 1996
Creator: Briere, M. A.; Schenkel, T.; Bauer, P. & Amau, A.
Partner: UNT Libraries Government Documents Department

Surface charge compensation for a highly charged Ion emissionmicroscope

Description: A surface charge compensation electron flood gun has been added to the Lawrence Livermore National Laboratory (LLNL) highly charged ion (HCI) emission microscope. HCI surface interaction results in a significant charge residue being left on the surface of insulators and semiconductors. This residual charge causes undesirable aberrations in the microscope images and a reduction of the Time-Of-Flight (TOF) mass resolution when studying the surfaces of insulators and semiconductors. The benefits and problems associated with HCI microscopy and recent results of the electron flood gun enhanced HCI microscope are discussed.
Date: April 1, 2003
Creator: McDonald, J.W.; Hamza, A.V.; Newman, M.W.; Holder, J.P.; Schneider, D.H.G. & Schenkel, T.
Partner: UNT Libraries Government Documents Department

Electron transport through single carbon nanotubes

Description: We report on the transport of energetic electrons through single, well aligned multi-wall carbon nanotubes (CNT). Embedding of CNTs in a protective carbon fiber coating enables the application of focused ion beam based sample preparation techniques for the non-destructive isolation and alignment of individual tubes. Aligned tubes with lengths of 0.7 to 3 mu m allow transport of 300 keV electrons in a transmission electron microscope through their hollow cores at zero degree incident angles and for a misalignment of up to 1 degree.
Date: August 1, 2007
Creator: Schenkel, Thomas; Chai, G.; Heinrich, H.; Chow, L. & Schenkel, T.
Partner: UNT Libraries Government Documents Department

Towards quantum information processing with impurity spins insilicon

Description: The finding of algorithms for factoring and data base search that promise substantially increased computational power, as well as the expectation for efficient simulation of quantum systems have spawned an intense interest in the realization of quantum information processors [1]. Solid state implementations of quantum computers scaled to >1000 quantum bits ('qubits') promise to revolutionize information technology, but requirements with regard to sources of decoherence in solid state environments are sobering. Here, we briefly review basic approaches to impurity spin based qubits and present progress in our effort to form prototype qubit test structures. Since Kane's bold silicon based spin qubit proposal was first published in 1998 [2], several groups have taken up the challenge of fabricating elementary building blocks [3-5], and several exciting variations of single donor qubit schemes have emerged [6]. Single donor atoms, e. g. {sup 31}P, are 'natural quantum dots' in a silicon matrix, and the spins of electrons and nuclei of individual donor atoms are attractive two level systems for encoding of quantum information. The coupling to the solid state environment is weak, so that decoherence times are long (hours for nuclear spins, and {approx}60 ms for electron spins of isolated P atoms in silicon [7]), while control over individual spins for one qubit operations becomes possible when individual qubits are aligned to electrodes that allow shifting of electron spin resonances in global magnetic fields by application of control voltages. Two qubit operations require an interaction that couples, and entangles qubits. The exchange interaction, J, is a prime candidate for mediation of two qubit operations, since it can be turned on and off by variation of the wave function overlap between neighboring qubits, and coherent manipulation of quantum information with the exchange interaction alone has been shown to be universal [8]. However, detailed band structure ...
Date: March 1, 2004
Creator: Schenkel, T.; Liddle, J.A.; Bokor, J.; Rangelow, I.W.; Park,S.J. & Persaud, A.
Partner: UNT Libraries Government Documents Department

Novel Approaches to Surface Analysis and Materials Engineering Using Highly Charged Ions

Description: Complex problems in materials science require very sensitive, high spatial resolution (< 100 nm) determination of chemical (molecular) structures in near-surface volumes. Slow, highly charged ions (HCIs) provide a new, unique tool for probing chemical structure on a nanometer scale. The authors have explored the potential of these new highly charged ion based techniques in studies of materials with programmatic significance such as high explosives and actinide surfaces. Specifically the are studying HCI based surface analysis techniques (such as secondary ion mass spectrometry, SIMS) that are capable of achieving sensitivity of less than 10{sup 9} atoms/cm{sup 2}. In addition, this technique can determine chemical structure and hydrogen concentration. These attributes make this technique especially important to Laboratory missions in enhanced surveillance and nonproliferation. The unique advantage of HCIs over singly charged ions is the extreme energy density that is deposited into a nanometer-sized near-surface volume at the impact of a single HCI. For example, a Au{sup 69+} ion deposits about 0.5 MJ/cm{sup 3}. This high energy density causes the emission of a large number of secondary particles (electrons, ions, neutral atoms, and clusters) from surfaces. The emitted particles act as probes of the energy dissipation mechanism, and their yields are of technological significance. The HCI-emission microscope concept they developed uniquely combines all three aspects, high spatial resolution with highly sensitive compositional analysis and chemical structure determination. The experiments have shown that individual HCI impacts lead to copious electron emission, over 200 electrons per incident highly charged ion. In addition, highly charged ion induced secondary ion mass spectrometry (HCI-SIMS) provides considerably more information per ion impact than conventional SIMS. Combining these two phenomena provides a unique tool to study important materials issues necessary for the laboratory to accomplish its missions.
Date: February 2, 2000
Creator: Hamza, A.; Schenkel, T.; Barnes, A. & Schneider, D.
Partner: UNT Libraries Government Documents Department

Electrically detected magnetic resonance in a W-band microwave cavity

Description: We describe a low-temperature sample probe for the electrical detection of magnetic resonance in a resonant W-band (94 GHz) microwave cavity. The advantages of this approach are demonstrated by experiments on silicon field-effect transistors. A comparison with conventional low-frequency measurements at X-band (9.7 GHz) on the same devices reveals an up to 100-fold enhancement of the signal intensity. In addition, resonance lines that are unresolved at X-band are clearly separated in the W-band measurements. Electrically detected magnetic resonance at high magnetic fields and high microwave frequencies is therefore a very sensitive technique for studying electron spins with an enhanced spectral resolution and sensitivity.
Date: January 14, 2011
Creator: Lang, V.; Lo, C. C.; George, R. E.; Lyon, S. A.; Bokor, J.; Schenkel, T. et al.
Partner: UNT Libraries Government Documents Department

Electrically Detected Magnetic Resonance of Neutral Donors Interacting with a Two-Dimensional Electron Gas

Description: We have measured the electrically detected magnetic resonance of donor-doped silicon field-effect transistors in resonant X- (9.7 GHz) and W-band (94 GHz) microwave cavities. The two-dimensional electron gas (2DEG) resonance signal increases by two orders of magnitude from X- to W-band, while the donor resonance signals are enhanced by over one order of magnitude. Bolometric effects and spin-dependent scattering are inconsistent with the observations. We propose that polarization transfer from the donor to the 2DEG is the main mechanism giving rise to the spin resonance signals.
Date: April 20, 2011
Creator: Lo, C. C.; Lang, V.; George, R. E.; Morton, J. J. L.; Tyryshkin, A. M.; Lyon, A. et al.
Partner: UNT Libraries Government Documents Department

Ion Implantation with Scanning Probe Alignment

Description: We describe a scanning probe instrument which integrates ion beams with the imaging and alignment function of a piezo-resistive scanning probe in high vacuum. The beam passes through several apertures and is finally collimated by a hole in the cantilever of the scanning probe. The ion beam spot size is limited by the size of the last aperture. Highly charged ions are used to show hits of single ions in resist, and we discuss the issues for implantation of single ions.
Date: July 12, 2005
Creator: Persaud, A.; Liddle, J.A.; Schenkel, T.; Bokor, J.; Ivanov, Tzv. & Rangelow, I.W.
Partner: UNT Libraries Government Documents Department

Possible Diamond-Like Nanoscale Structures Induced by Slow Highly-Charged Ions on Graphite (HOPG)

Description: The interaction between slow highly-charged ions (SHCI) of different charge states from an electron-beam ion trap and highly oriented pyrolytic graphite (HOPG) surfaces is studied in terms of modification of electronic states at single-ion impact nanosizeareas. Results are presented from AFM/STM analysis of the induced-surface topological features combined with Raman spectroscopy. I-V characteristics for a number of different impact regions were measured with STM and the results argue for possible formation of diamond-like nanoscale structures at the impact sites.
Date: January 6, 2009
Creator: Sideras-Haddad, E.; Schenkel, T.; Shrivastava, S.; Makgato, T.; Batra, A.; Weis, C. D. et al.
Partner: UNT Libraries Government Documents Department

Critical issues in the formation of quantum computer test structures by ion implantation

Description: The formation of quantum computer test structures in silicon by ion implantation enables the characterization of spin readout mechanisms with ensembles of dopant atoms and the development of single atom devices. We briefly review recent results in the characterization of spin dependent transport and single ion doping and then discuss the diffusion and segregation behaviour of phosphorus, antimony and bismuth ions from low fluence, low energy implantations as characterized through depth profiling by secondary ion mass spectrometry (SIMS). Both phosphorus and bismuth are found to segregate to the SiO2/Si interface during activation anneals, while antimony diffusion is found to be minimal. An effect of the ion charge state on the range of antimony ions, 121Sb25+, in SiO2/Si is also discussed.
Date: April 6, 2009
Creator: Schenkel, T.; Lo, C. C.; Weis, C. D.; Schuh, A.; Persaud, A. & Bokor, J.
Partner: UNT Libraries Government Documents Department

Detection of low energy single ion impacts in micron scaletransistors at room temperature

Description: We report the detection of single ion impacts throughmonitoring of changes in the source-drain currents of field effecttransistors (FET) at room temperature. Implant apertures are formed inthe interlayer dielectrics and gate electrodes of planar, micro-scaleFETs by electron beam assisted etching. FET currents increase due to thegeneration of positively charged defects in gate oxides when ions(121Sb12+, 14+, Xe6+; 50 to 70 keV) impinge into channel regions. Implantdamage is repaired by rapid thermal annealing, enabling iterative cyclesof device doping and electrical characterization for development ofsingle atom devices and studies of dopant fluctuationeffects.
Date: October 15, 2007
Creator: Batra, A.; Weis, C.D.; Reijonen, J.; Persaud, A.; Schenkel, T.; Cabrini, S. et al.
Partner: UNT Libraries Government Documents Department

Beam measurements on the H- source and Low Energy Beam Transport system for the Spallation Neutron Source

Description: The ion source and Low Energy Beam Transport section of the front-end systems presently being built by Berkeley Lab are required to provide 50 mA of H - beam current at 6% duty factor (1 ms pulses at 60 Hz) with a normalized rms emittance of less than 0.20 p-mm-mrad. Experimental results, including emittance, chopping, and steering measurements, on the performance of the ion source and LEBT system operated at the demanded beam parameters will be discussed.
Date: September 1, 2001
Creator: Thomae, R.; Gough, R.; Keller, R.; Leung, K.N.; Schenkel, T.; Aleksandrov, A. et al.
Partner: UNT Libraries Government Documents Department

Plasma ignition schemes for the SNS radio-frequency driven H- source

Description: The H{sup -} ion source for the Spallation Neutron Source (SNS) is a cesiated, radio-frequency driven (2 MHz) multicusp volume source which operates at a duty cycle of 6% (1 ms pulses and 60 Hz). In pulsed RF driven plasma sources, ignition of the plasma affects the stability of source operation and the antenna lifetime. We are reporting on investigations of different ignition schemes, based on secondary electron generation in the plasma chamber by UV light, a hot filament, a low power RF plasma (cw, 13.56 MHz), as well as source operation solely with the high power (40 kW) 2 MHz RF. We find that the dual frequency, single antenna scheme is most attractive for the operating conditions of the SNS H{sup -} source.
Date: September 6, 2001
Creator: Schenkel, T.; Staples, J.W.; Thomae, W.; Reijonen, J.; Gough, R.A.; Leung, K.N. et al.
Partner: UNT Libraries Government Documents Department

Sample method for formation of nanometer scale holes in membranes

Description: When nanometer scale holes (diameters of 50 to a few hundred nm) are imaged in a scanning electron microscope (SEM) at pressures in the 10{sup -5} to 10{sup -6} torr range, hydrocarbon deposits built up and result in the closing of holes within minutes of imaging. Additionally, electron beam deposition of material from a gas source allows the closing of holes with films of platinum or TEOS oxide. In an instrument equipped both with a focused ion beam (FIB), and an SEM, holes can be formed and then covered with a thin film to form nanopores with controlled openings, ranging down to only a few nanometers.
Date: February 24, 2003
Creator: Schenkel, T.; Stach, E.A.; Radmilovic, V.; Park, S.-J. & Persaud, A.
Partner: UNT Libraries Government Documents Department