scholarly journals Tunnel Contacts for Spin Injection into Silicon: The Si-Co Interface with and without a MgO Tunnel Barrier—A Study by High-Resolution Rutherford Backscattering

2012 ◽  
Vol 2012 ◽  
pp. 1-13 ◽  
Author(s):  
S. P. Dash ◽  
D. Goll ◽  
P. Kopold ◽  
H. D. Carstanjen
Keyword(s):  
High Resolution ◽  
Room Temperature ◽  
Spin Injection ◽  
Schottky Contact ◽  
Tunnel Barrier ◽  
Si Substrate ◽  
High Crystalline Quality ◽  
Tunnel Barriers ◽  
Interface Structures

In order to obtain high spin injection efficiency, a ferromagnet-semiconducor Schottky contact must be of high crystalline quality. This is particularly important in the case of ferromagnet-silicon interfaces, since these elements tend to mix and form silicides. In this study Co-Si (100) interfaces were prepared in three different ways: by evaporation at room temperature, low temperature (), and with Sb as surfactant, and their interface structures were analyzed by high-resolution RBS (HRBS). In all cases more or less strong in-diffusion of Co with subsequent silicide formation was observed. In order to prevent the mixing of Co and Si, ultra thin MgO tunnel barriers were introduced in-between them. In situ HRBS characterization confirms that the MgO films were very uniform and prevented the mixing of the Si substrate with deposited Co and Fe films effectively, even at .

scholarly journals Reduction of charge offset drift using plasma oxidized aluminum in SETs

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Yanxue Hong ◽  
Ryan Stein ◽  
M. D. Stewart ◽  
Neil M. Zimmerman ◽  
J. M. Pomeroy
Keyword(s):  
High Vacuum ◽  
Ultra High Vacuum ◽  
Tunnel Barrier ◽  
Plasma Oxidation ◽  
Single Electron Transistors ◽  
Tunnel Barriers ◽  
Close Proximity ◽  
Electron Transistors ◽  
Charge Defect

Abstract Aluminum oxide ($${\text {AlO}}_x$$ AlO x )-based single-electron transistors (SETs) fabricated in ultra-high vacuum (UHV) chambers using in situ plasma oxidation show excellent stabilities over more than a week, enabling applications as tunnel barriers, capacitor dielectrics or gate insulators in close proximity to qubit devices. Historically, $${\text {AlO}}_x$$ AlO x -based SETs exhibit time instabilities due to charge defect rearrangements and defects in $${\text {AlO}}_x$$ AlO x often dominate the loss mechanisms in superconducting quantum computation. To characterize the charge offset stability of our $${\text {AlO}}_x$$ AlO x -based devices, we fabricate SETs with sub-1 e charge sensitivity and utilize charge offset drift measurements (measuring voltage shifts in the SET control curve). The charge offset drift ($$\Delta {Q_0}$$ Δ Q 0 ) measured from the plasma oxidized $${\text {AlO}}_x$$ AlO x SETs in this work is remarkably reduced (best $$\Delta {Q_0}=0.13 \, \hbox {e} \, \pm \, 0.01 \, \hbox {e}$$ Δ Q 0 = 0.13 e ± 0.01 e over $$\approx 7.6$$ ≈ 7.6 days and no observation of $$\Delta {Q_0}$$ Δ Q 0 exceeding $$1\, \hbox {e}$$ 1 e ), compared to the results of conventionally fabricated $${\text {AlO}}_x$$ AlO x tunnel barriers in previous studies (best $$\Delta {Q_0}=0.43 \, \hbox {e} \, \pm \, 0.007 \, \hbox {e}$$ Δ Q 0 = 0.43 e ± 0.007 e over $$\approx 9$$ ≈ 9 days and most $$\Delta {Q_0}\ge 1\, \hbox {e}$$ Δ Q 0 ≥ 1 e within one day). We attribute this improvement primarily to using plasma oxidation, which forms the tunnel barrier with fewer two-level system (TLS) defects, and secondarily to fabricating the devices entirely within a UHV system.

Spin-Polarized Current in Spin Valves and Magnetic Tunnel Junctions

MRS Bulletin ◽  
2006 ◽  
Vol 31 (5) ◽  
pp. 389-394 ◽  
Author(s):  
Stuart Parkin
Keyword(s):  
Room Temperature ◽  
Tunnel Junctions ◽  
Magnetic Tunnel Junctions ◽  
Memory Storage ◽  
Tunnel Barrier ◽  
Tunnel Magnetoresistance ◽  
Ferromagnetic Electrodes ◽  
Diffusive Scattering ◽  
Spin Polarized ◽  
Tunnel Barriers

AbstractSpin-polarized currents can be generated by spin-dependent diffusive scattering in magnetic thin-film structures or by spin-dependent tunneling across ultrathin dielectrics sandwiched between magnetic electrodes.By manipulating the magnetic moments of the magnetic components of these spintronic materials, their resistance can be significantly changed, allowing the development of highly sensitive magnetic-field detectors or advanced magnetic memory storage elements.Whereas the magneto-resistance of useful devices based on spin-dependent diffusive scattering has hardly changed since its discovery nearly two decades ago, in the past five years there has been a remarkably rapid development in both the basic understanding of spin-dependent tunneling and the magnitude of useful tunnel magnetoresistance values.In particular, it is now evident that the magnitude of the spin polarization of tunneling currents in magnetic tunnel junctions not only is related to the spin-dependent electronic structure of the ferromagnetic electrodes but also is considerably influenced by the properties of the tunnel barrier and its interfaces with the magnetic electrodes.Whereas the maximum tunnel magnetoresistance of devices using amorphous alumina tunnel barriers and 3d transition-metal alloy ferromagnetic electrodes is about 70% at room temperature, using crystalline MgO tunnel barriers in otherwise the same structures gives tunnel magnetoresistance values of more than 350% at room temperature.

High resolution electron microscopy of ion-irradiated GdBa2Cu3O7

1991 ◽  
Vol 6 (4) ◽  
pp. 677-681 ◽  
Author(s):  
G. Van Tendeloo ◽  
M-O. Ruault ◽  
H. Bernas ◽  
M. Gasgnier
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Room Temperature ◽  
High Resolution Electron Microscopy ◽  
Extended Defects ◽  
Twin Boundaries ◽  
Resolution Electron

GdBa2Cu3O7 crystals were irradiated at room temperature with 200 keV Ne ions and 300 keV Xe ions. In situ standard TEM and further HREM studies show two types of extended defects: (i) mobile extended defects, which account for the preferential defect pinning to twin boundaries reported earlier. These defects are rapidly recovered and difficult to observe by HREM investigations; (ii) stable amorphous areas which are clearly identified by HREM observations. Their overlapping and aggregation conceivably lead to amorphization of the sample.

scholarly journals Epitaxial Growth of High Curie-Temperature Ge1-xMnx quantum dots on Si(001) by auto-assembly

2014 ◽  
Vol 24 (1) ◽  
pp. 69 ◽  
Author(s):  
Luong Thi Kim Phuong ◽  
An Manh Nguyen
Keyword(s):  
Quantum Dots ◽  
Curie Temperature ◽  
Epitaxial Growth ◽  
Room Temperature ◽  
Spin Injection ◽  
High Curie Temperature ◽  
Secondary Phases ◽  
Si Substrate ◽  
Mn Diffusion ◽  
Ferromagnetic Ordering

We report on successful growth of epitaxial and high Curie-temperature Ge1-xMnx quantum dots on Si (001) substrates using the auto-assembled approach. By reducing the growth temperature down to 400 °C, we show that the Mn diffusion into the Si substrate can be neglected. No indication of secondary phases or clusters was observed. Ge1-xMnx quantum dots were found to be epitaxial and perfectly coherent to the Si substrate. We also observe ferromagnetic ordering in quantum dots at a temperature higher 320 K. It is believed that single-crystalline quantum dots exhibiting a high Curie temperature are potential candidates for spin injection at temperatures higher than room temperature.

Uniformity of Arsenic Dimer and Tetramer Fluxes from a Valved Arsenic Cracking Source in MBE

1995 ◽  
Vol 378 ◽  
Author(s):  
George A. Patterson ◽  
James S.C. Chang ◽  
Forrest G. Kellert
Keyword(s):  
Standard Deviation ◽  
Room Temperature ◽  
Flux Distribution ◽  
High Crystalline Quality ◽  
Lattice Match ◽  
X Ray ◽  
Sapphire Substrates ◽  
Case Characteristics ◽  
Substrate Temperatures

AbstractWe have studied the uniformity of the arsenic flux from a commercially available valved arsenic cracker source for MBE. There are many epitaxial structures that require a uniform arsenic flux distribution for rotated epitaxial growth and, in the non-rotated case, for RHEED. For non-stoichiometric GaAs growth at low substrate temperatures, which results in arsenic precipitates being formed during the in-situ anneal process, a specific As/Ga ratio must be used to maintain high crystalline quality and to achieve the desired electrical properties. Also, in the growth of InGaAsP the As/P ratio is equally important for lattice match and quality device results. We report on the uniformity of amorphous arsenic (a-As) films condensed on the surface of 3" diameter sapphire wafers slightly below room temperature. Sapphire substrates were used in place of GaAs wafers to facilitate the use of x-ray fluorescence for the measurement of the arsenic film uniformity. Uniformity maps will be presented for rotated and non-rotated a-As depositions of As2 and As4. Results indicate the uniformity of a-As, As4, films to have a standard deviation of < 2.5% across a 3" diameter substrate for the rotated case. Characteristics of the non-rotated case will be presented.

Ge δ-Layers on Si(111) and Si(001) Grown by MBE and SPE

1994 ◽  
Vol 375 ◽  
Author(s):  
J. Falta ◽  
T. Gog ◽  
G. Materlik ◽  
B. H. Müjller ◽  
M. Horn-Von Hoegen
Keyword(s):  
Room Temperature ◽  
Molecular Beam ◽  
Solid Phase ◽  
Standing Waves ◽  
Solid Phase Epitaxy ◽  
High Crystalline Quality ◽  
X Ray ◽  
High Annealing

AbstractGe δ-layers on Si(111) and Si(001), grown by molecular beam epitaxy (MBE) and solid phase epitaxy (SPE) were characterized in-situ by high-resolution low-energy electrondiffraction and post-growth by x-ray standing waves. LEED intensity oscillations are used to determine the growth mode of Ge on Si which is found to proceed in a double bilayer fashion for Ge on Si(111). X-ray standing waves are employed to investigate crystal quality of the Ge layer. SPE on Si(111) requires high annealing temperatures (600°C) for sufficient recrystallization of defects in the Ge δ-layer. On Si(001), Ge δ-layers of surprisingly high crystalline quality are grown by solid phase epitaxy at room temperature.

scholarly journals Synthesis of Co Filled Carbon Nanotubes by In Situ Reduction of CoCl2 Filled Nanotubes by NaBH4

2013 ◽  
Vol 2013 ◽  
pp. 1-4 ◽  
Author(s):  
J. Mittal
Keyword(s):  
Carbon Nanotubes ◽  
Electron Microscope ◽  
High Resolution ◽  
Room Temperature ◽  
Cobalt Metal ◽  
In Situ Reduction ◽  
Transmission Electron ◽  
Before And After ◽  
Multiwall Nanotubes

An alternative process of filling the multiwall nanotubes (MWCNTs) with cobalt metal was developed. Empty core of nanotubes was first filled with CoCl2 by stirring with CoCl2 and alcohol at room temperature for six hours. CoCl2 filling inside MWCNTs was then converted into Co after treating with NaBH4 at room temperature. High resolution transmission electron microscope (HRTEM) studies showed the filling of the CoCl2 and Co inside the nanotubes before and after the treatment. EDX studies show the nonexistence of chlorine after the reduction with NaBH4. Amount of filling was also reduced after the treatment. Paper describes the possible mechanism of filling CoCl2 inside nanotube and its reduction by NaBH4.

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