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J. Nagel,
A. Buchter,
F. Xue,
O. F. Kieler, T. Weimann,
J. Kohlmann,
A. B. Zorin,
D. Rüffer,
E. Russo-Averchi,
R. Huber,
P. Berberich,
A. Fontcuberta i Morral,
D. Grundler,
R. Kleiner,
D. Koelle,
M. Poggio,
M. Kemmler
[show abstract]
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ABSTRACT: Nanoscale magnets might form the building blocks of next generation memories.
To explore their functionality, magnetic sensing at the nanoscale is key. We
present a multifunctional combination of a scanning nanometer-sized
superconducting quantum interference device (nanoSQUID) and a Ni nanotube
attached to an ultrasoft cantilever as a magnetic tip. We map out and analyze
the magnetic coupling between the Ni tube and the Nb nanoSQUID, demonstrate
imaging of an Abrikosov vortex trapped in the SQUID structure - which is
important in ruling out spurious magnetic signals - and reveal the high
potential of the nanoSQUID as an ultrasensitive displacement detector. Our
results open a new avenue for fundamental studies of nanoscale magnetism and
superconductivity.
05/2013;
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[show abstract]
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ABSTRACT: We investigated, at temperature $4.2\,\mathrm{K}$, electric transport, flux
noise and resulting spin sensitivity of miniaturized Nb direct current
superconducting quantum interference devices (SQUIDs) based on submicron
Josephson junctions with HfTi barriers. The SQUIDs are either of the
magnetometer-type or gradiometric in layout. In the white noise regime, for the
best magnetometer we obtain a flux noise
$S_{\Phi}^{1/2}=250\,\mathrm{n}\Phi_0/\mathrm{Hz}^{1/2}$, corresponding to a
spin sensitivity $S^{1/2}_\mu\,\ge\,29\,\mu_B/\mathrm{Hz}^{1/2}$. For the
gradiometer we find $S_{\Phi}^{1/2}=300\,\mathrm{n}\Phi_0/\mathrm{Hz}^{1/2}$
and $S^{1/2}_\mu\,\ge\,44\,\mu_B/\mathrm{Hz}^{1/2}$. The devices can still be
optimized with respect to flux noise and coupling between a magnetic particle
and the SQUID, leaving room for further improvement towards single spin
resolution.
06/2011;
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[show abstract]
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ABSTRACT: We address fabrication challenges for the single-electron tunneling (SET) devices, based on ultrasmall junctions Al/AlO<sub>x</sub>/Al. Nanoscale SET components are known to be very fragile in respect to electrostatic breakdown, which turns out to be a critical problem for devices, fabricated on insulating substrates. For the breakdown prevention, we successfully realized on-chip silicon shunts, whose conductivity advantageously vanished at low temperatures, making possible undisturbed SET operation at T ~ 100 mK.
Nanotechnology Materials and Devices Conference, 2009. NMDC '09. IEEE; 07/2009
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[show abstract]
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ABSTRACT: The electrical properties of single ZnO nanowires grown by vapor phase transport were investigated. While some samples were contacted by Ti/Au electrodes, another set of samples was investigated using a manipulator tip in a low energy electron point-source microscope. The deduced resistivities range from 1 to 10(3) Ωcm. Additionally, the resistivities of nanowires from multiple publications were brought together and compared to the values obtained from our measurements. The overview of all data shows enormous differences (10(-3)-10(5) Ωcm) in the measured resistivities. In order to reveal the origin of the discrepancies, the influence of growth parameters, measuring methods, contact resistances, crystal structures and ambient conditions are investigated and discussed in detail.
Nanotechnology 09/2008; 19(36):365707. · 3.98 Impact Factor
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[show abstract]
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ABSTRACT: We report the electrochemical growth of zinc oxide nanorods in a zinc nitrate/hexamethylenetetramine solution at 70°C. High-density
vertical nanorods were grown on Au films on silicon substrates with a texture coefficient better than 99.9%. By varying the
reactant concentration the diameter can be varied between 100 and 250nm, with corresponding lengths of 1 to 4μm. Furthermore,
this approach was used for the selective growth on Ti/Au strip conductors ordered in an interdigitated structure on an insulating
substrate. We achieved the growth of ZnO nanorods between neighbouring strip conductors bridging the gap between them. In
this configuration the nanorods are already contacted and electrical measurements can be directly performed. First I–V measurements
show a good conductivity of the as-grown nanorods and the resistance could be estimated to be 0.1Ω cm. Under UV illumination
the ZnO nanorods demonstrate a photoconductivity, but only after annealing the sample at 300°C in N2.
Applied Physics A 01/2008; 91(4):595-599. · 1.63 Impact Factor
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M. Punke,
M. Stroisch,
T. Woggon,
A. Putz,
M.P. Heinrich,
M. Gerken,
U. Lemmer,
M. Bruendel,
D.G. Rabus,
Jing Wang, T. Weimann
[show abstract]
[hide abstract]
ABSTRACT: This work has demonstrated the feasibility of both UV and thermal nanoimprinting as fabrication tools for organic laser resonators. In conjunction with the realized waveguide coupling, an important step towards an integrated organic laser source for optical sensor systems is presented.
IEEE/LEOS Summer Topical Meetings, 2007 Digest of the; 08/2007
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ABSTRACT: Two-dimensional photonic crystal lasers based on the small molecule organic semiconductor tris-(8-hydroxyquinoline) aluminum (Alq <sub>3</sub>) doped with 4-Dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) are optically pumped with a conventional low-cost pulsed (In)GaN laser diode. We compare photonic crystal resonators providing first- and second-order distributed feedback and find threshold values of 1.9 and 3.2kW/cm<sup>2</sup>, respectively. Such inorganic-organic hybrid laser systems open up a way to inexpensive, tunable, and all solid-state lasers in the full visible wavelength range
IEEE Photonics Technology Letters 06/2007; · 2.19 Impact Factor
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ABSTRACT: Shifts in the threshold voltage (ΔV<sub> th </sub>) of transparent zinc tin oxide (ZTO) transistors under gate bias stress are studied. The effect of composition and processing temperature on the device stability has been investigated. Based on the research, highly stable transistors with ΔV<sub> th </sub> as small as 30 mV after 1000 min of operation have been fabricated with a composition of [ Zn ]:[ Sn ]=36:64 . As current drivers in active matrix displays their stability renders ZTO thin film transistors (TFTs) a very attractive alternative to TFTs based on established technologies.
Applied Physics Letters 03/2007; · 3.84 Impact Factor
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ABSTRACT: The authors present organic semiconductor distributed feedback lasers based on thin films of the conjugated polymer poly[9,9-dioctylfluorene-co-9,9-di(4-methoxy-phenyl)fluorene] and employing an improved resonator design. In order to combine the advantages of first- and second-order distributed feedback resonators, the authors utilize a mixed-order grating design: A second-order Bragg scattering region that provides efficient vertical outcoupling of the laser radiation is surrounded by first-order scattering regions that give rise to strong feedback. By optimizing the film thickness to obtain laser oscillation at the polymer maximum gain wavelength, a very low laser threshold of 45 pJ/pulse (approximate to 36 nJ/cm(2)) was realized with this resonator concept. (c) 2007 American Institute of Physics.
Applied Physics Letters 01/2007; 90(13). · 3.84 Impact Factor
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[show abstract]
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ABSTRACT: A new planar thin film design of multijunction thermocouples on a silicon chip containing a window with a SiO2-membrane for low heat conductance underneath of the thermocouples is described. It is used as the sensor for the temperature difference in a multijunction thermal converter for ac-dc transfer of electrical quantities like voltage, current and power via Joule heat in a thin film resistor. By coating the heater with an optically absorbing layer it is used as a highly sensitive radiometer transferring absorbed energy to Joule heat in the resistor. The design can easily be optimized for all different frequency applications. It offers the possibility of the mass production of transfer standards at highest level of accuracy.
Physica Scripta 09/2006; 41(5):718. · 1.20 Impact Factor
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T. Rabe,
K. Gerlach,
T. Riedl,
H.-H. Johannes,
W. Kowalsky,
J. Niederhofer,
W. Gries,
J. Wang, T. Weimann,
P. Hinze,
F. Galbrecht,
U. Scherf
[show abstract]
[hide abstract]
ABSTRACT: The operation of organic thin-film distributed feedback lasers at repetition rates up to 5 MHz is studied. The active organic medium consists of a highly efficient, modified poly(9,9-dioctylfluorene) derivative containing 12% of statistical intrachain 6,6′ -(2,2′-octyloxy-1,1′-binaphthalene) binaphthyl spacer groups. The threshold energy density of these pulsed optically pumped lasers remains virtually unaltered at elevated repetition rates up to 5 MHz. Therefore, we conclude that on this time scale photoinduced absorption which might affect the waveguide loss or the overall quantum efficiency is negligible in our active polymer. These results state an organic solid-state laser operating at repetition rates in the megahertz range which for many applications can be considered as quasi-cw.
Applied Physics Letters 08/2006; 89(8):081115-081115-3. · 3.84 Impact Factor
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C. Karnutsch,
V. Haug,
C. Gaertner,
U. Lemmer,
T. Farrell,
B. Nehls,
U. Scherf,
J. Wang, T. Weimann,
G. Heliotis,
C. Pflumm,
J. deMello,
D. D. C. Bradley
[show abstract]
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ABSTRACT: We report low threshold blue polyfluorene distributed-feedback (DFB) lasers. Second-order lasers exhibit a laser threshold of 0.28 nJ/pulse while the threshold is reduced to 0.16 nJ/pulse for first-order gratings. Laser diode pumping is demonstrated.
Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference. CLEO/QELS 2006. Conference on; 06/2006
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[show abstract]
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ABSTRACT: We demonstrate an organic thin-film distributed feedback (DFB) laser pumped by an inorganic violet laser diode (λ = 406 nm). The active organic medium consists of a highly efficient, modified poly(9,9-dioctylfluorene) derivative containing 12% of statistical intrachain 6,6′-(2,2′-octyloxy-1,1′-binaphthalene) binaphthyl spacer groups. The polymer is doped with 4 wt % of the stilbene dye 1,4-bis(2-(4-(N,N-di(p-tolyl)amino)phenyl)vinylbenzene). This guest-host system features minimum lasing threshold energy densities below 1 μJ/cm2 for second order DFB resonator geometries and significant absorption (7.3×104 cm−1) at the wavelength of the pumping diode laser. The entire setup states an extremely compact and cost effective, laser source tunable between 496 and 516 nm.
Applied Physics Letters 06/2006; 88(24):241116-241116-3. · 3.84 Impact Factor
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C Karnutsch,
C Gyrtner,
V Haug,
U Lemmer,
T Farrell,
B S Nehls,
U Scherf,
J Wang, T Weimann,
G Heliotis,
C Pflumm,
J C,
D D C Bradley
[show abstract]
[hide abstract]
ABSTRACT: We report on the fabrication of low threshold distributed feedback (DFB) polymer lasers based on a polyfluorene derivative containing statistical binaphthyl units (BN-PFO). First- and second-order feedback lasers have been realized. The emission was tuned in the wavelength range from 438 to 459 nm by varying the grating period and the film thickness. A threshold energy of 280 pJ/pulse was observed in second-order DFB structures, which could be further reduced to 160 pJ/pulse by employing first-order feedback in electron beam lithographically patterned structures with a period of 140 nm. In these first-order structures, laser oscillation at both edges of the photonic stop band was observed. These very low threshold values render BN-PFO a very promising material for future electrically pumped organic semiconductor laser diodes. (c) 2006 American Institute of Physics.
Applied Physics Letters 01/2006; 89(20). · 3.84 Impact Factor
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[show abstract]
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ABSTRACT: Long superconducting niobium coplanar waveguides (CPW) on silicon wafers have been implemented with inner conductor width, thickness and length of about 50 nm×250 nm×3.2 mm, respectively. CPW tapers yield the transition from small to large cross sections for 50 Ω coaxial SMA connectors. Microwave properties are measured at 4.2 K via λ/2-resonators where the inner conductor width w<sub>i</sub> is about half the London penetration depth. Due to the dominant kinetic inductance the measured quality factor is close to an evaluated minimum value for w<sub>i</sub><50 nm. The quality factors of such nanolines with niobium are approximately 150 at 10 GHz, i.e., more than two orders of magnitude larger than with aluminum at the same temperature. An unexpected power dependence of the intermodulation amplitudes and the corresponding dc properties are described.
IEEE Transactions on Appiled Superconductivity 07/2003; · 1.04 Impact Factor
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ABSTRACT: A superconducting transistor structure comprising two Josephson tunnel junctions connected in series and a small island in between, which is capacitively coupled to a gate, is considered. When self-capacitances of the junctions are sufficiently small that the corresponding charging energy E
c
is of the order of magnitude of the Josephson coupling strength E
J (and both are k
B
T), the interplay of the charging and Josephson effects in the circuit becomes essential. This leads to a characteristic IV curve which can be effectively modulated by the gate in two limit cases of external electrodynamic impedance Z
s
(): (a) Z
s
= R
s
R
Q
6.5 k and (b) R
s
R
Q
. Both circuits can serve as electrometers which are competitive with traditional single-electron devices. Preliminary experimental results are discussed.
Journal of Superconductivity 11/1999; 12(6):747-755.
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[show abstract]
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ABSTRACT: A novel method for the fabrication of sub-1-μm Nb/AlO<sub>x
</sub>/Nb tunnel junctions has been developed, that is based on spin-on
glass planarization. The Nb/AlO<sub>x</sub>/Nb sandwich and the Nb
wiring layer are structured by reactive ion etching using e-beam
lithography. The insulation between the base electrode and the wiring
layer is realized by planarised spin-on glass. Single electron
transistors with junction areas of 0.3 μm×0.3 μm and linear
arrays of junctions with sizes down to 0.5 μm×0.5 μm have
been fabricated and measured
IEEE Transactions on Appiled Superconductivity 07/1999; · 1.04 Impact Factor
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[show abstract]
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ABSTRACT: Technological processes for the fabrication of
Nb/AlO<sub>x</sub>/Nb Josephson junctions with areas as small as 0.04
μm<sup>2</sup>, based on anodization techniques, are investigated. A
cross strip process requiring only two masks is compared with a standard
three mask etching and anodization process. Details of the fabrication
processes as well as the electrical characterization at 4.2 K and 30 mK
of tunnel junctions fabricated by the different methods are presented.
Limitations and applications of the two different processes are
discussed
IEEE Transactions on Appiled Superconductivity 07/1999; · 1.04 Impact Factor
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[show abstract]
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ABSTRACT: We have fabricated the Bloch transistor shunted on-chip by a
small-sized Cr resistor with R<sub>s</sub>=1 kΩ. The Bloch
transistor normally consists of two small Josephson junctions connected
in series, which in our case have been replaced by two superconducting
interferometer loops, each with two junctions in parallel. A
capacitively coupled gate is supplied to control the induced charge of
the small intermediate electrode (island) of the transistor. The
measured I-V curves show no hysteresis and correspond to the operation
of a effective Josephson junction at the high-damping and strong-noise
limits. The critical current of the system was found to be close to its
nominal value, that is in accordance with the electromagnetic
environment theory. The I-V curves were modulated by the gate with a
period of e and a maximum swing of about 2 μV. Such rather moderate
modulation results from the Josephson-to-charging energies ratio,
E<sub>J</sub>/E<sub>C</sub>≈9, in our sample being far from its
optimum value (≈0.3+1)
IEEE Transactions on Appiled Superconductivity 07/1999; · 1.04 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We have fabricated the Bloch transistor shunted on-chip by a small-sized Cr resistor with Rs about 1 kOhm. The Bloch transistor normally consists of two small Josephson junctions connected in series, which in our case have been replaced by two superconducting interferometer loops, each with two junctions in parallel. A capacitively coupled gate is supplied to control the induced charge of the small intermediate electrode (island) of the transistor. The measured I-V curves show no hysteresis and correspond to the operation of a effective Josephson junction at the high-damping and strong-noise limits. The critical current of the system was found to be close to its nominal value, that is in accordance with the electromagnetic environment theory. The I-V curves were modulated by the gate with a period of e and a maximum swing of about 2 /mu_V. Such rather moderate modulation results from the Josephson-to- charging energies ratio, Ej/Ec about 9, in our sample being far from its optimum value of 0.3 up to 1.
02/1999;
