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9 Oct 2000

Volume 77, Issue 15, pp. 2271-2423

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Monte Carlo study of spin relaxation in AlGaAs/GaAs quantum wells

A. Bournel, P. Dollfus, E. Cassan, and P. Hesto

Appl. Phys. Lett. 77, 2346 (2000); http://dx.doi.org/10.1063/1.1316771 (3 pages) | Cited 14 times

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An original approach is developed to investigate the electron spin dynamics in III–V quantum wells using a particle Monte Carlo transport model. We study the spin precession related to the D’yakonov–Perel’ mechanism, which is believed to be the predominant spin relaxation phenomenon in AlGaAs/GaAs quantum wells at room temperature. Using a Monte Carlo approach, the effect of electron/crystal scatterings on the D’yakonov–Perel’ mechanism can be both simply and accurately taken into account. Finally, including interface roughness in the calculation leads to spin relaxation times in good agreement with the experimental data. © 2000 American Institute of Physics.
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73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
63.20.K- Phonon interactions
71.38.-k Polarons and electron-phonon interactions
68.35.Ct Interface structure and roughness

Investigation of deep electronic centers in low-temperature grown GaAs using extremely thin layers

K.-F. G. Pfeiffer, S. Tautz, P. Kiesel, C. Steen, S. Malzer, and G. H. Döhler

Appl. Phys. Lett. 77, 2349 (2000); http://dx.doi.org/10.1063/1.1316078 (3 pages) | Cited 3 times

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We report on an approach to investigate the deep electronic defect centers in low-temperature grown GaAs (LT-GaAs). Using an extremely thin LT-GaAs layer (comparable with the penetration depth of an electric field in bulk material) incorporated in the i layer of a p-i-n diode, we are able to charge or to deplete the deep centers in the energy gap by applying a reverse bias. The corresponding space charge is monitored by the field changes across the LT-GaAs layer, both optically by Franz–Keldysh experiments and electrically by n-channel conductance changes. From our results, we derive a deep trap density of 1018 cm−3 centered at around 500–700 meV below the conduction band. © 2000 American Institute of Physics.
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71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
85.30.Kk Junction diodes
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Dominant role of surface states in photoexcited carrier dynamics in CdSe nanocrystalline films prepared by chemical deposition

P. Malý, J. Kudrna, F. Trojánek, D. Mikeš, P. Němec, A. C. Maciel, and J. F. Ryan

Appl. Phys. Lett. 77, 2352 (2000); http://dx.doi.org/10.1063/1.1317536 (3 pages) | Cited 6 times

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We report on ultrafast carrier dynamics in nanocrystalline CdSe thin films prepared by chemical solution deposition. The photoluminescence and transient absorption dynamics have spectrally dependent decay faster at shorter wavelengths. The spectral behavior of the decay rates in samples with different nanocrystal sizes and the sensitivity of the dynamics on the surface modification indicate the dominant role of the surface states in the photoluminescence. © 2000 American Institute of Physics.
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78.66.Hf II-VI semiconductors
73.20.At Surface states, band structure, electron density of states
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
78.66.Vs Fine-particle systems
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
73.22.-f Electronic structure of nanoscale materials and related systems
81.07.-b Nanoscale materials and structures: fabrication and characterization

Spin-dependent Coulomb blockade in a silicon-on-insulator-based single-electron transistor

S. D. Lee, K. S. Park, J. W. Park, Y. M. Moon, Jung B. Choi, K.-H. Yoo, and J. Kim

Appl. Phys. Lett. 77, 2355 (2000); http://dx.doi.org/10.1063/1.1317540 (3 pages) | Cited 7 times

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We report low-temperature conductance measurement on a Coulomb-blockaded dot in a silicon-on-insulator-based single-electron transistor with in-plane side gates. The linear conductance for 4.2 K at zero magnetic field exhibits up to three paired peaks, indicating simple alternating odd (spin 1/2)-even(spin 0) filling. Three intrapair spacings are found to be nearly a constant value, corresponding to the single charging energy U, whereas two interpair spacings are different which are associated with U+ΔE1 and U+ΔE2, i.e., successive quantized level spacings added to U. The quantized level spacings were also revealed in the nonlinear current staircases. © 2000 American Institute of Physics.
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85.35.Gv Single electron devices
85.35.Ds Quantum interference devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.23.Hk Coulomb blockade; single-electron tunneling
85.30.De Semiconductor-device characterization, design, and modeling

Approach to enhance deuterium incorporation for improved hot carrier reliability in metal-oxide-semiconductor devices

Kangguo Cheng, Jinju Lee, and Joseph W. Lyding

Appl. Phys. Lett. 77, 2358 (2000); http://dx.doi.org/10.1063/1.1317546 (3 pages) | Cited 12 times

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The deuterium isotope effect has been widely demonstrated to improve hot-carrier reliability in metal-oxide-semiconductor transistors. Most of the interface traps, however, may have been passivated by hydrogen before the final deuterium anneal due to the ubiquitous presence of hydrogen in modern complementary metal-oxide-semiconductor processing technology. Therefore, effective deuteration requires both deuterium diffusion to the SiO2–Si interface and displacement of the previously bonded hydrogen. We have introduced a “prestress” process in which hydrogen is depassivated before deuterium annealing. We found that the prestressed transistors are more robust to hot-carrier stress than control transistors without the prestress. We have also found that the replacement of hydrogen with deuterium is the rate-limiting step for deuterium incorporation at the SiO2–Si interface. With the prestress, a lower deuterium annealing temperature can be applied without compromising the reliability improvement. © 2000 American Institute of Physics.
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85.30.Tv Field effect devices
81.65.Rv Passivation
61.72.Cc Kinetics of defect formation and annealing

Meyer–Neldel rule in amorphous strontium titanate thin films

K. Morii, T. Matsui, H. Tsuda, and H. Mabuchi

Appl. Phys. Lett. 77, 2361 (2000); http://dx.doi.org/10.1063/1.1317543 (3 pages) | Cited 10 times

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In this letter, we report the experimental result indicating that the electrical conductivity in thin films of amorphous strontium titanate (a-STO) is well fit to the Meyer–Neldel (MN) rule over the temperature range 300–470 K. The films were ion-beam sputtered and annealed in two different atmospheres: a vacuum and flowing oxygen. The MN plots for the films show two parallel straight lines depending on the annealing atmosphere, which give the identical MN parameters of about 35 meV with the conductivity prefactors of 9.3×10−10 and 2.3×10−14(Ω cm)−1 for the vacuum- and oxygen- annealed films, respectively. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
73.61.-r Electrical properties of specific thin films

Effects of boundary roughness on the conductance of quantum wires

D. Csontos and H. Q. Xu

Appl. Phys. Lett. 77, 2364 (2000); http://dx.doi.org/10.1063/1.1311606 (3 pages) | Cited 13 times

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The generic effects induced by boundary roughness on the electron transport through quantum wires have been studied. It is found that the conductance of the rough quantum wires shows rapid fluctuations and strong, broad dips between adjacent plateaus at very low temperatures, and a recovery of the plateau structure at increased temperatures. It is also found that in the recovered plateau structure, the step values are suppressed and the conductance shows long transition regions between adjacent steps. These results agree with existing experiments and can be used as a guideline for the evaluation of the fabrication process of quantum wires. © 2000 American Institute of Physics.
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73.61.-r Electrical properties of specific thin films
68.35.Ct Interface structure and roughness
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Highly stable dye-sensitized solid-state solar cell with the semiconductor 4CuBr 3S(C4H9)2 as the hole collector

K. Tennakone, G. K. R. Senadeera, D. B. R. A. De Silva, and I. R. M. Kottegoda

Appl. Phys. Lett. 77, 2367 (2000); http://dx.doi.org/10.1063/1.1312858 (3 pages) | Cited 26 times

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Construction of a dye-sensitized solid-state solar cell with the semiconductor 4CuBr 3S(C4H9)2 as the hole collector is reported. The cell is unusually stable compared to dye-sensitized solid state cells reported previously and delivers a short-circuit photocurrent and an open-circuit voltage of ∼4.3 mA cm−2 and 400 mV respectively, at 1.5 air mass, 1000 W m−2 sunlight. © 2000 American Institute of Physics.
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84.60.Jt Photoelectric conversion
73.61.Ph Polymers; organic compounds
73.50.Pz Photoconduction and photovoltaic effects
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Local probing of the giant magnetoresistance

S. J. C. H. Theeuwen, J. Caro, S. Radelaar, L. Canali, L. P. Kouwenhoven, C. H. Marrows, and B. J. Hickey

Appl. Phys. Lett. 77, 2370 (2000); http://dx.doi.org/10.1063/1.1315634 (3 pages) | Cited 3 times

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We have contacted the tip of a scanning tunneling microscope (STM) to a Co/Cu magnetic multilayer to locally measure the giant magnetoresistance (GMR) of the multilayer. Apart from a point-contact GMR, the measured MR also reflects a magnetostriction effect in the STM. The resulting GMR ratios are typically 10%, with occasional ratios up to 60%. We attribute spot-to-spot variations of the ratio to differences in the local structure of the magnetic multilayer. © 2000 American Institute of Physics.
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75.47.De Giant magnetoresistance
81.05.Bx Metals, semimetals, and alloys
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
72.15.Gd Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.61.At Metal and metallic alloys
75.80.+q Magnetomechanical effects, magnetostriction
73.40.Jn Metal-to-metal contacts

Néel “orange-peel” coupling in magnetic tunneling junction devices

B. D. Schrag, A. Anguelouch, S. Ingvarsson, Gang Xiao, Yu Lu, P. L. Trouilloud, A. Gupta, R. A. Wanner, W. J. Gallagher, P. M. Rice, and S. S. P. Parkin

Appl. Phys. Lett. 77, 2373 (2000); http://dx.doi.org/10.1063/1.1315633 (3 pages) | Cited 58 times

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We present measurements of the magnitude of Néel “orange-peel” coupling due to interface roughness in a series of magnetic tunneling junction devices. Results from magnetometry and transport measurements are shown to be in good agreement with the theoretical model of Néel. In addition, we have used transmission electron microscopy to directly probe the sample interface roughness and obtain results consistent with the values obtained by magnetometry and transport methods. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.45.+j Macroscopic quantum phenomena in magnetic systems
85.70.-w Magnetic devices
72.15.Gd Galvanomagnetic and other magnetotransport effects
68.35.Ct Interface structure and roughness
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
73.40.Gk Tunneling

Magnetic domains and twin structure of the La0.7Sr0.3MnO3 single crystal

A. Khapikov, L. Uspenskaya, I. Bdikin, Ya. Mukovskii, S. Karabashev, D. Shulyaev, and A. Arsenov

Appl. Phys. Lett. 77, 2376 (2000); http://dx.doi.org/10.1063/1.1316773 (3 pages) | Cited 22 times

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Using a magneto-optical indicator film imaging technique and an x-ray topography, we have observed a strong correlation between magnetic and twin structure of a single crystal of La0.7Sr0.3MnO3 (LSMO). The correlation between magnetic and twin domains can be understood in terms of a rhombohedral deformation of the cubic cell of LSMO which is accompanied by an occurrence of a magnetic anisotropy. Our data and analysis suggest that twin domains play a fundamental role in a low-field magnetization behavior and in magnetotransport properties of LSMO. © 2000 American Institute of Physics.
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75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ch Domain walls and domain structure
61.72.Mm Grain and twin boundaries
78.20.Ls Magneto-optical effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy
75.47.Gk Colossal magnetoresistance

(Ga,Mn)As as a digital ferromagnetic heterostructure

R. K. Kawakami, E. Johnston-Halperin, L. F. Chen, M. Hanson, N. Guébels, J. S. Speck, A. C. Gossard, and D. D. Awschalom

Appl. Phys. Lett. 77, 2379 (2000); http://dx.doi.org/10.1063/1.1316775 (3 pages) | Cited 110 times

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(Ga,Mn)As digital ferromagnetic heterostructures are grown by incorporating submonolayer planes of MnAs into GaAs using molecular beam epitaxy. Structural and magnetic measurements indicate single-crystalline superlattice structure and ferromagnetic order with Curie temperatures (TC) up to 50 K. By varying the spacing between neighboring Mn layers, we observe that TC initially decreases with increasing spacer thickness, followed by a regime with weak dependence on the spacer thickness. The persistence of ferromagnetism for interlayer spacings of at least 200 ML (∼560 Å) suggests that the individual Mn layers are ferromagnetic. © 2000 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
75.50.Pp Magnetic semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.Ct Interface structure and roughness
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Magnetic pair-making double exchange coupling in Ru substituted orthomanganites, La0.7A0.3Mn0.9Ru0.1O3

Ranjan K. Sahu and S. Sundar Manoharan

Appl. Phys. Lett. 77, 2382 (2000); http://dx.doi.org/10.1063/1.1317539 (3 pages) | Cited 17 times

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A detailed study of Ru substitution at the Mn site in La0.7A0.3Mn0.9Ru0.1O3 (A=Ca, Sr, Pb, Ba) polycrystalline samples shows an unusual magnetic pair between Ru+4/Ru+5 and Mn+4/Mn+3 redox couple. As a result, in the entire 10 at. % Ru-substituted compositions, the TC varies only by 10–30 K. The similarity of Mn4+/Ru4+:eg parentage facilitates a redox interaction between Mn and Ru ions, Ru+4/+5/Mn+3/+4. Ruthenium (IV) low spin state has a magnetic moment of 2.7–2.9μB, and with an extended 4d orbital, it enhances exchange coupling between Mn and Ru sites. © 2000 American Institute of Physics.
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75.30.Et Exchange and superexchange interactions
75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
72.60.+g Mixed conductivity and conductivity transitions
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Yttrium silicate formation on silicon: Effect of silicon preoxidation and nitridation on interface reaction kinetics

J. J. Chambers and G. N. Parsons

Appl. Phys. Lett. 77, 2385 (2000); http://dx.doi.org/10.1063/1.1316073 (3 pages) | Cited 51 times

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The effects of oxygen and nitrogen pretreatments on interface reaction kinetics during yttrium silicate formation on silicon are described. X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (MEIS) are used to determine chemical bonding and composition of films formed by oxidation of yttrium deposited on silicon. Capacitance–voltage testing is used to determine the quality of the dielectric and the electrical thickness. The effect of ultrathin silicon oxide, nitrided oxide, and nitrided silicon interfaces on metal oxidation kinetics is also described. When yttrium is deposited on clean silicon and oxidized, XPS and MEIS indicate significant mixing of the metal and the silicon, resulting in a film with Y–O–Si bonding and composition close to yttrium orthosilicate (Y2O3⋅SiO2). A thin (∼10 Å) in situ preoxidation step is not sufficient to impede the metal/silicon reaction, whereas a nitrided silicon interface significantly reduces the silicon consumption rate, and the resulting film is close to Y2O3. The mechanisms described for yttrium are expected to occur in a variety of oxide and silicate deposition processes of interest for high-k dielectrics. Therefore, in addition to thermodynamic stability, understanding the relative rates of elementary reaction steps in film formation is critical to control composition and structure at the dielectric/Si interface. © 2000 American Institute of Physics.
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81.65.Mq Oxidation
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.05.Cy Elemental semiconductors
61.50.Lt Crystal binding; cohesive energy
68.55.-a Thin film structure and morphology
82.20.-w Chemical kinetics and dynamics
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
79.60.Dp Adsorbed layers and thin films
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.35.Ct Interface structure and roughness
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation

Enhanced-response pyroelectric heterostructures

C. Wesley Tipton, K. Kirchner, R. Godfrey, M. Cardenas, S. Aggarwal, H. Li, and R. Ramesh

Appl. Phys. Lett. 77, 2388 (2000); http://dx.doi.org/10.1063/1.1316774 (3 pages) | Cited 5 times

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We have observed enhanced pyroelectric responses in sub-100 nm, epitaxial Pb–Zr–Ti–O films contacted with conducting perovskite oxide top and bottom electrodes. These enhancements are obtained in capacitors where the bottom electrode is processed under reducing conditions. This leads to an asymmetric, temperature-dependent internal electric field that is produced within the ferroelectric capacitor and manifests itself as a strongly shifted ferroelectric hysteresis loop. Because the shifted coercive voltage lies near the unbiased operating point, the pyroelectric film has a large value of dP/dE. The product (dP/dE)/(dE/dT) gives rise to an enhanced pyroelectric response. Our data show that a 10–30 times increase in the pyroelectric response can be obtained over symmetric devices, with a concomitant improvement of the sensing figure-of-merit by three times. © 2000 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.70.+a Pyroelectric and electrocaloric effects
84.32.Tt Capacitors
77.80.Dj Domain structure; hysteresis

Subsecond relaxation of internal field after polarization reversal in congruent LiNbO3 and LiTaO3 crystals

Jung Hoon Ro and Myoungsik Cha

Appl. Phys. Lett. 77, 2391 (2000); http://dx.doi.org/10.1063/1.1316781 (3 pages) | Cited 16 times

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We developed an experimental method for measuring subsecond temporal evolution of the internal field after polarization reversal in ferroelectric crystals, congruent LiNbO3 and LiTaO3 crystals. In each crystal the internal field exhibited two distinct relaxations, suggesting that they originate from two different types of defects. The fast one decays in subsecond range while the slow one lasts over days at room temperature. The subsecond relaxation could be fit to a stretched exponential. This method can be applied to other ferroelectric crystals to investigate the properties of defects. © 2000 American Institute of Physics.
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77.22.Ej Polarization and depolarization
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
71.70.Ch Crystal and ligand fields
77.80.-e Ferroelectricity and antiferroelectricity
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Self-assembled Ge nanostructures as field emitters

V. N. Tondare, B. I. Birajdar, N. Pradeep, D. S. Joag, A. Lobo, and S. K. Kulkarni

Appl. Phys. Lett. 77, 2394 (2000); http://dx.doi.org/10.1063/1.1316076 (3 pages) | Cited 13 times

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Self-assembled two-dimensional arrays of Ge islands on Si(111)7×7 were grown by depositing Ge on Si(111)7×7 substrates held at 650 K. It was observed that these islands were conical in shape as well as nearly uniform in size and shape. Consequently, the substrates of about 1 cm2 area were used as field-emitter arrays. It was found that the arrays exhibited a low onset voltage for field emission, large emission current, as well as high current stability. © 2000 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
81.05.Cy Elemental semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
79.70.+q Field emission, ionization, evaporation, and desorption
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Temperature-dependent internal friction in silicon nanoelectromechanical systems

S. Evoy, A. Olkhovets, L. Sekaric, J. M. Parpia, H. G. Craighead, and D. W. Carr

Appl. Phys. Lett. 77, 2397 (2000); http://dx.doi.org/10.1063/1.1316071 (3 pages) | Cited 43 times

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We report the temperature-dependent mechanical properties of nanofabricated silicon resonators operating in the megahertz range. Reduction of temperature leads to an increase of the resonant frequencies of up to 6.5%. Quality factors as high as 1000 and 2500 are observed at room temperature in metallized and nonmetallized devices, respectively. Although device metallization increases the overall level of dissipation, internal friction peaks are observed in all devices in the T = 160–180 K range. © 2000 American Institute of Physics.
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07.10.Cm Micromechanical devices and systems
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.05.Cy Elemental semiconductors
85.40.Ls Metallization, contacts, interconnects; device isolation
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
85.35.-p Nanoelectronic devices

Resonant-cavity-enhanced p-type GaAs/AlGaAs quantum-well infrared photodetectors

A. Shen, H. C. Liu, M. Gao, E. Dupont, M. Buchanan, J. Ehret, G. J. Brown, and F. Szmulowicz

Appl. Phys. Lett. 77, 2400 (2000); http://dx.doi.org/10.1063/1.1317548 (3 pages) | Cited 10 times

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Resonant cavities are used to enhance the absorption efficiency in p-type GaAs/AlGaAs quantum-well infrared photodetectors. The cavities are fabricated by applying thick gold films on the detector bottom sides after substrate removal via selective wet etching. The observed peak enhancement and spectral shape are in good agreement with model predictions. Peak absorption of about 25% is obtained for the device studied. © 2000 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.65.Cf Surface cleaning, etching, patterning

Role of CsF on electron injection into a conjugated polymer

Pongpun Piromreun, HwanSool Oh, Yulong Shen, George G. Malliaras, J. Campbell Scott, and Phil J. Brock

Appl. Phys. Lett. 77, 2403 (2000); http://dx.doi.org/10.1063/1.1317547 (3 pages) | Cited 76 times

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We studied electron injection from Al and Au cathodes into the conjugated polymer poly[2-methoxy,5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEH–PPV). When a thin CsF layer is inserted between MEH–PPV and Al, a substantial enhancement in electron injection is observed. Insertion of the same layer between MEH–PPV and Au does not have a similar effect, indicating that the enhancement mechanism is specific to CsF and Al. Thin Cs layers enhance electron injection regardless of the cathode metal. A mechanism that explains these observations is proposed. © 2000 American Institute of Physics.
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85.60.Jb Light-emitting devices
73.40.Ns Metal-nonmetal contacts
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Ultraviolet lithography of self-assembled monolayers for submicron patterned deposition

Susanne Friebel, Joanna Aizenberg, Silvia Abad, and Pierre Wiltzius

Appl. Phys. Lett. 77, 2406 (2000); http://dx.doi.org/10.1063/1.1316066 (3 pages) | Cited 20 times

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We report on a lithographic technique that uses self-assembled monolayers (SAMs) as a resist to fabricate patterned, chemically functionalized surfaces. Large area line, square, and triangular patterns with a periodicity of 532 nm were generated exposing SAMs of hydrophobic or hydrophilic alkanethiolates to an ultraviolet laser interference pattern at 193 nm for only a few minutes (corresponding to ∼16 J/cm2) followed by the immersion into an alternating thiol. Patterned films of CaCO3, Zn(OH)2, and polymers were directly deposited on these templates. Using substrates patterned with oppositely charged SAMs, large periodic arrays of charged colloids were fabricated. © 2000 American Institute of Physics.
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85.40.Hp Lithography, masks and pattern transfer
81.65.Cf Surface cleaning, etching, patterning
68.18.-g Langmuir-Blodgett films on liquids

Nonadiabatic heat-capacity measurements using a superconducting quantum interference device magnetometer

A. I. Kharkovski, Ch. Binek, and W. Kleemann

Appl. Phys. Lett. 77, 2409 (2000); http://dx.doi.org/10.1063/1.1316769 (3 pages) | Cited 1 time

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Nonadiabatic measurements of the heat capacity involving sample-inherent thermometry are proposed. The method is realized with superconducting quantum interference device magnetometry and applied to FeBr2 single crystals by using the magnetization for both thermometry and relaxation calorimetry. When heating with a step pulse of laser light, the magnetization relaxes on a characteristic time scale τ = RC, where C is the heat capacity and R is the heat resistance between the sample and the bath. R is independently determined from the temperature dependence of the magnetic moment measured with and without stationary light irradiation. © 2000 American Institute of Physics.
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75.30.Sg Magnetocaloric effect, magnetic cooling
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
07.55.Jg Magnetometers for susceptibility, magnetic moment, and magnetization measurements
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Cr Saturation moments and magnetic susceptibilities
75.90.+w Other topics in magnetic properties and materials (restricted to new topics in section 75)

Modeling of nitrogen depth profiles in iron after nitriding with a homogenized laser beam

E. Carpene, F. Landry, and P. Schaaf

Appl. Phys. Lett. 77, 2412 (2000); http://dx.doi.org/10.1063/1.1316779 (3 pages) | Cited 8 times

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In this letter we propose a phenomenological model to explain the nitrogen depth profile in iron after laser nitriding. The model is based on the one-dimensional diffusion equation and two sets of functions are use to fit the experimental profiles: complementary error function (erfc) and Gaussian. The different nature of these profiles reflects the presence of two stages in the process: the nitrogen is supplied in the sample as an erfc, while the diffusion to larger depths takes place as Gaussians. © 2000 American Institute of Physics.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Bg Metals and alloys
66.30.J- Diffusion of impurities
61.72.S- Impurities in crystals

Semiconductor sieves as nonlinear optical materials

I. M. Tiginyanu, I. V. Kravetsky, J. Monecke, W. Cordts, G. Marowsky, and H. L. Hartnagel

Appl. Phys. Lett. 77, 2415 (2000); http://dx.doi.org/10.1063/1.1316770 (3 pages) | Cited 33 times

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Electrochemical etching techniques were used to fabricate semiconductor sieves of gallium phosphide, i.e., two-dimensionally nanostructured membranes exhibiting an enhanced optical second harmonic generation (SHG) in comparison with the bulk material. The SHG rotational and fundamental polarization dependencies studied under sample excitation by a 1064-nm Nd-YAG laser beam indicate optical homogeneity and uniaxial symmetry of the membranes. The artificial anisotropy and the enhanced nonlinear optical response induced by nanotexturization make semiconductor sieves very promising for use in all-optical devices. © 2000 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Fd III-V semiconductors
81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.65.Cf Surface cleaning, etching, patterning
81.05.Rm Porous materials; granular materials
82.45.-h Electrochemistry and electrophoresis
82.39.Wj Ion exchange, dialysis, osmosis, electro-osmosis, membrane processes

Advances in the molecular-beam epitaxial growth of artificially layered heteropolytypic structures of SiC

Andreas Fissel, Bernd Schröter, Ute Kaiser, and Wolfgang Richter

Appl. Phys. Lett. 77, 2418 (2000); http://dx.doi.org/10.1063/1.1311955 (3 pages) | Cited 22 times

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The controlled growth of SiC heteropolytypic structures consisting of hexagonal and cubic polytypes has been performed by solid-source molecular-beam epitaxy. On on-axis substrates, 4H/3C/4H–SiC(0001) and 6H/3C/6H–SiC(0001) structures were obtained by first growing the 3C–SiC layer some nanometer thick at lower substrate temperatures (T = 1550 K) and Si-rich conditions and a subsequent growth of α-SiC on top of the 3C–SiC layer at higher T (1600 K) under more C-rich conditions. On off-axis substrates, multiheterostructures consisting of 4H/3C- or 6H/3C-stacking sequences were also obtained by first nucleating selectively one-dimensional wire-like 3C–SiC on the terraces of well-prepared off-axis α-SiC(0001) substrates at low T(<1500 K). Next, SiC was grown further in a step-flow growth mode at higher T and Si-rich conditions. After the growth, many wire-like regions consisting of 3C–SiC were found also within the hexagonal layer material matrix indicating a simultaneous step-flow growth of both the cubic and the hexagonal SiC material. © 2000 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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