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Using scanning tunneling microscopy, we have conducted an in situ study of the room-temperature growth of Ag structures on a Si(111)-(7 × 7) surface. By observing the STM images at various Ag cover...

We have used a time-dependent tunneling current mode based on scanning tunneling microscopy/spectroscopy (STM/STS) to study the tracer diffusion of CO molecules along steps and on terraces of Pt(1 1 1). The results show that the hopping rate of CO molecules along steps is about 10 times faster than that on terraces in the measured temperature range. The diffusion activation energies are 5.1 kcal/mol and 3.8 kcal/mol on terraces and along steps, respectively. The lower activation energy and faster hopping rate for CO molecules diffusing along steps provide evidence that steps provide fast diffusion channels for CO molecules on stepped Pt(1 1 1) surfaces.

The interaction between the metallic film/island and the semiconductor substrate is important to the electronic properties of metallic nanostructure grown on semiconductor substrate. Here, we report a series of comparison experiments to investigate the effect of doping concentration of Si substrates on the quantum well state (QWS). Using scanning tunneling microscopy, we observed that the apparent QWS energy positions show a strong dependence on the substrate used and on the sample temperature. Further experimental results by varying the height of scanning tunneling microscope tip over the Pb island uncovered that the observed apparent QWS energy position changes mainly come from the partial bias voltage drop on the combined resistance of the Pb wetting layer and the substrate, which is comparable with the vacuum tunneling resistance at low temperatures.

Iron–iron oxide granular films are fabricated using dc magnetron sputtering. Their structural, magnetic and transport properties are studied in the vicinity of percolation threshold. X-ray photoelectron spectroscopy and transmission electron microscopy confirm the coexistence of iron and FeOx. Magnetic measurement indicates the exchange coupling between the iron and the FeOx matrix. Metal–insulator transition is observed. The non-monotonic temperature dependencies of resistivity occur near the percolation threshold and the mechanism is investigated with the longitudinal and transverse magnetic transport measurement in terms of weak localization.

Fe/In multilayers were prepared by the DC magnetron sputtering method, and their electrical and magnetic properties were studied. Negative giant magnetoresistance (GMR) with a maximum of −0.84% at 10 K was observed. The magnitude of GMR and the saturation field ( H s ) were found to oscillate with a period about 1.3 nm when varying the thickness of In layers. Atomic force microscope images of samples were taken to investigate the surface morphology. The GMR effect is composed of antiferromagnetic coupling between the neighboring Fe layers and superparamagnetic spins effect at the Fe/In interface. A reduction of the anomalous GMR effect with decreasing temperature is presented.

Giant magnetoresistance was found in DC magnetron sputtering Fe/ITO multilayers. The magnetic properties, electrical properties and magnetoresistance were investigated. A critical temperature is found around 50 K where the temperature dependence of resistivity and magnetoresistance ratio exhibit an abruptly change. The temperature dependence of resistance is found to obey Mott's 1/4 law for low temperature. The max magnetoresistance ratio of 2.0% and 6.7% is found at room temperature and 12.5 K, respectively. The increase of magnetoresistance ratio at low temperature is due to the decrease of spin-mixing effect.

The magnetic, transport and thermal properties of single crystal Co2FeGa have been investigated. The small coercivity 20 Oe and saturation field 4000 Oe of Co2FeGa sample at temperature 5 K indicates that the single crystal is magnetically soft. The resistivity (rho) behaves according to rho similar to T-1/2 power law below temperature T = 40 K, which is due to electron-electron interaction effects in the presence of disorder. The thermal conductivity of Co2FeGa single exhibits anomalous temperature dependence above 50 K, i.e., the conductivity increases with the temperature, or dk/dT > 0. We conclude that this anomalous thermal conductivity is due to the strong atomic disorder between the Fe and Co atoms. (C) 2007 Elsevier B.V. All rights reserved.

We have experimentally determined that a Pb wetting layer grown on Si(1 1 1)-7 × 7 is conductive, while In and Ag wetting layers are not, despite the fact that they are all made of metallic atoms. We have further demonstrated that the conduction of the Pb wetting layer at low temperatures plays an important role for the study of low temperature tunneling spectroscopy of metal nanostructures formed on Si(1 1 1) substrates.

We fabricate Fe/Fe oxide granular film by DC sputtering and study the magnetic and transport properties in the insulator region. X-ray photoelectron spectroscopy and transmission electron microscopy confirm the coexistence of iron and Fe2O3. Accompanied with the nonlinear I–V curve and magnetic measurement, we investigate mechanism of sizable magnetoresistance in detail and found the spin in the interface has crucial contribution to the spin tunneling process.

The discovery of the single-walled carbon nanotubes (SWCNTs) with a diameter of 0.4 nm has attracted extensive attentions. In this paper we report our attempt with two methods to directly observe these SWCNTs by AFM. The first one is to deposit the SWCNTs extracted from the zeolite matrix to a flat surface for AFM observation. While one-dimensional features have been observed, the SWCNT was suspected not to adhere well to the substrate. To overcome the difficulties of weak adhesion, we attempt to expose only part of the SWCNT from the zeolite channel by cutting the zeolite crystal at an angle. This alternative method, in which the SWCNT contained zeolite crystal is polished and etched by HCl, however, did not result in a smooth enough surface and thus no one-dimensional features can be observed. The difficulties in sample preparation and possible improvements are discussed.

The single crystal Ni54Fe19Ga27 shows a martensitic transformation at 281 K on cooling and 283 K on warming. Large jumps in the temperature-dependent resistance curve, temperature-dependent magnetization curve and temperature-dependent thermal conductivity curve are observed at the martensitic transition temperature (TM). Negative magnetoresistance due to spin disorder scattering was observed in Ni54Fe19Ga27 single crystal in all temperature ranges. The Ni54Fe19Ga27 sample exhibited a temperature dependence of thermal conductivity κ(T)(dκ/dT>0) due to atomic disorder above a temperature of 50 K.

Large negative magnetoresistance (MR) ( | Δ R / R | = | [ R ( H ) - R max ] / R max | > 50 % ) has been observed in the broken cold-pressed CrO2 powder samples near the room temperature, which is ascribed to the magnetic field-induced mechanical contact variation. This large, room-temperature negative MR might easily lead to a wrong conclusion that the spin-polarization is still very high at high temperatures. This observation may also point to the possibility to develop field sensors based on the mechanical MR.

Sb1−x(SiO2)x granular films were prepared by the co-sputtering method with the volume fraction of SiO2, x, ranging from 0 (i.e. pure Sb) to about 30%. Systematic electronic transport studies, including resistivity, magnetoresistance, Hall effect and Seebeck effect, were carried out against the temperature, magnetic field and volume fraction x of SiO2. With the gradual increase of the SiO2 content, the mean grain size of the Sb decreases, and eventually the film becomes amorphous, as illustrated by the changes of the x-ray diffraction patterns. The temperature coefficient of resistivity also changes its sign from positive to negative, indicating a semimetal–semiconductor or insulator transition. Magnetoresistance studies using the weak localization theory revealed that the electron dephasing time follows approximately a T−2 law. This behaviour indicates that the electron–phonon (e–ph) scattering still dominates the electron dephasing processes in these granular systems with a fair number of SiO2 inclusions. The Hall coefficient decreases monotonically with temperature and with the volume fraction of SiO2. The giant Hall effect is absent in these granular films. Finally, an interesting but rather complicated behaviour of the Seebeck coefficient versus temperature was observed when the volume content of the SiO2 exceeded 18%.

Resistivity of cold-pressed CrO 2 powder has been measured over the temperature range of 2 to 350 K with a magnetic field up of to 50 kOe. High resolution transmission electron microscopy (HRTEM) images show that the CrO 2 particles are needle-shaped with an aspect ratio of 7:1 and have an average length of 200 nm, and are covered with an ultra-thin (∼2.5 nm) native Cr 2 O 3 layer. Temperature dependent conductivity can be well described by the expression exp[-(Δ/T) 1/2 ] below 55 K, a feature of electron tunneling, and by the higher-order hopping for temperature above 55 K. The magnetoresistance, MR = [ρ(max) - ρ(H)]/ρ(max), reaches ∼33.5% at 2 K and decreases to nearly zero at room temperature. Temperature dependent saturation magnetization follows well the relation M(r)=M s (1-BT 3/2 ) below 240 K. The spin-wave stiffness constant, D, is estimated to be -91 meV A 2 . By fitting the specific heat measured in the temperature range of 1.8-34 K by the relation C =γT + βT 3 +β 1 T 5 +αT 3/2 , we obtained the electronic specific heat coefficient γ=1.7 mJ/mol K 2 , this corresponds to a density of states at the Fermi level of 0.73 states/eV, which is in good accordance with the theoretical value of 0.69 states/eV.

We have systematically measured the electrical transport properties of several RuO2 and IrO2 single crystals over a wide temperature range from 300 K down to 0.3 K to study the conduction mechanisms in these oxides. Our measured resistivities are in close agreement with the recent band-theory calculations for these materials. The characteristic temperatures for the acoustic-mode and optical-mode phonons are determined. Our measured magnetoresistances are positive and follow the Kohler rule, indicating that the transport properties of these oxides exhibit normal behaviour as described by the Boltzmann equation. In contrast, we do not find any signature of superconductivity down to 0.3 K, though the band-theory calculations predict a superconducting transition temperature of K. Magnetization measurements suggest a very low level of paramagnetic impurities in our crystals.

The martensitic transformation and magnetic properties of ferromagnetic shape memory alloy Ni50 + x Fe25 − x Ga25 (x = −1, 0, 1, 2, 3, 4) ribbons have been systematically studied. It has been found that with the increase of Ni concentration, the martensitic transformation temperature increases, but the Curie temperature decreases. Both the two-step thermally induced structural transformation and the one-step transition have been observed in NiFeGa alloys with different compositions. It is found that the two-step transition became the one-step transitio n after the ribbon being heat treated at 873 K or higher. X-ray diffraction patterns show that only L21 → B2 transition occurs in the samples treated at 873 K, while the γ phase will form in the samples treated at higher temperature. Transmission electron microscopy (TEM) studies show that the alloys with martensitic transformation temperature above the room temperature are non-modulated martensite with the large domain size, being different from the stoichiometric Ni2FeGa alloy that is a modulated martensite with small domain size. The influences of Fe substitution for Ni in Ni2FeGa on the saturation magnetization and exchange interaction are also discussed.  2004 Elsevier B.V. All rights reserved.

A large change in the magnetic entropy, |ΔS|, was observed in the Fe-based NaZn13-type compound LaFe11.375Al1.625, which was nearly temperature independent over a wide temperature range (an about 70 K span from ~ 140 to 210 K). This behaviour of the magnetic entropy change is associated with two closely spaced magnetic transitions. X-ray diffraction investigation at different temperatures indicates that the crystal structure remains cubic, of NaZn13 type, when the magnetic state changes with temperature, but the cell parameter changes dramatically at the first-order transition point.

TM x –(SiO 2 ) 1− x (TM=Fe, Co, Ni) thin films were prepared in a wide concentration range (0.35 ⩽ x ⩽1). Structure was studied with transmission electron microscopy (TEM), X-ray diffraction (XRD) and small angle X-ray scattering (SAXS). Magnetic and magnetotransport properties were investigated by means of magnetization and Hall effect measurements. TEM images display nanometric spherical structures embedded in a SiO 2 amorphous matrix, with typical sizes increasing from 3 to 5 nm when TM volume concentration x is increased. SAXS measurements indicate a complex structure formed by nanosized objects. XRD measurements show that the structure is composed by amorphous SiO 2 and TM crystallites. Slightly above the percolation threshold all samples display giant Hall effect. The observed magnetic properties are dependent on x , and display an evolution resulting from the progressive increase of the mean particle size.

A comprehensive review of the giant Hall effect (GHE) is presented, with emphasis on novel experimental data obtained in Ni–SiO2 and Co–SiO2 films prepared by co-sputtering. GHE is observed close to and on both sides of the metal–insulator transition. From the point of view of microscopic conduction mechanisms, this means a crossover from metallic conductivity with weak localization to tunneling, or hopping, between separate granules across insulating barriers. Magnetic percolation is also interrupted at this concentration of metal, leading to superparamagnetic behavior of the composite and blocking phenomena. Temperature dependencies of magnetization and extraordinary Hall coefficient in the composites near the critical concentration are compared. In single phase magnetic metals and alloys, the extraordinary Hall is believed to be directly proportional to the total magnetization, due to side jumps or skew scattering. In a metal–insulator composite, only those electrons traveling in conduction critical paths can contribute to the Hall signal, thus only magnetization of the material belonging to these paths is important in the Hall measurements. Comparison with the magnetic results leads to new possibilities in understanding both the electronic and magnetic properties of granular nanocomposites. r 2003 Elsevier Science B.V. All rights reserved.

We have studied the magnetic relaxation of monodispersed 4 nm cubic e-cobalt nanocrystals in both randomly oriented and pre-aligned assemblies.The blocking temperature TB, for the closely packed Co nanocrystal assemblies, is 30% higher than that of the highly diluted and well-dispersed Co nanocrystal-organic composites.This increase is attributed to the strong magnetic dipole interaction induced from the close packing of the nanocrystals.It is found that the frequency-dependent susceptibility data, obtained from the diluted samples, can be fitted to the half-circle Argand Diagrams, indicating a single barrier (or very narrow energy distribution) of the nanocrystals.This agrees well with the physical observation from TEM that the nanocrystals are monodispersed.The long time magnetic relaxation measurements reveal that energy barrier distribution in a pre-aligned nanocrystal assembly is significantly different from that in a randomly oriented one. r 2002 Elsevier Science B.V. All rights reserved.

The relationship between nanostructure, exchange coupling and magnetic properties of Nd-2(Fe, Co, Mo) B/alpha-Fe nanocomposite magnets prepared by mechanical alloying (MA) has been studied systematically. Different categories of grain interfaces have been directly observed, which correspond to different types of exchange couplings in the Nd2Fe14B/alpha-Fe-type nanocomposite magnets. The notable decrease of the spin-reorientation temperature T-sr of Nd2Fe14B phase convincingly demonstrates the presence of strong inter-grain exchange coupling in the Nd2Fe14B/alpha-Fe-type nanocomposites. For as-annealed Nd8.4Fe87.1-xMoxB4.5 (x=0, 0.6, 1.1 and 1.6) and Nd8.4Fe80.4Co5.6Mo1.1B4.5 alloys, the intrinsic coercivity mu(0)H(c) and the maximum magnetic energy product (BH)(max) are remarkably improved in the alloys with only Mo-additions as well as in the Nd8.4Fe80.4Co5.6Mo1.1B4.5 alloy. The improvement of the magnetic properties is the result of an enhancement of the exchange coupling, because of the modifications of nanostructural factors and phase components by a proper substitution of 3d elements for Fe. (C) 2002 Elsevier Science B V All rights reserved.

A YBa2Cu3O7 (30 nm) superconductor layer and a YBa2Cu3O7 (30 nm)/ Pr0.67Sr0.33MnO3 (30 nm) superconducting/ferromagnetic bilayer were epitaxially grown on the single-crystal (100) SrTiO3 substrates. Magnetic characterizations on both samples were very carefully performed over wide temperature and field ranges. The enhanced flux pinning by the ferromagnetic layer in the bilayer sample is clearly seen in the comparison of the temperature-dependent magnetization data obtained in the zero-field-cooled and field-cooled processes for both samples. The fact that the temperature-dependent remanent magnetization in the bilayer shows a sharper transition near the TC than that in the YBCO single layer is also consistent with the picture of the enhanced flux pinning. The above observations are confirmed by the enhanced critical current density, Jc ΔM, where ΔM is the magnetic irreversibility in the hysteresis loops.

Large magnetic entropy changes were observed in RCoAl compounds, where R = Gd, Tb, Dy, and Ho, at their Curie temperatures. These RCoAl alloys have a hexagonal, MgZn2 structure and their Curie temperatures fall in the temperature range 10-100 K. A `table-like' behaviour was found in the temperature dependence of the magnetic entropy change (-ΔS(T)) obtained in the soft magnetic GdCoAl alloys, which can be used either to fill up the gap (near 100 K) in the profile of magnetic entropy change versus temperature required by an eight-stage magnetic refrigerator or to complete an Ericsson circle. It has also been shown that soft ferromagnetic materials with Curie temperatures in the temperature range from 10 K to 100 K can be obtained by using multi-R elements instead of a single-R element in the RCoAl compounds.

Co3(BO3)2/surfactant composites have been prepared by the controlled precipitation of aqueous cobalt cations together with surfactant. The composite shows a layered structure as determined by x-ray diffraction, in which the Co3(BO3)2 layers of about 6 A in thickness are in alternation with surfactant bilayers. The temperature-dependent magnetization measured in the zero-field-cooled (ZFC) and field-cooled (FC) processes and the AC-magnetic susceptibility measured at different frequencies indicate that there is a freezing temperature at low temperature (

Shell-core structures of Fe(C), Co(C) and Fe-Co(C) nanocapsules, prepared by an arc discharge process in a mixture of methane and helium, have been demonstrated by means of high-resolution transmission electron microscopy (HRTEM). These nanoscale magnetic cores are protected by graphite shells. It has been found that the zero-field-cooled (ZFC) magnetization of Fe-Co(C) nanocapsules that display different characteristics in three temperature ranges can be well interpreted in terms of the unblocking of magnetization of small single-domain particles and the depinning of large multidomain particles. The saturation magnetization of these nanocapsules decreases monotonically, while the coercivity decreases significantly with increasing temperature.

Exchange biasing and magnetoresistance (MR) behaviors have been investigated in La0.67Ca0.33MnO3/La0.5Ca0.5MnO3 bilayers with specially designed interfacial structures. The exchange coupling is found to be strongly related to interfacial structures. Exchange field H-E decreases as the cooling field N-fc increases at high H-fc region. Especially, the coercivity H-C is enhanced by exchange coupling for bilayers with rough interface, while it is reduced for relatively smooth interface. Also, large low-field MR has been achieved by introducing regular in-plane grain boundaries, and a biasing of R-H loop has been observed.

Ultrathin Fe nanowire (about 5 nm in diameter) arrays have been fabricated by electrodeposition using anodic porous alumina templates. These ultrathin nanowires exhibited uniaxial anisotropy and a quite large coercivity (4190 Oe) at 5 K. In addition, the field needed to saturate the magnetization, when the field was applied perpendicularly to the easy axis, was much larger than the shape anisotropy field (2πM S ). This saturation field increased with decreasing temperature. We believed that this enhanced saturation field was mainly due to the contribution of the surface spins.

In situ measurements of resistance were made on cosputtered Co/sub 0.35/[SiO/sub 2/]/sub 0.65/ granular films during annealing. The aim is to control the thermal treatment parameters and map the microstructural changes of the samples, with the respective magnetotransport response. Results of transmission electron microscopy, dc magnetization, and temperature dependence of resistivity, after annealing, show a clear evolution in the nanostructure of the samples, with increasing average Co grain sizes and wider dispersion.

Magnetization and magnetotransport were measured in CoxAg1−x granular composites as a function of temperature and applied magnetic field. A transition from blocked to superparamagnetic behavior with increasing temperatures can be observed in magnetization, giant magnetoresistance and the extraordinary Hall effect measurements. However, the blocking temperature determined from magnetotransport measurements is systematically lower than the one estimated from magnetic measurements. This is due to the selective magnetic scattering, which is enhanced for smaller particles, while the magnetization probes the whole particle size distribution.

We have measured the thermopower S and electrical conductivity σ in a series of Cux(SiO2)1−x nanogranular films between 2 and 300 K with Cu volume fraction x varying from 0.43 up to 1.0. At low temperatures, disorder-enhanced electron–electron interaction effects dictate the behavior of σ. A crossover of the temperature dependence from σ∝T to σ∝T1/3 is observed as x is lowered and the metal–insulator transition is approached. S is small, shows linear temperature dependence, and is rather insensitive to the change of x. Effects of annealing are also discussed.

Epitaxial growth of Ni thin films on GaAs(0 0 1) and their magnetic property have been investigated using reflection high energy electron diffraction and magneto-optical Kerr effect. The result shows that a body-centered-cubic (BCC) phase of Ni which does not exist in nature can grow epitaxially up to 2.5 nm on the GaAs(0 0 1) substrate, and it is determined to be ferromagnetic showing a four-fold in-plane magnetic anisotropy with the easy axes along the 〈1 0 0〉 directions.

As the most efficient thin film solar cells, Cu(InGa)Se 2 based solar cell has attracted extensive studies recently. In this paper we have briefly reviewed recent progress of CIGS solar cells both in the laboratory and in the industry. For the research status, we focused on recent progress in cell structure and material selection/preparation for different functional layers in the highly efficient CIGS solar cells. We also summarized the main achievements from several leading research groups in producing high efficiency CIGS solar cells and presented their efficiency records on different substrates (glass, stainless steel, Ti and polymer). For CIGS industrialization, we reviewed the main progress in several representative CIGS companies. We summarized the fabrication technology and characteristics, and the main achievements in the production capacity for many CIGS companies worldwide. We also reviewed the research progress of our group (CUHK and SIAT) on small size CIGS solar cells and mini-modules. We believe that the CIGS production capacity and actual production will increase very fast and play important role in photovoltaic industry in the near future.

Atomic manipulation has been rarely used in the studies of complex structures and a low temperature requirement usually limits its application. Herein we have demonstrated a vertical manipulation technique to reproducibly and reversibly manipulating Ag atoms on an Si(111)-(7×7) surface by a scanning tunneling microscope tip at room temperature. Simple and complex Ag nanoclusters were assembled and disassembled with a precise control of single Ag atoms, which provided critical information on the size of these nanoclusters. The manipulation showed the growth processes of these Ag clusters and even partly unveiled their atomic structures. This technique can form a fundamental basis for further studies of the Ag/Si(111)-(7×7) system and for fabricating functional nanodevices in various metal-semiconductor systems.

Solar cells based on Cu(In, Ga)Se2 (CIGS) have made significant strides in the past decades with a record efficiency of over 20% [1]. A problem with CIGS modules is the high resistive losses along the transparent top contact. One solution is to deposit highly-conductive metal grids to collect the current. We use finite-element analysis to determine the effectiveness of the metal grid under a variety of parameters. We identify the resistance of the top contact and the width of the scribes as the most important factors in determining whether a metal grid would present a significant efficiency gain. Using the same model, we also investigate methods to optimize the design of the grid.

Magnetization, resistance and Hall effect are studied in granular magnetic Co–SiO2 nanocomposites in the temperature range 5–300 K and fields up to 6 T. Relative contributions from spin-independent and spin-dependent processes to the giant Hall effect near the metal–insulator transition are analysed.

A cluster consisting of as few as three Ag atoms deposited on $\text{Si}(111)\text{\ensuremath{-}}(7\ifmmode\times\else\texttimes\fi{}7)$ surface was found to behave as a strong electric rectifier, with a rectification ratio as large as $\ensuremath{\sim}150$. Based on first-principles calculations, we found that the wave functions of electronic states at different energies spread out from the surface to different distances. We demonstrated by theoretical simulations and experiments that the observed rectification is a result of coupling the scanning tunneling microscope tip with selective wave functions of the cluster.

We demonstrate the charge state of ${\mathrm{C}}_{60}$ on a Cu(111) surface can be made optimal, i.e., forming $\mathrm{C}_{60}{}^{3\ensuremath{-}}$ as required for superconductivity in bulk alkali-doped ${\mathrm{C}}_{60}$, purely through interface reconstruction rather than with foreign dopants. We link the origin of the $\mathrm{C}_{60}{}^{3\ensuremath{-}}$ charge state to a reconstructed interface with ordered ($4\ifmmode\times\else\texttimes\fi{}4$) 7-atom vacancy holes in the surface. In contrast, ${\mathrm{C}}_{60}$ adsorbed on unreconstructed Cu(111) receives a much smaller amount of electrons. Our results illustrate a definitive interface effect that affects the electronic properties of molecule-electrode contact.

Measurements of both the ordinary and extraordinary components of the Hall effect in co-sputtered granular magnetic Co-SiO2 nanocomposites are presented. The experiments were done in the temperature range 5 - 300 K, and fields up to 7 T. Both components show a large enhancement when the metal volume fraction is reduced to the metal-insulator transition. However the enhancement of the ordinary Hall effect is much weaker than that of the extraordinary one. We discuss the implications of this observation for understanding of the giant Hall effect.

Scanning tunneling spectroscopy measurements of Pb islands on Si(111) at high energy resolution reveal a novel pseudogap, or a pseudopeak in special cases, around the Fermi level in addition to the usual quantum well states. These gap or peak features persist to temperatures as high as approximately 80 K and are uniquely related to the quantum well nanostructure of the Pb islands. A systematic analysis indicates that electron-phonon scattering is responsible for the observed electronic structure.

Using scanning tunneling spectroscopy, we have investigated the local electronic property change upon single Co atom adsorption on Pb nanoislands and/or films grown on a $\text{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ surface. The quantum well states formed on the clean Pb film were found to be locally destroyed by the adsorbed single Co atom. Moreover, the differential conductance $dI/dV$ curves, exhibiting an asymmetric line shape with a dip and a hump, respectively, below and above the Fermi level, demonstrated a Kondo effect from the adsorbed Co atom on the Pb film. The similar line shapes of the $dI/dV$ spectra and the similar Kondo temperatures for Co atoms adsorbed on Pb island areas of different Pb thicknesses further showed that the different densities of states at the Fermi level originated from the quantum well states do not play a significant role, possibly due to the destruction of the quantum well states upon the Co atom adsorption.

Using scanning tunneling microscopy and spectroscopy and first principles calculations, we have systematically studied the morphological and electronic structures of a ${\mathrm{C}}_{60}$ monolayer on Ag(100). Our results reveal that the bright-dim contrast has a definite geometric origin and there are two types of dim ${\mathrm{C}}_{60}$ molecules, one a monomer and the other a dimer. With distinctive electronic properties and distinctive charge transfers in the differently adsorbed ${\mathrm{C}}_{60}$ molecules, this ${\mathrm{C}}_{60}$ monolayer is highly inhomogeneous and aperiodic.

Using scanning tunneling microscopy and first-principles density functional calculations, we have investigated systematically the initial stages of single Ge atoms adsorbed on a $\mathrm{Si}(111)\text{\ensuremath{-}}(7\ifmmode\times\else\texttimes\fi{}7)$ surface. When the deposition is at an elevated temperature of $420\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, single Ge atoms are found to substitute for the Si adatoms randomly. When the deposition is at room temperature, single Ge atoms do not replace the Si adatoms but move frequently within half unit cells. When the room temperature prepared sample is imaged at $78\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, the Ge atoms are observed to either adsorb at the stable high coordination sites near the corner Si adatoms or hop among the high coordination sites near the center Si adatoms. The adsorption sites of Ge atoms at high coordination positions have been determined by first-principles calculations and comparisons with measured scanning tunneling microscopic images.

We have found a perfect thermoelastic intermartensitic transformation between the seven-layer modulation $(7M)$ and the five-layer modulation $(5M)$ martensites in an unstressed ${\mathrm{Ni}}_{52}{\mathrm{Mn}}_{24}{\mathrm{Ga}}_{24}$ single crystal. In particular, we found that the intermartensitic transformation is very sensitive to the internal stress built up during the grinding process. Based on our calculation, an average internal stress of $13.8\ifmmode\pm\else\textpm\fi{}1.08 \mathrm{MPa}$ stored in the distorted lattice will force the parent phase to take a totally different martensitic transformation path during cooling and results in the entire suppression of the intermartensitic transformation. These results can be interpreted in terms of the formation of a $5M$ martensite which is facilitated by the elastic deformation.

During the past decade, a significant effort has been devoted to the study of photonic crystals (PC) [1–2], The existence of a spectrum gap in PC provides an opportunity to confine and control the propagation of electromagnetic waves. It can give rise to some peculiar physical phenomena, as well as wide applications in several scientific and technical areas [2–3]. Since all the novel properties as well as the application of PC rely on the existence of photonic band gaps (PBG), it is essential to design a crystal structure that can produce a large spectrum gap. Despite the tremendous progress that has been made in this direction, it remains an important issue to find a generic method that allows us to engineer a gap. In this work, as the first example of using the perturbative approach to the study of PC, we show that a perturbation analysis can provide us a simple, systematic, and efficient way to engineer an existing PBG.

We studied the resistive switching (RS) effect in LaAlO3/Nb:SrTiO3 heterostructures at different temperatures with AC impedance technique in addition to the conventional I–V measurements. It was demonstrated that the bipolar RS effect originates from LaAlO3/Nb:SrTiO3 interface and the resistance and capacitance states are controlled by the filling status of traps. A model based on the variation of trap state was proposed to explain the RS effect and the thermal history dependent electronic transport behavior. This work demonstrates the key role of trap state in the RS effect and electronic transport.

By measuring the temperature-dependent tunneling spectroscopy of a set of flat-top Pb islands from 3.2 to 15 K, the limiting size of a nine-monolayer-thick Pb island with superconductivity above 3.2 K was determined to be ∼ 30 nm(2), in good agreement with the Anderson criterion. Further analysis indicates that the zero-temperature energy gap decreases significantly faster than the transition temperature when the Pb island size approaches this limit. This leads to a decrease of 2Δ(0)/k(B)T(C) from 4.5 to 3.3, thus showing that the Pb island superconductors undergo a change from strong to weak electron-phonon coupling.

The multilayer relaxation of the Pt(210) stepped and kinked surface is analyzed by low-energy-electron diffraction. This is the first application of the new real-space multiple-scattering theory of LEED, designed specifically for such open surfaces where conventional theories fail. Combined with an automated tensor LEED method, it efficiently detects nonalternating atomic relaxations which are oriented primarily perpendicular to the surface. These relaxations are in qualitative agreement with new embedded-atom-method results.

A general approach is presented for investigation of the anisotropy of the degree of transport spin polarization (P) in ferromagnets both in the ballistic regime, P(1,i), and in the diffusive regime, P(2,i), as a function of crystal direction. The validity of this approach is confirmed by the benchmark calculation for the isotropic P. By this approach, we have investigated the anisotropy of P in bcc Fe, fcc Co, fcc Ni and hcp Co. For cubic structures, P(1,i) shows a small but appreciable anisotropy, due to the difference in the electronic orbital extension for spin-up and spin-down conduction bands. However, P(2,i) shows an isotropic feature for the cubic structure, as a result of the combination of its dependence on the square of electron velocity and the lattice symmetry. On the other hand, for hcp Co, both P(1,i) and P(2,i) show a very strong anisotropy. The large anisotropy of P(1,i) and P(2,i) in hcp Co is mainly attributed to the anisotropy of spin-down ballistic (diffusive) conductance.

Effect of a magnetic field on martensitic transformation in the NiCoMnGa alloys was investigated. A field-induced reversible martensitic transformation from the martensitic phase of low magnetization to the parent phase of high magnetization has been realized. The substitution of Co for Ni atoms has turned the magnetic ordering of the parent phase from partially antiferromagnetic to ferromagnetic, resulting in a large magnetization change across the transformation, which dramatically enhances the magnetic field driving force. The transformation temperature can be downshifted by magnetic field at a rate up to 14K∕T in Ni37Co13Mn32Ga18. Other mechanism details were also discussed.