Tuning the deposition of molecular graphene nanoribbons by surface functionalization

We show that individual, isolated graphene nanoribbons, created with a molecular synthetic approach, can be assembled on functionalised wafer surfaces treated with silanes. The use of surface groups with different hydrophobicities allows tuning the density of the ribbons and assessing the products of the polymerisation process.

Long- versus Short-Range Scattering in Doped Epitaxial Graphene

Tuning the electronic properties of graphene by adatom deposition unavoidably introduces disorder into the system, which directly affects the single-particle excitations and electrodynamics. Using angle-resolved photoemission spectroscopy (ARPES) we trace the evolution of disorder in graphene by thallium adatom deposition and probe its effect on the electronic structure. We show that the signatures of quasiparticle scattering in the photoemission spectral function can be used to identify thallium adatoms, although charged, as efficient short-range scattering centers. Employing a self-energy model for short-range scattering, we are able to extract a δ-like scattering potential δ = -3.2 ± 1 eV. Therefore, isolated charged scattering centers do not necessarily act just as good long-range (Coulomb) scatterers but can also act as efficient short-range (δ-like) scatterers; in the case of thallium, this happens with almost equal contributions from both mechanisms.

Uptake and depuration of gold nanoparticles in Daphnia magna

This study presents a series of short-term studies (total duration 48 h) of uptake and depuration of engineered nanoparticles (ENP) in neonate Daphnia magna. Gold nanoparticles (Au NP) were used to study the influence of size, stabilizing agent and feeding on uptake and depuration kinetics and animal body burdens. 10 and 30 nm Au NP with different stabilizing agents [citrate (CIT) and mercaptoundecanoic acid (MUDA)] were tested in concentrations around 0.5 mg Au/L. Fast initial uptake was observed for all studied Au NP, with CIT stabilized Au NP showing similar rates independent of size and MUDA showing increased uptake for the smaller Au NP (MUDA 10 nm > CIT 10 nm, 30 nm > MUDA 30 nm). However, upon transfer to clean media no clear trend on depuration rates was found in terms of stabilizing agent or size. Independent of stabilizing agent, 10 nm Au NP resulted in higher residual whole-animal body burdens after 24 h depuration than 30 nm Au NP with residual body burdens about one order of magnitude higher of animals exposed to 10 nm Au NP. The presence of food (P. subcapitata) did not significantly affect the body burden after 24 h of exposure, but depuration was increased. While food addition is not necessary to ensure D. magna survival in the presented short-term test design, the influence of food on uptake and depuration kinetics is essential to consider in long term studies of ENP where food addition is necessary. This study demonstrates the feasibility of a short-term test design to assess the uptake and depuration of ENP in D. magna. The findings underlines that the assumptions behind the traditional way of quantifying bioconcentration are not fulfilled when ENPs are studied.

A diamond-based scanning probe spin sensor operating at low temperature in ultra-high vacuum

We present the design and performance of an ultra-high vacuum (UHV) low temperature scanning probe microscope employing the nitrogen-vacancy color center in diamond as an ultrasensitive magnetic field sensor. Using this center as an atomic-size scanning probe has enabled imaging of nanoscale magnetic fields and single spins under ambient conditions. In this article we describe an experimental setup to operate this sensor in a cryogenic UHV environment. This will extend the applicability to a variety of molecular systems due to the enhanced target spin lifetimes at low temperature and the controlled sample preparation under UHV conditions. The instrument combines a tuning-fork based atomic force microscope (AFM) with a high numeric aperture confocal microscope and the facilities for application of radio-frequency (RF) fields for spin manipulation. We verify a sample temperature of <50 K even for strong laser and RF excitation and demonstrate magnetic resonance imaging with a magnetic AFM tip.

A natural topological insulator

The earth's crust and outer space are rich sources of technologically relevant materials which have found application in a wide range of fields. Well-established examples are diamond, one of the hardest known materials, or graphite as a suitable precursor of graphene. The ongoing drive to discover novel materials useful for (opto)electronic applications has recently drawn strong attention to topological insulators. Here, we report that Kawazulite, a mineral with the approximate composition Bi2(Te,Se)2(Se,S), represents a naturally occurring topological insulator whose electronic properties compete well with those of its synthetic counterparts. Kawazulite flakes with a thickness of a few tens of nanometers were prepared by mechanical exfoliation. They exhibit a low intrinsic bulk doping level and correspondingly a sizable mobility of surface state carriers of more than 1000 cm(2)/(V s) at low temperature. Based on these findings, further minerals which due to their minimized defect densities display even better electronic characteristics may be identified in the future.

Superexchange-mediated ferromagnetic coupling in two-dimensional Ni-TCNQ networks on metal surfaces

We investigate the magnetic coupling of Ni centers embedded in two-dimensional metal-coordination networks self-assembled from 7,7,8,8-tetracyanoquinodimethane (TCNQ) molecules on Ag(100) and Au(111) surfaces. X-ray magnetic circular dichroism measurements show that single Ni adatom impurities assume a spin-quenched configuration on both surfaces, while Ni atoms coordinating to TCNQ ligands recover their magnetic moment and exhibit ferromagnetic coupling. The valence state and the ferromagnetic coupling strength of the Ni coordination centers depend crucially on the underlying substrate due to the different charge state of the TCNQ ligands on the two surfaces. The results suggest a superexchange coupling mechanism via the TCNQ ligands.

Giant ambipolar Rashba effect in the semiconductor BiTeI

We observe a giant spin-orbit splitting in the bulk and surface states of the noncentrosymmetric semiconductor BiTeI. We show that the Fermi level can be placed in the valence or in the conduction band by controlling the surface termination. In both cases, it intersects spin-polarized bands, in the corresponding surface depletion and accumulation layers. The momentum splitting of these bands is not affected by adsorbate-induced changes in the surface potential. These findings demonstrate that two properties crucial for enabling semiconductor-based spin electronics-a large, robust spin splitting and ambipolar conduction-are present in this material.

In-plane magnetic anisotropy of Fe atoms on Bi2Se3(111)

The robustness of the gapless topological surface state hosted by a 3D topological insulator against perturbations of magnetic origin has been the focus of recent investigations. We present a comprehensive study of the magnetic properties of Fe impurities on the prototypical 3D topological insulator Bi(2)Se(3) using local low-temperature scanning tunneling spectroscopy and integral x-ray magnetic circular dichroism techniques. Single Fe adatoms on the Bi(2)Se(3) surface, in the coverage range ≈ 1% of a monolayer, are heavily relaxed into the surface and exhibit a magnetic easy axis within the surface plane, contrary to what was assumed in recent investigations on the supposed opening of a gap. Using ab initio approaches, we demonstrate that an in-plane easy axis arises from the combination of the crystal field and dynamic hybridization effects.

Background-free imaging of plasmonic structures with cross-polarized apertureless scanning near-field optical microscopy

We present advances in experimental techniques of apertureless scanning near-field optical microscopy (aSNOM). The rational alignment procedure we outline is based upon a phase singularity that occurs while scanning polarizers around the nominal cross-polarized configuration of s-polarized excitation and p-polarized detection. We discuss the theoretical origin of this topological feature of the setup, which is robust against small deviations, such as minor tip misalignment or shape variations. Setting the polarizers to this singular configuration point eliminates all background signal, allowing for reproducible plasmonic eigenmode mapping with optimal signal-to-noise ratio.

Levetiracetam compared to phenytoin for the prevention of postoperative seizures after craniotomy for intracranial tumours in patients without epilepsy

Anticonvulsant drugs are frequently given after craniotomy. Phenytoin (PHT) is the most commonly used agent; levetiracetam (LEV) is a new anticonvulsant drug with fewer side effects. To compare the incidence of seizures in patients receiving either prophylactic PHT or LEV perioperatively, 971 patients undergoing a craniotomy were analysed retrospectively during a 2-year period. PHT was used routinely and LEV was administered when PHT was contraindicated. Seizures documented during the first 7 days after craniotomy were considered. A total of 235 patients were treated with an antiepileptic drug: 81 patients received LEV, and 154 patients, PHT. Two patients receiving LEV (2.5%) and seven receiving PHT (4.5%) had a seizure despite this treatment. No patient had a documented side effect or drug interaction. The data show that LEV may be an alternative option in patients with contraindications to PHT.

Ge-Quantum Dots on SI(001) Tailored by Carbon Predeposition

The morphology of Si(001) after carbon deposition of 0.05 to 0.11 monolayers (ML) was investigated in situ by ultrahigh vacuum scanning tunneling microscopy (UHV-STM). The carbon induces a c(4×4)-reconstruction of the surface. In addition, carbon increases the surface roughness compared to clean Si(001) (2×1). In a second step, the influence of the carbon induced restructuring on Ge-island nucleation was investigated. The 3D-growth sets in at considerably lower Ge coverage compared to the clean Si(001) (2×1) surface. This leads to a high density of small though irregularly shaped dots, consisting of stepped terraces, already at 2.5 ML Ge. Increasing the Ge-coverage beyond the critical thickness for facet formation, the dots show { 105 }- facets well known from Ge-clusters on bare Si(001) (2×1). However, they are flat on top with a (001)-facet showing the typical buckled Ge rows and missing dimers. This indicates that the compressive strain is not fully relaxed in these hut clusters.

Fractal and Dendritic Growth of Surface Aggregates

The similarity of patterns formed in non-equilibrium growth processes in physics, chemistry and biology is conspicuous and many attempts have been made to discover common mechanisms underlying their growth. The central question in this context is what causes some patterns to be dendritic, as e.g. snowflakes, while others grow fractal (randomly ramified). Here we report a crossover from fractal to dendritic patterns for growth in two dimensions: the diffusion limited aggregation of Ag atoms on a Pt(111) surface as observed by means of variable temperature STM. The microscopic mechanism of dendritic growth can be analyzed for the present system. It originates from the anisotropy of the diffusion of adatoms at corner sites which is linked to the trigonal symmetry of the substrate. This corner diffusion is observed to be active as soon as islands form, therefore, the classical DLA clusters with the hit and stick mechanism do not form. The ideas on the mechanism for dendritic growth have been verified by kinetic Monte-Carlo simulations which are in excellent agreement with experiment.

Versatile optical access to the tunnel gap in a low-temperature scanning tunneling microscope

We developed a setup that provides three independent optical access paths to the tunnel junction of an ultrahigh vacuum low temperature (4.2 K) scanning tunneling microscope (STM). Each path can be individually chosen to couple light in or out, or to image the tunnel junction. The design comprises in situ adjustable aspheric lenses to allow tip exchange. The heat input into the STM is negligible. We present in detail the beam geometry and the realization of lens adjustment. Measurements demonstrate the characterization of a typical light source exemplified by emission from tip-induced plasmons. We suggest employing the Fourier transforming properties of imaging lenses and polarization analysis to obtain additional information on the light emission process. Performance and future potential of the instrument are discussed.

An Exploratory Study of the Biological Activity of Sunitinib as a Component of Neoadjuvant Therapy for Breast Cancer

Background: The neoadjuvant setting provides an ideal opportunity to explore the impact of sunitinib alone and in combination with paclitaxel on the functional status of tumor vasculature as indicated by changes in tumor interstitial pressure (IFP) and circulating progenitor cell (CPC) subsets.Methods: Patients(pts.) with newly diagnosed stage Ic-IIIc breast cancer were treated with sunitinib monotherapy (100 mg Day 1; 37.5 mg D2-14) prior to the initiation of paclitaxel (80 mg/M2 D1,8,15 every 28 days x 4 cycles) with sunitinib (25 mg/d). IFP and CPC subsets were assessed at baseline and after sunitinib monotherapy. IFP was measured in three separate areas of the tumor using a micropressure transducer catheter; mean and highest IFP recorded were analyzed. Improvements in poly-chromatic flow cytometry allowed distinction of pro-angiogenic (pCPC = Live/AC133+CD34bright/CD31+CD45dim\), from non-angiogenic (nCPC = Live/AC133-CD34bright/CD31+/CD45dim\), CPCs that cannot be quantified separately using previously reported protocols1. Baseline CPC subsets were also compared to age and gender matched healthy controls.Results: From July 2008 to May 2009, 14 pts were enrolled; baseline and post-sunitinib IFP and CPC data are available for 12 and 11 pts respectively. The median age was 48 (range 32-69). Mean pretreatment tumor diameter was 3.2 cm. Sunitinib monotherapy was generally well tolerated; two patients developed grade III toxicities including hypertension (n=1) and hand-foot syndrome (n=1). Sunitinib significantly decreased mean IFP (18.87 mmHg vs. 6.38 mmHg; p=0.002); similar results were obtained when only the maximum IFP was considered (22.32 mmHg vs. 8.36 mmHg; p=0.003). pCPC frequency was not different between pts and healthy controls (0.099% vs. 0.076%, p=0.24) but the p:nCPC ratio was significantly higher in pts compared to healthy controls (3.26 vs. 1.46; p=0.001) suggesting a shift toward vascular damage and/or active angiogenesis. Both pCPC frequency (0.099 vs. 0.022; p=0.001) and p:nCPC ratio (3.26 vs. 0.78; p=0.001) significantly decreased after sunitinib monotherapy. Analysis of paclitaxel + sunitinib is too early (n=4).Conclusion: Sunitinib, through its effects on VEGF-mediated vascular permeability, markedly reduces tumor IFP. In addition sunitinib profoundly reduces pCPCs that are thought to be important for angiogenesis in human cancers. Accrual is ongoing (planned N=40). Analysis of IFP and CPC subsets after paclitaxel + sunitinib as well as additional correlates will be presented.1 Duda et al. (2007). Nat. Protocol 2, 805-810.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 202.

An Exploratory Study of Sunitinib (SU) Plus Docetaxel (D) and Trastuzumab (T) for First-Line Therapy of HER2+ Advanced Breast Cancer (ABC)

Background: T + D is a standard 1st-line treatment (tx) for HER2+ ABC (locally recurrent or metastatic BC). SU is an oral, multitargeted tyrosine kinase inhibitor of VEGFRs, PDGFRs, KIT, RET, and FLT3 with single-agent activity in previously treated ABC. In this study, a SU/D/T combination was investigated as 1st-line tx for pts with HER2+ ABC.Materials and methods: Female pts (≥18 yrs, ECOG PS ≤1) with HER2+ ABC were enrolled. Starting doses were D: 75 mg/m2, q3w, iv, day 1; T q1w: 4 mg/kg, day 1, followed by 2 mg/kg q1w, iv or q3w: 8 mg/kg, day 1, followed by 6 mg/kg q3w, iv; SU: 37.5 mg/d, Schedule 2/1, po, day 2. The primary objective was safety. Antitumor activity and pharmacokinetics were secondary endpoints. On discontinuation of D, responsive pts (PR or SD) could continue SU + T until disease progression.Results: As of Mar 2009, 25 pts were enrolled. 1 pt did not receive tx, 1 pt received a dose of D/T (pt died from multiorgan failure after T administration), and 23 pts received ≥1 dose of SU/D/T; data from the latter group are reported. 12 pts (52%) were chemo-naïve. 5 pts continue on study tx; 18 have discontinued (8 due to PD, 2 due to pt decision, 7 due to AEs, 1 due to global deterioration). Pts received 201/128/211 cycles of SU/D/T, respectively, with a median of 9/6/10 cycles/pt (range: 1–18/1–12/1–18). The 37.5 mg/d SU dose was reduced to 25 mg/d in 14/23 pts and interrupted in 17/23 pts. AEs led to SU dose reductions/interruptions in 17 pts, most frequently grade (G) 3/4 neutropenia (n=8) and G3 febrile neutropenia, G3 fatigue, and G3 diarrhea (each n=2). In 23 evaluable pts, the most frequent non-hematologic G3 AEs were fatigue/asthenia (26%), diarrhea (13%), and stomatitis, vomiting, and dyspnea (each 9%). G4 AEs were transaminase increase, accidental overdose of SU, and intestinal perforation (each n=1). 1 cardiac AE was reported (G3 supraventricular tachycardia) and transient G1/2 LVEF decline was seen in 2 pts (9%). G3/4 neutropenia was reported in 20 pts (91%); 5 pts (22%) had febrile neutropenia. 2 pts (9%) had G3 anemia and 1 pt (4%) had G3 thrombocytopenia. G-CSF was administered to 11 pts without complications. Preliminary median steady-state levels of SU and its metabolite: 40.6 and 15.6 ng/mL, respectively; end D infusion: 993 ng/mL; T levels: &lt;20 µg/mL. In 19 evaluable pts, ORR was 79% (1 CR [5%], 14 confirmed PRs [74%], 2 SD [11%]). Preliminary median PFS was 10.5 months (95% CI: 8.1–13.6) and median DR was 9.0 months (95% CI: 7.3–12.3).Conclusions: The combination of SU/D/T, given as 1st-line tx to HER2+ pts with ABC, is feasible. AEs were manageable through dose delay/reduction, and no new, unexpected AEs occurred. SU and D levels were consistent with known single-agent levels; evaluation of T levels is ongoing. Preliminary evidence of antitumor activity is encouraging and warrants further evaluation.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6088.

Sunitinib (SU) in Combination with Trastuzumab (T) for the Treatment of Advanced Breast Cancer (ABC): Activity and Safety Results from a Phase II Study

Background: SU is an oral, multitargeted tyrosine kinase inhibitor of VEGFRs, PDGFRs, KIT, RET, FLT3, and CSF-1R, with single-agent activity in patients (pts) with heavily pretreated ABC (locally recurrent or metastatic breast cancer). T is approved for 2nd-line monotherapy and in combination with taxane-based therapies for 1st-line ABC. The combination of SU + T in HER2+ ABC pts was investigated.Materials and methods: Eligible pts with HER2+ ABC received a starting dose of oral SU 37.5 mg/d (continuous daily dosing [CDD]) and either T administered wkly (iv loading 4 mg/kg then wkly 2 mg/kg) or q3w (loading 8 mg/kg then q3w 6 mg/kg). Due to changing standard of care, the trial was amended to include pts having prior chemotherapy in the 1st-line setting. Previous treatment (tx) with T (± lapatinib) was permitted. The primary endpoint was objective response rate (ORR). Secondary endpoints included safety, progression-free survival (PFS), pharmacokinetics (PK) and quality of life (QoL).Results: As of April 2009, 60 pts were enrolled (6 on the original protocol and 54 under the amendment). Of 54 pts enrolled post-amendment, 6 pts continue on study and 48 have discontinued, 12 due to AEs. Most (n=31; 57%) pts received SU + T as 1st-line tx and 11/31 pts were completely tx-naïve. Pts received a median of 5 cycles (range: 1–16) of SU and 4 cycles (range: 1–15) of T. SU was dose reduced from 37.5 mg/d to 25 mg/d in 39% of pts. All pts were evaluable for safety and 52 pts were evaluable for efficacy. ORR was 34.6% and clinical benefit rate was 48% (2 CR; 16 PR; 7 SD ≥24 wks). Of the 18 responders, 5 pts were completely tx-naïve and 9 pts were 1st-line. Median PFS was 25.3 wks (95% CI, 19.3, 29.1). Most AEs were G1/2. G3 non-hematologic AEs in ≥10% pts were asthenia (17%) and hypertension (11%) and 3 G4 events occurred (LVEF decline, pulmonary embolism, and pancreatitis). Hematologic AEs (G3/4 in ≥10% pts) were neutropenia (22%) and thrombocytopenia (17%). One G5 event (cardiogenic shock) was reported. LVEF decline/LV dysfunction occurred in 21 pts (6 pts had ≥G3 AEs); 18/21 pts (86%) had received prior anthracycline and 12 pts (57%) prior T. There was no significant on-tx change from baseline in the QoL domain. Mean (SD) steady state level for SU was 46.1 (25.9) ng/mL in agreement with prior observations.Conclusions: The combination of SU (37.5 mg/d; CDD schedule) + T (wkly or q3w) showed acceptable tolerability and antitumor activity in HER2+ ABC pts without adversely affecting overall QoL.

Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 201.

Silicon surface with giant spin splitting

We demonstrate a giant Rashba-type spin splitting on a semiconducting substrate by means of a Bi-trimer adlayer on a Si(111) wafer. The in-plane inversion symmetry is broken inducing a giant spin splitting with a Rashba energy of about 140 meV, much larger than what has previously been reported for any semiconductor heterostructure. The separation of the electronic states is larger than their lifetime broadening, which has been directly observed with angular resolved photoemission spectroscopy. The experimental results are confirmed by relativistic first-principles calculations.

Full simulations of the apertureless scanning near field optical microscopy signal: achievable resolution and contrast

We simulate apertureless near-field optical imaging and obtain phase and amplitude scans of structured substrates for elastic scattering. The solution of the three-dimensional Maxwell equations does not involve approximations and we include large tips and substrates, strong interaction, interferometric detection and demodulation at higher harmonics. Such modeling represents a significant step towards quantitative simulations and offers the attractive possibility to study the individual influence of each relevant experimental parameter. We typically obtain highly localized signatures of the interaction of the tip with gold inclusions, superposed on a slowly varying background signal. The relative importance of both contributions and the achievable lateral resolution are strongly dependent on the geometry and scanning conditions. The simulations show sensitivity mostly to the first nanometers of the sample and underline the importance of scanning near the sample and being careful with mechanical anharmonicities on the tip oscillation. They also help to determine the influence of oscillation amplitude and demodulation harmonic.

Magnetism of FePt surface alloys

The complex correlation of structure and magnetism in highly coercive monoatomic FePt surface alloys is studied using scanning tunneling microscopy, x-ray magnetic circular dichroism, and ab initio theory. Depending on the specific lateral atomic coordination of Fe either hard magnetic properties comparable to that of bulk FePt or complex noncollinear magnetism due to Dzyaloshinski-Moriya interactions are observed. Our calculations confirm the subtle dependence of the magnetic anisotropy and spin alignment on the local coordination and suggest that 3D stacking of Fe and Pt layers in bulk L1_{0} magnets is not essential to achieve high-anisotropy values.

Quasiparticle chirality in epitaxial graphene probed at the nanometer scale

Graphene exhibits unconventional two-dimensional electronic properties resulting from the symmetry of its quasiparticles, which leads to the concepts of pseudospin and electronic chirality. Here, we report that scanning tunneling microscopy can be used to probe these unique symmetry properties at the nanometer scale. They are reflected in the quantum interference pattern resulting from elastic scattering off impurities, and they can be directly read from its fast Fourier transform. Our data, complemented by theoretical calculations, demonstrate that the pseudospin and the electronic chirality in epitaxial graphene on SiC(0001) correspond to the ones predicted for ideal graphene.