Decay times of the spin-forbidden and spin-enabled transitions of Yb2+ doped in CsCaX3 and CsSrX3 (X = Cl, Br, I).

In this paper, a systematic study of the decay times of the spin-enabled and spin-forbidden transitions of Yb2+ doped into the halidoperovskites CsMX3 (M = Ca, Sr; X = Cl, Br, I) is presented. The spin-forbidden transitions are characterized by ms decay times, which are typical for Yb2+. On the contrary, the spin-enabled transitions show much shorter decay times in the range of µs and have so far only been rarely observed. These results allow detailed conclusions about systematics of the decay times of Yb2+ doped in similar compounds and their correlation to the local structure of the coordination sphere of Yb2+ as well as the role of vibrational interaction between the excited high spin (HS) and low spin (LS) states. The halidoperovskites are ideally suited as host lattices in this context and may work as text book examples due to their comparable structures, which allows a detailed interpretation of the decay times in relation to the local structure. An understanding of the impact of the composition and structure of the host material on the decay times of Yb2+ will be of relevance for future applications of this activator in scintillators or lighting materials.

Live birth in the Devonian period.

The extinct placoderm fishes were the dominant group of vertebrates throughout the Middle Palaeozoic era, yet controversy about their relationships within the gnathostomes (jawed vertebrates) is partly due to different interpretations of their reproductive biology. Here we document the oldest record of a live-bearing vertebrate in a new ptyctodontid placoderm, Materpiscis attenboroughi gen. et sp. nov., from the Late Devonian Gogo Formation of Australia (approximately 380 million years ago). The new specimen, remarkably preserved in three dimensions, contains a single, intra-uterine embryo connected by a permineralized umbilical cord. An amorphous crystalline mass near the umbilical cord possibly represents the recrystallized yolk sac. Another ptyctodont from the Gogo Formation, Austroptyctodus gardineri, also shows three small embryos inside it in the same position. Ptyctodontids have already provided the oldest definite evidence for vertebrate copulation, and the new specimens confirm that some placoderms had a remarkably advanced reproductive biology, comparable to that of some modern sharks and rays. The new discovery points to internal fertilization and viviparity in vertebrates as originating earliest within placoderms.

An exceptional Devonian fish from Australia sheds light on tetrapod origins.

The transition from fishes to tetrapods was one of the most dramatic events in the evolution of vertebrates, but many pivotal fossils are incomplete, resulting in gaps in the data that are used for phylogenetic reconstruction. Here we present new observations from the most complete, acid-prepared Devonian tetrapodomorph fish yet discovered, Gogonasus, which was previously placed just crownward of Kenichthys and rhizodontids, the most primitive taxa on the tetrapod lineage. Unexpectedly, Gogonasus shows a mosaic of plesiomorphic and derived tetrapod-like features. Whereas the braincase and dermal cranial skeleton exhibit generalized morphologies with respect to Eusthenopteron or Panderichthys, taxa that are traditionally considered to be phyletically close to tetrapods, the presence of a deeply invaginated, wide spiracle, advanced internal spiracular architecture and near-horizontal hyomandibula are specialized features that are absent from Eusthenopteron. Furthermore, the pectoral fin skeleton of Gogonasus shares several features with that of Tiktaalik, the most tetrapod-like fish. A new phylogenetic analysis places Gogonasus crownward of Eusthenopteron as the sister taxon to the Elpistostegalia. Aspects of the basic tetrapod limb skeleton and middle ear architecture can now be traced further back within the tetrapodomorph radiation.

In vivo tumour imaging employing regional delivery of novel gallium radiolabelled polymer composites.

BACKGROUND: Understanding the regional vascular delivery of particles to tumour sites is a prerequisite for developing new diagnostic and therapeutic composites for treatment of oncology patients. We describe a novel imageable 67Ga-radiolabelled polymer composite that is biocompatible in an animal tumour model and can be used for preclinical imaging investigations of the transit of different sized particles through arterial networks of normal and tumour-bearing organs. RESULTS: Radiolabelling of polymer microspheres with 67Ga was achieved using a simple mix and wash method, with tannic acid as an immobilising agent. Final in vitro binding yields after autoclaving averaged 94.7%. In vivo stability of the composite was demonstrated in New Zealand white rabbits by intravenous administration, and intrahepatic artery instillations were made in normal and VX2 tumour implanted rabbit livers. Stability of radiolabel was sufficient for rabbit lung and liver imaging over at least 3 hours and 1 hour respectively, with lung retention of radiolabel over 91%, and retention in both normal and VX2 implanted livers of over 95%. SPECT-CT imaging of anaesthetised animals and planar imaging of excised livers showed visible accumulation of radiolabel in tumours. Importantly, microsphere administration and complete liver dispersal was more easily achieved with 8 µm diameter MS than with 30 µm MS, and the smaller microspheres provided more distinct and localised tumour imaging. CONCLUSION: This method of producing 67Ga-radiolabelled polymer microspheres is suitable for SPECT-CT imaging of the regional vascular delivery of microspheres to tumour sites in animal models. Sharper distinction of model tumours from normal liver was obtained with smaller MS, and tumour resolution may be further improved by the use of 68Ga instead of 67Ga, to enable PET imaging.

99mTc-radiolabeled composites enabling in vivo imaging of arterial dispersal and retention of microspheres in the vascular network of rabbit lungs, liver, and liver tumors.

PURPOSE: Selective internal radiation therapy (SIRT) is an effective treatment option for liver tumors, using Y-90-loaded polymer microspheres that are delivered via catheterization of the hepatic artery. Since Y-90 is a beta emitter and not conveniently imaged by standard clinical instrumentation, dosimetry is currently evaluated in each patient using a surrogate particle, 99mTechnetium-labeled macroaggregated albumin (99mTc-MAA). We report a new composite consisting of 99mTc-labeled nanoparticles attached to the same polymer microspheres as used for SIRT, which can be imaged with standard SPECT. METHODS: Carbon nanoparticles with an encapsulated core of 99mTc were coated with the polycation protamine sulfate to provide electrostatic attachment to anionic polystyrene sulfonate microspheres of different sizes (30, 12, and 8 µm). The in vivo stability of these composites was determined via intravenous injection and entrapment in the capillary network of normal rabbit lungs for up to 3 hours. Furthermore, we evaluated their biodistribution in normal rabbit livers, and livers implanted with VX2 tumors, following intrahepatic artery instillation. RESULTS: We report distribution tests for three different sizes of radiolabeled microspheres and compare the results with those obtained using 99mTc-MAA. Lung retention of the radiolabeled microspheres ranged from 72.8% to 92.9%, with the smaller diameter microspheres showing the lowest retention. Liver retention of the microspheres was higher, with retention in normal livers ranging from 99.2% to 99.8%, and in livers with VX2 tumors from 98.2% to 99.2%. The radiolabeled microspheres clearly demonstrated preferential uptake at tumor sites due to the increased arterial perfusion produced by angiogenesis. CONCLUSION: We describe a novel use of radiolabeled carbon nanoparticles to generate an imageable microsphere that is stable in vivo under the shear stress conditions of arterial networks. Following intra-arterial instillation in the normal rabbit liver, they distribute in a distinct segmented pattern, with the smaller microspheres extending throughout the organ in finer detail, while still being well retained within the liver. Furthermore, in livers hosting an implanted VX2 tumor, they reveal the increased arterial perfusion of tumor tissue resulting from angiogenesis. These novel composites may have potential as a more representative mimic of the vascular distribution of therapeutic microspheres in patients undergoing SIRT.

Imaging honey bee brain anatomy with micro-X-ray-computed tomography.

Technologies for imaging in three dimensions are greatly desired by researchers in many biological disciplines. However, when imaging small animals such as invertebrates, the achievement of satisfactory spatial resolution and adequate contrast between tissues often requires the use of expensive and time-consuming procedures. Micro-X-ray-computed tomography (muCT) is a convenient technique which is finding greater use alongside conventional microscopies. Staining with heavy metal salts, such as osmium tetroxide improves imaging in muCT, and allows visualization of the 3D structure of the honey bee brain undistorted within the intact head capsule. We obtained detailed information about the morphology of the different brain compartments and were able to show their orientations, relative to each other, within the head capsule. This technique offers a significant improvement in resolution, time, and expense for the quantitative, three-dimensional analysis of developing bee brain centers. In this article, we introduce a rapid, high-resolution, and inexpensive technique for the three-dimensional visualization of different compartments of the honey bee brain. A detailed discussion of the honey bee brain anatomy is provided, demonstrating that muCT, with osmium staining, can indeed visualise these structures. Hence, our results show that muCT is ideally suited for researchers who are interested in the 3D visualization of small invertebrate brains.

Quenching of the red Mn4+ luminescence in Mn4+-doped fluoride LED phosphors.

Red-emitting Mn4+-doped fluorides are a promising class of materials to improve the color rendering and luminous efficacy of white light-emitting diodes (w-LEDs). For w-LEDs, the luminescence quenching temperature is very important, but surprisingly no systematic research has been conducted to understand the mechanism for thermal quenching in Mn4+-doped fluorides. Furthermore, concentration quenching of the Mn4+ luminescence can be an issue but detailed investigations are lacking. In this work, we study thermal quenching and concentration quenching in Mn4+-doped fluorides by measuring luminescence spectra and decay curves of K2TiF6:Mn4+ between 4 and 600 K and for Mn4+ concentrations from 0.01% to 15.7%. Temperature-dependent measurements on K2TiF6:Mn4+ and other Mn4+-doped phosphors show that quenching occurs through thermally activated crossover between the 4T2 excited state and 4A2 ground state. The quenching temperature can be optimized by designing host lattices in which Mn4+ has a high 4T2 state energy. Concentration-dependent studies reveal that concentration quenching effects are limited in K2TiF6:Mn4+ up to 5% Mn4+. This is important, as high Mn4+ concentrations are required for sufficient absorption of blue LED light in the parity-forbidden Mn4+ d-d transitions. At even higher Mn4+ concentrations (>10%), the quantum efficiency decreases, mostly due to direct energy transfer to quenching sites (defects and impurity ions). Optimization of the synthesis to reduce quenchers is crucial for developing more efficient highly absorbing Mn4+ phosphors. The present systematic study provides detailed insights into temperature and concentration quenching of Mn4+ emission and can be used to realize superior narrow-band red Mn4+ phosphors for w-LEDs.

Co-precipitation Synthesis and Optical Properties of Mn4+-doped Hexafluoroaluminate w-LED Phosphors.

Mn4+-activated hexafluoroaluminates are promising red-emitting phosphors for white light emitting diodes (w-LEDs). Here, we report the synthesis of Na3AlF6:Mn4+, K3AlF6:Mn4+ and K2NaAlF6:Mn4+ phosphors through a simple two-step co-precipitation method. Highly monodisperse large (~20 µm) smoothed-octahedron shaped crystallites are obtained for K2NaAlF6:Mn4+. The large size, regular shape and small size distribution are favorable for application in w-LEDs. All Mn4+-doped hexafluoroaluminates show bright red Mn4+ luminescence under blue light excitation. We compare the optical properties of Na3AlF6:Mn4+, K3AlF6:Mn4+ and K2NaAlF6:Mn4+ at room temperature and 4 K. The luminescence measurements reveal that multiple Mn4+ sites exist in M3AlF6:Mn4+ (M = Na, K), which is explained by the charge compensation that is required for Mn4+ on Al3+ sites. Thermal cycling experiments show that the site distribution changes after annealing. Finally, we investigate thermal quenching and show that the luminescence quenching temperature is high, around 460-490 K, which makes these Mn4+-doped hexafluoroaluminates interesting red phosphors for w-LEDs. The new insights reported on the synthesis and optical properties of Mn4+ in the chemically and thermally stable hexafluoroaluminates can contribute to the optimization of red-emitting Mn4+ phosphors for w-LEDs.

Photonic Effects for Magnetic Dipole Transitions.

The radiative transition probability is a fundamental property for optical transitions. Extensive research, theoretical and experimental, has been conducted to establish the relation between the photonic environment and electric dipole (ED) transition probabilities. Recent work shows that the nanocrystal (NC)-cavity model accurately describes the influence of the refractive index n on ED transition rates for emitters in NCs. For magnetic dipole (MD) transitions, theory predicts a simple n3 dependence. However, experimental evidence is sparse and difficult to obtain. Here we report Eu3+-(with distinct ED+MD transitions) and Gd3+-(MD transitions) doped ß-NaYF4 NC model systems to probe the influence of n on ED and MD transition probabilities through luminescence lifetime and ED/MD intensity ratio measurements. The results provide strong experimental evidence for an n3 dependence of MD transition probabilities. This insight is important for understanding and controlling the variation of spectral distribution in emission spectra by photonic effects.

Questioning hagfish affinities of the enigmatic Devonian vertebrate Palaeospondylus.

Palaeospondylus gunni Traquair, 1890 is an enigmatic Devonian vertebrate whose taxonomic affinities have been debated since it was first described. Most recently, Palaeospondylus has been identified as a stem-group hagfish (Myxinoidea). However, one character questioning this assignment is the presence of three semicircular canals in the otic region of the cartilaginous skull, a feature of jawed vertebrates. Additionally, new tomographic data reveal that the following characters of crown-group gnathostomes (chondrichthyans + osteichthyans) are present in Palaeospondylus: a longer telencephalic region of the braincase, separation of otic and occipital regions by the otico-occipital fissure, and vertebral centra. As well, a precerebral fontanelle and postorbital articulation of the palatoquadrate are characteristic of certain chondrichthyans. Similarities in the structure of the postorbital process to taxa such as Pucapampella, and possible presence of the ventral cranial fissure, both support a resolution of Pa. gunni as a stem chondrichthyan. The internally mineralized cartilaginous skeleton in Palaeospondylus may represent a stage in the loss of bone characteristic of the Chondrichthyes.

MicroCT reveals domesticated rice (Oryza sativa) within pottery sherds from early Neolithic sites (4150-3265 cal BP) in Southeast Asia.

Rice (Oryza sativa) was domesticated in the Yangtze Valley region at least 6000-8000 years ago, yet the timing of dispersal of domesticated rice to Southeast Asia is contentious. Often rice is not well-preserved in archaeobotanical assemblages at early Neolithic sites in the wet tropics of Southeast Asia and consequently rice impressions in pottery have been used as a proxy for rice cultivation despite their uncertain taxonomic and domestication status. In this research, we use microCT technology to determine the 3D microscale morphology of rice husk and spikelet base inclusions within pottery sherds from early Neolithic sites in Vietnam. In contrast to surface impressions, microCT provides images of the entire husk and spikelet base preserved within the pottery, including the abscission scar characteristic of domesticated rice. This research demonstrates the potential of microCT to be a new, non-destructive method for the identification of domesticated plant remains within pottery sherds, especially in contexts where archaeobotanical preservation is poor and chaff-tempered sherds are rare and unavailable for destructive analysis. The method has the potential to greatly advance the understanding of crop domestication and agricultural dispersal for ceramic cultures in different parts of the world.

Structure and properties of clinical coralline implants measured via 3D imaging and analysis.

The development and design of advanced porous materials for biomedical applications requires a thorough understanding of how material structure impacts on mechanical and transport properties. This paper illustrates a 3D imaging and analysis study of two clinically proven coral bone graft samples (Porites and Goniopora). Images are obtained from X-ray micro-computed tomography (micro-CT) at a resolution of 16.8 microm. A visual comparison of the two images shows very different structure; Porites has a homogeneous structure and consistent pore size while Goniopora has a bimodal pore size and a strongly disordered structure. A number of 3D structural characteristics are measured directly on the images including pore volume-to-surface-area, pore and solid size distributions, chord length measurements and tortuosity. Computational results made directly on the digitized tomographic images are presented for the permeability, diffusivity and elastic modulus of the coral samples. The results allow one to quantify differences between the two samples. 3D digital analysis can provide a more thorough assessment of biomaterial structure including the pore wall thickness, local flow, mechanical properties and diffusion pathways. We discuss the implications of these results to the development of optimal scaffold design for tissue ingrowth.

Compact quantum dot-antibody conjugates for FRET immunoassays with subnanomolar detection limits.

A novel two-step approach for quantum dot (QD) functionalization and bioconjugation is presented, which yields ultra-compact, stable, and highly luminescent antibody-QD conjugates suitable for use in FRET immunoassays. Hydrophobic InPZnS/ZnSe/ZnS (emission wavelength: 530 nm), CdSe/ZnS (605 nm), and CdSeTe/ZnS (705 nm) QDs were surface functionalized with zwitterionic penicillamine, enabling aqueous phase transfer under conservation of the photoluminescence properties. Post-functionalization with a heterobifunctional crosslinker, containing a lipoic acid group and a maleimide function, enabled the subsequent coupling to sulfhydryl groups of proteins. This was demonstrated by QD conjugation with fragmented antibodies (F(ab)). The obtained F(ab)-QD conjugates range among the smallest antibody-functionalized nanoprobes ever reported, with a hydrodynamic diameter <13 nm, PL quantum yield up to 66% at 705 nm, and colloidal stability of several months in various buffers. They were applied as FRET acceptors in homogeneous, time-gated immunoassays using Tb-antibodies as FRET donors, both coupled by an immunological sandwich complex between the two antibodies and a PSA (prostate specific antigen) biomarker. The advantages of the compact surface coating for FRET could be demonstrated by an 6.2 and 2.5 fold improvement of the limit of detection (LOD) for PSA compared to commercially available hydrophilic QDs emitting at 605 and 705 nm, respectively. While the commercial QDs contain identical inorganic cores responsible for their fluorescence, they are coated with a comparably thick amphiphilic polymer layer leading to much larger hydrodynamic diameters (>26 nm without biomolecules). The LODs of 0.8 and 3.7 ng mL(-1) obtained in 50 µL serum samples are below the clinical cut-off level of PSA (4 ng mL(-1)) and demonstrate their direct applicability in clinical diagnostics.

Micromanipulation of phospholipid bilayers by atomic force microscopy.

The molecular details of adhesion mechanics in phospholipid bilayers have been studied using atomic force microscopy (AFM). Under tension fused bilayers of dipalmitoylphosphatidylcholine (DPPC) yield to give non-distance dependent and discrete force plateaux of 45.4, 81.6 and 113+/-3.5 pN. This behaviour may persist over distances as great as 400 nm and suggests the stable formation of a cylindrical tube which bridges the bilayers on the two surfaces. The stability of this connective structure may have implications for the formation of pili and hence for the initial stage of bacterial conjugation. Dimyristoylphosphatidylcholine (DMPC) bilayers also exhibit force plateaux but with a much less pronounced quantization. Bilayers composed of egg PC, sterylamine and cholesterol stressed in a similar way show complex behaviour which can in part be explained using the models demonstrated in the pure lipids.

Photonic effects on the radiative decay rate and luminescence quantum yield of doped nanocrystals.

Nanocrystals (NCs) doped with luminescent ions form an emerging class of materials. In contrast to excitonic transitions in semiconductor NCs, the optical transitions are localized and not affected by quantum confinement. The radiative decay rates of the dopant emission in NCs are nevertheless different from their bulk analogues due to photonic effects, and also the luminescence quantum yield (QY, important for applications) is affected. In the past, different theoretical models have been proposed to describe the photonic effects for dopant emission in NCs, with little experimental validation. In this work we investigate the photonic effects on the radiative decay rate of luminescent doped NCs using 4 nm LaPO4 NCs doped with Ce(3+) or Tb(3+) ions in different refractive index solvents and bulk crystals. We demonstrate that the measured influence of the refractive index on the radiative decay rate of the Ce(3+) emission, having near unity QY, is in excellent agreement with the theoretical nanocrystal-cavity model. Furthermore, we show how the nanocrystal-cavity model can be used to quantify the nonunity QY of Tb(3+)-doped LaPO4 NCs and demonstrate that, as a general rule, the QY is higher in media with higher refractive index.

First shark from the Late Devonian (Frasnian) Gogo Formation, Western Australia sheds new light on the development of tessellated calcified cartilage.

BACKGROUND: Living gnathostomes (jawed vertebrates) comprise two divisions, Chondrichthyes (cartilaginous fishes, including euchondrichthyans with prismatic calcified cartilage, and extinct stem chondrichthyans) and Osteichthyes (bony fishes including tetrapods). Most of the early chondrichthyan ('shark') record is based upon isolated teeth, spines, and scales, with the oldest articulated sharks that exhibit major diagnostic characters of the group--prismatic calcified cartilage and pelvic claspers in males--being from the latest Devonian, c. 360 Mya. This paucity of information about early chondrichthyan anatomy is mainly due to their lack of endoskeletal bone and consequent low preservation potential. METHODOLOGY/PRINCIPAL FINDINGS: Here we present new data from the first well-preserved chondrichthyan fossil from the early Late Devonian (ca. 380-384 Mya) Gogo Formation Lägerstatte of Western Australia. The specimen is the first Devonian shark body fossil to be acid-prepared, revealing the endoskeletal elements as three-dimensional undistorted units: Meckel's cartilages, nasal, ceratohyal, basibranchial and possible epibranchial cartilages, plus left and right scapulocoracoids, as well as teeth and scales. This unique specimen is assigned to Gogoselachus lynnbeazleyae n. gen. n. sp. CONCLUSIONS/SIGNIFICANCE: The Meckel's cartilages show a jaw articulation surface dominated by an expansive cotylus, and a small mandibular knob, an unusual condition for chondrichthyans. The scapulocoracoid of the new specimen shows evidence of two pectoral fin basal articulation facets, differing from the standard condition for early gnathostomes which have either one or three articulations. The tooth structure is intermediate between the 'primitive' ctenacanthiform and symmoriiform condition, and more derived forms with a euselachian-type base. Of special interest is the highly distinctive type of calcified cartilage forming the endoskeleton, comprising multiple layers of nonprismatic subpolygonal tesserae separated by a cellular matrix, interpreted as a transitional step toward the tessellated prismatic calcified cartilage that is recognized as the main diagnostic character of the chondrichthyans.

The uptake of soluble and nanoparticulate imaging isotope in model liver tumours after intra-venous and intra-arterial administration.

Delivery of chemotherapeutic drugs to tumours by reformulation as nanoparticles has often been proposed as a means of facilitating increased selective uptake, exploiting the increased permeability of the tumour vasculature. However realisation of this improvement in drug delivery in cancer patients has met with limited success. We have compared tumour uptake of soluble Tc99m-pertechnetate and a colloid of nanoparticles with a Tc99m core, using both intra-venous and intra-arterial routes of administration in a rabbit liver VX2 tumour model. The radiolabelled nanoparticles were tested both in untreated and cationised form. The results from this tumour model in an internal organ show a marked advantage in intra-arterial administration over the intra-venous route, even for the soluble isotope. Tumour accumulation of nanoparticles from arterial administration was augmented by cationisation of the nanoparticle surface with histone proteins, which consistently facilitated selective accumulation within microvessels at the periphery of tumours.

Analysis of 3D bone ingrowth into polymer scaffolds via micro-computed tomography imaging.

This paper illustrates the utility of micro-computed tomography (micro-CT) to study the process of tissue engineered bone growth. A micro-CT facility for imaging and visualising biomaterials in three dimensions (3D) is described. The facility is capable of acquiring 3D images made up of 2000(3) voxels on specimens up to 60mm in extent with resolutions down to 2 microm. This allows the 3D structure of tissue engineered materials to be imaged across three orders of magnitude of detail. The capabilities of micro-CT are demonstrated by imaging the Haversian network within human femoral cortical bone (distal diaphysis) and bone ingrowth into a porous scaffold at varying resolutions. Phase identification combined with 3D visualisation enables one to observe the complex topology of the canalicular system of the cortical bone. Imaging of the tissue engineered bone at a scale of 1cm and resolutions of 10 microm allows visualisation of the complex ingrowth of bone into the polymer scaffold. Further imaging at 2 microm resolution allows observation of bone ultra-structure. These observations illustrate the benefits of tomography over traditional techniques for the characterisation of bone morphology and interconnectivity and performs a complimentary role to current histomorphometric techniques.

Photonic effects on the Förster resonance energy transfer efficiency.

Förster resonance energy transfer (ET) between luminescent species is applied in bio-imaging, lighting and photovoltaics, and has an important role in photosynthesis. However, the fundamental question of whether ET rates and efficiencies can be tuned by the photonic environment remains under debate. Here we show that ET rates are independent of the photonic environment, using the model system of LaPO4 nanocrystals co-doped with Ce(3+) donors and Tb(3+) acceptors. Although the radiative emission rate of the Ce(3+) excited state increases with the refractive index of the solvent in which the nanocrystals are dispersed, the Ce(3+)-to-Tb(3+) ET rate does not. We demonstrate that, as a result, lower refractive index solvents enable higher ET efficiencies leading to higher Tb(3+) emission intensities. Furthermore, an analytical model for ET in (nano)crystalline host materials is presented, able to predict the dependence of ET efficiencies on the photonic environment and the concentration of acceptor ions.

Laser actuation of cantilevers for picometre amplitude dynamic force microscopy.

As nanoscale and molecular devices become reality, the ability to probe materials on these scales is increasing in importance. To address this, we have developed a dynamic force microscopy technique where the flexure of the microcantilever is excited using an intensity modulated laser beam to achieve modulation on the picoscale. The flexure arises from thermally induced bending through differential expansion and the conservation of momentum when the photons are reflected and absorbed by the cantilever. In this study, we investigated the photothermal and photon pressure responses of monolithic and layered cantilevers using a modulated laser in air and immersed in water. The developed photon actuation technique is applied to the stretching of single polymer chains.