Kjeld Møller Pedersen

Plasmonic black gold by adiabatic nanofocusing and absorption of light in ultra-sharp convex grooves

Excitation of localized and delocalized surface plasmon resonances can be used for turning excellent reflectors of visible light, such as gold and silver, into efficient absorbers, whose wavelength, polarization or angular bandwidths are however necessarily limited owing to the resonant nature of surface plasmon excitations involved. Nonresonant absorption has so far been achieved by using combined nano- and micro-structural surface modifications and with composite materials involving metal nanoparticles embedded in dielectric layers. Here we realize nonresonant light absorption in a well-defined geometry by using ultra-sharp convex metal grooves via adiabatic nanofocusing of gap surface plasmon modes excited by scattering off subwavelength-sized wedges. We demonstrate experimentally that two-dimensional arrays of sharp convex grooves in gold ensure efficient (>87%) broadband (450-850 nm) absorption of unpolarized light, reaching an average level of 96%. Efficient absorption of visible light by nanostructured metal surfaces open new exciting perspectives within plasmonics, especially for thermophotovoltaics.

General Practice and Primary Health Care in Denmark

General practice is the corner stone of Danish primary health care. General practitioners (GPs) are similar to family physicians in the United States. On average, all Danes have 6.9 contacts per year with their GP (in-person, telephone, or E-mail consultation). General practice is characterized by 5 key components: (1) a list system, with an average of close to 1600 persons on the list of a typical GP; (2) the GP as gatekeeper and first-line provider in the sense that a referral from a GP is required for most office-based specialists and always for in- and outpatient hospital treatment; (3) an after-hours system staffed by GPs on a rota basis; (4) a mixed capitation and fee-for-service system; and (5) GPs are self-employed, working on contract for the public funder based on a national agreement that details not only services and reimbursement but also opening hours and required postgraduate education. The contract is (re)negotiated every 2 years. General practice is embedded in a universal tax-funded health care system in which GP and hospital services are free at the point of use. The current system has evolved over the past century and has shown an ability to adapt flexibly to new challenges. Practice units are fairly small: close to 2 GPs per unit plus nurses and secretaries. The units are fully computerized, that is, with computer-based patient records and submission of prescriptions digitally to pharmacies etc. Over the past few years a decrease in solo practices has been seen and is expected to accelerate, in part because of the GP age structure, with many GPs retiring and new GPs not wanting to practice alone. This latter workforce trend is pointing toward a new model with employed GPs, particularly in rural areas.

Generation of a Danish TTO value set for EQ-5D health states:

Aims: Health policy decisions should be based on national social preferences. In the absence of a set of Danish health preferences, patient outcome studies using the EQ-5D instrument have typically used UK health state valuations. This article describes the development of a Danish EQ-5D value set. Methods: Regression modelling was based on Time Trade-Off (TTO) data derived from computer-assisted interviews conducted with 1,332 respondents from the Danish general population. Using a split-sample technique, 46 health states were directly valued by the respondents. Five different model types were tested and compared on statistical and theoretical grounds. Eleven different specifications were then tested for the chosen model type to identify the most appropriate model that had high explanatory power and parameters that were both consistent (positively signed) and statistically significant. Results: An additive random effects model was found to be superior to ordinary least squares, fixed effects, random coefficient and censored Tobit modelling approaches. From the 11 model specifications tested, the TTO3 model (main effects model, without an N3 factor) performed best and was used to generate a Danish set of health state preferences. Conclusions: An additive random effects model appears to adequately generate a Danish set of EQ-5D health state preferences. The model has high explanatory power and produces consistent and significant parameters for EQ-5D dimensions and levels. It is recommended that this value set be used in Danish cost-utility studies using EQ-5D.

Danish EQ-5D population norms

Background: The EQ-5D is a widely used generic health-related quality of life instrument that has been used to describe population health and health outcomes in clinical trials and health economic evaluations. Aims: To generate Danish population norms for the EQ-5D index score, stratified by age and gender. Methods: The EQ-5D data from three population health surveys were pooled, thus providing EQ-5D profile data for 15,700 individuals aged 20-79 years. The Danish TTO scoring algorithm was used to weight each respondents profile data to derive a single index score. Mean values were computed by gender and 10-year age groups, and educational groups. Results: In a random sample from the general Danish population, the mean EQ-5D index score ranged between 0.93 for 20—29 year-olds and 0.83 for 70—79 year-olds. Men had a significantly higher score than women in all age groups. Longer education was associated with higher EQ-5D index score in most age groups. Conclusions: The calculated mean values for the EQ-5D index score may be used as reference values for comparative purposes in future Danish population health and evaluative studies.

Optical properties of graphene antidot lattices

Undoped graphene is semimetallic and thus not suitable for many electronic and optoelectronic applications requiring gapped semiconductor materials. However, a periodic array of holes (antidot lattice) renders graphene semiconducting with a controllable band gap. Using atomistic modeling, we demonstrate that this artificial nanomaterial is a dipole-allowed direct-gap semiconductor with a very pronounced optical-absorption edge. Hence, optical infrared spectroscopy should be an ideal probe of the electronic structure. To address realistic experimental situations, we include effects due to disorder and the presence of a substrate in the analysis.

Second-harmonic imaging of ferroelectric domain walls

Domain walls in periodically poled ferroelectric KTiOPO4 and LiNbO3 crystals are observed by making use of second-harmonic (SH) generation enhancement in the transition regions between neighboring domains. SH images of domain walls obtained with various samples for different polarization configurations are presented. The SH generation enhancement is found especially pronounced for the polarization of the SH radiation being perpendicular to the domain walls. The origin and selection rules for the contrast in SH images of domain walls are discussed. The results obtained suggest that the domain walls produce a deteriorating effect on SH generation by quasiphase matching.

Growth of a stacked silicon nitride/silicon oxide dielectric on Si(100)

We have recently developed processes to grow ultrathin amorphous silicon oxide and amorphous silicon nitride layers on clean Si(111) and Si(100) surfaces exploring the self-limiting nature of the direct oxidation of Si with O2, and the self-limiting nature of the direct nitridation of Si with atomic N produced by microwave dissociation of N2, at processing temperatures around 500°C. In some of today’s microprocessor devices mixed dielectric systems are used as complementary metal oxide semiconductor gate dielectrics. We demonstrate the use of our processes to produce such systems in various structures, and with maximum control, by exposing oxide to N, or nitride to O2 at 500°C. In addition we produce a stacked layer, consisting of 7–8A of SiO2 on top of Si(100), with a layer of varying thickness of Si3N4 grown on top of this structure. The growth of Si3N4 occurs at room temperature in this process. Such structures or thermally postprocessed structures thereof should be further examined as potential stacke...

Extremely confined gap surface-plasmon modes excited by electrons

High-spatial and energy resolution electron energy-loss spectroscopy (EELS) can be used for detailed characterization of localized and propagating surface-plasmon excitations in metal nanostructures, giving insight into fundamental physical phenomena and various plasmonic effects. Here, applying EELS to ultra-sharp convex grooves in gold, we directly probe extremely confined gap surface-plasmon (GSP) modes excited by swift electrons in nanometre-wide gaps. We reveal the resonance behaviour associated with the excitation of the antisymmetric GSP mode for extremely small gap widths, down to ~5 nm. We argue that excitation of this mode, featuring very strong absorption, has a crucial role in experimental realizations of non-resonant light absorption by ultra-sharp convex grooves with fabrication-induced asymmetry. The occurrence of the antisymmetric GSP mode along with the fundamental GSP mode exploited in plasmonic waveguides with extreme light confinement is a very important factor that should be taken into account in the design of nanoplasmonic circuits and devices.

Second-harmonic imaging of poled silica waveguides

Electric-field poled silica-based waveguides are characterized by measurements of second-harmonic generation (SHG) and of the linear electro-optic effect (LEO). A SHG scanning technique allowing for high-resolution imaging of poled devices is demonstrated. Scans along the direction of the poling field show that the second-order optical nonlinearity is located near the interface between differently doped glass layers. Both SHG and LEO measurements indicate that the ratio between the main elements of the second-order nonlinear optical susceptibility tensor, χ33(2) and χ31(2), is significantly smaller than three.

Self-care within a model for demand for medical care

Self-care is interpreted from a health economic point of view. Various approaches are presented. It is stressed that the decision-oriented approach used by other health service researchers is an integral part of the economic approach to the topic as is the idea of a continuum of care, from self-care to professional care. A new approach is taken to the modeling of self-care, in that self-care becomes part of a four-part demand for care model. This makes it possible to model the demand for care for three different groups separately: 1--persons with zero episodes; 2--persons with pure illness episodes and illness episodes with self-care; 3--persons with episodes involving professional care or professional care combined with self-care. Another contribution is due to the so-called episodic approach to the demand for care. The natural counting units are illness and treatment episodes, i.e. instead of counting for instance number of times a general practitioner is consulted we ought to count the number of episodes involving professional care, self-care or both types of care. The episodic approach seems to be well suited for work with self-care. The empirical part is based on a unique Danish panel study using health diaries returned weekly. Data from 27 of the 52 reporting weeks are used, involving more than 14,000 episodes distributed across about 2800 persons belonging to about 1000 households. The use of health diaries seems to be very well suited to the study of self-care in that less salient events and activities than professional care are picked up far better in prospective health diary studies than in retrospective questionnaire based surveys. Descriptive and regression (logistic and ordinary) results are presented.