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Regulating the temperature of buildings has the highest expenditure of energy (35–40%); thus, transparent heat reflectors (THRs) have been at the forefront of passive cooling technology due to its ability to reflect near-infrared (NIR) wavelengths without compromising optical transmission. Current designs like metallic thin films and dielectric–metal–dielectric are expensive and face complications with material incompatibility, oxidation, and interdiffusion, which hamper their performance. A cost-effective THR using a single-layer coating has not yet been achieved due to the susceptibility of metals to oxidation. In this work, a layer of CuS was fabricated onto flexible polyethylene terephthalate (PET) via radio frequency magnetron sputtering (RFMS), a high throughput method known for its conformal large-area fabrication. The 150 nm-thick CuS-PET films demonstrated a visible transmission T550 nm of 64.1% and NIR reflectance of 50% that resulted in 8 °C passive cooling. Additionally, wetting the surface re...

Superlattices exhibit desirable electronic properties such as resonant tunneling. However, there is a high technology barrier for fabricating such structures, using methods such as molecular beam epitaxy (MBE). We fabricated multilayer structures of amorphous materials using the technologically simple method of rotational evaporation, and observed physical characteristics related to superlattice structures. The multi-layer structure was confirmed using Time of Flight Secondary Ion Mass Spectroscopy (TOF-SIMS). The energy band structure of the superlattice was measured using Deep Level Transient Spectroscopy (DLTS). The results show minibands associated with superlattice structures, and oscillations in the transport properties. Using Current-Voltage (I-V) characterization, we could clearly observe such oscillations. From these results, quantum features associated with superlattices could be observed in multilayer amorphous Se fabricated using the rotational evaporation.

Superlattice structures have a variety of electrical and optical properties that allow for interesting applications like quantum cascade lasers and ultrasensitive photo-detectors. However, such structures require high-tech fabrication methods like molecular beam epitaxy, and this technology barrier means that these promising devices are not in widespread use. Using the simple method of rotational evaporation, we fabricated films with alternating multi-nanolayers of amorphous selenium (Se) and arsenic selenide (As2Se3). We investigated the optical properties of the individual materials, and the resulting multi-layer structure using spectroscopic ellipsometry. The results were modeled using Cody–Lorentz oscillators to obtain the refractive index (n) and extinction coefficient (k). The models showed the optical band gaps of Se and As2Se3 to be 1.97 and 1.69 eV, respectively. The absorption coefficient (α) of the multi-layer structure showed a series of five ‘steps’ in energy at 1.72, 1.82, 1.89, 1.97, and 2.04 eV. These are confirmed to stem from the transitions between confined quantum well levels due to the superlattice structure. In this way, the optical measurement using spectroscopic ellipsometry confirms the possibility of fabricating good quality nanostructutres using amorphous materials and rotational evaporation.

In this article, a field-induced electron emission from hydrogen (H)-terminated surface of heavily phosphorus (P)-doped diamond is discussed based on the barrier lowering model. Ultraviolet photoelectron spectroscopy suggested that an upward band bending of 1.45 eV existed at the surface of the diamond. A field emission characteristic as a function of the distance between an anode and diamond was measured to evaluate an average electric field in the vacuum. The barrier lowering model was introduced to estimate the reduction of the internal barrier due to the electric field at the diamond surface. The barrier lowering effect was confirmed from energies of emitted electrons, measured by combined ultraviolet photoelectron spectroscopy/field-induced electron spectroscopy (UPS/FES). As a result, it was shown that the electron emission from n-type diamond having NEA surface could be modulated by controlling a local electric field.

The electronic properties of the junction formed between multi-nanolayer amorphous selenium and silicon are studied. The current–voltage (I–V) relationship of this type of junction was characterised and the result showed pn junction rectification. Capacitance–voltage (C–V) measurements were also used to obtain the value of the diffusion potential of the junction. From these data, the ideality factor and built-in potential were evaluated. The results show potential in the application of amorphous selenium and silicon as materials in tandem photovoltaic cells and in wide spectral range photodetectors.

Amorphous Se is a well-known photoconductor from its early applications in xerography and ultra-sensitive photodetectors like the High-gain Avalanche Rushing Photoconductor (HARP) device. The established way of fabricating the photoconductor for the HARP is rotational thermal evaporation using multilayers of Se and As2Se3. However, the electronic effects of multilayering have not yet been clarified. In this report, we investigated the multilayer structure as a superlattice of Se and As2Se3 fabricated using rotational evaporation and show that the superlattice structure results in the uniformization of the defect levels in the base materials. We found four energy levels associated with defects in As2Se3 and three levels in amorphous Se. In comparison, the superlattice structure of the two materials shows two clear energy levels at EC,Se − 0.533 eV and EV,Se + 0.269 eV. The resulting two occupied energy levels explain the photoelectronic and transport properties observed in multilayer amorphous Se. This result “reinvents” the multilayer structure as a material with observed quantum effects, which significantly improves the material performance in photodetection.

We investigated the response time of a-Se based vacuum photodetector driven by diamond cold cathode. To characterize the response time, the a-Se surface was illuminated using pulsating white light and the variation of emission current from diamond field emitter was measured on an oscilloscope. The results show that there is a relationship between the response time, measured through the time constant, and the quantum efficiency. As the quantum efficiency increases, the detector time constant decreases.

In this article, we introduce an electrochemical doping method of amorphous selenium (a-Se) using NaCl(aq). Recently, an a-Se photovoltaic device fabricated using this method [I. Saito, W. Miyazaki, M. Onishi, Y. Kudo, T. Masuzawa, T. Yamada, A. Koh, D. Chua, K. Soga, M. Overend, M. Aono, G. A. J. Amaratunga, and K. Okano, Appl. Phys. Lett. 98, 152102 (2011)] has been announced and opened up the potential of a new impurity doping method. This study will further explore its possibilities by doping chlorine (Cl) and sodium (Na) and aim to fabricate a p–n junction by reversing the applied voltage during the electrolysis. The device is characterized through photoelectric measurements. The I–V characteristics show rectification under light illumination.

In this study, amorphous selenium based photoconductor with different film thicknesses were fabricated and applied to prototype photodetectors. The use of thick photoconductor resulted in higher sensitivity due to carrier multiplication. Advantages and disadvantages of the thick photoconductor were investigated.

Energies of emitted electrons from n-type diamond NEA surface and graphene/n-type diamond junction were measured by combined field emission spectroscopy/ultraviolet photoelectrons spectroscopy (FES/UPS) system. For n-type diamond NEA surface, the energies of emitted electrons indicated that the electrons emitted from conduction band of the diamond. For graphene/diamond junction, electron emission from both valance bands of diamond and graphene are confirmed.

In the present study, high-sensitivity photodetection has been demonstrated using an amorphous selenium (a-Se) based photodetector driven by nitrogen-doped diamond cold cathode. The emission current – applied voltage characteristics are compared between different lighting conditions, and their sensitivities are evaluated in terms of nominal quantum efficiency. The estimated nominal quantum efficiency was 10–40 for visible and up to 1000 for ultraviolet, proving a successful photodetection utilizing carrier multiplication in a-Se.

In this study, a graphene/n-type diamond heterojunction was fabricated by a wet-transfer process on hydrogen-terminated heavily phosphorus-doped diamond. Ultraviolet photoelectron spectroscopy (UPS) and field-emission electron spectroscopy were conducted to study the band structure of the graphene/n-type diamond heterojunction and its field emission mechanism. UPS suggests that an internal barrier is formed in the diamond by upward band bending near the graphene–diamond interface. The work function of graphene is estimated to be 3.72 eV. Field emission occurs from the Fermi level of graphene at low voltages, and then electron emission from the valence band of diamond starts at increased voltages. The results indicate that electron emission limited by surface termination changes to graphene-oriented emission following the formation of the heterojunction.

A mille-feuille structured amorphous selenium (a-Se)–arsenic selenide (As2Se3) multi-layered thin film and a mixed amorphous Se–As2Se3 film is compared from a durability perspective and photo-electric perspective. The former is durable to incident laser induced degradation after numerous laser scans and does not crystallise till 105° of annealing, both of which are improved properties from the mixed evaporated film. In terms of photo-electric properties, the ratio between the photocurrent and the dark current improved whereas the increase of the dark current was higher than that of As2Se3 due to the unique current path developed within the mille-feuille structure. Implementing this structure into various amorphous semiconductors may open up a new possibility towards structure-sensitive amorphous photoconductors.

Amorphous-selenium (a-Se) based photodetectors are promising candidates for imaging devices, due to their high spatial resolution and response speed, as well as extremely high sensitivity enhanced by an internal carrier multiplication. In addition, a-Se is reported to show sensitivity against wide variety of wavelengths, including visible, UV and X-ray, where a-Se based flat-panel X-ray detector was proposed. In order to develop an ultra high-sensitivity photodetector with a wide detectable wavelength range, a photodetector was fabricated using a-Se photoconductor and a nitrogen-doped diamond cold cathode. In the study, a prototype photodetector has been developed, and its response to visible and ultraviolet light are characterized.

High-sensitivity ultraviolet (UV) photodetection has been attempted by utilizing the carrier multiplication effect in amorphous selenium. The prototype photodetector presented in this Letter showed an extremely high sensitivity to UV light, so that up to 1000 carriers are generated per incident photon. This result should lead to the development of an ultrahigh-sensitivity photodetector that can be used for spectrometric applications covering the visible to UV region. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Although present imaging devices are mostly silicon-based devices such as CMOS and CCD, these devices are reaching their sensitivity limit due to the band gap of silicon. Amorphous selenium (a-Se) is a promising candidate for high- sensitivity photo imaging devices, because of its low thermal noise, high spatial resolution, as well as adaptability to wide-area deposition. In addition, internal signal amplification is reported on a-Se based photodetectors, which enables a photodetector having effective quantum efficiency over 100 % against visible light. Since a-Se has sensitivity to UV and soft X-rays, the reported internal signal amplification should be applicable to UV and X-ray detection. However, application of the internal signal amplification required high voltage, which caused unexpected breakdown at the contact or thin-film transistor-based signal read-out. For this reason, vacuum devices having electron-beam read-out is proposed. The advantages of vacuum-type devices are vacuum insulation and its extremely low dark current. In this study, we present recent progresses in developing a-Se based photoconductive films and photodetector using nitrogen-doped diamond electron beam source as signal read-out. A novel electrochemical method is used to dope impurities into a-Se, turning the material from weak p-type to n-type. A p-n junction is formed within a-Se photoconductive film, which has increased the sensitivity of a-Se based photodetector. Our result suggests a possibility of high sensitivity photodetector that can potentially break the limit of silicon-based devices.

In this study, the field emission properties of P-doped diamond with various surface treatments were measured in order to understand the effects of surface treatments on the barrier height. The emission properties were acquired for diamond with C-reconstructed, oxidized, and H-plasma treated surfaces. The voltage drop across the vacuum was estimated for each surface, using threshold voltage–anode distance (V–d) measurement. The estimated electric fields near the diamond surface were 4.95, 26.6, and 54.1 V/µm for the C-reconstructed, oxidized, and H-plasma treated surfaces, respectively. The barrier height ratio of these surfaces derived from their electric fields was 1:3.1:4.9, which agrees with the result derived from Fowler–Nordheim (F–N) plots. Considering the electron affinities of all surfaces and the obtained results, positive electron affinities dominate the field emission properties of the C-reconstructed and oxidized surfaces. An internal barrier due to upward band bending on the H-plasma treated surface limits the field emission properties, even though it has a negative electron affinity. Our results suggest that the emission properties strongly depend on the barrier height, which is modified by surface treatment.

The mechanism of low-threshold electron emission from heavily nitrogen-doped diamond was clarified using computer simulation. Possibility of internal field emission at metal–diamond contact was evaluated expecting that the electron injection can explain the low-threshold electron emission. As a result, it was proved that electron injection could be achieved even for a deep donor of 1.7 eV, when donor concentration exceeded 1e20 cm−3. The result was in good agreement with previous experiments.

Clarification of the electron emission mechanism of diamond has been one challenging topic in the field of vacuum nanoelectronics. Electric field of less than 5 V/µm is enough to extract electrons from diamond, which is orders of magnitude lower than the value required for electron emission from metal emitter in general. There have been number of studies on the clarification of electron emission mechanism, however, unified model has not been proposed. The difficulty largely lies in determining the origin of emitted electrons. In this study, we succeeded in clarifying the electron emission mechanism of hydrogenated natural type IIb diamond (111) surface by using combined x-ray photoemission spectroscopy/ultraviolet photoemission spectroscopy/field emission spectroscopy (XPS/UPS/FES) system. Obtained spectra clearly defined the origin of emitted electrons at the valence band maximum (VBM). As applied voltage was increased, the number of emitted electrons increased, however, the origin remained at VBM independent of the applied voltage.

An imaging device that could detect weak light of approximately 0.001 lx with high SN ratio is capable of opening up the possibility of creating artificial visions as a substitute for a human eye. In terms of sensitivity and SN ratio, amorphous selenium (a-Se) is known to be one of the best candidates among other photoconductive target. Combined with a-Se, a diamond cold cathode would be one of the best options in order to steadily emit electrons under low vacuum. The a-Se film is modified with Arsenic (As) and Tellurium (Te) to prevent crystallization and narrow the optical gap for red light detection. An RGB filtered light from a halogen light source was illuminated onto this modified a-Se film and the photo-response was measured for each color. The device could detect extremely weak illumination of under 0.39 lx, which is approximately the darkness under moonlight. Results of the photo-response compared between films with and without Te clarified that Te dopants enhances red light detection significantly. The illuminated light was then pulsed at 10 mHz and the current to time stability was observed. It showed clear correspondence between the intensity of the luminance and current, which the Te modified samples showed good response to other colored light as well.

Field emission from heavily phosphorus-doped homoepitaxial (111) diamonds after surface modifications are discussed. To develop a model for emission, we applied X-ray photoelectron spectroscopy (XPS) to characterize surface properties of H-plasma treated, oxidized and carbon-reconstructed surfaces. In addition, reflection high energy electron diffraction (RHEED) is used to evaluate atomic arrangements. Atomic force microscopy (AFM) is used to investigate surface morphologies. From AFM, no major difference is observed between H-terminated, oxidized and carbon reconstructed surfaces. Field emission properties of carbon reconstructed surfaces show a lower threshold than hydrogen-terminated or oxidized surfaces.

The ‘PLUMBICON’ was one of the first successful imaging tubes using amorphous selenium (a-Se) and many followed. Significant properties of a-Se based imaging tubes have been rediscovered through the invention of the ‘HARP (high-gain avalanche rushing amorphous photoconductor)’, but its operational mechanism and the physics, however are yet poorly described. Previously, we have fabricated photodetectors using nitrogen (N)-doped diamond as a cold cathode and a-Se as a photoconducting target, which successfully responded to light illumination, The device performance,in this case, deteriorates after continuous use largely due to the degradation of a-Se. In this paper, a-Se and amorphous arsenic selenide (a-As 2 Se 3 ) films have been deposited Stoichiometry has been determined by XPS (X-ray photoelectron spectroscopy) followed by Raman spectroscopy characterization. We have found that even an extremely weak incident laser power causes sample degradation during signal accumulation. We speculate that either the incident laser itself and/or the temperature rise due to illumination causes the phase transition in a-Se films. In addition, when As is added into the film, the phase transition leading the degradation is hardly observed, implying that As affects the formation of crystalline Se making chemical bonds in the crystallographic network stronger.

An attempt was made to fabricate diamond field emitter array that can utilize negative electron affinity. Nitrogen-doped polycrystalline diamond was shaped into flat-topped pyramids by using mold-growth method. Field emission property of the fabricated diamond FEA was evaluated using I–V characteristic.

The structures and characteristics of pressure–heat-induced gels of chicken myofibrils and pork patty were investigated. The M-line and Z-line in the chicken myofibril in 0.2 M NaCl were disrupted, and both of the thin and thick filaments were dissociated by pressure treatment. The microstructure of pressure–heat-induced chicken myofibrillar gel was composed of three-dimensional fine strands. Pressurization, at 200 MPa, prior to heating, increased the apparent elasticities of chicken myofibrillar gel and pork patty; however, pressure treatment above 200 MPa decreased it. The apparent elasticity of the pressure-treated (200 MPa) thermal myofibrillar gel was three times higher, and that of pork patty was twice higher than those of the unpressurized ones. The rheological properties of the low salt (1% NaCl) pork sausage can be improved by pressure treatment at 200 MPa prior to heating.

The superior material properties of diamond as a semiconducting material can be exploited in many power devices. In this study we show an optically triggered Schottky Barrier Diode (SBD) structure which operates by going into avalanche breakdown with the aid of incident photons from a light source. The source shines through a window patterned into the Schottky cathode contact. The avalanche multiplication is aided by the large electric field set up by the reverse bias applied across a near intrinsic diamond layer. We will demonstrate numerically that the triggering voltage can be controlled by the intensity of irradiated light onto the device, thus increasing the applicability of this device in high voltage switching modules where isolated switches are used.

Heavily nitrogen (N)-doped polycrystalline diamond is reported to have excellent electron emission properties although its emission sites are limited. This report describes the fabrication processes, characterisation and electron emission properties of N-doped heteroepitaxial diamond which posses high potential as broad area emitter devices. We have obtained epitaxial diamond films on iridium (Ir) substrates by hot filament CVD using urea [(NH 2 ) 2 CO] as a dopant for N. The Ir substrates are bias treated via direct current plasma CVD (d.c. plasma CVD) method prior to the growth. Surface of the deposited films is smooth and continuous in scanning electron microscopy (SEM) observation. The epitaxial diamond growth is confirmed from reflective high energy electron diffraction (RHEED) pattern. It is found that the electron emission from heteroepitaxial diamond film is dominated by standard Fowler-Nordheim type emission due to the existence of strong electric field in the vacuum with the value of 26 V/μm.

A new idea of power device, which contains highly nitrogen-doped CVD diamond and Schottky contact, is proposed to actualise a power device with diamond. Two-dimensional simulation is conducted using ISE TCAD device simulator. While comparably high current is obtained in a transient simulation as expected, this current does not contribute to the drain–source current because of the symmetry of the device. Using an asymmetric structure or bias conditions, the device has high potential as an electric device for extremely high power, high frequency and high temperature.

It was reported that although nitrogen (N) forms either 1.7 or 4.0 eV deep level donor in diamond, these levels do not contribute to the electrical conduction at room temperature. It was also reported that hydrogen (H)-termination of diamond surfaces results in the p-type electrical conduction in CVD diamond, and that this conduction can be diminished by subsequent oxygen (O) treatment. In this paper, the conduction type of N-doped CVD diamond studied through thermoelectric measurements is presented. The measurements of the Seebeck coefficient indicate that: (i) as-grown N-doped CVD diamond shows p-type conduction, (ii) once it is oxidized, it presents n-type electrical conduction with carrier concentrations of about 10 1 8 cm - 3 . The results suggest the presence of competing bipolar transport between the surface and the bulk in CVD diamond.

The electron emission properties of N-doped homoepitaxially grown diamond have been measured and discussed in order to clarify the electron emission mechanism by excluding the effects of polycrystallinity. As a result, N-doped homoepitaxially grown diamond exhibits extremely low threshold electron emission even from extremely flat smooth surfaces without grain boundaries. This result strongly implies that the low threshold electron emission from N-doped diamond should be caused by the resistance of the film rather than by high β whatever the underlying mechanism is.

Although we had reported the remarkable low threshold emission from polycrystalline diamond heavily doped with nitrogen (N) [Nature 381 (1996) 140], the problems caused by polycrystallinity still remain for understanding the electron emission mechanism. This paper describes the growth of N-doped homoepitaxial diamond film {100}, {111} and {110}, and their electron emission properties. N-doped homoepitaxial diamond is grown on synthetic diamond by hot filament chemical vapor deposition. Urea [(NH2)2CO] is used as a dopant for N. Atomic force microscope (AFM) observations indicate that the relatively smooth surface morphologies are obtained for all the films. The epitaxial growth of all the film is confirmed using reflective high energy electron diffraction (RHEED) patterns. Reflective electron energy loss spectra (REELS) indicate that the very surfaces of {100} and {111} are diamond while {110} is graphite rather than diamond. Raman spectra suggest that the bulk of the obtained films are diamond. The resistivities of the films are found to be much higher than the detection limit of the system. The relatively low threshold emission was observed even from the smooth surface and the threshold voltage is confirmed to depend on the crystal orientation. It is speculated from the film characterizations and the electron emission properties that the low threshold emission is due to high resistance rather than rough surface and/or grain boundaries.

In this study, photoconductor made of amorphous selenium (a-Se) is studied to improve a sensitivity of vacuum-tube type photodetectors. An electrochemical process was applied to a-Se films to form a p-n structure within the film. The formation of p-n structure was confirmed by time-of-flight secondary ion mass spectroscopy as well as its electronic property. The a-Se film was then combined into a prototype photodetector, and enhancement of sensitivity was evaluated in terms of nominal quantum efficiency and signal-to-noise ratio. The results showed that the formation of a p-n junction within a-Se film increased the sensitivity of the photodetector, especially at relatively low operation voltages.

We present a controllable way of establishing a p-n junction in amorphous selenium (a-Se) using electrolysis. Amorphous selenium is used as an anode in the electrolysis of NaCl solution. By varying the duration of the electrolysis, we can make the contact to a-Se either Ohmic or rectifying and control the built-in potential and full depletion voltage of the contacts and junctions formed in the a-Se. I-V and C-V measurements show that after electrolysis rectification occurs and that as the duration of electrolysis increases, the direction of rectification changes, with the magnitudes of the built-in potential and the full depletion becoming higher. From the results, we present a model for the electrochemical process of forming the p-n junction and highlight the dependence on the duration of the electrolysis.

sp 3 and sp 2 -rich nitrogen (N)-doped diamond electron emitters are prepared by modifying the substrate temperature. Their electron emission properties have been measured in order to examine the effect of the sp 2 /sp 3 ratio on the electron emission from N-doped diamond. The obtained electron emitters have been characterized by reflective high energy electron diffraction, X-ray diffraction and Raman spectroscopy. The electrical resistivities of the sp 3 -rich diamond is 100 G Ω cm or higher while that of the sp 2 -rich diamond is 100 Ω cm. In electron emission characteristics, the threshold voltage of the sp 3 -rich emitter is found to be lower than that of the sp 2 -rich emitter. From the threshold voltage versus the anode-diamond spacing characteristics, it has been found that most of the anode voltage drops in the bulk of the sp 3 -rich emitter and almost no voltage drop takes place in the sp 2 -rich emitter. The difference in electron emission properties should be explained by the resistivity of the N-doped diamond bulk.

Due to its negative affinity, diamond is expected to exhibit much better electron emission characteristics than other cold cathode materials. The authors used the mold method for fabricating boron-added pyramidal diamond with array surface control. When its electron emission characteristic is measured, it is found that the rise characteristic is lower than other cold cathode materials with identical shapes. It becomes clear that a stable current can be obtained from the surface after hydrogen treatment. On the other hand, the electron emission characteristic of nitrogen-doped diamond grown with urea as the impurity source exhibits extremely low rise and can be driven by a battery. Further, the analysis of the electron emission mechanism of diamond is investigated. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(11): 54–64, 1998

The synthesis of tritiated 1α-25-dihydroxy-2β-(3-hydroxypropoxy)vitamin D3 (ED-71), [2β-(3-3H)]ED-71 ((3) and [26,27-3H6]ED-71 (4) is described. The former was prepared by reduction of a precausor containing a formyl group in the A-ring part with sodium borotritiide while the latter was labeled in the side chain using tritiated methylmagnesium iodide. The specific activity of 3 was 13.2 Ci/mmol and that of 4 138.0 Ci/mmol. Copyright © 1999 John Wiley & Sons, Ltd.

Electron emission from boron (B)- and nitrogen (N)-doped diamond electron emitter with silver (Ag)-loaded conductive epoxy, titanium (Ti)/gold (Au), aluminum (Al) and amorphous carbon contacts are studied. Both Ti/Au and amorphous carbon contacts on B-doped diamond electron emitters lead to lower turn-on voltage compared to other contacts, while the turn-on voltage of N-doped diamond electron emitter is independent on the backcontacts.