Thermoelectric effect in laser annealed printed nanocrystalline silicon layers

Nanocrystalline boron and phosphorus doped silicon particles were produced in a microwave reactor, collected, and dispersed in ethanol. Pulsed laser annealing of spin‐coated films of these particles resulted in p‐ and n‐type conductive layers on flexible substrates if a threshold laser energy density of 60 mJ/cm² was exceeded. The thermopower of the laser sintered layers exhibits a distinct maximum at a doping concen‐ tration around 10¹⁹ cm^–3 for both boron and phosphorus doping with an absolute value of the Seebeck coefficient of about 300 µV/K. Since the thermal conductivity of the layers is reduced by nearly the same factor compared to bulk crystalline silicon as the electrical conductivity, these results are promising for the application of such nanocrystalline layers in thin film thermoelectric devices. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

同质与异质外延掺杂CVD金刚石薄膜的结构与性能

采用化学气相沉积(CVD)技术,以高温高压(HTHP)合成的(100)金刚石和p型(100)Si为衬底制备了硫掺杂和硼-硫共掺杂金刚石薄膜,利用原子力显微镜(AFM)、扫描隧道显微镜(STM)及隧道电流谱(CITS)等手段分析同质和异质外延CVD掺杂金刚石薄膜的结构和性能.结果表明:异Si衬底上CVD金刚石的形核密度低,薄膜表面比较粗糙,粗糙度达到18.5nm;同质HTHP金刚石衬底上CVD金刚石薄膜晶粒尺寸约为10—50nm,表面平整,表面粗糙度为1.8nm.拉曼测试和电阻测量的结果显示,在HTHP金刚 关键词： 金刚石 掺杂 外延     

Enhanced diamond nucleation on copper substrates by graphite seeding and CO2 laser irradiation

Diamond nucleation on copper (Cu) substrates was investigated by graphite seeding and CO₂ laser irradiation at initial stages of the combustion-flame deposition. A graphite aerosol spray was used to generate a thin layer of graphite powders (less than 1 μm) on Cu substrates. The graphite-seeded Cu substrates were then heated by a continuous CO₂ laser to about 750 °C within 1 min. It was found that diamond nucleation density after this treatment was more than three times as much as that on the virgin Cu substrates. As a consequence, diamond films up to 4 μm were obtained in 5 min. The enhancement of diamond nucleation on the graphite-seeded Cu substrates was attributed to the formation of defects and edges during the etching of the seeding graphite layers by the OH radicals in the flame. The defects and edges served as nucleation sites for diamond formation. The function of the CO₂ laser was to rapidly heat the deposition areas to create a favorable temperature for diamond nucleation and growth.     

Effect of nanostructured AlN coatings on the oxidation-resistant properties of optical diamond films

Diamond film is an ultra-durable optical material with high thermal conductivity and good transmission in near-infrared and far-IR (8-14 μm) wavebands. CVD diamond is subjected to oxidation at temperature higher than 780 °C bared in air for 3 min, while it can be protected from oxidation for extended exposure in air at temperature up to 900 °C by a coating of aluminum nitride. Highly oriented AlN coatings were prepared for infrared windows on diamond films by reactive sputtering method and the average surface roughness (R_a) of the coatings was about 10 nm. The deposited films were characterized by X-ray diffraction (XRD) and atom force microscope (AFM). XRD confirmed the preferential orientation nature and AFM showed nanostructures. Optical properties of diamond films coated AlN thin film was investigated using infrared spectrum (IR) compared with that for as-grown diamond films.     

Synthesis and characterization of Gd0.1Ce0.9O1.95 thin films by spray pyrolysis technique

The Gd doped ceria (CGO) in thin layers is of great interest for low temperature operation. In the present investigation, we report on the use of spray pyrolysis technique for the synthesis of CGO thin films. The process parameters were optimized for synthesizing Gd_0.1Ce_0.9O_1.95 films. Films were characterized by XRD, EDS, SEM, and AFM and are observed to be phase pure and dense with surface roughness of the order of ∼5 nm. The d.c. conductivity was also measured and is observed to be ∼0.5 S/cm at 623 K.     

Novel post‐process for the passivation of a CMOS biosensor

Sensors, which are designed and fabricated in complementary metal oxide semiconductor (CMOS) technology, have become increasingly important in the field of bioelectronics. The standardized industry processes enable a fast, cheap, and reliable fabrication of biosensor devices with integrated addressing and processing units. However, the interfacing of such chips with a liquid environment has been a challenge in recent years. Especially for interfacing living cells with CMOS biosensors different elaborate post‐processes have been proposed. In this article we describe a novel and single step passivation of a CMOS biosensor using a bio‐compatible high‐permittivity thin film, which can be directly applied to the top aluminium layer of a CMOS process. The aluminium oxide and hafnium oxide multi‐layer thin films were prepared using atomic layer deposition at low process temperatures. Electrical I –V and capacitance measurements as well as electrochemical leakage current measurements were performed on films grown on aluminium bottom electrodes. The films showed a very low leakage current and were stable up to 6 V at a thickness of just 50 nm. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nucleation and growth of aluminium films on carbon layers

New experimental data are presented about the nucleation and growth of aluminium on carbon layers, both evaporated onto rocksalt at temperatures between 170 and 315°C in ultra high vacuum at pressures below 10^?10 mbar. From micrographs taken from the stripped layers, nucleation rates and saturation densities of the Al particles are determined. By comparison of the data with a theoretical model for the kinetics of nucleation and growth of thin films, information is obtained about the critical nucleus, the adsorption energy, and the activation energy for surface diffusion. The results show that the kinetics are distinctly different for at least two distinguishable sets of deposition conditions, depending on the temperature of the carbon layers.     

Surface‐enhanced Raman spectroscopy on novel black silicon‐based nanostructured surfaces

Two different black silicon nanostructured surfaces modified with thin gold layers were tested for analytical signal enhancement with Surface‐Enhanced Raman Spectroscopy (SERS). The relationship between the thicknesses of the gold layers and the analytical signal enhancement was studied. Also, effects of Ti and Ti/Pt adhesion layers underneath the gold layers on the analytical signal enhancement were tested. An enhancement factor of 7.6 × 10⁷ with the excitation laser 785 nm was achieved for the tested analyte, Rhodamine 6G, and non‐resonance SER spectra were recorded in a 5 s acquisition mode. Such an enhancement enables to achieve a detection limit down to 2.4 pg of Rhodamine 6G on a black silicon‐based nanosurface coated with a 400‐nm‐thin layer of gold. Copyright © 2009 John Wiley & Sons, Ltd.     

Anomalous two-phonon absorption in diamond nanocrystals embedded in amorphous carbon

Observation of anomalously strong IR absorption are reported in the region of two-phonon diamond frequencies in amorphous hydrogenated carbon films grown by cosputtering graphite and copper in a plasma. Up to five structural elements of bands having frequencies close to or coinciding with the figures quoted in the literature for two-phonon absorption bands in bulk diamond were observed. This suggests the presence of diamond nanocrystals in the grown layers. Observation of two-phonon absorption in thin films is in itself remarkable because of the smallness of its coefficient in bulk diamond. An estimate of the absorption coefficient in the dominant band at 2140 cm^?1 yields about 200 cm^?1, which exceeds by more than an order of magnitude that for bulk diamond. This can be assigned to an anomalous enhancement of the two-phonon absorption coefficient due to phonon confinement in the small diamond particles nucleated in the amorphous carbon matrix. An estimate of these inclusions from the band width yields about 20 Å. The reasons for the catalytic activity of copper in diamond nucleation are analyzed.     

Nanoimprint texturing of transparent flexible substrates for improved light management in thin‐film solar cells

We present a nanoimprint based approach to achieve efficient light management for solar cells on low temperature transparent polymer films. These films are particularly low‐priced, though sensitive to temperature, and therefore limiting the range of deposition temperatures of subsequent solar cell layers. By using nanoimprint technology, we successfully replicated optimized light trapping textures of etched high temperature ZnO:Al on a low temperature PET film without deterioration of optical properties of the substrate. The imprint‐textured PET substrates show excellent light scattering properties and lead to significantly improved incoupling and trapping of light in the solar cell, resulting in a current density of 12.9 mA/cm², similar to that on a glass substrate. An overall efficiency of 6.9% was achieved for a flexible thin‐film silicon solar cell on low cost PET substrate. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

The evolution of magnetic,electrical and structural properties of nanogranular [FeCoBN/SiN]×n thin films

Some results concerning the magnetic, electrical and microstructural properties of multilayer [FeCoBN/Si₃N₄]×n films in view of their utilization for manufacturing thin film magnetic inductors are presented. A comparison between the magnetic, electrical and structural properties of FeCoBN and [FeCoBN/Si₃N₄]×n thin films is also reported. The [FeCoBN/Si₃N₄]×n thin films with the thickness of the FeCoBN layers varied from 10 to 30 nm, exhibit good soft magnetic characteristics and high values for electrical resistivity such as Ms of 172–185 A m²/kg, Hc of 318–1433 A/m and ρ of 82–48×10⁻⁷ Ω m, respectively. These physical properties of the samples are discussed in relation with the microstructure of the multilayer system.     

The effect of (00l) crystal plane orientation on the thermoelectric properties of Bi2Te3 thin film

Highly (00l)-oriented pure Bi₂Te₃ films with in-plane layered grown columnar nanostructure have been fabricated by a simple magnetron co-sputtering method. Compared with ordinary Bi₂Te₃ film and bulk materials, the electrical conductivity and Seebeck coefficient of such films have been greatly increased simultaneously due to raised carrier mobility and electron scattering parameter, while the thermal conductivity has been decreased due to phonon scattering by grain boundaries between columnar grains and interfaces between each layers. The power factor has reached as large as 33.7 μW cm⁻¹ K⁻², and the out-of-plane thermal conductivity is reduced to 0.86 W m⁻¹ K⁻¹. Our results confirm that tailoring nanoscale structures inside thermoelectric films effectively enhances their performances.     

Ultra‐thin (002)‐oriented Al‐doped zinc oxide transparent electrode grown on oxygen‐controlled homo‐seed layer

Highly (002)‐oriented Al‐doped zinc oxide (AZO) thin films with the thickness of less than 200 nm have been deposited on an oxygen‐controlled homo‐seed layer at 200 °C by DC magnetron sputtering. With the homo‐seed layer being employed, the full‐width at half maximum (FWHM) of the (002) diffraction peak for the AZO ultra‐thin films decreased from 0.33° to 0.22°, and, the corresponding average grain size increased from 26.8 nm to 43.0 nm. The XRD rocking curves revealed that the AZO ultra‐thin film grown on the seed layer deposited in atmosphere of O₂/Ar of 0.09 exhibited the most excellent structural order. The AZO ultra‐thin film with homo‐seed layer reached a resistivity of 4.2 × 10^–4 Ω cm, carrier concentration of 5.2 × 10²⁰ cm^–3 and mobility of 28.8 cm² V^–1 s^–1. The average transmittance of the AZO ultra‐thin film with homo‐seed layer reached 85.4% in the range of 380–780 nm including the substrate. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of polarity inversion on the electrical properties of Ga‐doped ZnO thin films

This study investigates how polarity inversion influences the relationship between the electrical properties of heavily Ga‐doped ZnO (GZO) films deposited by RF magnetron sputtering and their thickness. The electrical properties observed in very thin films are correlated with a change of polarity from O‐polar to Zn‐polar face upon increasing the film thickness based on results of valence band spectra measured by X‐ray photoelectron spectroscopy. It is found that the electrical properties of very thin GZO films deposited on Zn‐polar ZnO templates are significantly improved compared to those deposited on O‐polar face. A low resistivity of 2.62 × 10^–4 Ω cm, high Hall mobility of 26.9 cm²/V s, and high carrier concentration of 8.87 × 10²⁰ cm^–3 being achieved with 30 nm‐thick GZO films using Zn‐polar ZnO templates on a glass substrate. In contrast, the resistivity of 30 nm‐thick GZO films on bare glass that shows more likely O‐polar is very poor about 1.44 × 10^–3 Ω cm with mobility and carrier concentration are only 11.9 cm²/V s and 3.64 × 10²⁰ cm^–3, respectively. It is therefore proposed that polarity inversion plays an important role in determining the electrical properties of extremely thin GZO films. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Microscopic structure and structuring of perovskite surfaces and interfaces: SrTiO3, RBa2Cu3O7-δ

3 surfaces and bicrystal interfaces and the growth of YBa₂Cu₃O_7-δ thin films on such substrates using scanning tunneling microscopy and X-ray diffraction. Proper annealing of SrTiO₃ in oxygen and/or ultrahigh vacuum produces uniformly terminated, atomically flat and well-ordered surfaces. For vicinal SrTiO₃(001) surfaces the particular annealing sequence and miscut angle sensitively determines the resulting step structure and thus the microscopic surface morphology. Steps of SrTiO₃(001) surfaces can be adjusted to a height of one, two, or multiple times the unit-cell height (a_STO=0.3905 nm). The growth of YBa₂Cu₃O_7-δ films on these substrates by pulsed laser deposition was traced from the initial nucleation to a thickness of about 300 nm. The morphology, texture, and defect structure of the films is determined by the specific structure and morphology of the pristine substrate. Anisotropic, planar defects, originating from substrate step edges, strongly modify the electronic transport properties of the film leading to critical currents up to ≈9×10⁷ A/cm² at 4 K as well as pronounced transport anisotropies. Surfaces and interface energy terms are discussed, which also determine the observed structure of bicrystal boundaries. Received: 16 April 1998/Accepted: 21 August 1998     

Drude's model calculation rule on electrical transport in Sb-doped SnO2 thin films, deposited via sol-gel

The evaluation of free carrier concentration based on Drude's theory can be performed by the use of optical transmittance in the range 800-2000 nm (near infrared) for Sb-doped SnO₂ thin films. In this article, we estimate the free carrier concentration for these films, which are deposited via sol-gel dip-coating. At approximately 900 nm, there is a separation among transmittance curves of doped and undoped samples. The plasma resonance phenomena approach leads to free carrier concentration of about 5×10²⁰ cm⁻³. The increase in the Sb concentration increases the film conductivity; however, the magnitude of measured resistivity is still very high. The only way to combine such a high free carrier concentration with a rather low conductivity is to have a very low mobility. It becomes possible when the crystallite dimensions are taken into account. We obtain grains with 5 nm of average size by estimating the grain size from X-ray diffraction data, and by using line broadening in the diffraction pattern. The low conductivity is due to very intense scattering at the grain boundary, which is created by the presence of a large amount of nanoscopic crystallites. Such a result is in accordance with X-ray photoemission spectroscopy data that pointed to Sb incorporation proportional to the free electron concentration, evaluated according to Drude's model.     

负偏压热灯丝CVD金刚石膜核化和早期生长的研究

利用扫描电子显微镜、Raman谱和X射线光电子能谱，研究了Si衬底上热灯丝CVD金刚石膜的核化和早期生长.在-300V和100mA条件下预处理15min，镜面抛光的Si(100)表面上金刚石核密度超过了10⁹cm^-2，但是核的分布极不均匀且可分为三个区域：A区，边缘处以锥体为主；B区，位于边和中心之间过渡区是纳米金刚石；C区，中心处有SiC层.无偏压下生长4h后，A区形成许多大而弧立的金刚石颗粒，B区成为织构金刚石膜，而C区变为含有大量缺陷的连续金刚石膜.衬底负 关键词：     

Nucleation and initial growth of diamond by biased hot filament chemical vapour deposition

6 cm^-2 for non-scratched silicon. The maximum value of the nucleation density was over 10¹¹ cm^-2 on mirror-polished Si(100) at -300 V. The transportation process of the ion flux from the filament to the substrate is discussed in detail for biased substrates. The nucleation enhancement by the positive bias is believed to be a result of the increased impingement of the electrons emitted from the filament to the substrate surface. The studies have shown that electron emission from diamond plays a key role in negative-bias-enhanced nucleation by accelerating the dissociation of molecular hydrogen and hydrocarbon species into various free radicals and causing a plasma to be ignited near the substrate surface. The negative bias pretreatment is also a critical step in growing heteroepitaxial diamond films: the enlargement of the area of diamond clusters in contact with the substrate enhances the orientated growth of the films. Received: 18 October 1996/Accepted: 4 February 1997     

Effect of thickness on the stability of transparent conducting impurity‐doped ZnO thin films in a high humidity environment

The resistivity of transparent conducting Al‐ and Ga‐doped ZnO (AZO and GZO) thin films prepared with a thickness in the range from 20 to 200 nm on glass substrates at a temperature below 200 °C was found to increase with exposure time when tested in a high humidity environment (air at 90% relative humidity and 60 °C). The resistivity stability (resistivity increase) was considerably affected by the thin film thickness. In particular, thin films with a thickness below about 50 nm were very unstable. The increase in resistivity is interpreted as carrier transport being dominated by grain boundary scattering resulting from the trapping of free electrons due to oxygen adsorption on the grain boundary surface. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Wide band gap and p‐type conductive Cu–Nb–O films

Cu–Nb–O films with a thickness of ca. 150 nm were prepared on borosilicate glass substrates using CuNbO₃ ceramic target at substrate temperature of 500 °C by pulsed laser deposition. The X‐ray diffraction patterns showed that the Cu–Nb–O films were amorphous or an aggregation of fine crystals. The post‐annealed film at 300 °C in N₂ gas showed 80% transmission in visible light (band gap = 2.6 eV) and high p‐type conductivity of 21 S cm^–1. The Cu–Nb–O film with a thickness of 100 nm, fabricated from the target with a composition of Cu/Nb = 0.9, showed the highest p‐type conductivity of 116 S cm^–1. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)