• Applied Science and Convergence Technology
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• v.26 no.6
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• pp.208-213
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• 2017

Flexible opto-electronic devices are developed on the insulating layer deposited stainless steel (STS) substrates. The silicon dioxide ($SiO_2$) material as the diffusion barrier of Fe and Cr atoms in addition to the electrical insulation between the electronic device and STS is processed using the plasma enhanced chemical vapor deposition method. Noble silver (Ag) films of approximately 100 nm thickness have been formed on $SiO_2$ deposited STS substrates by E-beam evaporation technique. The films then were annealed at $650^{\circ}C$ for 20 min using the rapid thermal annealing (RTA) technique. It was investigated the variation of the surface morphology due to the interaction between Ag films and $SiO_2$ layers after the RTA treatment. The results showed the movement of Si atoms in silver film from $SiO_2$. In addition, the structural investigation of Ag annealed at $650^{\circ}C$ indicated that the Ag film has the material property of p-type semiconductor and the bandgap of approximately 1 eV. Also, the films annealed at $650^{\circ}C$ showed reflection with sinusoidal oscillations due to optical interference of multiple reflections originated from films and substrate surfaces. Such changes can be attributed to both formation of $SiO_2$ on Ag film surface and agglomeration of silver film between particles due to annealing.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.304.2-304.2
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• 2014

Chalcogenides (Te,Se) and pnictogens(Bi,Sb) materials have been widely investigated as thermoelectric materials. Especially, Bi2Te3 (Bismuth telluride) compound thermoelectric materials in thin film and nanowires are known to have the highest thermoelectric figure of merit ZT at room temperature. Currently, the thermoelectric material research is mostly driven in two directions: (1) enhancing the Seebeck coefficient, electrical conductivity using quantum confinement effects and (2) decreasing thermal conductivity using phonon scattering effect. Herein we demonstrated influence of annealing temperature on structural and thermoelectrical properties of Bismuth-telluride-selenide ternary compound thin film. Te-rich Bismuth-telluride-selenide ternary compound thin film prepared co-deposited by thermal evaporation techniques. After annealing treatment, co-deposited thin film was transformed amorphous phase to Bi2Te3-Bi2Te2Se1 polycrystalline thin film. In the experiment, to investigate the structural and thermoelectric characteristics of Bi2Te3-i2Te2Se1 films, we measured Rutherford Backscattering spectrometry (RBS), X-ray diffraction (XRD), Raman spectroscopy, Scanning eletron microscopy (SEM), Transmission electron microscopy (TEM), Seebeck coefficient measurement and Hall measurement. After annealing treatment, electrical conductivity and Seebeck coefficient was increased by defect states dominated by selenium vacant sites. These charged selenium vacancies behave as electron donors, resulting in carrier concentration was increased. Moreover, Thermal conductivity was significantly decreased because phonon scattering was enhanced through the grain boundary in Bi2Te3-Bi2Te2Se1 polycrystalline compound. As a result, The enhancement of thermoelectric figure-of-merit could be obtained by optimal annealing treatment.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.254-254
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• 2011

The memories with nano-particles are very attractive because they are promising candidates for low operating voltage, long retention time and fast program/erase speed. In recent, various nano-floating gate memories with metal-oxide nanocrystals embedded in organic and inorganic layers have been reported. Because of the carrier generation in semiconductor, induced photon pulse enhanced the program/erase speed of memory device. We studied photo-induced electrical properties of these metal-oxide nanocrystal memory devices. At first, 2~10-nm-thick Sn and In metals were deposited by using thermal evaporation onto Si wafer including a channel with $n^+$ poly-Si source/drain in which the length and width are 10 ${\mu}m$ each. Then, a poly-amic-acid (PAA) was spin coated on the deposited Sn film. The PAA precursor used in this study was prepared by dissolving biphenyl-tetracarboxylic dianhydride-phenylene diamine (BPDA-PDA) commercial polyamic acid in N-methyl-2-pyrrolidon (NMP). Then the samples were cured at 400$^{\circ}C$ for 1 hour in N atmosphere after drying at 135$^{\circ}C$ for 30 min through rapid thermal annealing. The deposition of aluminum layer with thickness of 200 nm was followed by using a thermal evaporator, and then the gate electrode was defined by photolithography and etching. The electrical properties were measured at room temperature using an HP4156a precision semiconductor parameter analyzer and an Agilent 81101A pulse generator. Also, the optical pulse for the study on photo-induced electrical properties was applied by Xeon lamp light source and a monochromator system.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1992.05a
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• pp.110-113
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• 1992

$n^{+}$-p homojunction InP diodes were fabricated using thermal diffusion of Sulfur into p-type InP substrates(Zn doped, LEC grown, p=2.3${\times}$10$^{16}$c $m^{-3}$). The Sulfur diffusion was carried out at 550$^{\circ}C$, 600$^{\circ}C$, 700$^{\circ}C$ for 4 hours in a sealed quartz ampule(～2ml in volume) containing 5mg I $n_2$ $S_3$ and Img of red phosphorus. The formed junction depth was below 0.5$\mu\textrm{m}$. After the removal of diffused layer on the rear surface of the wafer, the beak ohmic contacts to the p-side were made with a vacuum evaporation of An-Zn(2%) followed by an annealing at 450$^{\circ}C$ for 5 minutes in flowing Ar gas. The front contacts were made with a vacuum evaporation of Au-Ge(12%) followed by an annealing at 500$^{\circ}C$ for 3 minutes in flowing Ar gas. The remarkable sprctral response of the cells obtained at the region of 6000-8000${\AA}$ region. The open circuit voltage $V_{oc}$ , short circuit current density $J_{sc}$ , fill factor and conversion efficiency η of the fabricated pattern solar cells(diffusion condition : at 700$^{\circ}C$ for 4 hours) were 0.660V, 14.04㎃/$\textrm{cm}^2$, 0.6536 and 10.09%, respectively.y.

• Journal of the Semiconductor & Display Technology
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• v.15 no.1
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• pp.65-69
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• 2016

We have investigated the possibility of recycling of an organic material that is wasted during thermal evaporation. To this end, we have collected a wasted organic material (N,N'-diphenly-N,N'-bis(1,1'-biphenyl)-4,4'-diamine(NPB)) from a vacuum chamber, purified it by recrystallization, and fabricated bilayer organic light-emitting diodes (OLEDs) with the recycled NPB. It is found that the surface roughness of thin films coated with the purified NPB is much enhanced. OLEDs fabricated by thermal evaporation of the purified NPB show lower device efficiency than OLEDs with the original NPB. However, the power efficiency of OLED fabricated by spin coating of the purified NPB is comparable with that of OLED with the original NPB. Therefore, such a recycling method by recrystallization would be more suitable for solution-processed OLEDs.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.162-162
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• 2012

ZnPc and CuPc molecules stacked similar way in the film, but showed different growth modes in thermal evaporation. The distribution of CuPc crystals did not change by the film thickness, whereas the distribution of ZnPc became random as the increase of the film thickness. The disc type nanograins of CuPc were quite regularly distributed at the initial growth regime and the regular distribution of nanograins was kept during the film growth. On the other hand, ZnPc consisted in ellipsoid shaped nanograins and the distribution of nanograins was not regular in the initial growth regime. The irregular distribution of nanograins changed to the regular mode at the later growth regime by showing structure factor in GISAXS measurement. The different initial nanograin distribution in ZnPc and CuPc was related to the different nanostructure in the mixed layer with C60 to form the bulk heterojunction.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.255-256
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• 2006

The electrical properties of viologen ($VC_8SH$) were studied in terms of the tunneling current characteristics using self-assembling techniques and ultra high vacuum scanning tunneling microscopy (UHV-STM). We fabricated the Au substrate were deposited by thermal evaporation system($420^{\circ}C$). Self-assembled monolayers (SAMs) were prepared on Au(111), which had been thermally deposited onto freshly cleaved, heated mica. The Au substrate was exposed to a 1 mM/L solution of Octanethiol in ethanol for 24 h to form a monolayer. After through rinsing the sample, it was exposed to a 0.1 mM/L solution of $VC_8SH$ in ethanol for 30 min. We measurement of the morphology on the single viologen molecule. The current-voltage (I-V) properties were measured at arbitary configured points on the surface of the sample by using a STS.

• Journal of the Korean Applied Science and Technology
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• v.30 no.2
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• pp.290-296
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• 2013

We analysed interfacial traps in organic thin-film transistors (TFTs) in which pentacene and 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) organic semiconductors were deposited by means of vacuum-thermal evaporation and drop-coating methods, respectively. The thermally-deposited pentacene film consists of dentritic grains with the average grain size of around 1 m, while plate-like crystals over a few hundred microns are observed in the solution-processed TIPS-pentacene film. From the transfer characteristics of both TFTs, lower subthreshold slope of 1.02 V/decade was obtained in the TIPS-pentacene TFT, compared to that (2.63 V/decade) of the pentacene transistor. The interfacial trap density values calculated from the subthreshold slope are about $3.4{\times}10^{12}/cm^2$ and $9.4{\times}10^{12}/cm^2$ for the TIPS-pentacene and pentacene TFTs, respectively. Herein, lower subthreshold slope and less interfacial traps in TIPS-pentacene TFTs are attributed to less domain boundaries in the solution-processed TIPS-pentacene film.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.357.1-357.1
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• 2014

Superhydrophobic WOx nanowire (NW) arrays were fabricated using a thermal evaporation and surface chemistry modification methods by self-assembled monolayer (SAM). As-prepared non-wetting WOx NWs surface shows water contact angle of $163.2^{\circ}$ and has reliable stability in underwater conditions. Hence the superhydrophobic WOx NWs surface exhibits silvery surface by total reflection of water layer and air interlayer. The stability analysus of underwater superhydrophobicity of WOx NWs arrays was conducted by changing hydrostatic pressure and surface energy of WOx NWs arrays. The stability of superhydrophobicity in underwater conditions decreased exponentially as hydrostatic pressure applied to the substrates increased3. In addition, as surface energy decreased, the underwater stability of superhydrophobic surface increased sharply. Specifically, sueprhydrophobic stability increased exponentially as surface energy of WOx NWs arrays was decreased. Based on these results, the models for explaining tendencies of superhydrophobic stability underwater resulting from hydrostatic pressure and surface energy were designed. The combination of fugacity and Laplace pressure explained this exponential decay of stability according to hydrostatic pressure and surface energy. This study on fabrication and modeling of underwater stability of superhydrophobic W18O49 NW arrays will help in designing highly stable superhydrophobic surfaces and broadening fields of superhydrophobic applications even submerged underwater.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.315.2-315.2
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• 2014

Pt-functionalized ZnS nanowires were synthesized on Au-deposited c-plane sapphire substrates by thermal evaporation of ZnS powders followed by wet Pt coating and annealing. The $NO_2$ gas sensing properties of multiple-networked Pt-functionalized ZnS nanowire sensors were examined. Scanning electron microscopy showed the nanowires with diameters of 20-80 nm. Transmission electron microscopy and X-ray diffraction showed that the nanowires were wurtzite-structured ZnS single crystals. The Pt-functionalized ZnS nanowire sensors showed enhanced sensing performance to $NO_2$ gas at $150^{\circ}C$ compared to pristine ZnS nanowire sensors. Pristine and Pt-functionalized ZnS nanowire sensors showed responses of 140-211% and 207-488%, respectively, to 1-5 ppm $NO_2$, which are better than or comparable to those of many oxide semiconductor sensors. In addition, the underlying mechanism of the enhancement of the sensing properties of ZnS nanowires by Pt functionalization is discussed.