Change In Sheet Resistance Research Articles

Investigation of Cu growth phenomena on Ru substrate during electroless deposition using hydrazine as a reducing agent

Cu growth phenomena during electroless deposition (ELD) on Ru substrate were investigated in this study. Different to the formaldehyde based Cu ELD bath, the use of hydrazine based Cu ELD bath facilitated the observation of Cu growth phenomena during ELD. The whole surface-catalyzed ELD occurred on Ru, and electrochemical quartz crystal microbalance as well as linear sweep voltammetry studies revealed that Cu covered Ru surface within a few seconds of ELD. Measurement of sheet resistance change confirmed that Cu nucleation on Ru was continuous with forming a film. During the period, Cu film growth was monitored by an atomic force microscope imaging, indicating that Cu was deposited on Ru preferentially, rather than on the deposited Cu at the initial stage of the deposition. The whole surface-catalyzed ELD achieved 55nm gap-filling, and this showed the possibility of the practical adoption of ELD as a method for metallization in ultralarge-scale integration.

The effect of poly (N-vinylpyrrolidone) molecular weight on flash light sintering of copper nanopaste

The effect of poly (N-vinylpyrrolidone) (PVP) molecular weight (MW) on the flash light sintering of copper nanopaste was investigated. The copper nanopaste was coated on polyimide substrates using doctor blade method. PVP was used as reducing agent to functionalize the copper nanoparticles during flash light sintering process. To find the optimum sintering conditions of copper nanoparticles, the various MWs of PVP (10 000, 40 000 and 55 000) were used and the flash light irradiation energy was varied from 7.5J/cm2 to 17.5J/cm2. Meanwhile, other flash light irradiation conditions (pulse numbers, on-time and off-time durations) and amounts of PVP were fixed to clarify the effect of the PVP MW. As the results, it was found that flash light sintered copper nanofilms have the resistivity of 54μΩcm without any damages to the polymer substrate. To characterize the microstructures and transformation crystal phase of the sintered copper nanofilms, scanning electron microscopy and X-ray diffraction were conducted. In order to understand the interaction between oxidized copper and PVP, X-ray photoelectron spectroscopy was analyzed. To observe the electrical conductivity of flash light sintered copper nanofilms, the sheet resistance of the sintered copper nanofilms was measured using a four-point probe method and the sheet resistance changes during the flash light irradiation process were monitored using in-situ monitoring system.

High-performance NiO/Ag/NiO transparent electrodes for flexible organic photovoltaic cells.

Transparent electrodes with a dielectric-metal-dielectric (DMD) structure can be implemented in a simple manufacturing process and have good optical and electrical properties. In this study, nickel oxide (NiO) is introduced into the DMD structure as a more appropriate dielectric material that has a high conduction band for electron blocking and a low valence band for efficient hole transport. The indium-free NiO/Ag/NiO (NAN) transparent electrode exhibits an adjustable high transmittance of ∼82% combined with a low sheet resistance of ∼7.6 Ω·s·q(-1) and a work function of 5.3 eV after UVO treatment. The NAN electrode shows excellent surface morphology and good thermal, humidity, and environmental stabilities. Only a small change in sheet resistance can be found after NAN electrode is preserved in air for 1 year. The power conversion efficiencies of organic photovoltaic cells with NAN electrodes deposited on glass and polyethylene terephthalate (PET) substrates are 6.07 and 5.55%, respectively, which are competitive with those of indium tin oxide (ITO)-based devices. Good photoelectric properties, the low-cost material, and the room-temperature deposition process imply that NAN electrode is a striking candidate for low-cost and flexible transparent electrode for efficient flexible optoelectronic devices.

Mechanism for the large conductance modulation in electrolyte-gated thin gold films

Electrolyte gating using ionic liquid electrolytes has recently generated considerable interest as a method to achieve large carrier density modulations in a variety of materials. In noble metal thin films, electrolyte gating results in large changes in sheet resistance. The widely accepted mechanism for these changes is the formation of an electric double layer with a charged layer of ions in the liquid and accumulation or depletion of carriers in the thin film. We report here a different mechanism. In particular, we show using x-ray absorption near edge structure (XANES) that the previously reported large conductance modulation in gold films is due to reversible oxidation and reduction of the surface rather than the charging of an electric double layer. We show that the double layer capacitance accounts for less than 10\% of the observed change in transport properties. These results represent a significant step towards understanding the mechanisms involved in electrolyte gating.

A Printed Carbon Nanotube Sensor on a Flexible Substrate

Printing becomes an emerging manufacturing technology for mechanics, electronics, and consumer products. Carbon nanotubes have recently been used as a material for sensors and electrodes due to their unique electrical and mechanical properties. Printed electrodes and conductive traces particularly offer versatility of fabricating low-cost, disposable, and flexible sensors and devices. While screen-printing has been a conventional method for printing conductive traces and electrodes, inkjet-printing recently attracts a wide attention due to its unique advantages including no template requirement, rapid printing at low cost, on-demand printing capability, and precise control of the printed material. Computer generated conductive trace or electrode patterns can simply be printed on a flexible substrate with proper conductive ink. However, for inkjet-printing of nanotubes to form conductive traces and electrodes, there are few challenges that need to be addressed. One is nanotube dispersion in an ink base solution while others include adjusting surface tension and controlling viscosity of the ink and treating the surface of the printing substrate. This work presents carbon nanotube ink preparation and its demonstration in chemical sensing along with our recent achievements.It is essential to disperse carbon nanotubes to make a carbon nanotube ink. In our previous work, we have demonstrated an inkjet printed electrochemical sensor using an office HP inkjet printer and a carbon nanotube ink. Sodium dodecyl sulfate (SDS) was used as a dispersant and a surfactant in preparing the carbon nanotube ink. It should be noted that that a ratio of SDS concentration and carbon nanotube concentration would be an important factor determining the sheet resistance of a printed carbon nanotube pattern. A preliminary test result confirmed that there would be an optimum SDS:CNT ratio. For flexible sensor applications, sheet resistance change of the printed carbon nanotube patterns on a flexible substrate was measured for varying curvatures of the substrate. For a curvature up to 0.36 cm-1, the sheet resistance increase was less than 2.5% showing that the printed carbon nanotube patterns could be used for a flexible and printed sensor. Using the developed technologies, a fully printed carbon nanotube sensor on a flexible substrate will be demonstrated for chemical and biological sensing.

Temperature changes of copper nanoparticle ink during flash light sintering

The copper nanoparticle ink was coated on polyimide substrates using a doctor blade method. The films thus formed were then sintered by flash light irradiation at room temperature under ambient conditions. The flash light energy was varied from 2J/cm2 to 12J/cm2. To measure the temperature change, a non-inverting amplifier circuit with an op-amp and a type-K thermocouple was devised. The sheet resistance change was simultaneously monitored using a Wheatstone bridge circuit. An analytical temperature calculation was conducted, considering the heat transfer phenomena during the flash light irradiation. As the results, the temperature of the copper nanoparticle films was reached to (318°C) in 10ms at the flash light irradiation energy higher than 12J/cm2 and they were melted and fully sintered. The analytical solutions of the temperature profile of copper nanoparticles film and polyimide substrate (maximum temperature of copper nanoparticles film and polyimide substrates are 279°C and 140°C, respectively) in which the latent heats for phase changes of the copper nanoparticles and the binder (PVP) were concerned, agrees well with the experimentally measured temperature profiles of them (maximum temperature of copper nanoparticles film and polyimide substrates are 318°C and 135°C, respectively). The analytical calculation method proposed, could be used to design the flash light sintering variables applicable to various low-temperature flexible substrates.

Enhancement of Processability and Electrical Resistance by Use of Ag-Based Composite Inks Containing Ultrafine SAC305 Alloy Nanoparticles

We propose use of Ag/Sn-3.0 (wt.%) Ag-0.5 Cu (SAC305) composite ink to reduce sintering temperature, sintering time, and material costs. The SAC305 nanoparticle (NP) surfaces were not capped by any stabilizers, which are detrimental to the resistivity of the sintered tracks. Compared with commercial pure Ag ink, use of Ag/3.2 (vol.%) SAC305 composite ink containing ultrafine SAC305 NPs resulted in outstandingly enhanced processability, enabling faster sintering at low temperatures. The average sheet resistance of composite ink samples sintered for 25 min at 170°C was as low as 0.011 Ω/□, comparable with that of a pure Ag sample sintered for over 30 min at 220°C. The morphology and the differential scanning calorimetry curves enabled explanation of the changes in the sintering behavior and sheet resistance. The Ag/SAC305 clusters in the composite ink sintered at 170°C grew, on average, to ~201.1–226.1 nm as a result of faster local liquid-phase sintering, and most of the Ag particles were mutually linked, dramatically changing the microstructure.

Ultrasonic-sprayed Graphene Oxide and Air-sprayed Silver Nanowire for the Preparation of Flexible Transparent Conductive Films

Abstract Simple solution spray coating of graphene oxide (GO) and Ag nanowires (AgNWs) was employed to prepare transparent conductive films (TCFs). We used air and ultrasonic spraying, and the effects of different spraying methods on the properties of TCFs were investigated. Ultrasonic spraying exhibited a significant decrease in the length of AgNWs and increase of sheet resistance. Thin two-dimensional reduced graphene oxide (rGO) prepared by ultrasonic spraying with tightly bound conductive Ag nanowires prepared by air spraying effectively decreased the sheet resistance and increased the transparency of the hybrid films. Air-sprayed rGO (0.25 mL)–AgNW (0.45 mL)/poly(methyl methacrylate) exhibited a sheet resistance of 328 Ω/; however, the ultrasonic-sprayed rGO (0.25 mL)–air-sprayed AgNW (0.45 mL) on a poly(methyl methacrylate) showed a significant improvement of sheet resistance to 86 Ω/ with a light transmittance of 78%. The sprayed rGO–AgNW showed little change in sheet resistance after 200 bending cycles with a radius curvature of 10 mm.

Highly moisture resistant Ga-doped ZnO films with textured surface for thin-film solar cells with indium codoping fabricated by ion plating with direct-current arc discharge

Highly transparent conductive Ga-doped ZnO (GZO) films and GZO films with indium codoping (GZO:In) were deposited on glass substrates at 200 °C by ion plating using direct-current arc discharge. Etching in 0.1 wt % HCl solution made it possible to form a craterlike textured surface with a high haze value. For a textured GZO:In film with a remaining thickness of 388 nm, the sheet resistance was 8.1 Ω/□. Damp-heat test results showed that highly moisture-resistant GZO films with a textured surface could be achieved after indium codoping. For the textured GZO:In film, the relative change in sheet resistance was as low as 5.8% while maintaining a high transparency. The moisture-resistant GZO:In films with a textured surface have great potential for use as window layers in thin-film solar cells.

Effect of Gamma Irradiation on DC Performance of Circular-Shaped AlGaN/GaN High Electron Mobility Transistors

AlGaN/GaN High Electron Mobility Transistors (HEMTs) show great promise for applications such as military radar and satellite-based communications systems. Due to the applications in extreme radiation environments, it is important to characterize the performance after irradiation. There are many studies characterizing the performance under proton, neutron, and electron irradiations for AlGaN/GaN HEMTs. However, the studies for gamma irradiation are limited. Detailed studies are needed to characterize the performance of HEMTs after gamma irradiation. In this study, we characterize the DC performance after irradiation and extract the change of Vth, carrier concentration, mobility and resistance. Also, we use gate lag measurement and drain pulse measurement to characterize the defects generated after irradiation. AlGaN/GaN HEMT heterostructures were grown on c-plane sapphire by molecular beam epitaxy (MBE). The layer structure included a thin AlGaN nucleation layer followed with a 2 µm thick undoped GaN buffer topped by a 25 nm thick unintentionally doped Al0.28GaN layer. Mesa isolation was achieved by using an inductively coupled plasma system with Ar/Cl2-based discharges. The Ohmic contacts were formed by lifting-off e-beam evaporated Ti (200 Å)/Al (1000 Å)/Ni (400 Å)/Au (800 Å). 1-µm gates were defined by lift-off of e-beam deposited Ni/Au metallization. The contacts were annealed at 850°C for 45 s under a flowing nitrogen ambient in Heatpulse 610T system. The final step was deposition of e-beam evaporated Ti/Au (300 Å/1200 Å) interconnection contacts. Devices were exposed to 60Co γ-rays with different doses of 50, 300, 450, or 700 Gy. Irradiations were performed at temperatures <50°C. During device irradiation, the samples were held in nitrogen ambient. The device DC performance was characterized using HP 4156 parameter analyzer.As shown in Figure 1, IDSS after irradiation was increased from 293mA/mm to 339mA/mm after irradiation. The increase of IDSSincreases with dose before 450 Gy and saturates after that. From the transmission line method (TLM), there is no significant change in sheet resistance after irradiation. However, the device total resistance, the reciprocal of the current current voltage (I-V) curve slope in the lower drain bias voltage, decreased significantly, as illustrated in Figure 1. The total resistance consisted of the channel resistance and the source resistance as well as the drain resistance. Both The source resistance and the drain resistance determined from the transmission line method change less than 2%. While the channel resistance decreased around 5% as shown in Figure 2. The reduction of the channel resistance was mainly due to the increase of mobility and carrier concentration, which were extracted from the drain IV curve in the low field region and TLM data. Kurakin et. al 1 found a similar effect that mobility increases after irradiation due to the relaxation of strain. Berthet et. al 2 attributed the drain current increases after irradiation to the introduction of donor type defects through the implantation. From gate lag measurement, the dispersion of the drain current measured at 100kHz increased as a function of the gamma irradiation dose indicating additional traps generated between gate and drain electrode and enhanced the current collapse. There was no obvious current dispersion during the drain pulse measurement showing the defects created by the gamma irradiation were less than the original defects through the material growth in the buffer layer.In conclusion, low dose gamma irradiation improved the AlGaN/GaN HEMT dc performance. The effect may be due to the strain relaxation effect and due to the donor type defects generated during the gamma irradiation.

Direct Cu Electrodeposition on the Ni Alloy Barrier Layer Prepared By Electroless Deposition on SiO2

The formation of barrier layer by electroless deposition (ELD) takes great interest for the next generation ULSI metallization, because ELD contains various advantages including low process cost, low process temperature, and the excellent conformality[1,2]. Especially, the research on the Ni or Co based alloy barrier layer is widely conducted as the barrier layer property of the film was superior[1-3].Some researches realized the all-wet metallization by using ELD barrier layer, however, the formation of the conformal Cu seed layer is still a big issue before the electrodeposition (ED) of Cu. The Cu seed layer formation on the ELD barrier layer usually conducted by ELD of Cu and/or the displacement reaction between Cu and barrier metal. In the point of the productivity of the device, however, the elimination of the Cu seed layer formation step would be preferred. Hence, in this study, we investigated the direct ED of Cu without Cu seed layer on the electroless NiWP barrier layer.NiWP barrier layer was formed on a Pd-activated SiO2 substrate by ELD in an acidic electrolyte. The SiO2substrate was activated by the Pd nanocolloids immobilized via the self-assembled monolayer on the surface. Prior to the direct ED of Cu, the native oxide of the NiWP barrier layer was removed by the coulometric reduction method.The linear sweep voltammetry (LSV) for the Cu reduction was investigated on the electroless NiWP barrier layer after the native oxide removal. As can be seen in Figure 1, the charge transfer limiting region of Cu deposition was separated into two stages: the Cu nucleation stage and the Cu film growth stage. However, because the resistivity of the electroless NiWP barrier layer was high, it was difficult to form a smooth and uniform Cu film by means of the one-step potentiostatic method. The low nucleation density of Cu or the non-uniform Cu deposition was problematic at low or high overpotential case, respectively (Figure 2a and 2b)[4]. On the other hand, the two-step potentiostatic method could successfully deposit the smooth and uniform Cu film, because the high overpotential induced higher nucleation of Cu and the low overpotential resulted in the smooth and uniform film growth (Figure 2c).The barrier layer property was studied using the ED Cu / ELD NiWP / SiO2 stacked specimen. The adhesion between each layer (ELD NiWP / SiO2and ED Cu / ELD NiWP) was excellent, which was evaluated by the tape test method. The electroless NiWP barrier layer could endure the 500°C and 30 min of thermal treatment. The minimal change in sheet resistance and the absence of silicide-related peaks in XRD analysis attested the thermal stability of the barrier layer. In addition, the patterned specimen covered with the electroless NiWP barrier layer was successfully filled by the direct ED of Cu with the conventional additive combination for the gap-filling. In this symposium, the direct Cu ED process on the electroless NiWP barrier layer will be addressed in detail. In addition, we will also discuss the trench filling by the proposed method.

Highly stretchable and transparent nanomesh electrodes made by grain boundary lithography

Foldable photoelectronics and muscle-like transducers require highly stretchable and transparent electrical conductors. Some conducting oxides are transparent, but not stretchable. Carbon nanotube films, graphene sheets and metal-nanowire meshes can be both stretchable and transparent, but their electrical resistances increase steeply with strain <100%. Here we present highly stretchable and transparent Au nanomesh electrodes on elastomers made by grain boundary lithography. The change in sheet resistance of Au nanomeshes is modest with a one-time strain of ~160% (from ~21 Ω per square to ~67 Ω per square), or after 1,000 cycles at a strain of 50%. The good stretchability lies in two aspects: the stretched nanomesh undergoes instability and deflects out-of-plane, while the substrate stabilizes the rupture of Au wires, forming distributed slits. Larger ratio of mesh-size to wire-width also leads to better stretchability. The highly stretchable and transparent Au nanomesh electrodes are promising for applications in foldable photoelectronics and muscle-like transducers.

Fabrication of High-Quality VO2 Thin Films by Ion-Assisted Dual ac Magnetron Sputtering

The technique of cathodic ac dual magnetron sputtering along with the high energy ionic bombardment is known to yield high-quality thin films in terms of their uniformity and high density. This technique has been applied for the first time to achieve thermochromic VO2 thin films that show a high optical and electrical contrast between normal and switched states. In this two-step process Vanadium metal films were deposited and subsequently oxidized in optimum conditions to achieve stoichiometric VO2 films. Typical films switched between more than 40 % to less than 5 % transmission in the infrared region while undergoing an electrical sheet resistance change between 1 × 10(5) and 1 × 10(2) Ω/cm(2). The application potential of such VO2 films in integrated optics is deemed high.

Experimental investigation of change in sheet resistance and Debye temperatures in metallic thin films due to low-energy ion beam irradiation

We present a systematic experimental investigation of low-energy (0–1 kV) ion irradiation induced changes in sheet resistivity and Debye temperatures in metallic nano-films of Ag, Cu and Al of thickness d/λo ∼ 2–5, where d is the film thickness and λo is the bulk mean free path, as a function of ion beam induced defects and impurities in a controlled manner. Ions of both atomic (Ne, Ar and Kr) and molecular (H2, N2) gases are employed in the investigation and the number of defects and impurities in the nano-film can be varied in a controlled manner by varying the ionic mass number (1–84) and beam fluence (8.7 × 1015–1.4 × 1016 ions cm−2). Low-temperature measurements are carried out for pristine and irradiated films to obtain the residual sheet resistance (RRS). An empirical formula relating the variation of RRS with beam fluence and ionic mass number is proposed for the first time. The change in RRS is due to the large diffusion of the impurities inside the nano-films as confirmed from energy dispersive x-ray spectroscopy. The Debye temperature (ΘD) is determined from Bloch–Grüneisen fitting of the temperature variation of sheet resistance data and it is found that ΘD decreases with increase in both fluence and ionic mass number arising primarily from the change in bulk modulus of the nano-film.

Flexible, Transparent, and Conductive Film Based on Random Networks of Ag Nanowires

Flexible, transparent, and conductive films based on random networks of Ag nanowires were prepared by vacuum‐filtrating method. The size of Ag nanowires prepared by hydrothermal method is uniform, with a relatively smaller diameter and a longer length, thereby achieving a high aspect ratio (&gt;1000). The films fabricated by Ag nanowires exhibit the excellent transparency with a 92% optical transmittance and a low surface resistivity of 11 Ωsq−1. Importantly, both the transmittance and sheet resistance decrease with the increasing of the Ag nanowires contents. When the contents of Ag nanowires are up to 200 mg/m2 especially, the surface resistivity quickly falls below 5 Ωsq−1. Also, these films are robust, which have almost no change in sheet resistance after the repeating bends over 200 cycles. These encouraging results may have a potential application in flexible and transparent electronics and other heating systems.

Effects of Co content on the Cu diffusion barrier property of electroless NiCoP film

The characteristics of electroless NiCoP films were investigated as a function of Co content. Sheet resistance of a multi-stacked film of SiO2/Ta/Cu/NiP dramatically increased after annealing at 500 °C, but as more Co was co-plated in NiCoP film, the change in sheet resistance of the stacked film of SiO2/Ta/Cu/NiCoP at 500 °C became smaller. A CoP/Cu film showed no change in resistance value after annealing, which indicates the CoP film is the most effective Cu diffusion barrier. X-ray diffraction analysis showed that an as-plated NiP film of amorphous structure is easily crystallized by thermal annealing over 300 °C, while CoP showed an insignificant change in crystal structure by thermal annealing up to 500 °C. This result reveals that the CoP film is capable of preventing the diffusion of Cu at 500 °C due to the thermal stability of CoP film.

Moisture Resistant Ga-Doped ZnO Films with Highly Transparent Conductivity for Use in Window Layers of Thin-Film Solar Cells

ABSTRACTHighly transparent conductive Ga-doped ZnO (GZO) films are one of the promising transparent conductive oxide (TCO) films for use in electrodes of flat display panels and window layers of thin film solar cells. For the ZnO-based TCO films, the stability to damp-heat environment is a crucial issue for practical applications. We will report moisture resistant GZO codoped with indium films (GZO:In) on the basis of analysis of data obtained a damp-heat test for solar cells (85°C and 85% relative humidity for 1000 hours).We used ZnO sintered targets with contents of 3 wt% Ga2O3 and 0.25 wt% In2O3 to grow GZO:In films in ion plating with direct current arc-discharge system. GZO:In films with different thicknesses (0.1-1 μm) were deposited on glass substrates at 200°C under the O2 flow rate of 15 sccm. As the film thickness increased from 0.1 to 1 μm, the resistivity and sheet resistance decreased from 4.3 μΩm to 2.6 μΩm and from 42.7 Ω/Sq. to 2.6 Ω/Sq., respectively. And the average optical transmittance (Tav) in the range from 0.4 to 1 μm decreased from ∼ 86% to ∼ 75%. The GZO:In film with a thickness of ∼300 nm had a low sheet resistance of 10.5 Ω/Sq. and a Tav of 82.5%. After 1000 hours damp-heat (DH) test under 85°C and 85% relative humidity, the relative change of sheet resistance is 3.4% with a Hall mobility of 26.4 cm2/V.s and a Tav of 82.7% after test. The film thicker than 300 nm has a sheet resistance lower than 10 Ω/Sq. and a relative change of resistance of ∼3% after DH test.

In situ monitoring of a flash light sintering process using silver nano-ink for producing flexible electronics

In this work, a flash light sintering process using silver nano-inks is investigated. A silver nano-ink pattern was printed on a flexible PET (polyethylene terephthalate) substrate using a gravure-offset printing system. The printed silver nano-ink was sintered at room temperature and under ambient conditions using a flash of light from a xenon lamp using an in-house flash light sintering system. In order to monitor the light sintering process, a Wheatstone bridge electrical circuit was devised and changes in the voltage difference of the silver nano-ink were recorded during the sintering process using an oscilloscope. The sheet resistance changes during the sintering process were monitored using the in situ monitoring system devised, under various light conditions (e.g. light energy, on-time and off-time duration, and pulse numbers). The microstructure of the sintered silver film and the interface between the silver film and the PET substrate were observed using a scanning electron microscope, a focused ion beam and an optical microscope. The electrical sheet resistances of the sintered silver films were measured using a four-point probe method. Using the in situ monitoring system devised, the flash light sintering mechanism was studied for each type of light pulse (e.g. evaporation of organic binder followed by the forming of a neck-like junction and its growth, etc). The optimal flash light sintering condition is suggested on the basis of the in situ monitoring results. The optimized flash light sintering process produces a silver film with a lower sheet resistance (0.95 Ω/sq) compared with that of the thermally sintered silver film (2.03 Ω/sq) without damaging the PET substrate or allowing interfacial delamination between the silver film and the PET substrate.

Combined in situ x-ray scattering and electrical measurements for characterizing phase transformations in nanometric functional films

This paper presents a combination of in situ synchrotron techniques (diffraction and reflectivity of x-rays) and sheet resistance measurements to study the phase transformations in functional thin films. The association of the three techniques enables simultaneously extracting structural and electrical characteristics of thin films during thermal annealing. For illustrating such combined experiments, two different examples are presented and discussed: the first one deals with solid phase reactions involved in the formation of Ni-based silicides with Pd alloy element, while the second one refers to amorphous-to-crystalline phase transition in chalcogenide materials. For the first case, it is shown that the combined experiments enable measuring the kinetics of Ni-silicide formation by detecting growing and consumed phases (crystallized or amorphous) exhibiting different electrical properties. In the second case, the correlated changes in film density, thickness and sheet resistance are evidenced upon Ge2Sb2Te5 (GST) thin film crystallization. A spread of transition temperature deduced from the different measured parameters is also demonstrated for the thinner GST films.

Effect of doping on single-walled carbon nanotubes network of different metallicity

Effects of doping on single-walled carbon nanotubes (SWNT) networks with different metallicity are reported through the study of sheet resistance changes upon annealing and acid treatment. SWNT film with high metallic tube content is found to have relatively good chemical stability against post treatments, as demonstrated from its stable film performance in ambient after annealing, and merely 15% reduction in sheet resistance upon sulfuric acid treatment. Conversely, film stability of SWNT film with low metallic content which comprises largely of semiconducting SWNT varies with days in ambient, and its sheet resistance changes drastically after treated with acid, indicating the extreme sensitivity of semiconducting SWNT to surrounding environment. The results suggest that annealing removes unintentional oxygen doping from the ambient and shifts the Fermi level towards the intrinsic Fermi level. Acid treatment, on the other hand, introduces physisorbed and chemisorbed oxygen and shifts the Fermi level away from the intrinsic level and increases the hole doping.