How to Check Intrinsic Carrier Concentration How Toi Read Graph

Carrier Concentration

The carrier concentration (P) obtained from the Hall effect measurements were used to calculate the effective mass (m*) of the carriers past using the relationP=2(2πm*kT/h2)3/2 Exp(Ef/kT)

From: Free energy and the Surround , 1990

MCT backdrop, growth methods and characterization

Randolph E. Longshore , in Handbook of Infra-carmine Detection Technologies, 2002

7.3.3 Intrinsic carrier concentration

Carrier concentration variations with temperature and composition take been measured and empirical formulas developed. ^{16, 17,} Figure 7.5 shows a plot of the intrinsic carrier concentration (n_i ) versus temperature and limerick using the nearly contempo equation, n_i2 .

Figure 7.5. MCT intrinsic carrier concentration versus x and temperature.

(ten) $\begin{array}{ll}{\mathrm{northward}}_{i1}& =(5.585-3.82x+1.753\times {\mathrm{ten}}^{-3}T-1.364\times {\mathrm{x}}^{-3}\mathrm{10}T)\\ & \times {10}^{\mathrm{xiv}}{\mathrm{Eastward}}_g^{\mathrm{three}/4}{T}^{3/2}\exp \left(\frac{-E_g}{2gT}\right)\end{array}$

(11) ${\mathrm{north}}_{i2}=(A+Bx+CT+D\mathrm{10}T+F{\mathrm{ten}}^2+G{T}^{\mathrm{two}})\times {10}^{14}{E}_g^{\mathrm{iii}/4}{T}^{3/2}\exp \left(\frac{-E_g}{2\mathrm{chiliad}T}\right)$

where A=5.24256, B=−three.5729, C=−4.74019, D=1.25942 × 10⁻², F=five.77046 and G=−4.24123 × 10^{−half-dozen}.

This figure shows the intrinsic carrier concentration at 300 K and for lower temperatures common for the operation of IR detectors. Intrinsic carrier concentration values are useful in material analyses and in the pattern of IR detector.

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THz Quantum Cascade Lasers

Aaron Yard. Andrews , ... Gottfried Strasser , in Molecular Beam Epitaxy (Second Edition), 2018

26.3 Doping THz QCLs

Carrier concentration in THz QCLs is a critical component to control during growth. The low-doped active regions range from ${0.5-5.0\times \mathrm{x}}^{10}{\mathrm{cm}}^{-2}$ , which means the individually doped layers inside the agile region have doping levels on the order of ${0.1-1.0\times 10}^{\mathrm{sixteen}}{\mathrm{cm}}^{-3}$ . For the surface plasmon waveguides, the thickness and doping level ( ${1-\mathrm{five}\times 10}^{18}{\mathrm{cm}}^{-3}$ ) of the lower contact layer need to exist adjusted to optimize the waveguide losses. In the active region, there is a rest between gain and losses. This seems trivial, only doping too high leads to complimentary carrier losses (Drude absorption) (Carosella et al., 2012), plus electron-electron and impurity scattering (Callebaut et al., 2004), and doping too depression leads to negligible gain. Background doping affects the final carrier concentration in the agile region and the parasitic nonradiative relaxation by impurity scatting of carriers in the upper laser level. Ideally, the background doping should be $\le {1\times 10}^{14}{\mathrm{cm}}^{-3}$ , since the designed location of the dopants in the active region is only in the layers that will non negatively impact operation (Fig. 26.5).

Figure 26.5. Si Doping in GaAs.

Si doping in GaAs grown at 0.55   µm per hr. The Arrhenius dependence of n-blazon carrier concentration on the Si cell temperature is shown. The current chamber n-blazon background doping of $9\times {10}^{14}{\mathrm{cm}}^{-3}$ is adamant with the curve fit.

For GaAs-based structures, there is an upper limit to n-type doping with Si. Silicon is a group IV element that is amphoteric in Three–V zinc-blende semiconductors. The Si compensation doping begins $4\times {\mathrm{ten}}^{18}{\mathrm{cm}}^{-3}$ and this makes it difficult to dope much college without special techniques, similar delta doping (Newman, 1999). At the lower stop of the carrier concentration is the background doping in the growth bedchamber. This is dependent on source textile purity, machine contagion, growth temperature, and growth rate, and can be northward-type or p-type depending on the specific impurities and growth weather. Fig. 26.half-dozen shows the Arrhenius dependence of n-type carrier concentration on the Si cell temperature for GaAs growth at 0.55   µm per hour with As₄ at a growth temperature (T _chiliad) of 600°C. This data is directly later on an MBE service, cleaning, new source textile, organization blistering, and source material dump. The slope for the curve fit of –56.4669 is very close to the slope for Si vapor pressure of –54.4613; nevertheless, the groundwork doping is measureable at $9\times {10}^{\mathrm{xiv}}{\mathrm{cm}}^{-3}$ . By using the MBE organization and growing, the background carrier concentration will fall toward ane $\times {10}^{14}{\mathrm{cm}}^{-\mathrm{iii}}$ in this MBE entrada. This can additionally be measured electrically by the growth of an undoped QCL (Benz et al., 2007). Other groups report a p-type groundwork equally depression equally ane $\times {10}^{13}{\mathrm{cm}}^{-\mathrm{three}}$ (Li et al., 2015). It is important to notation that dopant activation depends greatly on the host material. For example, Si doping in AlGaAs results in a much lower carrier concentration than GaAs due to the deeper level of the donor (Chand et al., 1984) and for GaAsSb the compensation doping begins much sooner, due to the different amphoteric nature of Si in Three-Sb compounds (Detz et al., 2011b).

Effigy 26.6. Carrier Concentration versus Si Cell temp.

Carrier concentration in GaAs versus Si prison cell temperature for different growth rates. Shown in white is the range with which you can reliably dope GaAs. The biscuit area denotes the onset of amphoteric doping ( $\mathrm{iv}\times {10}^{18}{\mathrm{cm}}^{-3}$ ), while the turquoise area marks the background doping, which is chamber and growth conditions dependent n- or p-type. The experimental data is from Fig. 26.5, where the groundwork carrier concentration was northward-blazon $\mathrm{nine}\times {10}^{\mathrm{fourteen}}{\mathrm{cm}}^{-\mathrm{three}}$ .

The THz QCL active region is designed for a specific applied bias (kV   cm^−one). The threshold electric current J _th and J _max calibration linearly with the dopant concentration (Benz et al., 2007). In the I–V curves of Fig. 26.7, the knee for laser alignment, the laser dynamic range, and the misalignment nonlinear differential resistance (NDR) can exist observed (Fig. 26.8).

Effigy 26.vii. Electric current Density versus Applied Electrical Field.

Current density versus practical electrical field for an LO-phonon THz QCL for unlike values of carrier concentrations. The designs brainstorm to lase around viii   kV   cm⁻¹, the human knee just before the linear lasing region. The linear region around 8   kV   cm⁻¹ is the laser alignment and it shows the dynamic range and the J _max. About one   kV   cm⁻¹ after alignment marks the beginning of the negative differential resistance (NDR) region, where the gradient increases rapidly. The inset shows the behavior of an undoped QCL, where the background carrier concentration is calculated to be northward-type $\mathrm{i}\times {\mathrm{x}}^{14}{\mathrm{cm}}^{\mathrm{-}3}$ (Benz et al., 2007).

Effigy 26.8. Sheet carrier density versus laser threshold.

The carrier canvass density versus laser threshold current density J _th and maximum current density J _max. Since the lasing in QCLs is dependent on a specific minimum bias, there is a linear relationship betwixt the carrier concentration and the current density for J _th and J _max. As a consequence, the dynamic range scales linearly with the doping. The values for J _thursday extrapolates to zip, while the values for J _max extrapolate toward the background doping. The same effect is axiomatic independent of fabric system (Benz et al., 2007; Deutsch et al., 2017).

The pulsed and CW T _max are achieved with optimized active region doping (Deutsch et al., 2017; Liu et al., 2005). The P _max tends to scale linearly with doping; however, the output power is still dependent on the device processing.

In a majority semiconductor, the angular frequency $\omega$ dependent free carrier assimilation of photons past electrons is described (Wacker et al., 2011):

$\alpha \left(\omega \right)=\frac{n_e{\mathrm{due\; east}}^{\mathrm{ii}}\tau }{m_e^{*}c\sqrt{ϵ}{ϵ}_0}\frac{\mathrm{i}}{{\omega }^2{\tau }^{\mathrm{two}}+1}$

where ${\mathrm{due\; north}}_{\mathrm{due\; east}}$ is the electron carrier density and $\tau$ is the scattering time. For room temperature GaAs doped $1\times {10}^{\mathrm{xvi}}\mathrm{c}{\mathrm{k}}^{-\mathrm{iii}}$ , $\tau =\mathrm{0.ii}\mathrm{ps}$ , the free carrier absorption is $\alpha =120\mathrm{c}{\mathrm{m}}^{-\mathrm{one}}$ for 2   THz (8.27   meV). The losses increase for lower frequencies and greatly exceed the proceeds from ISB THz QCLs. Fortunately for intersubband structures, this is simply the limiting case for broad quantum wells or narrow barriers. In QCLs, the carriers are confined in the growth management, which coincides with the electrical field vector, therefore the carriers are not free and this leads to a reduction of the free carrier absorption to ~1% of bulk values (Carosella et al., 2012). Nevertheless, the presence of IFR, inhomogeneous alloy distribution, and impurities does enable free carrier assimilation in QCLs, which increases with temperature and therefore must still be taken into account when designing structures (Ndebeka-Bandou et al., 2014). Doped thick cladding layers and substrates cannot exist used for THz waveguides. It is also important to note that shallow dopants, necessary for carriers, lead to impurity scattering and have an activation energies in the THz, east.g., for Si in GaAs, there is a dopant activation of $E_D=6\mathrm{meV}$ and an acceptor activation of $E_A=35\mathrm{meV}$ (Ashen et al., 1975; Schubert, 1993).

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PHOTOCONDUCTIVITY AND OPTICAL Backdrop OF CuInSe2 FILMS FOR SOLAR Cell Awarding

S. CHAUDHURI , ... A.K. PAL , in Energy and the Environment, 1990

Electric Measurements

The carrier concentration of CIS films were adamant by the four probe technique using the cross shaped sample geometry. Table ane shows the resistivity (ρ), mobility (µ) and carrier concentration (P) of some representative CIS films. In full general films with carrier concentration > 10E19 cm -3 were found to exist degenerate, for which the variation of resistivity with temperature was practically temperature contained. Impurity band conduction seemed to be a predominant factor in decision-making the charge transport in the films. The degenerate behaviour of the films could be understood more conspicuously from TEP measurements. TEP (S) of a degenerate semiconductor may exist written as

$1/\text{southward}=\left(\right|\text{e}\left|\text{Efo}\right)/\left({\pi }^2{\text{k}}^2\text{T}\text{A}\mathrm{ane}\right)-\left(\right|\text{east}\left|\text{Efo}\right)/\left({\pi }^{\mathrm{ii}}{\text{k}}^{\mathrm{two}}\text{A}\mathrm{i}\right)$

where Ef is the Fermi free energy, then that Ef = Efo(one - YT) and Al is the scattering factor given by Al = 0.5 - s/3. The values of Efo and Y obtained from the i/South versus 1/T plot were plant to be 0.19 eV and 4.0E-iv eV/Chiliad respectively for a representative CIS picture show. The carrier concentration (P) obtained from the Hall outcome measurements were used to summate the effective mass (m*) of the carriers by using the relation

$\text{P}=\mathrm{ii}(2\pi \text{m}*\text{kT}/{\text{h}}^2){}^{\mathrm{iii/two}}\text{Exp}(\text{Ef}/\text{kT})$

and was observed to be 0.71 – 0.73 mo, where mo is the free electron mass. Now using this value of m*, the distance of the Fermi level from the top of the valence ring in a degenerate semiconductor may be obtained from

$\text{p}=2{(2\pi \text{k}*\text{kT}/{\text{h}}^{\mathrm{ii}})}^{3/\mathrm{two}}(2/\pi )\text{F}\mathrm{one}/2(\Delta \text{E}/\text{kT})$

where F1/2 is the Fermi-Dirac integral. Now if we put the ratio of East/kT = B, nosotros have F1/2 (B) 2/3 (B)^3/2 for B ≥ four and assuming m* = 0.71 mo we get Eastward =0.21 eV.

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Effect of Dopants on Thermoelectric Backdrop and Anisotropies for Unidirectionally Solidified n-Bi2Te3

N. Abe , ... I.A. Nishida , in Functionally Graded Materials 1996, 1997

3.1 Thermoelectric properties

The carrier concentration due north _e vertical to the c-axis of each specimen at room temperature were shown in tabular array i. It was observed that the n _e of each specimen were almost 1   ×   10²⁵  m^{−   3} equal to expected n _east.

Table 1. Thermoelectric properties (at R.T)

Dopant	ρ [10−   6 Ω m]	R H [ten−   7yard3C−   one]	μ [10−   2m2V−   1  s−   ane]	north eastward [ten25  yard−   three]	α [μVk−   1]	κ [WK−   1  m−   1]	Z [10−   3  Thou−   1]
HgBr2	7.13	2.74	three.84	0.98	−   210	1.78	three.44
HgIii	6.79	2.49	3.67	1.07	−   216	1.90	3.61
SbBr3	5.92	two.64	iv.46	1.01	−   205	1.99	three.57
SbIthree	5.46	2.68	4.91	1.00	−   212	ii.12	iii.88

The temperature dependence of p and R _H in the direction vertical to c-axis of each specimen are shown in fig. 3. The R _H of each specimen shows a same value over the observed temperature range because of the same n _e. The R _H of each specimen decreased suddenly at the temperature range more than well-nigh 300   K. Therefore it is obviously that it begins to be influenced by intrinsic range effectually 300   K. The ρ of each specimen increased with increasing temperature up to about 400   K, and decreased all of a sudden at the temperature range over 400   K. Information technology is institute that the ρ of specimens with iodide are less than those of specimens with bromide. It is also found that the ρ of specimens with Sb compounds are less than those with Hg compounds.

Fig.iii. Temperature dependence of Resistivity and Hall coefficient

The temperature dependence of hall mobility μ vertical to c-centrality of each specimen is shown in fig.iv. The μ of each specimen decreased with increasing temperature over the observed temperature. The μ of specimens with Sb compounds are larger than those of specimens with Hg compounds over the observed temperature range. This phenomena can be considered as follows; Hg ion traps more than electrons than Sb ion every bit reported that Bi_twoTe_three compounds are the aforementioned crystal construction as Bi₂Se_iii compounds, and Hg atom acts every bit acceptor in Bi₂Se₃ compounds[5]. Moreover, Sb atom influences Bi₂Te₃ direct, and ionic bond become weaker by doping with Sb compounds[six].

Fig.4. Temperature dependence of Hall mobility

The α, κ and Z vertical to c-axis of each specimens at room temperature are shown in tabular array i. The α becomes smaller past doping with Sb compounds. The κ of specimens with bromide are smaller than those with iodine. Information technology is considered as follows; the ion radius of bromine is smaller than that of iodine and shows a tendency to exist substitutionally in the Bi₂Te_three lattice, and the κ_lattice which is the lattice component of the κ becomes smaller The κ of specimens with Hg compounds are too smaller than those with Sb compounds. It might be caused by weak ionic bond due to doping with Sb compounds equally described above. The κ_electron which is the carrier component of the κ become larger. Therefore the Z of each specimen doped with iodine or Sb compounds are larger than those of specimens doped with bromide or Hg compounds. The Z of specimen doped with SbI_iii is the largest, iii.88   ×   x^{−   3}  M^{−   one}, because of very loftier μ. It is obviously shown that SbI_iii is the nigh excellent every bit the dopant.

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Electron Tubes

Marvin Chodorow , ... Joan Yater , in Reference Data for Engineers (Ninth Edition), 2002

Field Emission from Semiconductors—

The carrier concentration in semiconductors is substantially less than the conduction-ring electron density in metals, even nether loftier field. Ring bending occurs, then that electron affinity (free energy difference between vacuum level and bottom of the conduction band) is a more useful parameter for semiconductors than piece of work function (energy difference between vacuum level and Fermi level), equally for semiconductors the latter is afflicted past practical field. Emission arises from either the valence or conduction band or both, as well equally surface states and defects within the band gap. The nature of the current period depends on the type of doping ( n- or p-type) incorporated. Electric current resulting from pigsty transport tin can be pregnant. The constructive mass in a semiconductor is generally less than the electron rest mass in vacuum, and it depends on the crystallographic airplane. Surface layers, oxides, or adsorbates generally exist on the surface and contribute to emission fluctuations. If field emission is primarily from the valence band (eastward.m., diamond†), then the bulwark height encountered by the valence electrons is augmented by the band gap. Because of these complications, a current density formula for semiconductors with the simplicity of the Fowler–Nordheim equation for metals is not available except for conditional approximations (more than extensive treatments are available ^† ).

Electrons migrate to the surface to shield out an practical field, indicating that the electron density increases near the surface. The chemical potential is replaced by μ(x) = μ₀ + ϕ(x), where μ₀ is the bulk chemical potential (generally such that μ₀ < 0) and ϕ(x) is the solution to Poisson'south equation. μ(10) is referred to every bit the "electrochemical potential." If emission is primarily from the conduction band and all other complications are ignored, then the equation for J(F) for semiconductors is analogous to that for metals, but with the replacements: ^*

$\begin{array}{l}\phi \Rightarrow \chi -\mu \\ Q\Rightarrow \frac{K_s-1}{K_{\mathrm{south}}+\mathrm{ane}}Q\\ \frac{c_{\text{fn}}\pi \text{/}\beta }{\sin \left(c_{\text{fn}}\pi \text{/}\beta \right)}\Rightarrow \frac{c_{\text{fn}}\pi \text{/}\beta }{\sin \left(c_{\text{fn}}\pi \text{/}\beta \right)}-\left(1+c_{\text{fn}}\mu \right)\exp \left(-c_{\text{fn}}\mu \right)\end{array}$

where

10 = the electron analogousness in eV

Yard_{due south} = dielectric constant (east.grand., xi.9 for silicon)

At the surface, μ(ten) is related to F _vac by Poisson'due south equation for ϕ such that 1000_s δ _x ϕ = F _vac at the surface, from which

$F_{\text{vac}(\mu )}=\{\begin{array}{l}{\left(\frac{2{\pi }^2{\mathrm{Due\; north}}_c{K}_s}{\mathrm{three}\beta {\epsilon }_o}{\left(\frac{\beta \mu }{\pi }\right)}^{1/2}\left[\frac{\mathrm{viii}}{\mathrm{v}}{\left(\frac{\beta \mu }{\pi }\right)}^{\mathrm{ii}}+\mathrm{one}\right]\right)}^{\mathrm{i}/2}\beta \varphi larg\mathrm{eastward}\\ {\left(\frac{2N_c{\mathrm{Yard}}_s}{\beta {\epsilon }_o}\exp \left(\beta {\mu }_o\right)\left[\exp \left(\beta \varphi \right)-\beta \varphi -\mathrm{one}\right]\right)}_{\beta \varphi smal\mathrm{fifty}}^{1/\mathrm{ii}}\end{array}$

where

N_c = 2M_c (yard/(2 πβh ²))^1/ii

K_c = number of equivalent minima in the conduction ring (eastward.g., half dozen for silicon)

thou = effective electron mass in the semiconductor (e.grand., 0.3283 m ₀ for silicon)

F _vac = applied field in vacuum in eV/nm

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SiC and GaN Power Semiconductor Devices

Tanya Thousand. Gachovska , Jerry L. Hudgins , in Power Electronics Handbook (4th Edition), 2018

5.2.2.iii Intrinsic Carrier Concentration

The intrinsic carrier concentration of a semiconductor completely gratis of impurities and defects is the number of excited electrons from the valence band occupying energy-momentum states in the conduction band (and also the number of excited holes in the valence band) per unit of measurement volume. Information technology is given by the equation:

(5.8) $n_{{}_i}={\left({\mathrm{Northward}}_C{N}_V\right)}^{\frac{1}{\mathrm{two}}}{e}^{-\frac{E_G}{\mathrm{ii}\mathrm{one\; thousand}T}}$

where North_C and Northward₅ are the effective density of states in the conduction and in the valence band, respectively; E₁₀₀₀ is the energy bandgap; thousand is Boltzmann's constant (one.381   ×   10^{−   23}  J   K^{−   ane}); and T is the absolute temperature in Kelvin, and it is assumed that kT  ≤ E_Thou /5.

Due to the wide bandgaps of SiC and GaN materials, their room-temperature intrinsic carrier concentrations are very pocket-sized, ~   8.2   ×   10^{−   9}  cm^{−   3} for SiC and 1.half dozen   ×   10^{−   10} for GaN, while the intrinsic carrier concentration of Si is i.45   ×   10^ten  cm^{−   three}. Wide bandgap semiconductors have the reward of operating at loftier temperature and radiations fluxes because degradation effects due to thermally generated carriers are small. As the temperature increases, the electron's thermal energy in the valence band increases leading to a condition where any effects due to impurity doping are negated. This condition at elevated temperatures effectively causes the semiconductor to act every bit if it were intrinsic (no impurity doping). The temperature at which this condition occurs for Si is nearly 150°C, while SiC has a wide bandgap, and the valence electrons require more thermal free energy to move from valence to conducting band. This intrinsic temperature for SiC is ~   900°C.

Radiation energy/particle flux can also excite an electron and make information technology move to the conducting band. Like to temperature, a wide bandgap material will crave more than radiation energy to free an electron from the conducting band.

As a result of a wide bandgap, devices built with SiC and GaN can endure more rut and radiations without losing their designed electrical backdrop. Devices using the wide bandgap materials can theoretically operate in extreme conditions where Si-based devices cannot.

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Preparation, properties and electronic construction of SnO2

Karsten Henkel , ... Dieter Schmeißer , in Single Crystals of Electronic Materials, 2019

16.2.one.3 Electric properties and doping

High charge carrier concentrations in the range of 10 ¹⁸-10²¹  cm⁻³ and high charge carrier mobilities of 80–200   cmⁱⁱ/Vs have been achieved for SnO₂ single crystals as well as for thin amorphous SnO₁₀ layers, where more often than not higher mobilities were observed for the singe crystals [2,eighteen,22,23].

For rutile SnO_two static dielectric constants of 12 and 7 perpendicular and parallel to the tetragonal c-axis were calculated [24], while in early experiments corresponding values of nigh xiv and ix, respectively, were found [25].

Generally, SnO_two (similar the other TCOs) is predominantly n-type. As a footing for this property, either the ease of forming oxygen vacancies or cation interstitials is discussed [26] or, alternatively, hydrogen interaction with acceptor impurities is favored [xi,27,28]. A typical northward-type dopant is antimony [29]; ambipolar send is also reported [21]. Hence in that location is a major research interest in fabricating p-type SnO₂, and its realization would open many new perspectives in applications [30]. Thus the use of acceptor dopants such equally gallium, aluminum, indium, or nitrogen is investigated, where the oxygen atoms in the SnO_two matrix are replaced by the corresponding acceptor atoms [21,31]. However, instability of North-doped SnO₂ is still an outcome to be overcome [21].

Recently, dual acceptor codoping was suggested to meliorate the stability of N dopants in SnO₂. Researchers take demonstrated that a regulation of the polarity of conduction and carrier concentration tin can be achieved past GaN doping connected with proper thermal treatment [21]. These authors observed the transition of northward   →   p   →   north, which was mainly attributed to NO substitutions (n   →   p) in GaN:SnO₂ films and their decomposition at college temperatures (p   →   due north).

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Supported Liquid Membranes in Pharmaceutics and Biotechnology

Zisu Hao , West.S. Winston Ho , in Current Trends and Hereafter Developments on (Bio-) Membranes, 2019

nine.iii Effect of Carrier Concentration

An increase of carrier concentration provides a high extraction adequacy, leading to a loftier extraction charge per unit as more target species can exist partitioned to the organic membrane stage. However, farther increasing the carrier concentration over the optimal value increases the viscosity of organic solutions. Thus, the mass transfer operation may not be further improved as the diffusion of the species-carrier complex in the membrane phase decreases with an increment of viscosity ( Ren et al., 2009a; Sahoo et al., 1997). For the Cephalexin-Aliquat 336 system, an increase in Aliquat 336 from ane.25 to five.0   wt% enhanced the extraction rates (Vilt and Ho, 2009). Similar results were also observed for the recovery of Pen G using a FSSLM that the mass transfer functioning improved with an increment of carrier concentration from 0 to 200   mM, while no further improvement was observed with higher concentrations (Lee et al., 1993). The similar phenomenon was also reported for the recovery of Pen K-DOA system in a HFRLM process (Ren et al., 2009a, 2010) and for a Cephalosporin C-Aliquat 336 system through a FSSLMs (Ghosh et al., 1995). For an Amoxicillin-Aliquat 336 arrangement in a HFSLM, Pirom et al. (2015a) reported an increment of extraction efficiency with increasing the Aliquat 336 concentration (ii to 6   mM) and a decrease of the extraction efficiency from 85% to 75% with farther increase of the carrier concentration to 8   mM.

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Belittling Applications of Graphene for Comprehensive Belittling Chemical science

Suresh Bandi , Ajeet K. Srivastav , in Comprehensive Analytical Chemistry, 2020

3.1 Graphene alone for gas sensing

The larger carrier concentration and mobility at room temperature with less electric racket generation is a blessing from this magic material for chemiresistive gas sensing. Like to the metal oxide semiconductors, the graphene as well exhibits a change in electrical resistance upon interaction with gas molecules. Just, the graphene works on a straight charge transfer mechanism which is quite different from the metal oxide sensors [34]. The adsorption of gas molecules on graphene changes the localized charge carrier concentration depending on the type of gas molecules, i.e. oxidizing or reducing. The oxidizing gas acts every bit an electron acceptor and reducing gas acts as an electron donor. Graphene exhibits p-type semiconducting behaviour. Thus the interaction with reducing gas decreases the conductivity and the oxidizing gas enhances the conductivity every bit per the nature of p-type semiconductors [34–36]. Owing to its inherent low electronic noise, it is capable of detecting the infinitesimal changes in carrier concentration caused even by few gas molecules. The schematic representation of the sensing behaviour of graphene based on the nature of testing gas is shown in Fig. 5.

Fig. 5. The chemiresistive gas sensor representation based on graphene (p-type semiconductor). The change in resistance values upon interaction with reducing and oxidizing gases are as shown.

Though the chemiresistive gas sensing has been established five decades agone, the usage of graphene in this field was started in 2007 by Schedin et al. [12]. They have reported the ultimate sensing backdrop of graphene against NO_two, NH₃, CO, and H_ii for the concentration of 1   ppm at room temperature. Further, the sensing properties are fully recoverable later vacuum annealing at 150°C or a piddling exposure to the UV illumination [12]. The sensor has exhibited a quicker response and recovery to the adsorption and desorption of a single NO₂ molecule and the values are significantly higher than whatever sensor reported till then. Since and then, the graphene has shown excellent sensing properties with lowest detection (LOD) limits towards various toxic gases and organic vapours too.

Instead of pristine graphene, the defective graphene (mainly rGO) is widely used for chemiresistive gas sensing (or other electronic devices) applications due to its low cost and scalable preparation approaches. The rGO derives from the GO via chemical or thermal reduction treatments. The Become consists of diverse functional groups over its surface with disrupted sp ² hybridized carbon atoms. The reduction treatment could not achieve the consummate memory of graphene where the material ends up with few untreated functional groups and defects. Hence it is called rGO. The defective structure of graphene affects its electrical properties negatively, despite its backdrop for gas sensing are sufficient and besides its selective gas sensing is encouraging [37,38]. The ppb level detection of rGO for chemic warfare agents and explosives with a reduced level of racket has been reported by Robinson et al. [37]. The influence of the caste of reduction on device sensitivity is some other key finding of this study. The defects in graphene sheets raise the adsorption capabilities towards certain gaseous molecules. The defective graphene possesses a stiff interaction with CO, NO, and NO₂ but weakly with NH₃ equally reported by Zhang et al. [39] through the first principle calculations.

The selectivity of the graphene sensors could exist well explained by taking resistance fluctuation spectra (i.eastward. noise spectra) to the consideration along with their resistance measurements [forty]. The graphene is a low electrical dissonance frequency material as explained already, but it'due south worthy to highlight that the depression-frequency noise of the textile is sensitive to the gaseous molecules. A few gases could crusade distinctive bulges in the noise spectra (i.eastward. over the ane/f background which arises due to fluctuations in the carrier mobility and densities [37]) of graphene forth with the resistance changes. These characteristic bulgy features are distinct to various gaseous environments. Thus, this noise can be used to differentiate between various gases [41]. Information technology eliminates the pattern of an array of sensors made for the detection of each gas individually. A single graphene sensor can be used to sense the gases selectively [41].

Unlike pristine graphene devices, the rGO based devices consist of many rGO flakes of different shape, thickness (few layers of graphene sheets) sizes, and degrees of reduction. Information technology causes the electrical property variation between these sheets and the formation of random junction between these flakes farther increases it. Hence it shows property differences between whatsoever two devices made of rGO. Withal, the selectivity measurements based on noise spectra differences are likewise not feasible [38]. Lipatov et al. [38], reported a way for the selective detection of methanol, ethanol, and isoproponal which are weakly selective to detect. Where the sensor system consists of an array of rGO sensing chips, and the experiment was conducted at the room temperature nether normal atmospheric conditions.

Other than taking reward of defects and functional groups in graphene, many implications can be fabricated to improve its sensing properties further. For example, the lacking graphene shows a weak interaction for NH₃ though information technology works well with other toxic gases [39]. Hither the impurity doping and design of graphene heterostructures are other approaches for property enhancement. Apart from proficient adsorption capability of gas molecules, the defects in graphene (i.due east. rGO) also instigates the functionalization adequacy of rGO with other materials [37,42].

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Microstructure and thermoelectric backdrop of p-type Bi0.5Sb1.5Te3 fabricated by hot pressing

Doo-Myun Lee , ... Ichiro Shiota , in Functionally Graded Materials 1996, 1997

3.ii Thermoelectric properties

Fig. three shows the carrier concentration n _c and mobility μ as a function of the pressing temperature. With increasing the pressing temperature, the carrier concentration and mobility of the compound are decreased and increased, respectively. The increase in mobility results from the porosity decrease.

Fig. 3. Carrier concentration n_c and mobility μ as a part of the hot pressing temperature.

The variation of Seebeck coefficient α with hot pressing temperature is shown in Fig. 4. Every bit the temperature is increased, the Seebeck coefficient is slightly increased because of the decrease in carrier concentration. The human relationship betwixt the α and n_c can exist expressed as follows: α ~   r-ln n_c, where r is the handful gene [4].

Fig. 4. Variation of Seebeck coefficient α with hot pressing temperature.

The variation of electrical resistivity ρ with hot pressing temperature is shown in Fig. 5. Equally the hot pressing temperature is increased, the electrical resistivity of the compound is decreased. The electrical resistivity tin can be expressed as the following relationship: ρ =   one/due north_ce μ. As a event, ii competing factors, carrier concentration and mobility, determine the electric resistivity. Therefore, it seems that the decrease in electrical resistivity with increasing the pressing temperature would result from a significant increase in mobility and a slight subtract in carrier concentration.

Fig. v. Variation of electrical resistivity ρ with hot pressing temperature.

Fig. 6 shows a plot of thermal conductivity κ vs. hot pressing temperature. The thermal conductivity is increased with the pressing temperature probably because of the density increase. Fig. 7 shows the figure of merit Z of the compound hot pressed at various hot pressing temperatures. The figure of merit is increased with the pressing temperature because of the decrease in porosity and increment in preferred orientation. The compound hot pressed at 420   °C shows the highest figure of merit (Z   =   2.69   ×   10^{−   3}/One thousand).

Fig. 6. Relationship between the thermal conductivity κ and hot pressing temperature.

Fig. 7. Figure of merit Z of the compounds hot pressed at diverse hot pressing temperatures.

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